全文获取类型
收费全文 | 7469篇 |
免费 | 1046篇 |
国内免费 | 2106篇 |
专业分类
化学 | 4677篇 |
晶体学 | 284篇 |
力学 | 2143篇 |
综合类 | 58篇 |
数学 | 434篇 |
物理学 | 3025篇 |
出版年
2024年 | 28篇 |
2023年 | 124篇 |
2022年 | 298篇 |
2021年 | 337篇 |
2020年 | 311篇 |
2019年 | 226篇 |
2018年 | 176篇 |
2017年 | 311篇 |
2016年 | 384篇 |
2015年 | 308篇 |
2014年 | 429篇 |
2013年 | 552篇 |
2012年 | 516篇 |
2011年 | 553篇 |
2010年 | 506篇 |
2009年 | 556篇 |
2008年 | 553篇 |
2007年 | 614篇 |
2006年 | 485篇 |
2005年 | 472篇 |
2004年 | 469篇 |
2003年 | 418篇 |
2002年 | 317篇 |
2001年 | 254篇 |
2000年 | 230篇 |
1999年 | 187篇 |
1998年 | 171篇 |
1997年 | 142篇 |
1996年 | 130篇 |
1995年 | 95篇 |
1994年 | 93篇 |
1993年 | 52篇 |
1992年 | 71篇 |
1991年 | 45篇 |
1990年 | 37篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 27篇 |
1986年 | 30篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 12篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
The Wiener-Hopf method is used to find a solution to a symmetric problem that gives a criterion for the onset of growth of
long shear cracks emanating from a corner point on the boundary of a hole and filled with a plastic material
__________
Translated from Prikladnaya Mekhanika, Vol. 42, No. 4, pp. 83–90, April 2006. 相似文献
972.
This paper is concerned with the theoretical treatment of the transient piezothermoelastic problem involving a thick functionally graded thermopiezoelectric strip due to nonuniform heat supply in the width direction. The thermal, thermoelastic and piezoelectric constants of the strip are assumed to vary exponentially in the thickness direction. The transient two-dimensional temperature is analyzed by the methods of Laplace and finite sine transformations. We obtain the exact solution for a simply supported strip under the state of plane strain. Some numerical results for the temperature change, the displacement, the stress and electric potential distributions are presented in figures and table. Furthermore, the influence of the nonhomogeneity of the material and that of the electric boundary conditions are investigated. 相似文献
973.
974.
G. PuglisiL. Truskinovsky 《Journal of the mechanics and physics of solids》2002,50(2):165-187
The nontrivial behavior of an elastic chain with identical bi-stable elements may be considered prototypical for a large number of nonlinear processes in solids ranging from phase transitions to fracture. The energy landscape of such a chain is extremely wiggly which gives rise to multiple equilibrium configurations and results in a hysteretic evolution and a possibility of trapping. In the present paper, which extends our previous study of the static equilibria in this system (Puglisi and Truskinovsky, J. Mech. Phys. Solids (2000) 1), we analyze the behavior of a bi-stable chain in a soft device under quasi-static loading. We assume that the system is over-damped and explore the variety of available nonequilibrium transformation paths. In particular, we show that the “minimal barrier” strategy leads to the localization of the transformation in a single spring. Loaded periodically, our bi-stable chain exhibits finite hysteresis which depends on the height of the admissible barrier; the cold work/heat ratio in this model is a fixed constant, proportional to the Maxwell stress. Comparison of the computed inner and outer hysteresis loops with recent experiments on shape memory wires demonstrates good qualitative agreement. Finally we discuss a relation between the present model and the Preisach model which is a formal interpolation scheme for hysteresis, also founded on the idea of bi-stability. 相似文献
975.
Most cellular solids are random materials, while practically all theoretical structure-property relations are for periodic models. To generate theoretical results for random models the finite element method (FEM) was used to study the elastic properties of open-cell solids. We have computed the density (ρ) and microstructure dependence of the Young's modulus (E) and Poisson's ratio (ν) for four different isotropic random models. The models were based on Voronoi tessellations, level-cut Gaussian random fields, and nearest neighbour node-bond rules. These models were chosen to broadly represent the structure of foamed solids and other (non-foamed) cellular materials. At low densities, the Young's modulus can be described by the relation E∝ρn. The exponent n and constant of proportionality depend on microstructure. We find 1.3<n<3, indicating a more complex dependence than indicated by periodic cell theories, which predict n=1 or 2. The observed variance in the exponent was found to be consistent with experimental data. At low densities we found that ν≈0.25 for three of the four models studied. In contrast, the Voronoi tessellation, which is a common model of foams, became approximately incompressible (ν≈0.5). This behaviour is not commonly observed experimentally. Our studies showed the result was robust to polydispersity and that a relatively large number (15%) of the bonds must be broken to significantly reduce the low-density Poission's ratio to ν≈0.33. 相似文献
976.
Intersonic crack propagation in homogeneous media under shear-dominated loading: theoretical analysis 总被引:1,自引:0,他引:1
Dhirendra V. Kubair Philippe H. Geubelle Yonggang Y. Huang 《Journal of the mechanics and physics of solids》2002,50(8):1547-1564
The mechanics of cohesive failure under mixed-mode loading is investigated for the case of a steadily propagating subsonic and intersonic dynamic crack subjected to a follower tensile and shear distributed load. The cohesive failure model chosen in this study is rate independent but accounts for the coupling between normal and tangential damage. Special emphasis is placed here on mixed-mode cases with predominantly shear loading. The analysis shows that the size of the mixed-mode cohesive zone is smaller than that obtained in the pure shear case. The relative extent of the shear and tensile cohesive damage zones depends on the crack speed and the mode mixity. In the intersonic regime, the failure process takes place exclusively in shear, even under remote mixed-mode loading conditions. 相似文献
977.
Micromechanics of cleavage fracture initiation in ferritic steels by carbide cracking 总被引:1,自引:0,他引:1
Cleavage fracture in ferritic steels is often initiated in brittle carbides randomly distributed in the material. The carbides break as a result of a fibre loading mechanism in which the stress levels in the carbides are raised, as the surrounding ferrite undergoes plastic deformation. The conditions in the vicinity of the nucleated micro-crack will then determine whether the crack will penetrate or be arrested by the ferrite. The ferrite is able to arrest nucleated cracks through the presence of mobile dislocations, which blunt and shield the microcrack and thus lowers the stresses at the crack tip. Hence, the macroscopic toughness of the material directly depends on the ability of the ferrite to arrest nucleated micro-cracks and in turn on the plastic rate sensitivity of the ferrite. The initiation of cleavage fracture is here modelled explicitly in the form of a micro-crack, which nucleates in a brittle carbide and propagates into the surrounding ferrite. The carbide is modelled as an elastic cylinder or in a few cases an elastic sphere and the ferrite as an elastic viscoplastic material. The crack growth is modelled using a cohesive surface, where the tractions are governed by a modified exponential cohesive law. It is shown that the critical stress, required to propagate a microcrack from a broken carbide, increases with decreasing plastic rate sensitivity of the ferrite. The results also show that a low stress triaxiality and a high aspect ratio of the carbide promote the initiation of cleavage fracture from a broken carbide. 相似文献
978.
Fan Xijun 《Acta Mechanica Sinica》1992,8(4):295-306
The constitutive equation for a semiconcentrated fibre suspension in the Oldroyd-B fluid has been derived from a statistical
model of such a suspension by employing the molecular theory for polymeric liquids. To circumvent theoretical difficulties
in viscoelastic fluid mechanics, several simplified models are used to account for the interactions of fibres and polymer
molecules. Some of material functions are calculated in terms of the constitutive equation.
The project Supported by the University of Melbourne of Australia, the National Natural Science Foundation of China and Zhejiang
Province 相似文献
979.
复合材料界面状态是衡量复合质量优劣的主要评定因素之一,焊接参数和界面状态之间存在着紧密的联系。为了获得理想的复合质量,必须正确选择爆炸焊接参数。本文在实验的基础上,通过理论研究和数值计算,探讨了爆炸复合的力学模型及物理机制,验证了碰撞角对再入射流的质量(或再入射流的厚度)和爆炸复合材料界面状态存在的影响,得出了波形的变化趋势与碰撞角的变化趋势相一致的结论,同时确立了波形参数和碰撞角的半定量表达式,拓展和深化了爆炸复合的研究领域,丰富和发展了爆炸复合的成波机理,从而能够更好地指导工程应用,减少工程损耗,提高复合质量和工作效率。 相似文献
980.