全文获取类型
收费全文 | 328篇 |
免费 | 48篇 |
国内免费 | 42篇 |
专业分类
航空 | 99篇 |
航天技术 | 142篇 |
综合类 | 4篇 |
航天 | 173篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 19篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 12篇 |
2014年 | 24篇 |
2013年 | 19篇 |
2012年 | 20篇 |
2011年 | 21篇 |
2010年 | 20篇 |
2009年 | 25篇 |
2008年 | 13篇 |
2007年 | 21篇 |
2006年 | 13篇 |
2005年 | 15篇 |
2004年 | 24篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1991年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有418条查询结果,搜索用时 15 毫秒
101.
Sergei Rudenko Denise Dettmering Saskia Esselborn Tilo Schöne Christoph Förste Jean-Michel Lemoine Michaël Ablain David Alexandre Karl-Hans Neumayer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
During the last decade a significant progress has been reached in the investigation of the gravity field of the Earth. Besides static, also time variable geopotential models have been recently created. In this paper we investigate the impact of the recent time variable geopotential models on altimetry satellite orbits and such altimetry products based on these orbits, as global and regional mean sea level trends. We show that the modeling of time variable gravity improves the orbit solutions, at least for the GRACE period where time variable gravity is sufficiently accurately observed by this mission. Our analysis includes six geopotential models jointly developed by GFZ German Research Centre for Geosciences and Space Geodesy Research Group (CNES/GRGS) Toulouse: the stationary model EIGEN-GL04S, a stationary version of EIGEN-6S (EIGEN-6S_stat), a corrected version of EIGEN-6S and three enhanced versions of EIGEN-6S called EIGEN-6S2, EIGEN-6S2A and EIGEN-6S2B. By “stationary” we mean “containing periodic parameters such as annual and semi-annual variations, but no secular (drift) terms”. We computed precise orbits for the radar altimetry satellites ERS-1, ERS-2, TOPEX/Poseidon, and Envisat over 20 years between 1991 and 2011. The orbit, single-mission and multi-mission altimetry crossover analyses show that the time variable models EIGEN-6S_corrected, EIGEN-6S2 and its two precursors EIGEN-6S2A/B perform notably better than the stationary models for the GRACE period from 2003 onwards. Thus, using EIGEN-6S2 and EIGEN-6S2A/B we have got 3.6% smaller root mean square fits of satellite laser ranging observations for Envisat, as when using EIGEN-GL04S. However, for the pre-GRACE period 1991–2003, the stationary geopotential models EIGEN-GL04S and EIGEN-6S_stat as well as EIGEN-6S2 having no drift terms for degree 3–50 at this time interval perform superior compared to EIGEN-6S_correct and EIGEN-6S2A/B which contain drifts for this period. We found, that the time variable geopotential models have a low (0.1–0.2 mm/yr) impact on our results for the global mean sea level trend. However, we found strong East/West differences up to 3 mm/yr in the regional mean sea level trends when using orbits of all four satellites based on time variable and stationary geopotential models. We show that these differences are related to the relative drifts of the centers-of-origin between the orbit solutions based on the time variable and stationary geopotential models. From the results of our detailed study, we conclude that the final version of the time variable gravity field model EIGEN-6S2 performs best for the four satellites tested. This model provides the most reliable and mission-consistent sea level estimates for the whole time period from 1992 to 2010. This model is of maximum spherical harmonic degree and order 260 and contains time series for drifts as well as annual and semiannual variations of the spherical harmonic coefficients for degree 2–50. 相似文献
102.
Asteroid and comet hazard: Identification problem of observed space objects with the parental bodies
M.G. Sokolova Y.A. Nefedyev N.Y. Varaksina 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
This article focuses on the genetic identification of observed small cosmic bodies with alleged parental bodies; namely, comets, asteroids and meteoroid swarms. There is a problem of the upper D-value limit as a measure of proximity between the orbits of the bodies in the five-dimensional phase space (Southworth and Hawkins, 1963). In the study of genetic relationships of the comet and meteor complexes, the D value is usually taken as equal to 0.2 for all meteor showers. However, the upper D limit should be investigated for each meteoroid complex. For example, such investigation was performed for the Taurid meteor complex (Porub?an et al., 2006). In this paper, the upper D-criterion limit value was investigated for the Perseid meteor shower. The 1862 III Swift–Tuttle comet is its parental comet. 相似文献
103.
盘腔积液现象在舰用燃气轮机工作过程中时有发生,汽化的滑油和水蒸气凝结形成积液。转子带动腔内的积液旋转,引发振动失稳,严重时会对发动机结构造成致命性破坏。为此,本文开展燃气轮机压气机盘腔积液的模拟实验研究,以双盘双支承的卧式柔性转子系统作为研究对象,重点关注小积液量的特点,对积液转子的动力学稳定性进行了研究。观测到转子的失稳现象,开展了不同积液体积、不同积液类型(水、植物油和滑油)等因素的影响规律研究,揭示了小积液的卧式转子动力学特征。研究结果表明:①对于积液失稳振动,存在失稳边界积液量,当积液量大于该边界值时,失稳将会发生。②失稳边界转速及恢复转速均高于临界转速。当转速高于失稳边界转速时,失稳将会发生。转速进一步增加,高于恢复转速时,失稳现象可能消失。③失稳时的振动特征为:出现幅值突增,次谐波成分也随之增加;基频和次谐波发生调制,表现出拍振特征。④随着积液体积的增加,失稳边界转速先减小后增加。⑤随着积液粘度系数增大,失稳边界转速和边界积液量均增大。 相似文献
104.
Benjamin S. Schwarz Adrian R.L. Tatnall Hugh G. Lewis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Coastal salinity is characterised by large and variable salinity contrasts on relatively small scales. Measurements of salinity at a resolution compatible with these coastal regions on a regular basis would provide a rich source of information that could be used for a number of applications that have a fundamental bearing on the world’s lifestyle. Doppler radiometry offers an approach to capture such measurements, as it reduces the number of required antennas needed to form an image, compared with an Interferometer type instrument. 相似文献
105.
F.J. Montojo T. López Moratalla C. Abad 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In the project titled “Astrometric Positioning of Geostationary Satellite” (PASAGE), carried out by the Real Instituto y Observatorio de la Armada (ROA), optical observation techniques were developed to allow satellites to be located in the geostationary ring with angular accuracies of up to a few tenths of an arcsec. These techniques do not necessarily require the use of large telescopes or especially dark areas, and furthermore, because optical observation is a passive method, they could be directly applicable to the detection and monitoring of passive objects such as space debris in the geostationary ring. 相似文献
106.
何利军%赵云峰%詹茂盛%游少雄 《宇航材料工艺》2007,37(3):9-12
从组成、制备工艺、阻尼机理讨论了有机小分子杂化阻尼材料的研究现状,并给出了一些该类阻尼材料的实例及其阻尼性能数据,提出了有机小分子杂化阻尼材料目前存在的问题,指出该类阻尼材料阻尼性能突出、Tg可设计,是一种颇有前景的材料。 相似文献
107.
108.
109.
随着小卫星应用领域的日益广阔和小卫星数量的不断增长,对小卫星轨道控制技术的要求也越来越高。本文以某搭载小卫星(下面简称搭载星)为例,对太阳同步轨道小卫星的轨道特性、轨道控制策略等问题进行了较深入的探讨,并对变轨策略实施的理论计算结果和实测定轨结果进行了对比分析。 相似文献
110.