全文获取类型
收费全文 | 11976篇 |
免费 | 1962篇 |
国内免费 | 3167篇 |
专业分类
测绘学 | 358篇 |
大气科学 | 505篇 |
地球物理 | 2800篇 |
地质学 | 8038篇 |
海洋学 | 615篇 |
天文学 | 1447篇 |
综合类 | 545篇 |
自然地理 | 2797篇 |
出版年
2024年 | 20篇 |
2023年 | 123篇 |
2022年 | 358篇 |
2021年 | 460篇 |
2020年 | 507篇 |
2019年 | 540篇 |
2018年 | 532篇 |
2017年 | 423篇 |
2016年 | 547篇 |
2015年 | 576篇 |
2014年 | 783篇 |
2013年 | 885篇 |
2012年 | 737篇 |
2011年 | 823篇 |
2010年 | 734篇 |
2009年 | 927篇 |
2008年 | 907篇 |
2007年 | 966篇 |
2006年 | 975篇 |
2005年 | 751篇 |
2004年 | 675篇 |
2003年 | 610篇 |
2002年 | 548篇 |
2001年 | 455篇 |
2000年 | 416篇 |
1999年 | 350篇 |
1998年 | 299篇 |
1997年 | 217篇 |
1996年 | 207篇 |
1995年 | 135篇 |
1994年 | 123篇 |
1993年 | 94篇 |
1992年 | 98篇 |
1991年 | 57篇 |
1990年 | 66篇 |
1989年 | 48篇 |
1988年 | 44篇 |
1987年 | 18篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 5篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Ellerman bombs and type Ⅱ white-light flares share many common features despite the large energy gap between them.Both are considered to result from local heation in the solar lower atmosphere.This paper presents numerical simulations of magnetic reconnection occurring in such a deep atmosphere,with the aim to account for the common features of the two phenomena.Our numerical results manifest the following two typical characteristics of the assumed reconnection process:(1)magnetic reconnection saturates in-600-900s,which is just the lifetime of the two phenomens;(2)ionization in the upper chromosphere consumes quite a large part of the energy released through reconnection,making the heation effect most significant in the lower chromosphere.The applicationof the reconnection model to the two phenomena is discussed in detail. 相似文献
52.
C. Debi Prasad Ashok Ambastha Nandita Srivastava Sushanta C. Tripathy Mona J. Hagyard 《Journal of Astrophysics and Astronomy》1997,18(1):39-55
Super-active region NOAA 6555 was highly flare productive during the period March 21st–27th, 1991 of its disk passage. We
have st udied its chromospheric activity using high spatial resolution Hα filtergrams taken at Udaipur along with MSFC vector
magnetograms. A possible relationship of flare productivity and the variation in shear has been explored. Flares were generally
seen in those subareas of the active region which possessed closed magnetic field configuration, whereas only minor flares
and/or surges occurred in subareas showing open magnetic field configuration. Physical mechanisms responsible for the observed
surges are also discussed. 相似文献
53.
54.
在太阳活动区的物理研究中,特别是在二维动力学光谱分析中,迫切需要相应活动区的磁图资料。本文介绍了在太阳光谱仪的入射狭缝后安装一种新型偏振器进行活动区二维磁场观测的新方法。这种方法不仅能获得日面上任一点的磁场强度,且可快速获得活动区的纵向场磁图。除此之外,还可利用多条谱线的同时观测,获得有关磁力线管结构等方面的资料。 相似文献
55.
Motivated by recent high-resolution observations of the solar surface, we investigate the problem of non-linear magnetoconvection in a three-dimensional compressible layer. We present results from a set of numerical simulations which model the situation in which there is a weak imposed magnetic field. This weak-field regime is characterized by vigorous granular convection and spatially intermittent magnetic field structures. When the imposed field is very weak, magnetic flux tends to accumulate at the edges of the convective cells, where it forms compact, almost 'point-like' structures which are reminiscent of those observed in the quiet Sun. If the imposed field is slightly stronger, there is a tendency for magnetic flux to become concentrated into 'ribbon-like' structures which are comparable to those observed in solar plages. The dependence of these simulations upon the strength of the imposed magnetic field is analysed in detail, and the concept of the fractal dimension is used to make a further, more quantitative comparison between these simulations and photospheric observations. 相似文献
56.
The process of non-linear ambipolar diffusion in the region overlying the solar surface can be an effective mechanism for producing sharp magnetic structures and current sheets. These may be the sites responsible for the occurrence of connectivity of magnetic field lines, and the subsequent explosive input of energy for heating of some of the features in the atmosphere of the Sun.. 相似文献
57.
58.
We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase
of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for
by the field growth theories. 相似文献
59.
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
60.