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   41582篇
  免费   445篇
  国内免费   539篇
安全科学   1218篇
废物处理   1869篇
环保管理   5082篇
综合类   7790篇
基础理论   10483篇
环境理论   23篇
污染及防治   10684篇
评价与监测   2759篇
社会与环境   2444篇
灾害及防治   214篇
  2022年   391篇
  2021年   390篇
  2020年   279篇
  2019年   356篇
  2018年   617篇
  2017年   602篇
  2016年   959篇
  2015年   734篇
  2014年   1103篇
  2013年   3212篇
  2012年   1323篇
  2011年   1846篇
  2010年   1477篇
  2009年   1569篇
  2008年   1833篇
  2007年   1901篇
  2006年   1669篇
  2005年   1393篇
  2004年   1345篇
  2003年   1411篇
  2002年   1278篇
  2001年   1642篇
  2000年   1107篇
  1999年   703篇
  1998年   479篇
  1997年   512篇
  1996年   519篇
  1995年   586篇
  1994年   598篇
  1993年   504篇
  1992年   504篇
  1991年   503篇
  1990年   527篇
  1989年   455篇
  1988年   418篇
  1987年   388篇
  1986年   345篇
  1985年   360篇
  1984年   388篇
  1983年   377篇
  1982年   383篇
  1981年   329篇
  1980年   278篇
  1979年   296篇
  1978年   279篇
  1977年   212篇
  1975年   224篇
  1974年   215篇
  1972年   202篇
  1971年   212篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
601.
602.
603.
Maternal age specific rates for all major chromosome aberrations have been determined in 52 965 pregnancies in mothers 35 years of age and over at the time of amniocentesis. Rates increase exponentially with advancing maternal age for trisomies 21, 18 and 13, and for the XXX and XXY syndromes, but in the autosomal trisomies this rise appears to be followed by a levelling off at the upper end of the age range. A significant inverse relationship with maternal age is found for 45,X cases. It is postulated that these various patterns are the result of the interaction of three principal factors: a maternal age effect acting particularly on first meiotic nondisjunction: a higher spontaneous abortion rate with advancing maternal age for aneuploid as compared to euploid conceptions; and an increased probability of spontaneous abortion before the time of amniocentesis for conceptions with more extensive chromosome imbalance. A stepwise logistic regression analysis of 13 299 pregnancies in which both parental ages are known shows that the father's age does not influence these maternal age specific rates, with the possible exception of the 47,XXY syndrome.  相似文献   
604.
The increasing interest in the parasites of man in the Federal Republic of Germany is connected with the unbounded keenness of German people to travel. They favor southern regions with warm climates which are usually infested with parasites. Thus the general practitioner is nowadays confronted in his daily routine with “imported” pathogenic organisms and diseases as yet unknown to him or with which he need not have reckoned in the past. Furthermore, new information now exists on the development of well-known parasites of our regions, which can be pathogenic to man. Fortunately, new reliable drugs have come on the market, rendering some parasitic diseases harmless.  相似文献   
605.
Circulating placental [human chorionic gonadotrophin (hCG), Schwangerschafts protein 1 (SP1), pregnancy-associated plasma protein A (PAPP-A), decidual (pregnancy protein) 12 (PP12), and fetal alphafetoprotein (AFP)] proteins were measured immediately before and within 1 h in 18 women undergoing diagnostic chorionic villus sampling (CVS) in the first trimester. An elevation of serum AFP levels was consistently seen, while fluctuations in excess of 10 per cent of the pre-CVS levels of SP1 and PP12 were seen in the majority of patients. Fluctuations in hCG and PAPP-A were consistently less than 10 per cent of pre-CVS values. Post-CVS changes in levels were not apparently associated with any feature of the technique, the pregnancy, or its outcome (one missed abortion). As feto-maternal haemorrhage is a common event, anti-D should be offered to rhesus-negative women undergoing CVS. In the prediction of subsequent miscarriage, only hCG and PAPP-A measurements should be considered.  相似文献   
606.
607.
608.
609.
610.
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