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   21763篇
  免费   261篇
  国内免费   170篇
安全科学   672篇
废物处理   805篇
环保管理   3051篇
综合类   5795篇
基础理论   4785篇
环境理论   10篇
污染及防治   5008篇
评价与监测   1171篇
社会与环境   782篇
灾害及防治   115篇
  2022年   171篇
  2019年   159篇
  2018年   312篇
  2017年   304篇
  2016年   449篇
  2015年   329篇
  2014年   464篇
  2013年   1532篇
  2012年   582篇
  2011年   796篇
  2010年   682篇
  2009年   774篇
  2008年   812篇
  2007年   832篇
  2006年   729篇
  2005年   645篇
  2004年   668篇
  2003年   592篇
  2002年   565篇
  2001年   698篇
  2000年   497篇
  1999年   345篇
  1998年   272篇
  1997年   248篇
  1996年   248篇
  1995年   304篇
  1994年   311篇
  1993年   269篇
  1992年   278篇
  1991年   268篇
  1990年   286篇
  1989年   261篇
  1988年   208篇
  1987年   216篇
  1986年   216篇
  1985年   215篇
  1984年   237篇
  1983年   222篇
  1982年   240篇
  1981年   245篇
  1980年   198篇
  1979年   194篇
  1978年   175篇
  1977年   153篇
  1976年   149篇
  1974年   151篇
  1968年   157篇
  1967年   184篇
  1966年   154篇
  1964年   152篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
431.
432.
Unemployment effects of climate policy   总被引:1,自引:0,他引:1  
This paper models the unemployment effects of restrictions on greenhouse gas emissions, embodying two of the most significant types of short-term economic imperfections that generate unemployment: sectoral rigidities in labor mobility and sectoral rigidities in wage adjustments. A labor policy is also analyzed that would reduce the direct negative economic effects of the emissions restrictions.The politics of limiting greenhouse gas emissions are often dominated by relatively short-term considerations. Yet the current economic modeling of emissions limitations does not embody economic features that are likely to be particularly important in the short term, in particular, the politically sensitive unemployment rate. Moreover, only a few of these studies also consider policies that would offset the negative direct economic effects of emissions restrictions. For plausible estimates of the parameters, the model shows that, with the labor market imperfections, if there were no offsetting policies, the reductions in GNP in the U.S. in the first 10 years after emissions restrictions were imposed would be as much as 4%. However, if there were two policies, instead of just one: a counteracting labor market policy, as well as the emissions restrictions, the negative direct economic effects could be completely eliminated.  相似文献   
433.
434.
Dedicated to Prof. Jürgen Aschoff on the occasion of his 80th birthday.  相似文献   
435.
436.
437.
438.
We present a remarkable chain of events in which percutaneous umbilical cord sampling was performed in an attempt to clarify a situation of possible fetal sex chromosome mosaicism in an amniotic fluid culture and led to the discovery that the mother herself had a 45,X/46,XX/ 47.XXX chromosome constitution. This may have simply represented the chance concurrence of pseudo-mosaicism in the amniotic fluid culture of a woman with an abnormal sex chromosome constitution, but it is also possible that the 45,X colony was maternal in origin. Although clearly a most unusual circumstance, the possibility should be kept in mind when termination of a pregnancy is being considered because of apparent mosaicism in a prenatal diagnostic study.  相似文献   
439.
440.
 Self-diffusion coefficients were studied for the highly polar liquid N-methylformamide at pressures up to 200 MPa between the melting pressure curves and 420 K by the spin-echo method. N-Methylformamide exists as a mixture of two conformers in the neat liquid. These conformers have large differences at lower temperatures in their dynamic and structural properties. The self-diffusion coefficient of the cis-conformer being 17% lower than that of the trans-conformer at the same T and p. This is the first observation of such an effect. The experimental study is supported by Monte Carlo (MC) calculations which show that the first neighbors around a cis conformer are arranged differently than in an all trans liquid. The difference leads in the simulations to a much lower dielectric constant for the trans-cis mixture and might also explain the retardation of diffusion for the cis conformer. Received: 15 November 1999 / Accepted in revised form: 28 February 2000  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