全文获取类型
收费全文 | 3466篇 |
免费 | 465篇 |
国内免费 | 319篇 |
专业分类
化学 | 1323篇 |
晶体学 | 36篇 |
力学 | 1366篇 |
综合类 | 31篇 |
数学 | 433篇 |
物理学 | 1061篇 |
出版年
2024年 | 13篇 |
2023年 | 53篇 |
2022年 | 67篇 |
2021年 | 95篇 |
2020年 | 142篇 |
2019年 | 100篇 |
2018年 | 112篇 |
2017年 | 155篇 |
2016年 | 171篇 |
2015年 | 104篇 |
2014年 | 149篇 |
2013年 | 355篇 |
2012年 | 172篇 |
2011年 | 149篇 |
2010年 | 128篇 |
2009年 | 169篇 |
2008年 | 206篇 |
2007年 | 208篇 |
2006年 | 212篇 |
2005年 | 188篇 |
2004年 | 150篇 |
2003年 | 145篇 |
2002年 | 97篇 |
2001年 | 92篇 |
2000年 | 95篇 |
1999年 | 104篇 |
1998年 | 64篇 |
1997年 | 79篇 |
1996年 | 71篇 |
1995年 | 67篇 |
1994年 | 48篇 |
1993年 | 37篇 |
1992年 | 50篇 |
1991年 | 44篇 |
1990年 | 22篇 |
1989年 | 14篇 |
1988年 | 27篇 |
1987年 | 21篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4250条查询结果,搜索用时 15 毫秒
71.
各向异性两相材料尖劈奇性场的非协调元分析 总被引:2,自引:1,他引:2
提出了一个基于位移的、分析柱状各向异性两相材料尖劈端部邻域的奇性位移场和应力场问题的非协调元特征分析法. 该方法从柱状扇区的散度定理出发,将柱状扇区控制方程的弱式化为一个与虚功原理相同形式的方程,采用一种新的非协调元技术把所导出的``虚功原理'转化为标准一阶特征方程的求解问题. 非协调元法中,尖劈端部邻域的位移场假定没有采用奇异变换技术,有限元的单元形式是一维的. 将柱状各向异性两相材料尖劈视为``广义平面应变'问题,位移场与坐标z无关,只关注界面端的幂奇异性而不考虑对数奇异性. 运用该方法给出了柱状各向异性两相材料尖劈端部奇性应力指数、奇性位移角分布和应力角分布的算例. 所有的计算结果表明,该方法使用的单元少而且精度较高. 相似文献
72.
A PREDICTIVE APPROACH TO THE IN-PLANE MECHANICAL PROPERTIES OF STITCHED COMPOSITE LAMINATES 总被引:1,自引:0,他引:1
Zhang Junqian Wei Yuqing 《Acta Mechanica Solida Sinica》2007,20(2):130-140
This contribution attempts to model the alteration of the in-plane elastic properties in laminates caused by stitching,and to predict the in-plane effective tensile strength of the stitched composite laminates.The distortion of in-plane fibers is considered to be the main cause that affects the in-plane mechanical properties.A fiber distortion model is proposed to characterize the fiber misalignment and the fiber content concentration due to stitching.The undistorted region,the fiber distortion region,the resin-rich pocket and the through-thickness reinforcement section are taken into account.The fiber misalignment and inhomogeneous fiber content due to stitching have been formulated by introducing two parameters,the distortion width and maximum misalignment.It has been found that the ply stress concentration in stitched laminates is influenced by the two concurrent factors,the stitch hole and inhomogeneous fiber content.The stitch hole brings about the stress concentration whereas the higher fiber content at the local region induced by stitching restrains the local deformation of the composite.The model is used to predict the tensile strength of the [0/45/0/-45/90/45/0/-45]_(2s) T300/QY9512 composite laminate stitched by Kevlar 29 yarn with different stitching configurations,showing an acceptable agreement with experimental data. 相似文献
73.
74.
A rectangular cell of known boundary conditions is cut out from a medium containing the doubly periodic array of inclusions. The stress and strain relationship of the rectangular cell is obtained by using the classical boundary element methods. By matching the boundary condition requirements, the effective elastic properties of the doubly periodic array of inclusions can then be calculated. Numerical examples from the sub-domain boundary element method and the single domain boundary element method are compared and discussed. However, the present method cannot be readily extended to domains having circular or curved boundary parts. 相似文献
75.
舰船推进轴系是舰船动力装置的重要组成部分,它的稳定性是舰船生命力的基本保证.本文以舰船主推进轴系为研究对象,考虑了非线性油膜力的作用,在推进轴的非线性油膜力模型中,考虑了油膜涡动效应和挤压效应以及多个轴承油膜力的耦合影响,并考虑了轴承结构本身的刚度.文中采用弹性体动力学方法对推进轴建模,考虑了在外冲击作用下转速和轴承油膜力对于转轴冲击响应的影响,考虑横向运动与转动耦合作用,导出以非线性偏微分方程描述的舰船主推进轴的动力学方程,并用经典理论对其进行离散,最后采用龙格-库塔法进行数值仿真.实例分析指出转速对于转轴冲击响应的影响不可忽略. 相似文献
76.
鼓膜法测定纳米多孔氧化铝薄膜的弹性模量 总被引:1,自引:4,他引:1
本文的多孔氧化铝薄膜含有直径均一、互相平行且与表面垂直的有序纳米孔阵列。它有广阔的应用前景。多孔氧化铝膜与氧化铝陶瓷材料的宏观力学性能有很大的区别。本文用鼓膜法结合实时电子散斑干涉(ESPI)技术,测量薄膜压力与离面位移的关系,再用周边固支平板小挠度模型计算出多孔氧化铝薄膜的宏观弹性模量。本实验中厚76微米的多孔氧化铝薄膜的宏观弹性模量为32.5GPa,比热压氧化铝陶瓷的弹性模量几乎小一个数量级,主要是由于晶相和细观结构不同造成的。这种方法较适合测量此类结构薄膜的力学性能。 相似文献
77.
Based on the theory of elastic dynamics, multiple scattering of elastic waves and dynamic stress concentrations in fiber-reinforced
composite are studied. The analytical expressions of elastic waves in different regions are presented. The mode coefficients
of elastic waves are determined in accordance with the continuous conditions of displacement and stress on the boundary of
the multi-interfaces. By using the addition theorem of Hankel functions, the formula of scattered wave fields in different
local coordinates are transformed into those in one local coordinate to determine the unknown coefficients and dynamic stress
concentration factors (DSCFs). The influences of the distance between two inclusions, material properties and structural size
on the DSCFs near the interfaces are analyzed. As examples, the numerical results of DSCFs near the interfaces for two kinds
of fiber-reinforced composites are presented and discussed.
The project supported by the National Natural Science Foundation of China (19972018) 相似文献
78.
79.
80.
Application of a new fast multipole BEM for simulation of 2D elastic solid with large number of inclusions 总被引:8,自引:0,他引:8
A fast multipole method (FMM) is applied for BEM to reduce both the operation and memory requirement in dealing with very
large scale problems. In this paper, a new version of fast multipole BEM for 2D elastostatics is presented and used for simulation
of 2D elastic solid with a large number of randomly distributed inclusions combined with a similar subregion approach. Generalized
minimum residual method (GMRES) is used as an iterative solver to solve the equation system formed by BEM iteratively. The
numerical results show that the scheme presented is applicable to certain large scale problems.
The project supported by the National Nature Science Foundation of China (10172053) and the Ministry of Education 相似文献