全文获取类型
收费全文 | 8961篇 |
免费 | 12篇 |
国内免费 | 28篇 |
专业分类
航空 | 4078篇 |
航天技术 | 3140篇 |
综合类 | 25篇 |
航天 | 1758篇 |
出版年
2021年 | 84篇 |
2019年 | 54篇 |
2018年 | 185篇 |
2017年 | 123篇 |
2016年 | 126篇 |
2015年 | 60篇 |
2014年 | 208篇 |
2013年 | 274篇 |
2012年 | 257篇 |
2011年 | 392篇 |
2010年 | 288篇 |
2009年 | 395篇 |
2008年 | 449篇 |
2007年 | 274篇 |
2006年 | 194篇 |
2005年 | 251篇 |
2004年 | 237篇 |
2003年 | 279篇 |
2002年 | 189篇 |
2001年 | 290篇 |
2000年 | 160篇 |
1999年 | 212篇 |
1998年 | 241篇 |
1997年 | 159篇 |
1996年 | 212篇 |
1995年 | 258篇 |
1994年 | 263篇 |
1993年 | 156篇 |
1992年 | 182篇 |
1991年 | 73篇 |
1990年 | 76篇 |
1989年 | 185篇 |
1988年 | 79篇 |
1987年 | 75篇 |
1986年 | 88篇 |
1985年 | 243篇 |
1984年 | 217篇 |
1983年 | 172篇 |
1982年 | 166篇 |
1981年 | 294篇 |
1980年 | 77篇 |
1979年 | 66篇 |
1978年 | 70篇 |
1977年 | 63篇 |
1976年 | 53篇 |
1975年 | 73篇 |
1974年 | 60篇 |
1973年 | 57篇 |
1972年 | 68篇 |
1970年 | 54篇 |
排序方式: 共有9001条查询结果,搜索用时 31 毫秒
101.
Yakimenko O.A. Kaminer I.I. Lentz W.J. Ghyzel P.A. 《IEEE transactions on aerospace and electronic systems》2002,38(4):1181-1200
This paper addresses the problem of determining the relative position and orientation of an unmanned air vehicle with respect to a ship using three visible points of known separation. The, images of the points are obtained from an onboard infrared camera. The paper develops a numerical solution to this problem. Both simulation and flight test results are presented. 相似文献
102.
C Lindberg G Horneck 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(3):277-280
The ESA MarsNet mission proposal consists most probably of a trio of Mars landers. These landers each contain a variety of scientific equipment. The network of stations demands for a definition of its planetary protection requirements. With respect to the MarsNet mission only forward contamination problems will be considered. Future involvement of European efforts in planetary exploration including sample returns will also raise the problem of back contamination. A tradeoff study for the overall scientific benefit with respect to the approximative cost is necessary. Planetary protection guide-lines will be proposed by an interdisciplinary and international board of experts working in the fields of both biology and planetary science. These guide-lines will have to be flexible in order to be modified with respect to new research results, e.g. on adaptation of microorganisms to extreme (space) conditions. Experiments on the survival of microorganisms at conditions of simulated Mars surface and subsurface will have to be conducted in order to obtain a baseline data collection as a reference standard for future guide-lines. 相似文献
103.
An analysis is presented that forms the basis for an algorithm for calculating the IGBT losses in a power factor correction (PFC) circuit. The method employs experimental data from an off-line test circuit that closely resembles the switching conditions in the actual PFC. This technique provides calculated values of both the conduction and switching losses of the main transistor in a boost-type PFC circuit. Results for a 6 kW PFC are included 相似文献
104.
Hwu S.U. Loh Y.C. Dobbins J.A. Kroll Q.D. Sham C.C. 《Aerospace and Electronic Systems Magazine, IEEE》2005,20(10):9-14
Computational investigations and experimental measurements were performed to evaluate the Space Shuttle UHF communication system performance for payload bay antenna at the proposed new location. To insure adequate communication coverage at relocated new location, the link margin for the Extravehicular Activity (EVA) astronauts and between Space Shuttle Orbiter and International Space Station (SSO-ISS) during rendezvous were analyzed. The multipath effects from the vehicle structures surrounding the antenna were investigated. The Radio Frequency (RF) electromagnetic radiation to the Orbiter Docking System (ODS) pyrotechnics was also analyzed to ensure the EMC/EMI compliances. 相似文献
105.
106.
D.I. Kosenko S.I. Blinnikov K.A. Postnov P. Lundqvist E.I. Sorokina 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2705-2710
Time-dependent thermal X-ray spectra are calculated from physically plausible conditions around GRB. It is shown that account for time-dependent ionization processes strongly affects the observed spectra of hot rarefied plasma. These calculations may provide an alternative explanation to the observed X-ray lines of early GRBs afterglows (such as GRB 011211). Our technique will allow one to obtain independent constraints on the GRB collimation angle and on the clumpiness of circumstellar matter. 相似文献
107.
The fine structure of the Auroral Kilometric Radiation (AKR) is studied using multicomponent measurements of the electric component of the electromagnetic field in the frequency band 4 kHz–1 MHz (the POLRAD experiment onboard the INTERBALL-2 satellite). Special attention is paid to the measurements near the source of the AKR: under conditions when the lower boundary of the emission range descended sufficiently low, down to the local gyrofrequency of electrons. From the analysis of the electric field structure the conclusion is drawn that the bulk of the AKR power is carried by the signal component fast variable in time and frequency (flickering component). The power of a constant component (continuum) is lower by at least an order of magnitude. During strong bursts of the AKR, the relative contribution of the flickering component increases. The spatial structure of the zone of generation has at least three characteristic scales along and across the magnetic field. 相似文献
108.
H. M. Fischer J. D. Mihalov L. J. Lanzerotti G. Wibberenz K. Rinnert F. O. Gliem J. Bach 《Space Science Reviews》1992,60(1-4):79-90
The Energetic Particles Investigation (EPI) instrument operates during the pre-entry phase of the Galileo Probe. The major science objective is to study the energetic particle population in the innermost regions of the Jovian magnetosphere — within 4 radii of the cloud tops — and into the upper atmosphere. To achieve these objectives the EPI instrument will make omnidirectional measurements of four different particle species — electrons, protons, alpha-particles, and heavy ions (Z > 2). Intensity profiles with a spatial resolution of about 0.02 Jupiter radii will be recorded. Three different energy range channels are allocated to both electrons and protons to provide a rough estimate of the spectral index of the energy spectra. In addition to the omnidirectional measurements, sectored data will be obtained for certain energy range electrons, protons, and alpha-particles to determine directional anisotropies and particle pitch angle distributions. The detector assembly is a two-element telescope using totally depleted, circular silicon surfacebarrier detectors surrounded by a cylindrical tungsten shielding with a wall thickness of 4.86 g cm-2. The telescope axis is oriented normal to the spherical surface of the Probe's rear heat shield which is needed for heat protection of the scientific payload during the Probe's entry into the Jovian atmosphere. The material thickness of the heat shield determines the lower energy threshold of the particle species investigated during the Probe's pre-entry phase. The EPI instrument is combined with the Lightning and Radio Emission Detector (LRD) such that the EPI sensor is connected to the LRD/EPI electronic box. In this way, both instruments together only have one interface of the Probe's power, command, and data unit. 相似文献
109.
A Izumi-Kurotani M Yamashita Y Kawasaki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(1):263-266
Japanese treefrogs (Hyla japonica) are planned to be sent to the space station MIR. Experimental system was developed to observe their behaviors under microgravity. 相似文献
110.
A.G. Lyne 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2716-2720
A recent multibeam pulsar survey of the outer Galactic plane at Parkes has discovered the first-known double-pulsar binary, a very compact double neutron star system in which both stars are observable as radio pulsars. In this review, we briefly describe the discovery and the studies which have been enabled by the unique properties of the system. These range from the most precise confirmation yet of the theory of general relativity, with the possibility of even more new tests and the measurement of second-order post-Newtonian effects, to studies of the magnetospheres and emission properties of the two pulsars. The discovery also results in a significant increase in the expected rate of occurrence of the mergers of double neutron star systems, and hence the rate of detection of such events by the new ground-based gravitational wave detectors. 相似文献