全文获取类型
收费全文 | 318篇 |
免费 | 81篇 |
国内免费 | 30篇 |
专业分类
航空 | 65篇 |
航天技术 | 189篇 |
综合类 | 11篇 |
航天 | 164篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 16篇 |
2021年 | 26篇 |
2020年 | 16篇 |
2019年 | 25篇 |
2018年 | 29篇 |
2017年 | 14篇 |
2016年 | 22篇 |
2015年 | 21篇 |
2014年 | 46篇 |
2013年 | 14篇 |
2012年 | 25篇 |
2011年 | 25篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 21篇 |
2007年 | 13篇 |
2006年 | 20篇 |
2005年 | 3篇 |
2004年 | 13篇 |
2003年 | 1篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有429条查询结果,搜索用时 31 毫秒
1.
Mats Holmström 《Space Science Reviews》2006,126(1-4):435-445
Observations and simulations show that Mars' atmosphere has large seasonal variations. Total atmospheric density can have
an order of magnitude latitudinal variation at exobase heights. By numerical simulations we show that these latitude variations
in exobase parameters induce asymmetries in the hydrogen exosphere that propagate to large distances from the planet. We show
that these asymmetries in the exosphere produce asymmetries in the fluxes of energetic neutral atoms (ENAs) and soft X-rays
produced by charge exchange between the solar wind and exospheric hydrogen. This could be an explanation for asymmetries that
have been observed in ENA and X-ray fluxes at Mars. 相似文献
2.
3.
Steven D. Howe 《Space Policy》2001,17(4):275-283
The potential benefits to humankind of space exploration are tremendous. Space is not only the final frontier but is also the next marketplace. The orbital space above Earth offers tremendous opportunities for both strategic assets and commercial development. The critical obstacle retarding the use of the space around the Earth is the lack of low cost access to orbit. Further out, the next giant leap for mankind will be the human exploration of Mars. Almost certainly within the next 30 years, a human crew will brave the isolation, the radiation, and the lack of gravity to walk on and explore the Red planet. Both of these missions will change the outlook and perspective of every human being on the planet. However, these missions are expensive and extremely difficult. Chemical propulsion has demonstrated an inability to achieve orbit cheaply and is a very high-risk option to accomplish the Mars mission. An alternative solution is to develop a high performance propulsion system. Nuclear propulsion has the potential to be such a system. The question will be whether humanity is willing to take on the challenge. 相似文献
4.
Y. Futaana S. Barabash A. Grigoriev D. Winningham R. Frahm M. Yamauchi R. Lundin 《Space Science Reviews》2006,126(1-4):315-332
As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case
of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board
the Mars Express satellite. The “subsolar ENA jet” is generated by the interaction between the solar wind and the Martian
exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485
of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed
by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was
most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can
be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation
region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went
out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic
flux variations of the ENA flux at the spacecraft location. 相似文献
5.
王越 《华北航天工业学院学报》2006,16(3):46-48
本文详细介绍了为何要编制合并会计报表,哪些应纳入合并会计报表范围,在公司连续编制情况下, 对以前年度已做抵销的事项在今后编制合并会计报表时为何还要进行抵销进行了论述。 相似文献
6.
7.
对机动再入飞行器弧段的复合制导方案进行了研究,首先提出了通过高低空复合制导控制再入飞行器的终端速度和弹道倾角的思路;然后分别给出了高空最优制导律和大气厚再入最优制导律;最后对此复合制导方案进行了数字仿真。仿真结果表明此方案在理论上是可行的。 相似文献
8.
文章主要介绍了美国火星探测用降落伞研制过程以及在研制过程中的一些主要试验,并同时指出了试验中的一些特点。 相似文献
9.
火星探测着陆系统开伞控制方法研究 总被引:1,自引:0,他引:1
文章通过对火星探测进入轨道的分析,提出了一种以动压为控制目标的开伞控制方法,并借鉴过载-时间控制法的相关思想,结合火星探测进入轨道的特点,研究了该开伞控制法的原理和实现方法。根据火星探路者的实际进入条件,采用该方法的分析结果与实际飞行中的开伞情况基本吻合。 相似文献
10.
基于阻力与能量关系的优化剖面,以该再入剖面作为基准轨迹,给出了跟踪这一基准轨迹的空间飞行器再入制导律与控制律,将基准轨迹转化为相应的迎角剖面和滚转角剖面,设计了相应的结构配置。仿真结果表明,基于阻力与能量关系剖面设计的制导律满足了各项约束条件,并能成功地控制飞行器到达所要求的位置。 相似文献