全文获取类型
收费全文 | 1843篇 |
免费 | 211篇 |
国内免费 | 242篇 |
专业分类
航空 | 674篇 |
航天技术 | 802篇 |
综合类 | 98篇 |
航天 | 722篇 |
出版年
2024年 | 10篇 |
2023年 | 38篇 |
2022年 | 51篇 |
2021年 | 80篇 |
2020年 | 66篇 |
2019年 | 55篇 |
2018年 | 72篇 |
2017年 | 42篇 |
2016年 | 56篇 |
2015年 | 59篇 |
2014年 | 110篇 |
2013年 | 110篇 |
2012年 | 103篇 |
2011年 | 167篇 |
2010年 | 131篇 |
2009年 | 103篇 |
2008年 | 85篇 |
2007年 | 113篇 |
2006年 | 109篇 |
2005年 | 89篇 |
2004年 | 69篇 |
2003年 | 63篇 |
2002年 | 51篇 |
2001年 | 53篇 |
2000年 | 50篇 |
1999年 | 56篇 |
1998年 | 38篇 |
1997年 | 39篇 |
1996年 | 22篇 |
1995年 | 27篇 |
1994年 | 34篇 |
1993年 | 27篇 |
1992年 | 27篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 11篇 |
排序方式: 共有2296条查询结果,搜索用时 281 毫秒
921.
吊钟形涡流室内涡流及气体温度分布的研究 总被引:1,自引:0,他引:1
杨海青 《南京航空航天大学学报》1997,29(4):449-453
用热线风速仪测量了拖动工况下涡流室式柴油机吊钟形涡流室内的气流平均速度和气体温度。研究了涡流室内气流切向速度和气体温度的空间分布及随其曲轴转角变化的规律。 相似文献
922.
对同一结构环境中从事独立任务的多移动机器人的无冲突运动规划进行了系统的研究,提出了一种实时的多移动机器人无冲突运动规划方法--基于优先权的规则法PBR(Priority Based Rules Method).该方法综合了规则法和优先权法的优点,不仅可以采用规则实时地避免机器人与其他物体之间的碰撞和冲突,而且可以根据冲突机器人间优先权的不同在线地解决那些不可避免的冲突.PBR可以提高机器人运动的鲁棒性和执行任务的效率. 相似文献
923.
924.
全面介绍了BIRMM从1986~1992年间从事利用时间GPS进行时间传递与频率比对技术研究方面的情况,包括所建立的CPS定时校频系统、单站定时、SA对定时精度的影响、GPS定时信号噪声模型、卡尔曼滤波、电离层时延估算、GPS共视试验、CPS校频、接收系统差测量等。 相似文献
925.
926.
针对中继卫星系统日益增长的海量数据存储需求,探索将云技术应用于中继卫星地面存储系统中,研究并设计了适用于中继卫星系统的分布式云存储的体系架构.该架构通过分布式存储和存储虚拟化技术,对存储资源进行了整合,将分布在不同地理位置上的存储网络,集合成一个大规模广域云存储系统,可提供整体存储和访问的功能,并实现对数据的高效“存”、“取”、“管”.与传统NAS(Network Attached Storage,网络附加存储)架构分析比较,该架构从系统扩展性、可靠性和服务性等多个方面均更加具有优势,能够适应日益增长的中继卫星系统海量数据存储需求,解决中继卫星系统中大容量数据存储的瓶颈. 相似文献
927.
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
928.
《中国航空学报》2021,34(5):364-372
In order to understand the physical phenomenon of the reflected shock/turbulent boundary layer interaction, the Large Eddy Simulation (LES) is conducted to investigate shock wave and turbulent boundary layer interaction in a compression ramp with inlet high Mach number of 2.9. Rescaling/recycling method is used as inflow turbulence generation technique and validated on a supersonic flat plate turbulent boundary layer. The flow field of recycling plane in the plate computation domain is obtained to give the inlet boundary condition for the LES computation. This paper focuses on the reflected shock/turbulent boundary layer interaction region, where the fine flow structure and instantaneous flow field are analyzed in detail. It is found that the unsteady motion of the shock wave leads to the increase of wall pressure fluctuation. 相似文献
929.
Kewei Xi Xiaoya Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(12):4054-4065
The ionospheric error affects the accuracy of the Global Navigation Satellite Systems observation and precise orbit determination. Usually, only the first order ionospheric error is considered, which can be eliminated by the ionospheric-free linear combination observation. But the remaining higher order ionospheric error will affect the accuracy of observations and their applications. In this paper, the influence of the higher order ionospheric error have been studied by using the International Geomagnetic Reference Field 13 and the Global Ionosphere Maps model produced by the Center for Orbit Determination in Europe. Focus on ionospheric error, the experiment of paper at doy 302 in 2019, which show that the second order ionospheric error impacting BeiDou Navigation Satellite System (BDS) B1I and B3I observation is 6.3569 mm and 11.8484 mm, respectively. Whereas, the third order ionospheric error impacting BDS B1I and B3I observation is 0.1734 mm and 0.3977 mm, respectively. Due to the current measurement accuracy of BDS carrier-phase observation can reach 2 mm, the influence of high order ionospheric error on observation should be considered. For BDS precise orbit determination, the orbit overlapping results are indicated that its orbit accuracy can be improved approximately 5 mm with the higher order ionospheric error correction, which is also in agreement with the results of Satellite Laser Ranging in this work. 相似文献
930.
Burak Yaglioglu Ozan Tekinalp 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(11):3546-3558
The problem of obtaining long term relative orbit configurations for spacecraft clusters with realistic operational considerations such as safety, station keeping and inter-spacecraft distances is addressed. Two different approaches are developed for station keeping and safety objectives. In the first approach, relative orbit configurations, or relative TLEs, are found minimizing deviations from reference mean orbit which would maximize the station-keeping objective. In second one, relative configurations are found from a reference initial condition by minimizing probability of collision, hence maximizing the safety objective, between the spacecraft in the cluster which are propagated numerically through a high precision orbit propagator. For the design optimization, a derivative free algorithm is proposed. Effectiveness of the approaches is demonstrated through simulations. Using this design framework, several configurations can be found by exploring the limits of the clusters in terms of spacecraft number, distance bounds and probabilities of collision for long time intervals. 相似文献