全文获取类型
收费全文 | 3817篇 |
免费 | 118篇 |
国内免费 | 20篇 |
专业分类
化学 | 2701篇 |
晶体学 | 79篇 |
力学 | 109篇 |
数学 | 297篇 |
物理学 | 769篇 |
出版年
2023年 | 33篇 |
2022年 | 85篇 |
2021年 | 90篇 |
2020年 | 95篇 |
2019年 | 97篇 |
2018年 | 76篇 |
2017年 | 73篇 |
2016年 | 138篇 |
2015年 | 113篇 |
2014年 | 184篇 |
2013年 | 310篇 |
2012年 | 244篇 |
2011年 | 301篇 |
2010年 | 157篇 |
2009年 | 134篇 |
2008年 | 226篇 |
2007年 | 243篇 |
2006年 | 161篇 |
2005年 | 158篇 |
2004年 | 110篇 |
2003年 | 81篇 |
2002年 | 76篇 |
2001年 | 39篇 |
2000年 | 33篇 |
1999年 | 19篇 |
1998年 | 32篇 |
1997年 | 23篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 19篇 |
1985年 | 29篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 22篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 27篇 |
1977年 | 16篇 |
1976年 | 23篇 |
1974年 | 16篇 |
1973年 | 13篇 |
排序方式: 共有3955条查询结果,搜索用时 0 毫秒
61.
Wieslaw Kubiak Suresh Sethi Chelliah Sriskandarajah 《Annals of Operations Research》1995,57(1):203-216
We study the problem of minimizing makespan in a two-machine job shop with unit processing time operations. An efficient algorithm with respect to a succinct encoding of the problem instances is proposed. The algorithm is an improvement of earlier algorithms proposed for the problem by Brucker [1,2], Hefetz and Adiri [7], and Timkovskiy [15]. The idea behind the algorithm has the potential of extension to job shops with parallel machines.This research is supported in part by NSERC Grants A4619, OGP0105675, OGP0104900, General Motors of Canada, and the Manufacturing Research Corporation of Ontario. 相似文献
62.
Yu. V. Knyazev A. V. Lukoyanov Yu. I. Kuz’min A. Haldar K. G. Suresh 《Optics and Spectroscopy》2014,117(3):414-418
Optical properties of two intermetallic compounds TbNi4Fe and TbNi4Co have been studied employing ellipsometry in a spectral range 0.22–15 μm to reveal their characteristic features in comparison with the parent compound TbNi5. The electronic structure of TbNi4Fe and TbNi4Co was calculated within the LSDA + U method (local spin density approximation with Hubbard U-correction). Based on the calculated electronic structure results, the theoretical optical conductivity was calculated and used to interpret experimental conductivity in the range of interband optical absorption. 相似文献
63.
64.
We propose a new method viz., using stochastic partial differential equations to study the pathwise uniqueness of stochastic (ordinary) differential equations. We prove the existence and pathwise uniqueness of a class of stochastic differential equations with coefficients in suitable Hermite-Sobolev class using our approach. 相似文献
65.
U. Dadwal R. Scholz M. Reiche P. Kumar S. Chandra R. Singh 《Applied Physics A: Materials Science & Processing》2013,112(2):451-456
GaN epitaxial layers were implanted by 100 keV H+ ions at different implantation temperatures (LN2, RT and 300 °C) with a fluence of 2.5×1017 cm?2. The implanted samples were characterized using Nomarski optical microscopy, AFM, XRD, and TEM. Topographical investigations of the implanted surface revealed the formation of surface blistering in the as-implanted samples at 300 °C and after annealing at higher temperature for the implantation at LN2 and RT. The physical dimensions of the surface blisters/craters were dependent on the implantation temperature. XRD showed the dependence of damage-induced stress on the implantation temperature with higher stress for the implantation at 300 °C. TEM investigations revealed the formation of a damage band in all the cases. The damage band was filled with large area microcracks for the implantation at 300 °C, which were responsible for the as-implanted surface blistering. 相似文献
66.
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
67.
Focusing properties of the radially polarized axisymmetric Bessel-modulated Gaussian beam with quadratic radial dependence (QBG beam) and annular aperture are investigated theoretically by vector diffraction theory. Simulation results show that the intensity distribution in the focal region of the radially polarized axisymmetric QBG beam can be adjusted considerably by small beam parameter (μ) and annular aperture (δ). When μ increases, the focal spot may change to focal hole and changes focal pattern remarkably. On introducing annular aperture, focus can split or extends along the optical axis for different μ. In this paper, we have shown the generation of the focal spot, dark focal spot, focal split and increase in focal depth in the axial direction of the incident beam propagating through the aligned optical system. 相似文献
68.
l-Valinium oxalate (LVO) single crystal has been grown by solution growth technique at room temperature. The crystal structure and lattice parameters were determined for the grown crystal by single crystal X-ray diffraction studies. Optical constants like band gap, refractive index, reflectance, extinction coefficient and electric susceptibility were determined from UV–vis–NIR spectrum. The microhardness studies reveal the mechanical strength of the grown crystal. The dielectric constant, dielectric loss and AC conductivity of the compound were calculated at different temperatures and frequencies to analyze the electrical properties. Nonlinear optical property was discussed to confirm the SHG efficiency of the grown crystal. 相似文献
69.
Arun Aravind K. Hasna M. K. Jayaraj Mukesh Kumar Ramesh Chandra 《Applied Physics A: Materials Science & Processing》2014,115(3):843-849
Phase pure Zn1?x Co x O thin films grown by pulsed laser deposition have transmittance greater than 75 % in the visible region. Raman studies confirm the crystalline nature of Zn1?x Co x O thin films. Zn0.95Co0.05O thin films show room temperature ferromagnetism with saturation magnetization of 0.4μ B /Co atom. The possible origin of paramagnetism at higher Co doping concentrations can be attributed to the increased nearest-neighbor antiferromagnetic interactions between Co2+ ions in ZnO matrix. XPS confirms the substitution of Co2+ ions into the ZnO host lattice. 相似文献
70.
A study of damping in fiber-reinforced composites 总被引:1,自引:0,他引:1
Damping contributions from the viscoelastic matrix, interphase and the dissipation resulting from damage sites are considered to evaluate composite material damping coefficients in various loading modes. The paper presents the results of the FEM/Strain energy investigations carried out to predict anisotropic-damping matrix comprising of loss factors η11, η22, η12 and η23 considering the dissipation of energy due to fiber and matrix (two phase) and correlate the same with various micromechanical theories. Damping in three phase (i.e., fiber-interphase-matrix) composite is also calculated as an attempt to understand the effect of interphase. The contribution of energy dissipation due to sliding at the fiber-matrix interface is incorporated to evaluate its effect on η11, η22, η12 and η23 in fiber-reinforced composite having damage in the form of hairline debonding. Comparative studies of the various micromechanical theories/models with FEM/Strain energy method for the prediction of damping coefficients have shown consistency when both the effect of variable nature of stress and the fiber interaction is considered. Parametric damping studies for three phase composite have shown that the change in properties of fiber, matrix and interphase leads to a change in the magnitude of effectiveness of interphase, but the manner in which the interphase would affect the various loss factors depends predominately upon whether the hard or soft interphase is chosen. Analysis of the effect of damage on composite damping indicates that it is sensitive to its orientation and type of loading. 相似文献