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331.
S. Benck M. Cyamukungu J. Cabrera 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,42(9):1538-1549
The topic of relativistic electron dynamics in the outer radiation belt has received considerable attention for many years. Nevertheless, the problem of understanding the physical phenomenon involved is far from being resolved. In this paper, we use DEMETER observations to examine the variations of the energetic electron fluxes and ELF/VLF wave intensities in the inner magnetosphere during the intense 8 November 2004 magnetic storm. Electron flux spectra and associated wave intensity spectra are analysed throughout the magnetic storm and common characteristics or differences to other storm events are retained. The overall objective of this study is to identify and derive parameters that are relevant for particle flux modelling; the time constant characterizing the persistent decay after particle enhancement was found to be one of these important model parameters.The analysis of the 8 November 2004 event reveals that for L-shell parameter higher than 4, an electron flux dropout is observed during the storm’s main phase for electrons in the energy range 0.1–1 MeV, as has been reported from other measurements. Characteristic wave spectra accompanying this phase are analysed. They show a typical enhancement in the frequency range 0.3–10 kHz at onset for all L-shell values under consideration (2 < L < 5). During the first stage of the recovery phase, the electron fluxes are increased to a level higher than the pre-storm level, whereas the level of wave intensity in the frequency range observed below 300 Hz is at its highest. In the second stage, the particle flux decrease goes hand in hand with a global wave activity decline, the relaxation time of the latter being smaller than the former’s one. In some other cases, long-lasting electron enhancement associated with constant wave activity has been observed during this latter stage. For the above mentioned storm, while at low L values the decay time constants are higher for low energy electrons than for high energy electrons, this order is reversed at high L values. At about L = 3.6 the time constant is independent of electron energy. 相似文献
332.
333.
334.
一种磁悬浮飞轮用新型永磁偏置径向磁轴承 总被引:10,自引:1,他引:9
为了克服现有永磁偏置径向混合磁轴承的缺陷,提出了一种磁悬浮飞轮用新型永磁偏置径向混合磁轴承,分析了其工作原理,并分别利用等效磁路法及有限元方法对该永磁偏置径向混合磁轴承进行了电磁分析.分析结果表明:所提出的新型永磁偏置径向混合磁轴承采用永磁磁场作为偏置磁场,并且其永磁磁路与电励磁磁路在任一径向截面中共面,可使磁轴承轴向长度大为减小,与现有永磁偏置径向混合磁轴承相比具有体积更小的优点,同时该种永磁偏置径向混合磁轴承产生的偏置磁场在X,Y方向上不会产生耦合,可使控制更加容易,特别适用于高速、低功耗等场合. 相似文献
335.
S. Sen A. Mangalam 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(2):617-627
We build a single vertical straight magnetic fluxtube spanning the solar photosphere and the transition region which does not expand with height. We assume that the fluxtube containing twisted magnetic fields is in magnetohydrostatic equilibrium within a realistic stratified atmosphere subject to solar gravity. Incorporating specific forms of current density and gas pressure in the Grad–Shafranov equation, we solve the magnetic flux function, and find it to be separable with a Coulomb wave function in radial direction while the vertical part of the solution decreases exponentially. We employ improved fluxtube boundary conditions and take a realistic ambient external pressure for the photosphere to transition region, to derive a family of solutions for reasonable values of the fluxtube radius and magnetic field strength at the base of the axis that are the free parameters in our model. We find that our model estimates are consistent with the magnetic field strength and the radii of Magnetic bright points (MBPs) as estimated from observations. We also derive thermodynamic quantities inside the fluxtube. 相似文献
336.
337.
Shiqiang Zheng Bangcheng Han 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper presents an integrated angular velocity measurement and attitude control system of spacecraft using magnetically suspended double-gimbal control moment gyros (MSDGCMGs). The high speed rotor of MSDGCMG is alleviated by a five-degree-of-freedom permanent magnet biased AMB control system. With this special rotor supported manner, the MSDGCMG has the function of attitude rate sensing as well as attitude control. This characteristic provides a new approach to a compact light-weight spacecraft design, which can combine these two functions into a single device. This paper discusses the principles and implementations of AMB-based angular velocity measurement. Spacecraft dynamics with DGMSCMG actuators, including the dynamics of magnetically suspended high-speed rotor, the dynamics of inner gimbal and outer gimbal, as well as the determination method of spacecraft angular velocity are modeled, respectively. The effectiveness of the proposed integrated system is also validated numerically and experimentally. 相似文献
338.
M.T. Menna A. Papitto L. Burderi T. Di Salvo F. DAntona N.R. Robba 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2704-2706
We analyze the three outbursts of the X-ray millisecond pulsar SAX J1808.4-3658 that occurred in 1998, 2000, and 2002 observed with RXTE. With a technique based on epoch folding search we find an unique orbital solution valid over the five years of high temporal resolution data available. We revise the estimate of the orbital period, Porb = 7249.1569(1) s and of its error, which we decrease by one order of magnitude. We also give the first constraint on the orbital period derivative, . We find that in 2002 the pulse profile shape is clearly asymmetric, showing a secondary peak at about 145° from the main pulse, which is different from the sinusoidal shape reported at the beginning of the 1998 outburst. 相似文献
339.
The surface wave induced magnetic reconnection (SWIMR) model based on Alfven Resonance theory will be discussed briefly both
for collisional and collisionless plasmas. It is shown that the spatial scales and time delays associated with Flux Transfer
Events and Pulsed Ionospheric Flows, as observed by satellites and SuperDARN radars and the magnetic bubbles, observed at
the high latitude boundary of the magnetopause, can be explained by the SWIMR model.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
340.
Steven R. Spangler 《Space Science Reviews》2005,121(1-4):189-200
I discuss a method for determining the strength and spatial structure of the coronal magnetic field by observations of the
Faraday rotation of a radio galaxy which is in conjunction with the Sun. Given a knowledge of the plasma density in the outer
corona, and the magnetic field sector structure (both independently available), the strength of the coronal field can be determined,
as well as the magnitude of spatial variations on scales of 1000 km to several solar radii. Such knowledge is crucial for
testing computational models of the solar corona, which are prominently featured in this meeting. Results are presented from
observations with the Very Large Array radio telescope of the radio galaxy 3C228 on August 16, 2003, when the line of sight
to the source was at heliocentic distances of 7.1−6.2R
⊙. The observations are consistent with a coronal magnetic field which is proportional to the inverse square of the distance
in the range 6 ≤ r ≤ 10R
⊙, and has a value of 39 mG at 6.2R
⊙. The Faraday rotation is uniform across the source, indicating an absence of strong plasma inhomogeneity on spatial scales
up to 35,000 km. 相似文献