全文获取类型
收费全文 | 48916篇 |
免费 | 6185篇 |
国内免费 | 4886篇 |
专业分类
化学 | 12290篇 |
晶体学 | 950篇 |
力学 | 12139篇 |
综合类 | 702篇 |
数学 | 19237篇 |
物理学 | 14669篇 |
出版年
2024年 | 62篇 |
2023年 | 503篇 |
2022年 | 766篇 |
2021年 | 1032篇 |
2020年 | 1382篇 |
2019年 | 1171篇 |
2018年 | 1213篇 |
2017年 | 1706篇 |
2016年 | 1926篇 |
2015年 | 1487篇 |
2014年 | 2470篇 |
2013年 | 3559篇 |
2012年 | 2856篇 |
2011年 | 3336篇 |
2010年 | 2829篇 |
2009年 | 3184篇 |
2008年 | 3133篇 |
2007年 | 3140篇 |
2006年 | 2904篇 |
2005年 | 2693篇 |
2004年 | 2339篇 |
2003年 | 2156篇 |
2002年 | 1921篇 |
2001年 | 1611篇 |
2000年 | 1428篇 |
1999年 | 1322篇 |
1998年 | 1189篇 |
1997年 | 1017篇 |
1996年 | 834篇 |
1995年 | 823篇 |
1994年 | 698篇 |
1993年 | 533篇 |
1992年 | 556篇 |
1991年 | 437篇 |
1990年 | 354篇 |
1989年 | 260篇 |
1988年 | 195篇 |
1987年 | 156篇 |
1986年 | 110篇 |
1985年 | 143篇 |
1984年 | 124篇 |
1983年 | 72篇 |
1982年 | 78篇 |
1981年 | 54篇 |
1980年 | 32篇 |
1979年 | 49篇 |
1978年 | 33篇 |
1977年 | 41篇 |
1976年 | 15篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
车辆与轨道的动态相互作用,是铁路轮轨接触式运输系统中最基本的问题之一,它直接制约着铁路运营速度的提高和运载重量的增加,也影响着铁路安全运行。本文采用有限元方法,对我国C61型运煤货车,按照车辆/轨道系统的实际几何形状、材料性质和边界条件建立了包括车辆和轨道系统的有限元模型,应用大型非线性动力分析程序LS-DYNA3D来模拟车辆通过轨道错牙接头时的轮/轨动态响应过程。计算结果表明车轮和轨道之间的竖向动态接触力大约是静轮载的2倍,与已有的现场试验结果基本吻合。因此应用有限元方法研究车辆/轨道耦合系统是可行和可靠的。 相似文献
992.
Parametric analysis of lugged wheel performance for a lunar microrover by means of DEM 总被引:1,自引:0,他引:1
H. Nakashima H. Fujii A. Oida M. Momozu Y. Kawase H. Kanamori S. Aoki T. Yokoyama 《Journal of Terramechanics》2007,44(2):153-162
The purpose of this study was to develop a numerical tool to simulate the performance of lugged wheels designed for a lunar microrover. The performance was analyzed using a Discrete Element Method (DEM) whose accuracy was validated for interactions between lugged wheels and soil. DEM analysis indicated that, on flat horizontal lunar surfaces, wheels with 18 10-mm-high lugs would provide less net traction than would wheels with 36 5-mm-high lugs. 相似文献
993.
One-dimensional unsteady inertial flow in phreatic aquifers induced by a sudden change of the boundary head 总被引:2,自引:0,他引:2
Konstadinos N. Moutsopoulos 《Transport in Porous Media》2007,70(1):97-125
We are examining the classical problem of unsteady flow in a phreatic semi-infinite aquifer, induced by sudden rise or drawdown
of the boundary head, by taking into account the influence of the inertial effects. We demonstrate that for short times the
inertial effects are dominant and the equation system describing the flow behavior can be reduced to a single ordinary differential
equation. This equation is solved both numerically by the Runge-Kutta method and analytically by the Adomian’s decomposition
approach and an adequate polynomial-exponential approximation as well. The influence of the viscous term, occurring for longer
times, is also taken into account by solving the full Forchheimer equation by a finite difference approach. It is also demonstrated
that as for the Darcian flow, for the case of small fluctuations of the water table, the computation procedure can be simplified
by using a linearized form of the mass balance equation. Compact analytical expressions for the computation of the water stored
or extracted from an aquifer, including viscous corrections are also developed. 相似文献
994.
E. Héripré M. Dexet J. Crépin L. Gélébart A. Roos M. Bornert D. Caldemaison 《International Journal of Plasticity》2007
This paper presents a methodology for multiscale coupling between the morphology and texture of a microstructure as has been characterised experimentally, and the results of mechanical strain field analysis. This methodology is based on a coupling between experimental characterisation of the microstructure, in situ and/or ex situ mechanical tests, local strain field measurements performed at the grain scale, and finite element simulations. First, with orientation imaging microscopy, a map of the microstructure is generated that can be meshed. Then, finite element calculations are carried out on this mesh, using a constitutive law which takes into account the crystallographic orientation of each grain, as has been determined by the orientation imaging itself. These numerical results are then compared to the experimental strain field as obtained by digital image correlation at the scale of the grains. 相似文献
995.
996.
为精确模拟预应力钢桁架中连续长索在支撑点的滑动,本文创建了一种考虑摩擦力影响的新单元。被称为摩擦滑移索单元的新单元有三个节点,中间节点为支撑点。本文首先利用弹性悬链线的解析解,建立了弹性悬链线单元,并推导了单元两端点的张拉刚度。摩擦滑移索单元由两个弹性悬链线单元组合而成,根据支撑点处索的滑动方向、索力差、滑动摩擦力和滑移刚度调整两索段的原长,使支撑点两侧的索力满足给定的摩擦关系。算例验证了新单元算法的正确性和高效性,对设计的预应力钢桁架的分析,显示了张拉过程中及使用荷载作用下新单元在结构分析中的应用。新单元可直接用于常规的有限元分析,研究在工作状态或施工中存在连续长索滑移的索结构。 相似文献
997.
998.
Particle-laden water flows past a circular cylinder were numerically investigated. The discrete vortex method (DVM) was employed to evaluate the unsteady water flow fields and a Lagrangian approach was applied for tracking individual solid particles. A dispersion function was defined to represent the dispersion scale of the particle. The wake vortex patterns, the distributions and the time series of dispersion functions of particles with different Stokes numbers were obtained. Numerical results show that the particle distribution in the wake of the circular cylinder is closely related to the particle's Stokes number and the structure of wake vortices: (1) the intermediate sized particles with Stokes numbers, St, of 0.25, 1.0 and 4.0 can not enter the vortex cores and concentrate near the peripheries of the vortex structures, (2) in the circular cylinder wake, the dispersion intensity of particles decreases as St is increased from 0.25 to 4.0. 相似文献
999.
A new nonlinear wave equation of a finite deformation elastic circular rod simultaneously introducing transverse inertia and shearing strain was derived by means of Hamilton principle. The nonlinear equation includes two nonlinear terms caused by finite deformation and double geometric dispersion effects caused by transverse inertia and transverse shearing strain. Nonlinear wave equation and corresponding truncated nonlinear wave equation were solved by the hyperbolic secant function finite expansion method. The solitary wave solutions of these nonlinear equations were obtained. The necessary condition of these solutions existence was given also. 相似文献
1000.
MAXIMAL ELEMENTS OF A FAMILY OF GB-MAJORIZED MAPPINGS IN PRODUCT FC-SPACES AND APPLICATIONS 总被引:1,自引:1,他引:1
丁协平 《应用数学和力学(英文版)》2006,27(12):1607-1618
A new family of GB-majorized mappings from a topological space into a finite continuous topological spaces (in short, FC-space) involving a better admissible set-valued mapping is introduced. Some existence theorems of maximal elements for the family of GB-majorized mappings are proved under noncompact setting of product FCspaces. Some applications to fixed point and system of minimax inequalities are given in product FC-spaces. These theorems improve, unify and generalize many important results in recent literature. 相似文献