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991.
Generalized additive models were used to synthesize the data from 52 publications on the gonad growth and spawning seasonality
of Paracentrotus lividus and identify spatial and temporal patterns in the reproductive processes. According to our results, Atlantic populations
spawn in spring and develop large gonads (6.4 ± 0.2% of fresh body weight (mean ± SE)), which increase in size toward higher
latitudes. While in the Mediterranean, the gonads are smaller (3.1 ± 0.1%), possibly as the result of successive spawnings
which impede nutrients accumulating in the gonads. Differences were also observed between habitats: gonad production was higher
in seagrass meadows in the Mediterranean and in subtidal rocky substrates in the Atlantic. Food availability might cause these
variations as well as the negative correlation observed between depth and the gonad index for rocky substrates. Sex and body
size do not seem to influence greatly gonad growth. 相似文献
992.
Eva Friis Møller Christian Marc Andersen Borg Sigrún H. Jónasdóttir Suree Satapoomin Cornelia Jaspers Torkel Gissel Nielsen 《Marine Biology》2011,158(3):677-688
The vertical distribution of copepods, fecal pellets and the fecal pellet production of copepods were measured at seven stations
across the Southern Indian Ocean from productive areas off South Africa to oligotrophic waters off Northern Australia during
October/November 2006. We quantified export of copepod fecal pellet from surface waters and how much was retained. Furthermore,
the potential impact of Oncaea spp. and harpacticoid copepods on fecal pellets degradation was evaluated and found to be regional substantial. The highest
copepod abundance and fecal pellet production was found in the western nutrient-rich stations close to South Africa and the
lowest at the central oligotrophic stations. The in situ copepod fecal pellet production varied between 1 and 1,000 μg C m−3 day−1. At all stations, the retention of fecal pellets in the upper 400 m of the water column was more than 99% and the vertical
export of fecal pellets was low (<0.02 mg m−2 day−1). 相似文献
993.
John M. Logan Enrique Rodríguez-Marín Nicolas Goñi Santiago Barreiro Haritz Arrizabalaga Walter Golet Molly Lutcavage 《Marine Biology》2011,158(1):73-85
Atlantic bluefin tuna (Thunnus thynnus) are highly migratory predators whose abundance, distribution, and somatic condition have changed over the past decades.
Prey community composition and abundance have also varied in several foraging grounds. To better understand underlying food
webs and regional energy sources, we performed stomach content and stable isotope analyses on mainly juvenile (60–150 cm curved
fork length) bluefin tuna captured in foraging grounds in the western (Mid-Atlantic Bight) and eastern (Bay of Biscay) Atlantic
Ocean. In the Mid-Atlantic Bight, bluefin tuna diet was mainly sand lance (Ammodytes spp., 29% prey weight), consistent with historic findings. In the Bay of Biscay, krill (Meganyctiphanes norvegica) and anchovy (Engraulis encrasicolus) made up 39% prey weight, with relative consumption of each reflecting annual changes in prey abundance. Consumption of anchovies
apparently declined after the local collapse of this prey resource. In both regions, stable isotope analysis results showed
that juvenile bluefin tuna fed at a lower trophic position than indicated by stomach content analysis. In the Mid-Atlantic
Bight, stable isotope analyses suggested that >30% of the diet was prey from lower trophic levels that composed <10% of the
prey weights based upon traditional stomach content analyses. Trophic position was similar to juvenile fish sampled in the
NW Atlantic but lower than juveniles sampled in the Mediterranean Sea in previous studies. Our findings indicate that juvenile
bluefin tuna targeted a relatively small range of prey species and regional foraging patterns remained consistent over time
in the Mid-Atlantic Bight but changed in relation to local prey availability in the Bay of Biscay. 相似文献
994.
Age effect on the antioxidant activity of Daphnia magna (Anomopoda: Daphniidae): does younger mean more sensitivity? 总被引:1,自引:0,他引:1
Alberto AC Rocío OB Fernando MJ 《Journal of environmental biology / Academy of Environmental Biology, India》2011,32(4):481-487
It has been accepted that for most species newborns and senescent organisms are more sensitive than other ages to environmental stressors. Nevertheless, it must be considered that there are several biochemical and physiological compensatory processes which are not expressed with the same magnitude during the whole life cycle. With this aim, Daphnia magna individuals of different age were exposed to hexavalent chromium, Cr (VI), at two different sublethal concentrations (0.032 and 0.0064 mg l(-1)), and the activity of some antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and glutathione peroxidase (GPx) were evaluated during most of the life cycle of this cladoceran. The antioxidant enzymatic activity showed an inverse relationship with respect to age. The activity of CAT, GR and GPx were increased in the two treated groups, at all life stages tested. On the other hand, the activity of SOD decreased in the same groups. Both, increase and decrease in the antioxidant enzymatic activities, showed significant differences with respect to the control group, being higher for the 0.032 mg l(-1) group. The Cr (VI) LC50 was also estimated for these age groups, finding statistical differences among them. Even though adults exhibited higher responses, these enzymatic activity changes should not be interpreted as higher sensitivity, since the daphnids acute chromium toxicity followed a different pattern, with increasing LC50 values according to age. 相似文献
995.
In ecological and behavioral research, drawing reliable conclusions from statistical models with multiple predictors is usually
difficult if all predictors are simultaneously in the model. The traditional way of handling multiple predictors has been
the use of threshold-based removal-introduction algorithms, that is, stepwise regression, which currently receives considerable
criticism. A more recent and increasingly propagated modelling method for multiple predictors is the information theoretic
(IT) approach that quantifies the relative suitability of multiple, potentially non-nested models based on a balance of model
fit and the accuracy of estimates. Here, we examine three shortcomings of stepwise regression, subjective critical values,
model uncertainty, and parameter estimation bias, which have been suggested to be avoided by applying information theory.
We argue that, in certain circumstances, the IT approach may be sensitive to these issues as well. We point to areas where
further testing and development could enhance the performance of IT methods and ultimately lead to robust inferences in behavioral
ecology. 相似文献
996.
Fiscal spending and the environment: Theory and empirics 总被引:1,自引:0,他引:1
Ramón López Gregmar I. Galinato Asif Islam 《Journal of Environmental Economics and Management》2011,62(2):180-198
During economic crises, governments often increase fiscal spending to stimulate the economy. While the fiscal spending surge may be temporary, spending composition is often altered in favor of expenditures on social programs and other public goods which may persist over time. We model and measure the impact of fiscal spending patterns on the environment. The model predicts that a reallocation of government spending composition towards social and public goods reduces pollution. However, increasing total government spending without altering its composition does not reduce pollution. We empirically test these predictions for air and water pollutants showing that they are fully supported. 相似文献
997.
The present study provides the longest and most intensive plankton and larval fish seasonal variability analysis in the Canary
Islands and forms a basis for understanding life cycle scheduling and interactions among species, as well as the potential
variability in transport processes of early life stages. Larval fish assemblages were studied weekly at Gran Canaria Island,
Canary Islands, from January 2005 to June 2007, which represented two contrasting hydrological and biological periods. The
former year was characterized by lower temperature and salinity that increased through 2006 and 2007. In contrast, chlorophyll
concentration and mesozooplankton biomass decreased through the same period, especially when only the late winter bloom period
was evaluated. However, ichthyoplankton abundance did not exhibit any clear pattern, as larger values were observed during
2006. The larval fish community of this oceanic island, located near the NW African upwelling, was composed of both neritic
and oceanic taxa. Two families accounted for almost half of the collected larvae: Clupeidae (21.9%) and Myctophidae (20.5%).
Although total larval concentration did not exhibit any seasonal peak linked to changes in zooplankton, the ichthyoplankton
composition gradually changed during the year due to the high diversity and extended spawning periods of the fish species
represented in samples. “Winter” and “summer” larval assemblages were identified, corresponding to the mixing and stratification
periods of the water column, respectively. These assemblages were characterized by changes in the contribution of the most
abundant annual taxa (Sardinella aurita,
Cyclothone braueri, Ceratoscopelus spp. and Gobids) and by the presence of larvae of winter (Pagellus bogaraveo, Pomacentridae sp1) or summer spawners (Pomacentridae sp2, Trachinus draco, Arnoglossus thori, Tetraodontidae sp1). Upwelling filaments shed from the NW African coast reached the sampling area three times during this
study, but changes in the local larval community were only detected in August 2005. 相似文献
998.
Cynthia A. Ursino María C. De Mársico Mariela Sued Andrés Farall Juan C. Reboreda 《Behavioral ecology and sociobiology》2011,65(12):2279-2286
Obligate avian brood parasites lay their eggs in nests of other species (hosts), which raise parasitic young. Parasitic nestlings
are likely to influence host’s parental behaviours as they typically beg for food more vigorously than young host for a given
hunger level. However, few studies have tested this idea, with conflicting results. These prior studies were largely limited
to biparental hosts, but little is known about the effect of brood parasitism on parental behaviours in hosts that breed cooperatively.
We followed a multimodel approach to examine the effect of brood parasitism on nest provisioning and helper recruitment in
the baywing (Agelaioides badius), a cooperative breeder parasitised by screaming (Molothrus rufoaxillaris) and shiny (Molothrus bonariensis) cowbirds. Multimodel inference results indicated that feeding visits increased with nestling age, cooperative group size
and number of cowbird nestlings in the brood. Brood size had little influence on feeding visits, which further suggests that
baywings adjusted their provisioning effort in response to cowbird parasitism. In addition, nests parasitised artificially
with shiny cowbird eggs or hatchlings recruited more helpers than unmanipulated nests having only host or screaming cowbird
young. Our results provide novel evidence that brood parasitism and cooperative breeding interact in determining the levels
of nest provisioning. 相似文献
999.
László Zsolt Garamszegi 《Behavioral ecology and sociobiology》2011,65(1):1-11
Scientific thinking may require the consideration of multiple hypotheses, which often call for complex statistical models at the level of data analysis. The aim of this introduction is to provide a brief overview on how competing hypotheses are evaluated statistically in behavioural ecological studies and to offer potentially fruitful avenues for future methodological developments. Complex models have traditionally been treated by model selection approaches using threshold-based removal of terms, i.e. stepwise selection. A recently introduced method for model selection applies an information-theoretic (IT) approach, which simultaneously evaluates hypotheses by balancing between model complexity and goodness of fit. The IT method has been increasingly propagated in the field of ecology, while a literature survey shows that its spread in behavioural ecology has been much slower, and model simplification using stepwise selection is still more widespread than IT-based model selection. Why has the use of IT methods in behavioural ecology lagged behind other disciplines? This special issue examines the suitability of the IT method for analysing data with multiple predictors, which researchers encounter in our field. The volume brings together different viewpoints to aid behavioural ecologists in understanding the method, with the hope of enhancing the statistical integration of our discipline. 相似文献
1000.
E. Petter Axelsson Joakim Hj?lt��n Thomas G. Whitham Riitta Julkunen-Tiitto Gilles Pilate Anders Wennstr?m 《Chemoecology》2011,21(3):161-169
Bioassays with a non-target slug (Deroceras spp.) and chemical analyses were conducted using leaf tissue from already existing genetically modified insect-resistant
aspen trees to examine whether genetic modifications to produce Bacillus thuringiensis (Bt) toxins could affect plant phytochemistry, which in turn might influence plant–herbivore interactions. Three major patterns
emerged. First, two independent modifications for Bt resistance affected the phytochemical profiles of leaves such that both
were different from the isogenic wild-type (Wt) control leaves, but also different from each other. Among the contributors
to these differences are substances with a presumed involvement in resistance, such as salicortin and soluble condensed tannins.
Second, bioassays with one Bt line suggest that the modification somehow affected innate resistance (“Innate” is used here
in opposition to the “acquired” Bt resistance) in ways such that slugs preferred Bt over Wt leaves. Third, the preference
test suggests that the innate resistance in Bt relative to Wt plants may not be uniformly expressed throughout the whole plant
and that leaf ontogeny interacts with the modification to affect resistance. This was manifested through an ontogenetic determined
increase in leaf consumption that was more than four times higher in Bt compared to Wt leaves. Our result are of principal
importance, as these indicate that genetic modifications can affect innate resistance and thus non-target herbivores in ways
that may have commercial and/or environmental consequences. The finding of a modification–ontogeny interaction effect on innate
resistance may be especially important in assessments of GM plants with a long lifespan such as trees. 相似文献