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   53334篇
  免费   535篇
  国内免费   454篇
安全科学   1536篇
废物处理   2096篇
环保管理   7106篇
综合类   8221篇
基础理论   14776篇
环境理论   28篇
污染及防治   13963篇
评价与监测   3337篇
社会与环境   2891篇
灾害及防治   369篇
  2022年   418篇
  2021年   406篇
  2020年   314篇
  2019年   409篇
  2018年   730篇
  2017年   753篇
  2016年   1081篇
  2015年   885篇
  2014年   1360篇
  2013年   4274篇
  2012年   1630篇
  2011年   2313篇
  2010年   1900篇
  2009年   1945篇
  2008年   2273篇
  2007年   2432篇
  2006年   2151篇
  2005年   1792篇
  2004年   1779篇
  2003年   1721篇
  2002年   1672篇
  2001年   2104篇
  2000年   1496篇
  1999年   929篇
  1998年   684篇
  1997年   707篇
  1996年   750篇
  1995年   813篇
  1994年   747篇
  1993年   665篇
  1992年   672篇
  1991年   636篇
  1990年   638篇
  1989年   662篇
  1988年   569篇
  1987年   529篇
  1986年   480篇
  1985年   509篇
  1984年   511篇
  1983年   536篇
  1982年   542篇
  1981年   472篇
  1980年   419篇
  1979年   444篇
  1978年   387篇
  1977年   338篇
  1976年   315篇
  1975年   314篇
  1973年   326篇
  1972年   341篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
681.
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   
682.
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   
683.
684.
685.
686.
687.
688.
689.
690.
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