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931.
发展并验证了一种新的支持多面体网格的欧拉方程离散算法,采用Fortran 95编写了支持任意网格拓扑及三维复杂外形的通用求解器.在空间离散上,基于径向基函数理论提出了一种新的梯度计算方法,并采用动能通量分裂格式来得到准确并且稳定的二阶精度重构.该方法不依赖于网格几何形状,因此对网格质量不敏感.由于在时间方向采用了点隐松... 相似文献
932.
933.
凸极式旋转变压器是近几年刚出现的新型测角元件,本文详细分析了其工作原理、定子绕组、转子凸极特征和电气性能;本文的结论得到了样机验证,本文还给出了提高测角精度的研究途径. 相似文献
934.
935.
《中国航空学报》2022,35(9):117-128
Based on the demands of compact heat exchangers and micro cooling channels applied for aviation thermal protection, the flow resistance characteristics of aviation kerosene RP-3 were experimentally studied in a vertically downward circular miniature tube with an inner diameter of 1.86 mm at supercritical pressures and constant heat fluxes. A long and short tube method was used to accurately calculate the frictional pressure drop, and experimental conditions are supercritical pressures of 4 MPa, mass flow rates of 2–4 g/s (i.e., mass fluxes of 736–1472 kg/(m2?s)), heat fluxes of 100–500 kW/m2, and inlet temperatures of 373–673 K. Results show that the sharp variations of thermophysical properties, especially density, have significant influences on frictional resistances. Generally, the frictional pressure drop and the friction factor increase with increasing inlet temperatures, and this trend speeds up in the relatively high-temperature region. However, the friction factor has a sudden decline when the fuel outlet temperature exceeds the pseudo-critical temperature. The frictional pressure drop and the friction factor basically remain unchanged with increasing heat flux when the inlet temperature is relatively low, but increase quickly when the inlet temperature is relatively high. Besides, a larger mass flux yields a higher pressure drop but does not necessarily yield a higher friction factor. Finally, an empirical friction factor correlation is proposed and shows better predictive performance than those of previous models. 相似文献
936.
937.
938.
The main effects caused by the interplanetary magnetic field (IMF) are analyzed in cases of supersonic solar wind flow around
magnetized planets (like Earth) and nonmagnetized (like Venus) planets. The IMF has a relatively weak strength in the solar
wind but it is enhanced considerably in the so-called plasma depletion layer or magnetic barrier in the vicinity of the streamlined
obstacle (magnetopause of a magnetized planet, or ionopause of a nonmagnetized planet). For magnetized planets, the magnetic
barrier is a source of free magnetic energy for magnetic reconnection in cases of large magnetic shear at the magnetopause.
For nonmagnetized planets, mass loading of the ionospheric particles is very important. The new created ions are accelerated
by the electric field related to the IMF, and thus they gain energy from the solar wind plasma. These ions form the boundary
layer within the magnetic barrier. This mass loading process affects considerably the profiles of the magnetic field and plasma
parameters in the flow region. 相似文献
939.
申儒林 《航空精密制造技术》2006,42(2):56-59
根据硬盘磁头加工的特点,分析了抛光机的运动学特性及抛光盘、抛光液、磨粒在抛光过程中的摩擦学行为等对磁头表面质量的影响。 相似文献
940.
J. Büchner 《Space Science Reviews》2006,122(1-4):149-160
Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection.
Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an
unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even
topological properties of a force-free coronal magnetic field. First, there are separatrices related to magnetic nulls. Through
separatrices the magnetic connectivity changes discontinuously. Coronal magnetic nulls are, however, very rare. Second, inspired
by the concept of generalized magnetic reconnection without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL
the magnetic connectivity changes continuously, though strongly. The strength of the connectivity change can be quantified
by measuring the squashing of the flux tubes which connect the magnetically conjugated photospheres.
We verify the QSL and separatrix concepts by comparing the sites of magnetic nulls and enhanced squashing with the location
of current concentrations in the corona. Due to the known difficulties of their direct observation, we simulated coronal current
sheets by numerically calculating the response of the corona to energy input from the photosphere, heating a simultaneously
observed Extreme Ultraviolet Bright Point. We did not find coronal current sheets at separatrices but at several QSL locations.
The reason is that, although the geometrical properties of force-free extrapolated magnetic fields can indeed hint at possible
current concentrations, a necessary condition for current sheet formation is the local energy input into the corona. 相似文献