全文获取类型
收费全文 | 1900篇 |
免费 | 192篇 |
国内免费 | 243篇 |
专业分类
化学 | 412篇 |
晶体学 | 14篇 |
力学 | 224篇 |
综合类 | 37篇 |
数学 | 658篇 |
物理学 | 990篇 |
出版年
2024年 | 4篇 |
2023年 | 8篇 |
2022年 | 22篇 |
2021年 | 26篇 |
2020年 | 38篇 |
2019年 | 49篇 |
2018年 | 47篇 |
2017年 | 53篇 |
2016年 | 46篇 |
2015年 | 47篇 |
2014年 | 78篇 |
2013年 | 152篇 |
2012年 | 103篇 |
2011年 | 131篇 |
2010年 | 128篇 |
2009年 | 106篇 |
2008年 | 121篇 |
2007年 | 126篇 |
2006年 | 135篇 |
2005年 | 130篇 |
2004年 | 104篇 |
2003年 | 81篇 |
2002年 | 83篇 |
2001年 | 72篇 |
2000年 | 68篇 |
1999年 | 58篇 |
1998年 | 55篇 |
1997年 | 29篇 |
1996年 | 36篇 |
1995年 | 37篇 |
1994年 | 21篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有2335条查询结果,搜索用时 93 毫秒
991.
First principles calculations have been performed to study the electronic and magnetic structures of double perovskites Ca2MWO6 (M=Co, Ni) using full potential linearized augmented plane wave method. The density of states and spin magnetic moments are calculated and we have examined the valence states of Co, Ni and W ions. The results predict the half-metallic ground state of Ca2CoWO6 and the insulating nature of Ca2NiWO6. 相似文献
992.
M. Bezi Javan N. TajaborM. Rezaee-Roknabadi M. Behdani 《Applied Surface Science》2011,257(17):7586-7591
Structural, electronic and magnetic properties of the small Con clusters (n = 2-7) endohedrally doped in C60 (Ih) and C82 (C2v) fullerenes were investigated using ab initio calculations based on the density functional theory. It is found that the encapsulated Con clusters inside C60 and C82 cages are energetically favorable except for Co7@C60. The encapsulation does not change significantly the structure of the enclosed clusters, but the magnetic moment of the clusters reduces due to a stronger Co-C hybridization for the larger clusters. 相似文献
993.
994.
ZHOU LiXing 《中国科学:物理学 力学 天文学(英文版)》2011,(6)
Turbulent dispersed multiphase flows,including gas-particle,gas-droplet and bubble-liquid flows,are widely encountered in various engineering facilities.Modeling of two-phase turbulence,in particular the dispersed phase turbulence,is the key problem in the Eulerian-Eulerian simulation of practical dispersed multiphase flows.Although different models were developed and used,the experimental validation shows that they cannot always give satisfactory prediction results.In this paper the present author give a d... 相似文献
995.
Peifeng Su Wei Wu Prof. Sason Shaik Prof. Philippe C. Hiberty Prof. 《Chemphyschem》2008,9(10):1442-1452
The electronic structures of the three lowest‐lying states of NF are investigated by means of modern valence bond (VB) methods such as the VB self‐consistent field (VBSCF), breathing orbital VB (BOVB), and VB configuration interaction (VBCI) methods. The wave functions for the three states are expressed in terms of 9–12 VB structures, which can be further condensed into three or four classical Lewis structures, whose weights are quantitatively estimated. Despite the compactness of the wave functions, the BOVB and VBCI methods reproduce the spectroscopic properties and dipole moments of the three states well, in good agreement with previous computational studies and experimental values. By analogy to the isoelectronic O2 molecule, the ground state 3Σ? possesses both a σ bond and 3‐electron π bonds. However, here the polar σ bond contributes the most to the overall bonding. It is augmented by a fractional (19 %) contribution of three‐electron π bonding that arises from π charge transfer from fluorine to nitrogen. In the singlet 1Δ and 1Σ+ excited states the π‐bonding component is classically covalent, and it contributes 28 % and 37 % to the overall bonding picture for the two states, respectively. The resonance energies are calculated and reveal that π bonding contributes at least 24, 35 and 42 kcal mol?1 to the total bonding energies of the 3Σ?, 1Δ and 1Σ+ states, respectively. Some unusual properties of the NF molecule, like the equilibrium distance shortening and bonding energy increasing upon excitation, the counterintuitive values of the dipole moments and the reversal of the dipole moments as the bond is stretched, are interpreted in the light of the simple valence bond picture. The overall polarity of the molecule is very small in the ground state, and is opposite to the relative electronegativity of N vs F in the singlet excited states. The values of the dipole moments in the three states are quantitatively accounted for by the calculated weights of the VB structures. 相似文献
996.
G. V. Loukova A. A. Milov V. P. Vasiliev V. A. Smirnov 《Russian Chemical Bulletin》2008,57(6):1166-1171
Electric dipole moments of a highly emissive metallocene precatalyst, namely, the ZrIV π-complex in the ground and triplet states, were estimated by the method of spectral shifts and quantum chemical DFT calculations.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1145–1150, June, 2008. 相似文献
997.
998.
We establish the moment estimates for a class of global weak solutions to the Navier–Stokes equations in the half‐space. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
999.
Samuel P. Schofield Mark A. Christon Vadim Dyadechko Rao V. Garimella Robert B. Lowrie Blair K. Swartz 《国际流体数值方法杂志》2010,63(8):931-952
This paper compares the numerical performance of the moment‐of‐fluid (MOF) interface reconstruction technique with Youngs, LVIRA, power diagram (PD), and Swartz interface reconstruction techniques in the context of a volume‐of‐fluid (VOF) based finite element projection method for the numerical simulation of variable‐density incompressible viscous flows. In pure advection tests with multiple materials MOF shows dramatic improvements in accuracy compared with the other methods. In incompressible flows where density differences determine the flow evolution, all the methods perform similarly for two material flows on structured grids. On unstructured grids, the second‐order MOF, LVIRA, and Swartz methods perform similarly and show improvement over the first‐order Youngs' and PD methods. For flow simulations with more than two materials, MOF shows increased accuracy in interface positions on coarse meshes. In most cases, the convergence and accuracy of the computed flow solution was not strongly affected by interface reconstruction method. Published in 2009 by John Wiley & Sons, Ltd. 相似文献
1000.
James Cederberg J. Randolph B. McDonald B. Paulson C. McEachern 《Journal of Molecular Spectroscopy》2008,250(2):114-116
The molecular beam electric resonance technique has been used to conduct a high precision examination of the hyperfine spectra of 39K79Br, 39K81Br and 39K127I. Coupling constants for the nuclear electric quadrupole interactions, the spin–rotation interactions, the tensor and scalar spin–spin interactions, as well as the electric dipole moment of KI, and their dependence on vibrational and rotational state have been determined. A few transitions observed for 41K127I show a small shift in the iodine nuclear electric quadrupole interaction, and the fit improves somewhat with the inclusion of an iodine nuclear electric hexadecapole interaction term. 相似文献