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991.
G. P. Romano 《Applied Scientific Research》1996,56(2-3):209-220
The near flow field of an axisymmetric water jet at Reynolds numbers between 2000 and 5000 is investigated using Particle-Tracking Velocimetry. Measurements are taken in the longitudinal section (along the mean flow) and in cross-sections (orthogonal to the mean flow). From the former, correlation coefficients of the two in-plane velocity components in a Lagrangian framework are obtained: thus Lagrangian integral scales can be computed. Those of the streamwise velocity (axial) component increase on moving away from the centreline, whereas the opposite happens for the vertical velocity (radial) component: integral time scales of the two components are almost equal at the interface between jet and ambient fluids. On the other hand, integral scales are almost constant or increase slightly with the axial direction. In cross-sections, fluid ejection and injection from the jet centreline are observed to be connected to counter-rotating vortices (mushroom): their number and size change with Reynolds number in agreement with results from other authors. The maximum ejection velocity (orthogonal to the mean jet flow), at 3 nozzle diameters downstream of the outlet, is found to be one half of the mean outlet velocity. 相似文献
992.
A solute transport through a porous medium is examined provided that the fluid leaving the porous sample returns back in a continuous way. The porous medium is thus included into a closed hydrodynamic circuit. This cycling process is suggested as an experimental tool to determine porous medium parameters describing transport. In the present paper the mathematical theory of this method is developed. For the advective type of transport with solute retention and degradation in porous medium, the system of transport equations in a closed circuit is transformed to a delay differential equation. The exact analytical solution to this equation is obtained. The solute concentration manifests both the oscillatory and monotonous behaviors depending on system parameters. The number of oscillation splashes is shown to be always finite. The maximum/minimum points are determined as solutions of a polynomial equation whose degree depends on the unknown solution itself. The cyclic methods to determine porous medium parameters as porosity and retention rate are developed. 相似文献
993.
In this study, a high-resolution characteristic-based finite-volume (FV) method on unstructured grids [Int. J. Numer. Method Eng. 50 (2001) 11; Int. J. Heat Fluid Flow 21 (2000) 432] is extended by a matrix-free implicit dual-time stepping scheme for the numerical simulation of steady and unsteady flow and heat transfer with porous media. The method has been used to study the characteristics of a complex problem: flow and heat transfer in a channel with multiple discrete porous blocks, which was originally proposed by Huang and Vafai [J. Thermophys. Heat Transfer 8 (3) (1994) 563]. In addition, flow and heat transfer in a channel partially or fully filled with porous layers and containing solid protruding blocks with constant heat flux on its lower surface are also investigated in details. Hydrodynamic and heat transfer results are reported for both steady and transient flow cases. In particular, the effects of Darcy and Reynolds numbers on heat transfer augmentation and pressure loss are studied. An in-depth discussion of the formation and variation of recirculation is presented and the existence of optimum porous insert is demonstrated. At high Reynolds numbers the flow in the porous channel exhibits a cyclic characteristics although unlike the non-porous channel flow, the cyclic vortex development is only restricted to a small area behind the last solid block, while temperature changes more slowly and does not exhibit cyclic variations over a long period of time. It is shown that for all the cases studied altering some parametric values can have significant and interesting effects on both flow pattern as well as heat transfer characteristics. 相似文献
994.
本文旨在以矩阵的相似变换理论为基础,以电子计算机为工具,提供一种无需求解离散?矩阵方程,而直接由系统矩阵来构造离散时间系统?函数和判定系统稳定性的方法. 相似文献
995.
In this work, experimental determinations are carried out using a home-made device called an erythrodeformeter, which has
been developed and constructed for rheological measurements on red blood cells subjected to definite fluid shear stress. A
numerical method formulated on the basis of the fractal approximation for ordinary and fractionary Brownian motion1 is proposed to evaluate the viscoelastic behavior of mammalian erythrocyte membranes. The diffraction pattern, which is circular
when the mammalian erythrocyte membranes are at rest, becomes elliptical when the cells undergo shear stress. Photometric
readings of light intensity variation along the major axis of the elliptical diffraction pattern are recorded during the creep
and recovery process. These data series are used to calculate, fractal rheological parameters of self-affine Brownian motion
on the erythrocytes, averaged over several millions of cells. Three different parameters over the time dependent process could
be obtained, which are: correlation coefficient <C(t)>, correlation integral, andK
2-entropy, and very different results were obtained. 相似文献
996.
997.
998.
重庆“朝天扬帆”钢结构工程风振研究 总被引:1,自引:0,他引:1
“朝天扬帆”是位于重庆朝天间广场的钢结构雕塑工程,该工程建筑型体复杂、结构布局不规则,通过该雕塑工程缩尺模型的几洞试验,确定其风载计算的体型系数;用时程法计算结构的风振响应,且在模拟作用于结构上的脉动风时程曲线时考虑结构的高度相关性,应用ALGOR93软件对结构进行风振时程分析,并自编程序加以前、后处理。通过对比该结构在脉动风和平均风作用下的杆件内力、节点位移响应,约定结构风振系数,为该雕塑工程抗风设计参数的确定提供理论依据。 相似文献
999.
对线性系统模态控制及其时滞补偿进行研究。模态控制分控制全部模态和控制有限模态两种情况 ,时滞补偿采用移相补偿。最后结合算例对两种控制模态下的控制效果和控制有限模态时的时滞补偿进行了数值计算和结果对比 相似文献
1000.
Summary We study the two-dimensional instantaneous Stokes flow driven by gravity in a viscous triangular prism supported by a horizontal
rigid substrate and a vertical wall. The oblique side of the prism, inclined at an angle α with respect to the substrate,
is a fluid-air interface, where the stresses are zero and surface tension is neglected. We develop the stream function ψ in
polar coordinates (r,θ) centered at the vertex of α and split it into an inhomogeneous part, which accounts for gravity effects, and a homogeneous
part, which is expressed as a series expansion. The inhomogeneous part and the first term of the expansion may be envisioned,
respectively, as self-similar solutions of the first kind and of the second kind for r→0, each one holding in complementary α domains with a crossover at α
c
=21.47∘, which we study in some detail. The coefficients of the series are calculated by truncating the expansion and using the method
of direct collocation with a suitable set of points at the wall. The solution strictly holds for t=0, because later the free surface ceases to be a plane; nevertheless, it provides a good approximation for the early time
evolution of the fluid profile, as shown by the comparison with numerical simulations. For 0<α<45∘, the vertex angle remains constant and the edge remains strictly at rest; the transition at α
c
manifests itself through a change in the rate of growth of the curvature. The time at which the edge starts to move (waiting
time) cannot be calculated since the instantaneous solution ceases to be valid. For α>45∘, the instantaneous local solution indicates that the surface near the vertex is launched against the substrate so that the
edge starts to move immediately with a power law dependence on time t. However, due to the high value of the exponent, the vertex may seem to be at rest for some finite time even in this case.
Received 29 August 1997; accepted for publication 21 January 1998 相似文献