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   20479篇
  免费   169篇
  国内免费   117篇
安全科学   469篇
废物处理   774篇
环保管理   2078篇
综合类   6329篇
基础理论   4290篇
环境理论   10篇
污染及防治   4953篇
评价与监测   1032篇
社会与环境   763篇
灾害及防治   67篇
  2018年   273篇
  2017年   268篇
  2016年   368篇
  2015年   294篇
  2014年   410篇
  2013年   1321篇
  2012年   458篇
  2011年   683篇
  2010年   592篇
  2009年   659篇
  2008年   754篇
  2007年   743篇
  2006年   654篇
  2005年   568篇
  2004年   588篇
  2003年   537篇
  2002年   542篇
  2001年   674篇
  2000年   461篇
  1999年   313篇
  1998年   233篇
  1997年   225篇
  1996年   227篇
  1995年   258篇
  1994年   273篇
  1993年   225篇
  1992年   255篇
  1991年   261篇
  1990年   275篇
  1989年   252篇
  1988年   199篇
  1987年   191篇
  1986年   198篇
  1985年   195篇
  1984年   215篇
  1983年   201篇
  1982年   210篇
  1981年   222篇
  1980年   182篇
  1979年   194篇
  1978年   164篇
  1976年   161篇
  1974年   160篇
  1973年   165篇
  1968年   165篇
  1967年   202篇
  1966年   173篇
  1965年   186篇
  1964年   170篇
  1963年   168篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
41.
42.
ABSTRACT: This paper describes the formulation of an Index of Water Quality to evaluate the level of pollution in fresh water. A Four-Round Delphi equation, using a panel of seven nationally recognized water scientists, was performed to ascertain the pollutants to be included in the index, the relationship between the quantity of these pollutants in the water and the resulting quality of the water, and the importance of each pollution variable to each water use as well as to overall pollution. A multiplicative index was used to bring the pollutants together into one system.  相似文献   
43.
Living veligers of the Cassoidea have been observed to use a mantle appendage to form and resorb periostracum. Anatomical and histological examinations of a ranellid (Cymatium sp.) larva collected from the Red Sea in 1987 revealed the structure and location of the pallial appendage. The mantle edges of juvenile or adult species of the Cassoidea do not show a comparable specialization. It is demonstrated that cassoid larval conch characters are sufficient to prove the existence of a pallial appendage without anatomical confirmation. A mantle appendage is not known from teleplanic (long-living planktic) veligers of other gastropod superfamilies. In cases where the larval strategies of the latter are known they are totally different. Therefore it is suggested that the adaptation of cassoid larvae to pelagic life is unique among gastropods representing an autapomorphic character of the superfamily.  相似文献   
44.
   Global change, i.e. the mega-process radically transforming the relationship between nature and human civilization since the end of World War II, is investigated from the point of view of systems analysis. It is argued that this unbridled process should rather be domesticated by planetary control strategies transpiring from a new science called “geocybernetics”. The formal aspects of geocybernetic theory are sketched and illustrated in a tutorial theatre world reflecting the overall environment and development problematic. Within this setting a straightforward operationalization of the sweeping “sustainable development” ideal through a set of concise paradigms can be achieved. Evidence is provided that geocybernetics is actually feasible on the basis of earth system modelling and fuzzy-control techniques.  相似文献   
45.
46.
Simplicity and efficiency in design and estimation are all important in deciding on sampling strategies. A simple model is given and illustrated for four practical situations to show how a good sampling strategy should be selected.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.  相似文献   
47.
This study examines 45 cases of trisomy 13 and 59 cases of trisomy 18 and reports an algorithm to identify pregnancies with a fetus affected by trisomy 13 or 18 by a combination of maternal age fetal nuchal translucency (NT) thickness, and maternal serum free β-hCG and PAPP-A at 11–14 weeks of gestation. In this mixed trisomy group the median MoM NT was increased at 2.819, whilst the median MoMs for free β-hCG and PAPP-A were reduced at 0.375 and 0.201 respectively. We predict that with the use of the combined trisomy 13 and 18 algorithm and a risk cut-off of 1 in 150 will for a 0.3% false positive rate allow 95% of these chromosomal defects to be identified at 11–14 weeks. Such algorithms will enhance existing first trimester screening algorithms for trisomy 21. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
48.
49.
The interdependences between climate and humanity are becoming increasingly apparent, which makes climatology an upto-date and strongly discussed subject. Its task is to identify and examine relatively long-term, regional and global, natural and anthropogenic developments. A global, long-term view reveals a striking increase of surfacenear air temperature since the beginning of the industrial age. On a regional scale, trends differ considerably, but also Germany shows an apparent trend of increasing temperature and precipitation. The development of extreme events is more difficult to judge; the heat summer of 2003 in Europe, however, is among the phenomena that are likely to occur more frequently in the future. The influence of different natural and anthropogenic factors on the climate is expressed, amongst others, through their radiative forcings. Greenhouse gases emitted from anthropogenic activities are of particular significance since their concentration in the atmosphere keeps increasing. Mathematical modeling has made it possible to reconstruct the climate development of the past with increasing precision. The currently observed warming can only be comprehended by assuming anthropogenic influences. For the future development different scenarios have been calculated in order to deduce strategies for necessary action.  相似文献   
50.
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