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861.
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866.
随着控制理论的不断发展,主动控制的实现方式也多种多样。在线辨识是自适应控制的关键所在,而辨识算法也是多种多样,这样结合在线辨识功能的自适应控制种类就更多。本文旨在对已经应用或者即将应用和可能应用到在直升机振动控制上的,并具有在线辨识功能的多种结构响应主动控制技术进行比较,并提出其中值得研究的若干问题,有助于今后的进一步研究。 相似文献
867.
由随机发生的严重布料不均匀引起的强烈机械振动难以用机械方法加以解决只能靠增加对机械振动强度的监测灵敏度。当振动强度超过一定值时,PLC控制程度执行一系列操作以保护机械系统和拖动电机的安全。因此设计并制作高灵敏度测振电路板对系统安全至关重要。本文详细描述了此电路板的设计和制作过程。该电路板对分蜜机有可靠的保护作用。 相似文献
868.
The forecast of the terrestrial ring current as a major contributor to the stormtime Dst index and a predictor of geomagnetic storms is of central interest to ‘space weather’ programs. We thus discuss the dynamical
coupling of the solar wind to the Earth's magnetosphere during several geomagnetic storms using our ring current-atmosphere
interactions model and coordinated space-borne data sets. Our model calculates the temporal and spatial evolution of H+, O+, and He+ ion distribution functions considering time-dependent inflow from the magnetotail, adiabatic drifts, and outflow from the
dayside magnetopause. Losses due to charge exchange, Coulomb collisions, and scattering by EMIC waves are included as well.
As initial and boundary conditions we use complementary data sets from spacecraft located at key regions in the inner magnetosphere,
Polar and the geosynchronous LANL satellites. We present recent model simulations of the stormtime ring current energization
due to the enhanced large-scale convection electric field, which show the transition from an asymmetric to a symmetric ring
current during the storm and challenge the standard theories of (a) substorm-driven, and (b) symmetric ring current. Near
minimum Dst there is a factor of ∼ 10 variation in the intensity of the dominant ring current ion specie with magnetic local time, its
energy density reaching maximum in the premidnight to postmidnight region. We find that the O+ content of the ring current increases after interplanetary shocks and reaches largest values near Dst minimum; ∼ 60% of the total ring current energy was carried by O+ during the main phase of the 15 July 2000 storm. The effects of magnetospheric convection and losses due to collisions and
wave-particle interactions on the global ring current energy balance are calculated during different storm phases and intercompared.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
869.
We use a simplified atmospheric general circulation model (AGCM) to investigate the response of the lower atmosphere to thermal
perturbations in the lower stratosphere. The results show that generic heating of the lower stratosphere tends to weaken the
sub-tropical jets and the tropospheric mean meridional circulations. The positions of the jets, and the extent of the Hadley
cells, respond to the distribution of the stratospheric heating, with low latitude heating displacing them poleward, and uniform
heating displacing them equatorward. The patterns of response to the low latitude heating are similar to those found to be
associated with solar variability in previous observational data analysis, and to the effects of varying solar UV radiation
in sophisticated AGCMs. In order to investigate the chain of causality involved in converting the stratospheric thermal forcing
to a tropospheric climate signal we conduct an experiment which uses an ensemble of model spin-ups to analyse the time development
of the response to an applied stratospheric perturbation. We find that the initial effect of the change in static stability
at the tropopause is to reduce the eddy momentum flux convergence in this region. This is followed by a vertical transfer
of the momentum forcing anomaly by an anomalous mean circulation to the surface, where it is partly balanced by surface stress
anomalies. The unbalanced part drives the evolution of the vertically integrated zonal flow. We conclude that solar heating
of the stratosphere may produce changes in the circulation of the troposphere even without any direct forcing below the tropopause.
We suggest that the impact of the stratospheric changes on wave propagation is key to the mechanisms involved. 相似文献
870.
Gerhard Haerendel 《Space Science Reviews》2006,124(1-4):317-331
Three types of processes, occurring in the weakly ionized plasmas of the Earth’s ionosphere as well as in the solar chromosphere,
are being compared with each other. The main objective is to elaborate on the differences introduced primarily by the grossly
different magnitudes of the densities, both with respect to the neutral and, even more so, to the plasma constituents. This
leads to great differences in the momentum coupling from the plasma to the neutral component and becomes clear when considering
the direct electric current component transverse to the magnetic field, called “Pedersen current”; in the ionosphere, which
has no quasi-static counterpart in the chromosphere. The three classes of processes are related to the dynamical response
of the two plasmas to energy influx from below and from above. In the first two cases, the energy is carried by waves. The
third class concerns plasma erosion or ablation in the two respective regions in reaction to the injection of high Poynting
and/or energetic particle fluxes. 相似文献