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   53642篇
  免费   588篇
  国内免费   638篇
安全科学   1726篇
废物处理   2494篇
环保管理   7094篇
综合类   8450篇
基础理论   14427篇
环境理论   25篇
污染及防治   13109篇
评价与监测   3678篇
社会与环境   3538篇
灾害及防治   327篇
  2022年   478篇
  2021年   530篇
  2020年   360篇
  2019年   443篇
  2018年   1069篇
  2017年   1094篇
  2016年   1443篇
  2015年   947篇
  2014年   1409篇
  2013年   4092篇
  2012年   1869篇
  2011年   2782篇
  2010年   2150篇
  2009年   2203篇
  2008年   2681篇
  2007年   2781篇
  2006年   2067篇
  2005年   1815篇
  2004年   1701篇
  2003年   1791篇
  2002年   1651篇
  2001年   1937篇
  2000年   1375篇
  1999年   835篇
  1998年   622篇
  1997年   618篇
  1996年   632篇
  1995年   749篇
  1994年   706篇
  1993年   593篇
  1992年   633篇
  1991年   619篇
  1990年   608篇
  1989年   570篇
  1988年   504篇
  1987年   449篇
  1986年   414篇
  1985年   425篇
  1984年   475篇
  1983年   444篇
  1982年   463篇
  1981年   386篇
  1980年   310篇
  1979年   340篇
  1978年   299篇
  1977年   228篇
  1975年   245篇
  1973年   232篇
  1972年   243篇
  1971年   224篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
771.
772.
773.
 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   
774.
Two types of fermented organic waste (trade and industry waste and fruit and vegetable waste) were successfully used as a sole carbon source to produce poly-3-hydroxybutyrate-co-valerate (PHBV) by Ralstonia eutrophus (formerly Alcaligenes eutrophus) via oxygen limitation.The production of PHBV could be optimized by optimizing the oxygen transfer through the fermentor. Thereby, a peak concentration of 1.1 g PHBV per liter cell suspension, 40 w% of cell dry weight, was obtained at an aeration rate of 0.24 mol O2/h·kg biomass. The yield of PHBV on the fatty acid concentration in the organic waste was 0.16 g polymer/g volatile organic matter. The process obtained, compares well with the commercial production process of PHBV based on glucose.  相似文献   
775.
776.
777.
One hundred and fifty-one women of advanced maternal age who underwent genetic termination of pregnancy (TOP) were studied for their reproductive behaviour and the type of procedure for prenatal diagnosis in a subsequent pregnancy. A total of 59 women (39 per cent) had a further pregnancy. In all continuing pregnancies prenatal diagnosis was performed, of which 75 per cent consisted of chorionic villus sampling (CVS). Reproductive behaviour following a genetic termination was negatively correlated with maternal age and parity. Both reproductive behaviour and the choice to undergo a diagnostic procedure in the next pregnancy were independent of the type of diagnostic procedure in the previous affected pregnancy.  相似文献   
778.
This paper, based on the autonomy concept, continues to investigate hierarchical forms and spatial structure of ecosystems. The former can lead to limits for the selection of the component parts of an ecosystem and a distinction between its endogenous and exogenous variables; and the latter can be lead to a hypothesis of the space of an ecosystem: the space of an ecosystem = its habitat area + supporting area + impact area, and two characteristics of ecosystems, space-overlapping and the area of ecosystem space, have been further studied referring to human activities.  相似文献   
779.
780.
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