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91.
S. Takechi K. Nogami T. Miyachi M. Fujii N. Hasebe T. Iwai S. Sasaki H. Ohashi H. Shibata E. Grün R. Srama N. Okada 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
A cosmic dust monitor for use onboard a spacecraft is currently being developed using a piezoelectric lead zirconate titanate element (PZT). Its characteristics of the PZT sensor is studied by ground-based laboratory impact experiments using hypervelocity particles supplied by a Van de Graaff accelerator. The output signals obtained from the sensor just after the impact appeared to have a waveform that was explicitly related to the particle’s impact velocity. For velocities less than ∼6 km/s, the signal showed an oscillation pattern and the amplitude was proportional to the momentum of the impacting particle. For higher velocities, the signal gradually changed to a single waveform. The rise time of this single waveform was proportional to the particle’s velocity for velocities above ∼6 km/s. The present paper reports on results for the low velocity case and especially discusses the effect of an outer coating of the sensor with a paint, which is used to reduce heating by solar radiation. 相似文献
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This paper deals with the relative navigation of a formation of two spacecrafts separated by hundreds of kilometers based on processing dual-frequency differential carrier-phase GPS measurements. Specific requirements of the considered application are high relative positioning accuracy and real-time on board implementation. These can be conflicting requirements. Indeed, if on one hand high accuracy can be achieved by exploiting the integer nature of double-difference carrier-phase ambiguities, on the other hand the presence of large ephemeris errors and differential ionospheric delays makes the integer ambiguities determination challenging. Closed-loop schemes, which update the relative position estimates of a dynamic filter with feedback from integer ambiguities fixing algorithms, are customarily employed in these cases. This paper further elaborates such approaches, proposing novel closed loop techniques aimed at overcoming some of the limitations of traditional algorithms. They extend techniques developed for spaceborne long baseline relative positioning by making use of an on-the-fly ambiguity resolution technique especially developed for the applications of interest. Such techniques blend together ionospheric delay compensation techniques, nonlinear models of relative spacecraft dynamics, and partial integer validation techniques. The approaches are validated using flight data from the Gravity Recovery and Climate Experiment (GRACE) mission. Performance is compared to that of the traditional closed-loop scheme analyzing the capability of each scheme to maximize the percentage of correctly fixed integer ambiguities as well as the relative positioning accuracy. Results show that the proposed approach substantially improves performance of the traditional approaches. More specifically, centimeter-level root-mean square relative positioning is feasible for spacecraft separations of more than 260 km, and an integer ambiguity fixing performance as high as 98% is achieved in a 1-day long dataset. Results also show that approaches exploiting ionospheric delay models are more robust and precise of approaches relying on ionospheric-delay removal techniques. 相似文献
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Maria S. Pulinets Elizaveta E. Antonova Maria O. Riazantseva Svetlana S. Znatkova Igor P. Kirpichev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Crossings of the magnetopause near the subsolar point are analyzed using data of THEMIS mission. Variations of the magnetic field near magnetopause measured by one of THEMIS satellites are studied and compared with simultaneous measurements in the solar wind by another THEMIS satellite. The time delay of the solar wind arrival at the subsolar point of the magnetopause is taken into account. 30 and 90 s averaging of the magnetic field in the magnetosheath is produced. The results of averaging are compared with the results of measurements in the solar wind before the bow shock and foreshock. It is shown, that Bx component of the magnetic field near magnetopause is near to zero, which supports the possibility to consider the magnetopause as the tangential discontinuity. Comparatively good correlation of By component in the solar wind and near the magnetopause is observed. The correlation of Bz component near the magnetopause and IMF is practically absent, the sign of the Bz near the subsolar point does not coincide with the sign of IMF Bz in ∼30% cases. 相似文献
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脉冲推力轨道拦截可达性描述及求解方法 总被引:2,自引:1,他引:1
针对航天器单脉冲轨道拦截可达性分析问题,基于共面变轨、逆轨拦截假设,考虑能量、时间和交会角约束,提出了拦截航天器可拦截区和可发射区的概念。在航天器单脉冲空间可达范围的基础上,进一步考虑了目标轨道的约束,建立了目标轨道命中区的计算策略,对异面轨道交叉点为燃料最省点做出了解释。把拦截可达性相关的问题归纳为8个基本拦截问题,通过这8个问题的组合,描述了考虑能量、时间和交会角约束下拦截问题的可拦截区和可发射区的计算方法。采用圆轨道共面变轨、逆轨拦截场景进行了仿真验证,结果表明该方法能够快速有效地计算出约束条件下航天器的拦截可达范围,能够用于分析特定任务情况下的拦截可达性。 相似文献
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地球卫星重力测量计划CHAMP(CHAllenging Minisatellite Payload)、GRACE(Gravity Recovery and Climate Experiment)、GOCE(Gravity field and steady-state Ocean Circulation Explorer)和月球卫星重力测量计划(Gravity Recovery and Interior Laboratory,GRAIL)的成功实施,以及下一代地球重力卫星(GRACE Follow-On)的即将发射昭示着我们将迎来一个前所未有的高精度和高空间分辨的深空卫星重力探测时代。围绕深空卫星重力测量的研究背景、必要性、可行性、卫星重力反演软件平台构建、轨道摄动和未来研究方向开展了研究论证。研究表明:深空卫星重力测量作为新世纪重力探测技术,在精化量体重力场、提高惯性导航精度、天体动力学、天体物理学和军事技术的研究,以及促进国民经济发展和提高社会效益等方面具有广泛的应用前景。 相似文献
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针对遥感卫星成像任务规划时对点目标的聚类效果不佳的问题,提出了一种改进的单轨最优团划分聚类方法。根据聚类约束条件,构建任务聚类图模型,并为图模型中的每一条边赋权值;根据图模型中边的权值,构建权值矩阵P;以卫星单轨姿态机动的最大次数作为聚类任务的数量限制,由P依次计算每个聚类任务所有可能的最优聚类方案,并生成对应的收益矩阵M和终点矩阵N;通过循环遍历的方式计算各个聚类方案下的总收益,其中总收益最大的方案即为最优团划分聚类方案。仿真结果表明:提出的改进的团划分聚类方法,能将点目标有效聚类,与传统任务聚类方法相比,可明显提高遥感卫星对点目标的观测效率。研究结果可为我国遥感卫星自主任务规划技术研究提供参考。 相似文献