全文获取类型
收费全文 | 1241篇 |
免费 | 102篇 |
国内免费 | 47篇 |
专业分类
航空 | 619篇 |
航天技术 | 411篇 |
综合类 | 55篇 |
航天 | 305篇 |
出版年
2024年 | 4篇 |
2023年 | 37篇 |
2022年 | 22篇 |
2021年 | 21篇 |
2020年 | 30篇 |
2019年 | 27篇 |
2018年 | 19篇 |
2017年 | 15篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 63篇 |
2013年 | 34篇 |
2012年 | 52篇 |
2011年 | 87篇 |
2010年 | 31篇 |
2009年 | 43篇 |
2008年 | 81篇 |
2007年 | 92篇 |
2006年 | 64篇 |
2005年 | 86篇 |
2004年 | 45篇 |
2003年 | 62篇 |
2002年 | 37篇 |
2001年 | 76篇 |
2000年 | 34篇 |
1999年 | 39篇 |
1998年 | 38篇 |
1997年 | 22篇 |
1996年 | 28篇 |
1995年 | 26篇 |
1994年 | 73篇 |
1993年 | 23篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1984年 | 4篇 |
排序方式: 共有1390条查询结果,搜索用时 265 毫秒
901.
Y. Terada M. Ishida K. Mukai T. Dotani K. Makishima S. Naik T. Hayashi S. Okada R. Nakamura T. Enoto 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):512-517
Although rotating neutron stars (NSs) have been regarded as being textbook examples of astrophysical particle acceleration sites for decades, details of the acceleration mechanism remain a mystery; for example, we cannot yet observationally distinguish “polar cap” models from “outer gap” models. To solve the model degeneracy, it is useful to study similar systems with much different physical parameters. Strongly magnetized white dwarfs (WDs) are ideal for this purpose, because they have essentially the same system geometry as NSs, but differ largely from NSs in the system parameters, including the size, magnetic field, and the rotation velocity, with the induced electric field expected to reach 1013–1014 eV. Based on this idea, the best candidate among WDs, AE Aquarii, was observed with the fifth Japaneses X-ray satellite, Suzaku. The hard X-ray detector (HXD) on-board Suzaku has the highest sensitivity in the hard X-ray band over 10 keV. A marginal detection in the hard X-ray band was achieved with the HXD, and was separated from the thermal emission. The flux corresponds to about 0.02% of its spin-down energy. If the signal is real, this observation must be a first case of the detection of non-thermal emission from WDs. 相似文献
902.
Chengming Tan Yihua Yan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(6):992-997
We have investigated the source characteristic and coronal magnetic field structure of six impulsive solar energetic particle (SEP) events selected from Wang et al. [Wang, Y.-M., Pick, M., Mason, G.M. Coronal holes, jets, and the origin of 3He-rich particle events. ApJ 639, 495, 2006] and Pick et al. [Pick, M., Mason, G.M., Wang, Y.-M., Tan, C., Wang, L. Solar source regions for 3He-rich solar energetic particle events identified using imaging radio, optical, and energetic particle observations. ApJ 648, 1247, 2006]. Some results are obtained: first, 2 events are associated with wide (≈100°) CMEs (hereafter wide CME events), another 4 events are associated with narrow (?40°) CMEs (hereafter narrow CME events); second, the coronal magnetic field configuration of narrow CME events appear more simple than that of the wide CME events; third, the photospheric magnetic field evolutions of all these events show new emergence of fluxes, while one case also shows magnetic flux cancellation; fourth, the EUV jets usually occurred very close to the footpoint of the magnetic field loop, while meter type III bursts occurred near or at the top of the loop and higher than EUV jets. Furthermore, the heights of type III bursts are estimated from the result of the coronal magnetic field extrapolations. 相似文献
903.
New methods of local helioseismology and uninterrupted time series of solar oscillation data from the Solar and Heliospheric
Observatory (SOHO) have led to a major advance in our understanding of the structure and dynamics of active regions in the
subsurface layers. The initial results show that large active regions are formed by repeated magnetic flux emergence from
the deep interior, and that their roots are at least 50 Mm deep. The active regions change the temperature structure and flow
dynamics of the upper convection zone, forming large circulation cells of converging flows. The helioseismic observations
also indicate that the processes of magnetic energy release, flares and coronal mass ejections, might be associated with strong
(1–2 km/s) shearing flows, 4–6 Mm below the surface. 相似文献
904.
905.
L.H. Deng Z.Q. Qu T. Liu W.J. Huang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
We investigate the north–south (N–S) asynchrony of the polar faculae and compare it with the hemispheric asynchrony of solar activity at low latitudes. We find that, (1) both the solar activity at high and low latitudes do not synchronously occur in the northern and southern hemispheres, there is phase shifts between the two hemispheres; (2) the N–S asynchrony of the polar faculae is a function of latitudes, implying that the asynchrony of the polar faculae between the two hemispheres is related to the hemispheric asymmetry and latitudinal distribution of the polar faculae. 相似文献
906.
A simplified data assimilation method for reconstructing time-series MODIS NDVI data 总被引:2,自引:0,他引:2
Juan Gu Xin Li Chunlin Huang Gregory S. Okin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The Normalized Difference Vegetation Index (NDVI) is an important vegetation index, widely applied in research on global environmental and climatic change. However, noise induced by cloud contamination and atmospheric variability impedes the analysis and application of NDVI data. In this work, a simplified data assimilation method is proposed to reconstruct high-quality time-series MODIS NDVI data. We extracted 16-Day L3 Global 1 km SIN Grid NDVI data sets for western China from MODIS vegetation index (VI) products (MOD13A2) for the period 2003–2006. NDVI data in the first three years (2003–2005) were used to generate the background field of NDVI based on a simple three-point smoothing technique, which captures annual features of vegetation change. NDVI data for 2006 were used to test our method. For every time step, the quality assurance (QA) flags of the MODIS VI products were adopted to empirically determine the weight between the background field and NDVI observations. Ultimately, more reliable NDVI data can be produced. The results indicate that the newly developed method is robust and effective in reconstructing high-quality MODIS NDVI time-series. 相似文献
907.
908.
主要对雷达中频信号数据录取和回放分系统研制可行性进行了分析,把系统分为录取和回放两部分,对初步实现方案和工程可行性进行了论证。 相似文献
909.
910.