全文获取类型
收费全文 | 8149篇 |
免费 | 810篇 |
国内免费 | 726篇 |
专业分类
化学 | 1694篇 |
晶体学 | 73篇 |
力学 | 3828篇 |
综合类 | 147篇 |
数学 | 1709篇 |
物理学 | 2234篇 |
出版年
2024年 | 6篇 |
2023年 | 52篇 |
2022年 | 117篇 |
2021年 | 269篇 |
2020年 | 211篇 |
2019年 | 150篇 |
2018年 | 169篇 |
2017年 | 244篇 |
2016年 | 303篇 |
2015年 | 250篇 |
2014年 | 365篇 |
2013年 | 551篇 |
2012年 | 373篇 |
2011年 | 454篇 |
2010年 | 351篇 |
2009年 | 451篇 |
2008年 | 469篇 |
2007年 | 524篇 |
2006年 | 497篇 |
2005年 | 448篇 |
2004年 | 409篇 |
2003年 | 355篇 |
2002年 | 297篇 |
2001年 | 293篇 |
2000年 | 273篇 |
1999年 | 247篇 |
1998年 | 202篇 |
1997年 | 195篇 |
1996年 | 180篇 |
1995年 | 150篇 |
1994年 | 131篇 |
1993年 | 106篇 |
1992年 | 110篇 |
1991年 | 90篇 |
1990年 | 60篇 |
1989年 | 45篇 |
1988年 | 59篇 |
1987年 | 47篇 |
1986年 | 41篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 26篇 |
1981年 | 22篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有9685条查询结果,搜索用时 31 毫秒
101.
The interaction of a screw dislocation with an interfacial edge crack in a two-phase piezoelectric medium is investigated.
Closed-form solutions of the elastic and electrical fields induced by the screw dislocation are derived using the conformal
mapping method in conjunction with the image principle. Based on the electroelastic fields derived, the stress and electric
displacement intensity factors, the image force acting on the dislocation are given explicitly. We find that the stress and
electric displacement intensity factors depend on the effective electroelastic material constants. In the case where one of
two phases is purely elastic, the stress intensity factor and image force are plotted to illustrate the influences of electromechanical
coupling effect, the position of the dislocation and the material properties on the interaction mechanism.
The project supported by the Doctoral Foundation of Hebei Province (B2003113) 相似文献
102.
103.
104.
105.
用 HAAKE RV2 0型流变仪 ,在不同外加电场强度和不同颗粒体积分数下测试了基于沸石和硅油的电流变液的剪切应力变化 .结果表明 :随着外加电场强度升高 ,电流变液的零电场粘度急剧增加 ,电流变液的剪切屈服应力增加 ;随着电流变液中沸石颗粒体积分数升高 ,电流变液的剪切屈服强度急剧上升 .这种变化可以用颗粒间作用力与颗粒间距的关系、单位面积的颗粒链数目变化以及多体作用对电流变液性能的影响来解释 相似文献
106.
纺织结构复合材料力学性能的实验研究 总被引:13,自引:1,他引:13
本文通过实验测定了三维编织结构复合材料侧边未切割、受切割和中央钻孔试件的拉伸性能,对比了受切割和未切割纤维对于试件侧边拉伸应变的影响,并且讨论了拉伸失效的机理和原因.发现受切割和钻孔试件的拉伸性能低于未加工试件的性能,受切割侧边的拉伸应变高于未切割侧边的拉伸应变,三维编织结构复合材料的拉伸失效主要由纤维断裂引起的.文中还对三维编织结构复合材料的孔边应力集中现象进行了研究,并进行了深入分析,得到一个重要结论,即四步法复合材料的孔边应力集中系数比传统层板复合材料和金属材料的低.从这个意义上说,三维编织结构复合材料适合于作为含孔结构的连接件. 相似文献
107.
Residual stress is the stress present in the unloaded equilibrium configuration of a body. Because residual stresses can significantly affect the mechanical behavior of a component, the measurement of these stresses and the prediction of their effect on mechanical behavior are important objectives in many engineering problems. Common methods for the measurement of residual stresses include various destructive experiments in which the body is cut to relieve the residual stress. The resulting strain is measured and used to approximate the original residual stress in the intact body. In order to predict the mechanical behavior of a residually stressed body, a constitutive model is required that includes the influence of the residual stress.In this paper we present a method by which the data obtained from standard destructive experiments can be used to derive constitutive equations that describe the mechanical behavior of elastic residually stressed bodies. The derivation is based on the idea that for each infinitesimal neighborhood in a residually stressed body, there exists a corresponding stress free configuration. We refer to this stress free configuration as the virtual configuration of the infinitesimal neighborhood. The derivation requires that the constitutive equation for the stress free material be known and invertible; it is used to relate the residual stress to the deformation of the virtual configuration into the residually stressed configuration. Although the concept of the virtual configuration is central to the derivation, the geometry of this configuration need not be determined explicitly, and it need not be achievable experimentally, in order to construct the constitutive equation for the residually stressed body.The general mathematical forms of constitutive equations valid for residually stressed elastic materials have been derived previously for a number of cases. These general forms contain numerous unknown material-response functions or material constants that must be determined experimentally. In contrast, the method presented here results in a constitutive equation that is an explicit function of residual stress and includes only the material parameters required to describe the stress free material.After presenting the method for the derivation of constitutive equations, we explore the relationship between destructive experiments and the theory used in the derivation. Specifically, we discuss the use of the theory to improve the design of destructive experiments, and the use of destructive experiments to obtain the data required to construct the constitutive equation for a particular material. 相似文献
108.
The elliptic blending approach is used in order to modify an Explicit Algebraic Reynolds Stress Model so as to reproduce the correct near wall behaviour of the turbulent stresses. The anisotropy stress tensor is expressed as a linear combination of tensor bases whose coefficients are sensitised to the non-local wall-blocking effect through the elliptic blending parameter γ. This parameter is obtained from a separate elliptic equation. The model does not use the distance from the wall thus it can be easily applied to complex geometries. It is validated against detailed DNS data for mean and turbulence quantities for the case of flow and heat transfer between parallel flat plates at three Reynolds numbers as well as against experimental data for the flow in a backward facing step at Re
H = 28,000. The comparison with DNS results or experiments is quite satisfactory and shows the validity of the approach. 相似文献
109.
Studies on Bifurcation and Chaos of a String-Beam Coupled System with Two Degrees-of-Freedom 总被引:1,自引:0,他引:1
In this paper, research on nonlinear dynamic behavior of a string-beam coupled system subjected to parametric and external
excitations is presented. The governing equations of motion are obtained for the nonlinear transverse vibrations of the string-beam
coupled system. The Galerkin's method is employed to simplify the governing equations to a set of ordinary differential equations
with two degrees-of-freedom. The case of 1:2 internal resonance between the modes of the beam and string, principal parametric
resonance for the beam, and primary resonance for the string is considered. The method of multiple scales is utilized to analyze
the nonlinear responses of the string-beam coupled system. Based on the averaged equation obtained here, the techniques of
phase portrait, waveform, and Poincare map are applied to analyze the periodic and chaotic motions. It is found from numerical
simulations that there are obvious jumping phenomena in the resonant response–frequency curves. It is indicated from the phase
portrait and Poincare map that period-4, period-2, and periodic solutions and chaotic motions occur in the transverse nonlinear
vibrations of the string-beam coupled system under certain conditions.
An erratum to this article is available at . 相似文献
110.
L. Nicola K.-S. Kim E. Van der Giessen 《Journal of the mechanics and physics of solids》2007,55(6):1120-1144
The indentation of single crystals by a periodic array of flat rigid contacts is analyzed using discrete dislocation plasticity. Plane strain analyses are carried out with the dislocations all of edge character and modeled as line singularities in a linear elastic solid. The limiting cases of frictionless and perfectly sticking contacts are considered. The effects of contact size, dislocation source density, and dislocation obstacle density and strength on the evolution of the mean indentation pressure are explored, but the main focus is on contrasting the response of crystals having dislocation sources on the surface with that of crystals having dislocation sources in the bulk. When there are only bulk sources, the mean contact pressure for sufficiently large contacts is independent of the friction condition, whereas for sufficiently small contact sizes, there is a significant dependence on the friction condition. When there are only surface dislocation sources the mean contact pressure increases much more rapidly with indentation depth than when bulk sources are present and the mean contact pressure is very sensitive to the strength of the obstacles to dislocation glide. Also, on unloading a layer of tensile residual stress develops when surface dislocation sources dominate. 相似文献