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991.
992.
Werner von Bloh Christine Bounama Klaus EisenackBrigitte Knopf Oliver Walkenhorst 《Ecological modelling》2008
To determine the influence of the biosphere on weathering we use a dynamic model of the global carbon cycle. It takes into account the most important processes for the long-term evolution of the Earth. The model is solved under a slowly changing environment of increasing solar luminosity and volcanic activity and continental area. By comparing the model results for the global average temperature with data derived from δ18O values from cherts it is possible to quantify the biogenic enhancement factor of weathering. For this purpose a newly developed inverse viability method is applied, which allows for calculating the range of possible biogenic enhancement factors consistent with the data. We find that in the Precambrian the weathering was 5.4 times lower than in the Phanerozoic era. This supports the hypothesis that the Cambrian explosion was caused by a positive feedback between the spread of biosphere, increased silicate weathering, and a consequent cooling of the climate. 相似文献
993.
Cooperation among non-kin has been attributed sometimes to reciprocal altruism: Two or more individuals exchange behaviour
that benefits the respective partner. According to direct reciprocity, cooperation is based on past behaviour of a known partner.
In contrast, in generalised reciprocity, cooperation is based on anonymous social experience where the identity of the partner
is irrelevant. In a previous study, female Norway rats (Rattus norvegicus) were found to cooperate according to a generalised reciprocity mechanism. In this study, we tested whether Norway rats would
also cooperate as predicted by a direct reciprocity mechanism and whether direct reciprocity would cause a higher propensity
to cooperate than generalised reciprocity. Focal animals were experimentally manipulated to receive social experience from
known or unknown, helpful or defecting partners in an instrumental cooperative task. Our first experiment shows that rats
are more helpful towards a partner from which they had received help before than towards a partner that had not helped (i.e.
direct reciprocity). Our second experiment revealed that after receiving help by others, rats were more helpful towards a
partner from which they had received help before than towards a new partner (i.e. direct reciprocity generated a higher cooperation
propensity than generalised reciprocity). We conclude that in female Norway rats, the tendency to cooperate is influenced
by partner-specific information. To our knowledge, this is the first study to demonstrate direct reciprocity in rodents, and
it is the first study testing direct vs generalised reciprocity in animals. 相似文献
994.
Insect larvae increase in size with several orders of magnitude throughout development making them more conspicuous to visually
hunting predators. This change in predation pressure is likely to impose selection on larval anti-predator behaviour and since
the risk of detection is likely to decrease in darkness, the night may offer safer foraging opportunities to large individuals.
However, forsaking day foraging reduces development rate and could be extra costly if prey are subjected to seasonal time
stress. Here we test if size-dependent risk and time constraints on feeding affect the foraging–predation risk trade-off expressed
by the use of the diurnal–nocturnal period. We exposed larvae of one seasonal and one non-seasonal butterfly to different
levels of seasonal time stress and time for diurnal–nocturnal feeding by rearing them in two photoperiods. In both species,
diurnal foraging ceased at large sizes while nocturnal foraging remained constant or increased, thus larvae showed ontogenetic
shifts in behaviour. Short night lengths forced small individuals to take higher risks and forage more during daytime, postponing
the shift to strict night foraging to later on in development. In the non-seasonal species, seasonal time stress had a small
effect on development and the diurnal–nocturnal foraging mode. In contrast, in the seasonal species, time for pupation and
the timing of the foraging shift were strongly affected. We argue that a large part of the observed variation in larval diurnal–nocturnal
activity and resulting growth rates is explained by changes in the cost/benefit ratio of foraging mediated by size-dependent
predation and time stress. 相似文献
995.
Coral Reef Habitats as Surrogates of Species, Ecological Functions, and Ecosystem Services 总被引:3,自引:0,他引:3
PETER J. MUMBY††† KENNETH BROAD† DANIEL R. BRUMBAUGH‡§ CRAIG P. DAHLGREN ALASTAIR R. HARBORNE ALAN HASTINGS†† KATHERINE E. HOLMES‡ CARRIE V. KAPPEL‡‡ FIORENZA MICHELI§§ JAMES N. SANCHIRICO 《Conservation biology》2008,22(4):941-951
Abstract: Habitat maps are often the core spatially consistent data set on which marine reserve networks are designed, but their efficacy as surrogates for species richness and applicability to other conservation measures is poorly understood. Combining an analysis of field survey data, literature review, and expert assessment by a multidisciplinary working group, we examined the degree to which Caribbean coastal habitats provide useful planning information on 4 conservation measures: species richness, the ecological functions of fish species, ecosystem processes, and ecosystem services. Approximately one‐quarter to one‐third of benthic invertebrate species and fish species (disaggregated by life phase; hereafter fish species) occurred in a single habitat, and Montastraea‐dominated forereefs consistently had the highest richness of all species, processes, and services. All 11 habitats were needed to represent all 277 fish species in the seascape, although reducing the conservation target to 95% of species approximately halved the number of habitats required to ensure representation. Species accumulation indices (SAIs) were used to compare the efficacy of surrogates and revealed that fish species were a more appropriate surrogate of benthic species (SAI = 71%) than benthic species were for fishes (SAI = 42%). Species of reef fishes were also distributed more widely across the seascape than invertebrates and therefore their use as a surrogate simultaneously included mangroves, sea grass, and coral reef habitats. Functional classes of fishes served as effective surrogates of fish and benthic species which, given their ease to survey, makes them a particularly useful measure for conservation planning. Ecosystem processes and services exhibited great redundancy among habitats and were ineffective as surrogates of species. Therefore, processes and services in this case were generally unsuitable for a complementarity‐based approach to reserve design. In contrast, the representation of species or functional classes ensured inclusion of all processes and services in the reserve network. 相似文献
996.
A Graph-Theory Framework for Evaluating Landscape Connectivity and Conservation Planning 总被引:9,自引:0,他引:9
Abstract: Connectivity of habitat patches is thought to be important for movement of genes, individuals, populations, and species over multiple temporal and spatial scales. We used graph theory to characterize multiple aspects of landscape connectivity in a habitat network in the North Carolina Piedmont (U.S.A).. We compared this landscape with simulated networks with known topology, resistance to disturbance, and rate of movement. We introduced graph measures such as compartmentalization and clustering, which can be used to identify locations on the landscape that may be especially resilient to human development or areas that may be most suitable for conservation. Our analyses indicated that for songbirds the Piedmont habitat network was well connected. Furthermore, the habitat network had commonalities with planar networks, which exhibit slow movement, and scale-free networks, which are resistant to random disturbances. These results suggest that connectivity in the habitat network was high enough to prevent the negative consequences of isolation but not so high as to allow rapid spread of disease. Our graph-theory framework provided insight into regional and emergent global network properties in an intuitive and visual way and allowed us to make inferences about rates and paths of species movements and vulnerability to disturbance. This approach can be applied easily to assessing habitat connectivity in any fragmented or patchy landscape. 相似文献
997.
Some characteristics of the distribution of heavy metals
in urban topsoil of Xuzhou,China 总被引:3,自引:0,他引:3
An assessment is presented of distribution characteristics of heavy metals in the urban topsoil from the city of Xuzhou. The
concentrations of Ag, Al, As, Au, Ba, Be, Bi, Cd, Co, Cr, Cu, Fe, Ga, Hg, Li, Mn, Mo, Ni, Pb, Pd, Pt, Sb, Sc, Se, Sn, V and
Zn have been determined from 21 soil samples. Examination of lognormal distribution plots indicates that the diagrams of Al,
Be, Fe, Ga, Li, and V are almost linear suggesting that these metals are almost unaffected by anthropogenic activities while
the plots for As, Cd, Cu, Pb, Pd, Pt, Se, Zn and others are not linear probably due to anthropogenic activities from which
these metals are delivered to the soils. Al is used for mineralogical normalization of these data. An evaluation of background
values for topsoil is also carried out by means of lognormal distribution plots. The results show our background values obtained
from the lognormal distribution plots are comparable to those values of uncontaminated soils of Xuzhou obtained by previous
work except for Cd and Hg. At present, no explanation for the exceptions Cd and Hg can be given. 相似文献
998.
低温等离子体技术在环境工程中的研究进展 总被引:11,自引:0,他引:11
低温等离子体技术是一种用来处理环境污染问题的高新技术。介绍了低温等离子体的概念和去除污染物的机理,阐述了该技术在国内外环境工程中的应用现状,分析其存在的问题,并指出今后的发展方向。 相似文献
999.
1000.