全文获取类型
收费全文 | 431065篇 |
免费 | 3035篇 |
国内免费 | 752篇 |
专业分类
化学 | 209353篇 |
晶体学 | 5440篇 |
力学 | 22525篇 |
综合类 | 18篇 |
数学 | 60462篇 |
物理学 | 137054篇 |
出版年
2020年 | 3307篇 |
2019年 | 3900篇 |
2018年 | 11806篇 |
2017年 | 12512篇 |
2016年 | 10286篇 |
2015年 | 4407篇 |
2014年 | 6814篇 |
2013年 | 15374篇 |
2012年 | 14726篇 |
2011年 | 23521篇 |
2010年 | 15921篇 |
2009年 | 16264篇 |
2008年 | 20909篇 |
2007年 | 23726篇 |
2006年 | 11659篇 |
2005年 | 15161篇 |
2004年 | 12050篇 |
2003年 | 11519篇 |
2002年 | 9929篇 |
2001年 | 10502篇 |
2000年 | 8042篇 |
1999年 | 6023篇 |
1998年 | 5090篇 |
1997年 | 4816篇 |
1996年 | 4442篇 |
1995年 | 4232篇 |
1994年 | 4120篇 |
1993年 | 3939篇 |
1992年 | 4583篇 |
1991年 | 4790篇 |
1990年 | 4646篇 |
1989年 | 4721篇 |
1988年 | 4666篇 |
1987年 | 4698篇 |
1986年 | 4370篇 |
1985年 | 5621篇 |
1984年 | 5657篇 |
1983年 | 4634篇 |
1982年 | 4769篇 |
1981年 | 4751篇 |
1980年 | 4377篇 |
1979年 | 4991篇 |
1978年 | 5167篇 |
1977年 | 5235篇 |
1976年 | 5176篇 |
1975年 | 4789篇 |
1974年 | 4670篇 |
1973年 | 4839篇 |
1972年 | 3618篇 |
1968年 | 3259篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
In this note we show how 1-factors in the middle two layers of the discrete cube can be used to construct 2-factors in the
Odd graph (the Kneser graph of (k − 1)-sets from a (2k − 1)-set). In particular, we use the lexical matchings of Kierstead and Trotter, and the modular matchings of Duffus, Kierstead
and Snevily, to give explicit constructions of two different 2-factorisations of the Odd graph.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
992.
993.
An indium-induced reduction-rearrangement reaction of nitro-substituted β-lactams has been used for facile synthesis of oxazines in aqueous ethanol. 相似文献
994.
Petro P Onys'ko Olena A SuvalovaYuliya V Rassukana Tetyana I ChudakovaAnatolii D Sinitsa 《Tetrahedron letters》2003,44(9):1855-1857
The reaction of alkyl trifluoro(organylsulfonylimino)propionates with phosphites occurs with NC transfer of the RSO2 group and leads to sulfonyl-substituted trifluoroalanine derivatives. The novel rearrangement is interpreted as cheletropic 1,4-cycloaddition of the phosphite and subsequent 1,2-shift of the sulfonyl group in the intermediate cyclic phosphorane. 相似文献
995.
Aldehydes undergo smooth conjugate addition to α,β-unsaturated ketones in the presence of 5-(2-hydroxyethyl)-1,3-thiazolium halides and DBU adsorbed onto the surface of basic alumina under microwave irradiation and solvent-free conditions to afford 1,4-diketones in enhanced yields and reduced reaction times compared to conventional methods. 相似文献
996.
Matveeva E. D. Podrugina T. A. Grishin Yu. K. Tkachev V. V. Zhdankin V. V. Aldoshin S. M. Zefirov N. S. 《Russian Journal of Organic Chemistry》2003,39(4):536-541
A mixed phosphonium-iodonium ylide, phenyliodoniumethoxycarbonylmethylenetriphenylphosphorane borofluoride, was synthesized. Its structure was established by means of X-ray diffraction analysis. Temperature dependence of 1H, 13C, and 31P spectra of the ylide synthesized was investigated. A dynamic equilibrium between Z and E-isomers was observed. 相似文献
997.
Curtis T. Mcmullen 《Acta Mathematica》2003,191(2):191-223
998.
A. Henderson 《Mathematische Zeitschrift》2003,243(1):127-143
We prove that the local intersection cohomology of nilpotent orbit closures of cyclic quivers is trivial when the two orbits
involved correspond to partitions with at most two rows. This gives a geometric proof of a result of Graham and Lehrer, which
states that standard modules of the affine Hecke algebra of GLd corresponding to nilpotents with at most two Jordan blocks are multiplicity-free.
Received: 7 February 2002 / Published online: 8 November 2002 相似文献
999.
It is proved that every finite group for which the degrees of its nonmonomial characters are primes is solvable. The proof uses the classification of the finite simple groups. 相似文献
1000.