全文获取类型
收费全文 | 1656篇 |
免费 | 41篇 |
国内免费 | 12篇 |
专业分类
化学 | 980篇 |
晶体学 | 6篇 |
力学 | 43篇 |
数学 | 280篇 |
物理学 | 400篇 |
出版年
2022年 | 16篇 |
2021年 | 13篇 |
2020年 | 30篇 |
2019年 | 30篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 28篇 |
2015年 | 29篇 |
2014年 | 33篇 |
2013年 | 71篇 |
2012年 | 61篇 |
2011年 | 79篇 |
2010年 | 52篇 |
2009年 | 46篇 |
2008年 | 73篇 |
2007年 | 74篇 |
2006年 | 73篇 |
2005年 | 80篇 |
2004年 | 65篇 |
2003年 | 66篇 |
2002年 | 42篇 |
2001年 | 22篇 |
2000年 | 18篇 |
1999年 | 23篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1985年 | 30篇 |
1984年 | 21篇 |
1983年 | 20篇 |
1982年 | 36篇 |
1981年 | 35篇 |
1980年 | 23篇 |
1979年 | 11篇 |
1978年 | 19篇 |
1977年 | 9篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1974年 | 15篇 |
1973年 | 14篇 |
1972年 | 10篇 |
1971年 | 9篇 |
1965年 | 9篇 |
排序方式: 共有1709条查询结果,搜索用时 46 毫秒
81.
82.
Anna Doppler Leo D.M. Nicholls Christopher Golz Manuel Alcarazo Michael John 《Magnetic resonance in chemistry : MRC》2019,57(11):961-967
Two functionalized [6]carbohelicenes, one of which was also available in its two enantiomeric pure forms, were oriented in stretched polystyrene in CDCl3, and in a recently introduced chiral thermoresponsive lyotropic polyaspartate (poly(benzyl)0.5(phenethyl)0.5-L-aspartate) in C2D2Cl4. From the resulting 1H,13C residual dipolar couplings, the helical pitch of a methylated [6]carbohelicene was determined and found to be in agreement with theoretical predictions and existing crystal structures (d(C2,C2′) ≈ 4.3 Å). For a second [6]carbohelicene with para-methoxyphenyl substituents, a clear conformational preference of the substituents was observed. The orientational properties of the two helicene enantiomers in the chiral polyaspartate are very similar, but both drastically change around 306 K. We suggest this behavior is due to an unusual phase transition in the liquid crystal. 相似文献
83.
Pierre Bonami Leo Liberti Andrew J. Miller Annick Sartenaer 《Mathematical Programming》2012,136(2):229-231
84.
In this work crack formation and development is addressed and implemented in a planar layered reinforced-concrete beam element. The crack initiation and growth is described using the strength criterion in conjunction with exact kinematics of the interlayer connection. In this way a novel embedded-discontinuity beam finite element is derived in which the tensile stresses in concrete at the crack position reaching the tensile strength will trigger a crack to open. Since the element is multi-layered, in this way the crack is allowed to propagate through the depth of the beam. The cracked layer(s) will involve discontinuity in the cross-sectional rotation equal to the crack-profile angle, as well as a discontinuity in the position vector of the layer’s reference line. A bond–slip relationship is superimposed onto this model in a kinematically consistent manner with reinforcement being treated as an additional layer of zero thickness with its own material parameters and a constitutive law implemented in the multi-layered beam element. 相似文献
85.
86.
Leo Iu Jos A. Fuentes Mesfin E. Janka Kevin J. Fontenot Matthew L. Clarke 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(7):2142-2146
The hydroformylation of propene to give predominantly iso‐butanal has been achieved; class‐leading selectivity is possible even at higher temperatures that deliver fast conversion. Racemic rhodium complexes of bidentate phospholane phosphites derived from tropos‐biphenols and unusual solvent systems are the key to the selectivity observed. 相似文献
87.
88.
Jinsong Zhang Chris Taylor Erich Bowman Leo Savage-Low Michael W. Lodewyk Larry Hanne Guang Wu 《Tetrahedron letters》2013
A process for synthesizing 1,4-benzodioxin, through oxidation of a phenol to an o-quinone followed by treatment with an enamine, has been developed. Adduct stereochemistry is found to be retained via this one-pot reaction. The method uses hypervalent iodine reagent under mild conditions and is compatible with a wide scope of phenols and enamines. 相似文献
89.
90.
Argus Adrian Dunca Kara E. Kohler Monika Neda Leo G. Rebholz 《Mathematical Methods in the Applied Sciences》2012,35(10):1205-1219
This work presents a rigorous analysis of mathematical and physical properties for solutions of multiscale deconvolution turbulence models. We show that solutions of these models exactly conserve model quantities for the integral invariants of fundamental physical importance: kinetic energy, helicity, and (in two dimensions) enstrophy. The kinetic energy conservation is the key that allows us to next apply the phenomenology of homogeneous, isotropic turbulence to establish the existence of a model energy cascade and, in particular, that the cascade exhibits enhanced energy dissipation in a secondary accelerated cascade, which ends at the model's microscale (which we establish is larger than the Kolmogorov microscale). We also prove that the model dissipates energy at the same rate as true turbulent flow, ~ O(U3 ∕ L), independent of Reynolds number. Lastly, we prove the existence of global attractors for the model solutions; the proof of which also shows that solutions are actually one degree of regularity higher than previously known. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献