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371.
372.
建立了缠绕管件三维有限元模型,通过应力分析发现轴压条件下缠绕管件受压端面存在明显应力集中现象,由此预测管件受压端面边缘效应会导致管件轴压强度下降,通过三维有限元模型对端头加强和未加强管件的轴压强度分别进行了定量计算,得出端头加强管件的轴压强度明显高于未加强管件的轴压强度。在理论分析的基础上,设计了缠绕管件轴压性能实验,实验结果对理论分析结果进行了验证。研究结果表明,对缠绕管件进行端头加强后,可有效减轻端面效应对轴压强度的负面影响,轴压强度可提高30%以上。 相似文献
373.
针对非均匀气动加热条件下三维复杂防热瓦结构的轻量化需求,基于变厚度设计理念,发展了一种基于网格变形技术(ASD)和热固耦合分析相结合的防热瓦结构优化方法。优化结果表明,基于网格变形技术能够快速有效地解决优化过程中的网格自动更新问题,避免了网格重新划分的耗费及复杂结构网格重构的困难,并得到了光滑柔顺的厚度形状曲线;相比等厚设计,变厚度设计可以有效考虑载荷的非均匀效应,并极大地减轻结构重量;优化后可以更充分发挥防热瓦结构各层材料的承载能力。 相似文献
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375.
《中国航空学报》2021,34(5):331-340
The morphing trailing edge based compliant mechanism is a developing technology which can increase lift-drag ratio for variable flight modes by bending down the trailing edge. Composite material design is integrated into topology optimization for the morphing trailing edge based compliant mechanism in the paper. A two-step optimization strategy is established to solve the integrated design problem. Initially, lamination parameters are introduced and viewed as a bridge between structure stiffness and fiber angles for composite material. Design variables include the lamination parameters and element density. The least-squares between actual and desired displacements at output points along trailing edge is adopted to evaluate the deformed capability of the trailing edge. An integrated optimization model for the composite morphing trailing edge is established with the volume constraints. The optimal topologic shape and lamination parameters are initially obtained. Subsequently, a least-squares optimization between fiber angles and the optimal lamination parameters is implemented to obtain optimal fiber angles. Finally, morphing capability of composites trailing edge based compliant mechanism is investigated by simulation and experiments. The results indicate the composites trailing edge based compliant mechanism can approximately bend down 8 degrees and satisfies the design requirement. 相似文献
376.
《中国航空学报》2020,33(12):3535-3549
Titanium alloys are widely used in the aviation and aerospace industries due to their unique mechanical and physical properties. Specifically, thin-walled titanium (Ti) cylinders have received increasing attention for their applications as rocket engine casings, aircraft landing gear, and aero-engine hollow shaft due to their observed improvement in the thrust-to-weight ratio. However, the conventional cutting (CC) process is not appropriate for thin-walled Ti cylinders due to its low thermal conductivity, high strength, and low stiffness. Instead, high-speed ultrasonic vibration cutting (HUVC) assisted processing has recently proved highly effective for Ti-alloy machining. In this study, HUVC technology is employed to perform external turning of a thin-walled Ti cylinder, which represents a new application of HUVC. First, the kinematics, tool path, and dynamic cutting thickness of HUVC are evaluated. Second, the phenomenon of mode-coupling chatter is analyzed to determine the effects and mechanism of HUVC by establishing a critical cutting thickness model. HUVC can increase the critical cutting thickness and effectively reduce the average cutting force, thus reducing the energy intake of the system. Finally, comparison experiments are conducted between HUVC and CC processes. The results indicate that the diameter error rate is 10% or less for HUVC and 51% for the CC method due to a 40% reduction in the cutting force. In addition, higher machining precision and better surface roughness are achieved during thin-walled Ti cylinder manufacturing using HUVC. 相似文献
377.
座舱是战斗机三大电磁散射源之一,座舱盖雷达散射截面(RCS)的减缩技术是实现新一代战斗机全机雷达隐身性能的关键技术。基于新一代战斗机隐身外形平台,座舱盖在隐身技术、透明件结构、抗鸟撞、弹射救生、光学性能、结构变形控制等领域均面临新的挑战。本文以新一代战斗机为背景,研究了座舱盖性能提升的4项关键技术:座舱盖隐身性能提升技术、大型整体座舱盖透明件结构设计技术、复杂曲面座舱盖光学性能仿真优化技术、大尺寸活动部件变形及状态控制技术。经过上述关键技术研究,完成了新一代战斗机座舱盖设计技术体系的升级,促进了新一代战斗机座舱盖技术和性能的跨代提升。 相似文献
378.
《中国航空学报》2016,(5):1196-1204
The flow fields over a generic cranked double delta wing were investigated. Pressure and velocity distributions were obtained using a Pitot tube and a hot wire anemometer. Two different leading edge shapes, namely ‘‘sharp" and ‘‘round", were applied to the wing. The wing had two sweep angles of 55° and 30°. The experiments were conducted in a closed circuit wind tunnel at velocity 20 m/s and angles of attack of 5°–20° with the step of 5°. The Reynolds number of the model was about 2 ×10~5 according to the root chord. A dual vortex structure was formed above the wing surface. A pressure drop occurred at the vortex core and the root mean square of the measured velocity increased at the core of the vortices, reflecting the instability of the flow in that region. The magnitude of power spectral density increased strongly in spanwise direction and had the maximum value at the vortex core. By increasing the angle of attack, the pressure drop increased and the vortices became wider; the vortices moved inboard along the wing, and away from the surface; the flow separation was initiated from the outer portion of the wing and developed to its inner part. The vortices of the wing of the sharp leading edge were stronger than those of the round one. 相似文献
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380.
Effect of Nb contents on microstructure and magnetic properties of FeCoNbB films has been studied. X-ray diffraction (XRD) analysis reveals that Nb plays a role in refining grain and in facilitating formation of amorphous structure. When Nb content is more than 8 at%, the films transform from crystalline to amorphous structure, accompanied by variations in magnetic properties. An unusual out-of-plane anisotropy component is consequently observed. It can be suggested that the anisotropy induced by increasing Nb contents be attributed to stress-related magnetoelastic anisotropy. The undesirable anisotropy is greatly reduced by thermal annealing, reducing film thicknesses or applying an external magnetic field together with Si addition. 相似文献