全文获取类型
收费全文 | 3850篇 |
免费 | 3篇 |
国内免费 | 9篇 |
专业分类
航空 | 1732篇 |
航天技术 | 1412篇 |
综合类 | 10篇 |
航天 | 708篇 |
出版年
2021年 | 28篇 |
2018年 | 56篇 |
2017年 | 51篇 |
2016年 | 47篇 |
2014年 | 65篇 |
2013年 | 104篇 |
2012年 | 89篇 |
2011年 | 153篇 |
2010年 | 107篇 |
2009年 | 154篇 |
2008年 | 199篇 |
2007年 | 112篇 |
2006年 | 79篇 |
2005年 | 115篇 |
2004年 | 128篇 |
2003年 | 127篇 |
2002年 | 81篇 |
2001年 | 118篇 |
2000年 | 60篇 |
1999年 | 88篇 |
1998年 | 108篇 |
1997年 | 77篇 |
1996年 | 70篇 |
1995年 | 109篇 |
1994年 | 127篇 |
1993年 | 64篇 |
1992年 | 77篇 |
1991年 | 32篇 |
1990年 | 43篇 |
1989年 | 69篇 |
1988年 | 33篇 |
1987年 | 28篇 |
1986年 | 39篇 |
1985年 | 125篇 |
1984年 | 114篇 |
1983年 | 91篇 |
1982年 | 78篇 |
1981年 | 155篇 |
1980年 | 31篇 |
1979年 | 34篇 |
1978年 | 37篇 |
1977年 | 34篇 |
1976年 | 29篇 |
1975年 | 35篇 |
1974年 | 30篇 |
1973年 | 31篇 |
1972年 | 42篇 |
1971年 | 23篇 |
1970年 | 22篇 |
1969年 | 21篇 |
排序方式: 共有3862条查询结果,搜索用时 722 毫秒
621.
W.A. Gault G.G. Shepherd 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(7):111-114
A CCD imaging device has been designed which combines a spatial resolution of 0.1° with a spectral resolving power of 105, sufficient to measure Doppler shifts and line widths of individual atmospheric emission lines. It will be flown aboard Spacelab and will be used to study neutral winds and temperatures as functions of height, latitude and time of day. 相似文献
622.
J.M. Malherbe G. Simon P. Mein N. Mein B. Schmieder J.C. Vial 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(11):53-56
Disappearances of preflare filaments have been observed on June 22, 1980 (S07,W13) (flare at 13.04 U.T.) and September 3, 1980 (flare at 7.52 U.T.). The analysis of MSDP data (MEUDON) leads to the followings conclusions : - Disappearances begin a few minutes before the Hα impulsive phase. - The filaments can be seen again after the flares. - Upwards motions occur in several points, without disturbing significantly preëxisting downflows.Velocity maps suggest shears or velocity loops.The filament disappearance seems to be due to a heating mechanism beginning before the flare maximum. 相似文献
623.
The theoretical basis and methods of implementation of a moment algorithm for the range separation estimation of two closely spaced point targets are presented. Moment estimation and noise filtering techniques introduced here result in a considerable improvement over Baum's algorithm. The error bounds are established and it is shown that the spectral moment estimator exhibits optimum (zero bias, minimum variance) performance when the target separation normalized to the standard deviation of the Gaussian pulse is 2?1.5. Monte Carlo simulation is performed to verify the approximations made and to demonstrate the feasibility of the working models. 相似文献
624.
M. Grewing A. Vidal-Madjar A. Labeque C. Laurent A. Boksenberg C. Burgio S. di Serego Alighieri G.P. Whitcomb W. Burton C.I. Coleman R. Hoekstra C. Jamar J. Lequeux P. Rafanelli 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(4):147-151
Magellan is one of the future space projects being studied by the European Space Agency. The aim is to provide high resolution (λ/Δλ ≥ 2.5 × 104) spectra in the far and extreme UV (between 500 and 1550 Å) of faint galactic and extragalactic objects (V ≤ 16m). The instrument consists of a mechanical collimator, a concave holographic grating and a bidimensional photon-counting detector. A low resolution mode (λ/Δλ ≥ 103) will provide spectra of objects as faint as 18m.5. Magellan is planned as an observatory, operated in real time, and allowing interaction with the observer. 相似文献
625.
J.C. Henoux G. Chambe M. Semel B. Woodgate R. Shine J. Beckers 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(11):155-158
Linear polarization was observed in the S I 1437Å line in bright flaring points during the soft X-ray emission. The degree of polarization is about 25% and is detected at a signal to noise ratio of 2.9. The polarized electric vector is directed towards disk center to within 3°.This polarization could be due to collisional excitationm of S I by energetic electrons beamed in the vertical direction. We suggest that the heat flux in the region interconnecting the transition zone to the high chromosphere during the gradual phase of a flare could lead to an anisotropic excitation. Then the observed polarization would be due to vertical motions of the transition zone sweeping the preexisting chromosphere. 相似文献
626.
Comments on "Optimum Bandwidth of a Low-Pass Filter for Detection of a Pulse in Nonstationary Noise"
In a recent correspondence1 a calculation of the optimum bandwidth of a low-pass RC filter for the detection of a pulse signal in nonstationary noise was presented. The purpose of this correspondence is: 1) to point out additional references to the work which has been conducted in the stationary noise case, and 2) to present an interesting alternate derivation of the expected output noise power for the nonstationary noise case. 相似文献
627.
G.E. Thomas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(12):127-130
It is often observed that the stratospheric and mesospheric temperature structure undergoes transient disturbances from its averaged steady-state behavior. The causes may be traceable to gravity waves, planetary waves, solar proton and relativistic electron precipitation, etc. We examine the theoretical time behavior of the atmospheric temperature following the cessation of such heating phenomena as it relaxes toward its quiescent steady-state value. We also study the time-dependent response during a model stratospheric-warming/mesospheric-cooling event. In particular, we investigate the roles of eddy heat conduction, non-LTE cooling in the 15μm CO2 band, and an ambient vertical wind, and their relative importance as they depend upon altitude and time, in modifying temperature changes in this region. 相似文献
628.
The results of a survey of data on failures of aircraft electronic and electrical components that was conducted to identify problematic components are reported. The motivation for the work was to determine priorities for future work on the development of accident investigation techniques for aircraft electrical components. The primary source of data was the Airforce Mishap Database, which is maintained by the Directorate of Aerospace Safety at Norton Air Force Base. Published data from the Air Force Avionics Integrity Program (AVIP) and Hughes Aircraft were also reviewed. Statistical data from these three sources are presented. Two major conclusions are that problems with interconnections are major contributors to aircraft electrical equipment failures, and that environmental factors, especially corrosion, are significant contributors to connector problems 相似文献
629.
The issues associated with processing the outputs of an integrating acoustooptical spectrum analyzer (AOSA) to detect and identify the frequency and power of continuous wave (CW) signals are considered. The performance of the optimum detection strategy is presented, along with the Cramer-Rao bound on the performance of estimators of the frequency, and the performance of a simple peak-based frequency estimator. The performance of the maximum likelihood (ML) estimator of the power level is also presented. The results provide the behavior of the system as a function of the product of the aperture time and photodetector spacing amongst other parameters 相似文献
630.
Dimogianopoulos D.G. Hios J.D. Fassois S.D. 《IEEE transactions on aerospace and electronic systems》2007,43(4):1385-1396
A statistical method for the on-board detection and compensation of adverse oscillations in pilot-aircraft systems is presented. A recursively updated linear model representing the pilot-aircraft system is used to continuously check for stability loss. The instability-related oscillations are detected early, using a statistical hypothesis test. Furthermore, a specially designed stability augmentation system assists the pilot during the instability periods. The method's effectiveness is demonstrated via data obtained from a flight simulator and a detailed simulation model. 相似文献