全文获取类型
收费全文 | 2555篇 |
免费 | 7篇 |
国内免费 | 6篇 |
专业分类
航空 | 1255篇 |
航天技术 | 1025篇 |
综合类 | 5篇 |
航天 | 283篇 |
出版年
2021年 | 13篇 |
2019年 | 14篇 |
2018年 | 44篇 |
2017年 | 34篇 |
2016年 | 26篇 |
2015年 | 12篇 |
2014年 | 50篇 |
2013年 | 65篇 |
2012年 | 51篇 |
2011年 | 87篇 |
2010年 | 62篇 |
2009年 | 106篇 |
2008年 | 152篇 |
2007年 | 64篇 |
2006年 | 48篇 |
2005年 | 64篇 |
2004年 | 73篇 |
2003年 | 92篇 |
2002年 | 46篇 |
2001年 | 101篇 |
2000年 | 50篇 |
1999年 | 88篇 |
1998年 | 87篇 |
1997年 | 62篇 |
1996年 | 65篇 |
1995年 | 88篇 |
1994年 | 98篇 |
1993年 | 38篇 |
1992年 | 60篇 |
1991年 | 23篇 |
1990年 | 28篇 |
1989年 | 56篇 |
1988年 | 21篇 |
1987年 | 35篇 |
1986年 | 22篇 |
1985年 | 83篇 |
1984年 | 44篇 |
1983年 | 48篇 |
1982年 | 59篇 |
1981年 | 84篇 |
1980年 | 26篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 20篇 |
1976年 | 17篇 |
1975年 | 18篇 |
1974年 | 12篇 |
1972年 | 18篇 |
1969年 | 14篇 |
1966年 | 8篇 |
排序方式: 共有2568条查询结果,搜索用时 15 毫秒
831.
N.U. Crooker J.T. Gosling V. Bothmer R.J. Forsyth P.R. Gazis A. Hewish T.S. Horbury D.S. Intriligator J.R. Jokipii J. Kóta A.J. Lazarus M.A. Lee E. Lucek E. Marsch A. Posner I.G. Richardson E.C. Roelof J.M. Schmidt G.L. Siscoe B.T. Tsurutani R.F. Wimmer-Schweingruber 《Space Science Reviews》1999,89(1-2):179-220
Corotating interaction regions (CIRs) in the middle heliosphere have distinct morphological features and associated patterns
of turbulence and energetic particles. This report summarizes current understanding of those features and patterns, discusses
how they can vary from case to case and with distance from the Sun and possible causes of those variations, presents an analytical
model of the morphological features found in earlier qualitative models and numerical simulations, and identifies aspects
of the features and patterns that have yet to be resolved.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
832.
Malandraki O.E. Sarris E.T. Lanzerotti L.J. Maclennan C.G. Pick M. Tsiropoula G. 《Space Science Reviews》2001,97(1-4):263-268
In January 2000, the Ulysses spacecraft observed an ICME event at 43° S heliographic latitude and ∼ 4.1 AU. We use electron (E
e>38 keV) observations to trace the topology of the IMF embedded within the ICME. The still controversial issue of whether
ICMEs have been detached from the solar corona or are still magnetically anchored to it when they arrive at the spacecraft
is tackled. An in ecliptic ICME event is also presented.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
833.
O. Moullard R.G. Marsden T.R. Sanderson C. Tranquille R.J. Forsyth B.E. Goldstein 《Space Science Reviews》2001,97(1-4):289-292
We present and compare observations of energetic protons during the two first transits of the Ulysses spacecraft from low to high latitudes in the southern heliosphere. Protons in the energy range 1.8–3.8 MeV from the COSPIN
experiment are studied for global trends and in relation to some ambient structures in the solar wind (corotating interaction
region, forward/reverse shock). The global trends show the large dependence on the heliospheric condition and solar activity,
including indications of a larger ambient particle population during the rising phase of solar activity and more efficient
solar wind particle accelerators during the declining phase. More enhancements in the proton flux intensity are time associated
with forward shocks than reverse contrary to first pass. Recurrent structures are found even during the second transit. Some
latitude dependent periodicities are observed that could relate to the differential solar rotation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
834.
G. Wibberenz H.V. Cane I.G. Richardson T.T. von Rosenvinge 《Space Science Reviews》2001,97(1-4):343-347
The maximum inclination of the heliospheric current sheet (the tilt angle) and the magnitude B of the heliospheric magnetic field are often used to characterize cosmic ray (CR) modulation. The relevance of B is likely to be the coupling of the interplanetary diffusion coefficients K to the field magnitude in a relation K∝B
−n. In this paper we study the coupled influence of tilt angle and magnetic field variations on the modulation of cosmic rays
at neutron monitor energies for the 1974 mini-cycle and for the onsets of solar cycles 21, 22, and 23. It is suggested that
for A>0 polarity epochs, the sensitivity of the CR response to variations in B is partly controlled by the size of the tilt angle, α. The onsets of cycles 21 and 23 exhibit differences, related to phase
differences in these parameters. A simple model is used to predict the CR response to variations in B.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
835.
T. Ono A. Kumamoto Y. Kasahara Y. Yamaguchi A. Yamaji T. Kobayashi S. Oshigami H. Nakagawa Y. Goto K. Hashimoto Y. Omura T. Imachi H. Matsumoto H. Oya 《Space Science Reviews》2010,154(1-4):145-192
The Lunar Radar Sounder (LRS) onboard the KAGUYA (SELENE) spacecraft has successfully performed radar sounder observations of the lunar subsurface structures and passive observations of natural radio and plasma waves from the lunar orbit. After the transfer of the spacecraft into the final lunar orbit and antenna deployment, the operation of LRS started on October 29, 2007. Through the operation until June 10, 2009, 2363 hours worth of radar sounder data and 8961 hours worth of natural radio and plasma wave data have been obtained. It was revealed through radar sounder observations that there are distinct reflectors at a depth of several hundred meters in the nearside maria, which are inferred to be buried regolith layers covered by a basalt layer with a thickness of several hundred meters. Radar sounder data were obtained not only in the nearside maria but also in other regions such as the farside highland region and polar region. LRS also performed passive observations of natural plasma waves associated with interaction processes between the solar wind plasma and the moon, and the natural waves from the Earth, the sun, and Jupiter. Natural radio waves such as auroral kilometric radiation (AKR) with interference patterns caused by the lunar surface reflections, and Jovian hectometric (HOM) emissions were detected. Intense electrostatic plasma waves around 20 kHz were almost always observed at local electron plasma frequency in the solar wind, and the electron density profile, including the lunar wake boundary, was derived along the spacecraft trajectory. Broadband noises below several kHz were frequently observed in the dayside and wake boundary of the moon and it was found that a portion of them consist of bipolar pulses. The datasets obtained by LRS will make contributions for studies on the lunar geology and physical processes of natural radio and plasma wave generation and propagation. 相似文献
836.
B. Rani T.P. Krichbaum B. Lott L. Fuhrmann J.A. Zensus 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The GeV observations by Fermi-LAT give us the opportunity to characterize the high-energy emission (100 MeV–300 GeV) variability properties of the BL Lac object S5 0716+714. In this study, we performed flux and spectral analysis of more than 3 year long (August 2008 to April 2012) Fermi-LAT data of the source. During this period, the source exhibits two different modes of flux variability with characteristic timescales of ∼75 and ∼140 days, respectively. We also notice that the flux variations are characterized by a weak spectral hardening. The GeV spectrum of the source shows a clear deviation from a simple power law, and is better explained by a broken power law. Similar to other bright Fermi blazars, the break energy does not vary with the source flux during the different activity states. We discuss several possible scenarios to explain the observed spectral break. 相似文献
837.
Uttam Kumar S. Kumar Raja Chiranjit Mukhopadhyay T.V. Ramachandra 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Variable Endmember Constrained Least Square (VECLS) technique is proposed to account endmember variability in the linear mixture model by incorporating the variance for each class, the signals of which varies from pixel to pixel due to change in urban land cover (LC) structures. VECLS is first tested with a computer simulated three class endmember considering four bands having small, medium and large variability with three different spatial resolutions. The technique is next validated with real datasets of IKONOS, Landsat ETM+ and MODIS. The results show that correlation between actual and estimated proportion is higher by an average of 0.25 for the artificial datasets compared to a situation where variability is not considered. With IKONOS, Landsat ETM+ and MODIS data, the average correlation increased by 0.15 for 2 and 3 classes and by 0.19 for 4 classes, when compared to single endmember per class. 相似文献
838.
An onboard astronomical system is suggested, based on the developed method using virtual measurements of zenith distances of stars. Two algorithms of the method are described, their theory is given, and statistical results of the system’s simulation are presented. 相似文献
839.
C. S. Fish C. M. Swenson G. Crowley A. Barjatya T. Neilsen J. Gunther I. Azeem M. Pilinski R. Wilder D. Allen M. Anderson B. Bingham K. Bradford S. Burr R. Burt B. Byers J. Cook K. Davis C. Frazier S. Grover G. Hansen S. Jensen R. LeBaron J. Martineau J. Miller J. Nelsen W. Nelson P. Patterson E. Stromberg J. Tran S. Wassom C. Weston M. Whiteley Q. Young J. Petersen S. Schaire C. R. Davis M. Bokaie R. Fullmer R. Baktur J. Sojka M. Cousins 《Space Science Reviews》2014,181(1-4):61-120
Funded by the NSF CubeSat and NASA ELaNa programs, the Dynamic Ionosphere CubeSat Experiment (DICE) mission consists of two 1.5U CubeSats which were launched into an eccentric low Earth orbit on October 28, 2011. Each identical spacecraft carries two Langmuir probes to measure ionospheric in-situ plasma densities, electric field probes to measure in-situ DC and AC electric fields, and a science grade magnetometer to measure in-situ DC and AC magnetic fields. Given the tight integration of these multiple sensors with the CubeSat platforms, each of the DICE spacecraft is effectively a “sensor-sat” capable of comprehensive ionospheric diagnostics. The use of two identical sensor-sats at slightly different orbiting velocities in nearly identical orbits permits the de-convolution of spatial and temporal ambiguities in the observations of the ionosphere from a moving platform. In addition to demonstrating nanosat-based constellation science, the DICE mission is advancing a number of groundbreaking CubeSat technologies including miniaturized mechanisms and high-speed downlink communications. 相似文献
840.
Masserant B.J. Stuart T.A. 《IEEE transactions on aerospace and electronic systems》1997,33(3):930-938
A battery charger is described that uses an on-line microcontroller to maximize its output power. This is done by always operating at either the maximum allowable input current or the thermal limit imposed by the charger itself. In this case the thermal limit is determined by the junction temperatures of the two main insulated gate bipolar transistors (IGBTs). Since direct measurement of these temperatures is impractical, they must be calculated by a computer algorithm that uses various on-line measurements. Experimental results for an 8 kW charger indicate a reduction in the bulk charging time of about 26% when used with a set of NiFe batteries. 相似文献