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   31146篇
  免费   351篇
  国内免费   287篇
安全科学   932篇
废物处理   1221篇
环保管理   4374篇
综合类   5076篇
基础理论   8086篇
环境理论   14篇
污染及防治   8232篇
评价与监测   1964篇
社会与环境   1655篇
灾害及防治   230篇
  2022年   233篇
  2021年   262篇
  2020年   194篇
  2019年   250篇
  2018年   410篇
  2017年   449篇
  2016年   680篇
  2015年   556篇
  2014年   790篇
  2013年   2612篇
  2012年   969篇
  2011年   1288篇
  2010年   1031篇
  2009年   1161篇
  2008年   1327篇
  2007年   1416篇
  2006年   1268篇
  2005年   1034篇
  2004年   1048篇
  2003年   1022篇
  2002年   940篇
  2001年   1183篇
  2000年   890篇
  1999年   508篇
  1998年   400篇
  1997年   377篇
  1996年   441篇
  1995年   441篇
  1994年   418篇
  1993年   400篇
  1992年   373篇
  1991年   358篇
  1990年   375篇
  1989年   333篇
  1988年   311篇
  1987年   282篇
  1986年   274篇
  1985年   289篇
  1984年   310篇
  1983年   310篇
  1982年   300篇
  1981年   312篇
  1980年   270篇
  1979年   277篇
  1978年   200篇
  1977年   201篇
  1975年   159篇
  1974年   165篇
  1973年   170篇
  1972年   191篇
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
381.
A survey was conducted of the results of mid-trimester diagnostic amniocenteses in the Oxford Region from 1974 to 1981. The survey used data relating to all 4357 singleton pregnancies in which an amniocentesis was performed during this period. Follow-up information on outcome was obtained in respect of 4284 (98 per cent) pregnancies. A cell culture to determine karyotype and an alpha-fetoprotein determination was carried out in all cases. From 1974 to 1981 amniocenteses became increasingly common, rising from 2 to 32 per 1000 births. The most common indication for amniocentesis was a high risk of a chromosome abnormality–56 per cent of all amniocenteses. Within this group advanced maternal age was responsible for 89 per cent of the cases. The next most common indication was a high risk of a neural tube defect (37 per cent of all amniocenteses)–in 1974 a raised maternal serum alpha-fetoprotein level accounted for only 4 per cent of these; by 1981 this had risen to 67 per cent. There were seven false-positive and 132 true-positive diagnoses of neural tube defect; since 1981, with the introduction of amniotic fluid acetylocholinesterase determination as a secondary diagnostic test for neural tube defects, there have been no further false-positive diagnoses. In 1981 76 per cent of women aged 35 years or more did not have an amniocentesis. It is not known to what extent this was due to not offering women in this age group amniocentesis or to women not accepting such an offer.  相似文献   
382.
Hurler's disease was excluded in a fetus at 23 weeks' gestation by demonstrating normal iduronidase activity in fetal leucocytes following failure of amniotic cell culture after amnic-centesis at 16 and 19 weeks' gestation. The diagnosis was confirmed in the neonate.  相似文献   
383.
384.
385.
386.
387.
388.
389.
390.
The product service systems’ (PSS) sustainability potential is described in the framework of the new types of stakeholder relationships and/or partnerships, producing new convergence of economic interests, and a potential concomitant systemic resources optimization.In this perspective, it is argued that the design competencies should move towards those of the ‘strategic design’, thus introducing the concept of ‘strategic design for sustainability’: the design of an innovation strategy, shifting the business focus from designing (and selling) physical products only, to designing (and selling) a system of products and services which are jointly capable of fulfilling specific client demands, while re-orienting current unsustainable trends in production and consumption practices.Some examples of PSS are presented and discussed using the PSS categories ‘services providing added value to the product life cycle’, ‘services providing final results to customers’, and ‘services providing enabling platforms for customers’. The cases derive from an analysis of the ‘environmental friendly innovation’ yearly endowed prize submissions. The Politecnico di Milano University together with the Bocconi University and Legambiente (an environmental NGO) promotes the initiative in Italy.  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