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931.
Linking ground-water age and chemistry data along flow paths: implications for trends and transformations of nitrate and pesticides 总被引:2,自引:1,他引:1
Tesoriero AJ Saad DA Burow KR Frick EA Puckett LJ Barbash JE 《Journal of contaminant hydrology》2007,94(1-2):139-155
Tracer-based ground-water ages, along with the concentrations of pesticides, nitrogen species, and other redox-active constituents, were used to evaluate the trends and transformations of agricultural chemicals along flow paths in diverse hydrogeologic settings. A range of conditions affecting the transformation of nitrate and pesticides (e.g., thickness of unsaturated zone, redox conditions) was examined at study sites in Georgia, North Carolina, Wisconsin, and California. Deethylatrazine (DEA), a transformation product of atrazine, was typically present at concentrations higher than those of atrazine at study sites with thick unsaturated zones but not at sites with thin unsaturated zones. Furthermore, the fraction of atrazine plus DEA that was present as DEA did not increase as a function of ground-water age. These findings suggest that atrazine degradation occurs primarily in the unsaturated zone with little or no degradation in the saturated zone. Similar observations were also made for metolachlor and alachlor. The fraction of the initial nitrate concentration found as excess N2 (N2 derived from denitrification) increased with ground-water age only at the North Carolina site, where oxic conditions were generally limited to the top 5 m of saturated thickness. Historical trends in fluxes to ground water were evaluated by relating the times of recharge of ground-water samples, estimated using chlorofluorocarbon concentrations, with concentrations of the parent compound at the time of recharge, estimated by summing the molar concentrations of the parent compound and its transformation products in the age-dated sample. Using this approach, nitrate concentrations were estimated to have increased markedly from 1960 to the present at all study sites. Trends in concentrations of atrazine, metolachlor, alachlor, and their degradates were related to the timing of introduction and use of these compounds. Degradates, and to a lesser extent parent compounds, were detected in ground water dating back to the time these compounds were introduced. 相似文献
932.
Van Campenhout K Bervoets L Blust R 《Environmental pollution (Barking, Essex : 1987)》2007,145(3):905-914
The impact of several factors on the assimilation efficiency (AE) of Cd and Zn from food in the common carp (Cyprinus carpio) was studied. Tested prey species were midge larvae (Chironomus riparius), zebra mussels (Dreissena polymorpha) and oligochaetes (Tubifex tubifex). The Cd load of the larvae did not affect the Cd AE in the carp. The Zn AE however, was negatively related to the Zn load of the prey. Food quantity and starvation of the carp did not significantly affect the Cd AE. For Zn, a significant decrease in AE was found when carp were fed ad libitum. Decreasing the temperature from 25 degrees C to 15 degrees C did not influence the Cd AE, while for Zn a significant decrease of the AE was measured. Carp assimilated Cd from both zebra mussels and oligochaetes with a significantly lower efficiency in comparison to the midge larvae, although Zn AEs was prey independent. 相似文献
933.
Effect of temperature on statolith growth of the European squid Loligo vulgaris during early life 总被引:1,自引:0,他引:1
R. Villanueva 《Marine Biology》2000,136(3):449-460
Over the past decade, statolith interpretation has resulted in a major advance in our knowledge of squid population-dynamics,
but the way in which environmental conditions affect the statolith increment-deposition ratio remains virtually unknown. The
object of the present study was to determine the effect of temperature on this process, using tetracycline marks to validate
statolith growth in Loligo vulgaris Lamarck, 1798 under rearing conditions equivalent to severe winter (11 °C) and summer (19 °C) temperature regimes. Tetracycline
marking was performed every 10 d (at 10, 20, 30, 40, 50 and 60 d of age). The newly hatched squid paralarvae were slightly
smaller in summer than those hatched in winter. Survival rates were similar in both cultures, but growth rates (wet mass)
of summer squids were double those in winter. At hatching, statoliths were already longer in the summer squids, and growth
rates were 2% d−1 as opposed to 0.9% d−1 for winter statoliths. For the dorsal dome area of the statolith, where more increment counts were made, statolith growth
was of 3.25 μm d−1 in summer, and daily increment deposition was confirmed in 87% of the statoliths. The slow growth of statoliths at winter
temperatures yielded a mean growth of 1.1 μm d−1– insufficient to discern the increments using light microscopy. Subsequent SEM observation enabled only 21% of the winter
statoliths to be read; these also indicated a deposition rate of one increment d−1. Since the life span of L. vulgaris is ≃1 yr, squids will experience at least one winter during their life cycle, and this might be visible on the statolith.
Received: 28 June 1999 / Accepted: 20 December 1999 相似文献
934.
An experimental study on recolonization and succession of marine macrobenthos in defaunated sediment 总被引:3,自引:0,他引:3
Hypoxia/anoxia in coastal waters is a world wide problem which often results in mass mortality and defaunation of benthos.
In this study, field experiments were carried out to examine recolonization and succession of macrobenthic infauna in defaunated
sediments, and the time required for recovery from complete defaunation to a stable community. Trays (33 cm length × 25.5 cm
width × 11 cm depth) of defaunated sediment were exposed at the subtidal of a pristine site in subtropical Hong Kong. Temporal
changes of macrobenthic communities in defaunated sediment were analyzed by univariate and multivariate statistics, and compared
with those in undisturbed natural sediment at the same site. Initial colonization of macrobenthos occurred rapidly. A total
of 42 species was found, with an average of 258 animals per tray and 24 species per tray recorded in the first month. Abundance
showed a small peak (496 animals per tray) after 3 months, reached a sharp peak (1154 animals per tray) after 6 months, and
declined thereafter. Species number increased gradually, reached a maximum (68 species per tray) after 9 months, and then
decreased. Recolonization was predominantly contributed by larval settlement rather than adult migration. Temporal changes
in abundance, species number and diversity of the macrobenthic community in defaunated sediment resemble the spatial changes
along a decreasing pollution gradient previously defined by other authors. Results of this experiment suggest that newly available
sediment may allow more species to colonize (or coexist) than sediment pre-occupied by an established community. This is probably
due to less interspecific competition in the former habitat. No significant difference in abundance or species richness was
observed between defaunated and natural sediments after 15 months, suggesting that a stable community had been achieved, although
minor variations in species composition were still discernible between defaunated and natural sediments.
Received: 24 May 1999 / Accepted: 20 October 1999 相似文献
935.
Effects of dissolved ammonium addition and host feeding with Artemia salina on photoacclimation of the hermatypic coral Stylophora pistillata 总被引:6,自引:0,他引:6
E. Titlyanov K. Bil' I. Fomina T. Titlyanova V. Leletkin N. Eden A. Malkin Z. Dubinsky 《Marine Biology》2000,137(3):463-472
Effects of nutrient treatments on photoacclimation of the hermatypic coral Stylophora pistillata (Esper) were studied. Studies on photoacclimation of colonies from different light regimes in the field were evaluated and
used to design laboratory experiments. Coral colonies were collected in the Gulf of Eilat (Israel) from January to March 1993.
Exterior branches of colonies from different depths (1 to 40 m) displayed different trends in production characteristics at
reduced and very low levels of illumination. From 24 ± 3% to 12 ± 2% of incident surface photosynthetic active radiation (PARo), zooxanthella population density and chlorophyll a+c per 106 zooxanthellae increased, a trend seen in the range of light levels optimal for coral growth (90 to 30% PARo). The P
max of CO2 per 106 zooxanthellae decreased, while P
max of CO2 per 103 polyps increased, indicating an increase in zooxanthella population density at low light levels. Proliferous zooxanthella
frequency (PZF, a measure of zooxanthella division) declined significantly at light levels <18 ± 3% PARo. At the lowest levels of illumination (<5% PARo), zooxanthella population density decreased, as did the PZF; chl a+c per 106 zooxanthellae was unchanged. In 28-d experiments, exterior coral branches from the upper surfaces of colonies from 3 m depth
(65 ± 4% PARo) were incubated in aquaria under bright (80 to 90% PARo), reduced (20 to 30% PARo), and extremely low (2 to 4% PARo) light intensities. At each light intensity, the corals were maintained in three feeding treatments: sea water (SW); ammonium
enriched SW (SW + N); SW with Artemia salina nauplii (SW + A). An increase in P
max of CO2 per 103 polyps was found in corals acclimated to reduced light (20 to 30% PARo) in nutrient-enriched SW, while in SW, where the increase in zooxanthella population density was smaller, it did not occur.
Nutrient enrichments (SW + N at 2 to 4% PARo and SW + A at 20 to 30% PARo) increased zooxanthella population density, but had no effect on chl a+c per 106 zooxanthellae. Acclimation for 14 d to reduced (10 to 20% PARo) and extremely low (1 to 3% PARo) light intensities shifted 14C photoassimilation into glycerol and other compounds (probably glycerides), rather than sugars. Both ammonium addition and
feeding with Artemia salina nauplii resulted in an increase in photosynthetic assimilation of 14C into amino acids. We conclude that acclimation to reduced light consists of two processes: an increase in photosynthetic
pigments and in zooxanthella population density. Both processes require nitrogen, the increase in zooxanthella population
density needing more; this adaptation is therefore limited in nitrogen-poor sea water.
Received: 19 June 1998 / Accepted: 13 June 2000 相似文献
936.
Modulation of the free amino acid pool and protein content in populations of the brine shrimp Artemia spp. 总被引:3,自引:0,他引:3
S. Helland G. V. Triantaphyllidis H. J. Fyhn M. S. Evjen P. Lavens P. Sorgeloos 《Marine Biology》2000,137(5-6):1005-1016
Free amino acid (FAA) and protein content were measured in various developmental stages of Artemia franciscana, from cysts to Instar III metanauplii. In addition, decapsulated cysts of 15 Artemia populations from different localities were compared with respect to their FAA and protein content. Furthermore, the content
and composition of the FAA pool were modulated by hatching the cysts at various salinities, and by enriching the nauplii with
algae or a lipid-enrichment emulsion. The FAA content increased threefold from cysts to nauplii, and Instar III metanauplii
contained nearly 50% taurine of total FAA. Cysts of A. franciscana were found to contain one-third the amount of FAA compared to the other Artemia species investigated. The content and pool composition of FAA was successfully modulated in 11 of 13 populations, where by
the content of FAA was significantly increased when hatched at high salinity. Finally, enrichment elevated the content of
FAA and changed the pool composition, thereby showing a dietary effect. Algal enrichment also increased the protein content.
Received: 27 September 1999 / Accepted: 17 July 2000 相似文献
937.
The accumulation of lipofuscin, which is an indictor of physiological age, in the brain of juvenile European lobster (Homarus gammarus L.) was monitored for 22 mo in three experimental temperature regimes that simulated seasonal variation in temperature in
the geographic range of this species. Metabolic rate responses to changes in temperature were estimated by measuring the activity
of the electron transport system (ETS) in muscle tissue and in vivo rates of oxygen consumption. Lipofuscin accumulation oscillated
with simulated seasonal changes in temperature and was described by seasonalised von Bertalanffy growth functions. The incremental
accumulation in lipofuscin between sampling dates was linearly related to the number of degree days that accumulated between
dates, irrespective of the amplitude of temperature fluctuation that had occurred. ETS activity increased with acclimation
temperature and was modelled using a polynomial function. This indicated a lower temperature sensitivity in the temperature
mid-range (12 to 16 °C), although the Q10 for this mid-range was 2.1. ETS activity in lobsters acclimated to 8 and 18 °C and assayed at 13 °C was similar, indicating
no compensation for changes in environmental temperature. Oxygen consumption rate was significantly higher at 14 °C than at
10.5 °C and had a Q10 of 3.6, again suggesting no compensation to temperature change. The absence of metabolic compensation in response to temperature
change in H. gammarus is consistent with the predictability of changes in temperature and food availability in the sub-littoral environment of
this species. As lipofuscin accumulates according to metabolic rate, and metabolic rate in H. gammarus is directly correlated with temperature, geographic differences and long-term temporal trends in temperature will need to
be considered when converting physiological age indices, obtained from lipofuscin estimates, to a chronological scale.
Received: 27 April 2000 / Accepted: 21 July 2000 相似文献
938.
The endemic New Zealand echinoid, Evechinus chloroticus (Valenciennes), was sampled approximately monthly from September 1990 to October 1994 at three sites in Tory Channel, Marlborough
Sounds, New Zealand. These channel sites (outer, mid and inner) were up to 20 km from the open ocean and differed in their
shore type, exposure to wave action and macrophyte abundance. E. chloroticus showed an annual reproductive cycle at each site, with gametogenesis commencing in the late austral winter and spawning in
summer. Maximum gonad indices (reproductive potential) varied spatially, with the outer site generally having higher maximum
gonad indices than the inner site, and temporally, with maximum gonad indices occurring earlier in 3 of the 4 seasons at the
outer site than the inner site. The mid and inner sites showed much greater variation in maximum gonad indices (range 15.83
to 26.99% and 11.87 to 20.90%, respectively) than the outer site (range 19.31 to 22.95%). Reproductive output (weight of gametes
released per gram echinoid) also varied, with the different sites showing significantly different outputs in the different
years. A regression of maximum reproductive potential against reproductive output was significant ( p < 0.001), and had a positive slope with an r
2 of 0.79. While, the initiation of gametogenesis was relatively synchronous between sites and years, and is possibly cued
by increasing daylength, it progressed at different rates among populations. Spawning did show spatial and temporal variability,
occurring near the time of highest sea-surface temperatures (∼15 °C). The observed variations in reproductive cycle may be
related to small-scale variability in diet and environmental conditions. Furthermore, asynchronous spawning, variable spawning
duration, and variable reproductive output are likely to strongly influence annual recruitment variability in E. chloroticus, with different larval subpopulations contributing unequally in different years. The ecological consequences of this, both
for the ability of E. chloroticus to propagate itself in space and time and for the management of the developing E. chloroticus fishery in New Zealand, are discussed.
Received: 9 December 1998 / Accepted: 13 June 2000 相似文献
939.
Phylogenetic analyses of the left domain of the mitochondrial DNA control-region sequence have been used to examine the relationships
among species of the genus Merluccius (Rafinesque, 1810), and to compare these with hypotheses based on morphological, meristic and allozyme characters. Analysis
of aligned sequences revealed that transition bias was much lower than in mammalian mtDNA, and that nucleotide composition
of control-region sequences was biased toward A and T. We have roughly calibrated a molecular clock for the genus, based on
the rise of the Isthmus of Panamá, which is believed to have created a barrier to dispersal between marine species of the
Atlantic and Pacific Oceans. Our mtDNA-based phylogeny was highly congruent with allozyme-based phylogenies, but poorly so
with a previously described phylogeny based on morphology. Specifically, our phylogeny resolved two well-supported principal
clades, one of American (west Atlantic and east Pacific) species and the other of Euro–African (east Atlantic) species. This
suggests an evolutionary history during which the ancestral lineage of Merluccius was divided between two geographic regions, with subsequent dispersal and vicariant events resulting in the evolution and
distribution of extant taxa. However, the relationships between some taxa within the American clade could not be resolved.
We suggest that this is consistent with an hypothesis of a rapid origin and radiation of these taxa.
Received: 12 December 1998 / Accepted: 15 October 1999 相似文献
940.
The benthic response to a plume front was studied in two areas of the northern Adriatic (Mediterranean Sea) differently influenced
by the Po River freshwater input. Sediment samples were collected in June 1996 and February 1997 from 12 stations. The adopted
sampling strategy was able to identify the front line in real time by satellite images and to locate sampling stations along
an inner–outer plume gradient in order to cover the benthic area beneath the river plume, where enhanced biological production
was expected, and open-sea sediments not directly influenced by freshwater inputs. Meiofaunal parameters were compared to
the physical conditions and to phytodetritus inputs, organic matter accumulation and bacterial secondary production. The sediments
of the Adriatic Sea were characterised by high concentrations of phytopigments (0.6 to 13.9 μg g−1 for chlorophyll a and 1.2 to 17.7 μg g−1 for phaeopigments) and biopolymeric organic carbon (0.15 to 3.02 mg g−1). The plume system extended for a large sector of the northern Adriatic. In the northern area, a large and highly dynamic
plume area was coupled with a sediment organic matter concentration significantly higher than in open-sea sediments. In the
southern sector, where the plume area and the front line did not change markedly during the year, plume–benthic coupling was
evident only in the sediments beneath the front, and corresponded to phaeopigment accumulation. Bacterial parameters and secondary
production were high and significantly higher in the frontal area than at open-sea stations. Meiofauna density (1342 to 8541
ind. 10 cm−2) did not change either by season or between areas and was significantly correlated with phaeopigments and bacterial secondary
production. Meiofauna displayed different responses to plume inputs in the two sampling areas. In the northern sector, meiofauna
density was coupled with organic matter distribution and displayed highest values beneath the plume. In the southern sector,
the densities of copepods, turbellarians and kinorhynchs displayed highest values under the front in summer, and the same
applied to total meiofauna density in winter. Juvenile decapods and copepod nauplii significantly increased their densities
in sediments beneath the front. Data presented in the present study suggest that plume inputs and frontal systems, enhancing
phytodetritus accumulation and benthic bacterial response, might influence density, composition and distribution of meiofaunal
assemblages. As river plumes are highly variable systems affecting the trophic characteristics of the sediments underneath,
their dynamics should be considered when analysing mesoscale spatial changes of meiofaunal assemblages.
Received: 30 November 1999 / Accepted: 24 May 2000 相似文献