全文获取类型
收费全文 | 1613篇 |
免费 | 293篇 |
国内免费 | 349篇 |
专业分类
航空 | 1471篇 |
航天技术 | 319篇 |
综合类 | 231篇 |
航天 | 234篇 |
出版年
2024年 | 5篇 |
2023年 | 22篇 |
2022年 | 31篇 |
2021年 | 62篇 |
2020年 | 69篇 |
2019年 | 77篇 |
2018年 | 82篇 |
2017年 | 92篇 |
2016年 | 105篇 |
2015年 | 103篇 |
2014年 | 108篇 |
2013年 | 87篇 |
2012年 | 112篇 |
2011年 | 109篇 |
2010年 | 95篇 |
2009年 | 99篇 |
2008年 | 86篇 |
2007年 | 86篇 |
2006年 | 79篇 |
2005年 | 69篇 |
2004年 | 65篇 |
2003年 | 61篇 |
2002年 | 60篇 |
2001年 | 52篇 |
2000年 | 51篇 |
1999年 | 35篇 |
1998年 | 31篇 |
1997年 | 31篇 |
1996年 | 38篇 |
1995年 | 34篇 |
1994年 | 50篇 |
1993年 | 33篇 |
1992年 | 25篇 |
1991年 | 33篇 |
1990年 | 24篇 |
1989年 | 21篇 |
1988年 | 20篇 |
1987年 | 8篇 |
1986年 | 5篇 |
排序方式: 共有2255条查询结果,搜索用时 78 毫秒
981.
982.
Hancheol Cho 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(5):1454-1467
In this study, a two-step control methodology is developed for energy-optimal reconfiguration of satellites in formation in the presence of uncertainties or external disturbances. First, based on a linear deterministic system model, an optimal control law is analytically determined such that a satellite maneuvers from an initial state to a final state relative to another satellite. The structure of this optimal solution is predetermined and simply given by a linear combination of the fundamental matrix solutions associated with the original equations of relative motion. Only the coefficients are to be determined to satisfy given initial and final conditions. In the second step, an uncertain nonlinear formation system is considered and a robust adaptive controller is designed to compensate for the effects of uncertainties or disturbances that the formation system may encounter. Although the control strategy is inspired by sliding mode control, it produces smooth control signals, thereby avoiding chattering. Also, an adaptation law is added such that the uncertainty or disturbance effects are effectively and quickly eliminated without a priori information about them. The combination of these two controllers guarantees that the satellite accurately tracks the optimal path in the unknown environment. Numerical simulations demonstrate the effectiveness and accuracy of the proposed two-step control methodology, in which a satellite formation is optimally reconfigured under unknown environmental disturbances. 相似文献
983.
Behrad Vatankhahghadim Christopher J. Damaren 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(9):2746-2756
The deployment dynamics of a solar sail consisting of four flexible booms and four membrane quadrants are studied. First, previous work on modelling only one membrane quadrant attached to two axially moving beams using time-varying quasi-modal expansion is extended to be applicable to the complete four-quadrant system. This is achieved via “lifting” the quadrant-level matrices into system-level forms by mapping the former’s constituent blocks to the correct partitions in the latter. After the quadrant-to-system conversion of the matrices, the equations of motion from the authors’ previous work readily apply to the complete system. Modal analysis is performed on a constant-length sail to validate the model’s basic foundations against the results obtained by finite element methods in the past literature. Deployment simulation results are presented, numerical parameter studies that show possibility of instability are performed using the system’s eigenvalues, and the stability results are discussed. 相似文献
984.
Casing treatment is a mature stabilization technique which has been widely applied on aero-engines for modern aircrafts and turbo-chargers for automobiles. After the investigations of half century since the 1960s, this technique has been well developed for various configurations with different effectiveness. From the perspective of stabilization mechanism, this paper roughly categorizes the configurations of casing treatment into two types: traditional ones which work by affecting the flow structure of blade tip region; a novel one named as Stall Precursor-Suppressed (SPS) casing treatment. The effectiveness of both types will be demonstrated for their applications on axial compressors and centrifugal compressors with uniform or distorted inlet. And the stabilization mechanism of casing treatments for regular types and SPS one will also be explained respectively. In addition, this review will summarize the methodologies of casing treatments with the numerical simulations for regular grooved configurations and the eigenvalue approach for SPS casing treatment. Looking forward to the future of compressor stabilization, casing treatment technique will still exist as a general and inexpensive option, and the exploration for its effectiveness and mechanism will be deeper with the development of computational fluid dynamics and advanced measurement techniques. 相似文献
985.
通过对液浮陀螺电机轴向预紧力调整情况及声音异常现象的分析,归纳和完善了电机轴向预紧力调整过程中的经验调法,并对电机轴向预紧力的量化调整进行了摸索和探讨,提出了较为可行的解决措施,从一定程度上保证了电机装调质量,提高了小型化精密电机装调合格率。 相似文献
986.
采用雷诺平均的Navier-Stokes方程,对接网格技术和TRIP(TRI sonic Platform)软件,数值模拟了CT-1标模大迎角静态气动特性。来流马赫数0.5,迎角0°~100°,侧滑角0°和5°,在与1.2 m跨声速风洞试验结果对比的基础上,重点讨论了对流项离散方法、湍流模型、远场距离和不同尾部处理形式对CT-1标模大迎角静态气动特性影响。研究结果表明,不同尾部处理形式对大迎角静态气动特性数值模拟结果影响显著,模拟试验的尾部支杆是对比大迎角静态测力试验结果与计算结果的基本要求。 相似文献
987.
介绍了一种利用激光测距仪测距、CCD光学经纬仪测角对动态的舰载雷达天线进行定位的雷达标校方法。探讨了对动态目标的定位原理,给出了真值测量的数学模型,论证了方位标的设计原则,分析了雷达标校的精度。 相似文献
988.
文章研究了学习活动中的一些问题,归纳总结出了非线性阈值效应,建立非线性动力学模型,进行了分岔与稳定性分析,做了仿真模拟并结合经验进行了解释。 相似文献
989.
990.