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Michael A. Earl Philip W. Somers Konstantin Kabin Donald Bédard Gregg A. Wade 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(8):2135-2146
For the first time, the spin axis orientation of an inactive box-wing geosynchronous satellite has been estimated from ground-based optical photometric observations of Echostar-2’s specular reflections. Recent photometric light curves obtained of Echostar-2 over four years suggest that unusually bright and brief specular reflections were occurring twice within an observed spin period. These bright and brief specular reflections suggested two satellite surfaces with surface normals separated by approximately 180°. The geometry between the satellite, the Sun, and the observing location at the time of each of the brightest observed reflections, was used to estimate Echostar-2’s equatorial spin axis orientation coordinates. When considering prograde and retrograde rotation, Echostar-2’s spin axis orientation was estimated to have been located within 30° of either equatorial coordinate pole. Echostar-2’s spin axis was observed to have moved approximately 180° in right ascension, within a time span of six months, suggesting a roughly one year spin axis precession period about the satellite’s angular momentum vector. 相似文献
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《中国航空学报》2020,33(11):2907-2920
This paper investigates a time-varying anti-disturbance formation problem for a group of quadrotor aircrafts with time-varying uncertainties and a directed interaction topology. A novel Finite-Time Convergent Extended State Observer (FTCESO) based fully-distributed formation control scheme is proposed to enhance the disturbance rejection and the formation tracking performances for networked quadrotors. By adopting the hierarchical control strategy, the multi-quadrotor system is separated into two subsystems: the outer-loop cooperative subsystem and the inner-loop attitude subsystem. In the outer-loop subsystem, with the estimation of disturbing forces and uncertain dynamics from FTCESOs, an adaptive consensus theory based cooperative controller is exploited to ensure the multiple quadrotors form and maintain a time-varying pattern relying only on the positions of the neighboring aircrafts. In the inner-loop subsystem, the desired attitude generated by the cooperative control law is stably tracked under a FTCESO-based attitude controller in a finite time. Based on a detailed algorithm to specify the cooperative control protocol, the feasibility condition to achieve the time-varying anti-disturbance formation tracking is derived and the rigorous analysis of the whole closed-loop multi-quadrotor system is given. Some numerical examples are conducted to intuitively demonstrate the effectiveness and the improvements of the proposed control framework. 相似文献
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《中国航空学报》2020,33(10):2716-2727
In this paper, an Unmanned Aerial Vehicle (UAV) enabled Mobile Edge Computing (MEC) system is studied, in which UAV acts as server to offer computing offloading service to the Mobile Users (MUs) with limited computing capability and energy budget. We aim to minimize the total energy consumption of MUs by jointly optimizing the bit allocation for uplink, computing at the UAV and downlink, along with the UAV trajectory in a unified framework. To this end, a trajectory constraint model is employed to avoid sudden changes of velocity and acceleration during flying. Due to high-order information in use, we lead to a more reasonable nonconvex optimization problem than prior arts. An Alternating Direction Method of Multipliers (ADMM) method is introduced to solve the optimization problem, which is decomposed into a set of easy sub-problems, to meet the requirement on the efficiency in edge computing. Numerical results demonstrate that our approach leads a smoother UAV trajectory, significantly save the energy consumption for UAV during flying. 相似文献
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X.B. Zhao W.Z. Shao L.B. Zhao Y. Gao Y.Y. Hu X.Z. Yuan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3072-3086
The main objective of our work was to investigate the impact of rain on wave observations from C-band (~5.3 GHz) synthetic aperture radar (SAR) in tropical cyclones. In this study, 10 Sentinel-1 SAR images were available from the Satellite Hurricane Observation Campaign, which were taken under cyclonic conditions during the 2016 hurricane season. The third-generation wave model, known as Simulating WAves Nearshore (SWAN) (version 41.31), was used to simulate the wave fields corresponding to these Sentinel-1 SAR images. In addition, rainfall data from the Tropical Rainfall Measuring Mission satellite passing over the spatial coverage of the Sentinel-1 SAR images were collected. The simulated results were validated against significant wave heights (SWHs) from the Jason-2 altimeter and European Centre for Medium-Range Weather Forecasts data, revealing a root mean square error (RMSE) of ~0.5 m with a 0.25 scatter index. Winds retrieved from the VH-polarized Sentinel-1 SAR images using the Sentinel-1 Extra Wide-swath Mode Wind Speed Retrieval Model after Noise Removal were taken as prior information for wave retrieval. It was discovered that rain did indeed affect the SAR wave retrieval, as evidenced by the 3.21-m RMSE of SWHs between the SAR images and the SWAN model, which was obtained for the ~1000 match-ups with raindrops. The raindrops dampened the wave retrieval when the rain rate was < ~5 mm/hr; however, they enhanced wave retrieval for higher rain rates. It was also found that the portion of the rain-induced ring wave with a wave number > 0.05 rad/m (~125 m wavelength) was clearly observed in the SAR-derived wave spectra. 相似文献
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摘要: 针对利用角动量交换装置系统实现轨控期间姿态维持的情况,研究当轨控推力器存在大力矩扰动时系统角动量管理方法.结合对地运行航天器轨道运动特性,分析轨控干扰力矩的积累角动量变化规律;考虑角动量管理装置系统的角动量存贮容量,基于角动量积累规律提出了一种结合偏置角动量建立与对称分布轨控位置选择的系统角动量管理方法,实现了对称轨控位置积累角动量互相抵消的自平衡效果,极大程度地提高轨控效率且避免系统角动量饱和现象.所提出的方法适用于喷气欠驱动控制系统,方法的有效性通过了数学仿真验证及在轨型号应用. 相似文献
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retro-GEO是指逆行(retrograde)地球静止轨道(geostationary Earth orbit, GEO),该轨道与GEO轨道高度相同或相近,但倾角为180°,安装在retro-GEO卫星上的巡视器可每12h对GEO带空间资产附近碎片环境安全预警。直接西向发射retro-GEO卫星存在地面测控和发射能耗较大的困难。基于平面四体模型,为降低设计变量敏感性,以近月点参数为设计变量,建立了部署retro-GEO巡视器的月球借力飞行轨道设计模型,利用轨道动力学模型延拓策略,得到该类轨道绕月后返回地球飞行时长只能约为114.79h,该结论可用于求解该类轨道高精度轨道动力学模型解。 相似文献