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   32286篇
  免费   304篇
  国内免费   308篇
安全科学   847篇
废物处理   1461篇
环保管理   3858篇
综合类   4745篇
基础理论   8676篇
环境理论   8篇
污染及防治   8573篇
评价与监测   2401篇
社会与环境   2121篇
灾害及防治   208篇
  2022年   303篇
  2021年   297篇
  2020年   219篇
  2019年   264篇
  2018年   471篇
  2017年   496篇
  2016年   761篇
  2015年   573篇
  2014年   898篇
  2013年   2665篇
  2012年   1046篇
  2011年   1391篇
  2010年   1265篇
  2009年   1222篇
  2008年   1369篇
  2007年   1510篇
  2006年   1329篇
  2005年   1097篇
  2004年   1079篇
  2003年   1049篇
  2002年   1034篇
  2001年   1392篇
  2000年   977篇
  1999年   576篇
  1998年   408篇
  1997年   404篇
  1996年   445篇
  1995年   462篇
  1994年   435篇
  1993年   383篇
  1992年   396篇
  1991年   354篇
  1990年   375篇
  1989年   371篇
  1988年   319篇
  1987年   296篇
  1986年   257篇
  1985年   271篇
  1984年   293篇
  1983年   276篇
  1982年   295篇
  1981年   238篇
  1980年   211篇
  1979年   260篇
  1978年   198篇
  1977年   204篇
  1976年   167篇
  1975年   160篇
  1974年   157篇
  1973年   165篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
411.
412.
413.
The main objective of this project was to evaluate the possibility of reducing the quantity of fibre wasted at one of many hydrocyclone (centrifugal) cleaning processes in a paper mill. It was found that the application of elutriation water to both the tertiary and quaternary cleaners was essential to minimise the fibre discharged to the sewer, and the pressure of this elutriation water had a dramatic effect of reducing the fibre wastage. Accordingly, it has been shown that 150–160 kPa as the optimum pressure range to apply elutriation water to minimise the product grade fibre wasted whilst sending undesired shive fibre to the sewer. Also, monitoring of the press uhle box wastewater revealed that the paper mill has the potential to make substantial cost savings by reducing the waste stream. Further investigation is necessary to determine the types of fibre that are being wasted, and the viability of a screen to recycle the wasted fibre to the process. However, these fibres may be unsuitable to reuse in the process and alternative uses must be found.  相似文献   
414.
Chinese life cycle impact assessment factors   总被引:5,自引:0,他引:5  
IntroductionLifecycleassessment(LCA)isanenvironmentalmanagementtoolthatisusedtoexamineandevaluatetheenvironmentalimpactsassociatedwiththeexistenceofproducts(Jensen,1998;Weidema,1997;Wenzel,1997).ThefocusofLCAisontheentirelifecycleoftheproduct,i.e.fromtheextracti…  相似文献   
415.
IntroductionChengdu KunmingRailwayLineislocatedonthemountainregionofsouthwesternChina .Therearealotofdebrisflowgulliesspreadingbesidethisrailwayline .Onsummer,thedebrisflowoftenburstsandthreatensthesafetyoftherailwaytransportation.In 1981,alarge scaledebris…  相似文献   
416.
A multiple pregnancy of high rank may occur in a couple at risk for a Mendelian disorder. Prenatal diagnosis is hampered by the difficulty of (1) obtaining chorionic villi from each zygote arid (2) unequivocally relating each sample to the corresponding embryo. The calculation of the genetic risk according to the number of zygotes led us to propose a diagnostic strategy based on embryo reduction, a technique initially designed to improve the perinatal outcome of multiple pregnancies with normal embryos. We report a case in which this approach allowed rational use of first-trimester chorionic villus sampling in a quintuplet pregnancy at risk for non-ketotic hyperglycinaemia, resulting in the selective birth of unaffected twins.  相似文献   
417.
We describe a new method for the post-mortem examination of the fetal central nervous system. The brain is immobilized in gelatin prior to ultrasonic examination. Correlation with prenatal ultrasound is excellent and subsequent pathological examination is enhanced and facilitated.  相似文献   
418.
We report the first prenatal diagnosis of an affected fetus with Chediak-Higashi syndrome (CHS). Diagnosis was accomplished via fetal blood sampling at 17 menstrual weeks and was confirmed after birth. Retrospective measurement of the largest acid phosphatase-positive lysosomes in cultured amniotic fluid cells and chorionic villus cells showed that in CHS these lysosomes are significantly larger than those in normal cells. This method may be used for prenatal diagnosis of CHS by amniocentesis and chorionic villus sampling (CVS).  相似文献   
419.
Fetal nucleated erythrocytes (NRBC) in maternal blood are a non-invasive source of fetal DNA for prenatal genetic screening. We compared the effectiveness of three monoclonal antibodies for the separation of fetal cells from maternal blood by flow sorting. Mononuclear blood cells from 49 healthy pregnant women were incubated with antibody to CD 71, CD 36, and/or glycophorin A (GPA), employed singly or in combination with each other. These monoclonal antibodies recognize surface antigens on haematopoietic precursor cells. Successful isolation of fetal cells was defined as detection of Y chromosomal sequences in maternal blood from women carrying male fetuses, with absence of Y sequences when female fetuses were carried. Thus, gender prediction accuracy was used as a measure of fetal cell separation. Using anti-CD 71 to isolate fetal cells, gender prediction was 57 per cent correct; with anti-CD 36, it was 88 per cent correct. Anti-GPA, an erythrocyte-specific antigen, used alone or in combination with anti-CD 71 or 36, improved gender prediction to 100 per cent. We conclude that antibody to GPA improves the retrieval of fetal NRBC from maternal blood, permitting genetic analysis by the polymerase chain reaction.  相似文献   
420.
We describe the prenatal diagnosis of isolated bilateral fetal microphthalmia in a woman at increased risk of having a fetus with microphthalmia. Ultrasound examinations at 161 and 19-5 weeks' gestation demonstrated bilateral fetal microphthalmia with no other associated structural defects. The patient elected to terminate her pregnancy at 19.5 weeks. Pathological evaluation of the products of conception obtained by dilation and evacuation confirmed the prenatal diagnosis of isolated bilateral fetal microphthalmia.  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