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   13319篇
  免费   149篇
  国内免费   112篇
安全科学   375篇
废物处理   351篇
环保管理   2019篇
综合类   3285篇
基础理论   3161篇
环境理论   6篇
污染及防治   3353篇
评价与监测   593篇
社会与环境   372篇
灾害及防治   65篇
  2018年   127篇
  2017年   134篇
  2016年   192篇
  2015年   159篇
  2014年   207篇
  2013年   976篇
  2012年   318篇
  2011年   440篇
  2010年   313篇
  2009年   418篇
  2008年   464篇
  2007年   483篇
  2006年   448篇
  2005年   331篇
  2004年   351篇
  2003年   386篇
  2002年   335篇
  2001年   472篇
  2000年   336篇
  1999年   223篇
  1998年   157篇
  1997年   148篇
  1996年   181篇
  1995年   178篇
  1994年   206篇
  1993年   186篇
  1992年   185篇
  1991年   185篇
  1990年   208篇
  1989年   195篇
  1988年   166篇
  1987年   163篇
  1986年   151篇
  1985年   165篇
  1984年   148篇
  1983年   160篇
  1982年   163篇
  1981年   164篇
  1980年   149篇
  1979年   146篇
  1978年   144篇
  1977年   130篇
  1976年   136篇
  1975年   114篇
  1974年   144篇
  1973年   125篇
  1972年   126篇
  1971年   107篇
  1970年   107篇
  1967年   116篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
1.
2.
Energy efficiency is often stated to be the most cost-effective measure for satisfying our energy demand with minimal environmental damage. However, the potential energy savings attainable in 'the real world' are frequently overestimated, as is shown in an industrial case study of the glass industry. Nevertheless, there are significant energy savings to be realized, and the role of new technologies in this is important. However, the key to the effective use of new technology for improved energy efficiency is good management and. for best effect, it must be integrated into the normal resource management activities of a company.  相似文献   
3.
4.
Most genetic surveys of captive and endangered populations are carried out with single gene characters bearing no direct relationship to life history or other features for which genetic variation needs to be maintained. Quantitative genetic estimates of heritable variation for life-history traits may be a more direct and appropriate measure of genetic variation for some conservation purposes. Furthermore, recent theoretical and empirical results indicate that genetic variation measured on these two levels may not be concordant. We analyzed heterozygosity at 41 allozyme loci and heritability for body weight in captive cotton-top tamarins ( Saguinus oedipus ) from the Marmoset Research Center of the Oak Ridge Associated Universities in order to compare these two levels of genetic variation. Cotton-top tamarins are a highly endangered species native to Colombia. Many animals currently reside in research facilities and zoological parks. A total of 106 animals were used in the isozyme survey, while data on 364 animals contributed to the quantitative genetic study of body weight. We found a very low average heterozygosity ( H = 1%) for this colony. Body weight was moderately and significantly heritable ( h 2 = 35%). This heritability is within the normal range for natural animal populations. The finding of biologically significant levels of heritability in a population with abnormally low allozyme heterozygosity illustrates the point that low levels of allozyme heterozygosity should not be taken as an indication of overall lack of genetic variation in important quantitative characters such as life-history traits. Genetic variation required for adaptation of species to future environmental challenges can exist despite low levels of enzyme heterozygosity.  相似文献   
5.
6.
7.
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   
8.
9.
10.
The Trial     
  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