全文获取类型
收费全文 | 3510篇 |
免费 | 573篇 |
国内免费 | 420篇 |
专业分类
航空 | 1297篇 |
航天技术 | 1438篇 |
综合类 | 98篇 |
航天 | 1670篇 |
出版年
2024年 | 14篇 |
2023年 | 66篇 |
2022年 | 123篇 |
2021年 | 158篇 |
2020年 | 161篇 |
2019年 | 135篇 |
2018年 | 149篇 |
2017年 | 102篇 |
2016年 | 160篇 |
2015年 | 148篇 |
2014年 | 250篇 |
2013年 | 183篇 |
2012年 | 208篇 |
2011年 | 299篇 |
2010年 | 240篇 |
2009年 | 179篇 |
2008年 | 184篇 |
2007年 | 213篇 |
2006年 | 195篇 |
2005年 | 177篇 |
2004年 | 133篇 |
2003年 | 105篇 |
2002年 | 95篇 |
2001年 | 103篇 |
2000年 | 107篇 |
1999年 | 93篇 |
1998年 | 75篇 |
1997年 | 60篇 |
1996年 | 67篇 |
1995年 | 48篇 |
1994年 | 42篇 |
1993年 | 46篇 |
1992年 | 30篇 |
1991年 | 56篇 |
1990年 | 38篇 |
1989年 | 22篇 |
1988年 | 23篇 |
1987年 | 16篇 |
排序方式: 共有4503条查询结果,搜索用时 15 毫秒
991.
数据链作用距离的试飞结果受试验区电波传播衰减影响很大,需要对其进行精确计算,为分析试飞结果提供支持.Fock级数法是计算电波衰减的一种精确方法,本文详细讨论了应用该方法求解试验区电波传播衰减的工程计算问题. 相似文献
992.
在轨卫星异常报警和故障诊断方法研究 总被引:1,自引:0,他引:1
及时发现卫星出现的异常是卫星在轨管理的一项重要工作,它关系到卫星在轨使用寿命。能够及时发现并判断卫星异常的方法有很多,本文对这些方法进行了研究,并将其归纳为2类,一类是基于遥测参数超限报警方法,另一类是故障诊断方法。分别对这2类方法从功能、效果、软件实现的难度进行比较,结果表明,在不同的管理和实现难度要求下,这些方法完成卫星管理的效果不同。另外,本文还提出了一种遥测参数相对判断算法,简化了报警门限设置,能够及时发现卫星任何参数突跳,是一种有效的卫星异常报警方法。 相似文献
993.
O. Troshichev P. Stauning K. Liou G. Reeves 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The relationships between the magnetic disturbance onsets, aurora dynamics and particles injections at the geostationary orbit have been analyzed in detail for 25 sawtooth substorms. It is shown that inconsistency between the above signatures of the substorms onset is typical of the powerful sawtooth substorms, unlike the isolated (“classical”) magnetospheric substorms. The distinguishing feature of the aurora in case of saw-tooth substorms is permanently high level of auroral activity irrespective of the magnetic disturbance onsets and the double oval structure of the aurora display. The close relationship between the aurora behavior and the particle injections at geostationary orbit is also broken. The conclusion is made, that the classical concept of the substorm development, put forward by Akasofu (1964) for isolated substorms, is not workable in cases of the sawtooth disturbances, when the powerful solar wind energy pumping into the magnetosphere provides a permanent powerful aurora particle precipitation into the auroral zone. 相似文献
994.
995.
Guiping Feng S. Jin T. Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Sea level changes are threatening the human living environments, particularly along the European Coasts with highly dense population. In this paper, coastal sea level changes in western and southern Europe are investigated for the period 1993–2011 using Global Positioning System (GPS), Tide Gauge (TG), Satellite Altimetry (SA), Gravity Recovery and Climate Experiment (GRACE) and geophysical models. The mean secular trend is 2.26 ± 0.52 mm/y from satellite altimetry, 2.43 ± 0.61 mm/y from TG+GPS and 1.99 ± 0.67 mm/y from GRACE mass plus steric components, which have a remarkably good agreement. For the seasonal variations, annual amplitudes of satellite altimetry and TG+GPS results are almost similar, while GRACE Mass+Steric results are a little smaller. The annual phases agree remarkably well for three independent techniques. The annual cycle is mainly driven by the steric contributions, while the annual phases of non-steric (mass component) sea level changes are almost a half year later than the steric sea level changes. 相似文献
996.
Alankrita Isha Mrigakshi Daniel Matthiä Thomas Berger Günther Reitz Robert F. Wimmer-Schweingruber 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The radiation environment in space is a major concern for human spaceflight because of the adverse effects of high levels of radiation on astronauts’ health. Therefore, it is essential to perform radiation risk assessments already during the concept studies of a manned mission. Galactic Cosmic Rays (GCR) have been identified to be one of the primary sources of radiation exposure in space. 相似文献
997.
C. Lázaro M.F. Juliano M.J. Fernandes 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Satellite altimetry has been widely used to study the variability of the ocean currents such as the Azores Current (AzC) in the North Atlantic. Most analyses are performed over the region that encloses the current, thus being somehow affected by other oceanographic signals, e.g., eddies. In this study, a new approach for extracting the axis of a zonal current solely based on satellite altimetry is presented. This is a semi-automatic procedure that searches for the maximum values of the gradient of absolute dynamic topography (ADT), using the geostrophic velocity as auxiliary information. The advantage of this approach is to allow the analyses to be performed over a buffer centered on the current axis instead of using a wider region. It is here applied to the AzC for the period June 1995–October 2006. 相似文献
998.
Gabriele Giorgi Peter J.G. Teunissen Sandra Verhagen Peter J. Buist 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
GNSS (Global Navigation Satellite Systems)-based attitude determination is an important field of study, since it is a valuable technique for the orientation estimation of remote sensing platforms. To achieve highly accurate angular estimates, the precise GNSS carrier phase observables must be employed. However, in order to take full advantage of the high precision, the unknown integer ambiguities of the carrier phase observables need to be resolved. This contribution presents a GNSS carrier phase-based attitude determination method that determines the integer ambiguities and attitude in an integral manner, thereby fully exploiting the known body geometry of the multi-antennae configuration. It is shown that this integral approach aids the ambiguity resolution process tremendously and strongly improves the capacity of fixing the correct set of integer ambiguities. In this contribution, the challenging scenario of single-epoch, single-frequency attitude determination is addressed. This guarantees a total independence from carrier phase slips and losses of lock, and it also does not require any a priori motion model for the platform. The method presented is a multivariate constrained version of the popular LAMBDA method and it is tested on data collected during an airborne remote sensing campaign. 相似文献
999.
S. Valk A. Lemaître F. Deleflie 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
This paper provides a hamiltonian formulation of the equations of motion of an artificial satellite or space debris orbiting the geostationary ring. This theory of order 1 has been formulated using canonical and non-singular elements for eccentricity and inclination. The analysis is based on an expansion in powers of the eccentricity and of the inclination. The theory accounts for the influence of the Earth gravity field expanded in spherical harmonics, paying a particular attention to the resonance occurring for geosynchronous objects. The luni-solar perturbations are also taken into account. We present the resonant motion and its main characteristics: equilibria, stability, fundamental frequencies and width of the resonant area by comparison with a basic analytical model. Finally, we show some results concerning the long term dynamics of a typical space debris under the influence of the gravitational field of the Earth and the luni-solar interactions. 相似文献
1000.