全文获取类型
收费全文 | 4813篇 |
免费 | 2篇 |
国内免费 | 11篇 |
专业分类
航空 | 2516篇 |
航天技术 | 1549篇 |
综合类 | 181篇 |
航天 | 580篇 |
出版年
2021年 | 29篇 |
2018年 | 68篇 |
2017年 | 36篇 |
2016年 | 40篇 |
2014年 | 72篇 |
2013年 | 99篇 |
2012年 | 106篇 |
2011年 | 158篇 |
2010年 | 101篇 |
2009年 | 182篇 |
2008年 | 191篇 |
2007年 | 114篇 |
2006年 | 87篇 |
2005年 | 84篇 |
2004年 | 114篇 |
2003年 | 139篇 |
2002年 | 179篇 |
2001年 | 198篇 |
2000年 | 93篇 |
1999年 | 123篇 |
1998年 | 153篇 |
1997年 | 99篇 |
1996年 | 138篇 |
1995年 | 168篇 |
1994年 | 146篇 |
1993年 | 95篇 |
1992年 | 122篇 |
1991年 | 57篇 |
1990年 | 63篇 |
1989年 | 125篇 |
1988年 | 58篇 |
1987年 | 60篇 |
1986年 | 51篇 |
1985年 | 152篇 |
1984年 | 120篇 |
1983年 | 108篇 |
1982年 | 117篇 |
1981年 | 153篇 |
1980年 | 56篇 |
1979年 | 46篇 |
1978年 | 57篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 48篇 |
1974年 | 39篇 |
1973年 | 25篇 |
1972年 | 49篇 |
1971年 | 47篇 |
1970年 | 30篇 |
1969年 | 33篇 |
排序方式: 共有4826条查询结果,搜索用时 390 毫秒
381.
Flight demonstration of new thruster and green propellant technology on the PRISMA satellite 总被引:2,自引:0,他引:2
The concept of a storable liquid monopropellant blend for space applications based on ammonium dinitramide (ADN) was invented in 1997, within a co-operation between the Swedish Space Corporation (SSC) and the Swedish Defense Research Agency (FOI). The objective was to develop a propellant which has higher performance and is safer than hydrazine. The work has been performed under contract from the Swedish National Space Board and ESA. The progress of the development has been presented in several papers since 2000.ECAPS, a subsidiary of the Swedish Space Corporation was established in 2000 with the aim to develop and market the novel “high performance green propellant” (HPGP) technology for space applications. The new technology is based on several innovations and patents w.r.t. propellant formulation and thruster design, including a high temperature resistant catalyst and thrust chamber.The first flight demonstration of the HPGP propulsion system will be performed on PRISMA. PRISMA is an international technology demonstration program with Swedish Space Corporation as the Prime Contractor.This paper describes the performance, characteristics, design and verification of the HPGP propulsion system for PRISMA. Compatibility issues related to using a new propellant with COTS components is also discussed. The PRISMA mission includes two satellites in LEO orbit were the focus is on rendezvous and formation flying. One of the satellites will act as a “target” and the main spacecraft performs rendezvous and formation flying maneuvers, where the ECAPS HPGP propulsion system will provide delta-V capability.The PRISMA CDR was held in January 2007. Integration of the flight propulsion system is about to be finalized.The flight opportunity on PRISMA represents a unique opportunity to demonstrate the HPGP propulsion system in space, and thus take a significant step towards its use in future space applications. The launch of PRISMA scheduled to 2009. 相似文献
382.
F. R. Cleminson 《Space Policy》1988,4(2)
Verification of arms control treaties is essential to provide adequate international confidence in treaty compliance. This Viewpoint underlines the responsibility of non-superpower countries to become more closely involved in space surveillance of treaties to which they are parties. In Canada, Paxsat research has focused on two potential applications of space-based remote sensing to multi-lateral arms control verification. The necessary technology is readily available in non-superpower countries for the Paxsat concept to be put into operation. 相似文献
383.
384.
F. Bagenal A. Adriani F. Allegrini S. J. Bolton B. Bonfond E. J. Bunce J. E. P. Connerney S. W. H. Cowley R. W. Ebert G. R. Gladstone C. J. Hansen W. S. Kurth S. M. Levin B. H. Mauk D. J. McComas C. P. Paranicas D. Santos-Costa R. M. Thorne P. Valek J. H. Waite P. Zarka 《Space Science Reviews》2017,213(1-4):219-287
In July 2016, NASA’s Juno mission becomes the first spacecraft to enter polar orbit of Jupiter and venture deep into unexplored polar territories of the magnetosphere. Focusing on these polar regions, we review current understanding of the structure and dynamics of the magnetosphere and summarize the outstanding issues. The Juno mission profile involves (a) a several-week approach from the dawn side of Jupiter’s magnetosphere, with an orbit-insertion maneuver on July 6, 2016; (b) a 107-day capture orbit, also on the dawn flank; and (c) a series of thirty 11-day science orbits with the spacecraft flying over Jupiter’s poles and ducking under the radiation belts. We show how Juno’s view of the magnetosphere evolves over the year of science orbits. The Juno spacecraft carries a range of instruments that take particles and fields measurements, remote sensing observations of auroral emissions at UV, visible, IR and radio wavelengths, and detect microwave emission from Jupiter’s radiation belts. We summarize how these Juno measurements address issues of auroral processes, microphysical plasma physics, ionosphere-magnetosphere and satellite-magnetosphere coupling, sources and sinks of plasma, the radiation belts, and the dynamics of the outer magnetosphere. To reach Jupiter, the Juno spacecraft passed close to the Earth on October 9, 2013, gaining the necessary energy to get to Jupiter. The Earth flyby provided an opportunity to test Juno’s instrumentation as well as take scientific data in the terrestrial magnetosphere, in conjunction with ground-based and Earth-orbiting assets. 相似文献
385.
H. M. Cuppen C. Walsh T. Lamberts D. Semenov R. T. Garrod E. M. Penteado S. Ioppolo 《Space Science Reviews》2017,212(1-2):1-58
The cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of \({\sim}25\) experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions. 相似文献
386.
S. B. Mende H. U. Frey K. Rider C. Chou S. E. Harris O. H. W. Siegmund S. L. England C. Wilkins W. Craig T. J. Immel P. Turin N. Darling J. Loicq P. Blain E. Syrstad B. Thompson R. Burt J. Champagne P. Sevilla S. Ellis 《Space Science Reviews》2017,212(1-2):655-696
ICON Far UltraViolet (FUV) imager contributes to the ICON science objectives by providing remote sensing measurements of the daytime and nighttime atmosphere/ionosphere. During sunlit atmospheric conditions, ICON FUV images the limb altitude profile in the shortwave (SW) band at 135.6 nm and the longwave (LW) band at 157 nm perpendicular to the satellite motion to retrieve the atmospheric O/N2 ratio. In conditions of atmospheric darkness, ICON FUV measures the 135.6 nm recombination emission of \(\mathrm{O}^{+}\) ions used to compute the nighttime ionospheric altitude distribution. ICON Far UltraViolet (FUV) imager is a Czerny–Turner design Spectrographic Imager with two exit slits and corresponding back imager cameras that produce two independent images in separate wavelength bands on two detectors. All observations will be processed as limb altitude profiles. In addition, the ionospheric 135.6 nm data will be processed as longitude and latitude spatial maps to obtain images of ion distributions around regions of equatorial spread F. The ICON FUV optic axis is pointed 20 degrees below local horizontal and has a steering mirror that allows the field of view to be steered up to 30 degrees forward and aft, to keep the local magnetic meridian in the field of view. The detectors are micro channel plate (MCP) intensified FUV tubes with the phosphor fiber-optically coupled to Charge Coupled Devices (CCDs). The dual stack MCP-s amplify the photoelectron signals to overcome the CCD noise and the rapidly scanned frames are co-added to digitally create 12-second integrated images. Digital on-board signal processing is used to compensate for geometric distortion and satellite motion and to achieve data compression. The instrument was originally aligned in visible light by using a special grating and visible cameras. Final alignment, functional and environmental testing and calibration were performed in a large vacuum chamber with a UV source. The test and calibration program showed that ICON FUV meets its design requirements and is ready to be launched on the ICON spacecraft. 相似文献
387.
Reconfiguration of multiprocessor systems makes it possible to improve their failure-resistance that is especially important for the integrated modular avionics systems. The algorithm considered in this paper allows minimizing the reservation and providing the better safety level and more effective flight completion or even its further execution in the case of failures of airborne equipment. 相似文献
388.
R. Manuel S.E.S. FerreiraM.S. Potgieter R.D. StraussN.E. Engelbrecht 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Time-dependent cosmic ray modulation is calculated over multiple solar cycles using our well established two-dimensional time-dependent modulation model. Results are compared to Voyager 1, Ulysses and IMP cosmic ray observations to establish compatibility. A time-dependence in the diffusion and drift coefficients, implicitly contained in recent expressions derived by , , and , is incorporated into the cosmic ray modulation model. This results in calculations which are compatible with spacecraft observations on a global scale over consecutive solar cycles. This approach compares well to the successful compound approach of Ferreira and Potgieter (2004). For both these approaches the magnetic field magnitude, variance of the field and current sheet tilt angle values observed at Earth are transported time-dependently into the outer heliosphere. However, when results are compared to observations for extreme solar maximum, the computed step-like modulation is not as pronounced as observed. This indicates that some additional merging of these structures into more pronounced modulation barriers along the way is needed. 相似文献
389.
Pooja Dutt R.K. Sharma 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
A study of the evolution of the periodic and the quasi-periodic orbits near the Lagrangian point L2, which is located to the right of the smaller primary on the line joining the primaries and whose distance from the more massive primary is greater than the distance between the primaries, in the framework of restricted three-body problem for the Sun–Jupiter, Earth–Moon (relatively large mass ratio) and Saturn–Titan (relatively small mass ratio) systems is made. Two families of periodic orbits around the smaller primary are identified using the Poincaré surface of section method – family I (initially elliptical, gradually becomes egg-shaped with the increase in the Jacobi constant C and elongated towards the more massive primary) and family II (initially egg-shaped orbits elongated towards L2 and gradually becomes elliptical with the increase in C). The family I in the Sun–Jupiter and Saturn–Titan systems contains two separatrix caused by third-order and fourth-order resonances, while the Earth–Moon system has only one separatrix which is caused by third-order resonances. Also in the Sun–Jupiter and the Saturn–Titan systems, family I merge with family II, around Jacobian constant 3.0393 and 3.0163, respectively, while in the Earth–Moon system, family II evolves separately from two different branches. The two branches merge at C = 3.184515. In the Earth–Moon system, the family II contains a separatrix due to third-order resonances which is absent in the other two systems. 相似文献
390.
Built in cooperation with China, at the end of 2008 the Bolivarian Republic of Venezuela launched its first telecommunications satellite which operates in C, Ku and Ka bands. Using published and unpublished information, this report describes the potential role of the Venesat-1 satellite in promoting development in Venezuela and Latin America. The core of Venezuelan space policy has deep social roots and includes several applications in order to provide telecommunications services to people in all areas of the country. Potential roles of the Venezuelan Satellite in local and regional development include: strengthening environmental tele-education and telemedicine programs; improving disaster management through short-term development of broad networks to monitor environmental and meteorological features; coordination of emergency responses and humanitarian assistance using data and satellite communications; poverty reduction; and biodiversity conservation – communication networks could also be used to relay information about detected fires within protected areas faster, and to improve surveillance activities within them with in order to reduce illegal hunting, logging, habitat loss and fragmentation. Because the area covered by the satellite goes beyond Venezuela’s borders, its applications could have enormous relevance for human development at the regional level; they could be fundamental tools for bringing sustainable development into Latin America, by building capacity and increasing awareness among decision makers and lay people. 相似文献