全文获取类型
收费全文 | 616篇 |
免费 | 68篇 |
国内免费 | 148篇 |
专业分类
航空 | 310篇 |
航天技术 | 297篇 |
综合类 | 46篇 |
航天 | 179篇 |
出版年
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 29篇 |
2020年 | 18篇 |
2019年 | 24篇 |
2018年 | 23篇 |
2017年 | 29篇 |
2016年 | 28篇 |
2015年 | 32篇 |
2014年 | 56篇 |
2013年 | 50篇 |
2012年 | 49篇 |
2011年 | 47篇 |
2010年 | 52篇 |
2009年 | 68篇 |
2008年 | 44篇 |
2007年 | 30篇 |
2006年 | 29篇 |
2005年 | 21篇 |
2004年 | 13篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 19篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 1篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1984年 | 7篇 |
排序方式: 共有832条查询结果,搜索用时 46 毫秒
371.
针对跟踪雷达的反辐射导弹发射时机告警 总被引:2,自引:0,他引:2
介绍一种反辐射导弹发射时机警设备的基本原理和实施方案。根据雷达收到的载机和反辐射导弹回波信号特征,综合成exp(J2π(fo+fd)t)信号和exp(j2π(fo+fd+at/2)t)信号的数学模型。分雷达跟踪波门内外两种情况进行512点快傅里叶变换(FFT)谱分析,从频域上把载机和导弹区分开来,达到反辐射导弹发射时机靠警的目的。最后给出了仿真结果,结果是令人满意的。 相似文献
372.
含非均匀辐射气体空腔辐射特性计算研究 总被引:6,自引:0,他引:6
文章发展了求解积分辐射传输方程组的方法来计算充满非均匀辐射性气体封闭腔的辐射特性的方法,讨论了辐射空间分布及光谱分布的计算方法,并编制了相应的计算机程序.计算了某型发动机轴对称喷管的辐射分布,并与采用通常的辐射换热经验公式的计算结果进行了比较. 相似文献
373.
分析了圆柱形黑体腔腔内视在发射率的分布及腔体发射率,讨论了斜光线在光纤中的耦合与传输,并导出了光纤中传输的辐射功率表达式和光电探测器输出电流表达式。探测器输出电流的表达式表明,光电流的大小除随黑体腔温度变化外,还与探测器的下限、上限截止波长有关。下限、上限截止波长的间隔愈大,则光电流愈大,故在接收辐射功率时,探测器前不加窄带滤波片。文中还给出了光电流随温度变化的理论曲线和实验曲线,两者基本吻合。 相似文献
374.
《中国航空学报》2020,33(8):2204-2211
The stripped solar sail whose membrane is divided into separate narrow membrane strips is believed to have the best structural efficiency. In this paper, the stripped solar sail structure is regarded as an assembly made by connecting a number of boom-strip components in sequence. Considering the coupling effects between booms and membrane strips, an exact and semi-analytical method to calculate structural dynamic responses of the stripped solar sail subjected to solar radiation pressure is established. The case study of a 100 m stripped solar sail shows that the stripped architecture helps to reduce the static deflections and amplitudes of the steady-state dynamic response. Larger prestress of the membrane strips will decrease stiffness of the sail and increase amplitudes of the steady-state dynamic response. Increasing thickness of the boom will benefit to stability of the sail and reduce the resonant amplitudes. This proposed semi-analytical method provides an efficient analysis tool for structure design and attitude control of the stripped solar sail. 相似文献
375.
T. Bag M.V. Sunil Krishna Shilpa Gahlot Vir Singh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Severe geomagnetic storms and their effects on the 557.7 nm dayglow emission are studied in mesosphere. This study is primarily based on photochemical model with the necessary input obtained from a combination of experimental observations and empirical models. The model results are presented for a low latitude station Tirunelveli (8.7°N, 77.8°E). The volume emission rates are calculated using MSISE-90 and NRLMSISE-00 neutral atmospheric models. A comparison is made between the results obtained from these two models. A positive correlation amongst volume emission rate (VER), O, O2 number densities and Dst index has been found. The present results indicate that the variation in emission rate is more for MSISE-90 than in NRLMSISE-00 model. The maximum depletion in the VER of greenline dayglow emission is found to be about 30% at 96 km during the main phase of the one of the geomagnetic storms investigated in the case of MSISE-90 (which is strongest with Dst index −216 nT). The O2 density decreases about 22% at 96 km during the main phase of the same geomagnetic storm.The NRLSMSISE-00 model does not show any appreciable change in the number density of O during any of the two events. The present study also shows that the altitude of peak emission rate is unaffected by the geomagnetic storms. The effect of geomagnetic storm on the greenline nightglow emission has also been studied. It is found that almost no correlation can be established between the Dst index and variations in the volume emission rates using the NRLMSISE-00 neutral model atmosphere. However, a positive correlation is found in the case of MSISE-90 and the maximum depletion in the case of nightglow is about 40% for one of the storms. The present study shows that there are significant differences between the results obtained using MSISE-90 and NRLMSISE-00. 相似文献
376.
In deep space manned missions for the exploration and exploitation of celestial bodies of Solar System astronauts are not shielded by the terrestrial magnetic field and must be protected against the action of Solar Cosmic Rays (SCRs) and Galactic Cosmic Rays (GCRs). SCRs are sporadically emitted, and in very rare but possible events, their fluence can be so high to be lethal to a unprotected crew. Their relatively low energy allows us to conceive fully passive shields, also if active systems can somewhat reduce the needed mass penalty. GCRs continuously flow without intensity peaks, and are dangerous to the health and operability of the crew in long duration (>1year) missions. Their very high energy excludes the possible use of passive systems, so that recourse must be made to electromagnetic fields for preventing ionizing particles to reach the habitat where astronauts spend most of their living and working time. A short overview is presented of the many ideas developed in last decades of last century; ideas are mainly based on very intense electrostatic shields, flowing plasma bubbles, or enormous superconducting coil systems for producing high magnetic fields. In the first decade of this century the problem began to be afforded in more realistic scenarios, taking into account the present and foreseeable possibilities of launchers (payload mass, diameter and length of the shroud of the rocket, etc.) and of assembling and/or inflating structures in space. Driving parameters are the volume of the habitat to be protected and the level of mitigation of the radiation dose to be guaranteed to the crew. Superconducting magnet systems based on multi-solenoid complexes or on one huge magnetic torus surrounding the habitat are being evaluated for defining the needed parameters: masses, mechanical structures for supporting the huge magnetic forces, needed equipments and safety systems. Technological tests are in preparation or planned for improving density of the current, lightness and stability, to increase working temperature of superconducting cables, and for finding light supporting structures and suitable safety architectures, delineating a possible development program for affording this difficult problem. 相似文献
377.
In this paper we review the current predictions of numerical simulations for the origin and observability of the warm hot
intergalactic medium (WHIM), the diffuse gas that contains up to 50 per cent of the baryons at z∼0. During structure formation, gravitational accretion shocks emerging from collapsing regions gradually heat the intergalactic
medium (IGM) to temperatures in the range T∼105–107 K. The WHIM is predicted to radiate most of its energy in the ultraviolet (UV) and X-ray bands and to contribute a significant
fraction of the soft X-ray background emission. While O vi and C iv absorption systems arising in the cooler fraction of the WHIM with T∼105–105.5 K are seen in FUSE and Hubble Space Telescope observations, models agree that current X-ray telescopes such as Chandra and XMM-Newton do not have enough sensitivity to detect the hotter WHIM. However, future missions such as Constellation-X and XEUS might be able to detect both emission lines and absorption systems from highly ionised atoms such as O vii, O viii and Fe xvii. 相似文献
378.
杜芳莉 《西安航空技术高等专科学校学报》2012,(1):58-60
目的如何实现空调系统更好的节能环保;方法介绍地源热泵工作原理以及它在毛细管平面辐射空调系统中的应用;结果指出将地源热泵技术用在毛细管平面辐射空调系统中;结论为空调系统的节能与环保提供了新的发展方向。 相似文献
379.
380.
Kyle Copeland Herbert H. Sauer Frances E. Duke Wallace Friedberg 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
From 1 January 1986 through 1 January 2008, GOES satellites recorded 170 solar proton events. For 169 of these events, we estimated effective and equivalent dose rates and doses of galactic cosmic radiation (GCR) and solar cosmic radiation (SCR), received by aircraft occupants on simulated high-latitude flights. Dose rate and dose estimates that follow are for altitudes 30, 40, 50, and 60 kft, in that order. 相似文献