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   3828篇
  免费   61篇
  国内免费   368篇
安全科学   160篇
废物处理   224篇
环保管理   349篇
综合类   850篇
基础理论   862篇
环境理论   2篇
污染及防治   1316篇
评价与监测   247篇
社会与环境   206篇
灾害及防治   41篇
  2023年   24篇
  2022年   100篇
  2021年   73篇
  2020年   43篇
  2019年   51篇
  2018年   141篇
  2017年   81篇
  2016年   108篇
  2015年   122篇
  2014年   135篇
  2013年   311篇
  2012年   125篇
  2011年   203篇
  2010年   174篇
  2009年   175篇
  2008年   196篇
  2007年   212篇
  2006年   174篇
  2005年   148篇
  2004年   155篇
  2003年   168篇
  2002年   135篇
  2001年   244篇
  2000年   161篇
  1999年   83篇
  1998年   52篇
  1997年   55篇
  1996年   39篇
  1995年   49篇
  1994年   48篇
  1993年   46篇
  1992年   35篇
  1991年   37篇
  1990年   27篇
  1989年   32篇
  1988年   20篇
  1987年   18篇
  1986年   18篇
  1985年   15篇
  1984年   20篇
  1983年   22篇
  1982年   23篇
  1981年   17篇
  1980年   11篇
  1979年   13篇
  1978年   12篇
  1977年   8篇
  1975年   12篇
  1973年   9篇
  1972年   10篇
排序方式: 共有4257条查询结果,搜索用时 15 毫秒
991.
992.
Ultrasound examination of a 31-year-old woman at 27 weeks' gestation revealed fetal growth retardation, a bilateral cleft lip and palate, and the absence of median cerebral structures. Chromosome analysis after cordocentesis showed an abnormal karyotype with a structural abnormality of the long arm of chromosome 7: 46,XX,—7,+der(7), t(7;18) (q34;q21.3)mat. The pregnancy was terminated at week 29. The ultrasound findings were confirmed by post-mortem examination, which also revealed a semilobar holoprosencephaly.  相似文献   
993.
A total of 1068 patients were examined by ultrasound to ensure normality of pregnancy and followed prospectively from booking until 28 weeks. The spontaneous miscarriage rate was 2.7 per cent occuring within the first 16 weeks. Threatened miscarriage was associated with a 38 per cent fetal loss. Miscarriage was less likely as pregnancy advanced. The reduction in subsequent miscarriage rate before 11 weeks and from 11 weeks onwards is statistically significant (p<0.001). Gravidity, maternal age and a history of previous fetal loss did not contribute significantly to the miscarriage rate. Patients with a history of fetal loss were more likely to experience a threatened miscarriage. The relevance of these findings to chorion villus sampling is discussed.  相似文献   
994.
A predominantly triploid 69,XXY placenta was found associated with a normal 46,XX infant. Therefore, a triploid placenta is apparently capable of supporting normal fetal development. The chromosome and pathological results support the conclusion that the triploid placenta originates from a ‘vanishing twin’ pregnancy. This case is unusual in that persistence of the placenta from the vanished twin has virtually replaced most of the normal placenta.  相似文献   
995.
IntroductionAgrochemicalshavebeenactedaveryimportantroleinagriculturalproduction .Foravoidingdamageofcrops,manykindsofpesticidesareappliedforthereasonofinsect,diseasesandweedcontrolinChina .Scientistshavedonealotofworkonthefateandmetabolismofpesticides,…  相似文献   
996.
Twenty-six pregnant Chinese women who were at risk of giving birth to a fetus affected with homozygous α-thalassaemia-1 were examined serially by ultrasound. Six of these 26 pregnancies were affected. In one third of the affected pregnancies progressive fetal ascites appeared before 24 weeks gestation and these pregnancies were terminated. In the remaining two thirds abnormal estimated fetal weight-placental volume (EFW-PV) ratio and fetal growth retardation as evidenced by a falling biparietal diameter (BPD), femur length (FL) but a normal abdominal circumference (AC) was apparent by 28 weeks gestation. Increased transverse cardiac (TC) diameter was another consistent finding but appeared late. All these features appeared before the onset of fetal ascites. A normal EFW-PV ratio and fetal growth until 28 weeks gestation was a reassuring sign of normality. Abnormal EFW-PV ratio was the earliest sign to appear in affected pregnancies and a normal ratio until 28 weeks gestation had a 100 per cent predictive value.  相似文献   
997.
IntroductionThispaperconcernstheadaptationandapplicationofamesoscalemeteorologicalmodelforgeneratingthewindfieldsandothermeteorologicalparametersforfuturestudiesofairpollutioninthecomplexterrainofHongKongSpecialAdministrativeRegion (HKSAR) .Themainarea…  相似文献   
998.
IntroductionAnatmospheredispersionfieldexperimentwasdoneonthecoastalsiteofnuclearpowerplant (NPP)intheeastpartofChinaduring 1995— 1996 Thecontentofthisexperimentincludes:hourlyobservationofwindandtemperatureonthetowerof10 0m ;Observationofsurfacewindandseeandl…  相似文献   
999.
Electron microscopical observations on algal samples collected in 1992 in the middle or final stages of a red tide in Hiroshima Bay, Japan, revealed virus-like particles (VLPs) in the red tide alga Heterosigma akashiwo (Class Raphidophyceae). The host cells appeared moribund and the VLPs were located in and around the nuclear area. The VLPs were icosahedral, ca. 185 nm in diameter, and generated from the periphery of several viroplasms. VLPs were also observed in three other types of H. akashiwo-like cells, which were morphologically distinguishable from each other. The appearance of VLPs in the red tide alga could explain the dramatically rapid termination of this red tide.  相似文献   
1000.
快速实现原位取样是准确测定煤层瓦斯含量的基础,为研究不同取样方式对瓦斯含量测定的影响,以淮南潘二煤矿11223工作面为例,对比深孔定点取样与孔口接粉取样方式下取样效果,并对采取的煤样利用直接法进行瓦斯含量测定对比分析。结果表明:深孔定点取样装置满足现场取样要求,且采用深孔定点方式取样可提高瓦斯含量测定准确性。  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