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   33010篇
  免费   356篇
  国内免费   235篇
安全科学   832篇
废物处理   1426篇
环保管理   4259篇
综合类   5431篇
基础理论   9151篇
环境理论   15篇
污染及防治   8494篇
评价与监测   2126篇
社会与环境   1652篇
灾害及防治   215篇
  2022年   267篇
  2021年   238篇
  2019年   213篇
  2018年   405篇
  2017年   457篇
  2016年   670篇
  2015年   516篇
  2014年   833篇
  2013年   2584篇
  2012年   978篇
  2011年   1377篇
  2010年   1154篇
  2009年   1131篇
  2008年   1369篇
  2007年   1436篇
  2006年   1243篇
  2005年   1065篇
  2004年   1062篇
  2003年   1019篇
  2002年   996篇
  2001年   1259篇
  2000年   939篇
  1999年   526篇
  1998年   387篇
  1997年   440篇
  1996年   442篇
  1995年   509篇
  1994年   479篇
  1993年   412篇
  1992年   429篇
  1991年   409篇
  1990年   444篇
  1989年   416篇
  1988年   359篇
  1987年   371篇
  1986年   337篇
  1985年   319篇
  1984年   370篇
  1983年   329篇
  1982年   364篇
  1981年   314篇
  1980年   279篇
  1979年   294篇
  1978年   257篇
  1977年   241篇
  1976年   198篇
  1975年   205篇
  1974年   226篇
  1973年   234篇
  1972年   215篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
511.
A fetus with multiple structural defects was seen at prenatal ultrasound examination. After termination of the pregnancy a bilateral cleft lip, alveolus, and palate; micrognathia; and webbed joints were seen. Fetal tissues showed indications of infection, intranuclear inclusion bodies, chronic stress, haemolysis, arterial wall damage, and profuse haemorrhage. Parvovirus B19 DNA was detected in fetal tissues by dot hybridization after polymerase chain reaction. The possibility of parvovirus B19 infection leading to congenital malformations is discussed.  相似文献   
512.
Microorganisms (bacteria, fungi) are common residents of the roots, stems and leaves of higher plants. In order to explore the dependency of plant development on the presence of epiphytic microorganisms, the achenes (seeds) of sunflower (Helianthus annuus L.) were sterilized and germinated under aseptic conditions. The sterility of the seedlings was determined with the agar impression method. In seedlings from non-sterile seeds (control) that were likewise raised in a germ-free environment, all plant organs investigated (stem, cotyledons and primary leaves) were contaminated with bacteria. Hypocotyl elongation was not affected by epiphytic microorganisms. However, the growth rates of the cotyledons and primary leaves were higher in sterile seedlings compared with the control. The implications of this differential inhibition of organ development by epiphytic bacteria that are transmitted via the outer surface of the seed coat are discussed. We conclude that epiphytes in the above-ground phytosphere are not necessary for the development of the sunflower seedling.  相似文献   
513.
514.
515.
516.
First trimester prenatal cytogenetic diagnosis was attempted in 350 pregnancies after trans-abdominal chorionic villus sampling. The cytogenetic investigation was performed using both a short-term method (24 h incubation) and cell culture. Adequate samples were obtained in 99·1 per cent and in all these cases the fetal karyotype was established. A chromosome abnormality was found in 2·0 per cent of cases. A discrepancy between the karyotype obtained after 24 h incubation and the karyotype in cell culture was observed in 2·3 per cent. Maternal cell contamination in the cultures was confirmed in 13 of 181 cases where the 24 h incubation revealed a male karyotype. Studies of culture morphology showed that colonies of convoluted cells may serve as a marker for contamination with maternal cells in culture. For the present, we recommend using a short-term method as well as cell culture for cytogenetic investigation until the problems with karyotype discrepancy and maternal cell contamination have been further clarified.  相似文献   
517.
518.
A protocol for easy storage and later expansion of lymphocyte populations is given. Compared with methods using transformed cell lines, the method has a number of advantages for repeated production of cells for the isolation of DNA in amounts sufficient for use in diagnostic DNA technology.  相似文献   
519.
520.
 The “Linh Duong” (Pseudonovibos spiralis), a newly described Vietnamese bovid, has been shown to be related to the Caprinae on the basis of the mitochondrial cytochrome b gene sequencing from horn fragments. To integrate the greatest available biodiversity we performed a new phylogenetic analysis including all genera of Caprinae. Unexpectedly, Pseudonovibos is found to be robustly associated with Rupicapra, and closer to the Alpine than to the Pyrenean chamois. Several clues led us to interpret this result as a carry-over DNA contamination of Pseudonovibos by Rupicapra. Received: 19 July 1999 / Accepted in revised form: 20 October 1999  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