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   34855篇
  免费   392篇
  国内免费   418篇
安全科学   889篇
废物处理   1493篇
环保管理   4769篇
综合类   6407篇
基础理论   9074篇
环境理论   13篇
污染及防治   8219篇
评价与监测   2155篇
社会与环境   2479篇
灾害及防治   167篇
  2022年   255篇
  2021年   261篇
  2020年   232篇
  2019年   229篇
  2018年   911篇
  2017年   854篇
  2016年   996篇
  2015年   551篇
  2014年   736篇
  2013年   2299篇
  2012年   1120篇
  2011年   1981篇
  2010年   1371篇
  2009年   1562篇
  2008年   1844篇
  2007年   2068篇
  2006年   1189篇
  2005年   1063篇
  2004年   1056篇
  2003年   1058篇
  2002年   1028篇
  2001年   1156篇
  2000年   828篇
  1999年   552篇
  1998年   368篇
  1997年   401篇
  1996年   412篇
  1995年   460篇
  1994年   404篇
  1993年   385篇
  1992年   345篇
  1991年   369篇
  1990年   344篇
  1989年   314篇
  1988年   301篇
  1987年   266篇
  1986年   273篇
  1985年   270篇
  1984年   340篇
  1983年   291篇
  1982年   315篇
  1981年   282篇
  1980年   236篇
  1979年   252篇
  1978年   212篇
  1977年   199篇
  1976年   167篇
  1975年   183篇
  1974年   192篇
  1972年   170篇
排序方式: 共有10000条查询结果,搜索用时 209 毫秒
421.
422.
423.
424.
425.
We present a technique to aspirate amniotic fluid from both sacs in biamniotic twin pregnancies using a single abdominal insertion with a spinal needle. It was successful in 48 out of 55 cases of biamniotic twin pregnancies referred to our perinatal unit between 1985 and 1994. The single insertion technique was used when the inter-amniotic membrane was clearly evident and two separate free amniotic fluid pools could be reached by the operator with a single puncture. An adequate amount of amniotic fluid was sampled from both sacs to make a cytogenetic diagnosis in all cases. There were four fetuses with trisomy 21 in three twin pregnancies. In two cases, only one twin was affected whilst the co-twin was normal, so that a selective feticide was performed. No miscarriages due to genetic amniocentesis were reported. After 1990, all genetic amniocenteses in biamniotic twin pregnancies (except for one case due to late booking) were performed between 14 and 15 weeks of gestation and with all cases except one, it was possible to sample both twins by a single puncture. We suggest that early amniocentesis (14–15 weeks) by a single abdominal puncture could be a reliable and safe alternative to first-trimester chorionic villus sampling in twin pregnancies.  相似文献   
426.
The observation that thyroid disease is frequent in mothers of children with Down syndrome (DS) has suggested that maternal thyroid antibodies could be a factor predisposing to trisomy 21 in their offspring. In this study, the incidences of thyroglobulin (Tg) and thyroid peroxidase (TPO) antibodies were analysed with a sensitive solid-phase immunosorbent radioassay in sera from 29 mothers giving birth to children with trisomy 21 and 87 control mothers. The serum samples were collected at delivery. There was no statistical difference regarding the proportion of thyroid antibodies (against Tg and/or TPO) in the two groups. Thyroid antibodies were detected in 6/29 (20.7 per cent) of the DS mothers and in 23/87 (26.4 per cent) of the control mothers. Among the women with thyroid antibodies, 4/6 (66.7 per cent) of the DS mothers and 12/23 (52 per cent) of the control mothers had antibodies against both Tg and TPO. There was no increase in the relative risk of having a child with DS if the titre of either Tg or TPO antibodies or both were positive, i.e. ≥ 1/5. The results indicate that the presence of thyroid antibodies in the serum of a pregnant woman has no prognostic value for the birth of an infant with DS.  相似文献   
427.
Fifty-three patients who elected to reduce their pregnancies to a twin gestation in our centre are known to have subsequently undergone genetic amniocentesis. Five of these patients lost their entire pregnancy following the genetic amniocentesis procedure. This is equivalent to a 9·4 per cent pregnancy loss rate for reduced twin gestations in comparison with an expected loss rate of 2 per cent for non-reduced twin gestations.  相似文献   
428.
IntroductionTheprocessofmunicipalsolidwaste(MSW)isoneofthemostseriousissuesintermsofenvironmentalprotection.ProcessingofMSWwithoutfurtherdisastrouscontaminationcanbeachievedonlyinmodernizedmeasures,suchasincineratingandenergygeneratingconcurrently(Shen…  相似文献   
429.
IntroductionChengdu KunmingRailwayLineislocatedonthemountainregionofsouthwesternChina .Therearealotofdebrisflowgulliesspreadingbesidethisrailwayline .Onsummer,thedebrisflowoftenburstsandthreatensthesafetyoftherailwaytransportation.In 1981,alarge scaledebris…  相似文献   
430.
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   
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