全文获取类型
收费全文 | 4976篇 |
免费 | 3篇 |
国内免费 | 13篇 |
专业分类
航空 | 2580篇 |
航天技术 | 1582篇 |
综合类 | 182篇 |
航天 | 648篇 |
出版年
2021年 | 31篇 |
2019年 | 27篇 |
2018年 | 73篇 |
2017年 | 38篇 |
2016年 | 40篇 |
2014年 | 81篇 |
2013年 | 105篇 |
2012年 | 113篇 |
2011年 | 171篇 |
2010年 | 109篇 |
2009年 | 193篇 |
2008年 | 197篇 |
2007年 | 123篇 |
2006年 | 98篇 |
2005年 | 89篇 |
2004年 | 122篇 |
2003年 | 146篇 |
2002年 | 182篇 |
2001年 | 201篇 |
2000年 | 95篇 |
1999年 | 130篇 |
1998年 | 156篇 |
1997年 | 99篇 |
1996年 | 141篇 |
1995年 | 169篇 |
1994年 | 146篇 |
1993年 | 96篇 |
1992年 | 123篇 |
1991年 | 59篇 |
1990年 | 65篇 |
1989年 | 126篇 |
1988年 | 58篇 |
1987年 | 61篇 |
1986年 | 54篇 |
1985年 | 155篇 |
1984年 | 122篇 |
1983年 | 109篇 |
1982年 | 120篇 |
1981年 | 156篇 |
1980年 | 58篇 |
1979年 | 47篇 |
1978年 | 57篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 49篇 |
1974年 | 41篇 |
1972年 | 49篇 |
1971年 | 47篇 |
1970年 | 30篇 |
1969年 | 33篇 |
排序方式: 共有4992条查询结果,搜索用时 0 毫秒
471.
From magnetic fields and coronal heating observed in flares, active regions, quiet regions, and coronal holes, we propose
that exploding sheared core magnetic fields are the drivers of most of the dynamics and heating of the solar atmosphere, ranging
from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring and coronal heating in
active regions, to a multitude of fine-scale explosive events in the magnetic network, driving microflares, spicules, global
coronal heating, and, consequently, the solar wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
472.
Large-scale Coronal Heating, Clustering of Coronal Bright Points, and Concentration of Magnetic Flux
By combining quiet-region Fe XII coronal images from SOHO/EIT with magnetograms from NSO/Kitt Peak and from SOHO/MDI, we show that the population of network coronal bright points and the magnetic flux content of the network are both markedly greater under the bright half of the large-scale quiet corona than under the dim half. These results (1) support the view that the heating of the entire corona in quiet regions and coronal holes is driven by fine-scale magnetic activity (microflares, explosive events, spicules) seated low in the magnetic network, and (2) suggest that this large-scale modulation of the magnetic flux and coronal heating is a signature of giant convection cells. This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
473.
Using empirical velocity distributions derived from UVCS and SUMER ultraviolet spectroscopy, we construct theoretical models of anisotropic ion temperatures in the polar solar corona. The primary energy deposition mechanism we investigate is the dissipation of high frequency (10-10000 Hz) ion-cyclotron resonant Alfvén waves which can heat and accelerate ions differently depending on their charge and mass. We find that it is possible to explain the observed high perpendicular temperatures and strong anisotropies with relatively small amplitudes for the resonant waves. There is suggestive evidence for steepening of the Alfvén wave spectrum between the coronal base and the largest heights observed spectroscopically. Because the ion-cyclotron wave dissipation is rapid, even for minor ions like O5+, the observed extended heating seems to demand a constantly replenished population of waves over several solar radii. This indicates that the waves are generated gradually throughout the wind rather than propagated up from the base of the corona. This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
474.
475.
We review observations from Voyager 2 of CIRs and merged CIRs in the outer heliosphere. The rather simple characteristics
of the CIR-associated changes in plasma, magnetic field, and particles become more complex as observations are made at greater
and greater distances. Pickup ions from charge exchange undoubtedly play an important role in the structure, but the full
details are not yet understood.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
476.
R. Gendrin 《Space Science Reviews》1975,18(2):145-200
Recent space observations of waves, both electromagnetic and electrostatic, are reviewed and the role which they can play in the dynamics of magnetospheric particles is stressed. Wave particle interactions (WPI) in the exo- and intra-plasmaspheric media depend on the exact process of particle injection under the influence of magnetospheric electric fields, and on the spatial distribution of the cold plasma particles; these two aspects of the problem are studied to some extent. The concepts of optimum cold plasma density, critical energy, limiting flux, marginal stability, steady-state equilibrium are critically discussed. The non-linear aspects — both experimental and theoretical — of WPI's are reviewed and a special section is devoted to active experiments in space. An attempt is made to outline which kind of experiments could be made at high-latitudes, in conjunction with IMS spacecrafts, in order to arrive at a better understanding of magnetospheric processes involving waves and particles.Paper presented at the Esro Symposium on European Sounding Rocket and Scientific Balloon Activity at High Latitudes with Emphasis on the International Magnetospheric Study (Örenäs Slott, Sweden, 1974). 相似文献
477.
The application of Fourier Transform Spectroscopy (FTS) to planetary research is reviewed. The survey includes FTS observations of the Sun, all the planets except Uranus and Pluto, the Galilean satellites and Saturn's rings. Instrumentation and scientific results are considered. The prospects and limitations of FTS for planetary research in the forthcoming years are discussed. 相似文献
478.
Giardina C.R. Bronson R. Wallen L. 《IEEE transactions on aerospace and electronic systems》1975,(4):443-446
An attitude normalization scheme, based on quaternion updates' of the attitude matrix in a strapdown system, is presented which is optimal in the two-norm sense. Furthermore, the algorithm requires minimal computer time and memory load. 相似文献
479.
An experimental program is described that had the objective of measuring the effects of the time-dependent structure of downlink (air craft to ground) interference generated by the Air Traffic Control Radar Beacon System (ATCRBS) in an active air traffic terminal area that are relevant to system and ground controller response time. The results of this program indicate a number of interesting details concerning the correlation of the level of the downlink interference with changes in the arrival and departure rates of aircraft at the local terminal sites. 相似文献
480.
This paper describes a system of navigation by measurement of the Doppler shift in the radio transmissions from a near-Earth satellite, and simple equipment for making the measurements. It also shows that the current information which is needed by the navigator can be reduced to a number containing six decimal digits. Finally, it shows that the computations needed for the navigator to obtain a fix can be performed witlh the aid of tables that can be prepared at least 18 months in advance. Using these tables and a simple slide rule, but no other computational aids, a fix accurate to about 500 meters can be obtained in about 10 minutes. More accuracy can be obtained at the expense of time, or time can be saved at the expense of accuracy. 相似文献