全文获取类型
收费全文 | 3809篇 |
免费 | 3篇 |
国内免费 | 9篇 |
专业分类
航空 | 1712篇 |
航天技术 | 1402篇 |
综合类 | 10篇 |
航天 | 697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 | 88篇 |
2011年 | 153篇 |
2010年 | 107篇 |
2009年 | 150篇 |
2008年 | 197篇 |
2007年 | 111篇 |
2006年 | 78篇 |
2005年 | 112篇 |
2004年 | 127篇 |
2003年 | 123篇 |
2002年 | 81篇 |
2001年 | 117篇 |
2000年 | 60篇 |
1999年 | 86篇 |
1998年 | 107篇 |
1997年 | 77篇 |
1996年 | 70篇 |
1995年 | 109篇 |
1994年 | 125篇 |
1993年 | 64篇 |
1992年 | 76篇 |
1991年 | 32篇 |
1990年 | 42篇 |
1989年 | 68篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 38篇 |
1985年 | 125篇 |
1984年 | 111篇 |
1983年 | 91篇 |
1982年 | 77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 | 34篇 |
1974年 | 29篇 |
1973年 | 31篇 |
1972年 | 41篇 |
1971年 | 22篇 |
1970年 | 22篇 |
1969年 | 21篇 |
排序方式: 共有3821条查询结果,搜索用时 359 毫秒
591.
Mahle C.E. Geller B.D. Potukuchi J.R. Hyde G. 《Aerospace and Electronic Systems Magazine, IEEE》1988,3(11):3-10
Technology drivers for commercial communications satellites are examined based on the efficient use of spacecraft mass which is to be accomplished by increasing the efficiency of the microwave power amplifiers and antenna feed systems used for communications satellites, such as the INTELSAT series. The history of the INTELSAT series of satellites, the late 1980s market and available technology, and future directions of development are considered. Emphasis is on multibeam solid-state antennas, microwave switch matrices, solid-state power amplifiers, and the use of several filter modes in one physical cavity. By using quasimonolithic solid state techniques in a class B amplification mode they have achieved 40-60% efficiencies, compared with 20% for the conventional travelling wavetube amplifiers. It is concluded that technology directed towards improving the economics of satellite communications will continue to be a major driver of future communications satellite payloads. Through their use and their extension, the authors foresee more than doubling the telephone channels per satellite from the current 80000 to perhaps 200000 by the turn of the century 相似文献
592.
T.M. Bauer G. Paschmann R.A. Treumann W. Baumjohann N. Sckopke 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(12):1947-1950
For a rotational MHD discontinuity the bulk flow is Alfvénic in the de Hoffmann-Teller frame. Using AMPTE/IRM data, we present ion distribution functions during three crossings of the dayside low-latitude magnetopause. For these crossings a well defined de Hoffmann-Teller frame can be found, but the field-aligned bulk flow is always slower than the Alfvén speed. Nevertheless, we find signatures in the distribution functions that provide clear evidence for magnetic reconnection: solar wind ions reflected off the magnetopause, “D-shaped” solar wind ion distributions in the boundary layer, and counterstreaming of solar wind ions and ionospheric ions in the boundary layer. 相似文献
593.
Kelkar A.G. Joshi S.M. Alberts T.E. 《IEEE transactions on aerospace and electronic systems》1995,31(4):1325-1330
The stability characteristics of dynamic dissipative compensators are investigated for multibody flexible space structures having nonlinear dynamics. The problem addressed is that of proving asymptotic stability of dynamic dissipative compensators. The stability proof uses the Lyapunov approach and exploits the inherent passivity of such systems. For such systems these compensators are shown to be robust to parametric uncertainties and unmodeled dynamics. The results are applicable to a large class of structures such as satellites with multiple payloads and space-based manipulators 相似文献
594.
Modular pallet-type structures, designed for optimal usage of the Space Shuttle as a launch vehicle, can be used in three mission modes—Shuttle-attached, attached to an orbiting Power Module, or as fully autonomous free flyers. The requirements for such structures are defined and three structural solutions—the Spacelab pallet, a cubic framework structure and a honeycomb panel structure—are described. System and subsystem concepts of varying complexity and autonomy are indicated and their applications to several typical payload examples are shown. 相似文献
595.
A. Labeyrie G. Schumacher E. Savaria 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(4):11-22
FLUTE and TRIO are two versions of a proposed optical interferometer, intended as a first step towards large optical arrays. The two apertures of FLUTE are linked by solid members, while TRIO relies totally upon active stabilization techniques to maintain optical coherence with three satellites serving as array components. The feasibility of utilizing solar radiation pressure for fine control is studied.A natural and periodic variation of baseline spacing can be achieved by certain orbital configurations. Thus, skin panels having a tunable reflectivity suffice to obtain the fine corrections needed. Preliminary modelling indicates adequate controllability for such “chameleon” satellites. If suitable panel types can be developed, a TRIO system employing them would be preferred to FLUTE type structures. The longer (1 to 10 km) baselines achievable are of particular interest and the cost is probably lower. 相似文献
596.
L. Dezső G. Csepura O. Gerlei Á. Kovács I. Nagy 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):57-60
Using full-disc white light photoheliograms, we have studied umbrae motion and variations in sunspot areas in a large activity complex over 4 solar rotations. On the basis of the observational data we illustrate with typical examples to what extent rapid spot motions are associated with flare occurrences. 相似文献
597.
598.
G. Stanev M. Petrunova D. Teodosiev I. Kutiev K. Serafimov S. Chapkunov V. Chmyrev N. Isaev P. Puschaev I. Pimenov S. Bilichanko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(7):43-47
The instrument IESP-IPMP represents the complex unit measuring the vector of the DC electric field, the vectors of the electric and magnetic field in the frequency range of 0.2 – 6.5 Hz (wave form), autocorrelation functions of waves with frequencies of 0.1 – 5 kHz, and wave amplitudes in 8 bandpass channels. Some results are shown and compared in the various frequency ranges. 相似文献
599.
G.H. Schwehm R.H. Giese F. Giovane D.W. Schuerman J.L. Weinberg 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(8):121-125
The 1985 International Solar Polar Mission will provide the first opportunity to perform measurements from out of the ecliptic and from above the solar poles. Included in this mission is the Zodiacal Light/Background Starlight Experiment of the Ruhr-University Bochum, FRG (in collaboration with the State University of New York at Albany). The experiment is based on the use of a multicolor, sky-scanning photopolarimeter, which will be carried on the NASA S/C.The scientific objectives of the experiment are to investigate the intensity, polarization, and color of the diffuse sky brightness and determine the spatial distribution and physical properties of the interplanetary dust, including a possible interstellar component, as a function of S/C position in and out of the ecliptic.The instrument will allow simultaneous measurements in two separate wavelength bands. Measurements will be performed at 180, 220, 240, 280, 320, 350, 360, 440, 540, 640, 800 nm, including the state of polarization. Two different fields-of-view (1 sq deg and 5.6 sq deg) can be selected.The use of a microprocessor system in the instrument electronics will provide flexibility in measurement sequences and programs, on-board data processing and data quality control. 相似文献
600.
R.G. Walker H.H. Aumann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):197-201
The large beam size of the Infrared Astronomy Satellite (IRAS) focal plane detector array is well suited to measuring the low level thermal emission from cometary dust. Eight comets discovered in 1983 and nine previously known periodic comets were observed by IRAS during its ten month active lifetime. Dust production rates are derived for a wide range of heliocentric distances. Grain properties are inferred from application of simple models to the long wavelength spectral energy distribution. 相似文献