全文获取类型
收费全文 | 8162篇 |
免费 | 699篇 |
国内免费 | 768篇 |
专业分类
化学 | 2017篇 |
晶体学 | 22篇 |
力学 | 914篇 |
综合类 | 171篇 |
数学 | 5097篇 |
物理学 | 1408篇 |
出版年
2024年 | 6篇 |
2023年 | 75篇 |
2022年 | 102篇 |
2021年 | 141篇 |
2020年 | 184篇 |
2019年 | 208篇 |
2018年 | 223篇 |
2017年 | 241篇 |
2016年 | 288篇 |
2015年 | 205篇 |
2014年 | 375篇 |
2013年 | 605篇 |
2012年 | 418篇 |
2011年 | 456篇 |
2010年 | 424篇 |
2009年 | 498篇 |
2008年 | 525篇 |
2007年 | 559篇 |
2006年 | 477篇 |
2005年 | 466篇 |
2004年 | 386篇 |
2003年 | 388篇 |
2002年 | 315篇 |
2001年 | 263篇 |
2000年 | 244篇 |
1999年 | 213篇 |
1998年 | 181篇 |
1997年 | 142篇 |
1996年 | 139篇 |
1995年 | 94篇 |
1994年 | 142篇 |
1993年 | 84篇 |
1992年 | 93篇 |
1991年 | 62篇 |
1990年 | 55篇 |
1989年 | 48篇 |
1988年 | 41篇 |
1987年 | 38篇 |
1986年 | 37篇 |
1985年 | 39篇 |
1984年 | 34篇 |
1983年 | 11篇 |
1982年 | 30篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1969年 | 3篇 |
排序方式: 共有9629条查询结果,搜索用时 15 毫秒
81.
V. A. Storozhenko 《International Applied Mechanics》2003,39(12):1464-1472
A technique is proposed to identify the principal central axis of inertia in a joint-suspended inhomogeneous rigid body from its vertical revolution. The problem is reduced to synchronizing the revolution of the body with the revolution of a fictitious mathematical pendulum 相似文献
82.
There exist a sufficient condition for the existence of at least one periodic solution for a type of second order autonomous ordinary differential equations. The correctness of the condition has been pointed out by Schauder's fixed point theorem. In order to indicate the validity of the assumptions made, two illustrative examples, showing its application in the nonlinear vibration and relaxation oscillation are presented. 相似文献
83.
王向东 《应用数学和力学(英文版)》1998,(6)
I.IntroductionLetFbethen-dimensionalEuclideanspaceandGaboundeddomaininM,WI(C)andM(C)beusualSobolevspaces.Let0相似文献
84.
DRIVING FORCE AND DEFORMATION ANALYSIS FOR DYNAMIC CRACK PROPAGATION IN GAS PIPELINES UNDER DIFFERENT BOUNDARY CONDITIONS 总被引:1,自引:0,他引:1
Zhuang Zhuo 《Acta Mechanica Solida Sinica》1997,10(1):86-94
In the light of a growing need for fracture control of rapid crack propagation(RCP)ingas pipelines,a program PFRAC(Pipeline FRacture Analysis Code)has been developed to analysethc various events.In this paper,by using PFRAC for the simulation of axial crack propagation in gaspipelines,a number of dynamic analysis issues rclating to boundary effects for uncracked and crackedpipes are investigated.This indicates that the boundary conditions along the length of the pipe play animportant role for fracture analysis in the pipe.In contrast.the boundary condutions at thc ends of along pipeline have little effect on the dynamic fracture events. 相似文献
85.
A closed form solution to the convective instability in a composite system of fluid and porous layers with vertical throughflow is presented. The boundaries are considered to be rigid-permeable and insulating to temperature perturbations. Flow in the porous layer is governed by Darcy–Forchheimer equation and the Beavers–Joseph condition is applied at the interface between the fluid and the porous layer. In contrast to the single-layer system, it is found that destabilization due to throughflow arises, and the ratio of fluid layer thickness to porous layer thickness, , too, plays a crucial role in deciding the stability of the system depending on the Prandtl number. 相似文献
86.
讨论螺旋细杆的特殊形式扭转振动,即均匀扭转振动.以非圆截面杆和有原始曲率的圆截面杆为研究对象.杆作均匀扭转振动时各截面有相同的扭角变化规律,且杆中心线的几何形状不受振动过程的影响.研究表明,扭振来源于杆截面的非对称性及杆的原始曲率.杆的扭振规律与单摆运动相似,其动力学方程存在精确解.圆环杆的均匀扭振为螺旋杆的倾角为零时的特例. 相似文献
87.
Redistribution of a LNAPL lens (oil) at the phreatic surface is described using a multi-phase flow model, with emphasis on the effect of oil entrapment by water. The flow process is analyzed under the assumption that the vertical capillary and gravitational forces balance. Vertical integration leads to explicit functions which approximate the relations between the free oil volume per unit lateral area and the vertically averaged oil relative permeability on the one hand and the vertical position of the interface between zones with either two or three phases on the other hand. A linear relation between the trapped and free oil volume per unit lateral area approximates the vertically integrated nonlinear expression for the trapped oil saturation. The resulting differential equation admits a similarity solution describing the lateral spreading of free oil and the amount and location of trapped oil. Comparison with illustrative numerical computations, which are based on the nonreduced flow model in a two-dimensional planar or axisymmetric domain, shows that the analytical solution provides a good approximation of the free oil distribution at all later times. 相似文献
88.
Experiments on polymers indicate that large tensile stress can induce cavitation, that is, the appearance of voids that were
not previously evident in the material. This phenomenon can be viewed as either the growth of pre-existing infinitesimal holes
in the material or, alternatively, as the spontaneous creation of new holes in an initially perfect body. In this paper our
approach is to adopt both views concurrently within the framework of the variational theory of nonlinear elasticity. We model
an elastomer on a macroscale as a void-free material and, on a microscale, as a material containing certain defects that are
the only points at which hole formation can occur. Mathematically, this is accomplished by the use of deformations whose point
singularities are constrained. One consequence of this viewpoint is that cavitation may then take place at a point that is
not energetically optimal. We show that this disparity will generate configurational forces, a type of force identified previously
in dislocations in crystals, in phase transitions in solids, in solidification, and in fracture mechanics.
As an application of this approach we study the energetically optimal point for a solitary hole to form in a homogeneous and
isotropic elastic ball subject to radial boundary displacements. We show, in particular, that the center of the ball is the
unique optimal point. Finally, we speculate that the configurational force generated by cavitation at a non-optimal material
point may be sufficient to result in the onset of fracture. The analysis utilizes the energy-momentum tensor, the asymptotics
of an equilibrium solution with an isolated singularity, and the linear theory of elasticity at the stressed configuration
that the body occupies immediately prior to cavitation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
89.
本文研究溶质在作圆管和渠道层流的微极流体中的弥散规律,考虑了化学反应效应。利用Erinyen的微极流体理论,无偶应力边界条件和Taylor简化假定,导出相对浓度分布C和等效扩散系数D*的解析式,并作数值计算,分析了微极参数λ.k0和化学反应率参数β对上述量的影响。 相似文献
90.
Axisymmetric impingement of a hot jet on a flat plate: equilibrium flow analysis of high-temperature air 总被引:1,自引:0,他引:1
The flow structure of an underexpanded supersonic jet with high reservoir temperature impinging on a flat plate has been numerically investigated using a Total Variation Diminishing (TVD) scheme. When the temperature of the flow field is high enough to cause chemical reaction, the specific heat ratio,, is no longer equal to 1.4, nor constant. This explains the difference found in the literature between the flow properties of the calorically perfect gas and that of the chemically reacting flow. Under the equilibrium flow assumption the effect of high temperature gas on the impinging jet has been taken into account in the present paper by using specific heat ratio and speed of sound given by correlation polynomials of thermodynamic variables. The limiting case of cold jet calculation in the present numerical results agreed well with the existing experimental data. For the equilibrium jet with high reservoir temperature,T
o=1000K, qualitative support of the present result has been provided by means of the approximation theory.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献