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   29660篇
  免费   301篇
  国内免费   195篇
安全科学   765篇
废物处理   1286篇
环保管理   3964篇
综合类   5402篇
基础理论   7821篇
环境理论   14篇
污染及防治   7573篇
评价与监测   1826篇
社会与环境   1327篇
灾害及防治   178篇
  2022年   198篇
  2021年   214篇
  2018年   359篇
  2017年   357篇
  2016年   585篇
  2015年   443篇
  2014年   659篇
  2013年   2268篇
  2012年   813篇
  2011年   1162篇
  2010年   932篇
  2009年   982篇
  2008年   1164篇
  2007年   1251篇
  2006年   1114篇
  2005年   957篇
  2004年   944篇
  2003年   922篇
  2002年   865篇
  2001年   1100篇
  2000年   817篇
  1999年   490篇
  1998年   340篇
  1997年   370篇
  1996年   362篇
  1995年   454篇
  1994年   416篇
  1993年   378篇
  1992年   371篇
  1991年   397篇
  1990年   387篇
  1989年   375篇
  1988年   362篇
  1987年   330篇
  1986年   285篇
  1985年   282篇
  1984年   358篇
  1983年   318篇
  1982年   368篇
  1981年   298篇
  1980年   261篇
  1979年   286篇
  1978年   253篇
  1977年   221篇
  1976年   188篇
  1975年   215篇
  1974年   238篇
  1973年   220篇
  1972年   200篇
  1971年   190篇
排序方式: 共有10000条查询结果,搜索用时 910 毫秒
681.
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   
682.
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   
683.
684.
The significant processes controlling the fate of particulates are convection an dispersion on one hand, and sedimentation on the other hand. Due to inteparticulated reactions, larger aggregates can be formed from smaller units thus changing the sedimentation characteristics. These phenomena are summarized in a mathematical model whereby hydrodynamic effects as well as the control mechanisms of the dissolved phase are included. A relationship was derived on the basis of energy considerations leading to the formulation of a critical sedimentation velocity of the suspensa, which determines the transport capacity of the flowing system. The sedimentation term is calculated from the above discussed transport capacity, hydro-dynamic parameters and suspending media properties. Aggregation effects are taken into account as an increase of sedimentation velocities of the particles. The equations are solved in a particular computational routine such that the horizontal distribution of suspended solids in a natural system can be describe as function of the above discussed phenomena. The model was tested with in situ-measurements. It was found that the observed processes are described satisfactorily by this model.  相似文献   
685.
A disastrous flood in Ibadan City, Nigeria in April 1978 aroused public interest in the Ogunpa river channelization scheme which had earlier been embarked upon by government. A questionnaire survey of 399 residents near the river was designed to examine three issues: (a) the losses sustained and the people's reaction to and perception of the causes of the flood; (b) their perception of the present and future uses of the river; and (c) their perception of the prospects of the channelization scheme.The results show that about 75% of the respondents were affected by the flood; 41% each lost property worth about N2960.00. Yet, many could not hope to move out of the flood zone mainly because of shortage of residential accomodation in the city. The factors given as being responsible for the flood were poor drainage, heavy rains, refuse disposal in the river, shallowness of the river channel and the unplanned layout of streets and buildings. Indeed, the major use of the river has been as a refuse dump, so that it is heavily polluted. Many respondents would like the river to be reclaimed to alleviate some of the socioeconomic problems confronting them. Recreational use of the river was not much considered. Majority of respondents thought the channelization scheme would bring some benefit. But, they are sceptical about its lasting impact unless it is done within the framework of a comprehensive programme of urban land management and protection and the improvement of living conditions in the city.  相似文献   
686.
687.
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   
688.
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   
689.
690.
Cuny FC 《Disasters》1980,4(1):112-112
  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