全文获取类型
收费全文 | 18376篇 |
免费 | 36篇 |
国内免费 | 124篇 |
专业分类
航空 | 9878篇 |
航天技术 | 5581篇 |
综合类 | 257篇 |
航天 | 2820篇 |
出版年
2021年 | 157篇 |
2018年 | 206篇 |
2016年 | 150篇 |
2014年 | 440篇 |
2013年 | 523篇 |
2012年 | 418篇 |
2011年 | 573篇 |
2010年 | 398篇 |
2009年 | 746篇 |
2008年 | 793篇 |
2007年 | 365篇 |
2006年 | 427篇 |
2005年 | 400篇 |
2004年 | 446篇 |
2003年 | 548篇 |
2002年 | 487篇 |
2001年 | 572篇 |
2000年 | 370篇 |
1999年 | 453篇 |
1998年 | 441篇 |
1997年 | 333篇 |
1996年 | 406篇 |
1995年 | 480篇 |
1994年 | 488篇 |
1993年 | 358篇 |
1992年 | 351篇 |
1991年 | 253篇 |
1990年 | 243篇 |
1989年 | 430篇 |
1988年 | 208篇 |
1987年 | 244篇 |
1986年 | 243篇 |
1985年 | 652篇 |
1984年 | 529篇 |
1983年 | 416篇 |
1982年 | 491篇 |
1981年 | 612篇 |
1980年 | 247篇 |
1979年 | 187篇 |
1978年 | 189篇 |
1977年 | 146篇 |
1976年 | 155篇 |
1975年 | 195篇 |
1974年 | 180篇 |
1973年 | 161篇 |
1972年 | 188篇 |
1971年 | 148篇 |
1970年 | 143篇 |
1969年 | 147篇 |
1967年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
V. A. Grigoriev 《Space Science Reviews》1989,49(1-2):151-155
The scintillation time-of-flight triggering system of the Gamma-1 gamma-ray telescope provides for both the time-of-flight discrimination and the pulse height discrimination of the secondary particles. The paper gives some experimental results for energy dependence of the instrument efficiency in 30–300 MeV energy range for different trigger logics. 相似文献
113.
114.
Jovanovic M.M. Lee F.C. Chen D.Y. 《IEEE transactions on aerospace and electronic systems》1986,(2):138-145
Reverse-bias safe operating area (RBSOA) of high-power Darlington transistors is characterized using a 120 A/1000 V nondestructive reverse-bias second breakdown tester designed and fabricated at Virginia Polytechnic Institute and State University. Elaborate RBSOA characteristics are generated with different forward/reverse base drives and collector current levels. The effects of elevated case temperature and second-base drive on RBSOA of four-terminal Darlington devices are also discussed. 相似文献
115.
An Adaptive Extended Kalman Filter for Target Image Tracking 总被引:1,自引:0,他引:1
116.
117.
118.
Jovanovic M.M. Farrington R. Lee F.C. 《IEEE transactions on aerospace and electronic systems》1990,26(2):326-336
The performance of the half-bridge (HB) zero-current-switched (ZCS) quasi-resonant converter (QRC) and zero-voltage-switched (ZVS) multiresonant converter (MRC) is compared with respect to their efficiency, input voltage range, semiconductor stresses, power density, and reliability. The efficiency of the HB ZVS-MRC at a given nominal input is shown to be highly dependent on the range of the input voltage, and it suffers when the converter has to be designed to cover a wide range. However, this is not the case for the HB ZCS-QRC. Experimental versions of the HB ZCS-QRC and HB ZVS-MRC were designed for the input voltage range from 150 to 350 V and a maximum output power of 100 W, under the same constraints, to facilitate their comparison 相似文献
119.
R. E. Wilson 《Space Science Reviews》1989,49(3-4):191-203
Evidence on the issues of whether the W Serpentis stars are a coherent class, and how they may interface with the Algol systems, is reviewed, with emphasis on the idea that they are semi-detached systems in the latter part of the rapid phase of mass transfer, with optically and geometrically thick disks of transferred gas around the (now) more massive star. We are interested in what will be seen when the gas clears away, and mainly examine the idea that it will be an Algol-type system. More particularly, consideration is given to centrifugally limited accretion as a mechanism to build up a substantial disk, and the presumed evolutionary sequence is from a W Ser to a rapidly rotating Algol to a normal Algol system. Systems such as V367 Cyg and RW Tau fit into this scheme only with difficulty. Because it is extremely difficult to measure the rotation of some W Ser (mass) primaries, it is natural to look at the rotation statistics of Algols to test this idea. The badly behaved light curves and spectroscopy of some Algols (eg. U Cep, RZ Sct) may be attributable to the double contact condition, and the ramifications of this possibility are discussed. If so, the rotation statistics of Algols should show two spikes, corresponding to the two special conditions into which a system should be driven by tidal braking and centrifugally limited spinup. Present rotation statistics do show these spikes. Algols should flip between these states fairly quickly, depending on the mass transfer rate. Thus, to the extent that the meager statistics can be accepted as meaningful, the new (fourth) morphological type of close binary (double contact) has attained demonstrable reality. The rotation statistics are presented in terms of a particular rotation parameter, R, which is zero for synchronism and unity for the centrifugal limit. Future work should develop rotation statistics to see if the rotational lobe-filling (R = 1) spike persists. It should also look into whether W Ser primaries are on the hydrogen burning main sequence, or in general what they are. We also need more light curves of W Ser type systems, high resolution line profiles for the (mass) primaries (with particular attention to the W Ser-Algol transition cases), and spectroscopy of low inclination W Serpentis systems, such as KX And. 相似文献
120.
G. J. Peters 《Space Science Reviews》1989,49(3-4):9-22
The circumstellar plasma that produces H emission in Algol binaries has been investigated using phase-resolved, high dispersion data acquired from CCD and image tube detectors. Results are summarized in this paper, including discussions of the disk geometry and size, asymmetry in the distribution of material, long-term or non-phase dependent variability, mass outflow, the mean electron density, and how the latter properties vary with the system's period or location in the r-q diagram. Five systems which display permanent emission with periods ranging from 4.5 to 261 days (SW Cyg, UX Mon, TT Hya, AD Her, and RZ Oph) are intercompared. If P < 4.5 days, no permanent disks are observed, while if P > 6 days, stable disks with only slight long-term variations in their H brightness are seen. The most variable systems appear to be those in the 5 – 6 day range, but the star's position in the r-q diagram has the largest influence on its behavior. The trailing side of the accretion disk, where the gas stream impacts the inner disk, is usually brighter, and the leading side is often times more extended. The disk extends out to at least 95% of the Roche surface of the primary and is highly flattened (RP). Mass outflow near phase 0.5 is commonplace. 相似文献