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   26720篇
  免费   261篇
  国内免费   202篇
安全科学   731篇
废物处理   862篇
环保管理   3570篇
综合类   6157篇
基础理论   6552篇
环境理论   20篇
污染及防治   6668篇
评价与监测   1404篇
社会与环境   1069篇
灾害及防治   150篇
  2022年   176篇
  2019年   193篇
  2018年   336篇
  2017年   338篇
  2016年   476篇
  2015年   409篇
  2014年   536篇
  2013年   1902篇
  2012年   712篇
  2011年   1041篇
  2010年   773篇
  2009年   926篇
  2008年   1077篇
  2007年   1079篇
  2006年   973篇
  2005年   787篇
  2004年   738篇
  2003年   770篇
  2002年   748篇
  2001年   928篇
  2000年   669篇
  1999年   443篇
  1998年   309篇
  1997年   313篇
  1996年   350篇
  1995年   379篇
  1994年   401篇
  1993年   334篇
  1992年   328篇
  1991年   351篇
  1990年   366篇
  1989年   341篇
  1988年   285篇
  1987年   279篇
  1986年   280篇
  1985年   265篇
  1984年   254篇
  1983年   273篇
  1982年   274篇
  1981年   270篇
  1980年   239篇
  1979年   249篇
  1978年   214篇
  1977年   210篇
  1976年   204篇
  1975年   183篇
  1974年   204篇
  1973年   201篇
  1972年   190篇
  1967年   189篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
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   
152.
Deposition velocities have been determined for corn and soybeans in the first 4–6 weeks of growth in a full-scale study of canopy flow in a wind tunnel. Particles of 1, 5, 10 and 15 μm aerodynamic diameter made of sodium florescein were injected into the Environmental Wind Tunnel Facility at Colorado State University. Deposition velocities were determined as a function of free stream velocity (183, 305 and 610 cm/s) and approach flow turbulence intensity (~1% and 8%). Plants were arranged in realistic field configurations. Hot-wire anemometer studies confirmed that the fluid velocity profiles developed in the wind tunnel were similar to the flow realized in canopies in natural fields. An increase in velocity and turbulence intensity was found to decrease the deposition velocities. A minimum deposition velocity was observed at a particle diameter of 5 μm.  相似文献   
153.
154.
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   
155.
156.
157.
There is a growing recognition that knowledge of indigenous communities, based on accumulated observations and experience over time, is significant for sustainable environmental management in collaboration with modern scientific knowledge. A number of innovative policy initiatives are currently being implemented in New Zealand to enable indigenous Maori tribes and sub-tribes to rehabilitate and manage their local fisheries in accordance with customary values and practices. These policies are an important milestone from an historical perspective as they are meant to recognise and empower the role of Maori as Treaty partners. The fisheries management regime in New Zealand now provides for Maori representation at the local level within a co-management framework that enables local Maori communities to exercise their customary rights. These institutional arrangements have been crafted to facilitate Maori input, based on customary values and practices, to complement modern Western management practices for sustainable harvesting of marine resources. Nevertheless, the degree to which these initiatives constitute an adequate response to Maori Treaty aspirations is debatable. A major constraint in this respect is that the government is compelled to recognise the needs of other, economically and politically more dominant, non-Maori user-groups in allocating and managing access to fishery resources and the marine environment.  相似文献   
158.
In the UK for the period 1994-99, a broad range of environmental projects were given financial support through the European Agriculture Guidance and Guarantee Fund under the Objective 1 and Objective 5b programmes. This paper is concerned with the ex-post evaluation of these projects set within a Sustainable Development framework. The aim was to identify project types or characteristics that offered the greatest return on investment. A classification of six broad project types was adopted. The evaluation revealed that there were significant differences between individual projects with respect to the type and scale, and temporal and social distribution of the benefits they delivered. In particular, as well as delivering environmental and economic benefits, many projects made a significant contribution to the development of human and social capital. The paper concludes that it is possible to improve the basis for future project selection in order to maximise the returns on environmental investments in the context of sustainable development.  相似文献   
159.
Sciurus carolinensis ) have been labor intensive and costly, I demonstrate the use of line transect surveys to estimate gray squirrel density and determine the costs of conducting surveys to achieve precise estimates. Density estimates are based on four transects that were surveyed five times from 30 June to 9 July 1994. Using the program DISTANCE, I estimated there were 4.7 (95% CI = 1.86–11.92) gray squirrels/ha on the Clemson University campus. Eleven additional surveys would have decreased the percent coefficient of variation from 30% to 20% and would have cost approximately $114. Estimating urban gray squirrel density using line transect surveys is cost effective and can provide unbiased estimates of density, provided that none of the assumptions of distance sampling theory are violated.  相似文献   
160.
The creation of a cloned sheep from mammary tissue has raisedmajor social concern, and much talk about major ethical issuesoccasioned by this technology. It is necessary to separategenuine from spurious ethical issues here, a task made failureto initiate ethical discussion and explanation of new technologyas well as by fear reactions in society. As in geneticengineering of animals, issues about cloning fall into threecategories – suggestions that the technology is inherently wrong,risk emerging from the technology and harm to the creatureengendered. The issues regarding the cloning of humans can beanalyzed using the same categories.  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