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   44113篇
  免费   449篇
  国内免费   393篇
安全科学   1251篇
废物处理   1827篇
环保管理   5763篇
综合类   6634篇
基础理论   12211篇
环境理论   25篇
污染及防治   11578篇
评价与监测   3000篇
社会与环境   2367篇
灾害及防治   299篇
  2022年   347篇
  2021年   370篇
  2020年   262篇
  2019年   342篇
  2018年   649篇
  2017年   639篇
  2016年   955篇
  2015年   756篇
  2014年   1104篇
  2013年   3488篇
  2012年   1318篇
  2011年   1882篇
  2010年   1613篇
  2009年   1604篇
  2008年   1885篇
  2007年   2001篇
  2006年   1804篇
  2005年   1512篇
  2004年   1494篇
  2003年   1428篇
  2002年   1387篇
  2001年   1836篇
  2000年   1287篇
  1999年   806篇
  1998年   622篇
  1997年   604篇
  1996年   653篇
  1995年   655篇
  1994年   609篇
  1993年   563篇
  1992年   565篇
  1991年   515篇
  1990年   524篇
  1989年   549篇
  1988年   483篇
  1987年   402篇
  1986年   364篇
  1985年   403篇
  1984年   412篇
  1983年   432篇
  1982年   449篇
  1981年   366篇
  1980年   328篇
  1979年   383篇
  1978年   311篇
  1977年   271篇
  1976年   272篇
  1975年   253篇
  1974年   237篇
  1972年   248篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
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   
223.
224.
225.
226.
227.
The Intergovernmental Panel on Climate Change (IPCC) has developed guidelines to standardize the international reporting of greenhouse gas emissions and removals by signatory nations of the UN Framework Convention on Climate Change. With regard to forest sector carbon fluxes, the IPCC guidelines require only that those fluxes directly associated with human activities (i.e., harvesting and land-use change) be reported. In Canada, the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2) has been used to assess carbon fluxes from the entire forest sector. This model accounts for carbon fluxes associated with both anthropogenic and natural disturbances, such as wild fires and insects. We combined model results for the period 1985 to 1989 with additional data to compile seven different national carbon flux inventories for the forest sector. These inventories incorporate different system components under a variety of seemingly plausible assumptions, some of which are encouraged refinements to the default flux inventory described in the IPCC guidelines. The resulting estimated net carbon fluxes varied from a net removal of 185,000 kt carbon per year of the inventory period to a netemission of 89,000 kt carbon per year. Following the default procedures in the IPCC guidelines, while using the best available national data, produced an inventory with a net removal of atmospheric carbon. Adding the effect of natural disturbances to that inventory reversed the sign of the net flux resulting in a substantial emission. Including the carbon fluxes associated with root biomass in the first inventory increased the magnitude of the estimated net removal. The variability of these results emphasizes the need for a systems approach in constructing a flux inventory. We argue that the choice of which fluxes to include in the inventory should be based on the importance of these fluxes to the overall carbon budget and not on the perceived ease with which flux estimates can be obtained. The results of this analysis also illustrate two specific points. Even those Canadian forests which are most free from direct human interactions—forests in which no commercial harvesting occurs—are not in equilibrium, and their contribution to national carbon fluxes should be included in the reported flux inventory. Moreover, those forest areas that are subject to direct management are still substantially impacted by natural disturbances. The critical effect of inventory methodology and assumptions on inventory results has important ramifications for efforts to “monitor” and “verify” programs aimed at mitigating global carbon emissions.  相似文献   
228.
A protocol for easy storage and later expansion of lymphocyte populations is given. Compared with methods using transformed cell lines, the method has a number of advantages for repeated production of cells for the isolation of DNA in amounts sufficient for use in diagnostic DNA technology.  相似文献   
229.
230.
 The “Linh Duong” (Pseudonovibos spiralis), a newly described Vietnamese bovid, has been shown to be related to the Caprinae on the basis of the mitochondrial cytochrome b gene sequencing from horn fragments. To integrate the greatest available biodiversity we performed a new phylogenetic analysis including all genera of Caprinae. Unexpectedly, Pseudonovibos is found to be robustly associated with Rupicapra, and closer to the Alpine than to the Pyrenean chamois. Several clues led us to interpret this result as a carry-over DNA contamination of Pseudonovibos by Rupicapra. Received: 19 July 1999 / Accepted in revised form: 20 October 1999  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