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   30524篇
  免费   835篇
  国内免费   241篇
化学   20619篇
晶体学   156篇
力学   725篇
综合类   1篇
数学   5787篇
物理学   4312篇
  2022年   156篇
  2021年   286篇
  2020年   364篇
  2019年   330篇
  2018年   291篇
  2017年   311篇
  2016年   630篇
  2015年   644篇
  2014年   681篇
  2013年   1513篇
  2012年   1491篇
  2011年   1796篇
  2010年   1008篇
  2009年   877篇
  2008年   1562篇
  2007年   1573篇
  2006年   1648篇
  2005年   1492篇
  2004年   1429篇
  2003年   1176篇
  2002年   1117篇
  2001年   501篇
  2000年   449篇
  1999年   449篇
  1998年   412篇
  1997年   463篇
  1996年   428篇
  1995年   382篇
  1994年   415篇
  1993年   364篇
  1992年   351篇
  1991年   339篇
  1990年   301篇
  1989年   315篇
  1988年   274篇
  1987年   242篇
  1986年   274篇
  1985年   401篇
  1984年   420篇
  1983年   351篇
  1982年   386篇
  1981年   374篇
  1980年   374篇
  1979年   313篇
  1978年   338篇
  1977年   323篇
  1976年   248篇
  1975年   222篇
  1974年   229篇
  1973年   201篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
155.
156.
157.
158.
The light of the sun can be used directly for changing chemical structures photochemically. Any industrial application must conform to the limitations imposed by the spectral distribution of the photons from the sun, the interruptions to the radiation due to the day/night rhythm, and the weather. In this review, we describe the photochemical potential of the sun, give a fundamental treatment of the concept of photoreactors driven by sunlight (abbreviated to solar photoreactors), and give an account of the realization of this concept in the first pilot plant on the “Plataforma Solar de Almeria” in southern Spain and in other activities in this field. Based on experimental data from photochemical investigations on the pilot plant scale, possibilities, limitations, and the potential growth of solar photochemistry are described. Solar photochemistry, in our opinion, is a technique which could make a contribution to the chemistry of the future because of its photochemical synthesis potential, the avoidance of waste products, and the direct utilization of the sun, not only as a primary energy source, but also as a reaction partner.  相似文献   
159.
A method is described for the determination of the antitumor agent iphosphamide and seven of its metabolites in the plasma of cancer patients by multiple ion monitoring (MIM) GC-MS, mainly using the electron capture chemical ionization mode, of stable methyl and/or trifluoroacetyl derivatives. The metabolites determined were 2- and 3-dechloroethyliphosphamide, 4-ketoiphosphamide, carboxyiphosphamide, iphosphamide mustard, and two previously undetected metabolites, chloroethylamine and 1,3-oxazolidine-2-one. The isolation of the acidic and neutral metabolites was performed by solid phase extraction on to C18 adsorbent at pH 4. The weakly acidic iphosphamide mustard, isolated under these conditions with a yield of ca 50%, was measured as a stable methyltrifluoroacetyl derivative, in contrast to the corresponding phosphoramide mustard of the isomer cyclophosphamide which decomposes during derivatization. Chloroethylamine and 1,3-oxazolidine-2-one were isolated with high yield by liquid extraction with ethyl acetate at pH 10. Selective measurement of several metabolite derivatives with similar retention times was performed by multiple ion monitoring MS of specific ion masses, using a methyl phenyl siloxane capillary column previously employed in the study of cyclophosphamide metabolites. Quantitation of metabolites in patient plasma samples could be performed in the concentration range 3 ng to 20 μg per ml of original plasma.  相似文献   
160.
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