全文获取类型
收费全文 | 426篇 |
免费 | 97篇 |
国内免费 | 35篇 |
专业分类
航空 | 160篇 |
航天技术 | 144篇 |
综合类 | 7篇 |
航天 | 247篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 28篇 |
2021年 | 28篇 |
2020年 | 32篇 |
2019年 | 25篇 |
2018年 | 19篇 |
2017年 | 18篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 29篇 |
2013年 | 32篇 |
2012年 | 17篇 |
2011年 | 35篇 |
2010年 | 33篇 |
2009年 | 20篇 |
2008年 | 19篇 |
2007年 | 22篇 |
2006年 | 34篇 |
2005年 | 29篇 |
2004年 | 14篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 1篇 |
排序方式: 共有558条查询结果,搜索用时 46 毫秒
181.
《中国航空学报》2021,34(2):479-489
Unmanned Aerial Vehicle (UAV) navigation is aimed at guiding a UAV to the desired destinations along a collision-free and efficient path without human interventions, and it plays a crucial role in autonomous missions in harsh environments. The recently emerging Deep Reinforcement Learning (DRL) methods have shown promise for addressing the UAV navigation problem, but most of these methods cannot converge due to the massive amounts of interactive data when a UAV is navigating in high dynamic environments, where there are numerous obstacles moving fast. In this work, we propose an improved DRL-based method to tackle these fundamental limitations. To be specific, we develop a distributed DRL framework to decompose the UAV navigation task into two simpler sub-tasks, each of which is solved through the designed Long Short-Term Memory (LSTM) based DRL network by using only part of the interactive data. Furthermore, a clipped DRL loss function is proposed to closely stack the two sub-solutions into one integral for the UAV navigation problem. Extensive simulation results are provided to corroborate the superiority of the proposed method in terms of the convergence and effectiveness compared with those of the state-of-the-art DRL methods. 相似文献
182.
NPF算法在X射线脉冲星导航中的应用研究 总被引:1,自引:0,他引:1
针对X射线脉冲星导航中航天器模型的强非线性、高阶模型不确定性等问题,提出应用非线性预测滤波(NPF)算法实时估计航天器的轨道信息。首先,建立具有模型不确定性的X射线脉冲星导航定轨指标函数,优化得到满足指标函数最小的系统模型误差值,通过降低模型不确定性的影响来提高航天器自主定轨精度。对STK生成的“火星探路者”和“金星快车”及“北斗一号”三种航天器轨道数据进行分析,仿真结果表明,该算法比EKF算法具有更高的定轨精度,能够满足深空以及近地轨道航天器的自主定轨精度指标要求。 相似文献
183.
184.
185.
186.
187.
Borys Dabrowski Marek Banaszkiewicz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
The paper presents a method of determination an accurate position of a target (rover, immobile sensor, astronaut) on surface of the Moon or other celestial body devoid of navigation infrastructure (like Global Positioning System), by using a group of self-calibrating rovers, which serves as mobile reference points. The rovers are equipped with low-precision clocks synchronized by external broadcasting signal, to measure the moments of receiving radio signals sent by localized target. Based on the registered times, distances between transmitter and receivers installed on beacons are calculated. Each rover determines and corrects its own absolute position and orientation by using odometry navigation and measurements of relative distances and angles to other mobile reference points. Accuracy of navigation has been improved by the use of a calibration algorithm based on the extended Kalman filter, which uses internal encoder readings as inputs and relative measurements of distances and orientations between beacons as feedback information. The key idea in obtaining reliable values of absolute position and orientation of beacons is to first calibrate one of the rovers, using the remaining ones as reference points and then allow the whole group to move together and calibrate all the rovers in-motion. We consider a number of cases, in which basic modeling parameters such as terrain roughness, formation size and shape as well as availability of distance and angle measurements are varied. 相似文献
188.
椭圆轨道航天器自主接近的制导律研究 总被引:1,自引:0,他引:1
椭圆轨道自主交会接近制导律问题是当今空间技术领域中的一个研究不足。基于T\|H方程 ,设计了两种仅利用相对运动信息、控制力定常的椭圆轨道自主接近制导律:滑模制导律和 势函数制导律。从两种制导律的特性分析,滑模制导律对系统的运行轨迹更加苛刻,而势函 数制导律更加充分地利用了系统的自由运动,具有更好的控制性能。数值仿真结果也表明: 对 于相同的制导目标、制导时间和制导精度,势函数制导律所需的喷气开关次数和速度增量均较少。 相似文献
189.
190.