首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1647篇
  免费   235篇
  国内免费   51篇
化学   106篇
晶体学   8篇
力学   959篇
综合类   15篇
数学   318篇
物理学   527篇
  2024年   3篇
  2023年   13篇
  2022年   29篇
  2021年   27篇
  2020年   51篇
  2019年   36篇
  2018年   32篇
  2017年   35篇
  2016年   59篇
  2015年   40篇
  2014年   81篇
  2013年   83篇
  2012年   70篇
  2011年   97篇
  2010年   71篇
  2009年   75篇
  2008年   94篇
  2007年   112篇
  2006年   121篇
  2005年   111篇
  2004年   89篇
  2003年   93篇
  2002年   49篇
  2001年   48篇
  2000年   49篇
  1999年   49篇
  1998年   59篇
  1997年   51篇
  1996年   34篇
  1995年   30篇
  1994年   17篇
  1993年   23篇
  1992年   22篇
  1991年   18篇
  1990年   24篇
  1989年   6篇
  1988年   7篇
  1987年   8篇
  1986年   4篇
  1985年   5篇
  1984年   1篇
  1982年   2篇
  1981年   3篇
  1978年   1篇
  1957年   1篇
排序方式: 共有1933条查询结果,搜索用时 17 毫秒
91.
92.
The results of a comprehensive test program for the mechanical behavior of round concrete specimens confined by carbon-fiber epoxy tapes and prestressed carbon yarns are reported. Five different concrete batches of compressive strength from 20 to 100 MPa and the confinement of various thickness and pretension level were investigated. The specimens, which were subjected to monotonic or repeated compressive loadings, showed a nonlinear stress-strain behavior with a significant ductility and increased ultimate strength, in contrary to the brittle behavior of plain concrete. The limit of linearity on the stress-strain diagrams of the confined concrete roughly coincided with the ultimate strength of plain concrete. Above this limit, the damage accumulation and plastic deformations proceeded in the confined specimens. This fact was evidenced by the increasing slope of deformation diagrams in unloadings and repeated loadings and by the pronounced residual strains. The limit of linearity could be raised significantly by pretension of the carbon yarns during their winding. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 21–44, January–February, 2006.  相似文献   
93.
建立并求解了弹性介质中圆柱壳的径向位移控制方程,考虑边界条件及相容条件,得到了应力波传播及反射过程中圆柱壳的动力屈曲分叉条件.通过计算得到了不同时间段屈曲临界载荷与应力波波阵面到达圆柱壳的位置、弹性介质的刚度、壳体未嵌入弹性介质部分的长度与总长之比的关系.数值计算结果表明,弹性介质中的圆柱壳发生轴对称屈曲和非轴对称屈曲趋势一致;嵌入弹性介质部分越深、弹性介质刚度越大圆柱壳越难屈曲;屈曲临界载荷随着弹性介质刚度的增大经历了增长缓慢、增长迅速以及增长较慢3个阶段;应力波反射前波阵面通过分界面后,屈曲仅发生在应力波传播区域,反射波波阵面通过分界面前,临界载荷较小时屈曲先发生在反射端部,随着轴向阶数增大,屈曲覆盖整个圆柱壳区域,反射波波阵面通过分界面后,壳体发生的屈曲始终覆盖整个圆柱壳区域.  相似文献   
94.
The distribution of transverse stresses in the midlayer of a composite sandwich panel under multipoint loading is investigated. The stresses averaged across the thickness of a soft filler are estimated using a discrete model. Finite expressions for the compression of the filler along the length of the panel are derived by means of superposition of the local effects from the bending of face layers under an infinite system of transverse point forces constant across the panel thickness. The effects of compression and transverse extension of the filler, in the case of a high distribution frequency of these forces, i.e., when the distance between the forces is comparable to the panel thickness, are revealed. Compression of the panel by two systems of forces applied symmetrically or nonsymmetrically to the upper and lower faces is considered. The bending characteristics in the cases of loading with point forces and piecewise distributed loads are compared. The formulas obtained are used to determine the length of a small region on the panel surface for which the local effects from the distributed pressure and the point force are equivalent. The corresponding estimates are obtained in a closed form. The analysis, carried out with varied parameters of the structure, allows us to elucidate the peculiarities of the effect of discontinuous loads on the design characteristics in the local zones, using finite expressions derived by the operational method.  相似文献   
95.
湿热环境中复合材料层合圆柱薄壳的屈曲和后屈曲   总被引:5,自引:0,他引:5  
在宏-细观力学模型框架下,讨论湿热环境对复合材料层合圆柱薄壳在轴向压缩作用下屈曲和后屈曲行为的影响.基于细观力学模型复合材料性能与湿度和温度变化有关.壳体控制方程基于经典层合壳理论,并包括湿热效应.壳体屈曲的边界层理论被推广用于湿热环境的情况,相应的奇异摄动法用于确定层合圆柱薄壳的屈曲荷载和后屈曲平衡路径.分析中同时计及壳体非线性前屈曲变形和初始几何缺陷的影响.数值算例给出完善和非完善正交铺设层合圆柱薄壳在不同湿热环境中的后屈曲行为.讨论了温度和湿度,纤维体积比率,壳体几何参数,铺层数,铺层方式和初始几何缺陷等各种参数变化的影响.  相似文献   
96.
浅埋的圆柱形孔洞对SH波的散射与地震动   总被引:22,自引:1,他引:22  
研究了浅埋的圆柱形孔洞对以任意方向入射的平面SH波的散射与地震动问题。利用复变函数和多极坐标方法构造了问题的位移解。当入射波的波长与圆孔的半径相比较小时,地震动将受到较大的影响。影响地震动有三个主要参数:(1)SH波的入射角0;(2)入射波波数,即圆柱形孔洞的半径与入射波半波长之比;(3)h/R,即圆柱形孔洞至表面的距离与圆孔半径之比。当较大时,地震动幅值变化激烈,位移幅值可出现跳动和放大的现象。当h/R增大至10~12时,位移幅值变化恢复至半空间的情况,表明圆柱形孔洞的影响可被忽略。  相似文献   
97.
叠层靶板弹击实验及弹道侵彻机理的数值模拟研究   总被引:3,自引:0,他引:3  
陈晓  周宏 《爆炸与冲击》2003,23(6):509-515
为了提高军盔等防护装备的防弹性能,采用非线性动态显式有限元分析软件ANSYS/LS DYNA5.6.1模拟了几种复合材料防弹靶板的抗弹道侵彻过程,弹头采用标准1.1g模拟弹片。结合v50弹击实验分析了靶板在此类弹击下的破坏机理和吸能方式,对靶板的选材、铺层顺序、层数和制造工艺等提出合理化建议,主要是沿靶板厚向应采用非均匀的三段式结构和工艺。  相似文献   
98.
液体炸药滑移内爆加载下钢管的变形与层裂破坏研究   总被引:3,自引:1,他引:3  
用液体炸药滑移内爆加载方式,研究了不同炸药厚度和外壳条件下20钢圆管的内聚变形和破坏特征。实验中,钢管发生了较大径向应变,应变值大致随炸药厚度的增加而线性增大。在炸药厚度不低于3mm时钢管变形均匀,轴对称较好;药厚小于3mm时其变形不再是基本轴对称收缩,管子表面出现扭转褶皱。各种装药厚度下,均未观察到预期的层裂破坏。对未层裂的原因进行了初步分析。  相似文献   
99.
The subject of this investigation is to study the buckling of orthotropic cylindricalthin shells under torsion,which is a power function of time.The dynamic stability and compati-bility equations are obtained first.These equations are subsequently reduced to a time dependentdifferential equation with variable coefficient by using Galerkin's method.Finally,the critical dy-namic and static loading,the corresponding wave numbers,the dynamic factors,critical time andcritical impulse are found analytically by applying the Ritz type variational method.Using thoseresults,the effects of the variations of the power of time in the torsion load expression,of theloading parameter,the ratio of the Young's moduli and the ratio of the radius to thickness onthe critical parameters are studied numerically.It is observed that these factors have appreciableeffects on the critical parameters of the problem in the heading.  相似文献   
100.
Failure behavior of the delaminated stiffened composite plates under compression is studied by the finite element method, based on a Global-Local variational model. A virtual crack closure technique and a self-adaptive grid moving scheme are proposed to predict the delamination growth process. The contact effect along the delamination front is considered. The numerical results show that the influences of the distribution and location of the stiffeners, the configuration and size of the delamination, the boundary condition and the contact upon the failure behavior of the plates are significant. The project supported by the National Natural Science Foundation of China (59975014)  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号