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   1489093篇
  免费   30103篇
  国内免费   8336篇
化学   740941篇
晶体学   21113篇
力学   77411篇
综合类   123篇
数学   251852篇
物理学   403261篇
综合类   32831篇
  2021年   13618篇
  2020年   16061篇
  2019年   16182篇
  2018年   16940篇
  2017年   15667篇
  2016年   30058篇
  2015年   21404篇
  2014年   30875篇
  2013年   75056篇
  2012年   45205篇
  2011年   47928篇
  2010年   41892篇
  2009年   43331篇
  2008年   45302篇
  2007年   43118篇
  2006年   43846篇
  2005年   39437篇
  2004年   39331篇
  2003年   35497篇
  2002年   35230篇
  2001年   35033篇
  2000年   29052篇
  1999年   24795篇
  1998年   22060篇
  1997年   22092篇
  1996年   21659篇
  1995年   19488篇
  1994年   19266篇
  1993年   18789篇
  1992年   19537篇
  1991年   19711篇
  1990年   18976篇
  1989年   18835篇
  1988年   18328篇
  1987年   18322篇
  1986年   17103篇
  1985年   23518篇
  1984年   24524篇
  1983年   20555篇
  1982年   22044篇
  1981年   21256篇
  1980年   20614篇
  1979年   21286篇
  1978年   22427篇
  1977年   22005篇
  1976年   21741篇
  1975年   20507篇
  1974年   20408篇
  1973年   20580篇
  1972年   14975篇
排序方式: 共有10000条查询结果,搜索用时 187 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