全文获取类型
收费全文 | 5493篇 |
免费 | 14篇 |
国内免费 | 18篇 |
专业分类
航空 | 2707篇 |
航天技术 | 2036篇 |
综合类 | 21篇 |
航天 | 761篇 |
出版年
2021年 | 36篇 |
2019年 | 41篇 |
2018年 | 92篇 |
2017年 | 40篇 |
2016年 | 48篇 |
2014年 | 103篇 |
2013年 | 144篇 |
2012年 | 120篇 |
2011年 | 177篇 |
2010年 | 136篇 |
2009年 | 223篇 |
2008年 | 307篇 |
2007年 | 155篇 |
2006年 | 125篇 |
2005年 | 136篇 |
2004年 | 131篇 |
2003年 | 175篇 |
2002年 | 101篇 |
2001年 | 170篇 |
2000年 | 95篇 |
1999年 | 131篇 |
1998年 | 149篇 |
1997年 | 111篇 |
1996年 | 142篇 |
1995年 | 181篇 |
1994年 | 167篇 |
1993年 | 104篇 |
1992年 | 152篇 |
1991年 | 76篇 |
1990年 | 65篇 |
1989年 | 141篇 |
1988年 | 53篇 |
1987年 | 56篇 |
1986年 | 57篇 |
1985年 | 180篇 |
1984年 | 150篇 |
1983年 | 121篇 |
1982年 | 148篇 |
1981年 | 176篇 |
1980年 | 58篇 |
1979年 | 75篇 |
1978年 | 51篇 |
1977年 | 35篇 |
1976年 | 32篇 |
1975年 | 46篇 |
1974年 | 38篇 |
1973年 | 31篇 |
1972年 | 40篇 |
1970年 | 27篇 |
1969年 | 27篇 |
排序方式: 共有5525条查询结果,搜索用时 306 毫秒
941.
F. Fárník S. Fischer L. Křivský B. Valníček O.B. Likin V.N. Lutsenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(13):243-246
During the observation of solar cosmic rays on the Prognoz 6 and Helios 1 and 2 spacecrafts, several events with anomalous composition of accelerated particles (higher abundance of 3-He or Fe nuclei) occurred. We found seven such events from the period September to December 1977 for which data from the Prognoz 6 solar X-ray photometer are available. This material together with published optical and radio data from terrestrial observatories enabled us to identify more reliably the source flares and describe their characteristics. It turned out that the character of X-ray emission accompanying the emission of accelerated particles with anomalous composition shows no pronounced difference from other flares. No correlation has been found among the ratio 3-He/4-He and the angular distance between the field lines connected with the source flare and the place of observation. If a solar flare with anomalous ratio 3-He/4-He appears in a given active region, this region will probably produce other anomalous events. 相似文献
942.
C.R. Philbrick D.P. Sipler B.B. Balsley J.C. Ulwick 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(6):129-132
The ructure and tmospheric urbulence nvironment (STATE) experiment was conducted during the second week of June 1983 at Poker Flat Research Range, Alaska. The measurements focus on a study of the middle atmosphere dynamics by comparison between in-situ probe measurements and MST radar measurements. Rocket launchings were conducted at three periods which were selected by monitoring the doppler velocity spectra of the MST radar.The STATE program has included the efforts of several scientists in planning and carrying out the ground-based and rocket measurements. An overview of the program is given together with some preliminary results. The regions in intense backscatter signals detected by the MST radar are shown to correlate with large irregularities in the electron profiles measured. 相似文献
943.
G.S. Orton A.P. Ingersoll L. Froidevaux G. Neugebauer G. Münch S.C. Chase 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(8):179-182
The Pioneer 11 Infrared Radiometer instrument made observations of Saturn and its rings in broadband channels centered at 20 and 45 μm and obtained whole-disk information on Titan. A planetary average effective temperature of 96.5±2.5 K implies a total emission 2.8 times the absorbed sunlight. Correlation with radio science results implies that the molar fraction of H2 is 90±3% (assuming the rest is He). Temperatures at the 1 bar level are 137 to 140 K; regions appearing cooler may be overlain by a cloud acting as a 124 K blackbody surface. A minimum temperature averaging 87 K is reached near 0.06 bars. Ring boundaries and optical depths are consistent with those at optical wavelengths. Ring temperatures are 64–86 K on the south (illuminated) side, ~54 K on the north (unilluminated) side, and at least 67 K in Saturn's shadow. There is evidence for a south to north drop in ring temperatures. Titan's 45 μm brightness temperature is 75±5 K. 相似文献
944.
Temesmber C.L. Thompson W.E. 《IEEE transactions on aerospace and electronic systems》1975,(2):183-189
Useful new properties are obtained with a coherent pulse-burst waveform if the FM slopes are allowed to change from pulse to pulse. A design feature using such a "slope-coded" waveform is the ability to transfer, in a controllable manner, ambiguity volume from the range ambiguity peaks to regions located between the peaks (in the frequency direction). Slope coding thus provides a useful mechanism for matching the waveform to the environment; i. e., it permits the signal designer to make some compromise between range ambiguity-peak heights and low-velocity clutter rejection. 相似文献
945.
Matsumoto Y. Suzuki R. Kondo K. Khan M.H. 《IEEE transactions on aerospace and electronic systems》1992,28(3):718-727
In February of 1990, land mobile satellite propagation experiments were conducted in Kyoto City, Japan, using the Engineering Test Satellite V (ETS-V). The signal transmitted from the satellite was received and recorded at a mobile unit moving in different streets of the downtown area. The streets chosen have typical downtown medium and high rise buildings, electric utility poles, trees, etc., which caused obstruction to the satellite line of sight. The propagation characteristics such as fade/nonfade distribution, joint fade and nonfade distribution, phase distribution, and their dependence on the antenna type are discussed for the measured link. Error characteristics in digital communication for the above link have been qualitatively analyzed on the basis of the measured signal level fluctuation. Effect of interleaving and coding to improve the communication link is also discussed 相似文献
946.
The development of pulse compression radar at Sperry is related on the basis of the author's personal recollections. He discusses the first experiments, concept improvements, demonstration of the concept, system implementations, dealings with the US Patent Office, and finishing touches 相似文献
947.
An electrical power system for a space-based radar satellite is described. When the radar is on, its transmitter needs an average DC power of 30 kW. The problem of distributing the power efficiently in pulses to many transmit/receive modules is addressed. System requirements include a high-voltage battery and transmission line, load-sharing between the solar array, and the battery during sunlit periods, and a 25-kW solar array. A scaled-down version of the power system for a proof-of-concept demonstration is described 相似文献
948.
P S Haskins J E McKisson A G Weisenberger D W Ely T A Ballard C S Dyer P R Truscott R B Piercey A V Ramayya D C Camp 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(2-3):461-464
The Shuttle Activation Monitor (SAM) experiment was flown on the Space Shuttle Columbia (STS-28) from 8-13 August, 1989 in a 57 degrees, 300 km orbit. One objective of the SAM experiment was to determine the relative effect of different amounts of shielding on the gamma-ray backgrounds measured with similarly configured sodium iodide (NaI) and bismuth germante (BGO) detectors. To achieve this objective twenty-four hours of data were taken with each detector in the middeck of the Shuttle on the ceiling of the airlock (a high-shielding location) as well as on the sleep station wall (a low-shielding location). For the cosmic-ray induced background the results indicate an increased overall count rate in the 0.2 to 10 MeV energy range at the more highly shielded location, while in regions of trapped radiation the low shielding configuration gives higher rates at the low energy end of the spectrum. 相似文献
949.
The theoretical framework and experimental methodology used to interpret observations of ionospheric scintillations in terms of geophysical processes are reviewed and recent experimental observations of ionospheric scintillations are discussed in this paper. During the past 15 years significant progress has been made in several areas. In particular, significant advances have been made in theoretical understanding of the strong scintillation regime and the effects of short-term temporal variations of the scintillation producing irregularities on observations made with spaced-receiver geometries in both weak and strong scintillations. This improved understanding of the scintillation process has significantly increased the utility of the technique particularly in the equatorial latitudes where geometrical effects are least important. 相似文献
950.
A Bieger-Dose K Dose R Meffert M Mehler S Risi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(4):265-270
Exposure of fungal conidia (Aspergillus ochraceus) or spores of Bacillus subtilis to extreme dryness or vacuum induces DNA lesions, including strand breaks and the formation of DNA-protein cross-links. In wet cells only a small amount of protein is bound to DNA, but exposure to conditions of lowered water activity results in an increasing number of cross-links between DNA and proteins. In fungal conidia these cross-links are detected after selective iodination (125 J) of the DNA-bound proteins followed by gel electrophoresis and subsequent autoradiography. Another approach is the labelling of DNA with 32P by means of nick translation and the detection of differences in the electrophoretic mobility of DNA before and after digestion with proteinase K of proteins bound to DNA. 相似文献