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181.
The variation of main turbulent quantities in an isotropic turbulent flow, such as the decay of turbulent energy and the variation
of Taylor microscale of turbulence with time are obtained, by employing a hot-wire anemometer and a nearly isotropic turbulent
flow which is produced by a gridscreen located at the entrance of the test section in a low-level turbulence and low-speed
wind tunnel in Peking University. The experimental results of the decay of turbulent energy and the variation of Taylor microscale
of turbulence with time at the whole period from initial to final stage, normalized in an non-dimensional form, are consistent
quite well with the computational results by the theory of the statistical vorticity structure[1]. The experimental results presented in this paper also agree with Townsend's results obtained in earlier years[2] as well as with Bennett's in the seventy's[3]. 相似文献
182.
关于无振荡、无自由参数有限元格式的研究 总被引:2,自引:0,他引:2
利用双曲守恒律方程的Taylor弱解表达式,建立了有限元法修正方程,选择合适的展开式系数能得到一系列数值格式.通过稳定性分析研究了格式的稳定性、色散误差与有限元修正方程导数项系数之间的关系,该关系与差分法的NND格式一致.在选定格式下,通过CFL数可控制有限元离散解的振荡而使格式不含自由参数.最后,用数值算例验证了这一关系,并在二、三维欧拉方程作了推广应用. 相似文献
183.
184.
The Coriolis effect on a solidifying mushy layer is considered. A near-eutectic approximation and large far-field temperature is employed in the current study for large Stefan numbers. The linear stability theory is used to investigate analytically the Coriolis effect on convection in a rotating mushy layer for a new formulation of the Darcy equation. It was found that a large Stefan number scaling allows for the presence of both the stationary and oscillatory modes of convection. In contrast to the problem of a stationary mushy layer, rotating the mushy layer has a stabilising effect on convection. It was observed that increasing the Taylor number or the Stefan number encouraged the oscillatory mode of convection. 相似文献
185.
Wave angle for oblique detonation waves 总被引:3,自引:0,他引:3
The flow field associated with a steady, planar, oblique detonation wave is discussed. A revision is provided for- diagrams, where is the wave angle and is the ramp angle. A new solution is proposed for weak underdriven detonation waves that does not violate the second law. A Taylor wave, encountered in unsteady detonation waves, is required. Uniqueness and hysteresis effects are also discussed.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
186.
Dynamics of explosion bubbles formed during underwater detonations are studied experimentally by exploding fuel (hydrogen and/or carbon monoxide)–oxygen mixture in a laboratory water tank. Sub-scale explosions are instrumented to provide detailed histories of bubble shape and pressure. Using geometric and dynamic scaling analyses it has been shown that these sub-scale bubbles are reasonable approximations of bubbles formed during deep sea underwater explosions. The explosion bubble undergoes pulsation and loses energy in each oscillation cycle. The observed energy loss, which cannot be fully explained by acoustic losses, is shown here to be partly due to the excitation of instability at the interface between the gaseous bubble and the surrounding water. Various possible mechanisms for the dissipation of bubble energy are addressed. The analysis of the experimental data gives quantitative evidence (confirmed by recent numerical studies) that the Rayleigh–Taylor instability is excited near the bubble minimum. The dynamics of the bubble oscillation observed in these experiments are in good agreement with experimental data obtained from deep sea explosions 相似文献
187.
The coriolis effect on a solidifying mushy layer is considered. A near-eutectic approximation and large far-field temperature is employed in the current study for moderate Stefan numbers. The linear stability theory is used to investigate analytically the Coriolis effect on convection in a rotating mushy layer for a new formulation of the Darcy equation. It was found that only stationary convection is possible for moderate Stefan numbers. In contrast to the problem of a stationary mushy layer, rotating the mushy layer has a stabilizing effect on convection. It was also discovered that fot Taylor numbers larger than three (i.e., Ta > 3),increasing the retardability coefficient (hence increasing the solid fraction) destablished the convection. 相似文献
188.
Saneshan Govender 《Transport in Porous Media》2005,58(3):361-369
The current study investigates the Stefan number effect on the transition from stationary to oscillatory convection in a rotating mushy layer where the near eutectic approximation is applied. It is found that for rotating solidifying systems exhibiting a Stefan number of unit order (i.e., St=1), stationary convection is only possible up to Ta=3. Beyond Ta=3, for St=1, it is found that the oscillatory mode is the most dangerous mode of convection. A map showing the region of occurrence of the oscillatory mode is also presented for a range of Stefan numbers. The map reveals that the oscillatory mode is the most dangerous mode for intermediate values of Stefan number whilst the stationary mode is the most dangerous mode for very small and very large values of Stefan number. It is also demonstrated that increasing the rotation rate serves to render the oscillatory mode as the becoming the most dangerous mode of convection. 相似文献
189.
对函数f(x)的n阶Taylor公式中的Lagrange型余项Rn(x)是否能用f(x)的(n+1)阶导数表示,又能用(n+2)阶导数表示进行了研究,得到了用f(x)的(n+1)阶导数、(n+2)阶导数表示均可的结论,从而使奇偶函数展为Taylor公式更加灵活. 相似文献
190.