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   42175篇
  免费   463篇
  国内免费   358篇
安全科学   1254篇
废物处理   1694篇
环保管理   5914篇
综合类   6338篇
基础理论   11813篇
环境理论   28篇
污染及防治   11271篇
评价与监测   2558篇
社会与环境   1825篇
灾害及防治   301篇
  2022年   273篇
  2021年   310篇
  2020年   240篇
  2019年   330篇
  2018年   587篇
  2017年   576篇
  2016年   858篇
  2015年   735篇
  2014年   1058篇
  2013年   3333篇
  2012年   1265篇
  2011年   1812篇
  2010年   1480篇
  2009年   1539篇
  2008年   1839篇
  2007年   1951篇
  2006年   1719篇
  2005年   1434篇
  2004年   1431篇
  2003年   1347篇
  2002年   1355篇
  2001年   1684篇
  2000年   1203篇
  1999年   745篇
  1998年   582篇
  1997年   583篇
  1996年   620篇
  1995年   664篇
  1994年   604篇
  1993年   552篇
  1992年   533篇
  1991年   513篇
  1990年   510篇
  1989年   538篇
  1988年   464篇
  1987年   419篇
  1986年   376篇
  1985年   401篇
  1984年   395篇
  1983年   430篇
  1982年   438篇
  1981年   392篇
  1980年   332篇
  1979年   372篇
  1978年   302篇
  1977年   254篇
  1976年   257篇
  1975年   254篇
  1973年   238篇
  1972年   274篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
Ten out of the 12 new EU members, used to belong to the so-called “former eastern block”, with a post WWII environmental policy radically different from the tendencies followed in Western Europe. The lack of conservation regulations has resulted in a rather harmful industrialization, regarding natural resources and environmental quality. While air pollution transfer is a phenomenon of transboundary level, there is a particular interest in examining the contribution of the new EU member states to the environmental pressure faced by the older member states and vice versa. The current study utilises the official data for almost 20 years published by the European Monitoring and Evaluation Program concerning the transboundary transfer of NOx and SO2 in order to analyse the situation and discuss the present and future environmental policy regarding air pollution.  相似文献   
192.
A number of different models of CF carrier screening have now been tested in pilot trials. Apart from opportunistic and cascade testing (which are strictly speaking not true forms of screening), the major programmes have been directed either to young adults in primary care or to pregnant women in antenatal clinics. Only in the latter form of screening has sufficient data been collected to allow conclusions to be reached on the optimum mode of delivery. It seems very probable that when CF carrier screening passes into routine service, it will be the antenatal couple model that is used.  相似文献   
193.
The impact of prenatal sonographic diagnosis of oesophageal and gastrointestinal obstructions has been analysed over a 10-year period. Three groups of patients were evaluated. The first group consisted of 46 newborns with abnormal prenatal sonogratns, 41 of which were confirmed to have intestinal obstruction postnatally. The second group consisted of 17 neonates with normal prenatal sonograms who had intestinal obstruction postnatally. The third group included 56 newborns who did not undergo a prenatal sonogram but who had intestinal obstruction confirmed at surgery. Polyhydramnios without the appearance of a stomach on ultrasound was diagnostic of pure oesophageal atresia. Polyhydramnios with intestinal dilation was diagnostic of intestinal obstruction. Although surgery was performed earlier in the infants diagnosed prenatally with ultrasound, mortality was no less than in the group that did not undergo a prenatal sonogram, probably because of the high incidence of associated anomalies.  相似文献   
194.
As part of the Medical Research Council randomized trial of vitamin supplementation in the prevention of neural tube defects (NTDs), maternal serum alpha-fetoprotein (AFP) was available for 19 NTD pregnancies. Each of these was matched with four unaffected controls, by maternal age, participating centre, and duration of sample storage. The samples came from women whose gestational age ranged from 6 to 14 completed weeks. The median AFP level in the affected pregnancies was 1·2 multiples of the median value in unaffected pregnancies of the same gestational age (95 per cent confidence interval (CI) 0·83–1·59). This confirmed the view that serum AFP measurement is of no practical value in the detection of NTDs in the first trimester of pregnancy. The study also showed that folic acid supplementation, used as a method of preventing NTDs, had no effect on the concentrations of maternal serum AFP up to 14 weeks of pregnancy.  相似文献   
195.
196.
197.
198.
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   
199.
200.
Die Idee zu dieser Arbeit geht auf Diskussionen mit W. Priester über die Reduktion von Radiobeobachtungen ausgedehnter Galaxien im Jahre 1974 zurück. Die wesentlichen Teile wurden während eines Aufenthalts des Autors am Department of Astronomy, University of Florida, Gainesville, im Jahre 1987 entworfen. Ich habe ferner vielen Kollegen für hilfreiche Hinweise zu danken, darunter E. E. Baart, J. Condon, T. Cornwell, L. Erickson, S. Gottesman, J. Högbom, J. Skilling.  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