全文获取类型
收费全文 | 5010篇 |
免费 | 26篇 |
国内免费 | 16篇 |
专业分类
航空 | 2523篇 |
航天技术 | 1773篇 |
综合类 | 17篇 |
航天 | 739篇 |
出版年
2018年 | 72篇 |
2017年 | 63篇 |
2016年 | 52篇 |
2014年 | 88篇 |
2013年 | 122篇 |
2012年 | 106篇 |
2011年 | 156篇 |
2010年 | 112篇 |
2009年 | 183篇 |
2008年 | 238篇 |
2007年 | 122篇 |
2006年 | 93篇 |
2005年 | 129篇 |
2004年 | 130篇 |
2003年 | 156篇 |
2002年 | 99篇 |
2001年 | 162篇 |
2000年 | 100篇 |
1999年 | 93篇 |
1998年 | 139篇 |
1997年 | 95篇 |
1996年 | 133篇 |
1995年 | 166篇 |
1994年 | 179篇 |
1993年 | 95篇 |
1992年 | 121篇 |
1991年 | 58篇 |
1990年 | 60篇 |
1989年 | 131篇 |
1988年 | 51篇 |
1987年 | 52篇 |
1986年 | 74篇 |
1985年 | 158篇 |
1984年 | 135篇 |
1983年 | 117篇 |
1982年 | 114篇 |
1981年 | 155篇 |
1980年 | 51篇 |
1979年 | 45篇 |
1978年 | 51篇 |
1977年 | 45篇 |
1975年 | 51篇 |
1974年 | 45篇 |
1973年 | 41篇 |
1972年 | 36篇 |
1971年 | 45篇 |
1970年 | 34篇 |
1969年 | 39篇 |
1968年 | 34篇 |
1967年 | 36篇 |
排序方式: 共有5052条查询结果,搜索用时 31 毫秒
641.
642.
J L Shinn J E Nealy L W Townsend J W Wilson J S Wood 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):863-871
Using the Langley Research Center galactic cosmic ray (GCR) transport computer code (HZETRN) and the computerized anatomical man (CAM) model, crew radiation levels inside manned spacecraft on interplanetary missions are estimated. These radiation-level estimates include particle fluxes, LET (linear energy transfer) spectra, absorbed dose, and dose equivalent within various organs of interest in GCR protection studies. Changes in these radiation levels resulting from the use of various different types of shield materials are presented. 相似文献
643.
J. B. Blake M. C. McNab J. E. Mazur 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,28(12):1753-1757
The entry of energetic solar protons to the polar caps offers an interesting way to test models of the geomagnetic field. In this brief report, we present a comparison between SAMPEX observations of solar-particle intensity structure during a polar cap traversal with numerical trajectory calculations using the IGRF + T96 field model. 相似文献
644.
An adaptive array architecture is described which has improved convergence speed over the conventional Applebaum array when the eigenvalue spread of the input signal covariance matrix is large. The architecture uses N+1 Applebaum adaptive arrays in a two-layer cascaded configuration. The gain constants in the first layer are set so that large interfering sources are quickly nulled, but small interfering sources are suppressed more slowly. Since the first layer removes the large interfering signals, the gain constant for the second layer can be set to a large value to quickly null the smaller interferers. The adaptation time is examined for several combinations of signal levels and array sizes. It is shown that, in many signal environments, the computational requirements for the cascaded array compare favorably with those of conventional sample matrix inversion (SMI) methods for large arrays 相似文献
645.
Doppler imaging based on radar target precession 总被引:2,自引:0,他引:2
A unique form of target motion reminiscent of the precession of a rotating top is investigated. Images are generated with the radar looking either along the precession axis or orthogonally to it. Features of the two methods are discussed and demonstrated by imaging simulated point target scenes 相似文献
646.
Scoles D.L. Hayden J.W. Pickett D.F. Jr. Rao G.M. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(7):27-30
A nickel cadmium cell system which utilizes a polypropylene separator impregnated with polybenzimadazole, and which shows promise of providing an aerospace battery with performance equivalent to Super NiCd, and yet is more cost effective, is described. Background information, cell construction information, detailed test program information and data, and status of qualification are given 相似文献
647.
P.R. Ratcliff F. Gogu E. Grün R. Srama 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(12):111-115
A number of in-situ cosmic dust detectors derive the dust particle velocities from measurement of the risetimes of the impact plasma signal. Extensive calibration of these instruments has established a reliable empirical relationship but a quantitative explanation has not been available, with the result that confidence in flight data outside the range of the calibration data is hard to assess. Recent measurements taken at the dust accelerator facilities at the University of Kent (UK) and at MPI-K (Germany), supported by a theoretical analysis, have demonstrated that the relationship results from the time-spread of secondary impacts coupled with the mobility of ions in the impact plasma cloud, which is in turn determined by the magnitude and geometry of the applied electric field and on the ion species present. Results of the current investigations are presented, and the implications of measurements based on this principle at high particle velocities, at masses unobtainable in calibration studies, and for other instrument geometries, are considered. 相似文献
648.
W. I. Axford 《Space Science Reviews》1996,78(1-2):9-14
The history and current status of heliospheric physics are outlined very briefly. It is emphasized that the existing Voyager Interstellar Mission should go a long way to answering many of the outstanding questions during the next one or two decades, especially those concerning the nature and structure of the solar wind termination shock. 相似文献
649.
Fuzzy logic applications to multisensor-multitarget correlation 总被引:1,自引:0,他引:1
A consistent tactical picture requires data fusion technology to combine and propagate information received from diverse objects and usually vague situations. The information may be contained in two types of data; numerical data received from sensor measurements, and linguistic data obtained from human operators and domain experts. In real world situations, the numerical data may be noisy, inconsistent, and incomplete, and the linguistic information is imprecise and vague. To deal with these two types of data simultaneously, fuzzy sets and fuzzy logic provide a methodology to obtain an approximate but consistent tactical picture in a timely manner for very complex or ill-defined engineering problems. A functional paradigm for fuzzy data fusion is presented. It consists of four basic elements: (1) fuzzification of crisp elements, (2) fuzzy knowledge base derived from numerical input/output relations and humans, (3) fuzzy inference mechanism based on a class of fuzzy logic, (4) defuzzification of fuzzy outputs into crisp outputs for use by a plant. For real-time practical systems, the on-line determination of a fuzzy membership function from a given set of crisp inputs is vital. To this end, a methodology for estimating an optimal membership function from crisp input data has been implemented. This is based on the possibility/probability consistency principle as proposed by L.A. Zadeh. A relationship between the fuzzy membership function and the confidence level of statistical input data has been developed and it serves as a design parameter for fuzzification. This technique has been applied to a two-dimensional multisensor-multitarget tracking system. Fuzzy system performance evaluations have been presented. With simulated data in the laboratory environment, the simulation has been performed to evaluate the Mission Avionics Sensor Synergism (MASS) Systems. These results show better performance for the data correlation function using the fuzzy logic techniques. 相似文献
650.
H Houben R M Haberle R E Young A P Zent 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(8):1233-1236
The current Martian water cycle is extremely asymmetric, with large amounts of vapor subliming off a permanent north polar water ice cap in northern summer, but with no apparent major source of water vapor in the southern hemisphere. Detailed simulations of this process with a three-dimensional circulation model indicate that the summertime interhemispheric exchange (Hadley cell) is very much stronger than transport by eddies in other seasons. As a result, water ice would be distributed globally were it not for the buffering action of regolith soil adsorption which limits the net flux of water vapor off the north polar cap to amounts that are insignificant even on the scale of thousands of years. It has been suggested that the polar layered deposits are the result of exchange on these long time scales, driven by changes in Martian orbital parameters. We therefore are conducting simulations to test the effect of varied orbital parameters on the Martian water cycle. We find that when the perihelion summer pole is charged with a polar water ice cap, large quantities of water are quickly transfered to the aphelion summer pole, setting up an annual cycle that resembles the present one. Thus, the adsorptivity of the Martian regolith may be in the narrow range where it can limit net transport from the aphelion but not the perihelion pole. 相似文献