全文获取类型
收费全文 | 8515篇 |
免费 | 982篇 |
国内免费 | 2363篇 |
专业分类
化学 | 5980篇 |
晶体学 | 303篇 |
力学 | 2326篇 |
综合类 | 62篇 |
数学 | 345篇 |
物理学 | 2844篇 |
出版年
2024年 | 35篇 |
2023年 | 138篇 |
2022年 | 338篇 |
2021年 | 391篇 |
2020年 | 353篇 |
2019年 | 269篇 |
2018年 | 210篇 |
2017年 | 393篇 |
2016年 | 442篇 |
2015年 | 374篇 |
2014年 | 492篇 |
2013年 | 604篇 |
2012年 | 560篇 |
2011年 | 634篇 |
2010年 | 552篇 |
2009年 | 620篇 |
2008年 | 599篇 |
2007年 | 676篇 |
2006年 | 545篇 |
2005年 | 501篇 |
2004年 | 497篇 |
2003年 | 436篇 |
2002年 | 334篇 |
2001年 | 275篇 |
2000年 | 262篇 |
1999年 | 188篇 |
1998年 | 187篇 |
1997年 | 163篇 |
1996年 | 136篇 |
1995年 | 100篇 |
1994年 | 104篇 |
1993年 | 69篇 |
1992年 | 78篇 |
1991年 | 51篇 |
1990年 | 48篇 |
1989年 | 30篇 |
1988年 | 38篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A rate dependent crystal plasticity model for the α/β Ti–Al alloy Ti–6Al–4V with duplex microstructure is developed and presented herein. Duplex Ti–6Al–4V is a dual-phase alloy consisting of an hcp structured matrix primary α-phase and secondary lamellar α + β domains that are composed of alternating layers of secondary α laths and bcc structured residual β laths. The model accounts for distinct three-dimensional slip geometry for each phase, anisotropic and length scale dependent slip system strengths, the non-planar dislocation core structure of prismatic screw dislocations in the primary α-phase, and crystallographic texture. The model is implemented in the general purpose finite element code (ABAQUS, 2005. Ver 6.5, Hibbitt, Karlsson, and Sorensen, Inc., Pawtucket, RI) via a UMAT subroutine. 相似文献
992.
具有不同功能梯度分布函数的板件的三维分析 总被引:1,自引:0,他引:1
发展了一种新颖的功能梯度结构分析的细观元法。细观元法对结构的常规有限单元内部设置密集细观单元以反映材料特性梯度变化,又通过协调条件将各细观元结点自由度转换为同一常规有限元自由度,再上机计算。这种细观元法既能充分反映材料功能梯度变化特性;而其计算单元又和常规有限元一样,是一种针对功能梯度结构分析的有效数值方法。文中通过细观元技术进行计算、分析,给出了具有不同功能梯度分布函数板件的力学量三维分布形态。 相似文献
993.
对比研究了货车心盘用ZG25MnNb钢、AAR-C级钢及经过表面强化处理的锻钢20Mn、锻钢Q345和铸钢ZG25的耐磨性能;采用金相显微镜分析了材料金相结构对其耐磨性能的影响。结果表明,对货车心盘用钢材进行表面强化能够显著改善其耐磨性能ZG25MnNb钢和经表面强化处理的锻钢20Mn的耐磨性较优;表面硬度高而组织细小的材料组成的摩擦副的耐磨性较好。 相似文献
994.
We conducted dynamic and quasi-static compression experiments with low-density (ρ = 120 kg/m3) epoxy foam specimens. The specimens had a 10.0-mm-square cross-section and a length of 19.3 mm. Dynamic experiments were
conducted with a modified split Hopkinson pressure bar (SHPB), and the quasi-static experiments were conducted with a hydraulic
load frame device (MTS-810). In both cases, the specimens were loaded from one end at a constant velocity. Equally spaced
grid lines were marked on the specimens to monitor the deformation history. Digital images taken at equally spaced time intervals
gave the positions of each grid line. These images showed that a constant end-face velocity V produced a compaction wave front that traveled at a constant velocity C in both dynamic and quasi-static experiments. We described these results with a shockwave analysis that used a locking solid
material model. 相似文献
995.
The indentation modulus of elastically anisotropic materials for indenters of arbitrary shape 总被引:1,自引:0,他引:1
J.J. Vlassak M. Ciavarella X. Wang 《Journal of the mechanics and physics of solids》2003,51(9):1701-1721
The contact of an indenter of arbitrary shape on an elastically anisotropic half space is considered. It is demonstrated in a theorem that the solution of the contact problem is the one that maximizes the load on the indenter for a given indentation depth. The theorem can be used to derive the best approximate solution in the Rayleigh-Ritz sense if the contact area is a priori assumed to have a certain shape. This approach is used to analyze the contact of a sphere and an axisymmetric cone on an anisotropic half space. The contact area is assumed to be elliptical, which is exact for the sphere and an approximation for the cone. It is further shown that the contact area is exactly elliptical even for conical indenters when a limited class of Green's functions is considered. If only the first term of the surface Green's function Fourier expansion is retained in the solution of the axisymmetric contact problem, a simpler solution is obtained, referred to as the equivalent isotropic solution. For most anisotropic materials, the contact stiffness determined using this approach is very close to the value obtained for both conical and spherical indenters by means of the theorem. Therefore, it is suggested that the equivalent isotropic solution provides a quick and efficient estimate for quantities such as the elastic compliance or stiffness of the contact. The “equivalent indentation modulus”, which depends on material and orientation, is computed for sapphire and diamond single crystals. 相似文献
996.
997.
V. M. Kulik 《Journal of Applied Mechanics and Technical Physics》2006,47(3):394-400
The velocity and the rate of decay of a strain wave in a layer of a viscoelastic material rigidly fixed on a solid foundation
are determined. The wave structure (ratio of the longitudinal to the transverse displacement) and the profiles of these displacements
are analyzed. Attenuation of waves in the first mode is found to be more significant than that in an infinite space. The most
intense decay is observed at resonance frequencies. A strong effect of compressibility of the medium on wave parameters is
revealed. Conditions at which such a system operates as a waveguide are found. For a loss tangent higher than 0.13 (for an
incompressible medium), the character of the dispersion dependence is observed to change drastically: the wave velocity decreases
with decreasing frequency.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 3, pp. 104–111, May–June, 2006. 相似文献
998.
The effect of transverse shear on delamination in layered, isotropic, linear-elastic materials has been determined. In contrast to the effects of an axial load or a bending moment on the energy-release rate for delamination, the effects of shear depend on the details of the deformation in the crack-tip region. It therefore does not appear to be possible to deduce rigorous expressions for the shear component of the energy-release rate based on steady-state energy arguments or on any type of modified beam theory. The expressions for the shear component of the energy-release rate presented in this work have been obtained using finite-element approaches. By combining these results with earlier expressions for the bending-moment and axial-force components of the energy-release rates, the framework for analyzing delamination in this type of geometry has been extended to the completely general case of any arbitrary loading. The relationship between the effects of shear and other fracture phenomena such as crack-tip rotations, elastic foundations and cohesive zones are discussed in the final sections of this paper. 相似文献
999.
C. Miehe M. Lambrecht E. Gürses 《Journal of the mechanics and physics of solids》2004,52(12):2725-2769
We propose an approach to the definition and analysis of material instabilities in rate-independent standard dissipative solids at finite strains based on finite-step-sized incremental energy minimization principles. The point of departure is a recently developed constitutive minimization principle for standard dissipative materials that optimizes a generalized incremental work function with respect to the internal variables. In an incremental setting at finite time steps this variational problem defines a quasi-hyperelastic stress potential. The existence of this potential allows to be recast a typical incremental boundary-value problem of quasi-static inelasticity into a principle of minimum incremental energy for standard dissipative solids. Mathematical existence theorems for sufficiently regular minimizers then induce a definition of the material stability of the inelastic material response in terms of the sequentially weakly lower semicontinuity of the incremental variational functional. As a consequence, the incremental material stability of standard dissipative solids may be defined in terms of the quasi-convexity or the rank-one convexity of the incremental stress potential. This global definition includes the classical local Hadamard condition but is more general. Furthermore, the variational setting opens up the possibility to analyze the post-critical development of deformation microstructures in non-stable inelastic materials based on energy relaxation methods. We outline minimization principles of quasi- and rank-one convexifications of incremental non-convex stress potentials for standard dissipative solids. The general concepts are applied to the analysis of evolving deformation microstructures in single-slip plasticity. For this canonical model problem, we outline details of the constitutive variational formulation and develop numerical and semi-analytical solution methods for a first-level rank-one convexification. A set of representative numerical investigations analyze the development of deformation microstructures in the form of rank-one laminates in single slip plasticity for homogeneous macro-deformation modes as well as inhomogeneous macroscopic boundary-value problems. The well-posedness of the relaxed variational formulation is indicated by an independence of typical finite element solutions on the mesh-size. 相似文献
1000.
从回收和再生利用高锰钢废料中铝资源的角度出发,探讨了以高锰钢废料作为主要原材料生产低碳中铝抗磨球星铸铁的可能性及存在的技术问题,并对比考察了所研制的材料同中铝抗磨球星铸铁KMTQMn6的磨粒磨损性能和环境协调性.研究结果表明,所研制的低碳中铝球星铸铁的耐磨性能更好、环境负荷更低,是具有良好环境协调性的球星铸铁. 相似文献