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361.
O. E. Ivashnev 《Fluid Dynamics》2008,43(3):390-401
Experiments show that in low-and high-velocity flows the boiling process is fundamentally different: in the former, the fluid boils on the walls, and in the latter in the volume. In high-velocity flows, the boiling intensity is orders of magnitude greater. In modeling fast and slow flows, the number of bubbles, which is a free parameter of the model and must be specified, differs by orders of magnitude. When high-speed flows of different kinds are modeled (vessel depressurization, nozzle flows) the number of bubbles specified also differs by orders of magnitude. In this study, we formulate the hypothesis that in both kinds of flows the process of boiling starts similarly, namely, on the walls. However, in high-speed flows the number of bubbles increases by orders of magnitude due to bubble fragmentation. As a result of intense fragmentation, the system “forgets” the initial number of bubbles and the process becomes volume boiling. This approach makes it possible to construct a universal model of boiling. To test this hypothesis, we constructed a mathematical model which takes into account the possibility of bubble fragmentation due to the instability developing under the action of centrifugal accelerations of the bubble surface. This model was used to calculate the process of depressurization of a high-pressure vessel. The calculations demonstrated that, for any initial number of bubbles, 1 ms after depressurization the bubble number attains the same level. Bubble fragmentation takes place in “self-sustained detonation waves”. The stationary structure of detonation waves in a boiling fluid is investigated. A scheme of the wave structure according to which the wave consists of a shock wave and a relaxation zone is proposed. Calculations of a boiling-fluid flow through a Laval nozzle reveal the periodic appearance of detonation waves. Accordingly, nozzle flows should be accompanied by significant oscillations of the parameters. 相似文献
362.
The resolution by Chen and Sun of divergent Chapman–Enskog expansion problem will not only build a unified foundation for non-equilibrium dynamics modeling at all Mach number and Knudsen number, but also shed light to a large class of difficult theoretical problems involving divergent expansion on strong nonlinearity. 相似文献
363.
Photon-assisted electronic and spin transport through two T-shaped three-quantum-dot molecules embedded in an Aharonov-Bohm interferometer
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We investigate the time-modulated electronic and spin transport properties through two T-shaped three-quantum-dot molecules embedded in an Aharonov-Bohm(A-B) interferometer. By using the Keldysh non-equilibrium Green's function technique, the photon-assisted spin-dependent average current is analyzed. The T-shaped three-quantum-dot molecule A-B interferometer exhibits excellent controllability in the average current resonance spectra by adjusting the interdot coupling strength, Rashba spin-orbit coupling strength, magnetic flux, and amplitude of the time-dependent external field.Efficient spin filtering and multiple electron-photon pump functions are exploited in the multi-quantum-dot molecule A-B interferometer by a time-modulated external field. 相似文献
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365.
石墨烯催化生长中的偏析现象及其调控方法 总被引:2,自引:0,他引:2
石墨烯是一种由sp2杂化碳原子组成的具有蜂窝状结构的二维原子晶体, 其一系列优异的电学、光学和力学等特性, 使得它在各领域都有广泛的应用前景, 而大面积高质量石墨烯的制备则是各类应用的前提. 金属基底上的催化生长方法是目前制备高质量石墨烯的主流技术. 系统地阐释了金属基底上石墨烯催化生长中的偏析现象以及我们发展的通过调控偏析过程来实现石墨烯控制生长的基本方法. 这些方法包括: 偏析生长法、共偏析法、Cu-Ni合金偏析法、互补性二元合金催化法等. 我们的工作表明, 偏析是金属表面石墨烯生长过程中无法回避的、同时也可以积极利用的一个关键基元步骤. 对偏析现象及其调控方法的研究, 有助于为石墨烯的控制生长提供新的解决方案, 进而推动石墨烯的工业化进程. 相似文献
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367.
The concept of polaron, emerged from condense matter physics, describes the dynamical interaction of moving particle with its surrounding bosonic modes. This concept has been developed into a useful method to treat open quantum systems with a complete range of system-bath coupling strength. Especially, the polaron transformation approach shows its validity in the intermediate coupling regime, in which the Redfield equation or Fermi’s golden rule will fail. In the polaron frame, the equilibrium distribution carried out by perturbative expansion presents a deviation from the canonical distribution, which is beyond the usual weak coupling assumption in thermodynamics. A polaron transformed Redfield equation (PTRE) not only reproduces the dissipative quantum dynamics but also provides an accurate and efficient way to calculate the non-equilibrium steady states. Applications of the PTRE approach to problems such as exciton diffusion, heat transport and light-harvesting energy transfer are presented. 相似文献
368.
369.
A correct formulation of the problem of the structure and stability of relaxation waves is given for arbitrary Lewis (Le) and Prandtl (Pr) numbers. The high activation-energy approximation in which the reaction to heating zone length ratio is assumed to be small is analyzed in detail.It is shown that the case Le = 1 is a singular point and that only at that point is the calculation method used in the paper of O. Yu. Travnikov et al. (Phys. Fluids, 1997, 9, 3935–3937) applicable. For Le 1 and small wavelengths, the Landau-Darrieus mechanism gives way to another mechanism of perturbation amplification in which the amplification factor strongly depends not only on the degree of non-equilibrium but also on the Lewis and Prandtl numbers. It is shown that with decrease in the thermal expansion coefficient of the medium the results go over into the well-known results obtained for diffusion-thermal instability. 相似文献
370.