全文获取类型
收费全文 | 945篇 |
免费 | 150篇 |
国内免费 | 27篇 |
专业分类
化学 | 67篇 |
晶体学 | 4篇 |
力学 | 578篇 |
综合类 | 6篇 |
数学 | 132篇 |
物理学 | 335篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 9篇 |
2020年 | 22篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 26篇 |
2015年 | 25篇 |
2014年 | 35篇 |
2013年 | 48篇 |
2012年 | 45篇 |
2011年 | 46篇 |
2010年 | 35篇 |
2009年 | 41篇 |
2008年 | 54篇 |
2007年 | 75篇 |
2006年 | 79篇 |
2005年 | 74篇 |
2004年 | 51篇 |
2003年 | 66篇 |
2002年 | 30篇 |
2001年 | 31篇 |
2000年 | 27篇 |
1999年 | 29篇 |
1998年 | 32篇 |
1997年 | 33篇 |
1996年 | 20篇 |
1995年 | 22篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 16篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4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1122条查询结果,搜索用时 31 毫秒
151.
This paper is concerned with the elastic buckling of stiffened cylindrical shells by rings and stringers made of functionally graded materials subjected to axial compression loading. The shell properties are assumed to vary continuously through the thickness direction. Fundamental relations, the equilibrium and stability equations are derived using the Sander’s assumption. Resulting equations are employed to obtain the closed-form solution for the critical buckling loads. The results show that the inhomogeneity parameter and geometry of shell significantly affect the critical buckling loads. The analytical results are compared and validated using the finite element method. 相似文献
152.
The piecewise algebraic variety is the set of all common zeros of multivariate splines. We show that solving a parametric
piecewise algebraic variety amounts to solve a finite number of parametric polynomial systems containing strict inequalities.
With the regular decomposition of semi-algebraic systems and the partial cylindrical algebraic decomposition method, we give
a method to compute the supremum of the number of torsion-free real zeros of a given zero-dimensional parametric piecewise
algebraic variety, and to get distributions of the number of real zeros in every n-dimensional cell when the number reaches the supremum. This method also produces corresponding necessary and sufficient conditions
for reaching the supremum and its distributions. We also present an algorithm to produce a necessary and sufficient condition
for a given zero-dimensional parametric piecewise algebraic variety to have a given number of distinct torsion-free real zeros
in every n-cell in the n-complex.
This work was supported by National Natural Science Foundation of China (Grant Nos. 10271022, 60373093, 60533060), the Natural
Science Foundation of Zhejiang Province (Grant No. Y7080068) and the Foundation of Department of Education of Zhejiang Province
(Grant Nos. 20070628 and Y200802999) 相似文献
153.
Yanqing Wang Li Liang Xinghui Guo Jian Li Jing Liu Panglun Liu 《Acta Mechanica Solida Sinica》2013,26(3):277-291
The nonlinear vibration of a cantilever cylindrical shell under a concentrated harmonic excitation moving in a concentric circular path is proposed. Nonlinearities due to large-amplitude shell motion are considered, with account taken of the effect of viscous structure damping. The system is discretized by Galerkin's method. The method of averaging is developed to study the nonlinear traveling wave responses of the multi-degrees-of-freedom system. The bifurcation phenomenon of the model is investigated by means of the averaged system in detail. The results reveal the change process and nonlinear dynamic characteristics of the periodic solutions of averaged equations. 相似文献
154.
为高效求解球床高温气冷堆物理-热工耦合问题,发展改进节块展开法求解圆柱几何下的对流扩散方程.针对圆柱几何和对流扩散方程的特殊性,采用三阶多项式和指数函数作为r向横向积分方程的展开函数,在节块展开法的框架下高效求解对流扩散方程.数值验证表明,改进的节块展开方法具有固有的迎风特性,在使用粗网节块时依然能保持稳定性和较高的计算精度. 相似文献
155.
Love’s first approximation theory is used to analyze the natural frequencies of rotating functionally graded cylindrical shells.To verify the validity of the present method,the natural frequencies of the simply supported non-rotating isotropic cylindrical shell and the functionally graded cylindrical shell are compared with available published results.Good agreement is obtained.The effects of the power law index,the wave numbers along the x-and θ-directions,and the thickness-to-radius ratio on the natural frequencies of the simply supported rotating functionally graded cylindrical shell are investigated by several numerical examples.It is found that the fundamental frequencies of the backward waves increase with the increasing rotating speed,the fundamental frequencies of the forward waves decrease with the increasing rotating speed,and the forward and backward waves frequencies increase with the increasing thickness-to-radius ratio. 相似文献
156.
157.
158.
白光横向平顶光束在定向背光式自由立体显示器中有重要应用.本文提出一种采用带蝶形小孔阵列的衍射掩模片获得白光横向平顶光束的方法.根据广义惠更斯-菲涅耳衍射积分和多波长叠加原理,推导出光强分布计算式.设计一套实验装置,数值模拟并实验验证出射光束在不同距离的横向光强分布以及小孔蝶形凹度(蝶形中心高度与边长的比值)对横向光强分布的影响.结果表明:当选择小孔蝶形凹度为0.50—0.66时,可以得到平顶因子F 0.89的白光横向平顶光束,横向平顶光束的宽度随着传输距离的增大而增大,而平顶因子基本不变.实验还发现柱面透镜的折射色散和衍射色散可以互相抵消,使白光横向平顶光束基本无色散. 相似文献
159.
Compression fracture in carbon fiber reinforced plastics (CFRP) involves multiple physical mechanisms operating at multiple scales ranging from angströms to cms and beyond. First, at the macro/meso-scale, combined effects of modal imperfections, transverse shear/normal deformation along with the non-linear hypo-elastic transverse shear (GTT) material property on the emergence of interlaminar shear crippling type instability modes, related to the localization (onset of deformation softening), delocalization (onset of deformation hardening) and propagation of mode II compression fracture/damage, in thick imperfect cross-ply very long cylindrical shells under applied hydrostatic pressure, are investigated. The primary accomplishment is the (hitherto unavailable) computation of the layer-wise mode II stress intensity factor, energy release rate and kink crack band-width, under hydrostatic compression, from a non-linear finite element analysis (FEA), using Maxwell’s construction and Griffith׳s energy balance approach. Numerical results include the effects of hypoelastic (GTT only) material property, on localization and delocalization leading to compression fracture.At the micro-scale, a novel three-dimensional eigenfunction expansion technique, based in part on separation of the cylinder length-variable and partly utilizing a modified Frobenius type series expansion in conjunction with an affine transformation to compute the local stress singularity, in the vicinity of a kinked-fiber/matrix trimaterial junction front. Such computed stress singularities represent a measure of the degree of inherent flaw sensitivity of unidirectional CFRP under compression. Finally, dislocation glide in graphite crystallites plays a dominant role in kink band nucleation and propagation at the nano-meter scale. 相似文献
160.
The study of cylindrically symmetric compressible fluid is interesting from both theoretical and numerical points of view. In this paper, the typical spherical symmetry properties of the numerical schemes are discussed, and an area weighted scheme is extended from a Lagrangian method to an arbitrary Lagrangian and Eulerian (ALE) method. Numerical results are presented to compare three discrete configurations, i.e., the control volume scheme, the area weighted scheme, and the plane scheme with the addition of a geometrical source. The fact that the singularity arises from the geometrical source term in the plane scheme is illustrated. A suggestion for choosing the discrete formulation is given when the strong shock wave problems are simulated. 相似文献