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221.
空间伸展臂是一类最基本的空间可展开结构,是大型复杂空间结构的基础,对迅速发展的空间活动有着十分重要的研究意义。文章总结并介绍了不同结构形式空间伸展臂的研究与应用情况,根据各方面性能进行了较为全面的对比分析,并从力学、材料、空间环境影响、振动控制几方面深入分析了空间伸展臂设计和应用的技术难点,初步探讨了空间伸展臂的发展方向,从而为空间伸展臂的设计、选型和分析提供必要的支持。 相似文献
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223.
《中国航空学报》2021,34(10):248-264
This study presents a method for measuring the imbalance in a small-sized cylindrical roller. The roller imbalance was calibrated on the built static-pressure-air flotation measurement machine. The impact of the roller imbalance on the dynamic characteristics of a cage were then studied on the aero-bearing test rig. The displacement spectrums with different roller imbalance of the obtained cage orbits under various bearing speed and radial load were used to evaluate the cage stability. The results show that the cage cannot form a stable operating state at a lower bearing speed with or without the unbalanced rollers. The cage with balanced rollers gradually develops stable motion with the increase of the bearing speed. The existence of a small roller imbalance causes the stability of the cage to deteriorate. With an increase in the bearing speed and radial load, the cage with the unbalanced rollers runs unsteadily accompanied by a high-frequency vibration when the roller imbalance is large enough. The vibration amplitude of the cage in the horizontal direction is greater than that in the vertical direction during an unstable operation, which is similar in the stable status. 相似文献
224.
This paper draws attention to the issue of the vibration absorption of nonlinear mechanical system coupled to nonlinear energy sink(NES) under the impact of the narrow band stochastic excitation. Firstly, based on the complex-averaging method and frequency detuning methodology,response regimes of oscillators have been researched under the linear impact of coupling a nonlinear attachment with less relativistic mass and an external sinusoidal forcing, of which results turn out that the quasi-periodicity response regime of system which occurs when the external excitation amplitude exceeds the critical values will be the precondition of the targeted energy transfer.Secondly, basing on the path integration method, vibration suppression of NES has been researched when it is affected by a main oscillator with a narrow band stochastic force in the form of trigonometric functions, of which results show that response regimes are affected by the amplitude of stochastic excitation and the disturbance strength. Finally, all these conclusions have been approved by the numerical verification and coincided with the theoretical analysis; meanwhile, after the comparing analysis with the optimal linear absorber, it turns out that the NES which is affected by the narrow band stochastic force could also suppress the vibration of system with a better effect. 相似文献
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226.
着陆缓冲火箭点火高度选择及缓冲效果估计 总被引:1,自引:0,他引:1
李大耀 《中国空间科学技术》1994,14(1)
首先列出着陆缓冲火箭工作期间物(回收飞行器)-伞(降落伞)系统运动方程一般形式的解;然后据此分析影响缓冲火箭点火高度和缓冲效果的各因素,并且给出了确定点火高度和估算缓冲效果的公式。 相似文献
227.
王先荣 《中国空间科学技术》1994,14(3):1-8
就微重力环境下处于外围流体浴槽之轴对称粘滞流体桥振动动力学问题,建立了近似振动传播模型。该模型综合考虑了流体桥本身及外围液体浴槽的粘滞效应,将其纳入相应的统一的数理方程之中。解之,得到了稳态流体桥振动的界面函数及相关的其它结论。这些结论与经由CosseratModel和LinearThree-DimensicnalModel所得结论相近,但却同时包纳了桥内外的粘滞效应。 相似文献
228.
This paper presents a dual-stage control system design method for the three-axis-rotational maneuver and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensors/actuators. In this design approach, attitude control system and vibration suppression were designed separately using lower order model. The design of attitude controller was based on variable-structure control (VSC) theory leading to a discontinuous control law. To accomplish asymptotic attitude maneuvering in the closed-loop system and be insensitive to the interaction of elastic modes in the presence of unknown disturbances/uncertainty and input saturation as well, a switching mechanism is employed to design the attitude controller such that outside the sliding region VSC law with a time-varying sliding surface is implemented and inside the region the VSC law with a linear sliding surface is activated. Furthermore, a hyperbolic tangent function in conjunction with a sharpness function permitted to vary with time according to a set of user-defined parameters is implemented to offset the disadvantages of existing saturation-respecting controller and chattering. In addition, for actively damping the excited elastic vibrations during attitude maneuvering, modal velocity feedback and strain rate feedback control design methods are presented and compared by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque, parameter uncertainty and control saturation nonlinearity. 相似文献
229.
Typical turboprop noise spectra exhibit a series of characteristic peaks which are directly related to the product of propeller rpm and number of propeller blades. These blade passage frequencies contribute significantly to the overall sound pressure level both outside and inside the aircraft. Their contribution to cabin noise is usually reduced by appropriately adjusted mass dampers. However, since the engine rpm varies for different flight stages, any fixed eigenfrequency absorber will merely be a sub-optimal compromise.The Tunable Vibration Absorber (TVA) introduced in this article has a variable resonant frequency which enables an adaptation to different flight phases providing largely improved performance. Frequency tuning is achieved through a piezo-electric stack actuator, which applies a pressure force to a pair of leaf springs thus reducing their effective bending stiffness.Among the main advantages of this particular approach are a static control signal and low power consumption. To enable a light-weight construction the components which generate the pressure loading are incorporated into the oscillating mass.The TVA allows to cover a wide frequency range using only a single device. Additionally, it features damping control capability and optional active multi-mode operation. Structural-acoustic simulations have indicated a noise reduction potential of approximately 10 dB.This article gives a short overview of different tuneable vibration absorber concepts, lines out the theoretical background of the proposed approach, discusses the general components layout and describes the experimental verification of a prototype TVA for the Airbus A400M. 相似文献
230.