全文获取类型
收费全文 | 5443篇 |
免费 | 7篇 |
国内免费 | 12篇 |
专业分类
航空 | 2616篇 |
航天技术 | 1956篇 |
综合类 | 21篇 |
航天 | 869篇 |
出版年
2021年 | 33篇 |
2018年 | 74篇 |
2017年 | 65篇 |
2016年 | 54篇 |
2014年 | 83篇 |
2013年 | 130篇 |
2012年 | 107篇 |
2011年 | 191篇 |
2010年 | 139篇 |
2009年 | 193篇 |
2008年 | 280篇 |
2007年 | 130篇 |
2006年 | 100篇 |
2005年 | 147篇 |
2004年 | 160篇 |
2003年 | 174篇 |
2002年 | 108篇 |
2001年 | 160篇 |
2000年 | 91篇 |
1999年 | 104篇 |
1998年 | 154篇 |
1997年 | 109篇 |
1996年 | 115篇 |
1995年 | 158篇 |
1994年 | 195篇 |
1993年 | 100篇 |
1992年 | 131篇 |
1991年 | 54篇 |
1990年 | 64篇 |
1989年 | 122篇 |
1988年 | 51篇 |
1987年 | 53篇 |
1986年 | 78篇 |
1985年 | 185篇 |
1984年 | 150篇 |
1983年 | 134篇 |
1982年 | 121篇 |
1981年 | 203篇 |
1980年 | 60篇 |
1979年 | 54篇 |
1978年 | 54篇 |
1977年 | 53篇 |
1976年 | 40篇 |
1975年 | 52篇 |
1974年 | 49篇 |
1973年 | 46篇 |
1972年 | 59篇 |
1971年 | 48篇 |
1970年 | 36篇 |
1969年 | 41篇 |
排序方式: 共有5462条查询结果,搜索用时 69 毫秒
161.
A two-pole filter is proposed as a detector for a scanning radar. The optimum values of the filter coefficients are found and are approximated by a simple expression. The optimum two-pole filter requires a 0.15-dB increase in signal-to-noise ratio in order to provide the same detection capability as the optimum detector, and yields azimuth estimates whose standard deviation are within 15 percent of the Cramér-Rao lower bound. The estimator is simple to implement, avoiding the storage requirements of the moving window detector and the bias complications of the feedback integrator. 相似文献
162.
A ground testing method has been devised to evaluate the dynamic errors of an inertial navigation system. A trimmed stationary inertial system in the navigation mode can be subjected to programmed platform orm drift rates, and generate position outputs which are compared with those of a perfect navigator. The linearized error equations for this testing mode are derived and the resulting position error propagation is analyzed using Kalman filtering in order to identify the error sources. A simulated platform with a fixed set of error sources is analyzed to evaluate this testing concept. An example is presented to show that the gyro and accelerometer scale factor and misalignment error coefficients can be estimated. 相似文献
163.
164.
165.
Parameters of expanding magnetic loops and arches and of mass flows generated by them in the corona have been computed in a 1D two-fluid approximation. Two possible trigger mechanisms of the coronal transients have been considered: (i) sudden increase of the background magnetic field strength, and (ii) heating and compression plasma inside these magnetic structures. We discuss the formation of shock waves and their dependence on dynamics and geometry of the magnetic structures. 相似文献
166.
J. P. Cox J. C. Wheeler C. J. Hansen D. S. King A. N. Cox S. W. Hodson 《Space Science Reviews》1980,27(3-4):529-535
The radial pulsations of very luminous, low-mass models (L/M 104, solar units), which are possible representatives of the R CrB stars, have been examined. These pulsations are extremely nonadiabatic. We find that there are in some cases at least one extra (strange) mode which makes interpretation difficult. The blue instability edges are also peculiar, in that there is an abrupt excursion of the blue edge to the blue for L/M sufficiently large. The range of periods of the model encompasses observed periods of the Cepheid-like pulsations of actual R CrB stars. 相似文献
167.
K. G. Ivanov 《Space Science Reviews》1982,32(1-2):49-63
The configuration, and the structure of shock waves from isolated solar flares and from a series of flares are discussed and classified.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia. 相似文献
168.
H. Borg L. -A. Holmgren B. Hultovist F. Cambou H. Rème A. Bahnsen G. Kremser 《Space Science Reviews》1978,22(5):511-535
Some preliminary new results are presented of the keV plasma experiment on GEOS-1. Electrons and ions have been observed to stream along the magnetic field lines in the dayside magnetosphere from the ionospheric side of the satellite towards the equatorial plane during magnetic storms, with streaming velocities corresponding to a kinetic energy of the order of a keV. The opposite streaming velocity has also been seen, but primarily in the ions only and with a smaller flux ratio for the two opposite directions along the field lines. The transition between the two opposite streaming directions, as seen by the satellite, has been found to occur even in a fraction of a second.In magnetic storm conditions azimuthal asymmetries in ion fluxes corresponding to electric field intensities of several tens of millivolts per meter have been observed. 相似文献
169.
Trunk G.V. Cantrell B.H. Gordon W.B. 《IEEE transactions on aerospace and electronic systems》1979,(6):883-887
The Cramer-Rao bound for an unbiased estimate of the elevation angle of a target in the presence of multipath is calculated for the symmetric (target and image symmetric about the elevation symmetry plane of antenna) and nonsymmetric cases for an antenna consisting of 21 elements. These bounds are compared to the maximum likelihood estimates and it is found that the rms error of the maximum likelihood estimate (which has a bias) is below the Cramer-Rao bound for unbiased estimates. 相似文献
170.
Trunk G.V. Gordon W.B. Cantrell B.H. 《IEEE transactions on aerospace and electronic systems》1990,26(1):146-153
A technique which uses maximum-likelihood estimates (MLEs) of target Doppler and target amplitude is developed for rejecting clutter residues. Multiple estimates are made and consistency checks are applied to the estimates. Simulation results indicate that for large clutter-to-noise ratios (C /N ⩾55 dB) the probability of false alarm from clutter residues is reduced from 1.0 to below 0.01 相似文献