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101.
MESSENGER: Exploring Mercury’s Magnetosphere 总被引:1,自引:0,他引:1
James A. Slavin Stamatios M. Krimigis Mario H. Acuña Brian J. Anderson Daniel N. Baker Patrick L. Koehn Haje Korth Stefano Livi Barry H. Mauk Sean C. Solomon Thomas H. Zurbuchen 《Space Science Reviews》2007,131(1-4):133-160
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission to Mercury offers our first opportunity
to explore this planet’s miniature magnetosphere since the brief flybys of Mariner 10. Mercury’s magnetosphere is unique in
many respects. The magnetosphere of Mercury is among the smallest in the solar system; its magnetic field typically stands
off the solar wind only ∼1000 to 2000 km above the surface. For this reason there are no closed drift paths for energetic
particles and, hence, no radiation belts. Magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere,
allowing solar wind ions to impact directly the regolith. Inductive currents in Mercury’s interior may act to modify the solar
wind interaction by resisting changes due to solar wind pressure variations. Indeed, observations of these induction effects
may be an important source of information on the state of Mercury’s interior. In addition, Mercury’s magnetosphere is the
only one with its defining magnetic flux tubes rooted beneath the solid surface as opposed to an atmosphere with a conductive
ionospheric layer. This lack of an ionosphere is probably the underlying reason for the brevity of the very intense, but short-lived,
∼1–2 min, substorm-like energetic particle events observed by Mariner 10 during its first traversal of Mercury’s magnetic
tail. Because of Mercury’s proximity to the sun, 0.3–0.5 AU, this magnetosphere experiences the most extreme driving forces
in the solar system. All of these factors are expected to produce complicated interactions involving the exchange and recycling
of neutrals and ions among the solar wind, magnetosphere, and regolith. The electrodynamics of Mercury’s magnetosphere are
expected to be equally complex, with strong forcing by the solar wind, magnetic reconnection, and pick-up of planetary ions
all playing roles in the generation of field-aligned electric currents. However, these field-aligned currents do not close
in an ionosphere, but in some other manner. In addition to the insights into magnetospheric physics offered by study of the
solar wind–Mercury system, quantitative specification of the “external” magnetic field generated by magnetospheric currents
is necessary for accurate determination of the strength and multi-polar decomposition of Mercury’s intrinsic magnetic field.
MESSENGER’s highly capable instrumentation and broad orbital coverage will greatly advance our understanding of both the origin
of Mercury’s magnetic field and the acceleration of charged particles in small magnetospheres. In this article, we review
what is known about Mercury’s magnetosphere and describe the MESSENGER science team’s strategy for obtaining answers to the
outstanding science questions surrounding the interaction of the solar wind with Mercury and its small, but dynamic, magnetosphere. 相似文献
102.
从战术与技术相结合的角度,建立了“一对一”空战中交战双方的运动学方程,运用瞬时跨距的方法分析了载机与目标的相对运动,研究了目标在载机坐标系中的运动特性。文中的研究结果对歼击机“一对一”空战的战术选择有一定的指导意义。 相似文献
103.
使用反舰导弹对舰艇进行饱和攻击是当前对舰攻击的主要方式。首先,提出了动态贝叶斯网络(DBN)的理论及算法;其次,根据反舰导弹的高度、速度、过载、机动方式等弹道特性和RCS、雷达频率等导弹自身特性,建立了对反舰导弹进行弹型识别的DBN模型;最后,通过仿真算例验证了DBN模型的有效性,这为实际解决反舰导弹进行弹型识别的问题,提供了一种思路。 相似文献
104.
为提高机场的整体运行效率和综合保障能力,提出了一种基于速度剖面拟合的航空器场面滑行4D轨迹预测方法。构建了航空器的滑行动态模型,进而引入标称速度剖面的概念。将DSW算法应用到速度剖面的拟合中,得出一种标称速度剖面的生成方法,并通过建立平均速度修正参数修正不同机型对滑行速度的影响,基于动力学平衡方程,构造了标称速度到瞬时速度的映射,结合BADA数据实现对瞬时速度的修正。在上述分析的基础上得到航空器场面滑行4D轨迹预测模型。案例表明,与基于动力学的方法相比计算结果更加准确,使平均误差降低47.3%,能够有效地预测航空器的4 D轨迹。 相似文献
105.
针对运载器大气层内的最优轨迹快速规划问题,提出一种将求解最优控制问题的间接法与直接法相结合的混合优化方法。首先,基于最优控制问题的一阶必要条件,将运载器大气层内的三维最优上升问题转化为Hamiltonian两点边值问题;然后,采用直接法中能以较少的节点获得较高求解精度的Gauss伪谱法进行求解,提高算法的求解效率;最后,采用真空解析解初值及密度同伦技术,解决初值猜测与算法收敛困难的问题。仿真结果表明,混合优化算法能够准确、快速地对运载器大气层内的最优上升轨迹问题进行求解,并在计算精度与效率上均优于间接法,可应用于运载器的轨迹在线规划与闭环制导。 相似文献
106.
This paper presents the model of calculating the total friction moment of space gyroscope ball bearings which usually work under ultra-low oscillatory motion and are very sensitive to the friction moment. The aim is to know the proportion of the friction moment caused by each frictional source in the bearing's total friction moment, which is helpful to optimize the bearing design to deduce the friction moment. In the model, the cage dynamic equations considering six degree-of-freedom and the balls dynamic equations considering two degree-of-freedom were solved.The good trends with different loads between the measured friction moments and computational results prove that the model under constant rate was validated. The computational results show that when the speed was set at 5 r/min, the bearing's maximum total friction moment when oscillation occurred was obviously larger than that occurred at a constant rate. At the onset of each oscillatory motion, the proportion of the friction moment caused by cage in the bearing's total friction moment was very high, and it increased with the increasing speed. The analyses of different cage thicknesses and different clearances between cage pocket and ball show that smaller thickness and clearance were preferred. 相似文献
107.
分析了月地返回飞行过程中的误差因素和量级采用蒙特卡洛法和统计理论,定量分析了月地返回轨道入轨时刻误差、入轨状态误差、入轨控制误差、转移段定轨误差、中途修正控制误差等各种误差对轨道终端参数的影响。给出了月地返回轨道中途修正的计算步骤,然后以预期再入时刻和目标再入点为修正目标,采用微分改正法计算中途修正所需的速度增量。结合误差分析结果和测控条件,给出第一次中途修正时机的建议和一个具体算例,计算结果表明所提中途修正方法和策略可以修正入轨误差、定轨误差和控制误差的影响,使月地返回轨道可以按预期的再入时刻返回预定再入点。 相似文献
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