全文获取类型
收费全文 | 743篇 |
免费 | 319篇 |
国内免费 | 185篇 |
专业分类
航空 | 549篇 |
航天技术 | 276篇 |
综合类 | 66篇 |
航天 | 356篇 |
出版年
2025年 | 7篇 |
2024年 | 20篇 |
2023年 | 31篇 |
2022年 | 39篇 |
2021年 | 48篇 |
2020年 | 57篇 |
2019年 | 48篇 |
2018年 | 66篇 |
2017年 | 42篇 |
2016年 | 48篇 |
2015年 | 69篇 |
2014年 | 69篇 |
2013年 | 46篇 |
2012年 | 77篇 |
2011年 | 85篇 |
2010年 | 58篇 |
2009年 | 48篇 |
2008年 | 47篇 |
2007年 | 57篇 |
2006年 | 42篇 |
2005年 | 24篇 |
2004年 | 33篇 |
2003年 | 25篇 |
2002年 | 16篇 |
2001年 | 26篇 |
2000年 | 21篇 |
1999年 | 13篇 |
1998年 | 19篇 |
1997年 | 14篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 5篇 |
排序方式: 共有1247条查询结果,搜索用时 15 毫秒
771.
Qijia Yao 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(6):1830-1843
Space manipulator is considered as one of the most promising technologies for future space activities owing to its important role in various on-orbit serving missions. In this paper, a novel adaptive fuzzy neural network (FNN) control scheme is proposed for the trajectory tracking control of an attitude-controlled free-flying space manipulator in the presence of output constraints and input nonlinearities. The parametric uncertainties and external disturbances are also taken into the consideration. First, a model-based controller is designed by using the barrier Lyapunov function (BLF) to prevent the position tracking errors from violating the predefined output constraints. Then, an adaptive FNN controller is designed by using two FNNs to compensate for the lumped uncertainties and input nonlinearities, respectively. Rigorous theoretical analysis for the semiglobal uniform ultimate boundedness of the whole closed-loop system is provided. The proposed adaptive FNN controller can guarantee the position and velocity tracking errors converge to the small neighborhoods about zero, while ensuring the position tracking errors within the output constraints even in the presence of input nonlinearities. To the best of the authors’ knowledge, there are relatively few existing controllers can achieve such excellent control performance in the same conditions. Numerical simulations illustrate the effectiveness and superiority of the proposed control scheme. 相似文献
772.
《中国航空学报》2021,34(4):403-415
A forced ignition probability analysis method is developed for turbulent combustion, in which kernel formation is analyzed with local kernel formation criteria, and flame propagation and stabilization are simulated with Lagrangian flame particle tracking. For kernel formation, the effect of turbulent scalar transport on flammability is modelled through the incorporation of turbulence-induced diffusion in a spherically outwardly propagating flame kernel model. The dependence of flammability limits on turbulent intensities is tabulated and serves as the flammability criterion for kernel formation. For Lagrangian flame particle tracking, flame particles are tracked in a structured grid with flow fields being interpolated from a Computational Fluid Dynamics (CFD) solution. The particle velocity follows a Langevin model consisting of a linear drift and an isotropic diffusion term. The Karlovitz number is employed for the extinction criterion, which compares chemical and turbulent timescales. The integration of the above two-step analysis approach with non-reacting CFD is achieved through a general interpolation interface suitable for general unstructured CFD grids. The method is demonstrated for a methane/air bluff-body flame, in which flow and fuel/air mixing characteristics are extracted from a non-reacting simulation. Results show that the computed ignition probability map agrees qualitatively with experimental results. A reduction of the ignition probability in the recirculation zone and a high ignition probability on the shear layer of the recirculation zone near the mean stoichiometric surface are well captured. The tools can facilitate optimization of spark placement and offer insights into ignition processes. 相似文献
773.
A novel soft robotic arm(SRA) composed of two soft extensible arms(SEAs) and a soft bendable joint(SBJ) for space capture systems is presented in this paper. A diamond origami pattern was applied in the design of the SEAs, and large deformations of the SEAs in positive pressure were simulated using the nonlinear finite element method. A kinematic model of the SRA using the Denavit–Hartenberg method based on the assumption of constant curvatures was proposed. A closed-loop model-free control syst... 相似文献
774.
刘建东 《沈阳航空工业学院学报》2007,24(5):32-34
位标器是导弹的重要组成部件,其能否正常工作直接影响导弹的跟踪能力。为此,从生产过程的工艺和装配过程出发,分析了造成位标器跟踪能力下降的主要因素,提出了解决问题的方法,对导弹的研制和生产有较强的实践指导意义。 相似文献
775.
前起落架突伸对舰载机起飞特性的影响 总被引:3,自引:0,他引:3
研究了前起落架突伸的实现模式和突伸对舰载机起飞特性的影响,分别对四种突伸模式及突伸机构设计参数的作用进行了比较分析,结果表明,前起落架突伸对于减少舰载机离舰后的下沉和缩短飞机起飞滑跑距离有明显的作用。 相似文献
776.
777.
Dipak K. Srinivasan Mark E. Perry Karl B. Fielhauer David E. Smith Maria T. Zuber 《Space Science Reviews》2007,131(1-4):557-571
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Radio Frequency (RF) Telecommunications Subsystem
is used to send commands to the spacecraft, transmit information on the state of the spacecraft and science-related observations,
and assist in navigating the spacecraft to and in orbit about Mercury by providing precise observations of the spacecraft’s
Doppler velocity and range in the line of sight to Earth. The RF signal is transmitted and received at X-band frequencies
(7.2 GHz uplink, 8.4 GHz downlink) by the NASA Deep Space Network. The tracking data from MESSENGER will contribute significantly
to achieving the mission’s geophysics objectives. The RF subsystem, as the radio science instrument, will help determine Mercury’s
gravitational field and, in conjunction with the Mercury Laser Altimeter instrument, help determine the topography of the
planet. Further analysis of the data will improve the knowledge of the planet’s orbital ephemeris and rotation state. The
rotational state determination includes refined measurements of the obliquity and forced physical libration, which are necessary
to characterize Mercury’s core state. 相似文献
778.
遥外测综合测量系统弹道计算新方法 总被引:2,自引:0,他引:2
遥外测综合测量系统在定位精度上有其局限性 ,布站不能接近同一平面 ,必须布置一个空中站来改善布站几何 ,否则容易引起定位无解或精度差 ,但布置空中站在工程上很难实现 ,且代价太高。针对这个问题 ,提出一种新的弹道计算方法 ,可以有效弥补上述局限性 ,取消空中站 ,并且显著提高定位精度。 相似文献
779.
780.