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   25592篇
  免费   268篇
  国内免费   129篇
安全科学   620篇
废物处理   1076篇
环保管理   3016篇
综合类   5153篇
基础理论   6806篇
环境理论   24篇
污染及防治   6572篇
评价与监测   1521篇
社会与环境   1062篇
灾害及防治   139篇
  2021年   178篇
  2019年   177篇
  2018年   328篇
  2017年   356篇
  2016年   509篇
  2015年   415篇
  2014年   607篇
  2013年   1853篇
  2012年   695篇
  2011年   1053篇
  2010年   804篇
  2009年   811篇
  2008年   1062篇
  2007年   1068篇
  2006年   934篇
  2005年   812篇
  2004年   768篇
  2003年   745篇
  2002年   758篇
  2001年   873篇
  2000年   665篇
  1999年   387篇
  1998年   316篇
  1997年   321篇
  1996年   328篇
  1995年   383篇
  1994年   372篇
  1993年   321篇
  1992年   322篇
  1991年   322篇
  1990年   335篇
  1989年   309篇
  1988年   273篇
  1987年   261篇
  1986年   251篇
  1985年   229篇
  1984年   285篇
  1983年   232篇
  1982年   298篇
  1981年   257篇
  1980年   209篇
  1979年   222篇
  1978年   208篇
  1977年   181篇
  1976年   175篇
  1975年   172篇
  1974年   182篇
  1973年   189篇
  1972年   173篇
  1971年   165篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
As part of a programme to characterize floating anthropogenic debris in the aquatic environment, the US Environmental Protection Agency (EPA) conducted 18 field surveys in the harbours of major metropolitan cities of the east, west, and Gulf coasts of the United States and the Mid-Atlantic Bight. the surveys were designed to provide information on the types, relative amounts, and distributions of aquatic debris in different geographic regions of the United States. Neuston nets (0.33 mm mesh) were used to collect surface debris during outgoing tides on two or three consecutive days in selected areas of each city. After each net tow, the debris, which ranged in size from small resin pellets to large plastic sheeting pieces, was identified, categorized, and counted. the data are being used to qualitatively characterize aquatic debris in coastal metropolitan areas, to examine potential regional variations, and to tentatively identify potential sources.  相似文献   
33.
This paper is concerned with developing a model for group decision making under multiple criteria. The multiple criteria group decision making (MCGDM)problem involves a set of feasible land use patterns that are evaluated on the basis of multiple, conflicting and noncommensurate criteria by a group of individuals. The model integrates the Analytic Hierarchy Process (AHP) and an integer mathematical programming method. The former provides a tool for structuring the decision problem and determining land suitability for different socio-economicactivities (the uses of land), the latter is used to identify the land use pattern that maximizes consensus among interest groups. The model is used to analyze environmental conflict over land resource allocation in the Cape Region of Mexico.  相似文献   
34.
35.
36.
37.
38.
This paper summarizes studies of carbon mitigation potential (MP) and costs of forestry options in seven developing countries with a focus on the role of agroforestry. A common methodological approach known as comprehensive mitigation assessment process (COMAP) was used in each study to estimate the potential and costs between 2000 and 2030. The approach requires the projection of baseline and mitigation land-use scenarios derived from the demand for forest products and forestland for other uses such as agriculture and pasture. By using data on estimated carbon sequestration, emission avoidance, costs and benefits, the model enables one to estimate cost effectiveness indicators based on monetary benefit per t C, as well as estimates of total mitigation costs and potential when the activities are implemented at equilibrium level. The results show that about half the MP of 6.9 Gt C (an average of 223 Mt C per year) between 2000 and 2030 in the seven countries could be achieved at a negative cost, and the other half at costs not exceeding $100 per t C. Negative cost indicates that non-carbon revenue is sufficient to offset direct costs of about half of the options. The agroforestry options analyzed bear a significant proportion of the potential at medium to low cost per t C when compared to other options. The role of agroforestry in these countries varied between 6% and 21% of the MP, though the options are much more cost effective than most due to the low wage or opportunity cost of rural labor. Agroforestry options are attractive due to the large number of people and potential area currently engaged in agriculture, but they pose unique challenges for carbon and cost accounting due to the dispersed nature of agricultural activities in the tropics, as well as specific difficulties arising from requirements for monitoring, verification, leakage assessment and the establishment of credible baselines.  相似文献   
39.
The production of brominated aromatics from combustion was shown to be influenced by the operating conditions. Brominated aromatics also showed high yields compared to their chlorinated analogues.  相似文献   
40.
Data on the existence of a specific system regulating the growth, size, and structure of enterobacterial populations are first summarized in terms of the chemical ecology concept formulated by S.S. Shvarts. The role of this system in transgene functioning is described using the example of the lux operon integrated into Escherichia coli. A relatively simple test for estimating such interactions is proposed.Translated from Ekologiya, No. 2, 2005, pp. 91–96.Original Russian Text Copyright © 2005 by Pshenichnov, Maslennikova, Nikitina.  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