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   17951篇
  免费   290篇
  国内免费   330篇
安全科学   664篇
废物处理   753篇
环保管理   2716篇
综合类   3031篇
基础理论   4600篇
环境理论   7篇
污染及防治   4621篇
评价与监测   1022篇
社会与环境   1029篇
灾害及防治   128篇
  2023年   89篇
  2022年   163篇
  2021年   172篇
  2020年   196篇
  2019年   147篇
  2018年   294篇
  2017年   269篇
  2016年   421篇
  2015年   333篇
  2014年   464篇
  2013年   1441篇
  2012年   619篇
  2011年   914篇
  2010年   677篇
  2009年   783篇
  2008年   850篇
  2007年   888篇
  2006年   743篇
  2005年   633篇
  2004年   636篇
  2003年   583篇
  2002年   561篇
  2001年   653篇
  2000年   532篇
  1999年   320篇
  1998年   213篇
  1997年   231篇
  1996年   229篇
  1995年   275篇
  1994年   217篇
  1993年   214篇
  1992年   183篇
  1991年   187篇
  1990年   183篇
  1989年   181篇
  1988年   161篇
  1987年   137篇
  1986年   159篇
  1985年   147篇
  1984年   192篇
  1983年   153篇
  1982年   175篇
  1981年   165篇
  1980年   136篇
  1979年   150篇
  1978年   95篇
  1977年   100篇
  1975年   88篇
  1974年   94篇
  1972年   96篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
161.
The prenatal diagnosis of cystinosis is currently based on the increased amount of free-cystine present in amniotic fluid cells. Amniocyte cultures must be grown for at least 2 weeks to obtain sufficient cells for such measurements. Thus, the diagnosis cannot be made until close to 20 weeks gestational age by this method. We report a case in which chorionic villi were used for direct cystine measurement resulting in the in utero diagnosis of cystinosis at 9 weeks gestational age. The diagnosis was confirmed by the study of cultured chorionic villus cells, and of the 10-week abortus.  相似文献   
162.
The prenatal diagnosis of The Turner Syndrome is described at a menstrual age of 12 weeks. Detection of cystic hygroma was followed by vaginal chorionic villous sampling (CVS) which revealed a 45,X karyotype. Early documentation of fetal karyotype in the presence of a cystic hygroma is essential for accurate diagnosis and genetic counselling.  相似文献   
163.
164.
165.
Online searching in publically available patent files opens up interesting possibilities to provide a rapid response to critical questions. A computerized analysis of all patents of leading German pharmaceutical companies over the last decade in important indication areas is described. Supported by subsequent manual processing of individual patents it is shown that duplicate experiments on animals practically never occur.  相似文献   
166.
The abundance patterns of ant communities were monitored with pitfall traps during 14 weeks in four northern California, dry farmed, apple orchards: an abandoned orchard undisturbed for 25 years, two ‘organically’ managed orchards, one with a cover crop of bell beans (Vicia faba) and grasses and the other kept clean of cover by discing, and a ‘commercial’ clean cultivated orchard sprayed with organophosphate insecticides. Six species of ants coexisted in the abandoned orchard, whereas only two species were found in the managed orchards. In both the organic and sprayed, clean cultivated systems, ants were more abundant in the orchard edges than in the vegetation-free centers. This trend was not apparent in the abandoned or organic cover orchards, where plant diversity in the center was similar to that of the edges. Ant predation on potato tuberworm larvae, Phthorimaea operculella, artificially placed on the orchard floor, declined with the intensity of management and vegetational simplication. A higher incidence of larval removal occurred in the edges than in the centers of the clean cultivated orchards. No noticeable populations of ants were detected on the trees in any of the orchards. Increased vegetational diversity and lack of disturbance appeared to affect ant locomotory activity and foraging efficiency by creating preferred sheltering and feeding sites.  相似文献   
167.
168.
169.
170.
The density of red imported fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae), necessary to limit boll weevil abundance, Anthonomus grandis Boheman (Coleoptera: Curculionidae), below the action level was determined. An inaction level of 0.4 fire ants per shake bucket sample (i.e., four ants per 10 plant terminals) will provide boll weevil control approximately 90% of the time. A dynamic inaction level is also provided. Total mortality of boll weevil developmental stages including eggs through teneral adults averaged 97.9%. Of 100 boll weevil eggs deposited in cotton squares (flower buds), an average of two adults survive of which about half are female. Thus, the net replacement rate per generation (Ro is 1.0 which, in this case, indicates a stable boll weevil population.  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