全文获取类型
收费全文 | 892篇 |
免费 | 140篇 |
国内免费 | 118篇 |
专业分类
航空 | 314篇 |
航天技术 | 280篇 |
综合类 | 14篇 |
航天 | 542篇 |
出版年
2024年 | 2篇 |
2023年 | 23篇 |
2022年 | 15篇 |
2021年 | 29篇 |
2020年 | 46篇 |
2019年 | 56篇 |
2018年 | 46篇 |
2017年 | 23篇 |
2016年 | 45篇 |
2015年 | 49篇 |
2014年 | 66篇 |
2013年 | 58篇 |
2012年 | 43篇 |
2011年 | 89篇 |
2010年 | 44篇 |
2009年 | 44篇 |
2008年 | 35篇 |
2007年 | 53篇 |
2006年 | 52篇 |
2005年 | 37篇 |
2004年 | 39篇 |
2003年 | 39篇 |
2002年 | 19篇 |
2001年 | 23篇 |
2000年 | 23篇 |
1999年 | 27篇 |
1998年 | 12篇 |
1997年 | 22篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 3篇 |
排序方式: 共有1150条查询结果,搜索用时 234 毫秒
371.
航天器在实施对空间非合作目标的近程操作任务中,需要接近目标并保持在目标附近的特定方位,对目标指定部位随动跟踪和观测。针对非合作机动目标的接近和视线跟踪的六自由度控制问题,根据视线坐标系下的相对轨道方程和体坐标系下的相对误差四元数姿态方程,建立了航天器间近距离相对运动的轨道和姿态联合控制模型。考虑模型的非线性、时变性和计算的快速性,采用θ-D控制方法进行接近和视线跟踪的轨道和姿态联合控制。为了减小跟踪同时存在轨道和姿态机动的非合作目标的控制误差,应用Lyapunov最小-最大定理设计了θ-D修正控制器,改善非合作目标同时进行姿态和轨道机动时的控制性能。仿真验证了模型的正确性和控制器良好的跟踪性能。 相似文献
372.
373.
374.
基于移动质心滚动控制方案,研究了其动力学系统建模和非线性耦合系统控制的问题。不同于移动质心控制系统建模中常用的牛顿力学建模和常规拉格朗日建模法,采用准坐标形式的拉格朗日法建立了完整的系统动力学方程,避免了牛顿力学中复杂的相互作用力分析和常规拉格朗日建模法物理意义不明确的缺点。鉴于移动质心滚动控制系统的非线性、耦合性和时变性,提出把系统的非线性耦合项和外部干扰统归为未知扰动,并采用自抗扰控制(ADRC)技术进行估计和补偿,相对于常用的比例微分(PD)控制,自抗扰控制器能更好地适应系统参数的变化,具有很强的鲁棒性。最后,通过数学仿真验证了整个控制方案的可行性。 相似文献
375.
Saleh Basha Alkhodari Renuganth Varatharajoo 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1897-1903
The combined attitude and thermal control system (CATCS) combines the conventional attitude control and thermal control subsystems. Its principle is based on circulating a heat conducting fluid inside a closed duct wielding the excess onboard heat in order to produce the attitude control torques. Previously only the proportional-integral (PI) controller has been tested for CATCS. In this paper two other control options for CATCS were designed based on the H2 and H∞ control methods to improve the attitude control performance of a small satellite. The control gain matrix with the minimum cost function is obtained by solving the Riccati equation and fed back to the system in order to achieve the system’s performance. The designed controllers can efficiently control the roll, pitch and yaw satellite attitudes. Simulations for the two techniques were carried out using Matlab and Simulink for ideal and non-ideal system models. Results show that the H2 controller has a better attitude control performance over the H∞ controller and PI controller itself. 相似文献
376.
基于RBF网络辨识的挠性卫星姿态自适应控制 总被引:2,自引:0,他引:2
为满足挠性卫星姿态控制的更高要求,提出了一种基于径向基函数(RBF)网络辨识的模糊自适应控制方法。根据卫星姿态动力学方程,将RBF辨识网络引入模糊神经网络的T-S模型,以辨识卫星,在线修改模糊神经控制器(FNC)参数,使卫星的姿态角度达到设定值。仿真结果表明:该法能有效克服卫星的不确定性,提高卫星姿态的控制精度。 相似文献
377.
某卫星挠性附件姿态动力学研究 总被引:1,自引:0,他引:1
根据导出的某有大型太阳帆板的挠性卫星数学模型,分析了模型中挠性振动对质心和姿态运动的影响,给出了卫星系统的动力学方程,并对帆板展开、卫星稳态运行的模型作工程化处理。分析和仿真结果表明:该方法能降低模型的复杂度,满足大型卫星的姿态指向精度和稳定度要求。 相似文献
378.
研究了扰动后的电离层对不同波段的电磁波传播的影响,并探讨了该项技术在通信对抗上的具体应用。结果表明:受扰电离层可以引导VLF波进行"哨声模式"传播,进而实现对潜通信;可以使得HF波传播轨迹发生偏转、逃逸、聚焦和散焦,进而实现短波干扰;可以降低卫星通信频率,进而利用新波段实现卫星保密通信,同时还能产生透镜效应,对实现卫星通信的VHF电波产生额外增益,增强通信效果。 相似文献
379.
The attitude determination capability of a nano satellite is limited by a lack of traditional high performance attitude sensors, a result of having small budgets for mass and power. Attitude determination can still be performed on a nano satellite with low fidelity sensors, but an accurate model of the spacecraft attitude dynamics is required. The passive magnetic stabilization systems commonly employed in nano satellites are known to introduce uncertainties in the parameters of the attitude dynamics model that cannot easily be resolved prior to launch. In this paper, a batch estimation problem is formulated that simultaneously solves for the attitude of the spacecraft and performs parameter estimation on the magnetic properties of the magnetic materials using only a measurement of the solar vector. The estimation technique is applied to data from NASA Ames Research Center's O/OREOS nano satellite and the University of Michigan's RAX-1 nano satellite, where clear differences are detected between the magnetic properties as measured before launch and those that fit the observed data. To date this is the first known on-orbit verification of the attitude dynamics model of a passively magnetically stabilized spacecraft. 相似文献
380.
Validation of a Compression Mass Gauge using ground tests for liquid propellant mass measurements 总被引:1,自引:0,他引:1
Juan Fu Xiaoqian Chen Yiyong Huang Xiaolong Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
To properly estimate orbital lifetimes and predict the maneuverability of spacecraft, the remaining liquid propellant mass must be accurately known at every moment of a space mission. This paper studies the Compression Mass Gauge (CMG) method to determine the mass of liquid contained in a tank in a low-gravity environment with high accuracy. CMG is a thermodynamic method used to determine the quantity of liquid by measuring the gas pressure change when the tank volume changes, and has been previously theoretically and experimentally studied by researchers. The primary objective of this investigation is to explore the effects of attitude disturbance and the spacecraft thermal environment on the accuracy of the method. A ground test system, consisting of several test apparatuses, was fabricated and described as part of this study. The test results and analyses indicate that the CMG performs well and has an accuracy of ±1%. Additionally, demonstrations were performed to show that measurement errors do not increase drastically or exceed ±1% when the test system is vibrated to simulate the tank being perturbed as a result of an attitude disturbance. Liquid sloshing resonance was found to have a significant effect on the gauging accuracy. Measurements in a real thermal environment in which heat transfers into and out of the propellant tank were also conducted. The results show that the gauging accuracy is acceptable for normal liquid propellant. Furthermore, theoretical research shows that heat leakage has a significant influence on cryogenic propellant mass gauging. 相似文献