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   33058篇
  免费   295篇
  国内免费   143篇
安全科学   674篇
废物处理   1820篇
环保管理   4455篇
综合类   4589篇
基础理论   9500篇
环境理论   13篇
污染及防治   7491篇
评价与监测   2425篇
社会与环境   2361篇
灾害及防治   168篇
  2022年   145篇
  2021年   162篇
  2019年   150篇
  2018年   1798篇
  2017年   1710篇
  2016年   1657篇
  2015年   484篇
  2014年   539篇
  2013年   1809篇
  2012年   1121篇
  2011年   2291篇
  2010年   1545篇
  2009年   1410篇
  2008年   1898篇
  2007年   2296篇
  2006年   880篇
  2005年   838篇
  2004年   768篇
  2003年   843篇
  2002年   830篇
  2001年   827篇
  2000年   630篇
  1999年   368篇
  1998年   316篇
  1997年   306篇
  1996年   309篇
  1995年   351篇
  1994年   331篇
  1993年   306篇
  1992年   298篇
  1991年   294篇
  1990年   305篇
  1989年   288篇
  1988年   263篇
  1987年   255篇
  1986年   232篇
  1985年   218篇
  1984年   284篇
  1983年   237篇
  1982年   289篇
  1981年   242篇
  1980年   195篇
  1979年   211篇
  1978年   190篇
  1977年   160篇
  1975年   146篇
  1974年   163篇
  1973年   164篇
  1972年   153篇
  1971年   151篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
A very dry climate which prevailed during the last glacial maximum of the Pleistocene from India to the Sahara, was replaced by variable weather conditions with alternating more or less humid phases, starting from the Pleistocene-Holocene transition period and lasting up to about 3000 years ago, when present arid conditions set in. A particularly wet phase is recognized throughout the region some 5000 years ago. Phase shifts within the region and in particular changes in rain distribution patterns, are interpreted as due to shifting spheres of influence of the monsoonal circulation, of Atlantic depressions and moisture originating from the Mediterranean Sea. The condition of the Mediterranean Sea itself, which is influenced by runoff and melt waters from the European Continent and by the Nile floods, as well as by the eustatic sea-level changes, is not a good indicator of local climate conditions.  相似文献   
62.
63.
Peptide chemistry has reached a plateau on which more work is devoted to the improvement of known basic principles than to the development of really new methods. As a consequence, routine syntheses of peptides concentrate on few protecting groups and coupling procedures only. The recent progress in purification of peptides by liquid chromatography helped to promote this trend. Meanwhile, recombinant technology permits the synthesis of proteins and possibly of some lower peptides, too. It cannot compete, however, with chemical solid-phase synthesis of a newly discovered peptide with up to about 40 amino acids in speed but may take over the synthesis for large-scale production. Peptides containing modified or non-natural structures, which are often superior to the natural compounds as drugs, will remain subject of chemical synthesis, too. Present research focuses on the role of peptide and protein factors in the immune response and on structure and biological activities of neuropeptides.  相似文献   
64.
65.
66.
67.
68.
69.
70.
No clear answer concerning whether multivitamin/folate supplementation prevents neural tube defects (NTDs) is provided by three studies in the United States. All these studies are occurrence in nature, no recurrence studies having been conducted. The Atlanta Birth Defects Study is subject to pronounced memory and recall biases, the length between event and interview being as long as 16 years. In a second study (Boston University), objections can be raised to certain aspects of the experimental design, and the claim that 22 per cent of women started vitamins sufficiently early after pregnancy diagnosis to influence NTD formation is suspicious. Our NICHD case control study of 541 women in California and Illinois revealed no evidence for multivitamins or folic acid preventing NTDs. U.S. public policy-makers face difficulties in applying results of recurrence or occurrence studies in high-risk areas to low-risk areas in the U.S.  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