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   21857篇
  免费   237篇
  国内免费   123篇
安全科学   529篇
废物处理   937篇
环保管理   2822篇
综合类   3812篇
基础理论   6105篇
环境理论   10篇
污染及防治   5586篇
评价与监测   1358篇
社会与环境   918篇
灾害及防治   140篇
  2021年   143篇
  2018年   243篇
  2017年   258篇
  2016年   420篇
  2015年   315篇
  2014年   482篇
  2013年   1647篇
  2012年   587篇
  2011年   854篇
  2010年   697篇
  2009年   700篇
  2008年   885篇
  2007年   906篇
  2006年   795篇
  2005年   697篇
  2004年   674篇
  2003年   658篇
  2002年   640篇
  2001年   806篇
  2000年   618篇
  1999年   355篇
  1998年   279篇
  1997年   306篇
  1996年   300篇
  1995年   357篇
  1994年   324篇
  1993年   302篇
  1992年   293篇
  1991年   308篇
  1990年   340篇
  1989年   293篇
  1988年   274篇
  1987年   256篇
  1986年   231篇
  1985年   217篇
  1984年   273篇
  1983年   223篇
  1982年   296篇
  1981年   228篇
  1980年   193篇
  1979年   219篇
  1978年   193篇
  1977年   165篇
  1976年   150篇
  1975年   150篇
  1974年   172篇
  1973年   169篇
  1972年   160篇
  1971年   155篇
  1969年   130篇
排序方式: 共有10000条查询结果,搜索用时 538 毫秒
521.
Concern for the acceleration in threats to species diversity in the United States led to the passage of the Endangered Species Act of 1973. In this paper, this legislation is examined in an economic context. A simple model is developed where management and constraints on economic activity are substitutes in the production of species stocks. Whether economic growth constraints (the primary policy tool of the 1973 Act) are justified for preservation purposes depends on technical substitution possibilities, relative cost ratios, and the existence of budget constraints for species management. Since the same combination of these factors will not occur for all species, it is argued that more flexibility in endangered species policy may preserve the same levels of species stocks at lower costs to society.  相似文献   
522.
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   
523.
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   
524.
525.
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   
526.
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   
527.
528.
529.
Random rubble     
Hughes R 《Disasters》1982,6(2):154-154
  相似文献   
530.
Bollag U 《Disasters》1979,3(4):413-415
An epidemic outbreak of typhoid fever in the largest refugee camp of the besieged capital of Phom-Penh, Cambodia; the concomitant lack of personal and public hygiene and the availability of a locally manufactured Tetanus-Typhoid-Paratyphoid vaccine, prompted us to test the practicability of a mass immunization campaign by carrying out a trial in the smaller, well delineated refugee camp of Pochentong. Attendances by adults as well as children throughout the three or four inoculation rounds showed a steady decline with only 30 (20%) of the people completing the course. The general initial acceptance by the people on the other hand was good, due to a comprehensive service (information, health education and individual care of patients). It is concluded from these results that multi-injection immunization campaigns against typhoid-paratyphoid are a waste of money in a war-torn situation with an unstable population.  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