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991.
以双盘悬臂立式转子-轴承系统为研究对象,建立了系统运动微分方程,并用数值方法分析了在非线性密封力和非线性油膜力作用下的裂纹转子的动力学特性。分析表明,在一定深度裂纹下,转子系统响应随不同角频率比表现出复杂的非线性现象,出现了周期k运动、拟周期运动和混沌运动等多种运动形式。在一定角速度时,工作在远离临界角速度区的转子系统对裂纹非常敏感,而工作在近临界角速度区的转子系统对裂纹不是特别敏感,但是裂纹对它的运动状态影响较大。该研究结果为该类转子-轴承系统的安全运行与故障诊断提供了一定的理论参考。 相似文献
992.
Gurtin recently proposed a strain-gradient theory for crystal plasticity in which the gradient effect originates from a defect energy that characterizes energy storage due to the presence of a net Burgers vector. Here we consider a number of different possibilities for this energy: specifically, working within a simple two-dimensional framework, we compare predictions of the theory with results of discrete-dislocation simulations of stress relaxation in thin films. Our objective is to investigate which specific defect energies are capable of capturing the size-dependent response of such systems for different crystal orientations. 相似文献
993.
994.
995.
A great number of studies have shown the complex nonlinear dynamics of mechanical systems with repeated normal impacts. An
oblique frictional impact introduces even more complicated dynamics such as stick-slip motions to those systems. Hence, the
dynamics of oblique vibro-impacting systems with possible sliding motion is an open problem. Based on a hybrid analysis of
vibro-impact dynamics, kinematics and complementary conditions, a piecewise analysis method is developed in the paper to describe
the sliding motion during an oblique impact. Thereby, a parametrically excited planar pendulum between two parallel rigid
walls is studied as an illustrative example. The example, together with the corresponding numerical results, shows that the
sliding impacts occur in such a system with a set of properly selected parameters.
The project supported by the National Natural Science Foundation of China (59905010) and by the Scientific Research Foundation
for the Returned Overseas Chinese Scholars, Ministry of Education, China 相似文献
996.
997.
R.C. Mehta 《Shock Waves》2002,11(6):431-440
The pressure oscillations over a forward facing spike attached to an axisymmetric blunt body are simulated by solving time-dependent
compressible Navier–Stokes equations. The governing fluid flow equations are discretized in spatial coordinates employing
a finite volume approach which reduces the equations to semidiscretized ordinary differential equations. Temporal integration
is performed using the two-stage Runge–Kutta time stepping scheme. A global time step is used to obtain a time-accurate numerical
solution. The numerical computation is carried out for a freestream Mach number of 6.80 and for spike length to hemispherical
diameter ratios of 0.5, 1.0 and 2.0. The flow features around the spiked blunt body are characterized by a conical shock wave
emanating from the spike tip, a region of separated flow in front of the hemispherical cap, and the resulting reattachment
shock wave. Comparisons of the numerical results are made with the available experimental results, such as schlieren pictures
and the surface pressure distribution along the spiked blunt body. They are found to be in good agreement. Spectral analysis
of the computed pressure oscillations are performed employing fast Fourier transforms. The surface pressure oscillations over
the spike and phase plots exhibit a behaviour analogous to that of the Van der Pol equation for a self-sustained oscillatory
flow.
Received 28 February 2001 / Accepted 17 January 2002 相似文献
998.
This article focuses on the formulation of a hysteretic model used as anisolator restoring force model. The proposed model is based on operatorgoverning input and output functions that depend on the deflection andthe restoring force of the isolator. First, the mathematical formulationis demonstrated, then the hysteretic model proposed is applied toisolators having different types of behavior. The model parameters aresought using the experimental force-deflection loop of each of theisolators studied. Next, the transient response of a flexible structuremounted on an all-metal isolator is predicted by coupling the firstorder differential equation of the restoring force and the second orderdifferential equations of the structure's motion. The experimentalinvestigation validates the proposed hysteretic model applied to theall-metal mount. 相似文献
999.
A numerical method to estimate spectral properties of nonlinear oscillators with random input is presented. The stationary system response is expanded into a trigonometric Fourier series. A set of nonlinear algebraic equations, solved by Newtons method, leads to the determination of the unknown Fourier series coefficients of single samples of the response process. For cubic polynomial nonlinearities, closed-form expressions are used to find the nonlinear terms at each step of the solution scheme. Further, a simple procedure yields an approximation of an arbitrary nonlinearity by a cubic polynomial. Power spectral density estimates for the response process are constructed by averaging the square modulus of the computed Fourier coefficients over various samples or by means of well-established smoothing techniques of spectral analysis. Two applications are presented illustrating the effectiveness of the method as compared to statistical linearization and digital Monte-Carlo simulation. 相似文献
1000.
为了提高对边坡体力学行为的认识,借助于FLAC有限差分软件的数值模拟,并结和相似理论的推导验证,研究了在仅有自重体积力作用的条件下,线弹性边坡体的一些力学特征及其与相关变量或物理力学参数的相关关系。没有外载荷影响时边坡地表最大主应力和最小主应力分别平行和垂直于地表,当深度增加时,主应力的取向逐渐变成竖直和水平两个方向,坡面处既有张应力区也有拉应力区,坡脚处亦存在较大的张应力,这是自重体积力作用下边坡体应力分布的一般性特征,在本文和前人的研究中都能体现。本文还重点揭露了:坡角线性增加时坡顶最大张应力的变化速率表现为:快——慢——快; 沿坡顶面竖直向下张应力随深度增加线性减小; 小变形条件下边坡应力场与弹性模量无关; 最后验证了满足相似理论的坡体,坡面对应点的位移比是其几何尺寸比的平方倍。本文不仅是对既有研究成果的进一步补充,而且为以后研究复杂条件下边坡体的力学特征奠定了基础,对于理论和实践都有一定的启发意义。 相似文献