全文获取类型
收费全文 | 1627篇 |
免费 | 198篇 |
国内免费 | 79篇 |
专业分类
航空 | 264篇 |
航天技术 | 846篇 |
综合类 | 8篇 |
航天 | 786篇 |
出版年
2023年 | 30篇 |
2022年 | 31篇 |
2021年 | 60篇 |
2020年 | 59篇 |
2019年 | 42篇 |
2018年 | 56篇 |
2017年 | 12篇 |
2016年 | 28篇 |
2015年 | 49篇 |
2014年 | 164篇 |
2013年 | 98篇 |
2012年 | 64篇 |
2011年 | 158篇 |
2010年 | 112篇 |
2009年 | 106篇 |
2008年 | 100篇 |
2007年 | 79篇 |
2006年 | 69篇 |
2005年 | 99篇 |
2004年 | 58篇 |
2003年 | 33篇 |
2002年 | 49篇 |
2001年 | 39篇 |
2000年 | 48篇 |
1999年 | 55篇 |
1998年 | 32篇 |
1997年 | 22篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 7篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 22篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1984年 | 2篇 |
排序方式: 共有1904条查询结果,搜索用时 703 毫秒
591.
B.J.M. Lim E.C. Leong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(6):1961-1978
Anomalous behavior of ionospheric total electron content (TEC) prior to earthquake has been observed in many studies. Evidence of such seismo-ionospheric coupling effects suggests that it is plausible to rely on TEC signatures for early earthquake warning. However, the detection of pre-earthquake TEC anomalies (PETA) has not been adopted in practice due to two pertinent issues. Firstly, the effects of space weather activity can affect TEC levels and cause anomalous behavior in the TEC. Usually arbitrary thresholds are set for space weather indices to eliminate TEC anomaly due to space weather effects. Secondly, the choice regarding moving time-window length used to characterise background variation of TEC within the statistical envelope approach has an effect on detection of PETA. While the rule-of-thumb in selecting the moving window length is to have a time window capable of capturing background variability and short-term fluctuations, the length of the time window used in the literature varies with little justification. In this study, a critical examination is conducted on the statistical envelope approach and in particular, to eliminate the effect of space weather activity without the use of arbitrary space indices to detect PETA. A two-part PETA identification procedure is proposed, consisting of wavelet analyses isolating non-earthquake TEC contributions, followed by the statistical envelope method using a moving window length standardized based on observed periodicities and statistical implications is suggested. The approach is tested on a database of 30 large earthquakes (M?≥?7.0). The proposed procedure shows that PETA can be detected prior to earthquakes at higher confidence levels without the need to separately check for space weather activity. More importantly, the procedure was able to detect PETA for studies where it was previously reported that PETA could not be detected or detected convincingly. 相似文献
592.
Jian Huang Dongya Wang Shuangzhi Xia 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(11):2777-2786
Large-scale distributed space surveillance radar is a very important ground-based equipment to maintain a complete catalogue for Low Earth Orbit (LEO) space debris. However, due to the thousands of kilometers distance between each sites of the distributed radar system, how to optimally implement the Transmitting/Receiving (T/R) beams alignment in a great space using the narrow beam, which proposed a special and considerable technical challenge in the space surveillance area. According to the common coordinate transformation model and the radar beam space model, we presented a two dimensional projection algorithm for T/R beam using the direction angles, which could visually describe and assess the beam alignment performance. Subsequently, the optimal mathematical models for the orientation angle of the antenna array, the site location and the T/R beam coverage are constructed, and also the beam alignment parameters are precisely solved. At last, we conducted the optimal beam alignment experiments base on the site parameters of Air Force Space Surveillance System (AFSSS). The simulation results demonstrate the correctness and effectiveness of our novel method, which can significantly stimulate the construction for the LEO space debris surveillance equipment. 相似文献
593.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2692-2710
The space environment around the Earth is populated by more than 130 million objects of 1 mm in size and larger, and future predictions shows that this amount is destined to increase, even if mitigation measures are implemented at a far better rate than today. These objects can hit and damage a spacecraft or its components. It is thus necessary to assess the risk level for a satellite during its mission lifetime. Few software packages perform this analysis, and most of them employ time-consuming ray-tracing methodology, where particles are randomly sampled from relevant distributions. In addition, they tend not to consider the risk associated with the secondary debris clouds. The paper presents the development of a vulnerability assessment model, which relies on a fully statistical procedure: the debris fluxes are directly used combining them with the concept of vulnerable zone, avoiding the random sampling the debris fluxes. A novel methodology is presented to predict damage on internal components. It models the interaction between the components and the secondary debris cloud through basic geometrical operations, considering mutual shielding and shadowing between internal components. The methodologies are tested against state-of-the-art software for relevant test cases, comparing results on external structures and internal components. 相似文献
594.
Survey of orbital dynamics and control of space rendezvous 总被引:2,自引:1,他引:1
Rendezvous orbital dynamics and control (RODC) is a key technology for operating space rendezvous and docking missions. This paper surveys the studies on RODC. Firstly, the basic relative dynamics equation set is introduced and its improved versions are evaluated. Secondly, studies on rendezvous trajectory optimization are commented from three aspects: the linear rendez- vous, the nonlinear two-body rendezvous, and the perturbed and constrained rendezvous. Thirdly, studies on relative navigation are briefly reviewed, and then close-range control methods including automated control, manual control, and telecontrol are analyzed. Fourthly, advances in rendezvous trajectory safety and robust analysis are surveyed, and their applications in trajectory optimization are discussed. Finally, conclusions are drawn and prospects of studies on RODC are presented. 相似文献
595.
The application of high-performance imaging sensors in space-based space surveillance systems makes it possible to recognize space objects and estimate their poses using vision-based methods. In this paper, we proposed a kernel regression-based method for joint multi-view space object recognition and pose estimation. We built a new simulated satellite image dataset named BUAA-SID 1.5 to test our method using different image representations. We evaluated our method for recognition-only tasks, pose estimation-only tasks, and joint recognition and pose estimation tasks. Experimental results show that our method outperforms the state-of-the-arts in space object recognition, and can recognize space objects and estimate their poses effectively and robustly against noise and lighting conditions. 相似文献
596.
597.
598.
599.
600.
目前基于模型的控制方法是空间机器人遥操作控制的主流方法,但该方法不可避免地会引入运动的累积误差,甚至造成控制失稳。针对这一问题,基于自抗扰控制方法为空间机器人主从遥操作设计了一类单关节控制器,并采用计算机仿真方法研究了其基本性能,结果表明所设计的自抗扰控制器能够实现稳定的遥操作控制,且具有良好的抗扰性和鲁棒性。特别是由于自抗扰控制方法不依赖于机器人的数学模型,因此十分适合作为现行基于模型控制的有益补充。 相似文献