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991.
Arm damage is a widely reported but superficially investigated aspect of the biology of the starfish Asterias rubens L. In the present study, the incidence of arm damage was surveyed in populations of A.
rubens at two sites in the Firth of Clyde, Scotland, and three sites in Gullmarsfjorden, Sweden. The mean (±SD) incidence across
all sites of individuals with basal arm damage (resulting from detachment at the basal autotomy plane) was 19.69 ± 8.86%,
the incidence of those with distal arm damage (resulting from amputation at more distal levels) was 7.74 ± 10.01%. The mean
incidence of arms with basal damage was 5.28 ± 4.12%, of those with distal damage 1.83 ± 2.45%. There was a significant negative
correlation between size and the incidence of basal damage at all but one site, but no significant correlation between size
and distal damage at any site. Mechanical tests on specimens of the aboral body wall from the basal region of the arm (which
included the autotomy plane) and from a more distal region revealed that with increasing body size there was a significant
increase in yield stress, ultimate stress and Young's modulus (stiffness) but no significant change in yield strain and ultimate
strain. There was no significant difference between the relationships for basal and distal specimens. It is hypothesised that
in larger individuals increased mechanical toughness replaces autotomy as an effective antipredator strategy. Using two methods
to induce autotomy, a significant positive correlation between size and the delay between the onset of stimulation and arm
detachment was found; this may represent a size-related decline in the efficiency of the autotomy mechanism through the relaxation
of selection pressure. Since size is an unreliable indicator of age in A.
rubens, the trends identified herein can be interpreted only tentatively as age-associated phenomena.
Received: 4 September 1999 / Accepted: 17 February 2000 相似文献
992.
The nature of heat coma was examined in the edible periwinkle Littorina littorea (L.). Duration of acclimation did not influence heat-coma temperature at 12 °C, although other acclimation temperatures were
important in influencing thermal tolerance, with positive shifts in coma temperature observed in response to elevated temperatures.
Previous thermal history also influenced heat-coma temperatures. Individuals subjected to repeat heat-coma events on a daily
basis showed significant declines (P < 0.05) in coma-temperature; in contrast individuals exposed to repeat heat-coma events on a weekly basis showed no decline
in thermal tolerance. Size-effects occurred at selected sites, where decreased heat-coma temperatures were recorded in large
individuals.
Received: 16 August 1999 / Accepted: 13 June 2000 相似文献
993.
Acoustic telemetry was used to examine patterns of activity and space utilisation of coelacanths, nocturnal predators which
spend the day in submarine caves. Nine coelacanths (Latimeria chalumnae) were tracked, each for a period of 1 to 16 nights at Grande Comore, West Indian Ocean. Activities lasted on average 9 h,
usually starting shortly after sunset and ending before sunrise. Vertically, coelacanths moved up and down at and below cave
level by following the bottom contour, mainly between 180 and 400 m depth. The deepest record was 698 m, the shallowest 133 m.
Most time was spent between 200 and 300 m depth. Large individuals performed deep excursions to depths below 400 m, usually
once per night. The fish spent most time in water temperatures of 15 to 19 °C; they rarely ventured into waters warmer than
22 °C measured at depths shallower than 160 m depth. Horizontally, coelacanths stayed in narrow areas ranging from <1 to 10 km
of coastline. Coelacanths are extremely slow drift-hunters with an estimated average swimming speed of 3.2 m min−1, often travelling not more than 3 km per night. They probably take advantage of local upwelling and downwelling and slow
currents occurring parallel to the steep slopes. This study shows that coelacanths are inhabitants of the subphotic zone,
where they are active mainly below the depth of their daytime refuges.
Received: 7 July 1999 / Accepted: 11 February 2000 相似文献
994.
Spatial and temporal patterns of predation on seeds of the seagrass Phyllospadix torreyi S. Watson were quantified at four sites near Santa Barbara, California, USA. Over a period of four flowering seasons during
1995 to 1998, monthly patterns of seed fall and intensity of seed predation were similar among sites, but were temporally
quite variable. Abundance of dispersed seeds varied greatly both among seasons and years. Within any one year, seeds were
present in the environment every month, but they peaked in abundance during the fall months following the annual flowering
period. Seeds were more abundant during the earlier years of the study. The intensity of predation steadily increased throughout
the study period, from a low of ≤10% seeds consumed during 1995 to ∼50% consumption by 1997, and it was not correlated with
abundance of seeds in the environment. Pre-dispersal seed loss also was estimated in two flowering seasons by counting the
numbers of seeds consumed prior to release from the plant, and was relatively low (<15%). No differences were detected among
the four study sites in patterns of pre-dispersal loss. Field surveys were done at two sites to identify potential seed predators.
Three of the most abundant species identified in these surveys were tested in the laboratory to determine size-specific patterns
of feeding activity and to assess which early life stages of P. torreyi (fruits within spadices, dehisced fruits, seedlings) were most vulnerable to predation. All three of the early life stages
were consumed. The crabs Pugettiaproducta (Randall) and Pachygrapsus crassipes Randall were much more voracious predators than the isopod Idotea resecata Stimpson.
Received: 8 June 1999 / Accepted: 2 February 2000 相似文献
995.
The reproductive ecology of two eastern Pacific zooxanthellate coral species was examined as part of a continuing series of studies relating bleaching/mortality events caused by the El Niño–Southern Oscillation disturbance, and is described for study sites in Costa Rica, Panamá, and the Galápagos Islands (Ecuador). This study deals with the sibling agariciid species Pavona varians and Pavona sp.a over a 13?yr period (1985 to 1997). Both Pavona species are broadcast-spawners with some gonochoric, but mostly sequential hermaphroditic colonies. Minimum colony sizes (and ages) at first reproduction were 5?cm (5?yr) and 3?cm (2 to 3?yr), respectively, in P. varians and Pavona sp.a. In the Panamá and Galápagos populations, gonochoric colonies spawn eggs or sperm at least monthly. Six fecundity attributes were not significantly different in the two species, but the eggs of P. varians are white to beige and positively buoyant, and those of Pavona sp.a are dark green and neutrally to negatively buoyant. Eggs of both species lack zooxanthellae. Both species are reproductively active year-round, with maximum activity in the dry season in the nonupwelling Gulf of Chiriquí, and in the wet season in the upwelling Gulf of Panamá. Spawning is predominantly during full moon, and possibly also at new moon at most study sites. Spawning in P. varians and Pavona sp.a is 12?h out of phase, with the former species spawning ~1?h before sunrise and the latter about 1?h after sunset. The fecundity of Pavona spp. at Caño and the Galápagos Islands was much greater (19?900 to 27?900 eggs cm?2?yr?1) than at all Panamá sites (14?800 to 19?800 eggs cm?2?yr?1). Intraspecific crosses in both species resulted in swimming planula larvae after 25 to 36?h. Recruitment of P. varians was highest in Panamá, moderate in Costa Rica, and nil in the Galápagos Islands, matching, respectively, the contributions of P. varians to the pre-1982/1983 El Niño coral-population abundances in these areas. Recruitment success of P. varians at Uva Island was significantly related to maximum monthly positive sea surface-temperature (SST) anomalies that occurred in the year preceding recruitment over the period 1982 to 1996; recruitment failed when SST anomalies exceeded 1.6 to 1.9?C° during the severe ENSO events of 1982/1983 and 1997/1998. 相似文献
996.
Genetic variation in 15 Holothuria (Microthele) nobilis (Selenka, 1867) populations on the Great Barrier Reef was studied at seven polymorphic allozyme loci. Although populations
were separated by distances up to 1300 km, there were no apparent restrictions to gene flow (F
ST
values were not significantly different from 0) and the maximum Nei's unbiased genetic distance was 0.003. Populations were
in Hardy–Weinberg equilibrium at all loci. The estimated maximum sexual input [this is the ratio of the number of sexually
produced individuals (N*) to the sample size (N
i
)] and the minimum sexual input [this is the ratio of the number of genotypes (N
go
) over the sample size (N
i
)] were used as estimators for the amount of asexual reproduction. Both parameters suggested that H. nobilis reproduces solely by sexual means (N*:N
i
: = 1; N
go
:N
i
= 0.74 to 1). The allozyme data indicated high gene flow between populations, but the possibility that allozyme frequencies
may not be at equilibrium means that it was not possible to distinguish whether the patterns reflect present-day dispersal
or dispersal that occurred in the past.
Received: 27 March 2000 / Accepted: 29 June 2000 相似文献
997.
L. Zane L. Ostellari L. Maccatrozzo L. Bargelloni J. Cuzin-Roudy F. Buchholz T. Patarnello 《Marine Biology》2000,136(2):191-199
Meganyctiphanes norvegica (M. Sars)is a pelagic crustacean that plays a key role in marine food webs of North Atlantic Ocean and marginal seas. We
studied eight population samples collected in the European Atlantic and Mediterranean Sea. By means of single strand conformation
polymorphism analysis (SSCP) and direct sequencing, we investigated a segment of 158 base pairs of the mitochondrial gene
coding for the subunit 1 of NADH dehydrogenase. We found 12 sequence variants among the 385 individuals studied. Analysis
of molecular variance (AMOVA) showed that 14.75% of the total genetic variability was explained by differences between populations,
thus indicating absence of panmixia for these populations. Pairwise comparisons revealed three distinct genetic pools: the
first one represented by Cadiz Bay, the second one by the Ligurian Sea, and the third one included all the NE Atlantic samples.
We also investigated one population from the Alboran Sea (within the Mediterranean basin, east of the Strait of Gibraltar).
This population was found to be genetically intermediate between the NE Atlantic samples and the Ligurian sample, suggesting
that the restriction to the gene flow is not associated with the Strait of Gibraltar, but possibly with the Oran–Almeria oceanographic
front. The present work indicates that M. norvegica, although endowed with a high dispersal capacity because of its pelagic habit, can develop separate breeding units inside
the same oceanic basin (the Atlantic). Furthermore, the Ligurian sample should be considered as a distinct evolutionary entity,
separated from the Atlantic population.
Received: 2 May 1999 / Accepted: 26 November 1999 相似文献
998.
Relatively few insects have invaded the marine environment, and only five species of sea skaters, Halobates Eschscholtz (Hemiptera: Gerridae), have successfully colonized the surface of the open ocean. All five species occur in the
Pacific Ocean, H. germanus White also occurs in the Indian Ocean, whereas H. micans Esch- scholtz is the only species found in the Atlantic Ocean. We sequenced a 780 bp long region of the mitochondrial cytochrome
oxidase subunit I gene (COI) for a total of 66 specimens of the five oceanic Halobates species. Our purpose was to investigate the genetic variation within species and estimate the amount of gene flow between
populations. We defined 27 haplotypes for H. micans and found that haplotype lineages from each of the major oceans occupied by this species are significantly different, having
sequences containing five to seven unique base substitutions. We conclude that gene flow between populations of H. micans inhabiting the Atlantic, Pacific, and Indian Ocean is limited and hypothesize that these populations have been separated
for 1 to 3 million years. Similarly, there may be limited gene flow between H. germanus populations found in the Pacific and Indian Ocean and between H. sericeus populations inhabiting the northern and southern parts of the Pacific Ocean. Finally, we discuss our findings in relation
to recent hypotheses about the influence of oceanic diffusion on the distribution and population structure of oceanic Halobates spp.
Received: 29 July 1999 / Accepted: 23 November 1999 相似文献
999.
The annual epidemic spawning period of a Scottish population of Arenicola marina (L.) has been recorded over a period of 13 yr. This population spawns between mid-October and mid-November in a discrete
spawning event over a period of 4 to 5 d. Endocrine manipulation experiments showed that spawning is induced in females only
if sufficient titres of PMH (prostomial maturation hormone) are present in the prostomia. These levels are attained during
the 2 to 3 wk prior to the natural spawning date. The East Sands, St. Andrews population always spawns during periods of spring
tides regardless of tidal amplitude or whether they are full- or new-moon tides. Meteorological data, including sea-temperature
data were collected for each year, and correlation of the environmental data with spawning time was attempted. Correlation
of spawning times with weather patterns showed that mean daily air pressures were significantly higher during the spawning
period than from September to November as a whole. Evidence also suggests that a reduction in sea temperature is required
prior to spawning. A significant moderate negative correlation was found between May to July air temperatures and spawning
date, suggesting that higher May to July temperatures may induce early spawning. Daily rainfall and wind speed were also lower
during the spawning period, but not significantly so. These results indicate that air pressure (or changes therein) may act
as a final spawning cue, and the advantages of this are discussed in relation to fertilization success. A model of the interplay
between environmental parameters and the endocrine mechanisms controlling the induction of spawning is proposed. Higher than
average summer temperatures may advance gametogenesis to bring the population into a state of maturity (full-size oocytes,
well-developed sperm morulae), and may also advance spawning time. Once the population has completed gametogenesis, a drop
in sea temperature is then required to trigger an increase in endocrine titres within the prostomium, without which spawning
cannot be induced by prostomial injection. The population spawns on spring tides; however a lack of clement weather coinciding
with the spring tide will result in population-wide spawning being aborted, as in 1996. Clement weather (high pressure, low
rainfall and wind speed) in conjunction with spring tides permits spawning to proceed to completion.
Received: 21 June 1999 / Accepted: 25 January 2000 相似文献
1000.
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