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101.
Regime diagram of the development of long-wave near-wall disturbances in a hypersonic boundary layer
A regime diagram of the development of slow near-wall disturbances induced by an unsteady self-induced pressure perturbation in a hypersonic boundary layer is constructed for a disturbance wavelength greater than the boundary layer thickness. It is shown that the main factors shaping the perturbed flow are the gas enthalpy near the body surface, the intensity of the viscous-inviscid interaction, and the nature (sub- or supersonic) of the main part of the boundary layer. Nonlinear boundary-value problems are formulated for regimes in which the near-wall boundary layer region plays a decisive role. Numerical and analytical solutions are obtained in the linear approximation. It is shown that intensification of the viscous-inviscid interaction or an increase in the role of the supersonic main region of the boundary layer impart generally supersonic properties to the main part of the boundary layer, i.e. the upstream propagation of the disturbances is damped and the disturbance growth downstream becomes more intense. Damping of the viscous-inviscid interaction and an increase in the role of the subsonic main part of the boundary layer have the opposite effect. Surface cooling increases the effect of the main part of the boundary layer on the formation of pressure disturbances and surface heating leads to an increase in the effect of the near-wall boundary layer region. It is also shown that for the regimes considered disturbances propagate in a direction opposite to that of the free stream from the turbulent flow region located downstream of the local disturbance development region.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, 2004, pp. 59–71. Original Russian Text Copyright © 2004 by Bogolepov and Neiland. 相似文献
102.
T. J. Heindel F. P. Incropera S. Ramadhyani 《International Journal of Heat and Fluid Flow》1995,16(6):511-518
Coupled conduction and natural convection transport within a discretely heated cavity have been investigated numerically. One vertical wall of the cavity is composed of discrete, isoflux heat sources mounted in a substrate of finite thermal conductivity. The opposite vertical wall and the horizontal walls are assumed to be isothermal and adiabatic, respectively. The governing steady-state partial differential equations for the fluid and solid region are solved simultaneously using a control volume formulation, coupled with an additive correction multigrid procedure that increases the convergence rate of the solution. The fluid Prandtl number and heater/fluid thermal conductivity ratio are fixed at 25 and 2350, respectively, corresponding to a dielectric fluid (FC-77) and heaters manufactured from silicon. With increasing modified Rayleigh number (104 < RaLz* < 109), the cavity flow becomes more boundary layer-like along the vertical walls, and multiple fluid cells develop in the central region. Thermal spreading in the substrate increases with decreasing modified Rayleigh number and with increasing values of the substrate/fluid thermal conductivity ratio (10−1 <- Rs ≤ 103). For large Rs, the discrete heat sources lose their thermal identity, and the streamlines and isotherms resemble those associated with a differentially heated cavity. Thermal spreading in the substrate also has a significant effect on circulation in the cavity and on maximum surface temperatures. 相似文献
103.
An original experimental investigation of heat transfer with steam condensation on a surface of a horizontal cooled tube immersed in a bubbling layer was carried out. A copper test section 16 mm in diameter and 285 mm in length was placed in a bubbling column 295 mm in diameter. Experiments were made under a pressure of 0.72-3.8 MPa with volume steam content 0-0.18, steam superficial velocities 0-0.18 m/s, and liquid-wall temperature difference 38–106 K. The heat transfer process in a bubbling layer under high pressures is shown to be of considerably intensity; with moderate values of steam content heat transfer coefficients reach 10–12 kW/(m2·K). The use of the known correlations assumed for the case of air bubbling under atmospheric pressure results in systematically underestimating heat transfer by 30–80%. Data were obtained on heat transfer with film condensation of steam and natural convection of subcooled water at high temperature differences outside the range investigated earlier. Experimental data table is appended. 相似文献
104.
采用RNG k-ε 湍流模型对超临界CO2流体在内径为4 mm, 长度2000 mm, 节距为10 mm, 曲率为0.1的水平螺旋管内的冷却换热进行了数值模拟.研究了质量流量、热流量以及压力对换热系数的影响, 并和超临界CO2在水平直管内的冷却换热进行了对比.研究结果表明, 超临界CO2在水平螺旋管内流动产生的二次流强于水平直管内的二次流, 前者的换热系数大于后者; 换热系数随质量流量的增加而增大; 在似气体区, 换热系数随着热流量的增加而增大, 而在似液体区, 热流量对换热系数几乎没有影响; 换热系数峰值点随着压力的升高而下降, 并向高温区偏移. 相似文献
105.
C.F. Lo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):93-95
Based upon the hidden Lie SU(1,1) symmetry, we have constructed the unitary decoupling transformation which diagonalizes the
multimode two-quantum Jaynes-Cummings model and provides us with an extremely convenient basis to gain a deeper understanding
of the dressing processes present in the matter-field interaction. This canonical transformation approach is very simple and
can be easily extended to other generalized Jaynes-Cummings models.
Received: 5 July 1997 / Revised: 3 November 1997 / Accepted: 14 November 1997 相似文献
106.
M. Kajita 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):55-59
Collisions between linear polar molecules that were electrostatically trapped were investigated. The collisional transition
from a low to a high field seeking state (inelastic collision) causes trap loss. The efficiency of evaporative cooling is
improved at higher elastic collision rates. We calculated cross-sections of inelastic and elastic collision using a semi-classical
treatment.
Received 6 December 2001 / Received in final form 26 February 2002 Published
online 28 June 2002 相似文献
107.
利用描述连续铸钢过程二冷区喷水控制下钢的热传导的半离散化模型 ,我们构造一包含温度梯度约束的最优控制问题 .针对此最优控制问题 ,采用直接配置法进行数值求解 ,得出相应的近似最优控制 . 相似文献
108.
Birefringence in polycarbonate: Molecular orientation induced by cooling stresses. I. Free quenching
The residual birefringence distributions in polycarbonate disks quenched in a liquid bath under various conditions are determined. Unbalanced distributions of approximately parabolic shape are obtained in the cross-sections in general. A systematic influence of the initial quench temperature on the imblance of the birefringence distributions is observed, with higher initial temperatures leading to a strong shift of birefringence in the positive direction. The systematic variation of the birefringence distribution with quenching conditions is interpreted in terms of a stress and an orientation contribution. The distributions are predicted correctly by a numerical program making use of the linear stress-optical rule with a different stress-optical coefficient above and below the glass-transition temperature. The contribution of molecular orientation is distinguished experimentally from the stress contribution by annealing experiments. © 1993 John Wiley & Sons, Inc. 相似文献
109.
110.