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   30407篇
  免费   309篇
  国内免费   266篇
安全科学   845篇
废物处理   1256篇
环保管理   3992篇
综合类   4521篇
基础理论   8283篇
环境理论   8篇
污染及防治   8261篇
评价与监测   1989篇
社会与环境   1623篇
灾害及防治   204篇
  2022年   230篇
  2021年   239篇
  2020年   185篇
  2019年   229篇
  2018年   402篇
  2017年   446篇
  2016年   647篇
  2015年   542篇
  2014年   850篇
  2013年   2512篇
  2012年   989篇
  2011年   1315篇
  2010年   1086篇
  2009年   1154篇
  2008年   1318篇
  2007年   1435篇
  2006年   1221篇
  2005年   1031篇
  2004年   1055篇
  2003年   1005篇
  2002年   990篇
  2001年   1243篇
  2000年   897篇
  1999年   510篇
  1998年   376篇
  1997年   392篇
  1996年   437篇
  1995年   461篇
  1994年   435篇
  1993年   367篇
  1992年   360篇
  1991年   341篇
  1990年   371篇
  1989年   346篇
  1988年   304篇
  1987年   304篇
  1986年   276篇
  1985年   284篇
  1984年   295篇
  1983年   283篇
  1982年   271篇
  1981年   268篇
  1980年   233篇
  1979年   251篇
  1978年   198篇
  1977年   199篇
  1976年   153篇
  1975年   171篇
  1973年   180篇
  1972年   164篇
排序方式: 共有10000条查询结果,搜索用时 504 毫秒
791.
792.
793.
Abstract: The U.S. Endangered Species Act (ESA) defines an endangered species as one “at risk of extinction throughout all or a significant portion of its range.” The prevailing interpretation of this phrase, which focuses exclusively on the overall viability of listed species without regard to their geographic distribution, has led to development of listing and recovery criteria with fundamental conceptual, legal, and practical shortcomings. The ESA's concept of endangerment is broader than the biological concept of extinction risk in that the “esthetic, ecological, educational, historical, recreational, and scientific” values provided by species are not necessarily furthered by a species mere existence, but rather by a species presence across much of its former range. The concept of “significant portion of range” thus implies an additional geographic component to recovery that may enhance viability, but also offers independent benefits that Congress intended the act to achieve. Although the ESA differs from other major endangered‐species protection laws because it acknowledges the distinct contribution of geography to recovery, it resembles the “representation, resiliency, and redundancy” conservation‐planning framework commonly referenced in recovery plans. To address representation, listing and recovery standards should consider not only what proportion of its former range a species inhabits, but the types of habitats a species occupies and the ecological role it plays there. Recovery planning for formerly widely distributed species (e.g., the gray wolf [Canis lupus]) exemplifies how the geographic component implicit in the ESA's definition of endangerment should be considered in determining recovery goals through identification of ecologically significant types or niche variation within the extent of listed species, subspecies, or “distinct population segments.” By linking listing and recovery standards to niche and ecosystem concepts, the concept of ecologically significant type offers a scientific framework that promotes more coherent dialogue concerning the societal decisions surrounding recovery of endangered species.  相似文献   
794.
Abstract: Avian conservation efforts must account for changes in vegetation composition and structure associated with climate change. We modeled vegetation change and the probability of occurrence of birds to project changes in winter bird distributions associated with climate change and fire management in the northern Chihuahuan Desert (southwestern U.S.A.). We simulated vegetation change in a process‐based model (Landscape and Fire Simulator) in which anticipated climate change was associated with doubling of current atmospheric carbon dioxide over the next 50 years. We estimated the relative probability of bird occurrence on the basis of statistical models derived from field observations of birds and data on vegetation type, topography, and roads. We selected 3 focal species, Scaled Quail (Callipepla squamata), Loggerhead Shrike (Lanius ludovicianus), and Rock Wren (Salpinctes obsoletus), that had a range of probabilities of occurrence for our study area. Our simulations projected increases in relative probability of bird occurrence in shrubland and decreases in grassland and Yucca spp. and ocotillo (Fouquieria splendens) vegetation. Generally, the relative probability of occurrence of all 3 species was highest in shrubland because leaf‐area index values were lower in shrubland. This high probability of occurrence likely is related to the species’ use of open vegetation for foraging. Fire suppression had little effect on projected vegetation composition because as climate changed there was less fuel and burned area. Our results show that if future water limits on plant type are considered, models that incorporate spatial data may suggest how and where different species of birds may respond to vegetation changes.  相似文献   
795.
796.
Mountain ecosystems are considered vulnerable to early impacts of climate change. Whether and how local residents of these areas perceive these changes, however, remain under-studied questions. By conducting a household survey in the Khumbu region of Nepal, this study assessed local residents’ experience-based perception of changes in climate trends and patterns, perceived risk, and attitudes towards climate issues. Multivariate cluster analysis based on residents’ climate change beliefs revealed three segments: “Cautious,” “Disengaged,” and “Alarmed.” A comparison of these segments along key psychosocial constructs of Protection Motivation Theory (PMT) revealed significant inter-segment differences in residents’ perception of severity, vulnerability, response efficacy, self-efficacy, and response cost associated with engaging in mitigating behavior. Results shed light on how residents of high elevation areas that are considered to be exposed to early impacts of climate change perceive the risk and intend to respond. These findings could also assist stakeholders working in other similar mountain ecosystems in understanding vulnerability and in working towards climate readiness.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01369-x) contains supplementary material, which is available to authorized users.  相似文献   
797.
Environmental Science and Pollution Research - The order Odonata has been regularly used as an indicator of the ecosystem’s condition. The objective of this review was to analyze the...  相似文献   
798.
Environmental Science and Pollution Research - In this study, the photocatalytic degradation of four fungicides, myclobutanil, penconazole and difenoconazole (triazole compounds) and boscalid...  相似文献   
799.
Environmental Science and Pollution Research - In this work, the activated persulfate oxidation of ciprofloxacin (CIP) using a low-grade titanium ore under sunlight or simulated sunlight were...  相似文献   
800.
Environmental Science and Pollution Research - The scientific knowledge produced by academic research can be valued in all sectors of human activity, including private sector. The ROVALTAIN...  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