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   1263692篇
  免费   29610篇
  国内免费   7604篇
化学   622136篇
晶体学   15701篇
力学   73436篇
综合类   101篇
数学   238878篇
物理学   350654篇
  2021年   13369篇
  2020年   15900篇
  2019年   16031篇
  2016年   27071篇
  2015年   20590篇
  2014年   30384篇
  2013年   74342篇
  2012年   34482篇
  2011年   28553篇
  2010年   34844篇
  2009年   37858篇
  2008年   28879篇
  2007年   23640篇
  2006年   32094篇
  2005年   23326篇
  2004年   25811篇
  2003年   25157篇
  2002年   26737篇
  2001年   24347篇
  2000年   22367篇
  1999年   21424篇
  1998年   20628篇
  1997年   20689篇
  1996年   21040篇
  1995年   19171篇
  1994年   18588篇
  1993年   18161篇
  1992年   17689篇
  1991年   17941篇
  1990年   17156篇
  1989年   16665篇
  1988年   16199篇
  1987年   16287篇
  1986年   15147篇
  1985年   21766篇
  1984年   23219篇
  1983年   19385篇
  1982年   21187篇
  1981年   20462篇
  1980年   19703篇
  1979年   19841篇
  1978年   21287篇
  1977年   20893篇
  1976年   20549篇
  1975年   19232篇
  1974年   18850篇
  1973年   19391篇
  1972年   13880篇
  1968年   11891篇
  1967年   12297篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
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   
994.
995.
996.
997.
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   
998.
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   
999.
1000.
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