全文获取类型
收费全文 | 6581篇 |
免费 | 743篇 |
国内免费 | 1965篇 |
专业分类
化学 | 4627篇 |
晶体学 | 243篇 |
力学 | 2044篇 |
综合类 | 52篇 |
数学 | 329篇 |
物理学 | 1994篇 |
出版年
2024年 | 26篇 |
2023年 | 114篇 |
2022年 | 275篇 |
2021年 | 318篇 |
2020年 | 280篇 |
2019年 | 211篇 |
2018年 | 156篇 |
2017年 | 297篇 |
2016年 | 343篇 |
2015年 | 294篇 |
2014年 | 375篇 |
2013年 | 484篇 |
2012年 | 437篇 |
2011年 | 466篇 |
2010年 | 436篇 |
2009年 | 492篇 |
2008年 | 478篇 |
2007年 | 544篇 |
2006年 | 424篇 |
2005年 | 402篇 |
2004年 | 402篇 |
2003年 | 361篇 |
2002年 | 274篇 |
2001年 | 206篇 |
2000年 | 199篇 |
1999年 | 149篇 |
1998年 | 140篇 |
1997年 | 123篇 |
1996年 | 110篇 |
1995年 | 77篇 |
1994年 | 76篇 |
1993年 | 44篇 |
1992年 | 63篇 |
1991年 | 41篇 |
1990年 | 32篇 |
1989年 | 21篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有9289条查询结果,搜索用时 15 毫秒
901.
含初缺陷复合材料圆柱曲板的动力屈曲分析 总被引:1,自引:1,他引:1
基于修正的一阶剪切变形理论,利用Hamilton原理导出包含横向剪切变形和转动惯量的复合材料长圆柱曲板的非线性动力方程,通过将位移和载荷展开为Fourier级数,把非线性偏微分方程组转化为二阶常微分方程组,并可由四阶Runge-Kutta方法数值求解,通过算例,讨论了有关因素对迭层复合材料圆柱曲板动力屈曲的影响。 相似文献
902.
等离子喷涂碳化铬-镍铬涂层的摩擦学特性 总被引:3,自引:1,他引:3
在发展新型高效节能的汽车和飞机发动机用耐磨材料中,碳化铬-镍铬涂层是很有开发前景的材料之一.为了扩大这种涂层的应用领域并为其应用提供科学依据,用MM-200磨损试验机,研究了等离子喷涂碳化铬-镍铬(质量比为3∶1)涂层分别与不锈钢、热压烧结Si3N4和石墨组成摩擦副的摩擦学特性;用扫描电子显微镜、X射线能量色散谱仪和X射线衍射技术,考察了磨痕和磨屑的形貌、元素分布和物相组成;讨论了涂层分别与给定的3种材料配副时的磨损机理.结果表明:涂层与不同材料对摩时的磨损量差别很大,磨损机理也明显不同——涂层与不锈钢对摩时的磨损表现为层状颗粒的断裂与剥离;涂层与Si3N4对摩时的磨损主要表现为涂层颗粒的断裂和断裂颗粒的脱碳氧化;石墨对涂层具有润滑作用 相似文献
903.
A stochastic-structurally based three dimensional finite-strain damage model for fibrous soft tissue
José F. Rodríguez Fernando Cacho José A. Bea Manuel Doblaré 《Journal of the mechanics and physics of solids》2006,54(4):864-886
A fully three dimensional finite-strain damage model for fibrous soft tissue is developed. The model assumes uncoupled contributions for the matrix and collagen fibers, and uncoupled bulk and deviatoric response over any range of deformations. A simple isotropic damage mechanism within the framework of continuum damage mechanics has been used to describe the softening behavior under deformation for the matrix. On the other hand, statistical aspects related to the length distribution of the reinforcing fibers lead to a damage model for the reinforcing material. As a result, a general theoretical framework for constitutive modeling of biological soft tissue with continuum damage is obtained. A theoretical example consisting of a biaxial test of a soft tissue reinforced with two families of collagen fibers has been considered to demonstrate the capabilities of the proposed model and to study the sensitivity to changes in the statistical parameters associated with the reinforcing material. Also, a preliminary numerical example is included to demonstrate the model on a inhomogeneous boundary value problem. Results show that the model is able to capture the typical stress-strain behavior observed in fibrous soft tissue and seems to confirm the soundness of the proposed formulation. 相似文献
904.
905.
906.
构造杂交应力单元的柔度矩阵H对角化方法 总被引:2,自引:1,他引:2
证明了杂交元柔度矩阵 H非奇异的充分必要条件是假设应力模式线性无关 ;以及等价应力模式形成相同的杂交元。在此基础上建立了假设应力模式的 Hilbert子空间 ,从而可以利用 Schmidt方法简单地得到等价的正交应力模式 ,实现了柔度矩阵 H对角化 ,使得杂交元形成过程中完全避免了繁杂的矩阵求逆运算 ,提高了杂交元分析的计算效率 ,特别在柔度矩阵不容易显式求逆的材料非线性分析中更具有实际意义 相似文献
907.
Wenyi YanNoel P. O'Dowd Esteban P. Busso 《Journal of the mechanics and physics of solids》2002,50(3):449-470
A computational approach is proposed to predict the sliding wear caused by a loaded spherical pin contacting a rotating disc, a condition typical of the so-called pin-on-disc test widely used in tribological studies. The proposed framework relies on the understanding that, when the pin contacts and slides on the disc, a predominantly plane strain region exists at the centre of the disc wear track. The wear rate in this plane strain region can therefore be determined from a two dimensional idealisation of the contact problem, reducing the need for computationally expensive three dimensional contact analyses. Periodic unit cell techniques are used in conjunction with a ratchetting-based failure criterion to predict the wear rate in the central plane strain region. The overall three dimensional wear rate of the disc is then determined by scaling the plane strain wear rate with a conversion factor related to the predicted shape of the wear track. The approach is used to predict pin-on-disc test data from an Al-Si coating using a tungsten carbide pin. The predicted results are found to be consistent with measured data. 相似文献
908.
Y. Ootao R. Kawamura Y. Tanigawa T. Nakamura 《Archive of Applied Mechanics (Ingenieur Archiv)》1998,68(10):662-676
Summary A neural network model is applied to optimization problems of material compositions for a functionally graded material plate
with arbitrarily distributed and continuously varied material properties in the thickness direction. Unsteady temperature
distribution is evaluated by taking into account the bounds of the number of the layers. Thermal stress components for an
infinite functionally graded material plate are formulated under traction-free mechanical conditions. As a numerical example,
a plate composed of zirconium oxide and titanium alloy is considered. In the optimization problem of minimizing the thermal
stress distribution, the numerical calculations are carried out making use of the neural network. The optimum material composition
is determined by taking into account the effect of temperature-dependence of material properties. The results obtained by
neural network and ordinary nonlinear programming method are compared.
Received 3 March 1998; accepted for publication 22 May 1998 相似文献
909.
In this paper, the dynamical cavitation behavior is analyzed for a sphere composed of a class of transversely isotropic incompressible hyper-elastic materials, where there is a pre-existing micro-void in the interior of the sphere. A second-order non-linear ordinary differential equation that governs the motion of the initial micro-void is obtained by using the boundary conditions. On analyzing the qualitative properties of the solutions of the differential equation, some interesting conclusions are proposed. It is proved that the number of equilibrium points of the differential equation depends on the values of the material parameters, and that the phase diagrams of the equation are closed, smooth and convex trajectories. For any prescribed surface tensile dead-loads, the motion of the initial micro-void undergoes a non-linear periodic oscillation. The dependence of the periodic motion of the initial micro-void on material parameters and the radius of the initial micro-void is examined, and numerical results are also provided. It is worth pointing out that the conclusions in this paper can be used to describe approximately the physical implications of the dynamical formation of a cavity in the sphere. 相似文献
910.
In this study, two-dimensional transient dynamic response of orthotropic plane layered media is investigated. The plane multilayered
media consist of N different generally orthotropic, homogeneous and linearly elastic layers with different ply angles. In the generally orthotropic
layer, representing a ply reinforced by unidirectional fibers with an arbitrary orientation angle, the principal material
directions do not coincide with body coordinate axes. The solution is obtained by employing a numerical technique which combines
the use of Fourier transform with the method of characteristics. The numerical results are displayed in curves denoting the
variations of stress and displacement components with time at different locations. These curves clearly reveal, in wave profiles,
the scattering effects caused by the reflections and refractions of waves at the boundaries and at the interfaces of the layers,
and also the effects of anisotropy caused by fiber orientation angle. The curves properly predict the sharp variations in
the response at the neighborhood of the wave fronts, which shows the power of the numerical technique employed in the study.
By suitably adjusting the elastic constants, the results for multilayered media with transversely isotropic layers, or layers
with cubic symmetry, or isotropic layers can easily be obtained from the general formulation. Furthermore, solutions for some
special cases, including Lamb’s problem for an elastic half-space, are obtained and compared with the available solutions
in the literature and very good agreement is found.
Preliminary version presented at the Second International Congress on Mechatronics (MECH2K3), Graz, Austria, July 14-17, 2003. 相似文献