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263.
Zhenzhong Xu Weimin Wang Nan Zhou Xiaofei Song Haotian Zhu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
The variation of TEC data at Wuhan station (geographic coordinate: 30.5°N, 114.4°E; geomagnetic coordinate: 19.2°N, 183.8°E) at crest of equatorial anomaly in China from January 1997 to December 2007 were analyzed. Variability with solar activity, annual, semiannual, diurnal and seasonal variation were also analyzed. The MSIS00 model and ISR model were used to analyze the possible mechanisms of the variabilities found in the results. The TEC data in 1997 and 2001 deduced from another crest station Xiamen (geographic coordinate: 24.4°N, 118.1°E; geomagnetic coordinate: 13.2°N, 187.4°E) were used to contrast. Analysis results show that long-term variations of TEC at Xiamen station are mainly controlled by the variations of solar activities. Typical diurnal variation behaves as a minimum of the TEC in the pre-dawn hours around 05:00–06:00LT and a maximum on the afternoon hours around 13:00–15:00LT. Some features like the semiannual anomaly and winter anomaly in TEC have been reported. The anomaly may be the result of common action of the electric field over the magnetic equatorial and the [O/N2] at the crest station. 相似文献
264.
基于响应面优化的结构有限元模型修正 总被引:3,自引:0,他引:3
针对结构有限元分析中模型精度低的问题,提出了响应面优化的模型修正方法.利用优化拉丁方试验设计样本点,F值检验筛选出修正参数构造不完全4阶多项式响应面并检验响应面有效性.引入遗传算法以响应面计算值与试验值的残差为目标来优化修正参数,将修正值代入初始模型中得到修正模型.三自由度系统数值算例,验证了模型中参数准确、参数不存在和参数有误差3种工况下,响应面优化方法的模型修正能力.以GARTEUR飞机模型为对象,筛选显著性参数进行模型修正,结果表明修正后模型不但在修正频段和预测频段具有良好的复现和预测能力,还能预测结构局部修改后的频率,证实了经过参数筛选后响应面优化的模型修正有效性. 相似文献
265.
Optimal diving maneuver strategy considering guidance accuracy for hypersonic vehicle 总被引:2,自引:0,他引:2
An optimal maneuver strategy considering terminal guidance accuracy for hypersonic vehicle in dive phase is investigated in this paper. First, it derives the complete three-dimensional nonlinear coupled motion equation without any approximations based on diving relative motion relationship directly, and converts it into linear decoupled state space equation with the same relative degree by feedback linearization. Second, the diving guidance law is designed based on the decoupled equation to meet the terminal impact point and falling angle constraints. In order to further improve the interception capability, it constructs maneuver control model through adding maneuver control item to the guidance law. Then, an integrated performance index consisting of maximum line-of-sight angle rate and minimum energy consumption is designed, and optimal control is employed to obtain optimal maneuver strategy when the encounter time is determined and undetermined, respectively. Furthermore, the performance index and suboptimal strategy are reconstructed to deal with the control capability constraint and the serous influence on terminal guidance accuracy caused by maneuvering flight. Finally, the approach is tested using the Common Aero Vehicle-H model. Simulation results demonstrate that the proposed strategy can achieve high precision guidance and effective maneuver at the same time, and the indices are also optimized. 相似文献
266.
液体多模态晃动充液航天器姿态机动复合控制 总被引:1,自引:0,他引:1
主要研究多模态液体晃动时充液航天器大角度姿态机动动力学与控制问题。采用液体晃动弹簧质量等效力学模型将液体燃料前两阶液体晃动模态纳入到充液航天器耦合动力学模型中;根据动量矩守恒定律推导出充液航天器耦合系统动力学方程。针对充液航天器大角度姿态机动同时抑制燃料晃动的问题,采用自适应动态输出反馈的姿态控制方法并结合基于前馈控制的多模态ZVD输入成型器设计复合控制器。通过数值模拟给出了液体晃动响应及航天器姿态机动的时间历程图,数值仿真结果表明了本文所给出复合控制方法的有效性。 相似文献
267.
了解和掌握弹性波在含有裂纹介质中的传播规律是开发利用页岩气等非常规油气资源中的关键科学问题.本文基于数值模拟的优点,采用商用有限元软件Nastran模拟弹性波在含裂纹介质中的激发及传播方式,分析了弹性波在该介质中裂纹微结构(密度和纵横比)对弹性波传播动力学特性的依赖程度.结果表明:有限元方法(FEM)可以用于该问题的研究;Hudson等效介质理论(EMT)不适用泊松比近0.5的材料;裂纹密度、纵横比的增大会减小纵波(P波)波速值,以及衰减位移时域响应的首波振幅,且裂纹密度对于该材料的各向异性的影响要远大于纵横比的作用. 相似文献
268.
Changchun Bao Jingyang Li Hexi Baoyin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):97-110
Accurate initial solutions for two-segment Earth-Moon free-return trajectories, with midcourse transfer opportunities for favorable lunar targeting, are developed analytically by using the pseudostate theory. A constrained flight-path angle quasi-Lambert problem is formulated to determine the lunar-orbiting phase of the free-return trajectory. Gradient and direct-shooting algorithms are used to correct the initial estimates of certain two-body parameters. Numerical simulations with a high-fidelity model are undertaken to verify the accuracy of the pseudostate solutions and to illustrate the efficiency of the proposed algorithm. Perilune altitude errors for the pseudostate method are less than 10% of their corresponding values for the patched conic technique. The differences between the pseudostate and the high-fidelity solutions can be eliminated rapidly. 相似文献
269.
成像传感器和定位子系统是先进机载成像系统的两个重要组成部分。以东、北、天坐标系为导航基准坐标系,建立了GPS-SINS组合系统状态的数学模型,详细推导了利用GPS双差相位及双差相位率的组合系统观测方程。仿真结果表明,该组合系统能达到厘米级定位精度,姿态精度为10″左右,可满足先进机载成像系统的要求。 相似文献
270.
包妙琴 《中国空间科学技术》1989,9(4):29-39
本文提出一种卫星研制成本的划分方法。把输入的资源和输出的产品取为划分成本的基本元素。应用这些元素建立一个划分和综合成本的矩阵。提出了几种不同的成本划分,用以在预研和方案设计阶段对卫星研制成本进行估算。 相似文献