全文获取类型
| 收费全文 | 5248篇 |
| 免费 | 760篇 |
| 国内免费 | 160篇 |
专业分类
| 化学 | 937篇 |
| 晶体学 | 121篇 |
| 力学 | 1094篇 |
| 综合类 | 61篇 |
| 数学 | 1400篇 |
| 物理学 | 2555篇 |
出版年
| 2025年 | 5篇 |
| 2024年 | 115篇 |
| 2023年 | 106篇 |
| 2022年 | 151篇 |
| 2021年 | 175篇 |
| 2020年 | 183篇 |
| 2019年 | 183篇 |
| 2018年 | 175篇 |
| 2017年 | 167篇 |
| 2016年 | 198篇 |
| 2015年 | 201篇 |
| 2014年 | 252篇 |
| 2013年 | 343篇 |
| 2012年 | 319篇 |
| 2011年 | 295篇 |
| 2010年 | 285篇 |
| 2009年 | 314篇 |
| 2008年 | 269篇 |
| 2007年 | 286篇 |
| 2006年 | 257篇 |
| 2005年 | 249篇 |
| 2004年 | 218篇 |
| 2003年 | 203篇 |
| 2002年 | 193篇 |
| 2001年 | 137篇 |
| 2000年 | 125篇 |
| 1999年 | 90篇 |
| 1998年 | 94篇 |
| 1997年 | 83篇 |
| 1996年 | 71篇 |
| 1995年 | 52篇 |
| 1994年 | 48篇 |
| 1993年 | 32篇 |
| 1992年 | 42篇 |
| 1991年 | 34篇 |
| 1990年 | 37篇 |
| 1989年 | 19篇 |
| 1988年 | 27篇 |
| 1987年 | 27篇 |
| 1986年 | 11篇 |
| 1985年 | 17篇 |
| 1984年 | 21篇 |
| 1983年 | 5篇 |
| 1982年 | 8篇 |
| 1981年 | 7篇 |
| 1980年 | 7篇 |
| 1979年 | 5篇 |
| 1978年 | 12篇 |
| 1977年 | 5篇 |
| 1976年 | 6篇 |
排序方式： 共有6168条查询结果，搜索用时 0 毫秒
101.
The free (or open) boundary condition (FBC, OBC) was proposed by Papanastasiou et al. (A new outflow boundary condition, International Journal for Numerical Methods in Fluids, 1992; 14:587–608) to handle truncated domains with synthetic boundaries where the outflow conditions are unknown. In the present work, implementation of the FBC has been tested in several benchmark problems of viscous flow in fluid mechanics. The FEM is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal or non‐isothermal, steady‐state conditions, for Newtonian fluids. The effects of inertia, gravity, compressibility, pressure dependence of the viscosity, slip at the wall, and surface tension are all considered individually in the extrudate‐swell benchmark problem for a wide range of the relevant parameters. The present results extend previous ones regarding the applicability of the FBC and show cases where the FBC is inappropriate, namely in the extrudate‐swell problem with gravity or surface‐tension effects. Particular emphasis has been given to the pressure at the outflow, which is the most sensitive quantity of the computations. In all cases where FBC is appropriate, excellent agreement has been found in comparisons with results from very long domains. The formulation for Picard‐type iterations is given in some detail, and the differences with the Newton–Raphson formulation are highlighted regarding some computational aspects. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
102.
103.
104.
考虑实际坡度条件下, 提出了基于压力传感器的汽车重心与安全车速实时监测系统的多元力学模型. 建立了考虑车辆重心高度、路面纵横双向坡度及路面半径等因素的车辆安全车速控制力学模型, 并在三维模型分析的基础上提出监测与报警机理, 可为汽车安全系统提供安全车速与重心计算的多维力学模型, 为研制汽车安全车速实时监测系统提供了必要参数与依据. 相似文献
105.
Gravity‐driven Stokes flow down an inclined plane over and around multiple obstacles is considered. The flow problem is formulated in terms of a boundary integral equation and solved using the boundary element method. A Hermitian radial basis function (RBF) is used for the interpolation of the free surface, generation of the unit normal and curvature, and to prescribe the far‐field conditions. For flow over an obstacle, hemispheres are taken. For flow around an obstacle, circular cylinders are modelled and the contact angle condition on the obstacle/free surface intersection specified using the RBF formulation. Explicit profiles are produced for flow over and around two obstacles placed in various locations relative to one another. Interaction due to two obstacles is given by comparisons made with the profiles for flow over and around individual obstacles. In general, when the obstacles are separated by a sufficiently large distance the flow profiles are identical to a single obstacle analysis. For flow over and around two obstacles in‐line with the incident flow, effects of the governing parameters are examined, with variations in plane inclination angle, Bond number, obstacle size, and in the case of obstacles intersecting the free surface, static contact angle is considered. Finally flows over and around three obstacles are modelled. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
106.
This study extends the upstream flux‐splitting finite‐volume (UFF) scheme to shallow water equations with source terms. Coupling the hydrostatic reconstruction method (HRM) with the UFF scheme achieves a resultant numerical scheme that adequately balances flux gradients and source terms. The proposed scheme is validated in three benchmark problems and applied to flood flows in the natural/irregular river with bridge pier obstructions. The results of the simulations are in satisfactory agreement with the available analytical solutions, experimental data and field measurements. Comparisons of the present results with those obtained by the surface gradient method (SGM) demonstrate the superior stability and higher accuracy of the HRM. The stability test results also show that the HRM requires less CPU time (up to 60%) than the SGM. The proposed well‐balanced UFF scheme is accurate, stable and efficient to solve flow problems involving irregular bed topography. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
107.
In this paper, a novel reconstruction of the gradient and Hessian tensors on an arbitrary unstructured grid, developed for implementation in a cell‐centered finite volume framework, is presented. The reconstruction, based on the application of Gauss' theorem, provides a fully second‐order accurate estimate of the gradient, along with a first‐order estimate of the Hessian tensor. The reconstruction is implemented through the construction of coefficient matrices for the gradient components and independent components of the Hessian tensor, resulting in a linear system for the gradient and Hessian fields, which may be solved to an arbitrary precision by employing one of the many methods available for the efficient inversion of large sparse matrices. Numerical experiments are conducted to demonstrate the accuracy, robustness, and computational efficiency of the reconstruction by comparison with other common methods. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
108.
为了求得复杂刚体重心的位置, 根据转动惯量平行轴定理, 由已知轴转动惯量和一定的几何关系推导出用于求重心的关系式, 从理论上给出两个可能重心坐标值, 再实际判断取舍.只要用实验仪器先测量刚体对3个平行转轴的转动惯量, 就可由该关系式计算得到刚体重心的位置. 这一方法有时要比直接测量重心更为简单. 相似文献
109.
Simulations of the bearing capacity and shear strength of regolith under Earth’s gravity produce different results from those under low gravity. A low-gravity simulation device was developed in this study, and an internal stress model of regolith simulant was established to correct the errors. The model revealed additional force on both shear plane in the shear test and the press plate area in the pressure–sinkage test. The sinkage and shear test results showed that low gravity decreased the deformable index n, frictional modulus kφ and cohesion c, whereas there were no obvious changes to the cohesive modulus kc and internal friction angle φ. The sinkage generally increased as the gravity decreased under a consistent normal load larger than 50 N, but when the wheel load was lower than 50 N, the sinkage of the TYII-1 simulant was larger under 1 G than 1/6 G. Gravity had little effect on the shear strength of the regolith. However, the tractive thrust of the TYII-1 simulant was lower under 1/6 G than 1 G. The smaller difference was due to differences in the way the soils responded to changes in the gravity level for the TYII-2 simulant. 相似文献
110.
This paper is concerned with the development of efficient iterative methods for solving the linear system of equations arising from stochastic FEMs for single‐phase fluid flow in porous media. It is assumed that the conductivity coefficient varies randomly in space according to some given correlation function and is approximated using a truncated Karhunen–Loève expansion. Distinct discretizations of the deterministic and stochastic spaces are required for implementations of the stochastic FEM. In this paper, the deterministic space is discretized using classical finite elements and the stochastic space using a polynomial chaos expansion. The highly structured linear systems which result from this discretization mean that Krylov subspace iterative solvers are extremely effective. The performance of a range of preconditioned iterative methods is investigated and evaluated in terms of robustness with respect to mesh size and variability of the conductivity coefficient. An efficient symmetric block Gauss–Seidel preconditioner is proposed for problems in which the conductivity coefficient has a large standard deviation.The companion paper, herein, referred to as Part 2, considers the situation in which Gaussian random fields are transformed into lognormal ones by projecting the truncated Karhunen–Loève expansion onto a polynomial chaos basis. This results in a stochastic nonlinear problem because the random fields are represented using polynomial chaos containing terms that are generally nonlinear in the random variables. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献