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   1449510篇
  免费   30016篇
  国内免费   7855篇
化学   740406篇
晶体学   20828篇
力学   77076篇
综合类   114篇
数学   250470篇
物理学   398487篇
  2021年   13611篇
  2020年   16083篇
  2019年   16210篇
  2018年   15557篇
  2017年   13893篇
  2016年   29485篇
  2015年   21321篇
  2014年   30848篇
  2013年   75226篇
  2012年   43861篇
  2011年   45349篇
  2010年   40713篇
  2009年   42102篇
  2008年   42950篇
  2007年   39995篇
  2006年   42504篇
  2005年   36600篇
  2004年   35951篇
  2003年   32935篇
  2002年   33285篇
  2001年   34178篇
  2000年   28397篇
  1999年   24211篇
  1998年   21765篇
  1997年   21610篇
  1996年   21501篇
  1995年   19496篇
  1994年   18987篇
  1993年   18596篇
  1992年   19290篇
  1991年   19423篇
  1990年   18618篇
  1989年   18608篇
  1988年   18232篇
  1987年   18092篇
  1986年   17081篇
  1985年   23410篇
  1984年   24407篇
  1983年   20401篇
  1982年   21938篇
  1981年   21182篇
  1980年   20525篇
  1979年   21027篇
  1978年   22091篇
  1977年   21799篇
  1976年   21591篇
  1975年   20321篇
  1974年   20011篇
  1973年   20394篇
  1972年   14868篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
981.
982.
983.
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   
984.
985.
986.
987.
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   
988.
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   
989.
990.
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