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   1473866篇
  免费   30509篇
  国内免费   8435篇
化学   735078篇
晶体学   20112篇
力学   81248篇
综合类   164篇
数学   266035篇
物理学   410173篇
  2021年   13504篇
  2020年   16041篇
  2019年   16142篇
  2018年   20541篇
  2017年   19423篇
  2016年   31740篇
  2015年   21827篇
  2014年   30842篇
  2013年   75114篇
  2012年   45471篇
  2011年   50831篇
  2010年   44746篇
  2009年   46560篇
  2008年   47720篇
  2007年   46425篇
  2006年   41279篇
  2005年   38892篇
  2004年   36687篇
  2003年   33816篇
  2002年   33121篇
  2001年   32045篇
  2000年   27186篇
  1999年   23647篇
  1998年   21571篇
  1997年   21446篇
  1996年   21487篇
  1995年   19441篇
  1994年   18863篇
  1993年   18421篇
  1992年   18709篇
  1991年   18928篇
  1990年   18078篇
  1989年   18068篇
  1988年   17692篇
  1987年   17556篇
  1986年   16597篇
  1985年   22980篇
  1984年   24110篇
  1983年   20181篇
  1982年   21881篇
  1981年   21047篇
  1980年   20403篇
  1979年   20322篇
  1978年   21619篇
  1977年   21248篇
  1976年   21099篇
  1975年   19797篇
  1974年   19508篇
  1973年   20038篇
  1972年   14493篇
排序方式: 共有10000条查询结果,搜索用时 15 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