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   1421300篇
  免费   30062篇
  国内免费   7778篇
化学   722530篇
晶体学   20683篇
力学   76175篇
综合类   111篇
数学   248757篇
物理学   390884篇
  2021年   13652篇
  2020年   16178篇
  2019年   16316篇
  2018年   14533篇
  2016年   29224篇
  2015年   21408篇
  2014年   31059篇
  2013年   75645篇
  2012年   42849篇
  2011年   42810篇
  2010年   39812篇
  2009年   41474篇
  2008年   40972篇
  2007年   37446篇
  2006年   41453篇
  2005年   34885篇
  2004年   34713篇
  2003年   31858篇
  2002年   32457篇
  2001年   32129篇
  2000年   27318篇
  1999年   23686篇
  1998年   21540篇
  1997年   21508篇
  1996年   21488篇
  1995年   19488篇
  1994年   18934篇
  1993年   18564篇
  1992年   18823篇
  1991年   19040篇
  1990年   18088篇
  1989年   18143篇
  1988年   17646篇
  1987年   17627篇
  1986年   16579篇
  1985年   22969篇
  1984年   24111篇
  1983年   20194篇
  1982年   21845篇
  1981年   21053篇
  1980年   20401篇
  1979年   20718篇
  1978年   21925篇
  1977年   21555篇
  1976年   21358篇
  1975年   20061篇
  1974年   19719篇
  1973年   20215篇
  1972年   14663篇
  1967年   12851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