全文获取类型
收费全文 | 366466篇 |
免费 | 4699篇 |
国内免费 | 962篇 |
专业分类
化学 | 188468篇 |
晶体学 | 5676篇 |
力学 | 16251篇 |
综合类 | 7篇 |
数学 | 44674篇 |
物理学 | 117051篇 |
出版年
2021年 | 3549篇 |
2020年 | 3906篇 |
2019年 | 4330篇 |
2018年 | 5999篇 |
2017年 | 6169篇 |
2016年 | 8725篇 |
2015年 | 5328篇 |
2014年 | 8218篇 |
2013年 | 18335篇 |
2012年 | 14719篇 |
2011年 | 17412篇 |
2010年 | 12551篇 |
2009年 | 12198篇 |
2008年 | 15344篇 |
2007年 | 15179篇 |
2006年 | 13931篇 |
2005年 | 12071篇 |
2004年 | 11100篇 |
2003年 | 9697篇 |
2002年 | 9606篇 |
2001年 | 11054篇 |
2000年 | 8301篇 |
1999年 | 6463篇 |
1998年 | 5353篇 |
1997年 | 5132篇 |
1996年 | 4913篇 |
1995年 | 4203篇 |
1994年 | 4145篇 |
1993年 | 4053篇 |
1992年 | 4427篇 |
1991年 | 4536篇 |
1990年 | 4327篇 |
1989年 | 4199篇 |
1988年 | 3971篇 |
1987年 | 4108篇 |
1986年 | 3850篇 |
1985年 | 4902篇 |
1984年 | 4930篇 |
1983年 | 4080篇 |
1982年 | 4182篇 |
1981年 | 3889篇 |
1980年 | 3815篇 |
1979年 | 4091篇 |
1978年 | 4088篇 |
1977年 | 4068篇 |
1976年 | 4089篇 |
1975年 | 3860篇 |
1974年 | 3782篇 |
1973年 | 3811篇 |
1972年 | 2724篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Highly Selective Copper‐Catalyzed Asymmetric [3+2] Cycloaddition of Azomethine Ylides with Acyclic 1,3‐Dienes 下载免费PDF全文
María González‐Esguevillas Ana Pascual‐Escudero Dr. Javier Adrio Prof. Dr. Juan C. Carretero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4561-4565
The first examples of the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides with acyclic activated 1,3‐dienes (and 1,3‐enynes) are described. Under copper catalysis, a selective cycloaddition at the terminal γ,δ‐C?C bond is observed. In addition, depending on the ligand used, either the exo or the endo adduct can be obtained with high selectivity. Under appropriate reaction conditions, the acyclic 1,6‐addition product is detected, suggesting a stepwise mechanism. The resulting C4‐alkenyl‐substituted pyrrolidines are suitable substrates for further access to polycyclic systems, as highlighted by the preparation of hexahydrochromeno[4,3‐b]pyrrole and the tetracyclic core of the alkaloid gracilamine. 相似文献
73.
74.
75.
76.
Paul S. Wesson 《General Relativity and Gravitation》2003,35(1):111-119
Results from 5D induced-matter and membrane theory with null paths are extended to show that a particle obeys the 4D Klein-Gordon equation but with a variable mass. The Dirac equation also follows, but raises concerns about 4D quantization in the two natural 5D gauges, and reopens the question of a Regge-like trajectory for the spin angular momenta and squared masses of gravitationally-dominated systems. 相似文献
77.
The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron... 相似文献
78.
A. Foussats C. Repetto O. P. Zandron O. S. Zandron 《International Journal of Theoretical Physics》2002,41(6):1053-1082
In order to describe the dynamics of the t–J model, two different families of first-order Lagrangians in terms of the generators of the Hubbard algebra are found. Such families correspond to different dynamical second-class constrained systems. The quantization is carried out by using the path-integral formalism. In this context the introduction of proper ghost fields is needed to render the model renormalizable. In each case the standard Feynman diagrammatics is obtained and the renormalized physical quantities are computed and analyzed. In the first case a nonperturbative large-N expansion is considered with the purpose of studying the generalized Hubbard model describing N-fold-degenerate correlated bands. In this case the 1/N correction to the renormalized boson propagator is computed. In the second case the perturbative Lagrangian formalism is developed and it is shown how propagators and vertices can be renormalized to each order. In particular, the renormalized ferromagnetic magnon propagator coming from our formalism is studied in details. As an example the thermal softening of the magnon frequency is computed. The antiferromagnetic case is also analyzed, and the results are confronted with previous one obtained by means of the spin-polaron theories. 相似文献
79.
D. J. Plazek C. A. Bero S. Neumeister G. Floudas G. Fytas K. L. Ngai 《Colloid and polymer science》1994,272(11):1430-1438
By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT
g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems 相似文献
80.
Experimental data on the effect of thallium and sodium impurities on the lattice heat conductivity of PbTe at room temperature
are reported. Because the lattice of lead chalcogenides is strongly polarized near charged impurities, the effect of impurities
on the lattice heat conductivity depends substantially on their charge state. This property of the material has been used
to determine the charge state of the thallium impurity in PbTe. The results obtained argue for a model of quasi-local thallium-impurity
states which assumes low electron-correlation energy at an impurity center.
Fiz. Tverd. Tela (St. Petersburg) 40, 1206–1208 (July 1998) 相似文献