全文获取类型
收费全文 | 607篇 |
免费 | 69篇 |
国内免费 | 146篇 |
专业分类
航空 | 308篇 |
航天技术 | 290篇 |
综合类 | 46篇 |
航天 | 178篇 |
出版年
2023年 | 5篇 |
2022年 | 15篇 |
2021年 | 29篇 |
2020年 | 18篇 |
2019年 | 24篇 |
2018年 | 23篇 |
2017年 | 29篇 |
2016年 | 28篇 |
2015年 | 31篇 |
2014年 | 54篇 |
2013年 | 49篇 |
2012年 | 47篇 |
2011年 | 47篇 |
2010年 | 51篇 |
2009年 | 68篇 |
2008年 | 43篇 |
2007年 | 30篇 |
2006年 | 29篇 |
2005年 | 21篇 |
2004年 | 13篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 19篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 1篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1984年 | 7篇 |
排序方式: 共有822条查询结果,搜索用时 15 毫秒
351.
The variability of the radio emission of RS CVn and Algol type binaries has been observed over 70 hours by Lefèvre et al. (1993). In this contribution simple model calculations are applied to discuss the relevant time scales. It is concluded that a significant fraction of the permanent radio emission of these systems is due to flare-like processes of energy release over a wide range of energies. 相似文献
352.
为了防止计算机辐射的危害,深入分析了计算机辐射的成因、危害、限额值、测量方法等问题。指出:这一研究作为电磁兼容学的一个分支,国内外正加强重视并扩大研究规模。文末指出了当前进一步研究的方向。 相似文献
353.
光从光密媒质射向光疏媒质时,若入射角大于临界角,则发生全反射,但在光疏媒质中仍有电磁波存在,这个电磁波称为消逝波。本文介绍了一种装置,使从光疏媒质一侧成象在界面上的红外象,转换成可见光象,从而间接证明了消逝波的存在;同时探讨了如何利用这种装置构成新型热象仪。 相似文献
354.
A. M. Hillas 《Space Science Reviews》1996,75(1-2):17-30
Cosmic gamma-ray ray sources may be sought if high-energy gamma-rays may be detected without confusion from the very intense isotropic background of hadronic cosmic rays. Ground-based methods are needed at energies above tens of GeV, using air showers, and at energies below tens of TeV, the detection of muons in showers is not the most efficient way to reject hadronic showers. The shape and orientation of erenkov images can reject far more than 99% of the background. The way in which erenkov radiation is distributed in showers is discussed, and the possibilities of using image shape, distribution of light on the ground, time profile, spectrum and polarization of the light are briefly discussed. Imaging alone appears to be the most powerful. Simulations suggest that the uv content of the light should not be a useful diagnostic. 相似文献
355.
任意形状凹面和相互可视表面φ2,φ3的分析计算 总被引:4,自引:0,他引:4
推导了空间任意形状凹面和相互可视表面的地球红外角系数φ3和地球反照角系数φ2的计算公式;并运用MonteCarlo法对半球凹地、抛物凹面、面相互可视的直角平板、平板表面外凸出圆柱表面的地球反照角系数和地球红外角系数进行了计算。运用这种方法,可以计算任意形状凹面和相互可视表面的φ2、φ3。 相似文献
356.
温度传感器辐射修正校准的准确性研究 总被引:1,自引:0,他引:1
为了确定温度传感器辐射修正校准的准确性,需要对温度传感器辐射修正校准结果进行对比及不确定度分析.本文介绍了在热校准风洞中进行温度传感器辐射修正校准的结果,并做了对比研究和不确定度分析. 相似文献
357.
介绍了射频电磁场对声级计进行电磁辐射干扰的详细情况以及利用工频磁场测试装置进行声级计抗工频磁场干扰的研究设计 相似文献
358.
359.
Reinhard Schlickeiser 《Space Science Reviews》1996,75(1-2):299-315
It is argued that the high-energy X-ray and -ray emission from flaring blazars is beamed radiation from the relativistic jet supporting the relativistic beaming hypothesis and the unified scenario for AGNs. Most probably the high-energy emission results from inverse Compton scattering by relativistic electrons and positrons in the jet of radiation originating external to the jet plus pair annihilation radiation from the jet. Future positive TeV detections of EGRET AGN sources will be decisive to identify the prominent target photon radiation field. Direct -ray production by energetic hadrons is not important for the flaring phase in -ray blazars, but the acceleration of energetic hadrons during the quiescent phase of AGNs is decisive as the source of secondary electrons and positrons through photo-pair and photo-pion production. Injection of ultrahigh energy secondary electrons and positrons into a stochastic quasilinear acceleration scheme during the quiescent AGN phase leads to cooling electron-positron distribution functions with a strong cut-off at low but relativistic energy that under certain local conditions may trigger a plasma instability that gives rise to an explosive event and the flaring -ray phase. 相似文献
360.
M.E.
zel H.A. Mayer-Haelwander 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
Poor angular resolution of present day gamma ray telescopes (1° at 100 MEV) together with the complicated gamma ray sky structures at compareable angular extents and poor statistics available necessitate the selection of those gammas which will increase the observable signal from a suspected source. A method for such a selection using the pre-known time signature of the source as its signal, has been developed (Özel and Mayer-Haβelwander, 1983). In an iterative procedure based on the improvement of source signal, generalized zones around the source are defined, from which gamma rays should be accepted to construct the optimum light curve of the source. These zones depend on the energy of the probed gamma rays, on the spatial structure and intensity of the background around the source, on the (estimated and/or tentative) intetnsity of the source and finally on the observing instrument's angular and energy response functions. The method, when applied to simulated and observed COS-B data demonstrated its feasibility and merits over the previonsly used circular event-acceptance cones method which was the basis of searches for gamma ray emission from radio pulsars (see for example Kniffen et al., 1974; Ögelman, et al. 1976; Kanbach, et al., 1977; and references therein). Present method does not introduce “trials” which usually reduce the significance of the results obtained, fully accounts the available knowledge on the topography of gamma ray sky, makes use of all the information about the sky, source and the instrument and therefore is the proper way of handling gamma ray data in pulsar-type searches.Presently, method is applied in the analyses of COS-B data in the context of searches for gamma ray emitting X-ray and radio pulsars. Results will be published elsewhere. 相似文献