全文获取类型
收费全文 | 4831篇 |
免费 | 2篇 |
国内免费 | 11篇 |
专业分类
航空 | 2519篇 |
航天技术 | 1556篇 |
综合类 | 183篇 |
航天 | 586篇 |
出版年
2021年 | 29篇 |
2018年 | 68篇 |
2017年 | 36篇 |
2016年 | 40篇 |
2014年 | 74篇 |
2013年 | 101篇 |
2012年 | 107篇 |
2011年 | 159篇 |
2010年 | 102篇 |
2009年 | 182篇 |
2008年 | 193篇 |
2007年 | 114篇 |
2006年 | 89篇 |
2005年 | 86篇 |
2004年 | 115篇 |
2003年 | 139篇 |
2002年 | 180篇 |
2001年 | 200篇 |
2000年 | 93篇 |
1999年 | 123篇 |
1998年 | 154篇 |
1997年 | 99篇 |
1996年 | 138篇 |
1995年 | 168篇 |
1994年 | 146篇 |
1993年 | 95篇 |
1992年 | 122篇 |
1991年 | 57篇 |
1990年 | 63篇 |
1989年 | 125篇 |
1988年 | 58篇 |
1987年 | 60篇 |
1986年 | 51篇 |
1985年 | 152篇 |
1984年 | 120篇 |
1983年 | 108篇 |
1982年 | 117篇 |
1981年 | 153篇 |
1980年 | 56篇 |
1979年 | 46篇 |
1978年 | 57篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 48篇 |
1974年 | 39篇 |
1973年 | 25篇 |
1972年 | 49篇 |
1971年 | 47篇 |
1970年 | 30篇 |
1969年 | 33篇 |
排序方式: 共有4844条查询结果,搜索用时 171 毫秒
641.
P. Ubertini A. Bazzano L. Boccaccini N.A. Dipper L. Iafrate C. LaPadula M. Mastropietro R. Patriarca V. Polcaro M.L. Urciuoli 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(1):105-108
A new design of position sensitive spectroscopic proportional counter is described, for use in a balloon borne hard x-ray telescope. Initial position and spectral resolution data from a one-dimensional laboratory prototype are reported. With this device, the final telescope will have an angular resolution of better than 10 minutes of arc. 相似文献
642.
R Tixador G Richoilley G Gasset H Planel N Moatti L Lapchine L Enjalbert J Raffin R Bost S N Zaloguev M P Bragina A F Moroz N G Antsiferova F M Kirilova 《Acta Astronautica》1985,12(2):131-134
Cytos 2 experiment, carried out during the French-Soviet manned flight (July 1982), has studied the antibiotics sensitivity of bacteria cultivated in vitro during the orbital flight. The results show an increase of the antibiotics resistance and a larger thickness of the cellular envelope for the inflight cells. The increase of antibiotics resistance can be related to a stimulating effect of space on the cell growth rate or to changes of the cellular envelope structure. 相似文献
643.
R.C. Elphic T.J. Kelly C.T. Russell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):131-134
Magnetic field measurements obtained in the nightside magnetosphere by the co-orbiting ISEE-1 and 2 spacecraft have been examined for signatures of field-aligned currents (FAC). Such currents are found on the boundary of the plasma sheet both when the plasma sheet is expanding and when it is thinning. Plasma sheet boundary layer current structure and substorm associated dynamics can be determined using the two spacecraft, although for slow traversals of the FAC sheet the spatial/temporal ambiguity is still an issue. We often find evidence for the existence of waves on the plasma sheet boundary, leading to multiple crossings of the FAC sheet. At times the boundary layer FAC sheet orientation is nearly parallel to the X-Z GSM plane, suggesting ‘protrusions’ of plasma sheet into the lobes. The boundary layer current polarity is, as expected, into the ionosphere in the midnight to dawn local time sector, and outward near dusk. Current sheet thicknesses and velocities are essentially independent of plasma sheet expansion or thinning, having typical values of 1500 km and 20–40 km/s respectively. Characteristic boundary layer current densities are about 10 nanoamps per square meter. 相似文献
644.
The Broad-Band X-Ray Telescope (BBXRT) has been designed to perform high sensitivity, moderate resolution spectrophototnetry of X-ray sources in the 0.3–12 keV band from the Shuttle. It consists of a coaligned pair of high throughput, conical X-ray imaging mirrors, with a cryogenically-cooled, multiple element, Si(Li) spectrometer at the focus of each. On axis, BBXRT will have an effective area of 580 cm2 at 2 keV and 250 cm2 at 7 keV, and a spectral resolution of 110 eV at 2 keV and 150 eV at 7 keV. A 104 s observation with BBXRT will allow a determination of the continuum spectral shape for sources near the Einstein deep survey limit. 相似文献
645.
Sorace R. Lee E. Baldauf J. Heffernan P. 《IEEE transactions on aerospace and electronic systems》1998,34(3):947-954
A study of the distribution of gain-to-noise-temperature (G/T) values for the Tracking and Data Relay Satellite (TDRS) satellite is described. The statistics of the G/T values are determined by a Monte Carlo simulation of the orbital geometry of the Sun and Moon, and the gain and noise temperature calculations is included. The results and their underlying assumptions are described 相似文献
646.
R. Kh. Makaeva 《Russian Aeronautics (Iz VUZ)》2008,51(2):214-217
Examples of application of the interference holography method for diagnostics of failure, technical condition and in nondestructive check of turbomachine parts are presented. 相似文献
647.
This article is devoted to the experimental works carried out in the R2Ch blow-down wind tunnel in the framework of the atmospheric re-entry PRE-X demonstrator program and to the fundamental studies performed on a hollow cylinder-flare relative to crucial problem of the transitional shock-wave/boundary-layer interaction.Shock-wave/boundary-layer interactions in hypersonic flows may have major consequences on thermal loads, especially if the shock is strong enough to induce separation. The heat-flux density levels in the interaction region strongly depend on the nature, laminar or turbulent of the boundary-layer. Special attention should be paid to transitional interactions, which are likely to exist at altitude where the Mach number is high and the density low.The wide Reynolds number range achievable in the R2Ch facility and reliable heat-flux measurements by infrared thermography have allowed to investigate the viscous interaction on the deflected flaps of the demonstrator model and to point out the laminar-to-turbulent boundary-layer natural and forced transition, in the light of the in-depth analysis of results obtained from the hollow cylinder-flare study. 相似文献
648.
Miller D.L. Wolfman G.J. Volanth A.J. Mullins R.T. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(4):22-26
Tower air traffic control is currently performed using several unintegrated systems. While each of these systems supports performing an isolated task, the compilation of tools presents a number of challenges. This paper reports ways in which the Tower Control Computer Complex (TCCC) will support and enhance user management of numerous systems. Areas that will be notably improved include the consistency in the user interface of the air traffic control toolset, the task of manually integrating tools and information, toolset alert management, and toolset organization and administration 相似文献
649.
Understanding properties of solar energetic particle (SEP) events associated with coronal mass ejections has been identified
as a key problem in solar-terrestrial physics. Although recent CME shock acceleration models are highly promising, detailed
agreement between theoretical predictions and observations has remained elusive. Recent observations from ACE have shown substantial
enrichments in the abundances of 3He and He+ ions which are extremely rare in the thermal solar wind plasma. Consequently, these ions act as tracers of their source material,
i.e.,
3He ions are flare suprathermals and He+ ions are interstellar pickup ions. The average heavy ion composition also exhibits unsystematic differences when compared
with the solar wind values, but correlates significantly with the ambient suprathermal material abundances. Taken together
these results provide compelling evidence that CME-driven shocks draw their source material from the ubiquitous but largely
unexplored suprathermal tail rather than from the more abundant solar wind peak. However, the suprathermal energy regime has
many more contributors and exhibits much larger variability than the solar wind, and as such needs to be investigated more
thoroughly. Answers to fundamental new questions regarding the preferred injection of the suprathermal ions, the spatial and
temporal dependence of the various sources, and the causes of their variability and their effects on the SEP properties are
needed to improve agreement between the simulations and observations. 相似文献
650.
A. Galli P. Wurz S. Barabash A. Grigoriev H. Gunell R. Lundin M. Holmström A. Fedorov 《Space Science Reviews》2006,126(1-4):267-297
We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle
detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at
the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet.
We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach
105 cm−2 sr−1 s−1, but no oxygen ENA signals above the detection threshold of 104 cm−2 sr−1 s−1 are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due
to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed.
Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 1010 m−3 and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 1012 m−3 and a temperature of 200 K predicted by Krasnopolsky and Gladstone (1996). Finally, we estimate the global atmospheric loss
rate of hydrogen and oxygen due to the production of ENAs. 相似文献