首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22448篇
  免费   596篇
  国内免费   2350篇
安全科学   988篇
废物处理   1042篇
环保管理   2960篇
综合类   5926篇
基础理论   5347篇
环境理论   9篇
污染及防治   6333篇
评价与监测   1220篇
社会与环境   1189篇
灾害及防治   380篇
  2023年   179篇
  2022年   408篇
  2021年   403篇
  2020年   373篇
  2019年   311篇
  2018年   479篇
  2017年   502篇
  2016年   627篇
  2015年   621篇
  2014年   851篇
  2013年   1954篇
  2012年   1036篇
  2011年   1308篇
  2010年   1028篇
  2009年   1102篇
  2008年   1160篇
  2007年   1150篇
  2006年   985篇
  2005年   790篇
  2004年   758篇
  2003年   741篇
  2002年   713篇
  2001年   794篇
  2000年   661篇
  1999年   463篇
  1998年   362篇
  1997年   344篇
  1996年   334篇
  1995年   387篇
  1994年   313篇
  1993年   278篇
  1992年   239篇
  1991年   228篇
  1990年   219篇
  1989年   204篇
  1988年   165篇
  1987年   143篇
  1986年   169篇
  1985年   150篇
  1984年   192篇
  1983年   152篇
  1982年   174篇
  1981年   157篇
  1980年   130篇
  1979年   149篇
  1978年   94篇
  1977年   98篇
  1975年   88篇
  1974年   93篇
  1972年   96篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
961.
Abstract: Uncertainties about biological data and human effects often delay decisions on management of endangered species. Some decision makers argue that uncertainty about the risk posed to a species should lead to precautionary decisions, whereas others argue for delaying protective measures until there is strong evidence that a human activity is having a serious effect on the species. We have developed a method that incorporates uncertainty into the estimate of risk so that delays in action can be reduced or eliminated. We illustrate our method with an actual situation of a deadlock over how to manage Hector's dolphin ( Cephalorhychus hectori ). The management question is whether sufficient risk is posed to the dolphins by mortalities in gillnets to warrant regulating the fisheries. In our quantitative risk assessment, we use a population model that incorporates both demographic ( between-individual) and environmental ( between-year) stochasticity. We incorporate uncertainty in estimates of model parameters by repeatedly running the model for different combinations of survival and reproductive rates. Each value is selected at random from a probability distribution that represents the uncertainty in estimating that parameter. Before drawing conclusions, we perform sensitivity analyses to see whether model assumptions alter conclusions and to recommend priorities for future research. In this example, uncertainty did not alter the conclusion that there is a high risk of population decline if current levels of gillnet mortality continue. Sensitivity analyses revealed this to be a robust conclusion. Thus, our analysis removes uncertainty in the scientific data as an excuse for inaction.  相似文献   
962.
Abstract: We examined six historical specimens of the endangered North Atlantic right whale ( Eubalaena glacialis ) using DNA isolated from documented baleen plates from the late nineteenth and early twentieth centuries. Sequences from the mitochondrial DNA (mtDNA) control region from these samples were compared with those from a near-exhaustive survey (269 of approximately 320 individuals) of the remaining right whales in the western North Atlantic Ocean. Our results suggest that there has been only relatively modest change in maternal lineage diversity over the past century in the North Atlantic right whale population. Any significant reduction in genetic variation in the species most likely occurred prior to the late nineteenth century. One historical specimen was from the last documented female capable of propagating one of the maternal lineages in the population today; no females in the existing population have been found to carry this mtDNA haplotype. Analysis of the only specimens from the eastern North Atlantic right whale population ever to be examined revealed that eastern and western North Atlantic right whales may not have been genetically differentiated populations. Loss of gene diversity experienced by North Atlantic right whales over the last century has been modest, and the six decades of protection have been successful in maintaining much of the maternal lineage diversity that was present in the late nineteenth century.  相似文献   
963.
Cougar Dispersal Patterns, Metapopulation Dynamics, and Conservation   总被引:4,自引:0,他引:4  
Abstract: We examined cougar (   Puma concolor ) dispersal, emigration, and immigration in the San Andres Mountains, New Mexico, from 1985 to 1995 to quantify the effects of dispersal on the local population and surrounding subpopulations. We captured, tagged, and radio-collared animals to detect the arrival of new immigrants and dispersal characteristics of progeny. We found that cougars in southern New Mexico exhibited a metapopulation structure in which cougar subpopulations were separated by expanses of noncougar habitat and linked by dispersers. Of 43 progeny (n = 20 males , 23 females ) studied after independence, only 13 females exhibited philopatric behavior. Males dispersed significantly farther than females, were more likely to traverse large expanses of noncougar habitat, and were probably most responsible for nuclear gene flow between habitat patches. We estimated that an average of 8.5 progeny (i.e., cougars born in the study area) successfully emigrated from and 4.3 cougars successfully immigrated to the San Andres Mountains each year. Concurrently, an average of 4.1 progeny were recruited into the San Andres cougar population. Protected cougar subpopulations can contribute to metapopulation persistence by supplying immigrants to surrounding subpopulations that are affected by fragmentation or offtake by humans. Cougar population dynamics and dispersal behavior dictate that cougar management and conservation should be considered on a regional scale.  相似文献   
964.
965.
The Natural Imperative for Biological Conservation   总被引:3,自引:0,他引:3  
  相似文献   
966.
967.
968.
969.
For the indigenous populations of Amazonia, invertebrates constitute an important component of the diet. We have information on entomophagy for 39 ethnic groups, about 21,4 per cent of the 182 groups known in the Amazon Basin, but the use of this non conventional food resource is probably much more widespread. We present here a data-base of all the information available for each ethnic group regarding the species included in the diet, the scientific and the ethno name if known, the stage of life-cycle consumed, the manner of preparation and, when known, the host plant. This data-base lists 115 species scientifically identified and 131 ethno names. In addition, we have information about other 384 ethno names, with unsecure link to the Linnean taxonomy suggesting that local knowledge is very extensive. The data-base represents not only an easy to consult resource, but also a support for further research. The knowledge of the relations between indigenous populations and ecosystem is indeed the base for the natural and cultural biodiversity preservation.  相似文献   
970.
Based on the data of 30 Chinese provinces for the period from 2004 to 2015, this paper expounds the carbon emissions effect of two-way foreign direct investment (FDI) from the perspective of scale effect and factor market distortions. This study uses Kaya identity to decompose carbon emission and construct simultaneous equations model to empirically examine the factor market distortion and the carbon emission scale effect of two-way FDI. The results show that the inward foreign direct investment (IFDI) increase regional carbon emission through scale effect and also exacerbates factor market distortion in China, whereas the outward FDI trends reduce carbon emission and reduces factor market distortions in China. The study also shows that human capital, research and development (R&D), trade openness, and capital accumulation are important determinants of two-way FDI. Therefore, the study proposes that IFDI policies should focus on acquiring green technologies. In addition, the domestic enterprises should be encouraged to participate in global business.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号