全文获取类型
收费全文 | 378篇 |
免费 | 12篇 |
国内免费 | 61篇 |
专业分类
航空 | 241篇 |
航天技术 | 132篇 |
综合类 | 10篇 |
航天 | 68篇 |
出版年
2021年 | 4篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2014年 | 18篇 |
2013年 | 11篇 |
2012年 | 49篇 |
2011年 | 37篇 |
2010年 | 17篇 |
2009年 | 26篇 |
2008年 | 21篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 15篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1968年 | 2篇 |
1967年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有451条查询结果,搜索用时 31 毫秒
321.
O.?Le?ContelEmail author P.?Leroy A.?Roux C.?Coillot D.?Alison A.?Bouabdellah L.?Mirioni L.?Meslier A.?Galic M.?C.?Vassal R.?B.?Torbert J.?Needell D.?Rau I.?Dors R.?E.?Ergun J.?Westfall D.?Summers J.?Wallace W.?Magnes A.?Valavanoglou G.?Olsson M.?Chutter J.?Macri S.?Myers S.?Turco J.?Nolin D.?Bodet K.?Rowe M.?Tanguy B.?de?la?Porte 《Space Science Reviews》2016,199(1-4):257-282
The tri-axial search-coil magnetometer (SCM) belongs to the FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission (Torbert et al. in Space Sci. Rev. (2014), this issue). It provides the three magnetic components of the waves from 1 Hz to 6 kHz in particular in the key regions of the Earth’s magnetosphere namely the subsolar region and the magnetotail. Magnetospheric plasmas being collisionless, such a measurement is crucial as the electromagnetic waves are thought to provide a way to ensure the conversion from magnetic to thermal and kinetic energies allowing local or global reconfigurations of the Earth’s magnetic field. The analog waveforms provided by the SCM are digitized and processed inside the digital signal processor (DSP), within the Central Electronics Box (CEB), together with the electric field data provided by the spin-plane double probe (SDP) and the axial double probe (ADP). On-board calibration signal provided by DSP allows the verification of the SCM transfer function once per orbit. Magnetic waveforms and on-board spectra computed by DSP are available at different time resolution depending on the selected mode. The SCM design is described in details as well as the different steps of the ground and in-flight calibrations. 相似文献
322.
N. Srivastava W.D. Gonzalez H.S. Sawant 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(12):2355-2358
In this paper, a study of the coronal mass ejections (CMEs) observed by Solar Maximum Mission satellite (SMM) during the period March – September, 1980, is presented. An attempt to identify various possible associations of the solar phenomena, for example, the location of coronal holes, the role of eruptive filaments or prominences, and current-sheets with the CMEs is carried out. It is shown that the combined associations of these three play an important role in the occurrence of geoeffective CMEs and also act as a tool to predict the associated geomagnetic activity. 相似文献
323.
金属材料摩擦挤压合金化研究 总被引:2,自引:0,他引:2
本文以LF6铝合金作为基材,Ni粉作为合金化添加粉末,试验用摩擦挤压的方法进行金属材料的合金化。利用X射线衍射仪及Topas(2)X射线分析软件进行物相分析。并测试了合金化区域的显微硬度。结果表明:摩擦挤压区域有Al3Ni以及AlNi3化合物生成,并且发现生成的金属间化合物Al3Ni含量高于AlNi3化合物含量;生成的Al3Ni和AlNi3的晶格常数增大,晶粒尺寸细小,几乎达到亚微米级;生成Ak3Ni的显微硬度达到520HV。研究结果表明:用摩擦挤压的方法能够实现金属材料的合金化。 相似文献
324.
正等测椭圆的简捷画法 总被引:1,自引:0,他引:1
在研究传统菱形法绘制正等测椭圆的基础上,运用逻辑分析和几何分析的方法,提出了一种六点共圆、三线共点的椭圆简捷画法,作图简便、快捷,效率高。 相似文献
325.
de Figueiredo R.J.P. Kehtarnavaz N. 《IEEE transactions on aerospace and electronic systems》1988,24(5):597-607
Orientation-dependent techniques for the identification of a three-dimensional (3-D) object by a machine vision system are represented in parts. In the first part, the data consist of intensity images of polyhedral objects obtained by a single camera, while in the second part, the data consist of range images of curved objects obtained by a laser scanner. In both cases, the attributed graph representation of the 3-D object surface is used to drive the respective algorithm. In this representation, a graph node represents a surface path and a link, the adjacency between two patches. The attributes assigned to nodes are moment invariants of the corresponding face for polyhedral objects. For range images, the Gaussian curvature is used as a segmentation criterion for providing symbolic shape attributes. Identification is achieved by an efficient graph-matching algorithm used to match the graph obtained from the data to a subgraph of one of the model graphs stored in the computer memory 相似文献
326.
327.
Elias-Fuste A.R. de Mercado M.G.G. de los Reyes Davo E. 《IEEE transactions on aerospace and electronic systems》1990,26(1):197-202
It is necessary for automatic detection radars to be adaptive to variations in background clutter in order to maintain a constant false alarm rate (CFAR). A CFAR based on an ordered statistic technique (OS CFAR) has some advantages over the cell-averaging technique (CA CFAR), especially in clutter edges or multiple target environments; unfortunately the large processing time required by this technique limits its use. The authors present two new OS CFARs that require only ahlf the processing time. One is an ordered statistic greatest of CFAR (OSGO), while the other is an ordered statistic smallest of CFAR (OSSO). The OSGO CFAR has the advantages of the OS CFAR with only a negligible increment to the CFAR loss 相似文献
328.
R. Lopes de Oliveira C. Motch F. Haberl I. Negueruela E. Janot-Pacheco 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2782-2784
A small number of early Be stars exhibit X-ray luminosities intermediate between those typical of early type stars and those radiated by Be/X-ray binaries in the quiescent state. We report on XMM-Newton observations of two such Be stars, HD 161103 and SAO 49725 which were originally discovered in a systematic cross-correlation between the ROSAT all-sky survey and SIMBAD. The new observations confirm the X-ray luminosity detected by ROSAT (LX 1032 erg s−1) and the hardness of their X-ray spectra (thin thermal with kT 8–10 keV or power law with photon index of 1.7) which are both unusual for normal early type stars. We discuss the possible origin of this excess X-ray emission in the light of the models proposed for γ-Cas, magnetic disc-star interaction or accretion onto a compact companion object, neutron star or white dwarf, and compare the properties of these two sources with those of the new massive systems discovered in the XMM- Newton/SSC survey of the Galactic plane. 相似文献
329.
E. Echer W.D. Gonzalez A. Dal Lago L.E.A. Vieira F.L. Guarnieri A.L.C. Gonzalez N.J. Schuch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2318-2322
Plasma and magnetic field parameter variations through fast forward interplanetary shocks were correlated with the peak geomagnetic activity index Dst in a period from 0 to 3 days after the shock, during solar maximum (2000) and solar minimum (1995–1996). Solar wind speed (V) and total magnetic field (Bt) were the parameters with higher correlations with peak Dst index. The correlation coefficients were higher during solar minimum (r2 = 56% for V and 39% for Bt) than during solar maximum (r2 = 15% for V and 12% for Bt). A statistical distribution of geomagnetic activity levels following interplanetary shocks was obtained. It was observed that during solar maximum, 36% and 28% of interplanetary shocks were followed by intense (Dst −100 nT) and moderate (−50 Dst < −100 nT) geomagnetic activity, whereas during solar minimum 13% and 33% of the shocks were followed by intense and moderate geomagnetic activity. It can be concluded that the upstream/downstream variations of V and Bt through the shocks were the parameters better correlated with geomagnetic activity level, and during solar maximum a higher relative number of interplanetary shocks can be followed by intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar cycle a shock has a probability of around 50% to be followed by intense/moderate geomagnetic activity. 相似文献
330.
C. de Jager P. Hoyng H. Lafleur A. Schadee Z. Svestka H. F. van Beek W. van Tend 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(13):251-254
We describe the development of the limb flare of 30 April 1980, 20:20 UT, as observed by the Hard X-ray Imaging Spectrometer (HXIS) aboard the Solar Maximum Mission (SMM). It consisted of a short-lived bright nucleus (FWHM < 10,000 km), just inside the Sun's limb; a longer lasting tongue, extending to a height of 30,000 km, and a more complicated feature, approximately situated at the Sun's limb. The tongue was a pre-existing magnetic structure that started emitting X-rays only a few seconds after the bright nucleus, and which had a slightly higher temperature than the nucleus; its X-ray emission may be caused by electrons escaped from the nucleus. 相似文献