全文获取类型
收费全文 | 4490篇 |
免费 | 900篇 |
国内免费 | 847篇 |
专业分类
航空 | 3179篇 |
航天技术 | 1048篇 |
综合类 | 740篇 |
航天 | 1270篇 |
出版年
2024年 | 21篇 |
2023年 | 47篇 |
2022年 | 135篇 |
2021年 | 140篇 |
2020年 | 181篇 |
2019年 | 130篇 |
2018年 | 147篇 |
2017年 | 189篇 |
2016年 | 145篇 |
2015年 | 221篇 |
2014年 | 276篇 |
2013年 | 277篇 |
2012年 | 291篇 |
2011年 | 278篇 |
2010年 | 356篇 |
2009年 | 336篇 |
2008年 | 303篇 |
2007年 | 302篇 |
2006年 | 283篇 |
2005年 | 234篇 |
2004年 | 168篇 |
2003年 | 181篇 |
2002年 | 141篇 |
2001年 | 160篇 |
2000年 | 164篇 |
1999年 | 177篇 |
1998年 | 142篇 |
1997年 | 130篇 |
1996年 | 128篇 |
1995年 | 84篇 |
1994年 | 94篇 |
1993年 | 79篇 |
1992年 | 75篇 |
1991年 | 61篇 |
1990年 | 39篇 |
1989年 | 40篇 |
1988年 | 20篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1965年 | 2篇 |
1900年 | 1篇 |
排序方式: 共有6237条查询结果,搜索用时 515 毫秒
932.
针对仅使用两行要素(Two Line Element,TLE)作为数据源的应用需求,研究了基于TLE轨道衰减的弹道系数计算方法。介绍了一种常用的基于两组TLE的直接计算法,分析TLE选取间隔对结果精度的影响;提出了一种基于多组TLE的迭代计算方法,以降低异常TLE对计算结果的影响;从弹道系数计算效果、在再入预报中的应用等方面对这两种方法进行比较分析。结果表明,两种方法各有优劣,基于多组TLE的迭代计算法稳定性更高、受TLE精度的影响更小;由于数据区间更短,基于两组TLE的计算结果对短期轨道衰减特性反应得更准确,用于临近再入时的预报效果更好。 相似文献
933.
Fuyu Sun Jianping Zhou Zheyao Xu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):189-206
This study proposes a new simulation platform named Simulation Integrated Management (SIM) for the analysis of parallel and distributed systems. The platform eases the process of designing and testing both applications and architectures. The main characteristics of SIM are flexibility, scalability, and expandability. To improve the efficiency of project development, new models of early-warning satellite system were designed based on the SIM platform. Finally, through a series of experiments, the correctness of SIM platform and the aforementioned early-warning satellite models was validated, and the systematical analyses for the orbital determination precision of the ballistic missile during its entire flight process were presented, as well as the deviation of the launch/landing point. Furthermore, the causes of deviation and prevention methods will be fully explained. The simulation platform and the models will lay the foundations for further validations of autonomy technology in space attack-defense architecture research. 相似文献
935.
A differential steering system is presented for electric vehicle with motorized wheels and a dynamic model of three-freedom car is built. Based on these models, the quantitative expressions of the road feel, sensitivity, and operation stability of the steering are derived. Then, according to the features of multi-constrained optimization of multi-objective function, a multi-island genetic algorithm (MIGA) is designed. Taking the road feel and the sensi- tivity of the steering as optimization objectives and the operation stability of the steering as a constraint, the system parameters are optimized. The simulation results show that the system optimized with MIGA can improve the steering road feel, and guarantee the operation stability and steering sensibility. 相似文献
936.
Xiang Wang Chen Zhou 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(9):2252-2258
Incoherent scatter radar (ISR) is the most powerful ground-based measurement facility to study the ionosphere. The plasma lines are not routinely detected by the incoherent scatter radar due to the low intensity, which falls below the measured spectral noise level of the incoherent scatter radar. The plasma lines are occasionally enhanced by suprathermal electrons through the Landau damping process and detectable to the incoherent scatter radar. In this study, by using the European Incoherent Scatter Association (EISCAT) UHF incoherent scatter radar, the experiment observation presents that the enhanced plasma lines were observed. These plasma lines were considered as manifest of the suprathermal electrons generated by the high-frequency heating wave during the ionospheric modification. The electron density profile is also obtained from the enhanced plasma lines. This study can be a promising technique for obtaining the accurate electron density during ionospheric modification experiment. 相似文献
938.
针对目前基于GNSS观测数据的对流层天顶总延迟(ZTD)模型缺乏有效质量控制手段的现状,提出了一套综合考虑数据量、网格分辨率以及模型稳定性的ZTD建模质量控制方法,并采用内华达大地测量实验室(NGL)解算的高空间分辨率GNSS对流层数据,选取了近十年德国及周边区域[47°N-55°N,5°E-15°E]183个测站的实测ZTD,对该方法进行了校验。实验结果表明:在该质量控制方法下建立的新模型精度稳定,平均均方根误差(RMS)为3.4 cm,相对于UNB3m、EGNOS、GPT2w+Saas平均改善了42.4%、35.8%、33.3%。本文提出的质量控制方法有效提升了基于GNSS观测数据的ZTD模型的性能,对于ZTD建模研究具有一定的参考价值。 相似文献
939.
940.