全文获取类型
收费全文 | 1828篇 |
免费 | 148篇 |
国内免费 | 58篇 |
专业分类
化学 | 198篇 |
晶体学 | 7篇 |
力学 | 920篇 |
综合类 | 22篇 |
数学 | 506篇 |
物理学 | 381篇 |
出版年
2024年 | 5篇 |
2023年 | 15篇 |
2022年 | 27篇 |
2021年 | 33篇 |
2020年 | 36篇 |
2019年 | 33篇 |
2018年 | 40篇 |
2017年 | 45篇 |
2016年 | 77篇 |
2015年 | 59篇 |
2014年 | 89篇 |
2013年 | 164篇 |
2012年 | 67篇 |
2011年 | 73篇 |
2010年 | 70篇 |
2009年 | 88篇 |
2008年 | 87篇 |
2007年 | 92篇 |
2006年 | 105篇 |
2005年 | 85篇 |
2004年 | 94篇 |
2003年 | 62篇 |
2002年 | 67篇 |
2001年 | 74篇 |
2000年 | 51篇 |
1999年 | 81篇 |
1998年 | 46篇 |
1997年 | 60篇 |
1996年 | 36篇 |
1995年 | 25篇 |
1994年 | 30篇 |
1993年 | 23篇 |
1992年 | 19篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2034条查询结果,搜索用时 15 毫秒
71.
在工程实际中旋转机械由于制造和加工误差,装配的不均匀性等原因,往往会脉动运行,这将使得机械系统发生参数振动. 当脉动参数满足一定关系时,这种参数振动将会失稳,进而影响机械结构的正常运转. 本文针对这一问题,引入压电材料对 脉动旋转悬臂梁系统的振动进行控制,研究主动控制悬臂梁系统的参数振动优化设计问题,采用 Hamilton 变分原理与一阶 Galerkin 离散相结合的方法,建立了受速度反馈传感器主动控制的压电旋转悬臂梁的一阶近似线性控制方程. 运用多尺度方法,得到了压电旋转悬臂梁系统在发生1/2亚谐波参数共振时稳定性边界的控制方程,并利用直接分析方法验证了解析摄动解的正确性. 将摄动解中临界阻尼比和轮毂角速度脉动幅值的无量纲参数作为评价系统稳定性能的指标. 通过数值算例,分析了轮毂半径、轮毂角速度平均值和脉动幅值、梁长以及速度传感器的反馈增益系数对系统稳定性区域的影响. 研究结果表明,梁长、轮毂半径、脉动幅值会降低系统稳定性,反馈增益系数可以提高系统稳定性,而轮毂角速度平均值与系统稳定性之间有非单调的关系. 为进一步设计压电旋转机械结构提供了理论依据. 相似文献
72.
黄民丰 《应用数学和力学(英文版)》1997,18(5):511-515
I.PrefaceAsweknow,theSaint-Venanttheoryisawell-knownanduniversallyacceptedtheory.Butasoneofthegeneraltheoriesofelasticmechanics,itisnotprovedperfectely,althoughitistestedbyexperiments.Infact,onlyforthesimplestproblemofelasticity,itisnoteasytofindanalytics… 相似文献
73.
BEM for simulation of a 2D elastic body with randomly distributed circular inclusions 总被引:7,自引:0,他引:7
Based on our 2D BEM software THBEM2 which can be applied to the simulation of an elastic body with randomly distributed identical
circular holes, a scheme of BEM for the simulation of elastic bodies with randomly distributed circular inclusions is proposed.
The numerical examples given show that the boundary element method is more accurate and more effective than the finite element
method for such a problem. The scheme presented can also be successfully used to estimate the effective elastic properties
of composite materials.
Project supported by the National Natural Science Foundation of China (No. 19772025). 相似文献
74.
75.
76.
由多组分聚合物混合物所形成的多尺度有序结构能够展现出许多新奇的物理化学性质, 从而使其在材料工程领域具有十分重要的潜 在应用价值. 本文通过计算机模拟, 在光敏性不相容三元混合物体系中创建了多尺度有序结构. 通过调节光照区域和掩膜形状, 获得了棋盘形、箭靶状等十分独特的形貌, 并且这些结构可以在实验上通过在适当的时间淬火而稳定较长的时间. 详细探讨了组分比、掩膜宽度、间距以及光照强度对体系的影响, 从而为实现多尺度长程序花样薄膜的制备提供了一个简便的途径, 同时也为纳米器件的制备提供了一定的指导. 相似文献
77.
A one-dimensional stress-based elasticity model with limited strain extensibility is developed in this paper, based on thermodynamics arguments. Such nonlinear elastic models can be used to model certain rubber-like and biological materials with limiting chain extensibility. The derived constitutive function is a non-smooth piecewise expression, which can be regularized for numerical or physical considerations. This non-smooth constitutive expression is derived from a Gibbs potential. A three-dimensional extension of this stress-based model is also proposed in the paper. Some simple structural examples are investigated for a bar composed of this non-smooth elastic body. A homogeneous bar composed of this new class of nonlinear elastic material that is loaded is studied for different tension states, namely for concentrated or distributed axial loading. It is shown that the displacement limit extensibility can be observed at the structural scale, with finite or infinite axial load parameters. 相似文献
78.
P. Ciarletta 《International Journal of Non》2011,46(9):1275-1279
A general implicit solution for determining volume-preserving transformations in the n-dimensional Euclidean space is obtained in terms of a set of 2n generating functions in mixed coordinates. For n=2, the proposed representation corresponds to the classical definition of a potential stream function in a canonical transformation. For n=3, the given solution defines a more general class of isochoric transformations, when compared to existing methods based on multiple potentials. Illustrative examples are discussed both in rectangular and in cylindrical coordinates for applications in mechanical problems of incompressible continua. Solving exactly the incompressibility constraint, the proposed representation method is suitable for determining three-dimensional isochoric perturbations to be used in bifurcation theory. Applications in non-linear elasticity are envisaged for determining the occurrence of complex instability patterns for soft elastic materials. 相似文献
79.
In this study, a Lagrange multiplier technique is developed to solve problems of coupled mechanics and is applied to the case of a Newtonian fluid coupled to a quasi-static hyperelastic solid. Based on theoretical developments in [57], an additional Lagrange multiplier is used to weakly impose displacement/velocity continuity as well as equal, but opposite, force. Through this approach, both mesh conformity and kinematic variable interpolation may be selected independently within each mechanical body, allowing for the selection of grid size and interpolation most appropriate for the underlying physics. In addition, the transfer of mechanical energy in the coupled system is proven to be conserved. The fidelity of the technique for coupled fluid–solid mechanics is demonstrated through a series of numerical experiments which examine the construction of the Lagrange multiplier space, stability of the scheme, and show optimal convergence rates. The benefits of non-conformity in multi-physics problems is also highlighted. Finally, the method is applied to a simplified elliptical model of the cardiac left ventricle. 相似文献
80.
On the existence,uniqueness and stability of solutions for semi-linear generalized elasticity equation with general damping term 下载免费PDF全文
Abita Rahmoune 《数学学报(英文版)》2017,33(11):1549-1564
In this paper, we consider a semi-linear generalized hyperbolic boundary value problem associated to the linear elastic equations with general damping term and nonlinearities of variable exponent type. Under suitable conditions, local and global existence theorems are proved. The uniqueness of the solution have been gotten by eliminating some hypotheses that have been imposed by other authors for different particular problems. We show that any solution with nontrivial initial datum becomes stable. 相似文献