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   27896篇
  免费   261篇
  国内免费   166篇
安全科学   602篇
废物处理   1324篇
环保管理   4269篇
综合类   4714篇
基础理论   7533篇
环境理论   14篇
污染及防治   5872篇
评价与监测   1897篇
社会与环境   1980篇
灾害及防治   118篇
  2021年   120篇
  2019年   134篇
  2018年   1773篇
  2017年   1707篇
  2016年   1564篇
  2015年   389篇
  2014年   355篇
  2013年   1312篇
  2012年   976篇
  2011年   2077篇
  2010年   1297篇
  2009年   1250篇
  2008年   1638篇
  2007年   2076篇
  2006年   628篇
  2005年   587篇
  2004年   544篇
  2003年   645篇
  2002年   619篇
  2001年   551篇
  2000年   416篇
  1999年   286篇
  1998年   243篇
  1997年   196篇
  1996年   234篇
  1995年   248篇
  1994年   265篇
  1993年   235篇
  1992年   233篇
  1991年   217篇
  1990年   239篇
  1989年   225篇
  1988年   189篇
  1987年   198篇
  1986年   185篇
  1985年   200篇
  1984年   205篇
  1983年   203篇
  1982年   207篇
  1981年   201篇
  1980年   173篇
  1979年   159篇
  1978年   168篇
  1977年   140篇
  1976年   148篇
  1975年   120篇
  1974年   146篇
  1973年   127篇
  1972年   132篇
  1967年   116篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
The past two decades have witnessed an increase in the exploration for, and development of, mineral resources at Arctic latitudes. Such effort has resulted in the commencement of production at a number of different localities in close proximity to the ocean. Since proximity to a source of transportation for the conveyance of concentrates to the market is a primary requirement governing the economic decisions for the mine to proceed, it is logical that ore deposits near a coastline are primary targets for development.

Closely tied to coastal mining developments is the need to dispose of tailings and waste rock in the most economical manner. Prior to the advent of heightened public awareness and environmental concern, and the enactment of pollution legislation, disposal practices were largely based upon convenience. Currently, however, proposed disposal and operating practices receive closer scrutiny, with a view to providing adequate protection for aquatic resources and habitat. This paper summarizes some of the features of three Arctic mines, wastes from which enter the marine environment, and compares the disposal practices used at each to measures of environmental change as indicated by metal concentrations in various media.  相似文献   
43.
44.
45.
An active capping demonstration project in Washington, D.C., is testing the ability to place sequestering agents on contaminated sediments using conventional equipment and evaluating their subsequent effectiveness relative to conventional passive sand sediment caps. Selected active capping materials include: (1) AquaBlokTM, a clay material for permeability control; (2) apatite, a phosphate mineral for metals control; (3) coke, an organic sequestration agent; and (4) sand material for a control cap. All of the materials, except coke, were placed in 8,000‐ft test plots by a conventional clamshell method during March and April 2004. Coke was placed as a 1.25‐cm layer in a laminated mat due to concerns related to settling of the material. Postcap sampling and analysis were conducted during the first, sixth, and eighteenth months after placement. Although postcap sampling is expected to continue for at least an additional 24 months, this article summarizes the results of the demonstration project and postcap sampling efforts up to 18 months. Conventional clamshell placement was found to be effective for placing relatively thin (six‐inch) layers of active material. The viability of placing high‐value or difficult‐to‐place material in a controlled manner was successfully demonstrated with the laminated mat. Postcap monitoring indicates that all cap materials effectively isolated contaminants, but it is not yet possible to differentiate between conventional sand and active cap layer performance. Monitoring of the permeability control layer indicated effective reductions in groundwater seepage rates through the cap, but also showed the potential for gas accumulation and irregular release. All of the cap materials show deposition of new contaminated sediment onto the surface of the caps, illustrating the importance of source control in maintaining sediment quality. © 2006 Wiley Periodicals, Inc.  相似文献   
46.
47.
48.
49.
Whereas past research has treated co-management of common pool resources as if villagers and project implementing authorities were the only relevant actors, numerous external factors beyond the control of these two partners create barriers to successful co-management. This paper draws on discussions with Forest Department officials to examine the influence of these forces on the outcomes of Joint Forest Management (JFM) in Tamil Nadu, India. An empirical inquiry into the operational aspects of JFM indicates the important roles of political parties, powerful people, and other state institutions and functionaries as well as the flow of foreign funding. Further, the strong demand by local people for socio-economic development interventions as opposed to improvement of degraded forests belittles the role of the Forest Department relative to other departments. Numerous other conditioning factors and relationships are explored. The authors call for reforms in public governance to allow better participation of all the actors involved for this participatory management approach to succeed and sustain.  相似文献   
50.
New experimental data on biological productivity of plant communities in oligotrophic and mesotrophic bogs of the middle taiga subzone over the past five years are presented. The relationship between net primary production and the stock of live phytomass is estimated. The stock of necromass in oligotrophic bog ecosystems increases from west to east, while the stock of live phytomass and net primary production decrease.  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