全文获取类型
收费全文 | 5440篇 |
免费 | 652篇 |
国内免费 | 1562篇 |
专业分类
安全科学 | 1558篇 |
废物处理 | 39篇 |
环保管理 | 657篇 |
综合类 | 3044篇 |
基础理论 | 851篇 |
环境理论 | 1篇 |
污染及防治 | 222篇 |
评价与监测 | 310篇 |
社会与环境 | 419篇 |
灾害及防治 | 553篇 |
出版年
2024年 | 50篇 |
2023年 | 180篇 |
2022年 | 309篇 |
2021年 | 380篇 |
2020年 | 333篇 |
2019年 | 343篇 |
2018年 | 277篇 |
2017年 | 335篇 |
2016年 | 356篇 |
2015年 | 394篇 |
2014年 | 345篇 |
2013年 | 495篇 |
2012年 | 499篇 |
2011年 | 545篇 |
2010年 | 349篇 |
2009年 | 357篇 |
2008年 | 255篇 |
2007年 | 323篇 |
2006年 | 335篇 |
2005年 | 215篇 |
2004年 | 157篇 |
2003年 | 132篇 |
2002年 | 119篇 |
2001年 | 65篇 |
2000年 | 91篇 |
1999年 | 76篇 |
1998年 | 43篇 |
1997年 | 48篇 |
1996年 | 42篇 |
1995年 | 33篇 |
1994年 | 42篇 |
1993年 | 25篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1972年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有7654条查询结果,搜索用时 15 毫秒
781.
Risk taking during parental care: a test of three hypotheses applied to the pied flycatcher 总被引:2,自引:0,他引:2
According to life-history theory, there will often be a conflict between investment in current versus future reproduction.
If a predator appears during breeding, parents must make a compromise between ensuring the growth and survival of offspring
(nest defence, feeding and brooding of young), and reducing the risk of predation to ensure their own survival. We model three
hypotheses for the outcome of this conflict which are particularly relevant for altricial birds. They are not mutually exclusive,
but focus on different costs and benefits. (1) Parental investment is determined by the parents’ own risk of predation. This
hypothesis predicts that a lone parent should take smaller risks than a parent that has a mate. (2) Parental investment is
related to the reproductive value of the offspring: Parents are predicted to take greater risks for larger broods, larger-sized
or older offspring. (3) Finally, we present the new hypothesis that parental investment is related to the harm that offspring
would suffer during a period of no parental care (incubation, brooding, feeding). This hypothesis predicts that parents should
take greater risks for younger offspring, or for offspring in poorer condition, because the marginal benefit of parental care
is largest in such cases. Hence, one may also expect that lone parents should take greater risks than two parents because
their offspring are more in need of care. We tested these hypotheses on the pied flycatcher (Ficedula hypoleuca) by presenting a stuffed predator of the parents (a sparrowhawk, Accipiter nisus) close to the nest when parents were feeding the young. Risk taking was measured as the time that elapsed until the first
visit to the nest. Most support was found for the ‘‘harm to offspring’’ hypothesis. Previous studies have usually measured
the intensity of nest defence against typical nest predators, and have found evidence for the ‘‘reproductive value of offspring’’
hypothesis. However, our model predicts that the importance of the reproductive value of the offspring should decrease relative
to the harm that offspring would suffer if they were not cared for when the predator type changes from a nest predator to
a predator of adults, and when conditions for breeding turn from good to bad.
Received: 13 April 1995/Accepted after revision: 11 March 1996 相似文献
782.
Designatable Units for Status Assessment of Endangered Species 总被引:8,自引:1,他引:8
DAVID M. GREEN 《Conservation biology》2005,19(6):1813-1820
Abstract: Species status assessment and the conservation of biological diversity may require defining units below the species level to portray probabilities of extinction accurately and to help set priorities for conservation efforts. What those units should be has been debated in the scientific literature largely in terms of evolutionarily significant units (ESUs), but this discourse has had little impact on government policy with regard to status assessment. As with species concepts, the variously proposed ESU concepts have not been resolvable into a single approach. The need for a practicable procedure to identify infraspecific entities for status assignment is the motivation behind employing designatable units (DUs). In aid of a policy to prevent elements of biodiversity from becoming extinct or extirpated, DUs are determined during the process of resolving a species' conservation status according to broadly applicable guidelines. The procedure asks whether putative DUs are distinguishable based on a reliably established taxonomy or a well-corroborated phylogeny, compelling evidence of genetic distinction, range disjunction, and/or biogeographic distinction as long as extinction probabilities also differ. The language of the DU approach avoids wording that implies value judgments concerning evolutionary importance or significance. Because species conservation status assessment is not science but, rather, the use of science to further policy, DUs contribute to a precautionary approach to listing whereby status may be assessed even though knowledge of systematic relationships below the species level may be lacking or unresolved. The pragmatic approach of using DUs has been adopted by the Committee on the Status of Endangered Wildlife in Canada for status assessment of species under the Canadian Species at Risk Act. 相似文献
783.
Market responses to hurricanes 总被引:7,自引:0,他引:7
Daniel G. Hallstrom V. Kerry Smith 《Journal of Environmental Economics and Management》2005,50(3):541-561
This paper uses one of the strongest hurricanes to hit the US, Andrew in 1992, to define a quasi-random experiment that permits estimation of the responses of housing values to information about new hurricanes. Lee County, Florida did not experience damage from Andrew. The storm was a “near-miss.” We hypothesize that Andrew conveyed risk information to homeowners in the county. A difference-in-differences (DND) framework identifies the effect of this information on property values in areas likely to experience significant storm damage. The DND findings indicate at least a 19 percent decline in property values. 相似文献
784.
Predation and hunger are threats for most organisms, and appropriate behavioural responses to both factors should be shaped by natural selection. In combination, however, the behavioural demands of predation avoidance and effective foraging often cannot be satisfied at the same time and lead to a conflict within organisms. We examined the behavioural responses of two closely-related species of tadpoles, Rana lessonae and R. esculenta, to simulated predation by fish and hunger. Tadpoles, hatched and reared in the laboratory, were tested in a three-way factorial (predation risk × hunger × species) experiment with four predation levels and four hunger levels. Both species decreased their swimming activity with increasing predation risk. Predation risk did not influence the amount of activity time invested in feeding but caused the tadpoles to spend less time in patches with food. Refuges were not used to avoid predation. R. esculenta was more sensitive to predation risk than R. lessonae. Hunger increased both the activity of tadpoles and the amount of activity time invested in feeding, thus indicating an increased energy intake. No interactions were observed between predation risk and hunger. These results show that tadpoles possess genetically-based behavioural mechanisms that allow them to respond in a graded manner to predation and hunger. However, they did not balance the two conflicting demands of predation avoidance and effective foraging; the two mechanisms appeared to act independently.
Correspondence to: R.D. Semlitsch 相似文献
785.
An important topic in the registration of pesticides and the interpretation of monitoring data is the estimation of the consequences of a certain concentration of a pesticide for the ecology of aquatic ecosystems. Solving these problems requires predictions of the expected response of the ecosystem to chemical stress. Up until now, a dominant approach to come up with such a prediction is the use of simulation models or safety factors. The disadvantage of the use of safety factors is a crude method that does not provide any insight into the concentration–response relationships at the ecosystem level. On the other hand, simulation models also have serious drawbacks like that they are often very complex, lack transparency, their implementation is expensive and there may be a compilation of errors, due to uncertainties in parameters and processes. In this paper, we present the expert model prediction of the ecological risks of pesticides (PERPEST) that overcomes these problems. It predicts the effects of a given concentration of a pesticide based on the outcome of already performed experiments using experimental ecosystems. This has the great advantage that the outcome is more realistic. The paper especially discusses how this model can be used to translate measured and predicted concentrations of pesticides into ecological risks, by taking data on measured and predicted concentrations of atrazine as an example. It is argued that this model can be of great use to evaluate the outcome of chemical monitoring programmes (e.g. performed in the light of the Water Framework Directive) and can even be used to evaluate the effects of mixtures. 相似文献
786.
Statistical inference on patch-specific survival and movement rates from marked animals 总被引:1,自引:0,他引:1
Michael J. Conroy Jon E. Anderson Stephen L. Rathbun David G. Krementz 《Environmental and Ecological Statistics》1996,3(2):99-116
Empirical estimates of patch-specific survival and movement rates are needed to parametrize spatially explicit population
models, and for inference on the effects of habitat quality and fragmentation on populations. Data from radio-marked animals,
in which both the fates and habitat locations of animals are known over time, can be used in conjunction with continuous-time
proportional hazards models to obtain inferences on survival rates. Discrete-time conditional logistic models may provide
inference on both survival and movement rates. We use Monte Carlo simulation to investigate accuracy of estimates of survival
from both approaches, and movement rates from conditional logistic regression, for two habitats. Bias was low (relative bias
< 0.04) and interval coverage accurate (close to the nominal 0.95) for estimates of habitat effect on survival based on proportional
hazards. Bias was high (
relative bias 0.60) and interval coverage poor (
= 0.26 vs. nominal 0.95) for estimates of habitat effect based on conditional logistic regression; bias was especially influenced
by heterogeneity in survival and the shape of the hazard function, whereas both bias and coverage were affected by ‘memory’
effects in movement patterns. Bias estimates of movement rate was low (
relative bias < 0.05), but interval coverage was poor (
= 0.48–0.80), possibly as a result of poor performance of a Taylor series estimate of variance. An example is provided from
a radio-telemetry study of 47 wintering American woodcock (Scolopax minor), illustrating practical difficulties in field studies to parametrize these models. We also discuss extensions of continuous-time
models to explicitly include a movement process, and further examine tradeoffs between continuous and discrete models. 相似文献
787.
基因组学、蛋白组学和代谢组学技术为生态毒理学的发展提供了生物高通量的技术手段,构成了新的交叉学科——生态毒理基因组学.生态毒理基因组学着重研究环境毒物暴露下非靶生物基因和蛋白的表达,能够在基因组水平上更深入地理解环境污染物的致毒机制,同时,它引进生物标志物为生态风险评价提供了平台.论文对生态毒理基因组学的发展历程、技术支持、模式生物及其在生态风险评价方面的应用进行了综述,以推动生态毒理基因组学技术在我国的进一步发展. 相似文献
788.
789.
Gilberto Pasinelli Mathis Müller Michael Schaub Lukas Jenni 《Behavioral ecology and sociobiology》2007,61(7):1061-1074
Studies of animal breeding dispersal have often focused on possible causes, whereas its adaptive significance has received
less attention. Using an information-theoretic approach, we assessed predictions of four hypotheses relating to causes and
consequences of breeding dispersal in a migratory passerine, the red-backed shrike Lanius collurio. As predicted by the reproductive performance hypothesis, probability of breeding dispersal in females (though not in males)
decreased with increasing annual average number of fledglings produced in the past year, but there was no association with
conspecific reproductive performance in either sex. The site choice hypothesis, stating that individuals disperse to improve
breeding site quality, received support in males only, as dispersal probability was positively associated to a measure indicating
low territory quality. The social constraints hypothesis, referring to dispersal in relation to intraspecific interactions,
received little support in either sex. The predation risk hypothesis was hardly supported either. Consequences of dispersal
were marginal in both sexes because neither fledgling production in females, nor territory quality in males improved after
dispersal. In addition, males settled on territories closer to the forest edge than those occupied predispersal, which is
opposite to the prediction of the predation risk hypothesis. We conclude that own reproductive success was the major factor
determining dispersal behavior in females, whereas territory quality and possibly predation risk were most important in males.
Overall, breeding dispersal appeared not to be adaptive in this dense population inhabiting an optimal habitat. 相似文献
790.
AbstractContaminated food chain is a serious contender for arsenic (As) uptake around the globe. In Nadia, West Bengal, we trace possible means of transfer of As from multiple sources reaching different trophic levels, and associated seasonal variability leading to chronic As uptake. This work considers possible sources-pathways of As transfer through food chain in rural community. Arsenic concentration in groundwater, soil, rice, and vegetable-samples collected detected in different harvest seasons of 2014 and 2016. Arsenic level in shallow groundwater samples ranged from 0.1 to 354?µg/L, with 75% of the sites above the prescribed limit by WHO (10?µg/L) during the boro harvest season. High soil As content (~20.6?mg/kg), resulted in accumulation of As in food crops. A positive correlation in As conc. with increase over period in all sites indicating gradual As accumulation in topsoil. Unpolished rice samples showed high As content (~1.75?mg/kg), polishing reduced 80% of As. Among vegetables, the plant family Poaceae with high irrigation requirements and Solanaceae retaining high moisture, have the highest levels of As. Contaminated animal fodder (Poaceae) and turf water for cattle are shown to contaminate milk (0.06 to 0.24?µg/L) and behoves strategies, practices to minimize As exposure. 相似文献