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   1413400篇
  免费   29732篇
  国内免费   7778篇
化学   712903篇
晶体学   19061篇
力学   76666篇
综合类   115篇
数学   248388篇
物理学   393777篇
  2021年   13463篇
  2020年   15934篇
  2019年   16068篇
  2018年   16461篇
  2017年   15153篇
  2016年   29486篇
  2015年   21116篇
  2014年   30400篇
  2013年   74309篇
  2012年   42359篇
  2011年   43565篇
  2010年   40698篇
  2009年   42363篇
  2008年   41787篇
  2007年   38910篇
  2006年   40218篇
  2005年   35751篇
  2004年   34779篇
  2003年   31850篇
  2002年   31961篇
  2001年   31081篇
  2000年   26494篇
  1999年   23356篇
  1998年   21318篇
  1997年   21208篇
  1996年   21246篇
  1995年   19236篇
  1994年   18714篇
  1993年   18279篇
  1992年   18495篇
  1991年   18735篇
  1990年   17939篇
  1989年   17946篇
  1988年   17613篇
  1987年   17504篇
  1986年   16439篇
  1985年   22828篇
  1984年   24005篇
  1983年   20141篇
  1982年   21729篇
  1981年   20524篇
  1980年   19837篇
  1979年   20269篇
  1978年   21507篇
  1977年   21202篇
  1976年   20958篇
  1975年   19723篇
  1974年   19339篇
  1973年   19913篇
  1972年   14385篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
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   
974.
975.
976.
977.
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   
978.
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   
979.
980.
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