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   31276篇
  免费   338篇
  国内免费   225篇
安全科学   840篇
废物处理   1160篇
环保管理   4389篇
综合类   6123篇
基础理论   8346篇
环境理论   15篇
污染及防治   7865篇
评价与监测   1764篇
社会与环境   1150篇
灾害及防治   187篇
  2018年   337篇
  2017年   354篇
  2016年   552篇
  2015年   436篇
  2014年   633篇
  2013年   2388篇
  2012年   833篇
  2011年   1196篇
  2010年   926篇
  2009年   997篇
  2008年   1198篇
  2007年   1254篇
  2006年   1130篇
  2005年   932篇
  2004年   917篇
  2003年   937篇
  2002年   877篇
  2001年   1116篇
  2000年   813篇
  1999年   494篇
  1998年   377篇
  1997年   403篇
  1996年   417篇
  1995年   467篇
  1994年   453篇
  1993年   422篇
  1992年   415篇
  1991年   424篇
  1990年   439篇
  1989年   431篇
  1988年   381篇
  1987年   363篇
  1986年   342篇
  1985年   333篇
  1984年   375篇
  1983年   351篇
  1982年   395篇
  1981年   353篇
  1980年   309篇
  1979年   315篇
  1978年   299篇
  1977年   258篇
  1976年   244篇
  1975年   233篇
  1974年   276篇
  1973年   262篇
  1972年   248篇
  1971年   221篇
  1970年   197篇
  1967年   196篇
排序方式: 共有10000条查询结果,搜索用时 859 毫秒
771.
The exploration of offshore areas for hydrocarbons has involved new technical and economic considerations and has posed new problems, not the least of which has been the changing relationship between companies and governments. In this article, the authors present an analysis of the different perspectives and policies which emanate from national governments on the one hand and from transnational oil companies on the other. The issues examined include the considerations involved in establishing exploration legislation, post-discovery problems, the impact on revenues of increased production, the interests of companies in developing fields and the overall economic environment within which decisions have to be agreed.  相似文献   
772.
Epidemiological procedures can be organised under disaster conditions by means of a simple surveillance system and with few personnel.
In the aftermath of the 4 February 1976 earthquake in Guatemala, an information system was organized by which the requisite information for decision-making was obtained with adequate speed and promptness.
The initial epidemiologic informution was based on reports collected during the early days on symptoms observed at hospitals and health centers and in localities and villages in the stricken area.
At a second, post-emergency stage a more elaborate surveillance system was instituted to provide guidance in the investigntwn of outbreaks, evaluate the health activities and establish basic criteria for preventive and control measures.  相似文献   
773.
774.
775.
The development of traceability in low-level radioactivity measurements is discussed. The role that the development of large quantities of natural matrix standards can play is also discussed.  相似文献   
776.
Although oil spill cleanup requirements have existed in the United States for years, recent increases in oil imports and marine transportation of petroleum products as well as growing environmental concern have exposed a new industry, the Oil Spill Cleanup Industry. This paper explores some of the microeconomic aspects of this industry which has come under increased scrutiny by the general public, big business, and the federal government.In addition to a brief history and definition, several basic questions about the economic viability of the oil spill cleanup industry are raised and explored, and the impact on the industry of cleanup from government sources is examined, both from the perspective of present operations and from apparent future increases in federal participation. The primary dilemma facing the industry, that of providing continued and immediate supply while confronted with stochastic demand, is discussed. The effects of the large spill on the industry both in terms of revenue and ability to meet cleanup requirements is also considered.Information for the paper is drawn from past and continuing involvement in the U.S. Coast Guard's Marine Environmental Protection Program by both authors. The statistical evidence presented here was compiled through personal interviews and from two computerized Coast Guard information systems; PIRS (the Pollution Incident Reporting System), and SKIM (the Spill Cleanup Equipment Inventory System).  相似文献   
777.
The “filter model” has been developed to explain the biologic effects of radiation and chemicals. We have examined nearly 300 sets of dose response data, of which 50 are presented here. Responses (induced by radiation and chemicals) which have been examined include in vitro survival studies on animal and plant tissues, induction of cellular aberrations and time to tumor or death. Similar data from in vivo studies has also been examined. All of the data appear to fit the model R = a lnD + b(lnD)2 + c, where R is the response, a and b are parameters fitted by regression to a particular set of data, and c is the response at zero (or lowest) dose. By writing this model in exponential form, it can be seen that the response R results from multistage filtering (by net amounts a and b) of the initial dose, D. The threshold is obtained from this model as the point, D?T, at which the second derivative becomes zero. This is given by D?T = exp(1 ? a2b) when a and b are oppositelt signed.  相似文献   
778.
779.
780.
It is shown by example that the results obtained by Gruver [11 concerning specialization of investment in either directly productive or pollution control capital arise because of an implicit linearity assumption on the underlying technology. Utilizing a strictly concave “eighth sphere” technology, results are obtained which imply joint investment in the two types of capital except in “rare” instances. The results indicate the need for incorporating more general technologies into the analysis of such problems.  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