全文获取类型
收费全文 | 4955篇 |
免费 | 2篇 |
国内免费 | 11篇 |
专业分类
航空 | 2605篇 |
航天技术 | 1579篇 |
综合类 | 181篇 |
航天 | 603篇 |
出版年
2021年 | 31篇 |
2019年 | 29篇 |
2018年 | 75篇 |
2017年 | 42篇 |
2016年 | 41篇 |
2014年 | 73篇 |
2013年 | 108篇 |
2012年 | 109篇 |
2011年 | 162篇 |
2010年 | 104篇 |
2009年 | 189篇 |
2008年 | 195篇 |
2007年 | 120篇 |
2006年 | 92篇 |
2005年 | 91篇 |
2004年 | 115篇 |
2003年 | 140篇 |
2002年 | 181篇 |
2001年 | 203篇 |
2000年 | 97篇 |
1999年 | 124篇 |
1998年 | 154篇 |
1997年 | 102篇 |
1996年 | 144篇 |
1995年 | 169篇 |
1994年 | 147篇 |
1993年 | 95篇 |
1992年 | 123篇 |
1991年 | 60篇 |
1990年 | 63篇 |
1989年 | 129篇 |
1988年 | 58篇 |
1987年 | 60篇 |
1986年 | 51篇 |
1985年 | 154篇 |
1984年 | 128篇 |
1983年 | 113篇 |
1982年 | 122篇 |
1981年 | 160篇 |
1980年 | 57篇 |
1979年 | 46篇 |
1978年 | 57篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 49篇 |
1974年 | 39篇 |
1972年 | 49篇 |
1971年 | 47篇 |
1970年 | 30篇 |
1969年 | 34篇 |
排序方式: 共有4968条查询结果,搜索用时 984 毫秒
541.
542.
R. Von Steiger 《Space Science Reviews》1998,85(1-2):407-418
This rapporteur paper discusses the solar corona and the solar wind in the context of their chemical composition. The abundances
of elements, both obtained by optical and by in situ observations, are used to infer the sources of the slow solar wind and
of the fast streams. The first ionisation potential (FIP) fractionation effect is also discussed, in particular the agreed
basics and the open questions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
543.
D. A. Gurnett R. R. Anderson F. L. Scarf R. W. Fredricks E. J. Smith 《Space Science Reviews》1979,23(1):103-122
In this paper we present an initial survey of results from the plasma wave experiments on the ISEE-1 and -2 spacecraft which are in nearly identical orbits passing through the Earth's magnetosphere at radial distances out to about 22.5R
e
. Essentially every crossing of the Earth's bow shock can be associated with an intense burst of electrostatic and whistler-mode turbulence at the shock, with substantial wave intensities in both the upstream and downstream regions. Usually the electric and magnetic field spectrum at the shock are quite similar for both spacecraft, although small differences in the detailed structure are sometimes apparent upstream and downstream of the shock, probably due to changes in the motion of the shock or propagation effects. Upstream of the shock emissions are often observed at both the fundamental, f
-
p
, and second harmonic, 2f
p
-
, of the electron plasma frequency. In the magnetosphere high resolution spectrograms of the electric field show an extremely complex distribution of plasma and radio emissions, with numerous resonance and cutoff effects. Electron density profiles can be obtained from emissions near the local electron plasma frequency. Comparisons of high resolution spectrograms of whistler-mode emissions such as chorus detected by the two spacecraft usually show a good overall similarity but marked differences in detailed structure on time scales less than one minute. Other types of locally generated waves, such as the (n+1/2)f
-
g
electron cyclotron waves, show a better correspondence between the two spacecraft. High resolution spectrograms of kilometric radio emissions are also presented which show an extremely complex frequency-time structure with many closely spaced narrow-band emissions. 相似文献
544.
R. N. DeWitt 《Space Science Reviews》1967,7(2-3):211-227
545.
L.M. Mukhin D.F. Nenarokov N.V. Porschnev V.B. Bondarev B.G. Gelman G. Israel F. Raulin J. Runavot R. Thomas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1987,7(12):329-335
SIGMA - 3 gas chromatograph on board VEGA 1 and 2 landing probes has been operated successfully in the 60 - 50 km altitude range, providing several in - situ chemical analysis of the gas and the aerosols of Venus cloud layers. Post flight calibration required to derive atmospheric abundancies from gas chromatograms were carried out using the SIGMA - 3 spare model. A Venus atmospheric aerosol simulation chamber was used in which sulfuric acid droplets were generated. Preliminary results of these calibration experiments indicate that the concentration of sulfuric acid in the upper part of the clouds ( 60 to 55 km) is about 1 mg/m3 and suggest that an additional constituant must be present in noticeable amount in the aerosols. From these experiments the mixing ratio upper limits of SO2 is 100 ppmV and of H2S and COS is few 10 ppmV. 相似文献
546.
A typical approach and landing operation is described. The microwave landing system (MLS) is then examined, its design characteristics and how it works are shown, and how the MLS design fulfils the user's operational requirements by protecting the guidance signal from reflected signal interference is highlighted. MLS angle system accuracy is discussed in great detail, and its reliability, integrity, and coverage volume are briefly considered. MLS availability at any runway to all aircraft types and their landing scenarios, which is accomplished using narrow scanning beam antennas, is examined 相似文献
547.
548.
549.
Thomas Hörberg 《Spatial Cognition & Computation》2013,13(3):193-218
Abstract Projective prepositions express the relation between two objects by referring to a direction in space and have traditionally been regarded as expressing purely geometric relations. Recent studies have shown that the appropriateness of English and Spanish projectives also depends on functional relations between objects. This study investigates if the acceptability of the Swedish projectives över, under, ovanför and nedanför are influenced by functional factors as well, and whether över and under are differentially influenced by function than ovanför and nedanför, as has been shown for their English cognates. It also investigates how the shape and parts of the related objects influence their functional interaction, and thereby the acceptability of the prepositions. This is done with respect to the predictions of the AVS-model, a model of the perceptual processes underlying the apprehension of projectives, which takes both the geometric and the functional relation between objects into account. It was found that acceptability judgments about the prepositions are influenced by function as their corresponding English and Spanish prepositions. The acceptability of över was more sensitive to function than ovanför, whereas under and nedanför were not differentially influenced by function, as has been shown for Spanish. It was further found that the shape and parts of both of the related objects influence acceptability regions associated with the prepositions in predictable ways, as functional interactions between objects largely depend on their parts. The results finally show that the AVS-model needs to be further developed in order to account for the form and function of the located object. 相似文献
550.
Robert A. Goehlich Jay K. AndersonNathan N. Harrold Joseph A. BemisMike T. Nettleingham Joshua M. CobinBradley R. Zimmerman Ben L. AvniMichael D. Gonyea Nicholas Y. Ilchena 《Space Policy》2013
This article sheds light on the key player needed for any space tourism adventure: the pilot who flies the spacecraft. The paper addresses the potential benefits of including a pilot at the controls when designing a space tourism spacecraft. It examines the basic qualifications and advanced skills required of space tourism pilots and discusses key training requirements for selected pilots and space pilots' pay and benefits. In addition, the research concludes that, just as the pioneers of passenger transport in aviation entertained and captured the interest of their passengers, the space pilot should have the skills of a tour guide. 相似文献