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   13559篇
  免费   148篇
  国内免费   118篇
安全科学   381篇
废物处理   367篇
环保管理   2085篇
综合类   3314篇
基础理论   3207篇
环境理论   7篇
污染及防治   3397篇
评价与监测   621篇
社会与环境   375篇
灾害及防治   71篇
  2018年   130篇
  2017年   136篇
  2016年   198篇
  2015年   167篇
  2014年   211篇
  2013年   1001篇
  2012年   321篇
  2011年   459篇
  2010年   325篇
  2009年   422篇
  2008年   473篇
  2007年   505篇
  2006年   448篇
  2005年   339篇
  2004年   353篇
  2003年   406篇
  2002年   338篇
  2001年   473篇
  2000年   325篇
  1999年   222篇
  1998年   168篇
  1997年   156篇
  1996年   185篇
  1995年   184篇
  1994年   203篇
  1993年   183篇
  1992年   188篇
  1991年   188篇
  1990年   211篇
  1989年   199篇
  1988年   172篇
  1987年   168篇
  1986年   151篇
  1985年   169篇
  1984年   155篇
  1983年   166篇
  1982年   165篇
  1981年   169篇
  1980年   155篇
  1979年   150篇
  1978年   146篇
  1977年   132篇
  1976年   136篇
  1975年   117篇
  1974年   145篇
  1973年   133篇
  1972年   126篇
  1971年   106篇
  1970年   106篇
  1967年   116篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
Ultrasound examination at 12 weeks' gestation revealed severe generalised subcutaneous oedema in a pregnancy at risk for achondrogenesis type II. Transvaginal scanning confirmed the oedema and suggested abnormal limb development. The prenatal diagnosis was confirmed by X-ray examination after transvaginal termination.  相似文献   
84.
85.
Model oligo esters of terephthalic acid with 1,2-ethanediol, 1,3-propanediol, and 1,4-butanediol have been investigated with regard to their biodegradability in different biological environments. Well-characterized oligomers with weight-average molar masses of from 600 to 2600 g/mol exhibit biodegradation in aqueous systems, soil, and compost at 60°C. SEC investigations showed a fast biological degradation of the oligomer fraction consisting of 1 or 2 repeating units, independent of the diol component used for polycondensation, while polyester oligomers with degrees of polymerization higher than 2 were stable against microbial attack at room temperature in a time frame of 2 months. At 60°C in a compost environment chemical hydrolysis also degrades chains longer than two repeating units, resulting in enhanced degradability of the oligomers. Metabolization of the monomers and the dimers as well by the microorganisms could be confirmed by comparing SEC measurements and carbon balances in a Sturm test experiment. Based on these results degradation characteristics of potential oligomer intermediates resulting from a primary chain scission from copolyesters consisting of aromatic and aliphatic dicarbonic acids can be predicted depending on their composition. These results will have an evident influence on the evaluation of the biodegradability of commercially interesting copolyesters and lead to new ways of tailor-made designing of new biodegradable materials as well.  相似文献   
86.
87.
It is shown by example that the results obtained by Gruver [11 concerning specialization of investment in either directly productive or pollution control capital arise because of an implicit linearity assumption on the underlying technology. Utilizing a strictly concave “eighth sphere” technology, results are obtained which imply joint investment in the two types of capital except in “rare” instances. The results indicate the need for incorporating more general technologies into the analysis of such problems.  相似文献   
88.
In the UK for the period 1994-99, a broad range of environmental projects were given financial support through the European Agriculture Guidance and Guarantee Fund under the Objective 1 and Objective 5b programmes. This paper is concerned with the ex-post evaluation of these projects set within a Sustainable Development framework. The aim was to identify project types or characteristics that offered the greatest return on investment. A classification of six broad project types was adopted. The evaluation revealed that there were significant differences between individual projects with respect to the type and scale, and temporal and social distribution of the benefits they delivered. In particular, as well as delivering environmental and economic benefits, many projects made a significant contribution to the development of human and social capital. The paper concludes that it is possible to improve the basis for future project selection in order to maximise the returns on environmental investments in the context of sustainable development.  相似文献   
89.
Sciurus carolinensis ) have been labor intensive and costly, I demonstrate the use of line transect surveys to estimate gray squirrel density and determine the costs of conducting surveys to achieve precise estimates. Density estimates are based on four transects that were surveyed five times from 30 June to 9 July 1994. Using the program DISTANCE, I estimated there were 4.7 (95% CI = 1.86–11.92) gray squirrels/ha on the Clemson University campus. Eleven additional surveys would have decreased the percent coefficient of variation from 30% to 20% and would have cost approximately $114. Estimating urban gray squirrel density using line transect surveys is cost effective and can provide unbiased estimates of density, provided that none of the assumptions of distance sampling theory are violated.  相似文献   
90.
Recent research has suggested that health damage from air pollution—most notably from inhalable particulate matter and lead—is a serious concern in many cities in developing countries. A comparative risk assessment conducted in Cairo in 1994 found these two pollutants to be especially worrisome, and an analysis of the potential economic benefits associated with controlling these pollutants suggests that their economic damage is significant. Control strategies to reduce ambient pollutant levels are under development, with point source controls on major industrial facilities—especially in the secondary lead smelling industry—a cost-effective initial step.  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