全文获取类型
收费全文 | 624篇 |
免费 | 30篇 |
国内免费 | 20篇 |
专业分类
航空 | 281篇 |
航天技术 | 303篇 |
综合类 | 25篇 |
航天 | 65篇 |
出版年
2023年 | 20篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 43篇 |
2013年 | 13篇 |
2012年 | 14篇 |
2011年 | 25篇 |
2010年 | 16篇 |
2009年 | 29篇 |
2008年 | 59篇 |
2007年 | 53篇 |
2006年 | 64篇 |
2005年 | 32篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 6篇 |
2001年 | 40篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 20篇 |
1997年 | 2篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 65篇 |
1993年 | 21篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1984年 | 17篇 |
排序方式: 共有674条查询结果,搜索用时 31 毫秒
651.
652.
D. Banerjee S. Vadawale 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
We present a forward modelling technique for calculating the surface X-ray spectra for a variety of lunar terrains. Our calculations considered variations in solar fluxes from solar quiescent condition to large flare activity (M1 flare), and expected elemental concentrations in the target, as well as yield, instrumental, and viewing geometry parameters for X-ray induced fluorescence from the lunar surface. Additionally, we present estimates of anticipated XRF signals from prominent Kα lines observable by a collimated 14 cm2 X-ray detector from a 100 km lunar orbit with ∼20 km spatial resolution. Our results show that Mg, Al and Si characteristic Kα lines can be observed for all solar conditions. The Ca Kα lines line can be differentiated from a fixed background during more energetic solar conditions such as C1 and M1 flares, whereas Ti and Fe lines are identifiable only during C1 and M1 solar flare conditions for Apollo 12 site composition. Both the Kα X-ray intensity ratios of Mg/Si and Al/Si correlate well with concentration ratios of Mg/Si and Al/Si, respectively, for B1 and M1 solar conditions. The Kα X-ray intensity ratios of Fe/Si and Ca/Si correlates with concentration ratios of Fe/Si and Ca/Si, respectively, for M1 solar condition. In principle, the modelling technique outlined here can be used to determine absolute elemental abundances (Mg, Al, Si, Ca, Ti and Fe) from X-ray spectra measured during recent and future lunar missions. 相似文献
653.
Sudip Bhattacharyya 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Measurement of at least three independent parameters, for example, mass, radius and spin frequency, of a neutron star is probably the only way to understand the nature of its supranuclear core matter. Such a measurement is extremely difficult because of various systematic uncertainties. The lack of knowledge of several system parameter values gives rise to such systematics. Low mass X-ray binaries, which contain neutron stars, provide a number of methods to constrain the stellar parameters. Joint application of these methods has a great potential to significantly reduce the systematic uncertainties, and hence to measure three independent neutron star parameters accurately. Here, we review the methods based on: (1) thermonuclear X-ray bursts; (2) accretion-powered millisecond-period pulsations; (3) kilohertz quasi-periodic oscillations; (4) broad relativistic iron lines; (5) quiescent emissions; and (6) binary orbital motions. 相似文献
654.
655.
R.I. Hayles C. Barat K. Hurley M. Niel G. Vedrenne I.V. Estulin V.G. Kurt A.V. Kuznetsov V.M. Zenchenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
A study of the morphology of 14 short ( 1 s) gamma ray bursts observed by the Franco Soviet SIGNE detectors onboard the VENERA spacecraft between 1978 and 1982 is presented. We find two major groups of short bursts characterised not only by their different durations ( 1 s and 100 ms respectively), but also by different e-folding rise and decay times. A study of the time history of the impulsive portion of the 1979 March 5 event at 2 ms resolution shows evidence for a previously undiscovered 23ms quasi periodicity. These results are discussed in the context of neutron star models for gamma ray bursters. 相似文献
656.
通过三个精密零件的成形实验,介绐了以粘塑性材料作传力介质的板料半模成形工艺的特点,研究了拉延过程中抗延力、压边力、容框内压的变化规律,工艺参数的控制对拉延所成败及产品质量的影响。 相似文献
657.
本文介绍了水杨醛缩-5-碘-8-氨基喹啉新西夫碱的合成、提纯与鉴定。特别对其性质及其与镓金属离子显色反应的光度特性作了研究,其配合物3.49×104L·mol(-1)·cm(-1). 相似文献
658.
本文是从阐述姿控系统仿真模型检测的重要性以及检测手段需不断改进的观点出发,介绍计算机频率特性测试软件(ftsp)的主要优点和用途。 相似文献
659.
Spiro K. Antiochos 《Space Science Reviews》1994,70(1-2):143-148
Although static loop models are often used to describe the structure of coronal loops, it is evident on both observational and theoretical grounds that mass motions play a crucial role in the physics of the corona and transition region. First we review the observations of emission-line broadening and wavelength shifts, which imply the presence of random motions and systematic downflows in coronal loops. Some discrepancies in the observations are discussed. It is argued that velocities due to gas pressure gradients are the most likely explanation for the observed flows. A number of models that have been proposed for these motions are reviewed. The implications of the various models on observations of the corona and transition region by SOHO are discussed. 相似文献
660.
Spicules are known as one of the most prevalent small-scale dynamic phenomena on the sun, which are likely to give considerable contribution to coronal heating and mass supply. We discuss a model of the spicules driven by a train of slow MHD shock waves propagating along a vertical expanding magnetic flux tube. The shocks are initiated due to compression of the tube by the increasing external pressure in the lower chromosphere. Downflow of spicular material depends on radiative cooling and other dissipative processes. 相似文献