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   1297177篇
  免费   29556篇
  国内免费   7615篇
化学   638684篇
晶体学   20380篇
力学   74273篇
综合类   104篇
数学   239597篇
物理学   361310篇
  2021年   13366篇
  2020年   15864篇
  2019年   15992篇
  2018年   12962篇
  2016年   27794篇
  2015年   20717篇
  2014年   30254篇
  2013年   74041篇
  2012年   35635篇
  2011年   31609篇
  2010年   36604篇
  2009年   39303篇
  2008年   31536篇
  2007年   27032篇
  2006年   32601篇
  2005年   25912篇
  2004年   27403篇
  2003年   26174篇
  2002年   27262篇
  2001年   25402篇
  2000年   22864篇
  1999年   21602篇
  1998年   20653篇
  1997年   20686篇
  1996年   20914篇
  1995年   19044篇
  1994年   18455篇
  1993年   17989篇
  1992年   17616篇
  1991年   17967篇
  1990年   17174篇
  1989年   17273篇
  1988年   16832篇
  1987年   16870篇
  1986年   15758篇
  1985年   22225篇
  1984年   23568篇
  1983年   19816篇
  1982年   21531篇
  1981年   20782篇
  1980年   20108篇
  1979年   20161篇
  1978年   21558篇
  1977年   21131篇
  1976年   20799篇
  1975年   19464篇
  1974年   19096篇
  1973年   19589篇
  1972年   14101篇
  1967年   12341篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
962.
963.
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   
964.
965.
966.
967.
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   
968.
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   
969.
970.
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