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61.
An analysis of steady laminar mixed-convection heat transfer from a rotating or nonrotating axisymmetric body is presented. A mixed-convection parameter is proposed to serve as a controlling parameter that determines the relative importance of the forced and the free convection. In addition, a rotation parameter is introduced to indicate the relative contributions of the flow forced convection and the rotational forced convection. The values of both these two parameters lie between 0 and 1. Furthermore, the coordinates and dependent variables are transformed to yield computationally efficient numerical solutions that are valid over the entire range of mixed convection from the forced-convection limit (rotating or nonrotating bodies) to the pure free-convection limit (non-rotating bodies) and the entire regime of forced convection from the pure flow forced-convection limit (nonrotating bodies) to pure rotational forced-convection limit (rotating bodies). The effects of mixed-convection intensity, body rotation, fluid suction or injection, and fluid Prandtl number on the velocity profiles, the temperature profiles, the skin-friction parameter, and heat transfer parameter are clearly illustrated for both cases of buoyancy assisting and opposing flow conditions. 相似文献
62.
分段吸气高层建筑减阻性能的数值研究 总被引:1,自引:0,他引:1
为减小高层建筑的风致阻力, 采用CFD方法研究了主动吸气控制下高层建筑模型的风载荷减阻性能,
分析了竖向开孔位置、吸气孔高度和吸气速度等参数对减阻性能的影响,
并详细展示流场,讨论吸气控制机理. 结果表明: 保持流量系数不变,
增加吸气孔高度(或减小吸气速度)使得模型各表面的风压折减效
率$\eta_{\rm{PR}}$, 阻
力折减效率$\eta_{\rm{DR}}$和基底弯矩折减效率$\eta_{\rm{MR}}$增大,
且只有$\eta_{\rm{MR}}$在较大吸气孔高度时超过1.0. 拟合了$\eta_{\rm{DR}}$
和$\eta_{\rm{MR}}$关于吸气孔中心高度、吸气孔高度和吸气速度的经验公式,
为分段吸气控制的应用提供参考. 基于最大风压折减效率和最小吸气功率,比较了
各分段吸气模型和全高吸气模型的减阻性能,
发现全高吸气模型的减阻性能优于分段吸气模型.
可在高层建筑中上部设置吸气装置来减小基底弯矩或改善其局部风压特性. 相似文献
63.
Ataollah Asgharian Davood D. Ganji Soheil Soleimani Sina Asgharian Nima Sedaghaty zade Behzad Mohammadi 《Mathematical Methods in the Applied Sciences》2011,34(18):2209-2217
An analytical study is performed on heat and mass transfer in MHD‐free convection from a moving permeable vertical surface and the results are compared with previous works on this phenomenon to test the validity. The coupled equations of boundary layer are transformed from their non‐linear form to ordinary form using similarity transformation and then are solved by a newly developed method, homotopy analysis method. Having different base functions, homotopy analysis method provides us with great freedom in choosing the solution of a nonlinear problem. Solving the boundry layer equations, the effects of different parameters such as magnetic field strength parameter (M), Prandtl number (Pr), Schmidt number (Sc), buoyancy ratio and suction/blowing parameter (fw) on velocity, temperature, and concentration profiles are taken into consideration. Obtained results show that increment of magnetic field strength parameter (M) leads to decrease in velocity profile. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
64.
65.
66.
Mei Lin Bo Su Shi-Cong Li Yan-Tao Yin Qiu-Wang Wang Yi-Tung Chen 《Journal of Turbulence》2018,19(8):621-646
The streamwise and the spanwise velocity time series are measured from the wall to the centre of the cross duct for the flow in a rectangular T-junction duct, which is similar to airflow conditions of high-speed train ventilation system. The turbulent statistical properties are reported at three streamwise locations which correspond to the upstream/downstream and the centreline of the T-junction (x/D?=?±1 and 0, respectively). Turbulence intensities, skewness and flatness factor, as well as probability density functions, have been investigated at the range of Reτ?=?5400–8700. Furthermore, the multiscale properties of the flatness factor are analysed by using orthogonal wavelet transform. It is found that the turbulent intensities remain a constant in the centre region for three streamwise locations while they are weakened in the turbulent boundary layer at x/D?=?1 by effect of suction. The location of the strongest intermittency is located at y/h?=?0.56 for x/D?=??1 and 0. While at downstream of T-junction (x/D?=?1), the location of the strongest intermittency shifts down to y/h?=?0.28. Also, the wavelet flatness factor is more clearly distinguished the intermittency of the small-scale turbulent structure compared with the conventional flatness factor and, the obtained experimental data are fitted and used to predict the mean streamwise velocity profiles. 相似文献
67.
R. RAVINDRAN M. GANAPATHIRAO 《应用数学和力学(英文版)》2013,34(11):1327-1338
The aim of this work is to study the effect of non-uniform single and double slot suction/injection into a steady mixed convection boundary layer flow over a vertical cone, while the axis of the cone is inline with the flow. The governing boundary layer equations are transformed into a non-dimensional form by a group of non-similar trans- formations. The resulting coupled non-linear partial differential equations are solved nu- merically by employing the quasi-linearization technique and an implicit finite-difference scheme. Numerical computations are performed for different values of the dimensionless parameters to display the velocity and temperature profiles graphically. Also, numerical results are presented for the skin friction and heat transfer coefficients. Results indicate that the skin friction and heat transfer coefficients increase with non-uniform slot suction, but the effect of non-uniform slot injection is just opposite. 相似文献
68.
Chao-Rong Zheng Yao-Chun Zhang Wen-Yuan Zhang 《International Journal of Computational Fluid Dynamics》2013,27(2):59-74
Separation control over a backward-facing step (BFS) flow by continuous suction was numerically investigated using the turbulence model of large eddy simulation (LES). The effect of suction control on the flow fields was scrutinised by altering the suction flow coefficient, and the results indicate that suction is not only very effective in shortening the reattachment length but also very influential in reducing the tangential velocity gradient and turbulence fluctuations of the reattached flows. With increasing increments of the absolute suction flow coefficient, the effect of suction control is more significant. Furthermore, the detailed flow fields (including the time-averaged stream and velocity fields) and turbulence characteristics (including the time-averaged resolved kinetic energy and RMS velocity) for the BFS models with or without suction are presented to discuss the mechanism of suction control. Comparisons of the time-averaged statistics between the numerical simulations and corresponding experiments are conducted, and it shows that the LES based on the dynamic kinetic energy subgrid-scale model (DKEM) can acquire exact results. Therefore, feasibility of the numerical methods to simulate suction-controlled models is validated. 相似文献
69.
In the present study, a flow control method is employed to mitigate vortex-induced vibration (VIV) of a circular cylinder by using a suction flow method. The VIV of a circular cylinder was first reproduced in a wind tunnel by using a spring–mass system. The time evolution of the cylinder oscillation and the time histograms of the surface pressures of 119 taps in four sections of the circular cylinder model were measured during the wind tunnel experiments. Four steady suction flow rates were used to investigate the effectiveness of the suction control method to suppress VIV of the circular cylinder. The vibration responses, the mean and fluctuating pressure coefficients, and the resultant aerodynamic force coefficients of the circular cylinder under the suction flow control are analyzed. The measurement results indicate clearly that the steady suction flow control method exhibits excellent control effectiveness and can distinctly suppress the VIV by dramatically reducing the amplitudes of cylinder vibrations, fluctuating pressure coefficients and lift coefficients of the circular cylinder model. By comparing the test cases with different suction flow rates, it is found that there exists an optimal suction flow rate for the maximum VIV control. The cases with higher suction flow rates do not necessarily behave better than those with lower suction flow rates. With the experimental setting used in the present study, the suction flow control method is found to behave better for VIV suppression when the ratio of the suction flow velocity to the oncoming flow velocity is less than one. 相似文献
70.
Rafael Cortell 《Applied mathematics and computation》2010,217(8):4086-4093
This paper presents an analysis of the boundary value problem resulting from the magnetohydrodynamic (MHD) viscous flow influenced by a shrinking sheet with suction for the cases of two-dimensional (m = 1) and axisymmetric (m = 2) shrinking. The influences of the parameter m as well as the effects of suction parameter s and Hartmann number M2 on similar entrainment velocity f(∞) and flow characteristics are studied. To this purpose, the resulting nonlinear ordinary differential equation is solved numerically using the 4th order Runge-Kutta method in combination with a shooting procedure. The obtained results elucidate reliability and efficiency of the technique from which interesting features between the skin friction coefficient f″(0) and the entrainment velocity f(∞) as function of the mass transfer parameter s can also be obtained. 相似文献