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   21459篇
  免费   208篇
  国内免费   219篇
安全科学   584篇
废物处理   1047篇
环保管理   2527篇
综合类   2922篇
基础理论   5478篇
环境理论   5篇
污染及防治   5886篇
评价与监测   1767篇
社会与环境   1528篇
灾害及防治   142篇
  2023年   99篇
  2022年   227篇
  2021年   245篇
  2020年   154篇
  2019年   193篇
  2018年   359篇
  2017年   362篇
  2016年   562篇
  2015年   390篇
  2014年   629篇
  2013年   1826篇
  2012年   714篇
  2011年   927篇
  2010年   850篇
  2009年   843篇
  2008年   951篇
  2007年   1036篇
  2006年   916篇
  2005年   759篇
  2004年   772篇
  2003年   764篇
  2002年   714篇
  2001年   959篇
  2000年   656篇
  1999年   412篇
  1998年   283篇
  1997年   257篇
  1996年   296篇
  1995年   282篇
  1994年   259篇
  1993年   245篇
  1992年   250篇
  1991年   211篇
  1990年   217篇
  1989年   225篇
  1988年   203篇
  1987年   160篇
  1986年   131篇
  1985年   146篇
  1984年   173篇
  1983年   160篇
  1982年   199篇
  1981年   137篇
  1980年   120篇
  1979年   152篇
  1978年   118篇
  1977年   107篇
  1976年   102篇
  1975年   83篇
  1974年   89篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
291.
292.
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   
293.
XII Ecdysone Workshop July 22–26, 1996 Barcelona, Spain  相似文献   
294.
295.
An integrated approach was developed to determine the critical levels of air pollution for ecological standard setting based on the unified index of biological response, by taking into account the effects of all pollution components simultaneously. An empirical model of plant productivity was taken as the dose response model for gaseous pollutant effect on the productivity of trees and the annual productivity of plants was used as the above mentioned index. The CO2 increase in the lower atmosphere was considered to potentially increase plant productivity and NO2 was estimated as neutral while being dangerous for plants as a chemical precursor of ozone or as a source of acidification. The maximum permissible chronic O3 and SO2 levels for trees were estimated and it was found that O3 is much more phytotoxic, as compared to SO2 , with a rather narrow range of permissible levels (27-33 ppb) which complicates its monitoring and control.  相似文献   
296.
297.
First trimester prenatal cytogenetic diagnosis was attempted in 350 pregnancies after trans-abdominal chorionic villus sampling. The cytogenetic investigation was performed using both a short-term method (24 h incubation) and cell culture. Adequate samples were obtained in 99·1 per cent and in all these cases the fetal karyotype was established. A chromosome abnormality was found in 2·0 per cent of cases. A discrepancy between the karyotype obtained after 24 h incubation and the karyotype in cell culture was observed in 2·3 per cent. Maternal cell contamination in the cultures was confirmed in 13 of 181 cases where the 24 h incubation revealed a male karyotype. Studies of culture morphology showed that colonies of convoluted cells may serve as a marker for contamination with maternal cells in culture. For the present, we recommend using a short-term method as well as cell culture for cytogenetic investigation until the problems with karyotype discrepancy and maternal cell contamination have been further clarified.  相似文献   
298.
299.
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   
300.
公路设计中的环境保护工作   总被引:1,自引:0,他引:1  
阐述了公路建设中环境保护工作的意义,提出在公路工程勘察设计工作中对环境保护的典型作法和取得的效果。  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