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   91411篇
  免费   1223篇
  国内免费   1098篇
安全科学   3767篇
废物处理   3334篇
环保管理   14128篇
综合类   21142篇
基础理论   26463篇
环境理论   75篇
污染及防治   15212篇
评价与监测   5458篇
社会与环境   3598篇
灾害及防治   555篇
  2022年   806篇
  2021年   801篇
  2020年   651篇
  2019年   863篇
  2018年   1131篇
  2017年   1169篇
  2016年   2168篇
  2015年   1837篇
  2014年   2578篇
  2013年   9256篇
  2012年   2231篇
  2011年   2492篇
  2010年   3285篇
  2009年   3418篇
  2008年   2044篇
  2007年   1904篇
  2006年   2339篇
  2005年   2303篇
  2004年   2598篇
  2003年   2442篇
  2002年   2020篇
  2001年   2302篇
  2000年   2022篇
  1999年   1499篇
  1998年   1369篇
  1997年   1363篇
  1996年   1489篇
  1995年   1588篇
  1994年   1481篇
  1993年   1343篇
  1992年   1324篇
  1991年   1296篇
  1990年   1253篇
  1989年   1226篇
  1988年   1061篇
  1987年   990篇
  1986年   992篇
  1985年   1071篇
  1984年   1165篇
  1983年   1173篇
  1982年   1176篇
  1981年   1107篇
  1980年   944篇
  1979年   933篇
  1978年   828篇
  1977年   717篇
  1976年   653篇
  1975年   627篇
  1973年   658篇
  1972年   655篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
721.
722.
723.
724.
 The “Linh Duong” (Pseudonovibos spiralis), a newly described Vietnamese bovid, has been shown to be related to the Caprinae on the basis of the mitochondrial cytochrome b gene sequencing from horn fragments. To integrate the greatest available biodiversity we performed a new phylogenetic analysis including all genera of Caprinae. Unexpectedly, Pseudonovibos is found to be robustly associated with Rupicapra, and closer to the Alpine than to the Pyrenean chamois. Several clues led us to interpret this result as a carry-over DNA contamination of Pseudonovibos by Rupicapra. Received: 19 July 1999 / Accepted in revised form: 20 October 1999  相似文献   
725.
726.
Fisheries management is the practice of analyzing and selecting options to maintain or alter the structure, dynamics, and interaction of habitat, aquatic biota, and man to achieve human goals and objectives. The theory of fisheries management is: managers or decision makers attempt to maximize renewable `output' from an aquatic resource by choosing from among a set of decision options and applying a set of actions that generate an array of outputs. Outputs may be defined as a tangible catch, a fishing experience, an existence value, or anything else produced or supported by renewable aquatic resources. Overall output is always a mix of tangible and intangible elements. However defined, management goals and objectives are essential components of fisheries management or any other field of renewable natural resource management. Reaching consensus on management goals and objectives has never been a simple task. Beyond the broad and often conflicting goals of an agency, managers must decide who should set specific management objectives — agency personnel, the public, or a combination of the two. Historically, rhetoric aside, fisheries managers in North America nearly always have consulted with professionals in governmental roles to set management objectives. In a strongly pluralistic society, this often resulted in protracted political and legal conflict. Increasingly, there are calls for use of risk assessment to help solve such ecological policy and management problems commonly encountered in fisheries management. The basic concepts of ecological risk assessment may be simple, but the jargon and details are not. Risk assessment (and similar analytical tools) is a concept that has evoked strong reactions whenever it has been used. In spite of the difficulties of defining problems and setting management objectives for complex ecological policy questions, use of risk assessment to help solve ecological problems is widely supported. Ecological risk assessment will be most useful (and objective) in political deliberations when the policy debate revolves around largely technical concerns. To the extent that risk assessment forces policy debate and disagreement toward fundamental differences rather than superficial ones, it will be useful in decision making.  相似文献   
727.
728.
Dedicated to Prof. H. Autrum on the occasion of his 85th birthday.  相似文献   
729.
730.
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