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   255440篇
  免费   16107篇
  国内免费   40121篇
安全科学   23891篇
废物处理   11690篇
环保管理   29311篇
综合类   105251篇
基础理论   47862篇
环境理论   211篇
污染及防治   54458篇
评价与监测   16742篇
社会与环境   15171篇
灾害及防治   7081篇
  2024年   855篇
  2023年   3954篇
  2022年   9450篇
  2021年   9504篇
  2020年   8954篇
  2019年   7153篇
  2018年   8357篇
  2017年   10116篇
  2016年   10290篇
  2015年   9846篇
  2014年   11518篇
  2013年   21144篇
  2012年   16330篇
  2011年   18210篇
  2010年   15925篇
  2009年   15710篇
  2008年   16091篇
  2007年   15779篇
  2006年   14722篇
  2005年   11402篇
  2004年   8820篇
  2003年   7769篇
  2002年   6895篇
  2001年   6277篇
  2000年   5312篇
  1999年   3638篇
  1998年   2454篇
  1997年   2213篇
  1996年   2240篇
  1995年   2311篇
  1994年   2035篇
  1993年   1510篇
  1992年   1513篇
  1991年   1370篇
  1990年   1258篇
  1989年   1147篇
  1988年   1018篇
  1987年   907篇
  1986年   859篇
  1985年   870篇
  1984年   896篇
  1983年   824篇
  1982年   918篇
  1981年   817篇
  1980年   627篇
  1979年   686篇
  1978年   585篇
  1977年   513篇
  1975年   467篇
  1974年   461篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The problem of resolving the homology of the digits of the avian hand has been framed as a conflict between paleontological and embryological evidence, the former thought to support a hand composed of digits I, II, III, because of similarity of the phalangeal formulae of the earliest known bird Archaeopteryx to that of Mesozoic pentadactyl archosaurs, while embryological evidence has traditionally favored a II, III, IV avian hand. We have identified the critical developmental period for the major features of the avian skeleton in a primitive bird, the ostrich. Analysis of digit anlagen in the avian hand has revealed those for digits/metacarpals I and V, thus confirming previous embryological studies that indirectly suggested that the avian hand comprises digits II, III, IV, and was primitively pentadactyl.  相似文献   
993.
994.
995.
996.
997.
998.
Mitigation and Adaptation Strategies for Global Change -  相似文献   
999.
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   
1000.
揭示了农业污染纠纷的内涵,提出了处理农业污染纠纷的4个“支撑点”,即运用农业技术先行界定,运用监测数据科学鉴证;运用因果关系逻辑推定,强化环境管理,疏通综合处理渠道等。  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