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31.
Nicholas L. Johnson 《Space Policy》1999,15(3):203
The geosynchronous orbital regime has long been recognized as a unique space resource, dictating special measures to ensure its continuing use for future generations. During the past 20 yr a variety of national and international policies have been developed to preserve this environment. A review of current practices involving the deployment and disposal of geosynchronous spacecraft, associated upper stages and apogee kick motors, and geosynchronous orbit transfer objects indicates both positive and negative trends. Most spacecraft operators are indeed performing end-of-mission maneuvers, but the boost altitudes normally fall short of policy guidelines. Russia, a major operator in geosynchronous orbit, maneuvers only 1 in 3 spacecraft out of the region, while China has never retired a spacecraft above GEO. The viability of voluntary protection measures for this regime depends upon the responsible actions of the aerospace community as a whole. 相似文献
32.
Kaplan L.J. Ormsby J.F.A. Fowle E.N. Johnson K.R. Bates R.H.T. Bickel S.H. 《IEEE transactions on aerospace and electronic systems》1969,(4):654-660
A satellite has been designed for application to radar calibration. Electromagnetic and mechanical characteristics of the satellite and their influence on the selection of shape and other parameters are discussed. Theoretical and experimental scattering data are included. 相似文献
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Stephen Malys Russell Solomon Jason Drotar Todd Kawakami Thomas Johnson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):834-844
The operational Terrestrial Reference Frames (TRFs) realized through the evaluation of broadcast ephemerides for GPS, GLONASS, Galileo, BeiDou-2 and BeiDou-3 have been compared to IGS14, the TRF realized by the International GNSS Service (IGS). The TRFs realized by the GPS, GLONASS, Galileo, and BeiDou-2 and BeiDou-3 broadcast ephemerides are the orbital realizations of WGS 84 (G1762′), PZ90.11, GTRF19v01, and BDCS respectively. These TRFs are compared using up to 56 days of data (21 July-14 Sept 2019) at a 5 or 15-min rate. The operational TRFs are compared to IGS14 in a 7-parameter similarity (Helmert) transformation. Numerical results show that the operational GNSS TRFs differ from IGS14 at a level no greater than 4 cm for Galileo, 6 cm for GPS and BeiDou-3, 13 cm for GLONASS, and 48 cm for a limited set of BeiDou-2 Medium Earth Orbit (MEO) vehicles. 相似文献
36.
D F Smart M A Shea M J Golightly M Weyland A S Johnson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(4):841-846
We have a developed a dynamic cutoff rigidity model based on computed world grids of vertical cutoff rigidities derived from employing the Tsyganenko magnetospheric model. The dynamic range of this model covers all magnetic activity levels specified by integer values of the Kp magnetic index. We present comparisons of the measured dose observed on the space shuttle during the August 1989 solar proton event with the dose computed from solar particles predicted to be allowed through the magnetosphere to the space shuttle position. We find a one-to-one correspondence between the portion of the orbit predicted to be subjected to solar protons and the portion of the orbit where solar particle dose measurements were obtained. 相似文献
37.
E. Grün G.W. Garneau R.J. Terrile T.V. Johnson G.E. Morfill 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):143-148
Voyager 2 images of Saturn's rings have been analyzed for spoke activity. More than 80 and 40 different spokes have been measured at the morning and at the evening ansa, respectively. Higher rate of spoke formation has been found at 145° ± 15° SLS and at 305° ± 15° SLS which persisted for at least 3 Saturn revolutions. Higher spoke activity (formation and growth in width) by more than a factor 3 has been observed over the nightside hemisphere of Saturn than over the dayside hemisphere. The age distribution (i.e. time from radial formation until observation, assuming Keplerian shear) of the leading (old) edges of spokes has its maximum at ~ 9,000 s and ~ 6,000 s for spokes observed at the morning ansa and at the evening ansa, respectively. The highest spoke age observed is ~ 20,000 s. The age distribution of the trailing (young) edges of spokes peaks at < 2,000 s at both ansae but has its mean at ~ 4,500 s and ~ 3,500 s, respectively. On the average the observed spokes grew in width for ~ 4,500 s at the morning ansa and for ~ 2,500 s at the evening ansa. The maximum time of growth in width was ~ 12,000 s. 相似文献
38.
Commercial standards adopted from the volume-driven electronics markets provide improved processing capacities over those widely used military standards and at reduced cost. Desired future capabilities and advanced functions, such as RPA, require the throughput, bandwidth, and memory provided by commercial processors and data buses. The primary issues needing resolution prior to implementation are related to operations in military rotorcraft environment, reliability, redundancy management, and fault and battle damage tolerance. In addition, some required network components presently do not exist in the preferred form factors. The ROSA project is providing effective laboratory demonstrations of COTS products and open systems specifications and standards to rotorcraft avionics. Preliminary cost estimates forecast large potential savings and create a compelling business case for follow-on research and transition to production systems. In addition, the project is developing a Rotorcraft Technical Architecture with the participation of many industry partners and will promote the resulting documentation as background materials for the JTA-A 相似文献
39.
Finn H.M. Johnson R.S. Peebles P.Z. 《IEEE transactions on aerospace and electronic systems》1971,(1):147-159
In an earlier paper, Maisel [6] considered two-channel detection systems using a sidelobe blanking logic when a nonfluctuating target was present. This paper is an extension of the earlier work to include fluctuating targets. The Swerling I, II, III, and IV models are considered when single-pulse detection is of interest. An adaptive threshold procedure is also briefly discussed whereby the probability of false alarm at any given resolution cell is maintained constant, even though the input clutter level may vary from cell to cell or from beam position to beam position. Useful data are presented for detection probabilities in the range 0.5 to 0.9, for false alarm probabilities in the range 104 to 10-8, and for a false detection probability of 0.1 for a sidelobe target yielding an apparent signal to total noise power density ratio of 13.0 dB in the main beam receiver. 相似文献
40.
A review is made of current techniques used in the statistical analysis of radio direction finding data which predict a region of probable transmitter location based upon a collection of intersecting lines of bearing measurements. This region has been conventionally defined by the elliptical error probability (EEP). Two characterizations for EEP are considered, and a technique is proposed for robust estimation of the elliptical region of probable location. 相似文献