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121.
122.
This investigation studies the effect of trailing-edge scalloping on the lift and drag force coefficients of flat, membrane wings that vibrate at low Reynolds numbers (<61,000). A series of rigid, flat plate frames with moderate aspect ratio and repeating membrane cell structure were studied and compared to a rigid plate and a rigid scalloped plate. Lift and drag measurements were acquired using an external force-balance; flow fluctuation measurements were captured with a hot-wire. Results showed that the size and aspect ratio of the latex cell had a greater impact on lift than scalloping and that scalloping had a greater effect on drag than the cell aspect ratio. Compared to the solid wings, the membrane wings exhibited higher lift and drag coefficients, likely due to both effective cambering and dynamic interaction with the free shear layer. While trailing-edge scalloping decreased both the lift and drag coefficients relative to no scalloping, the greater effect was on drag, thus, increasing aerodynamic efficiency. The maximum lift-to-drag ratio was attained for a 25% scallop with a repeating cell aspect ratio of one. A unique nondimensional scaling of the membrane vibration peak frequency is also presented. 相似文献
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124.
基于电化学沉积的高深宽比无源MEMS惯性开关的研制 总被引:1,自引:0,他引:1
基于电化学沉积技术在金属基底上制作了一种新型的无源MEMS惯性开关。针对高深宽比、细线宽微电铸用光刻胶模具制作过程中,由于SU-8胶膜严重侧蚀导致的胶膜制作困难、质量低下的问题,进行了紫外光刻试验研究。试验研究了不同曝光剂量和后烘时间对SU-8胶光刻效果的影响,优化了光刻工艺参数。采用降低曝光剂量和延长后烘时间相结合的方法解决了高深宽比、细线宽SU-8胶膜制作困难的问题,制作出高质量的微电铸用光刻胶模具。最后,在上述试验结果基础上制作了一种高深宽比、无源MEMS惯性开关。其外形尺寸为3935μm×3935μm×234μm,其中最细线宽12μm,单层最大深宽比达10∶1,多层最大深宽比达20∶1。 相似文献
125.
为减小偏流角对TDI-CCD(Time-Delay Integration-Charge Coupled Device,时间延迟积分-电荷耦合器件)相机成像的影响,分析了侧摆成像时偏流角产生的原因和计算方法,定量计算了偏流角在沿航方向和穿航方向产生的像移,并通过仿真分析了偏流角影响因素及其残差对成像的影响.最后通过实际飞行试验发现,平台调偏流时偏航方向的姿态角存在振荡,即偏流角存在残差.经分析,此现象产生原因除了卫星平台本身的姿态扰动外,主要是卫星平台响应机制,即卫星平台对调偏响应过慢导致平台调偏流出现超调现象.该分析结果对空间光学相机平台改进有一定的参考价值,并已应用于某型号卫星的改进型. 相似文献
126.
拖缆放出长度是拖靶飞行的重要参数,测长过程一旦发生故障势必造成严重后果。针对长度计数间断现象,从长度测量装置的结构原理、空中受力和飞行过程分析了计数错误原因,提出了结构改进方法和飞行机动航路要求,以实际应用验证了解决措施的有效性。 相似文献
127.
《中国航空学报》2021,34(5):239-252
Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention. However, the aerodynamic mechanism of birds' flapping wing kinematics still lacks in-depth understanding. In this paper, the aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics extracted from a free-flying owl wing has been numerically investigated. The overset mesh technique is used to deal with the large range movements of flapping airfoils. The bio-inspired kinematics consist of plunging and pitching movement. A pure sinusoidal motion and a defined motion composed of plunging of sinusoidal motion and pitching of the bio-inspired kinematics are selected for comparison. The other two NACA airfoils are also selected to figure out the advantages of the owl-like airfoil. It is found that the cambered owl-like airfoil can enhance lift during the downstroke. The bio-inspired kinematics have an obvious advantage in lift generation with a presence of higher peak lift and positive lift over a wider proportion of the flapping cycle. Meanwhile, the bio-inspired motion is more economical for a lower power consumption compared with the sinusoidal motion. The sinusoidal flapping motion is better for thrust generation for a higher peak thrust value in both upstroke and downstroke, while the bio-inspired kinematics mainly generate thrust during the downstroke but produce more drag during the upstroke. The defined motion has similar lift performance with the bio-inspired kinematics, while it consumes more energy and generates less thrust. The unsteady flow field around airfoils is also analyzed to explain the corresponding phenomenon. The research in this paper is helpful to understand the flight mechanism of birds and to design a micro air vehicle with higher performance. 相似文献
128.
《中国航空学报》2021,34(4):332-340
Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads. Their mainstream manufacturing method is molding. Due to most molds are made of silicon or silicon-based soft templates, and have poor wear resistant or vulnerability to high temperature, limiting their use in large-scale manufacturing. Nickel is widely used as an embossing mold in the micro/nano-imprint industrial process owing to its good mechanical properties. However, the processing of metal molds for the fabrication of tip-expanded microstructural arrays is extremely challenging. In this study, using electrodeposition techniques, the shape of the micropores is modified to obtain end-controlled pores. The effect of the non-uniformity of the electric field on the microporous morphology in the electrodeposition process is systematically investigated. Furthermore, the mechanism of non-uniformity evolution of the microporous morphology is revealed. The optimized microporous metal array is used as a mold to investigate the cavity evolution laws of the elastic cushions under pre-load during the manufacturing process. As a result, typical bionic adhesives with tip-expansion are obtained. Moreover, corresponding adhesion mechanics are analyzed. The results show that electrochemical modifications have broad application prospects in the fabrication of tip-expanded microstructures, providing a new method for the large-scale fabrication of bionic adhesives based on metal molds. 相似文献
129.
协同优化在卫星多学科设计优化中的初步应用 总被引:6,自引:0,他引:6
探讨以遗传算法为优化上具的协同优化方法在卫星总体优化设计中的应用以及各学科间耦合关系。首先对基本协同优化方法的流程及特点进行了探讨,然后以对地观测卫星总休优化设计为对象,研究如何利用协同优化方法建立此问题的优化模型。研究结果表明,融合了遗传算法的协同优化方法能够有效地解决对地观测卫星总休优化设计,学科间耦合设计变量以及耦合状态变量的一致性误差均接近0.01%。 相似文献
130.