全文获取类型
收费全文 | 2280篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
航空 | 1228篇 |
航天技术 | 832篇 |
综合类 | 13篇 |
航天 | 217篇 |
出版年
2018年 | 25篇 |
2017年 | 23篇 |
2014年 | 24篇 |
2013年 | 48篇 |
2012年 | 29篇 |
2011年 | 59篇 |
2010年 | 47篇 |
2009年 | 57篇 |
2008年 | 126篇 |
2007年 | 39篇 |
2006年 | 32篇 |
2005年 | 46篇 |
2004年 | 69篇 |
2003年 | 72篇 |
2002年 | 37篇 |
2001年 | 55篇 |
2000年 | 49篇 |
1999年 | 27篇 |
1998年 | 75篇 |
1997年 | 53篇 |
1996年 | 62篇 |
1995年 | 69篇 |
1994年 | 85篇 |
1993年 | 51篇 |
1992年 | 69篇 |
1991年 | 29篇 |
1990年 | 33篇 |
1989年 | 70篇 |
1988年 | 24篇 |
1987年 | 29篇 |
1986年 | 51篇 |
1985年 | 88篇 |
1984年 | 54篇 |
1983年 | 60篇 |
1982年 | 57篇 |
1981年 | 68篇 |
1980年 | 34篇 |
1979年 | 27篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1975年 | 24篇 |
1974年 | 24篇 |
1973年 | 24篇 |
1972年 | 21篇 |
1971年 | 31篇 |
1970年 | 17篇 |
1969年 | 25篇 |
1968年 | 18篇 |
1967年 | 20篇 |
1966年 | 19篇 |
排序方式: 共有2290条查询结果,搜索用时 0 毫秒
601.
G.S. Nkosi M.S. Potgieter W.R. Webber 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The modulation of cosmic ray electrons in the heliosphere plays an important role in improving our understanding and assessment of the processes applicable to low-energy galactic electrons. A full three-dimensional numerical model based on Parker’s transport equation is used to study the modulation of 10 MeV galactic electrons, in particular inside the heliosheath. The emphasis is placed on the role that perpendicular diffusion plays in causing the extraordinary large increase in the observed intensities of these electrons in the heliosheath. The modelling is compared with observations of 6–14 MeV electrons from the Voyager 1 mission. Results are shown for the radial intensity profiles of these electrons, as well as the modulation effects of varying the extent of the heliosheath by changing the location of the termination shock and the heliopause and the value of the local interstellar spectrum. We confirm that the heliosheath acts as a modulation ‘barrier’ for low-energy galactic electrons. The significance of this result depends on how wide the inner heliosheath is; on how high the very local interstellar spectrum is at these low energies (E < 100 MeV) and on how small perpendicular diffusion is inside the inner heliosheath. 相似文献
602.
T. Joseph W. Lazio R.J. MacDowall Jack O. Burns D.L. Jones K.W. Weiler L. Demaio A. Cohen N. Paravastu Dalal E. Polisensky K. Stewart S. Bale N. Gopalswamy M. Kaiser J. Kasper 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The Radio Observatory on the Lunar Surface for Solar studies (ROLSS) is a concept for a near-side low radio frequency imaging interferometric array designed to study particle acceleration at the Sun and in the inner heliosphere. The prime science mission is to image the radio emission generated by Type II and III solar radio burst processes with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Specific questions to be addressed include the following: (1) Isolating the sites of electron acceleration responsible for Type II and III solar radio bursts during coronal mass ejections (CMEs); and (2) Determining if and the mechanism(s) by which multiple, successive CMEs produce unusually efficient particle acceleration and intense radio emission. Secondary science goals include constraining the density of the lunar ionosphere by searching for a low radio frequency cutoff to solar radio emission and constraining the low energy electron population in astrophysical sources. Key design requirements on ROLSS include the operational frequency and angular resolution. The electron densities in the solar corona and inner heliosphere are such that the relevant emission occurs at frequencies below 10 MHz. Second, resolving the potential sites of particle acceleration requires an instrument with an angular resolution of at least 2°, equivalent to a linear array size of approximately 1000 m. Operations would consist of data acquisition during the lunar day, with regular data downlinks. No operations would occur during lunar night. 相似文献
603.
A.M. Jorgensen D. Ober J. Koller R.H.W. Friedel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In this paper we report on initial work toward data assimilative modeling of the Earth’s plasmasphere. As the medium of propagation for waves which are responsible for acceleration and decay of the radiation belts, an accurate assimilative model of the plasmasphere is crucial for optimizing the accurate prediction of the radiation environments encountered by satellites. On longer time-scales the plasmasphere exhibits significant dynamics. Although these dynamics are modeled well by existing models, they require detailed global knowledge of magnetospheric configuration which is not always readily available. For that reason data assimilation can be expected to be an effective tool in improving the modeling accuracy of the plasmasphere. In this paper we demonstrate that a relatively modest number of measurements, combined with a simple data assimilation scheme, inspired by the ensemble Kalman filtering data assimilation technique does a good job of reproducing the overall structure of the plasmasphere including plume development. This raises hopes that data assimilation will be an effective method for accurately representing the configuration of the plasmasphere for space weather applications. 相似文献
604.
R.A. Gowen A. Smith A.D. Fortes S. Barber P. Brown P. Church G. Collinson A.J. Coates G. Collins I.A. Crawford V. Dehant J. Chela-Flores A.D. Griffiths P.M. Grindrod L.I. Gurvits A. Hagermann H. Hussmann R. Jaumann A.P. Jones K.H. Joy O. Karatekin K. Miljkovic E. Palomba W.T. Pike O. Prieto-Ballesteros F. Raulin M.A. Sephton S. Sheridan M. Sims M.C. Storrie-Lombardi R. Ambrosi J. Fielding G. Fraser Y. Gao G.H. Jones G. Kargl W.J. Karl A. Macagnano A. Mukherjee J.P. Muller A. Phipps D. Pullan L. Richter F. Sohl J. Snape J. Sykes N. Wells 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
605.
V.A. McBride W. Coburn M.J. Coe P. Kretschmar I. Kreykenbohm R.E. Rothschild R. Staubert J. Wilms 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2768-2770
MXB 0656-072 is an accreting X-ray pulsar with a Be star companion, showing notable emission in H. In October 2003 this system exhibited a large and extended X-ray outburst. RXTE observations during this outburst indicated a pulse period of 160.4 s and a cyclotron resonance scattering feature in the spectrum at 32 keV. This paper presents pulse profile analysis and phase-resolved X-ray spectroscopy of RXTE observations during this outburst. 相似文献
606.
A method is shown for suppressing the adaptive switching transient that arises in complex adaptive (LMS and stochastic approximation) algorithms due to signal normalization with controlled switched gains. The method involves rescaling of the adaptive weights with the normalizing gains just prior to the first adaptation with the new gains. In addition, an effective method of rescaling the adaptive gain factor based on the maximum eigenvalues of the respective covariance matrices is shown. 相似文献
607.
The atmosphere, acting like a lens, causes a small loss in radarsignal strength [1]. Unlike atmospheric absorption [2], the lenseffect loss is different for distributed targets versus point targets.For a distributed target uniformly filling the radar beam, the lens effect loss (in decibels) is one-half the lens-effect loss for point targets. 相似文献
608.
Optimal Detection and Performance of Distributed Sensor Systems 总被引:1,自引:0,他引:1
Global optimization of a distributed sensor detection system withfusion is considered, where the fusion rule and local detectors aresolved to obtain overall optimal performance. This yields coupledequations for the local detectors and the fusion center.The detection performance of the distributed system with fusionis developed. The globally optimal system performance is comparedwith two suboptimal systems. Receiver operating characteristics(ROCs) are computed numerically for the problem of detecting aknown signal embedded in non-Gaussian noise. 相似文献
609.
610.
Terry W. Edwards 《Space Science Reviews》1980,27(3-4):627-633
The thermodynamic transport properties of special relativistic imperfect fluids, as found in dense stars, are investigated. These properties, which include thermal. and electrical conductivities, electrothermal coefficients, and bulk and shear viscosities may be formulated in terms of the momentum distribution functions obtained from the solution of the Boltzmann transport equation. Spherical harmonic solutions of the relaxation form of the relativistic magnetic Boltzmann transport equation have also been obtained which give the non-equilibrium momentum distribution function perturbation f-f(0) = f(p) in terms of electromagnetic and thermal fields. 相似文献