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 203 毫秒
591.
592.
H.A. Taylor H.G. Mayr R.E. Hartle L. Kramer R. Stirling 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(4):41-45
During January–August 1978, the global atmospheric angular momentum (M) exhibits distinct patterns of short term momentum interchange across latitudes. In the northern hemisphere winter-spring season, 30–50 day modulations of M are present in which momentum at mid-latitudes (20–30°) are closely matched by momentum at high latitudes (50–60°). During the same interval there are no corresponding variations in M evident in the southern hemisphere. Conversely, during southern hemisphere fall-winter, similar anticorrelations in monthly scale momentum excursions are evident between mid and high latitudes. In the northern hemisphere, the winter-spring momentum signatures are detected throughout the atmosphere, from the lower troposphere to the stratosphere. During the southern hemisphere fall-winter, the modulation patterns are not evident at the higher altitudes. Structural details of the momentum signatures indicate that the coupling is sometimes effective on very short time scales, e.g. 1–2 days, or less. The evidence of distinct anti-correlation between large regions has interesting implications for studies of global atmospheric circulation, and also for studies of the excitation of variations in earth rotation in response to short term modulations of M. 相似文献
593.
J. Fertig G.H. Schwehm 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):213-216
In March 1985 ESA's GIOTTO spacecraft will fly by P/Halley's nucleus at a distance of a few hundred kilometres. The near nucleus dust environment the probe will traverse poses a hazard with respect to physical damage as well as to attitude disturbance with the possible loss of ground station contact. To predict S/C survivability and dust impact rates for the experiments, a model of the spatial distribution of the dust in the nucleus' vicinity is required. In the ‘dynamic’ model, the local spatial dust density is derived from exact expressions for the dust particle dynamic motion. The model has been implemented in a software system which allows for fast simulations of a cometary fly-by. 相似文献
594.
T.H. Vonder Haar G.G. Campbell E.A. Smith A. Arking K. Coulson J. Hickey F. House A. Ingersoll H. Jacobowitz L. Smith L. Stowe 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(4):285-297
Two special measurements of the energy exchange between earth and space were made in connection with the FGGE. A global monitoring program using wide-field-of-view and scanner detectors from NASA's NIMBUS-7 satellite successfully returned measurements during the entire FGGE. This experiment system also used a black cavity detector to measure the total energy output of the sun to very high precision. A second set of high frequency time and space estimates of the radiation budget were determined from selected geostationary satellite data. Preliminary results from both radiation budget data sets and the solar “constant” measurements will be presented. 相似文献
595.
V. N. Oraevsky Yu. Ya. Ruzhin V. G. Korobeinikov A. S. Volokitin V. S. Skomarovsky 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(12):131-134
The paper presents the results and discussion of VLF wave measurements carried out in the course of two rocket experiments on injection of a dense cesium ion beam into the ionosphere at the heights of 165–240 km. The injection was accompanied by enhancement of the broad-band noise by several orders of magnitude. The wave measurements in the frequency range of 1–11 kHz revealed two pronounced frequencies somewhat exceeding that of the lower-hybrid resonance oscillations in the background plasma and the cesium beam. The oscillations were modulated by frequencies close to the ion-cyclotron frequencies of the background plasma. 相似文献
596.
G. Debouzy 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(4):99-103
The SIGMA mission is designed to obtain images of the sky in the hard X-ray/low energy gamma-ray domain 30 keV - 2 MeV, with an angular accuracy a few arc min., and a sensitivity for point sources down to a level of a few UFU. The principal scientific objectives of the SIGMA mission are described, as well as the anticipated performance of the instrument. 相似文献
597.
This paper presents the results of medical investigations performed in the Salyut-7 8-month mission in which a professional physician took part. The paper contains anthropometric measurements, results of investigating the vestibular function, cardiovascular function at rest and in response to multi-step tests (with emphasis on echocardiographic measurements), metabolic parameters and hormonal status. It also discusses medical aspects of the extravehicular activity. The medical investigations, although some new methods were applied, provided the continuity of methodical approaches and data accumulated in previous missions. 相似文献
598.
S.G. Ungar S.N. Goward 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(2):291-295
Improvements in crop discrimination can be realized by using mid-IR bands (1.55–1.75 μm and 2.08–2.35 μm) which are sensitive to canopy moisture content. Analyses of data from two growing seasons in Webster County, Iowa clearly indicate that corn and soybeans are highly separable in the mid-IR from early season through harvest. This contrasts sharply with visible and near-IR bands where corn and soybeans are confused throughout much of the growing season. The mid-IR temporal reflectance behavior appears to result from differences between C4 monocot and C3 dicot internal leaf structure. If this hypothesis holds, mid-IR observations should improve discrimination in other instances where similar differences in internal leaf structure are present. 相似文献
599.
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
600.
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