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   1387803篇
  免费   29811篇
  国内免费   7665篇
化学   699255篇
晶体学   16705篇
力学   75858篇
综合类   105篇
数学   245976篇
物理学   387380篇
  2021年   13483篇
  2020年   15976篇
  2019年   16103篇
  2018年   14686篇
  2017年   13189篇
  2016年   28870篇
  2015年   21028篇
  2014年   30567篇
  2013年   74675篇
  2012年   41123篇
  2011年   40571篇
  2010年   39078篇
  2009年   41007篇
  2008年   38798篇
  2007年   35218篇
  2006年   39180篇
  2005年   32431篇
  2004年   32820篇
  2003年   30480篇
  2002年   31110篇
  2001年   31735篇
  2000年   26674篇
  1999年   23421篇
  1998年   21401篇
  1997年   21395篇
  1996年   21292篇
  1995年   19326篇
  1994年   18802篇
  1993年   18355篇
  1992年   18706篇
  1991年   18918篇
  1990年   18135篇
  1989年   18179篇
  1988年   17155篇
  1987年   17100篇
  1986年   16078篇
  1985年   22545篇
  1984年   23722篇
  1983年   19758篇
  1982年   21391篇
  1981年   20589篇
  1980年   19926篇
  1979年   20414篇
  1978年   21582篇
  1977年   21288篇
  1976年   21100篇
  1975年   19764篇
  1974年   19482篇
  1973年   19987篇
  1972年   14425篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday  相似文献   
974.
975.
976.
977.
Levoglucosenone reacts with α-aminoazoles to yield azolo[1,5-a]pyrimidine systems fused with a carbohydrate fragment. The reaction oocurs much more smoothly than in the case of other α,β-unsaturated ketones. The reactions of levoglucosenone with β-dicarbonyl compounds (dimedone, barbituric acid) in the presence of a base results in the pyran ring closure, which has never been observed earlier in reactions of β-dicarbonyl compounds with α,β-unsaturated ketones under the conditions of basic catalysis. The structures of products were established by IR and NMR spectroscopy. For Part 3, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 553–558, March, 1997.  相似文献   
978.
The oxime and Schiff's base of N-furoylphenylhydroxylamine form complexes with Co2+, Cu2+, Zn2+ and Fe3+. These complexes were studied by means of the UV — Vis. spectra of nujol mulls, electron spin resonance (ESR) spectra and magnetic susceptibility to determine their stereochemistry. The complexes were characterized via elemental analyses, molar conductivities and thermogravimetric analyses. Organic reagents were used for the gravimetric determination of Co2+, Cu2+ and Fe3+ through the precipitation of their complexes. The compounds were also used for separation of a binary mixture of Cu2+ and Cu2+. Interferences were studied.  相似文献   
979.
980.
Thetrans-[Pt(NC5H4C(O)NHC2H4ONO2)2Cl2] complex (2) was prepared by the reaction of nicorandyl (N-nitroethoxynicotinamide), which is widely used in cardiology, with K2PtCl4 in water. The structure of2 was established by X-ray structural analysis. It was found that complex2 exhibits high antitumor activity, in particular, antimetastatic activity, unlike the analogous CuII complex with bromine atoms. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1672–1675, September, 1997.  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