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   40015篇
  免费   430篇
  国内免费   323篇
安全科学   1090篇
废物处理   1511篇
环保管理   5273篇
综合类   6430篇
基础理论   11374篇
环境理论   24篇
污染及防治   10368篇
评价与监测   2483篇
社会与环境   1950篇
灾害及防治   265篇
  2022年   278篇
  2021年   263篇
  2019年   293篇
  2018年   525篇
  2017年   559篇
  2016年   793篇
  2015年   670篇
  2014年   977篇
  2013年   3038篇
  2012年   1186篇
  2011年   1738篇
  2010年   1441篇
  2009年   1432篇
  2008年   1685篇
  2007年   1809篇
  2006年   1591篇
  2005年   1338篇
  2004年   1327篇
  2003年   1275篇
  2002年   1235篇
  2001年   1630篇
  2000年   1163篇
  1999年   718篇
  1998年   535篇
  1997年   560篇
  1996年   572篇
  1995年   630篇
  1994年   574篇
  1993年   510篇
  1992年   536篇
  1991年   490篇
  1990年   499篇
  1989年   528篇
  1988年   442篇
  1987年   403篇
  1986年   375篇
  1985年   401篇
  1984年   398篇
  1983年   419篇
  1982年   410篇
  1981年   347篇
  1980年   320篇
  1979年   350篇
  1978年   300篇
  1977年   265篇
  1976年   244篇
  1975年   244篇
  1974年   231篇
  1973年   245篇
  1972年   263篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
371.
Although prenatal genetic diagnosis can usually provide prospective parents with information as to whether their fetus is affected with certain genetic conditions, the presence of twins and the uncertainty about the phenotype of some chromosome variations pose a major dilemma and make genetic counselling very difficult. Here, a case report of an unusual chromosome aberration (pericentric inversion of chromosome no. 17) in a twin pregnancy which was originally suspected to be monoamniotic but later proved to have two sacs was presented.  相似文献   
372.
Social insects use complex chemical communication systems to govern many aspects of their life. We studied chemical changes in Dufours gland secretions associated with ovary development in several genotypes of honeybees. We found that C28–C38 esters were associated only with cavity nesting honeybee queens, while the alcohol eicosenol was associated only with their non-laying workers. In contrast, both egg-laying anarchistic workers and all parasitic Cape workers from queenright colonies showed the typical queen pattern (i.e. esters present and eicosenol absent), while egg-laying wild-type and anarchistic workers in queenless colonies showed an intermediate pattern, producing both esters and eicosenol but at intermediate levels. Furthermore, neither esters nor eicosenol were found in aerial nesting honeybee species. Both esters and eicosenol are biosynthetically similar compounds since both are recognizable products of fatty acid biosynthesis. Therefore, we propose that in honeybees the biosynthesis of esters and eicosenol in the Dufours gland is caste-regulated and this pathway has been conserved over evolutionary time.  相似文献   
373.
374.
375.
376.
377.
The Science of Nature -  相似文献   
378.
379.
Among social insects such as ants, scouts that modulate their recruiting behaviour, following simple rules based on local information, generate collective patterns of foraging. Here we demonstrate that features of the abiotic environment, specifically the foraging substrate, may also be influential in the emergence of group-level decisions such as the choice of one foraging path. Experimental data and theoretical analyses show that the collective patterns can arise independently of behavioural changes of individual scouts and can result, through self-organising processes, from the physico-chemical properties of the environment that alter the dynamics of information transfer by chemical trails.  相似文献   
380.
Using chemical process simulation to design industrial ecosystems   总被引:2,自引:0,他引:2  
Chemical process simulation (CPS) software has been widely used by chemical (process) engineers to design, test, optimise, and integrate process plants. It is expected that industrial ecologists to bring these same problem-solving benefits to the design and operation of industrial ecosystems can use CPS. This paper provides industrial ecology researchers and practitioners with an introduction to CPS and an overview of chemical engineering design principles. The paper highlights recent research showing that CPS can be used to model industrial ecosystems, and discusses the benefits of using CPS to address some of the technical challenges facing companies participating in an industrial ecosystem. CPS can be used to (i) quantitatively evaluate and compare the potential environmental and financial benefits of material and energy linkages; (ii) solve general design, retrofit, or operational problems; (iii) help to identify complex and often counter-intuitive solutions; and (iv) evaluate what-if scenarios. CPS should be a useful addition to the industrial ecology toolbox.  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