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   1487057篇
  免费   29973篇
  国内免费   7859篇
化学   761388篇
晶体学   21213篇
力学   78113篇
综合类   119篇
数学   254338篇
物理学   409718篇
  2021年   13641篇
  2020年   16092篇
  2019年   16226篇
  2018年   17680篇
  2017年   16405篇
  2016年   30378篇
  2015年   21464篇
  2014年   30796篇
  2013年   74928篇
  2012年   46171篇
  2011年   49963篇
  2010年   42657篇
  2009年   43751篇
  2008年   46942篇
  2007年   44567篇
  2006年   44479篇
  2005年   40179篇
  2004年   38522篇
  2003年   34761篇
  2002年   34467篇
  2001年   35138篇
  2000年   28882篇
  1999年   24485篇
  1998年   21833篇
  1997年   21610篇
  1996年   21553篇
  1995年   19503篇
  1994年   19025篇
  1993年   18572篇
  1992年   19379篇
  1991年   19485篇
  1990年   18710篇
  1989年   18662篇
  1988年   18386篇
  1987年   18215篇
  1986年   17146篇
  1985年   23491篇
  1984年   24465篇
  1983年   20482篇
  1982年   21959篇
  1981年   21172篇
  1980年   20513篇
  1979年   21095篇
  1978年   22133篇
  1977年   21856篇
  1976年   21562篇
  1975年   20340篇
  1974年   19996篇
  1973年   20388篇
  1972年   14868篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
994.
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   
995.
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   
996.
997.
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   
998.
2 laser of wide tunability to pump 13CD3OD we could observe 10 new far infrared laser lines ranging from 109 μm to 472 μm. The lines were generated by pumping infrared absorbing transitions of large offset appertaining to the C-O stretching Q-branch. All lines were characterised in wavelength, polarisation, optimum pressure of operation and precise offset measurements. Received: 17 September 1996/Revised version: 18 November 1996  相似文献   
999.
1000.
The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material.  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