全文获取类型
收费全文 | 2873篇 |
免费 | 433篇 |
国内免费 | 446篇 |
专业分类
测绘学 | 244篇 |
大气科学 | 124篇 |
地球物理 | 410篇 |
地质学 | 934篇 |
海洋学 | 225篇 |
天文学 | 1648篇 |
综合类 | 79篇 |
自然地理 | 88篇 |
出版年
2024年 | 19篇 |
2023年 | 49篇 |
2022年 | 51篇 |
2021年 | 75篇 |
2020年 | 108篇 |
2019年 | 107篇 |
2018年 | 61篇 |
2017年 | 88篇 |
2016年 | 94篇 |
2015年 | 83篇 |
2014年 | 143篇 |
2013年 | 109篇 |
2012年 | 126篇 |
2011年 | 108篇 |
2010年 | 125篇 |
2009年 | 199篇 |
2008年 | 157篇 |
2007年 | 213篇 |
2006年 | 189篇 |
2005年 | 184篇 |
2004年 | 223篇 |
2003年 | 175篇 |
2002年 | 156篇 |
2001年 | 150篇 |
2000年 | 134篇 |
1999年 | 130篇 |
1998年 | 142篇 |
1997年 | 65篇 |
1996年 | 44篇 |
1995年 | 56篇 |
1994年 | 53篇 |
1993年 | 25篇 |
1992年 | 28篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有3752条查询结果,搜索用时 15 毫秒
21.
22.
介绍了太阳22周峰年期间云南天文台米波射电频谱仪的观测结果。主要对1557个单个Spike的时间和频率分布作了统计分析,着重指出太阳快速精细结构的观测特征并定性地指出其产生机制。 相似文献
23.
24.
本文介绍了1994年7月SL-9彗星撞击木星期间3.6cm和12cm射电连续谱观测的结果.在3.6cm波长上,撞击事件无明显的视效应,在12cm波长上,木星的射电平均视流量增加约20%. 相似文献
25.
26.
27.
28.
Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggest that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field. 相似文献
29.
C. Caroubalos D. Maroulis N. Patavalis J.-L. Bougeret G. Dumas C. Perche C. Alissandrakis A. Hillaris X. Moussas P. Preka-Papadema A. Kontogeorgos P. Tsitsipis G. Kanelakis 《Experimental Astronomy》2001,11(1):23-32
We present the new solar radiospectrograph of the University of Athensoperating at the Thermopylae Station since 1996. Observations cover thefrequency range from 110 to 688 MHz. The radiospectrograph has a 7-meterparabolic antenna and two receivers operating in parallel. One is a sweepfrequency receiver and the other a multichannel acousto-optical receiver.The data acquisition system consists of a front-end VME based subsystem anda Sun Sparc-5 workstation connected through Ethernet. The two subsystems areoperated using the VxWorks real-time package. The daily operation is fullyautomated: pointing of the antenna to the sun, starting and stopping theobservations at pre-set times, data acquisition, data compression by`silence suppression', and archiving on DAT tapes. The instrument can beused either by itself to study the onset and evolution of solar radio bursts or in conjunction with other instruments including theNançay Decametric Array and the WIND/WAVES RAD1 and RAD2 low frequencyreceivers to study associated interplanetary phenomena. 相似文献
30.
OQ208 is used ore and more frequently as a VLBI calibrator of flux density. A VLBI image of OQ208 at 5 GHz is firstly provided in this paper. Its structure consists of a compact core and a component. The angular distance between the core and the component is about 7 milli-arcsecond; the position angle is −125 degrees. In principle, OQ208 is not an ideal VLBI calibrator of flux density. This paper provides the structural information for correcting the structure effect when OQ208 is to be used as a calibrator. 相似文献