全文获取类型
收费全文 | 18161篇 |
免费 | 36篇 |
国内免费 | 145篇 |
专业分类
航空 | 10118篇 |
航天技术 | 5161篇 |
综合类 | 243篇 |
航天 | 2820篇 |
出版年
2021年 | 167篇 |
2018年 | 256篇 |
2016年 | 176篇 |
2014年 | 434篇 |
2013年 | 520篇 |
2012年 | 428篇 |
2011年 | 632篇 |
2010年 | 461篇 |
2009年 | 824篇 |
2008年 | 822篇 |
2007年 | 425篇 |
2006年 | 421篇 |
2005年 | 396篇 |
2004年 | 435篇 |
2003年 | 498篇 |
2002年 | 471篇 |
2001年 | 547篇 |
2000年 | 348篇 |
1999年 | 448篇 |
1998年 | 406篇 |
1997年 | 307篇 |
1996年 | 348篇 |
1995年 | 434篇 |
1994年 | 380篇 |
1993年 | 352篇 |
1992年 | 290篇 |
1991年 | 246篇 |
1990年 | 232篇 |
1989年 | 374篇 |
1988年 | 201篇 |
1987年 | 233篇 |
1986年 | 227篇 |
1985年 | 638篇 |
1984年 | 516篇 |
1983年 | 403篇 |
1982年 | 486篇 |
1981年 | 609篇 |
1980年 | 246篇 |
1979年 | 185篇 |
1978年 | 189篇 |
1977年 | 145篇 |
1976年 | 156篇 |
1975年 | 182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 0 毫秒
961.
M.O. Riazantseva O.V. Khabarova G.N. Zastenker J.D. Richardson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2007,40(12):1802-1806
Sharp (<10 min) and large (>20%) solar wind ion flux changes are common phenomena in turbulent solar wind plasma. These changes are the boundaries of small- and middle-scale solar wind plasma structures which can have a significant influence on Earth’s magnetosphere. These solar wind ion flux changes are typically accompanied by only a small change in the bulk solar wind velocity, hence, the flux changes are driven mainly by plasma density variations. We show that these events occur more frequently in high-density solar wind. A characteristic of solar wind turbulence, intermittency, is determined for time periods with and without these flux changes. The probability distribution functions (PDF) of solar wind ion flux variations for different time scales are calculated for each of these periods and compared. For large time scales, the PDFs are Gaussian for both data sets. For small time scales, the PDFs from both data set are more flat than Gaussian, but the degree of flatness is much larger for the data near the sharp flux change boundaries. 相似文献
962.
H. Fuke Y. Tasaki K. Abe S. Haino Y. Makida S. Matsuda J.W. Mitchell A.A. Moiseev J. Nishimura M. Nozaki S. Orito J.F. Ormes M. Sasaki E.S. Seo Y. Shikaze R.E. Streitmatter J. Suzuki K. Tanaka T. Yamagami A. Yamamoto T. Yoshida K. Yoshimura 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(12):2050-2055
963.
分析了2000年和2001年期间52°N地区OI5577气辉强度的夜间变化特征和季节变化特征.利用由 OI5577气辉强度反演原子氧浓度峰值的方法反演出原子氧浓度的峰值,分析了峰值的夜间变化特征和季节变化特征.结果表明, OI5577气辉强度的夜间变化特征随季节变化, 2000年春季的夜间强度最大值出现在0000LT 之后,夏季和秋季的出现在0000LT之前,冬季的出现在0000LT,2001年春季和秋季的夜间强度最大值出现在0000LT之前,夏季和冬季的出现在0000LT;OI5577气辉强度在2000年2月份,8月份和10月份出现最大值,在2001年9月份有最大值.就主要特征而言,反演出的原子氧浓度峰值的夜间变化特征和季节变化特征分别与OI5577气辉强度的一致. 相似文献
964.
K. Dolag S. Borgani S. Schindler A. Diaferio A. M. Bykov 《Space Science Reviews》2008,134(1-4):229-268
Modern cosmological observations allow us to study in great detail the evolution and history of the large scale structure
hierarchy. The fundamental problem of accurate constraints on the cosmological parameters, within a given cosmological model,
requires precise modelling of the observed structure. In this paper we briefly review the current most effective techniques
of large scale structure simulations, emphasising both their advantages and shortcomings. Starting with basics of the direct
N-body simulations appropriate to modelling cold dark matter evolution, we then discuss the direct-sum technique GRAPE, particle-mesh (PM) and hybrid methods, combining the PM and the tree algorithms. Simulations of baryonic matter in the Universe often use hydrodynamic codes based on both particle
methods that discretise mass, and grid-based methods. We briefly describe Eulerian grid methods, and also some variants of
Lagrangian smoothed particle hydrodynamics (SPH) methods. 相似文献
965.
C.T. Russell G. Le H. Kawano S.M. Petrinec T.L. Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(12):1913-1917
Recently much attention has been focused on the transient behavior of the magnetopause in response to pressure pulses and southward fluctuations of the interplanetary magnetic field. We examine the motion of the magnetopause behind the foreshock and conclude that this motion is affected by foreshock pressure variations but not by fluctuations in the direction of the magnetic field. Neither magnetopause erosion nor flux transfer event occurrence is controlled by the foreshock. On the contrary, flux transfer events occur at times of steady IMF and thier quasi-periodic behavior is controlled by the magnetopause or the magnetosphere and is not driven by the external boundary conditions. Since flux transfer events are clearly due to reconnection, this observation implies that the IMF must be southward some time perhaps as long as 7 minutes before flux transfer begins. 相似文献
966.
I. C. F. Mueller-Wodarg D. F. Strobel J. I. Moses J. H. Waite J. Crovisier R. V. Yelle S. W. Bougher R. G. Roble 《Space Science Reviews》2008,139(1-4):191-234
This paper summarizes the understanding of aeronomy of neutral atmospheres in the solar system, discussing most planets as well as Saturn’s moon Titan and comets. The thermal structure and energy balance is compared, highlighting the principal reasons for discrepancies amongst the atmospheres, a combination of atmospheric composition, heliocentric distance and other external energy sources not common to all. The composition of atmospheres is discussed in terms of vertical structure, chemistry and evolution. The final section compares dynamics in the upper atmospheres of most planets and highlights the importance of vertical dynamical coupling as well as magnetospheric forcing in auroral regions, where present. It is shown that a first order understanding of neutral atmospheres has emerged over the past decades, thanks to the combined effects of spacecraft and Earth-based observations as well as advances in theoretical modeling capabilities. Key gaps in our understanding are highlighted which ultimately call for a more comprehensive programme of observation and laboratory measurements. 相似文献
967.
Development of thermal sensors and drilling systems for lunar and planetary regoliths 总被引:1,自引:0,他引:1
N.I. Kömle E. Kaufmann G. Kargl Yang Gao Xu Rui 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We consider some novel concepts for thermal properties experiments aboard lunar landers or rovers, that may lead to an improved understanding of both the structure of the lunar near surface layers and the lunar thermal history. The new instruments could be developed using the experience and heritage from recently developed systems, like the Rosetta Lander thermal conductivity experiment MUPUS and existing designs used for terrestrial measurements of thermal conductivity. We describe shortly the working principle of such sensors and the main challenges faced when using them in the airless regolith layers of the Moon or other airless bodies. In addition new concepts to create appropriate drill holes for thermal and other measurements in the lunar regolith are discussed. 相似文献
968.
Response of Hainan GPS ionospheric scintillations to the different strong magnetic storm conditions 总被引:2,自引:0,他引:2
S.P. Shang J.K. Shi P.M. Kintner W.M. Zhen X.G. Luo S.Z. Wu G.J. Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(4):579-586
Using the GPS ionospheric scintillation data at Hainan station (19.5°N, 109.1°E) in the eastern Asia equatorial regions and relevant ionospheric and geomagnetic data from July 2003 to June 2005, we investigate the response of L-band ionospheric scintillation activity over this region to different strong magnetic storm conditions (Dst < −100 nT) during the descending phase of the solar cycle. These strong storms and corresponding scintillations mainly took place in winter and summer seasons. When the main phase developed rapidly and reached the maximum near 20–21 LT (LT = UT + 8) after sunset, scintillations might occur in the following recovery phase. When the main phase maximum occurred shortly after midnight near 01–02 LT, following the strong scintillations in the pre-midnight main phase, scintillations might also occur in the post-midnight recovery phase. When the main phase maximum took place after 03 LT to the early morning hours no any scintillation could be observed in the latter of the night. Moreover, when the main phase maximum occurred during the daytime hours, scintillations could also hardly be observed in the following nighttime recovery phase, which might last until the end of recovery phase. Occasionally, scintillations also took place in the initial phase of the storm. During those scintillations associated with the nighttime magnetic storms, the height of F layer base (h’F) was evidently increased. However, the increase of F layer base height does not always cause the occurrence of scintillations, which indicates the complex interaction of various disturbance processes in ionosphere and thermosphere systems during the storms. 相似文献
969.
S. Gburek T. Mrozek M. Siarkowski J. Sylwester 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We use simultaneous observations from RESIK and RHESSI instruments to compare plasma properties of a major solar flare in its rise and gradual phase. This event occurred on 2002 August 3 (peak time at 19:06 UT). The flare had a very good coverage with RESIK data and well-resolved soft and hard X-ray sources were seen in RHESSI images. Spectra of X-ray radiation from RHESSI images are studied and compared with RESIK measurements in different flare phases. Result shows large differences in flare morphology and spectra between flare rise and gradual phase. 相似文献
970.
E.L. Afraimovich N.P. Perevalova I.V. Zhivetiev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We developed a method of estimation of a relative amplitude dI/I of the total electron content (TEC) variations in the ionosphere as deduced from the data of the global GPS receivers network. To obtain statistically significant results we picked out three latitudinal belts provided in the Internet by the maximum number of GPS sites. They are high-latitudinal belt (50–80°N, 200–300°E; 59 sites), mid latitude belt (20–50°N, 200–300°E; 817 sites), and equatorial belt (±20°N, 0–360°E; 76 sites). The results of the analysis of the diurnal and latitudinal dependencies of dI/I and dI/I distribution probability for 52 days with different levels of geomagnetic activity are presented. It was found that on average the relative amplitude of the TEC variations varies within the range 0–10% proportionally to the value of the Kp geomagnetic index. In quiet conditions the relative amplitude dI/I of the TEC variations at night significantly exceeds the daytime relative amplitude. At high levels of magnetic field disturbances, the geomagnetic control of the amplitude of TEC variations at high and middle latitudes is much more significant than the regular diurnal variations. At the equatorial belt, on average, the amplitude of TEC variations in quiet and disturbed periods almost does not differ. The obtained results may be useful for development of the theory of ionospheric irregularities. 相似文献