全文获取类型
收费全文 | 366篇 |
免费 | 62篇 |
国内免费 | 11篇 |
专业分类
航空 | 177篇 |
航天技术 | 121篇 |
综合类 | 39篇 |
航天 | 102篇 |
出版年
2024年 | 3篇 |
2023年 | 12篇 |
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 18篇 |
2019年 | 14篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 24篇 |
2013年 | 18篇 |
2012年 | 24篇 |
2011年 | 26篇 |
2010年 | 13篇 |
2009年 | 15篇 |
2008年 | 28篇 |
2007年 | 27篇 |
2006年 | 24篇 |
2005年 | 14篇 |
2004年 | 25篇 |
2003年 | 16篇 |
2002年 | 15篇 |
2001年 | 15篇 |
2000年 | 11篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
排序方式: 共有439条查询结果,搜索用时 156 毫秒
101.
O.S. Yakovchouk I.S. Veselovsky K. Mursula 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
We present and discuss here the first version of a data base of extreme solar and heliospheric events. The data base contains now 87 extreme events mostly since 1940. An event is classified as extreme if one of the three critical parameters passed a lower limit. The critical parameters were the X-ray flux (parameter R), solar proton flux (parameter S) and geomagnetic disturbance level (parameter G). We find that the five strongest extreme events based on four variables (X-rays SEP, Dst, Ap) are completely separate except for the October 2003 event which is one the five most extreme events according to SEP, Dst and Ap. This underlines the special character of the October 2003 event, making it unique within 35 years. We also find that the events based on R and G are rather separate, indicating that the location of even extreme flares on the solar disk is important for geomagnetic effects. We also find that S = 3 events are not extreme in the same sense as R > 3 and G > 3 events, while S = 5 events are missing so far. This suggests that it might be useful to rescale the classification of SEP fluxes. 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.
《中国航空学报》2020,33(8):2176-2188
This paper describes the general optimization design method of Solar-Powered Unmanned Aerial Vehicle which priority considering propulsion system planning. Based on the traditional solar powered aircraft design method, the propulsion system top-level target parameters which affect the path planning are integrated into the general optimization design. According to the typical mission requirements of Solar-Powered Unmanned Aerial Vehicle, considering the design variables such as wing area, aspect ratio, design mission date and so on, the general optimization is carried out with the minimum aircraft weight as the optimization objective. The influence of wing area and aspect ratio on the optimal design results is analyzed and compared with the traditional design method. The results show that the general design method of Solar-Powered Unmanned Aerial Vehicle for priority considering propulsion system can greatly reduce the electricity demand of energy storage battery, greatly reduce the aircraft weight of Solar-Powered Unmanned Aerial Vehicle. 相似文献
104.
105.
V. Iafolla D.M. Lucchesi S. Nozzoli M. Ravenna F. Santoli I.I. Shapiro E.C. Lorenzini M.L. Cosmo C. Bombardelli J. Ashenberg P.N. Cheimets S. Glashow 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We presents the results of an activity concerning the test of the Einstein Weak Equivalence Principle with an accuracy of about 5 × 10−15. The experiment will be performed in an “Einstein elevator” using a differential accelerometer with a final sensitivity of about 10−14 g⊕/Hz1/2. The differential accelerometer is spun about an horizontal axis at a frequency in the range 0.5–1 Hz in order to modulate, during the free fall, the signal from a possible violation of the Equivalence Principle. In the paper the perturbing effects with the same signature of the possible violation are analyzed and constrained. The experimental results obtained in the laboratory with a first prototype of the differential accelerometer are discussed, comparing this results with those obtained using a new prototype. 相似文献
106.
李俊波 《华北航天工业学院学报》2012,(1):35-37
本文从社会需要出发分析了专业人才的英语素质和大学英语综合应用能力培养过程中的问题,提出了搞好大学英语自身特色建设的建议,倡导基于专业人才培养定位的大学英语综合应用能力培养。 相似文献
107.
Benjamin Lenoir Agnès Lévy Bernard Foulon Brahim Lamine Bruno Christophe Serge Reynaud 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Radio tracking of interplanetary probes is an important tool for navigation purposes as well as for testing the laws of physics or exploring planetary environments. The addition of an accelerometer on board a spacecraft provides orbit determination specialists and physicists with an additional observable of great interest: it measures the value of the non-gravitational acceleration acting on the spacecraft, i.e. the departure of the probe from geodesic motion. 相似文献
108.
随着燃油价格的提高和航空公司人力成本的增加,航空公司的运行成本逐年攀升。如何降低运行成本成为航空公司非常关注的一个问题。在降低成本的各种方法中,有减少燃油消耗的方法,也有减少维修费用增加航空器可靠性的方法,还有优化航路、选择最佳飞行高度的方法等等。介绍一种综合考虑燃油成本和航空公司的直接运行成本,选择最佳的飞行速度,达到总运营成本最低的方法——成本指数方法。航空器在研发当中就应当对这种经济运行模式进行研究,并将其嵌入到飞行管理计算机当中。 相似文献
109.
以某型通用飞机产品为例,阐述其批产项目进度计划体系构建过程,实现批产项目进度计划管理的规范化、精细化、信息化,并建立一套适用于通用航空制造企业高效率、低成本的批产项目进度计划管理方法. 相似文献
110.
第21,22周峰年太阳射电爆发中毫秒级精细结构的分析 总被引:1,自引:0,他引:1
本文对第21周的2840MHz及22周峰年的2545MHz,2645MHz和2840MHz波段上所观测到的285个快速事件进行分析,发现两个峰年的快速事件具有多种多样的快速活动(快速精细结构).它们与耀斑的对应关系也做了统计分析. 相似文献