全文获取类型
收费全文 | 5342篇 |
免费 | 947篇 |
国内免费 | 919篇 |
专业分类
航空 | 2099篇 |
航天技术 | 2366篇 |
综合类 | 304篇 |
航天 | 2439篇 |
出版年
2024年 | 38篇 |
2023年 | 176篇 |
2022年 | 176篇 |
2021年 | 245篇 |
2020年 | 238篇 |
2019年 | 245篇 |
2018年 | 338篇 |
2017年 | 198篇 |
2016年 | 225篇 |
2015年 | 250篇 |
2014年 | 414篇 |
2013年 | 301篇 |
2012年 | 404篇 |
2011年 | 460篇 |
2010年 | 368篇 |
2009年 | 382篇 |
2008年 | 345篇 |
2007年 | 299篇 |
2006年 | 267篇 |
2005年 | 288篇 |
2004年 | 186篇 |
2003年 | 171篇 |
2002年 | 126篇 |
2001年 | 141篇 |
2000年 | 112篇 |
1999年 | 94篇 |
1998年 | 105篇 |
1997年 | 83篇 |
1996年 | 58篇 |
1995年 | 67篇 |
1994年 | 75篇 |
1993年 | 63篇 |
1992年 | 61篇 |
1991年 | 63篇 |
1990年 | 66篇 |
1989年 | 30篇 |
1988年 | 31篇 |
1987年 | 13篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有7208条查询结果,搜索用时 547 毫秒
131.
利用MF雷达对耀斑期间电离层D区电子密度的观测研究 总被引:1,自引:0,他引:1
利用MF雷达观测资料对X级别耀斑爆发期间在66-80km高度之间的电子密度进行了研究,观测到了耀斑爆发期间电子密度的突然增加,在较低高度上的电子密度的时间变化趋势与耀斑的软X射线辐射通量相关.电子密度的变化强度依赖于具体的耀斑参数,有些耀斑引起的电子密度增加高达400cm^-3,有些仅为100cm^-3左右.但耀斑期间在这一高度区间增加的总电子含量增量仅占耀斑辐射引起的整个电离层总电子含量增量的千分之一左右.最后,利用恢复阶段电子密度的时间变化过程估算了1997年11月4日耀斑期间部分高度上的有效复合系数. 相似文献
132.
133.
134.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(3):1070-1082
Solar sail halo orbits designed in the Sun-Earth circular restricted three-body problem (CR3BP) provide inefficient reference orbits for station-keeping since the disturbance due to the eccentricity of the Earth’s orbit has to be compensated for. This paper presents a strategy to compute families of halo orbits around the collinear artificial equilibrium points in the Sun-Earth elliptic restricted three-body problem (ER3BP) for a solar sail with reflectivity control devices (RCDs). In this non-autonomous model, periodic halo orbits only exist when their periods are equal to integer multiples of one year. Here multi-revolution halo orbits with periods equal to integer multiples of one year are constructed in the CR3BP and then used as seeds to numerically continue the halo orbits in the ER3BP. The linear stability of the orbits is analyzed which shows that the in-plane motion is unstable while the out-of-plane motion is neutrally stable and a bifurcation is identified. Finally, station-keeping is performed which shows that a reference orbit designed in the ER3BP is significantly more efficient than that designed in the CR3BP, while the addition of RCDs improve station-keeping performance and robustness to uncertainty in the sail lightness number. 相似文献
135.
Matteo Ceriotti Gregory May-Wilson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(9):2865-2877
The direction and magnitude of a solar sail acceleration are strongly related. For this reason, once the characteristic acceleration has been fixed, it is not possible to modulate the acceleration in a particular direction. In this work, a semi-analytical switching control law is derived, enabling a solar sail to emulate a smaller effective characteristic acceleration (without changes in geometry or optical properties); by periodically changing the pitch (cone) angle of the sail, in average over time, the acceleration produced by the sail matches exactly (in both direction and magnitude) that of a “smaller” sail. The range in which this is possible is determined, and the limitations on this range due to the size difference is computed. The method is validated on optimal Earth-Mars trajectories. 相似文献
136.
C. Mahesh Satya Prakash V. SathiyamoorthyR.M. Gairola 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
In this paper, an improved Kalpana-1 infrared (IR) based rainfall estimation algorithm, specific to Indian summer monsoon region is presented. This algorithm comprises of two parts: (i) development of Kalpana-1 IR based rainfall estimation algorithm with improvement for orographic warm rain underestimation generally suffered by IR based rainfall estimation methods and (ii) cooling index to take care of the growth and decay of clouds and thereby improving the precipitation estimation. 相似文献
137.
138.
139.
Ariadna Farrés Àngel Jorba 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In this work we focus on the dynamics of a solar sail in the Sun–Earth Elliptic Restricted Three-Body Problem with solar radiation pressure. The considered situation is the motion of a sail close to the L1 point, but displacing the equilibrium point with the sail so that it is possible to have continuous communication with the Earth. In previous works we derived a station keeping strategy for this situation but using the Circular RTBP as a model. 相似文献
140.
星地链路计算作为卫星通信的重要技术,是卫星通信系统设计的基础和理论依据,直接决定了卫星通信系统的链路通信质量。由于影响卫星链路的因素很多,设计中存在一处不合理即使得整条星地链路不可用,造成巨大的损失。而且在实际设计中无法做到最理想的链路状态,往往需要在某方面有所取舍,这也是链路计算中的一大难点。基于目前国际通用的链路计算方法,将星地链路上下行拆分,独立计算,综合分析,再结合实际工程经验,分析和计算实际工程案例,针对不同的链路配置给出相应合理的设计方法,可作为静止轨道通信卫星星地链路计算分析的参考。 相似文献