全文获取类型
收费全文 | 662篇 |
免费 | 64篇 |
国内免费 | 193篇 |
专业分类
航空 | 299篇 |
航天技术 | 293篇 |
综合类 | 65篇 |
航天 | 262篇 |
出版年
2023年 | 12篇 |
2022年 | 18篇 |
2021年 | 28篇 |
2020年 | 35篇 |
2019年 | 49篇 |
2018年 | 68篇 |
2017年 | 33篇 |
2016年 | 25篇 |
2015年 | 39篇 |
2014年 | 72篇 |
2013年 | 51篇 |
2012年 | 54篇 |
2011年 | 46篇 |
2010年 | 44篇 |
2009年 | 45篇 |
2008年 | 49篇 |
2007年 | 40篇 |
2006年 | 24篇 |
2005年 | 22篇 |
2004年 | 16篇 |
2003年 | 11篇 |
2002年 | 16篇 |
2001年 | 18篇 |
2000年 | 37篇 |
1999年 | 21篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
排序方式: 共有919条查询结果,搜索用时 15 毫秒
811.
Brandon A. Jones Alireza Doostan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper presents the application of polynomial chaos (PC) to estimating the probability of collision between two spacecraft. Common methods of quantifying this probability for conjunction assessment use either Monte Carlo analyses or include simplifying assumptions to improve tractability. A PC expansion, or PCE, provides a means for approximating the solution to a large set of stochastic ordinary differential equations, which includes orbit propagation. When compared to Monte Carlo methods, non-intrusive, i.e., sampling-based, PCE generation techniques may greatly reduce the number of orbit propagations required to approximate the possibly non-Gaussian, a posteriori probability density function. The presented PC-based method of computing collision probability requires no fundamental simplifying assumptions, and reduces the computation time compared to Monte Carlo. This paper considers two cases where the common conjunction assessment assumptions are no longer valid. The results indeed demonstrate a reduction in computation time when compared to Monte Carlo, and improved accuracy when compared to simplified techniques. 相似文献
812.
发展并验证了一种新的支持多面体网格的欧拉方程离散算法,采用Fortran 95编写了支持任意网格拓扑及三维复杂外形的通用求解器.在空间离散上,基于径向基函数理论提出了一种新的梯度计算方法,并采用动能通量分裂格式来得到准确并且稳定的二阶精度重构.该方法不依赖于网格几何形状,因此对网格质量不敏感.由于在时间方向采用了点隐松... 相似文献
813.
Space Debris Reentry Analysis Methods and Tools 总被引:2,自引:2,他引:0
The reentry of uncontrolled spacecraft may be broken into many pieces of debris at an altitude in the range of 75-85 km. The surviving fragments could pose great hazard and risk to ground and people. In recent years, methods and tools for predicting and analyzing debris reentry and ground risk assessment have been studied and developed in National Aeronautics and Space Ad-ministration (NASA), European Space Agency (ESA) and other organizations, including the group of the present authors. This paper reviews the current progress on this topic of debris reentry briefly. We outline the Monte Carlo method for uncertainty analysis, breakup prediction, and parameters affecting survivability of debris. The existing analysis tools can be classified into two categories, i.e. the object-oriented and the spacecraft-oriented methods, the latter being more accurate than the first one. The past object-oriented tools include objects of only simple shapes. For more realistic simulation, here we present an object-oriented tool debris reentry and ablation prediction system (DRAPS) developed by the present authors, which introduces new object shapes to 15 types, as well as 51 predefined motions and relevant aerodynamic and aerothermal models. The aerodynamic and aerothermal models in DRAPS are validated using direct simulation Monte Carlo (DSMC) method. 相似文献
814.
815.
Myrtille Laas-Bourez David Coward Alain Klotz Michel Boër 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The two TAROT (Télescopes à Action Rapide pour les Objets Transitoires; Rapid Action Telescopes for Transient Objects) installations are fully robotic optical observatories with optimized observation scheduling, data processing and archiving. Zadko is a 1 m telescope in Western Australia. The fully robotisation of the Zadko telescope has just been completed; it is now included in the TAROT network. In this paper we provide an overview of this international network of robotic optical telescopes. We discuss the advantages of using the network to participate in a satellite and space debris tracking program. This network will access almost all geostationary belt objects, and provide the first real-time satellite positioning capability. The inclusion of the 1 m Zadko telescope into the network significantly extends the efficiency and sensitivity of the existing two telescope configuration. 相似文献
816.
817.
润滑油金属磨粒的分类参数研究 总被引:9,自引:2,他引:9
针对润滑系统中普遍存在的 8类金属磨粒,通过引入数字图像描述方法和处理技术,分别对磨粒的尺寸、形态、表面纹理以及颜色等参数进行了详细的研究,获取了各类磨粒识别的最佳参数,并提出了磨粒的分层识别策略,最后运用模糊 C-均值聚类方法实现了 8类磨粒的有效聚类。算例表明了本文方法的有效性。 相似文献
818.
819.
Dust is an important constituent of cometary emission; its analysis is one of the major objectives of ESA’s Rosetta mission
to comet 67P/Churyumov-Gerasimenko (C–G). Several instruments aboard Rosetta are dedicated to studying various aspects of
dust in the cometary coma, all of which require a certain level of exposure to dust to achieve their goals. At the same time,
impacts of dust particles can constitute a hazard to the spacecraft. To conciliate the demands of dust collection instruments
and spacecraft safety, it is desirable to assess the dust environment in the coma even before the arrival of Rosetta. We describe
the present status of modelling the dust coma of 67P/C–G and predict the speed and flux of dust in the coma, the dust fluence
on a spacecraft along sample trajectories, and the radiation environment in the coma. The model will need to be refined when
more details of the coma are revealed by observations. An overview of astronomical observations of 67P/C–G is given, because
model parameters are derived from this data if possible. For quantities not yet measured for 67P/C–G, we use values obtained
for other comets, e.g. concerning the optical and compositional properties of the dust grains. One of the most important and
most controversial parameters is the dust mass distribution. We summarise the mass distribution functions derived from the
in-situ measurements at comet 1P/Halley in 1986. For 67P/C–G, constraining the mass distribution is currently only possible
by the analysis of astronomical images. We find that both the dust mass distribution and the time dependence of the dust production
rate of 67P/C–G are those of a fairly typical comet. 相似文献
820.
S.A. Dyadechkin V.S. Semenov H.K. Biernat T. Penz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Cosmic strings are topological defects which were generated at a transition phase of the very early Universe and are probably responsible for large-scale structure forming. However, they may pull through all history and exist in the recent epoch. Thus, they can have influence for the recent Universe interacting with different objects. We consider the cosmic string behavior in the vicinity of a spinning black hole by means of a numerical simulation. Here we present preliminary results of this work via a comparison of cosmic string and magnetic flux tube behavior in the Kerr metric. Such an approach follows from the similarity of the equations which describe these objects. Therefore, many aspects of this behavior may be comparable. 相似文献