全文获取类型
收费全文 | 5859篇 |
免费 | 27篇 |
国内免费 | 17篇 |
专业分类
航空 | 3015篇 |
航天技术 | 2004篇 |
综合类 | 20篇 |
航天 | 864篇 |
出版年
2021年 | 40篇 |
2019年 | 40篇 |
2018年 | 83篇 |
2017年 | 52篇 |
2016年 | 53篇 |
2015年 | 35篇 |
2014年 | 114篇 |
2013年 | 136篇 |
2012年 | 129篇 |
2011年 | 191篇 |
2010年 | 146篇 |
2009年 | 211篇 |
2008年 | 298篇 |
2007年 | 151篇 |
2006年 | 116篇 |
2005年 | 150篇 |
2004年 | 136篇 |
2003年 | 185篇 |
2002年 | 108篇 |
2001年 | 188篇 |
2000年 | 109篇 |
1999年 | 151篇 |
1998年 | 172篇 |
1997年 | 123篇 |
1996年 | 169篇 |
1995年 | 217篇 |
1994年 | 179篇 |
1993年 | 116篇 |
1992年 | 161篇 |
1991年 | 68篇 |
1990年 | 71篇 |
1989年 | 159篇 |
1988年 | 71篇 |
1987年 | 62篇 |
1986年 | 63篇 |
1985年 | 177篇 |
1984年 | 161篇 |
1983年 | 124篇 |
1982年 | 148篇 |
1981年 | 163篇 |
1980年 | 57篇 |
1979年 | 64篇 |
1978年 | 56篇 |
1977年 | 42篇 |
1976年 | 37篇 |
1975年 | 64篇 |
1974年 | 47篇 |
1973年 | 34篇 |
1972年 | 60篇 |
1967年 | 30篇 |
排序方式: 共有5903条查询结果,搜索用时 242 毫秒
661.
D. S. Ivanov N. A. Ivlev S. O. Karpenko M. Yu. Ovchinnikov D. S. Roldugin S. S. Tkachev 《Cosmic Research》2014,52(3):205-215
The attitude control system of the Chibis-M microsatellite is described. Results of flight experiments on damping the initial angular velocity (made using magnetorquers) are considered, as well as stabilization in the orbital referece frame, and orientation of solar arrays toward the Sun using reaction wheels. The operation of algorithms of satellite attitude determination on sunlit and shadow segments of the orbit is also under study. The general logic of operation of the attitude control system in automatic mode is presented and discussed. 相似文献
662.
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
663.
Wright C.H.G. Delp E.J. Gallagher N.C. Jr. 《IEEE transactions on aerospace and electronic systems》1990,26(1):122-145
A necessary requirement of a strategic defence system is the detection of incoming nuclear warheads in an environment that may include nuclear detonations of undetected or missed target warheads. A computer model which simulates incoming warheads as distant endoatmospheric targets is described. A model of the electromagnetic noise expected in the nuclear environment is developed. Predicted atmospheric effects are also included. The ability of nonlinear image enhancement algorithms to their ability to suppress the noise and atmospheric effects of the nuclear environment is examined. These algorithms are then tested, using the combined target and noise models, and evaluated in terms of noise removal and their ability to resolve closely spaced targets 相似文献
664.
665.
The US Navy has more than 300 ships equipped with over 500 PHALANX weapon systems. Ordalts (ordnance alterations) and casreps (casualty reports) are received frequently by Naval Ordnance. Ordalts are done when parts need replacing or a design is exchanged for an old. Casreps are an urgent request for parts or service. Information pertaining to ordalts and casreps is put into several databases, which are continually updated and used in reports among the PHALANX community. Ship locations are used for sending parts and/or assistance to the ship. The ordalt and casrep requests have been combined with the ship locations report to produce a more efficient manner in which to monitor ordalt requests, casrep requests and ship locations, using a sample database containing ordalt and casrep data and ship locations. The database is interfaced to a computer graphics program that monitors ship movement throughout the world and supplies information from the database whenever requested. The hardware and software used to implement the project are described 相似文献
666.
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
667.
668.
J T Lett A B Cox M D Story 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):99-104
Theories of cellular radiation sensitivity that preclude a significant role for cellular repair processes in the final biological expression of cellular damage induced by ionizing radiation are unsound. Experiments are discussed here in which the cell-cycle dependency of the repair deficiency of the S/S variant, of the L5178Y murine leukemic lymphoblast was examined by treatment with the heavy ions, 20Ne, 28Si, 40Ar, 56Fe and 93Nb. Evidence from those studies, which will be described in detail elsewhere, provide support for the notion that as the linear energy transfer (LET infinity) of the incident radiation increases the ability of the S/S cell to repair radiation damage decreases until effectively it is eliminated around 500 keV/micrometer. In the region of the latter LET infinity value, the behavior of the S/S cell approximates the ideal case of target theory where post-irradiation metabolism (repair) does not influence cell survival. The expression of this phenomenon among different cell types and tissues will depend upon the actual repair systems involved and other considerations. 相似文献
669.
V. A. Sadovnichiy A. M. Amelyushkin V. Angelopoulos V. V. Bengin V. V. Bogomolov G. K. Garipov E. S. Gorbovskoy B. Grossan P. A. Klimov B. A. Khrenov J. Lee V. M. Lipunov G. W. Na M. I. Panasyuk I. H. Park V. L. Petrov C. T. Russell S. I. Svertilov E. A. Sigaeva G. F. Smoot Yu. Shprits N. N. Vedenkin I. V. Yashin 《Cosmic Research》2013,51(6):427-433
At present, the Institute of Nuclear Physics of Moscow State University, in cooperation with other organizations, is preparing space experiments onboard the Lomonosov satellite. The main goal of this mission is to study extreme astrophysical phenomena such as cosmic gamma-ray bursts and ultra-high-energy cosmic rays. These phenomena are associated with the processes occurring in the early universe in very distant astrophysical objects, therefore, they can provide information on the first stages of the evolution of the universe. This paper considers the main characteristics of the scientific equipment aboard the Lomonosov satellite. 相似文献
670.
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