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31.
The objective of this study is to understand the flow structures of weak and strong spherical blast waves either propagating
in a free field or interacting with a flat plate. A 5th-order weighted essentially non-oscillatory scheme with a 4th-order
Runge-Kutta method is employed to solve the compressible Euler/Navier-Stokes equations in a finite volume approach. The real-gas
effects are taken into account when high temperature occurs. A shock-tube problem with the real-gas effect is first tested
in order to verify the solver accuracy. Moreover, unsteady shock waves moving over a stationary wedge with various wedge angles,
resulting in different types of shock wave reflections, are also tested. It is found that the computed results agreed well
with the existing data. Second, the propagation of a weak spherical blast wave, created by rupture of a high-pressure isothermal
sphere, in a free field is studied. It is found that there are three minor shock waves moving behind the main shock. Third,
the problem of a strong blast wave interacting with a flat plate is investigated. The flow structures associated with single
and double Mach reflections are reported in detail. It is found that there are at least three local high-pressure regions
near the flat plate.
Received 27 July 2000 / Accepted 25 January 2002 – Published online 17 June 2002 相似文献
32.
33.
应用二种截然不同的炸药PBX 95 0 1和T2 ,计算了爆轰波在不同入射角下与金属平板的斜相互作用。在正规反射区 ,计算结果与激波极线理论基本一致 ;应用燃烧模型 ,分别计算了Fe球壳装药JB90 0 3(HE)及JB90 14 (IHE)散心爆轰波的绕射传播 ,计算结果与实验很好地符合。在非正规反射区 ,二维拉氏程序计算结果明显地不同于经典理论结果 ,计算中没有出现Mach反射。计算结果显示 ,毗邻介质影响节点附近的爆轰波阵面形状及爆轰波速度 ;不同的反应率函数计算的节点图像不同。 相似文献
34.
The direct simulation Monte Carlo (DSMC) method is applied to simulation of nonstationary Mach reflection of strong shock waves. Normally the DSMC method is very time consuming in solving unsteady flow field problems especially for high Mach numbers, because of the necessity of iterative calculations to eliminate the inherent statistical fluctuation caused by a finite sample size. A central weighted smoothing technique is introduced to process the DSMC results, so that the iteration time can be significantly reduced. In spite of some relaxations of the shock wave structure, the smoothing technique is verified to be useful to estima te the flow fields qualitatively and even quantitatively by using a relatively small sample size. The comparison between the present approach and the kineticmodel approach (Xu et al. 1991a, 1991b) on the application to unsteady rarefied flow fields was also carried out.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
35.
François Golanski Véronique Fortuné Eric Lamballais 《Theoretical and Computational Fluid Dynamics》2005,19(6):391-416
The ability of Lighthill's analogy to predict the sound radiated by a transitional mixing layer is evaluated by means of direct
numerical simulation (DNS). The specific case of low Mach number flows with density variations is investigated. In order to
limit the global computational cost, the acoustic source information is based on numerical results where the sound waves have
been removed. It is shown that the low Mach number approximation coupled with the acoustic analogy can lead to very accurate
predictions for the radiated sound if the acoustic sources in Lighthill's equation are taken into account carefully. Results
for the acoustic intensity deduced from a repeated use of the Lighthill's analogy over a wide range of Mach numbers allow
us to discuss the adequacy of scaling laws proposed by previous authors (J. Sound Vib. 28(3), 563–585, 1973; 31(4), 391–397, 1973; 48(1), 95–111, 1976) for the prediction of noise from hot jets. 相似文献
36.
Jishan Fan Hongjun Gao Boling Guo 《Mathematical Methods in the Applied Sciences》2011,34(17):2181-2188
The low Mach number limit for classical solutions of the compressible magnetohydrodynamic equations without thermal conductivity is, here, studied. A uniform existence result for the Cauchy problem in is proved under the assumption that the initial data are uniformly bounded with respect to the Mach number in and are well‐prepared in . Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
37.
The impingement of an axisymmetric underexpanded ideal gas jet on a flat surface is investigated through numerical simulations. Different injection conditions, characterized by the nozzle pressure ratio (NPR), have been considered and for each, several standoff distances were studied. The study was conducted using the commercial finite volume general purpose code Fluent®. The numerical results are presented in terms of Mach number and static pressure to characterize the structure of the flow. Furthermore, the influence of the standoff distance upon the position and diameter of Mach disk is analysed. Some results are compared with literature data and good agreement is obtained. 相似文献
38.
In this paper, the authors study the piston problem for the unsteady
two-dimensional Euler system for a Chaplygin gas. The angle of the
piston is allowed to vary in a wide range. The piston can be pushed
forward into the static gas, or pulled back from the gas. The
global existence of solution to the piston problem with any initial
speed is established, and the structures of the global solutions are
clearly described. The authors find that for the proceeding piston
problem the front shock can be detached, attached or even adhere to
the surface of the piston depending on the parameters of the flow
and the piston; while for the receding problem the front rarefaction
wave is always detached and the concentration will never occur. 相似文献
39.
Jae-Soo Kim 《国际流体数值方法杂志》1993,17(7):567-587
The unsteady flow over an oscillatory NACA0012 aerofoil has been simulated by the calculation with Euler equations. The equations are discretized by an implicit Euler in time, and a second-order space-accurate TVD scheme based on flux vector splitting with van Leer's limiter. Modified eigenvalues are proposed to overcome the slope discontinuities of split eigenvalues at Mach = 0·0 and ± 1·0, and to generate a bow shock in front of the aerofoil. A moving grid system around the aerofoil is generated by Sorenson's boundary fitted co-ordinates for each time step. The calculations have been done for two angles of attack θ = 5·0° sin (ωt) and θ = 3·0° + 3·0° sin (ωt) for the free-stream Mach numbers 2·0 and 3·0. The results show that pressure and Mach cells flow along characteristic lines. To examine unsteady effects, the responses of wall pressure and normal force coefficients are analysed by a Fourier series expansion. 相似文献
40.
A finite volume method for inviscid unsteady flows at low Mach numbers is studied. The method uses a preconditioning of the
dissipation term within the numerical flux function only. It can be observed by numerical experiments that the preconditioned
scheme combined with an explicit time integrator is unstable if the time step Δt does not satisfy the requirement to be
as the Mach number M tends to zero, whereas the corresponding standard method remains stable up to
, M → 0, though producing unphysical results.
A comprehensive mathematical substantiation of this numerical phenomenon by means of a von Neumann stability analysis is presented,
which reveals that in contrast to the standard approach, the dissipation matrix of the preconditioned numerical flux function
possesses an eigenvalue growing like M–2 as M tends to zero, thus causing the diminishment of the stability region of the explicit scheme. The theoretical results are
afterwards confirmed by numerical experiments.
AMS subject classification (2000) 35L65, 35C20, 76G25 相似文献