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   41098篇
  免费   549篇
  国内免费   1373篇
安全科学   1267篇
废物处理   1445篇
环保管理   5593篇
综合类   8768篇
基础理论   10998篇
环境理论   28篇
污染及防治   10783篇
评价与监测   2218篇
社会与环境   1560篇
灾害及防治   360篇
  2022年   373篇
  2021年   339篇
  2020年   290篇
  2019年   365篇
  2018年   555篇
  2017年   588篇
  2016年   856篇
  2015年   789篇
  2014年   983篇
  2013年   3072篇
  2012年   1265篇
  2011年   1797篇
  2010年   1450篇
  2009年   1485篇
  2008年   1718篇
  2007年   1783篇
  2006年   1614篇
  2005年   1280篇
  2004年   1276篇
  2003年   1260篇
  2002年   1211篇
  2001年   1569篇
  2000年   1117篇
  1999年   770篇
  1998年   588篇
  1997年   583篇
  1996年   627篇
  1995年   632篇
  1994年   606篇
  1993年   546篇
  1992年   552篇
  1991年   508篇
  1990年   523篇
  1989年   544篇
  1988年   460篇
  1987年   414篇
  1986年   388篇
  1985年   424篇
  1984年   397篇
  1983年   433篇
  1982年   433篇
  1981年   391篇
  1980年   354篇
  1979年   373篇
  1978年   336篇
  1977年   285篇
  1976年   299篇
  1974年   282篇
  1973年   268篇
  1972年   290篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The karyotype of cultured amniotic fluid cells obtained on the indication of advanced maternal age was shown to be a mosaic 45,X/46,X,r(?). The small size and banding pattern made it difficult to determine whether the ring was derived from and X or a Y chromosome, or even from an autosome. By using an X-centromeric probe and fluorescence in situ hybridization (FISH), we demonstrated the ring to have an X centromere. Thus, a more complete genetic counselling was possible. This confirms the usefulness of FISH in identifying and characterizing this and other chromosome rearrangements in prenatal diagnosis.  相似文献   
132.
133.
We have investigated the ability of high-resolution proton NMR spectroscopy to provide a biochemical constituent screening of human amniotic fluid (AF). Proton NMR spectra were obtained at 300 MHz on AF from patients undergoing amniocentesis in the mid-trimester. Only AF from normal pregnancies (normal fetal karyotype, normal a-fetoprotein levels, normal birth outcome) was used in this study. The AF supernatant was lyophilized and resuspended in deuterated water containing 0.1 mm phosphate buffer and 6.02 mm disodium maleate. Identification of low molecular weight compounds was confirmed by two-dimensional NMR spectra (primarily correlated spectroscopy, or COSY) and standard addition techniques. A broad profile of compounds were ‘NMR visible’ in a single proton spectrum, including creatinine, glucose, organic acids (acetate, citrate, and lactate) and several amino acids (alanine, histidine, leucine, phenylalanine, tyrosine and valine). The proton spectrum was unaffected by prior freezing/thawing of AF samples. We were able to quantify compounds by comparison with an added concentration standard (maleate) at concentrations as low as 30 μm. Good agreement with literature values based on other analytical techniques was obtained.  相似文献   
134.
135.
The modern consumer is very much interested in healthy food. The reason is that a special group of consumers is focusing more and more attention on health and nutrition problems. Further, there is increased emphasis on education in food science at universities as well as polytechnics. For some years worldwide dietary goals are published with the intention to reduce nutrition-based sickness. For the first time in our nutrition report 1988, clear proposals for optimal nutrition were formulated.  相似文献   
136.
137.
138.
Online searching in publically available patent files opens up interesting possibilities to provide a rapid response to critical questions. A computerized analysis of all patents of leading German pharmaceutical companies over the last decade in important indication areas is described. Supported by subsequent manual processing of individual patents it is shown that duplicate experiments on animals practically never occur.  相似文献   
139.
140.
The excellent technical assistance of H. Führer and I. Leib is appreciated. Part of the work was supported by the Bundesministerium für Forschung und Technologie, the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and from the Leitz and Hoechst companies. This paper is part of the M. D. thesis of Ch.L.  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