全文获取类型
收费全文 | 1146篇 |
免费 | 110篇 |
国内免费 | 33篇 |
专业分类
航空 | 180篇 |
航天技术 | 549篇 |
综合类 | 2篇 |
航天 | 558篇 |
出版年
2024年 | 7篇 |
2023年 | 21篇 |
2022年 | 25篇 |
2021年 | 46篇 |
2020年 | 32篇 |
2019年 | 23篇 |
2018年 | 30篇 |
2017年 | 13篇 |
2016年 | 13篇 |
2015年 | 29篇 |
2014年 | 62篇 |
2013年 | 59篇 |
2012年 | 54篇 |
2011年 | 98篇 |
2010年 | 85篇 |
2009年 | 45篇 |
2008年 | 43篇 |
2007年 | 67篇 |
2006年 | 60篇 |
2005年 | 61篇 |
2004年 | 48篇 |
2003年 | 39篇 |
2002年 | 28篇 |
2001年 | 31篇 |
2000年 | 30篇 |
1999年 | 40篇 |
1998年 | 21篇 |
1997年 | 22篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 11篇 |
排序方式: 共有1289条查询结果,搜索用时 421 毫秒
501.
502.
503.
504.
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
505.
506.
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
507.
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
508.
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
509.
D. Kuang S. DesaiA. Sibthorpe X. Pi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We present a method to estimate the total neutral atmospheric density from precise orbit determination of Low Earth Orbit (LEO) satellites. We derive the total atmospheric density by determining the drag force acting on the LEOs through centimeter-level reduced-dynamic precise orbit determination (POD) using onboard Global Positioning System (GPS) tracking data. The precision of the estimated drag accelerations is assessed using various metrics, including differences between estimated along-track accelerations from consecutive 30-h POD solutions which overlap by 6 h, comparison of the resulting accelerations with accelerometer measurements, and comparison against an existing atmospheric density model, DTM-2000. We apply the method to GPS tracking data from CHAMP, GRACE, SAC-C, Jason-2, TerraSAR-X and COSMIC satellites, spanning 12 years (2001–2012) and covering orbital heights from 400 km to 1300 km. Errors in the estimates, including those introduced by deficiencies in other modeled forces (such as solar radiation pressure and Earth radiation pressure), are evaluated and the signal and noise levels for each satellite are analyzed. The estimated density data from CHAMP, GRACE, SAC-C and TerraSAR-X are identified as having high signal and low noise levels. These data all have high correlations with anominal atmospheric density model and show common features in relative residuals with respect to the nominal model in related parameter space. On the contrary, the estimated density data from COSMIC and Jason-2 show errors larger than the actual signal at corresponding altitudes thus having little practical value for this study. The results demonstrate that this method is applicable to data from a variety of missions and can provide useful total neutral density measurements for atmospheric study up to altitude as high as 715 km, with precision and resolution between those derived from traditional special orbital perturbation analysis and those obtained from onboard accelerometers. 相似文献
510.
Ole Baltazar Andersen Yongcun Cheng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Accurate sea level trend determination is fundamentally related to calibration of both the instrument as well as to investigate if there are linear trends in the set of standard geophysical and range corrections applied to the sea level observations. Long term changes in range corrections can leak into the observed sea level record and be interpreted as part of the sea level trend. Particularly if these exhibit anomalous trend close to the satellite calibration sites. 相似文献