全文获取类型
收费全文 | 307篇 |
免费 | 1篇 |
国内免费 | 10篇 |
专业分类
航空 | 186篇 |
航天技术 | 84篇 |
综合类 | 1篇 |
航天 | 47篇 |
出版年
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 15篇 |
2013年 | 8篇 |
2012年 | 13篇 |
2011年 | 31篇 |
2010年 | 9篇 |
2009年 | 16篇 |
2008年 | 22篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 14篇 |
2003年 | 6篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有318条查询结果,搜索用时 31 毫秒
291.
Leung-Pong Wong Yim-Shu Lee Ki-Wai Cheng D. Chow M.H.L. 《IEEE transactions on aerospace and electronic systems》2004,40(4):1294-1310
An interleaved two-phase forward converter using an integrated magnetic component is proposed for telecommunication and computer applications. The integrated magnetic component consists of two step-down transformers and two output-filtering inductors on a single magnetic core. The z-parameter (gyrator) model and the equivalent-circuit model of the integrated magnetic component are presented. The circuit operation and design criteria of the proposed converter are described. All theoretical analyses are verified by simulated and experimental results. 相似文献
292.
A review of global satellite-derived snow products 总被引:1,自引:0,他引:1
Allan Frei Marco Tedesco Shihyan Lee James Foster Dorothy K. Hall Richard Kelly David A. Robinson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Snow cover over the Northern Hemisphere plays a crucial role in the Earth’s hydrology and surface energy balance, and modulates feedbacks that control variations of global climate. While many of these variations are associated with exchanges of energy and mass between the land surface and the atmosphere, other expected changes are likely to propagate downstream and affect oceanic processes in coastal zones. For example, a large component of the freshwater flux into the Arctic Ocean comes from snow melt. The timing and magnitude of this flux affects biological and thermodynamic processes in the Arctic Ocean, and potentially across the globe through their impact on North Atlantic Deep Water formation. 相似文献
293.
Jinhy Hong J.J. Lee K.W. Min V.P. Kim V.V. Hegai 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We examined polar rain flux observed by STSAT-1 in the northern polar cap and compared it with solar wind parameters. We found that the differential energy spectrum of polar rain was similar to that of the solar wind for the energy range 100 eV – 1 keV, although we cannot rule out the possibility of a small amount of acceleration. On the other hand, the low-energy component of the solar wind showed no correlation and, naturally, the solar wind density had only a weak correlation with the polar rain flux. Polar rain flux in the northern hemisphere is most significant for the condition of the interplanetary magnetic field components Bz < 0, Bx < 0, and By > 0, and in this case it correlated well with the magnitude of By and Bz. For other interplanetary magnetic field conditions, the correlation was insignificant. The results are consistent with those reported previously. 相似文献
294.
Julia C. Lee 《Space Science Reviews》2010,157(1-4):93-101
High spectral resolution X-ray instruments on powerful X-ray satellites (e.g. Chandra, XMM-Newton) pointed through dust and gas at bright black holes and neutron stars can be used to study dust and intervening material in unique ways. With the new subfield of Condensed Matter Astrophysics as its goal, I will discuss current efforts to combine techniques and knowledge from condensed matter physics and astrophysics to determine the species-specific quantity and composition of interstellar gas and dust in the ISM and ionized environments. Prospects for improving on this work in future X-ray missions with higher throughput and spectral resolution are also presented in the context of spectral resolution goals for gratings and calorimeters. 相似文献
295.
The interaction between the input filter and the control loop of switching regulators often results in detrimental effects, such as loop instability, degradation of transient response, and audiosusceptibility, etc. The concept of pole-zero cancellation is employed to mitigate some of these detrimental effects and is implemented using a novel feedforward loop, in addition to existing feedback loops of a buck regulator. Experimental results are presented which show excellent correlation with theory. 相似文献
296.
V Andersen F Ballarini G Battistoni M Campanella M Carboni F Cerutti A Empl A Fassò A Ferrari E Gadioli M V Garzelli K Lee A Ottolenghi M Pelliccioni L S Pinsky J Ranft S Roesler P R Sala T L Wilson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(6):1302-1310
The FLUKA Monte Carlo transport code is widely used for fundamental research, radioprotection and dosimetry, hybrid nuclear energy system and cosmic ray calculations. The validity of its physical models has been benchmarked against a variety of experimental data over a wide range of energies, ranging from accelerator data to cosmic ray showers in the earth atmosphere. The code is presently undergoing several developments in order to better fit the needs of space applications. The generation of particle spectra according to up-to-date cosmic ray data as well as the effect of the solar and geomagnetic modulation have been implemented and already successfully applied to a variety of problems. The implementation of suitable models for heavy ion nuclear interactions has reached an operational stage. At medium/high energy FLUKA is using the DPMJET model. The major task of incorporating heavy ion interactions from a few GeV/n down to the threshold for inelastic collisions is also progressing and promising results have been obtained using a modified version of the RQMD-2.4 code. This interim solution is now fully operational, while waiting for the development of new models based on the FLUKA hadron-nucleus interaction code, a newly developed QMD code, and the implementation of the Boltzmann master equation theory for low energy ion interactions. 相似文献
297.
The function of the receiver in a binary digital communication system is to make a binary (?space?, ?mark? or ?"0?, ?1?) decision by comparing the signal values from the mark and space filters (or correlators) at known successive time intervals (?bit? or ?baud? time intervals). When the signal value out of the mark filter is greater than that out of the space filter, it is decided that mark or 1 is transmitted, and vice versa. It is of fundamental importance to know the exact instant of time at which the two filter outputs are to be compared. This is the problem of synchronization between the transmitter and the receiver. In this paper, we assume a system that is perfectly synchronized. In a practical system, the difference between the two filter outputs must differ from a threshold by some finite amount in order to cause the device to respond reliably. The examination of the effects of this dead zone (finite-width decision threshold) on digital transmission systems is of important practical interest. Its effects on binary differentially coherent phase-shift-keying, and m-level phase-shift-keying systems have been investigated previously. In this paper we consider its effects on binary coherent phase-shift-keying (CPSK), coherent orthogonal (CFSK), and noncoherent orthogonal (NCFSK) systems. The probability of bit error and the channel capacity of each system is obtained in terms of the dead zone threshold. 相似文献
298.
VEGA Balloon Science Team Lee S. Elson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1987,7(12):337-342
Instruments aboard the gondolas of the two VEGA balloons obtained in situ measurements of pressure, temperature, vertical velocity relative to the balloon, cloud particle backscatter, lightning and the ambient light level. Atmospheric motions at the balloon float altitudes were also determined from Earth-based tracking results. To illustrate the history of the balloon flights and to facilitate comparisons between some of the different observed quantities, measurements of pressure, temperature and backscatter are presented as time series for the entire lifetime of each balloon. Both long and short period variations have been detected. In addition, the environmental entropy encountered by each balloon will be discussed. 相似文献
299.
300.
Lee B. Holcomb Montemerlo Melvin D. 《Aerospace and Electronic Systems Magazine, IEEE》1987,2(4):19-26
This paper presents an overview of NASA's Automation and Robotics (A&R) technology development program, covering its history, objectives, organization and content. This program is being carried out by the Office of Aeronautics and Space Technology (OAST) which has the responsibility to provide long range, high risk aerospace technology. 相似文献