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   21967篇
  免费   175篇
  国内免费   131篇
安全科学   511篇
废物处理   882篇
环保管理   2235篇
综合类   6077篇
基础理论   4723篇
环境理论   7篇
污染及防治   5633篇
评价与监测   1251篇
社会与环境   877篇
灾害及防治   77篇
  2022年   237篇
  2021年   226篇
  2019年   171篇
  2018年   364篇
  2017年   373篇
  2016年   515篇
  2015年   381篇
  2014年   562篇
  2013年   1524篇
  2012年   641篇
  2011年   836篇
  2010年   706篇
  2009年   724篇
  2008年   862篇
  2007年   859篇
  2006年   744篇
  2005年   639篇
  2004年   655篇
  2003年   590篇
  2002年   543篇
  2001年   692篇
  2000年   446篇
  1999年   327篇
  1998年   225篇
  1997年   214篇
  1996年   214篇
  1995年   257篇
  1994年   269篇
  1993年   216篇
  1992年   241篇
  1991年   249篇
  1990年   271篇
  1989年   243篇
  1988年   196篇
  1987年   188篇
  1986年   198篇
  1985年   191篇
  1984年   207篇
  1983年   199篇
  1982年   211篇
  1981年   215篇
  1980年   177篇
  1979年   187篇
  1978年   155篇
  1973年   150篇
  1968年   157篇
  1967年   186篇
  1966年   166篇
  1965年   158篇
  1964年   155篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
411.
412.
413.
414.
415.
416.
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   
417.
In insect societies, the presence and condition of egg-layers can be assessed with pheromones. Exocrine secretions are expected to vary in time in order to give up-to-date information on an individuals reproductive physiology. In the queenless monogynous ant Streblognathus peetersi, we allowed a previously infertile high-ranking worker to accede to the alpha rank, thus triggering the onset of her oogenesis (15 replicates). We then studied her interactions with an established egg-layer from the same colony after different durations, ranging from 20 h to several days. Even though her eggs are only ready to be laid after 30 days, the new alpha was recognised within 1–2 days. Detection occurred at a distance of a few millimetres, suggesting the involvement of a pheromone with low volatility, such as cuticular hydrocarbons. When the new alpha had differentiated for >48 h, she was attacked by the established egg-layer. In all cases, low-ranking workers eventually immobilised one of the two alphas: the new alpha was the target if she had differentiated only recently, suggesting that police workers select the dominant worker with the less fertile odour. Using the behaviour of ants as our measure, we demonstrate that a dominants olfactory signal changes rapidly with a modification in her social status, and it occurs well before the onset of egg-laying.  相似文献   
418.
419.
Dedicated to Prof. Jürgen Aschoff on the occasion of his 80th birthday.  相似文献   
420.
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