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801.
802.
非线性系统可靠性分析的重要抽样法 总被引:2,自引:0,他引:2
简要介绍了广泛应用于非线性系统可靠性分析与评估的重要抽样法的基本内容,对这一方法的优缺点及其限制条件进行了评论,对国外在这一领域的研究进展及其存在的问题进行了剖析,对这一领域今后的发展方向和需要解决的问题提出了一些个人意见和建议。 相似文献
803.
关于开发适合我国国情的TDRSS的设想 总被引:4,自引:0,他引:4
简介国际“跟踪与数据中继卫星系统”(TDRSS)的概况,强调中国的特殊性,提出尽快建立军民两用、综合应用、中等性能的TDRSS,以尽早获得最基本的近全球的跟踪、通信与自主导航的能力,从而填补天基支撑的空白。主张综合功能一步到位,超过日本;性能上接近日本,逐步提高。在技术思路上,建议采用PCM-OQPSK 及PCM-CDMA-BPSK数据传输体制;星本体测控与用户的跟踪导航统一采用单通道单脉冲测角、伪码测距的单站定轨体制,并利用星本体测控数据提高用户的跟踪导航精度;主张在TDRSS的设计中全面贯彻CCSDS协议标准,尽早参与区域以至全球的高速信息网。最后,对下世纪初实现具有中国特色的TDRSS的技术关键与可能性,提出了看法。指出,中国的TDRSS将超越航天测控网的范畴,而成为全球战略技术信息的天基传递网,并终将成为全球高速信息网的重要组成部分 相似文献
804.
Given the diversity of missions it has accomplished and the myriad of adaptations it has undergone, the US Space Shuttle is widely regarded as a highly flexible space vehicle. With the Shuttle’s upcoming 2011 retirement, it is instructive to survey the history of this vehicle’s flexibility for the insights it can provide to the design and characterization of flexibility in future space systems. Data are presented on the evolution of mission requirements over time for 120 missions performed by the Space Shuttle over a period of some 27 years. Distinct trends in the time domain – as well as their causes – are identified and discussed, and early manifest plans from 1982 serve as a confirmation that these trends were not originally anticipated. Eight examples are then presented of engineering modifications that allowed the Shuttle to adapt and accommodate these requirement changes. Several additional instances of Shuttle flexibility are explored, such as post-Columbia disaster modification, upgrade programs and derived vehicles, and one case in which flexibility was inhibited by an early design decision. 相似文献
805.
C^4ISR系统评估环境的构建对C^4ISR系统效能评估至关重要。本文深入分析了C^4ISR系统特点和评估需求,提出了效能评估思路,设计了基于HLA的评估环境基本构架和C^4ISR系统模型体系结构,该研究对C^4ISR系统鉴定具有重要现实意义。 相似文献
806.
介绍了多惯性仪表冗余惯性测量系统数据融合前的测量异常值去除、系统误差修正和一致性检验的基本方法。针对测量数据一致性检验,讨论了置信距离测度和信任度函数两种处理方法。仿真结果表明后者能更好地确定一致性的惯性仪表测量数据。 相似文献
807.
808.
This paper describes the end-to-end validation process for the Attitude Control Subsystem (ACS) of the satellite INTA-NanoSat-1B (NS-1B). This satellite was launched on July 2009 and it has been fully operative since then. The development of its ACS modules required an exhaustive integration and a system-level validation program. Some of the tests were centred on the validation of the drivers of sensors and actuators and were carried out over the flying model of the satellite. Others, more complex, constituted end-to-end tests where the concurrency of modules, the real-time control requirements and even the well-formedness of the telemetry data were verified. This work presents an incremental and highly automatised way for performing the ACS validation program based on two development suites and an end-to-end validation environment. The validation environment combines a Flat Satellite (FlatSat) configuration and a real-time emulator working in closed-loop. The FlatSat is built using the NS-1B Qualification Model (QM) hardware and it can run a complete version of the on-board software with the ACS modules fully integrated. The real-time emulator, running on an industrial PC, samples the actuation signals and emulates the sensors signals to close the control loop with the FlatSat. This validation environment constitutes a low-cost alternative to the classical three axes tilt table, with the advantage of being easily configured for working under specific orbit conditions, in accordance with any of the selected tests. The approach has been successfully applied to the NS-1B in order to verify different ACS modes under multiple orbit scenarios, providing an exhaustive coverage and reducing the risk of eventual errors during the satellite's lifetime. The strategy was applied also during the validation of the maintenance and reconfiguration procedures required once the satellite was launched. This paper describes in detail the complete ACS validation process that was performed and it shows the most relevant errors detected and fixed during testing. Finally it summarises some of the most significant conclusions. 相似文献
809.
丁叙生 《南昌航空工业学院学报》2000,14(3):26-29
本文介绍以主轴系统刚度与总功耗之比值最大比值最大为目标函数、主轴系统刚度的校验准则为主要约束条件的液体静压轴承优化设计方法,与普通设计方法相比,两种不同结构液体静压承经优化设计后,其单位总功耗的主轴系统刚度都成倍增加。 相似文献
810.
Solar Nebula Magnetohydrodynamics 总被引:1,自引:0,他引:1
The dynamical state of the solar nebula depends critically upon whether or not the gas is magnetically coupled. The presence
of a subthermal field will cause laminar flow to break down into turbulence. Magnetic coupling, in turn, depends upon the
ionization fraction of the gas. The inner most region of the nebula (≲0.1 AU) is magnetically well-coupled, as is the outermost
region (≳10 AU). The magnetic status of intermediate scales (∼1 AU) is less certain. It is plausible that there is a zone
adjacent to the inner disk in which turbulent heating self-consistently maintains the requisite ionization levels. But the
region adjacent to the active outer disk is likely to be magnetically ``dead.' Hall currents play a significant role in nebular
magnetohydrodynamics.
Though still occasionally argued in the literature, there is simply no evidence to support the once standard claim that differential
rotation in a Keplerian disk is prone to break down into shear turbulence by nonlinear instabilities. There is abundant evidence—numerical,
experimental, and analytic—in support of the stabilizing role of Coriolis forces. Hydrodynamical turbulence is almost certainly
not a source of enhanced turbulence in the solar nebula, or in any other astrophysical accretion disk.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献