全文获取类型
收费全文 | 5979篇 |
免费 | 525篇 |
国内免费 | 320篇 |
专业分类
化学 | 311篇 |
晶体学 | 36篇 |
力学 | 2003篇 |
综合类 | 34篇 |
数学 | 572篇 |
物理学 | 1247篇 |
综合类 | 2621篇 |
出版年
2024年 | 23篇 |
2023年 | 43篇 |
2022年 | 77篇 |
2021年 | 90篇 |
2020年 | 135篇 |
2019年 | 103篇 |
2018年 | 117篇 |
2017年 | 155篇 |
2016年 | 196篇 |
2015年 | 165篇 |
2014年 | 249篇 |
2013年 | 394篇 |
2012年 | 286篇 |
2011年 | 278篇 |
2010年 | 209篇 |
2009年 | 294篇 |
2008年 | 305篇 |
2007年 | 353篇 |
2006年 | 358篇 |
2005年 | 321篇 |
2004年 | 275篇 |
2003年 | 259篇 |
2002年 | 215篇 |
2001年 | 213篇 |
2000年 | 203篇 |
1999年 | 209篇 |
1998年 | 145篇 |
1997年 | 150篇 |
1996年 | 145篇 |
1995年 | 132篇 |
1994年 | 94篇 |
1993年 | 88篇 |
1992年 | 91篇 |
1991年 | 101篇 |
1990年 | 72篇 |
1989年 | 55篇 |
1988年 | 67篇 |
1987年 | 40篇 |
1986年 | 42篇 |
1985年 | 23篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1957年 | 3篇 |
1955年 | 1篇 |
排序方式: 共有6824条查询结果,搜索用时 8 毫秒
111.
基于频域复坐标拉伸,给出一种解时谐弹性波散射问题的单轴优化完美匹配层(PML)方法.该方法通过在吸收函数中引入一个小参数ε_0,使散射问题优化PML方法的计算不再依赖PML层的厚度.结果表明,当参数ε_0充分小时,优化的PML解指数收敛于原弹性波散射问题的解. 相似文献
112.
The phonon dispersion curves, phonon frequency distribution function as well as the lattice specific heat of body-centred
tetragonal indium have been deduced using a lattice dynamical model which includes central, angular and volume forces. Six
elastic constants, four zone boundary frequencies and an equilibrium condition were used in the evaluation of the force constants.
It is shown that this model is elastically consistent and satisfies the symmetry requirements of the lattice, the phonon frequencies
of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical
values of Garrett and Swihart, and theθ
D values compare well with the experimental values over a wide temperature range. The apparent discrepancies in the phonon
dispersion curves and theθ
D-T curves obtained from deficient models, importance of umklapp processes and the significance of angular forces in the lattice
dynamical models are discussed. 相似文献
113.
1 INTRODUCTIONBecausesomeimportant propertiesofcrystal(suchasspecificheatathightemperature ,melting ,thermalexpansion ,temperaturede 相似文献
114.
115.
H.M. Ledbetter 《Ultrasonics》1985,23(1):9-13
For studying welds ultrasonically, the importance of knowing the material's single-crystal elastic constants, the Cijs, is explained. Where these constants are not known, some guidelines are given for estimating them from polycrystalline elastic constants such as Young's modulus and the shear modulus.The important case of [001] fibre texture is considered. Being transversely isotropic, this case exhibits five macroscopic elastic constants, which are related to the three cubic elastic constants: C11, C12, C44. From these five constants the angular variations of Young's modulus, the torsional modulus, and the sound velocities can be computed. For the same [001] fibre texture, results are given for a standard well-characterized material — copper, where the Cijs are well known. 相似文献
116.
Influence of power-law index on transitional Reynolds numbers for flow over a semi-circular cylinder
In this work, the governing partial differential equations (continuity and Cauchy’s momentum equations) describing the flow of power-law type non-Newtonian fluids across a semi-circular cylinder (oriented with its curved surface in the upstream direction) have been solved numerically. In particular, consideration has been given to the delineation of the critical Reynolds numbers denoting the onset of flow separation from the surface of the cylinder and the onset of the laminar vortex shedding regime. This information is germane to establish the scaling of the macroscopic characteristics like drag coefficient and Strouhal number on the governing parameters, namely, Reynolds number and power-law index. The present results clearly suggest that the transitional Reynolds numbers show a strong dependence on the type (shear-thinning and shear-thickening) of fluid behavior as well as on the severity of the shear-dependence of the viscosity. With reference to the behavior seen in Newtonian fluids, the flow remains not only attached to the surface up to higher Reynolds numbers, but shear-thinning behavior also delays the onset of the laminar vortex shedding regime. As expected, shear-thickening fluids, of course, display the opposite characteristics. 相似文献
117.
Fen Luo Zhi-Cheng Guo Xiu-Lu Zhang Chang-Ying Yuan Cheng-An Liu Ling-Cang Cai 《Molecular physics》2013,111(12):1501-1507
The study aims at the elastic, mechanical, electronic properties and hardness of Nb2AsC using first principles based on the density functional theory method within the generalised gradient approximation. The calculated lattice parameters of Nb2AsC are in good agreement with the experimental data. The five independent elastic constants are firstly calculated as a function of pressure, and our results indicate that it is mechanically stable in the applied pressure. The elastic anisotropy is examined through the computation of the direction dependence of Young's modulus. The pressure dependences of the bulk modulus, shear modulus, average velocity of acoustic waves and Debye temperature of Nb2AsC are systematically investigated. The band structure and density of states are discussed, and the results show that the strong hybridisations C p–Nb d and As p–Nb d would be beneficial to the structure stability of Nb2AsC. Based on the Mulliken population analysis, the hardness of Nb2AsC is predicted. 相似文献
118.
AbstractThe pressure dependence of the structural, elastic, electronic and thermal properties of Kondo insulator SmB6 have been systematically studied by density functional theory combined with the quasi-harmonic Debye model. The calculated structure at zero pressure is in good agreement with the available experimental results at low temperature. The obtained elastic constants, bulk modulus and shear modulus indicate that SmB6 is mechanically stable and behaves in a brittle manner under the applied pressure 0–20 GPa, consistent with available experimental data. In addition, the elastic-relevant properties, Young’s modulus and the Poisson ratio manifest that increasing pressure results in an enhancement in the stiffness of the compound. It is found that unlike temperature, pressure has little effect on the heat capacity of SmB6. What more important is that we observed an insulator to metal phase transition at about 5.5 GPa through the disappearance of the band gap, well consistent with the experimental data. This transition has little effect on the physical properties of SmB6. 相似文献
119.
An analogue simulation study for the stability investigations of nonlinear parametrically excited structural systems, exhibiting hard and soft spring characteristics is undertaken as a feasible alternative to current asymptotic and other analytic methods. It is shown that this technique locates the position of an unstable limit cycle, identifying the point of change of equilibrium states, which is ordinarily obscured in using the other existing schemes. 相似文献
120.
Liliana GRATIE 《数学年刊B辑(英文版)》2000,21(2):147-152
gi.TheTOpologicalDegreeforGeneralizedMonotoneOperatorsMonotoneoperatortheoryisoftenanefficienttoolforprovingtheexistenceofsolutionstononlinearProblems.Inparticular,thepseudo-monotoneoperatorsintroducedbyBrezis[2]areveryusefulforstudyingnonlinearellipticproblems.Weconsiderherethefollowingclassesofmappingsofgeneralizedmonotonetype.(QM)=theclassofquasi-mollotoneoperators,(S )=theclassofoperatorsoftype(S ),(PM)=theclassofpseudthmonotoneoperators,(LS)=theclassofLeray-Schauderoperators(compac… 相似文献