全文获取类型
收费全文 | 2010篇 |
免费 | 309篇 |
国内免费 | 544篇 |
专业分类
测绘学 | 57篇 |
大气科学 | 113篇 |
地球物理 | 567篇 |
地质学 | 1312篇 |
海洋学 | 167篇 |
天文学 | 446篇 |
综合类 | 58篇 |
自然地理 | 143篇 |
出版年
2024年 | 8篇 |
2023年 | 16篇 |
2022年 | 55篇 |
2021年 | 61篇 |
2020年 | 75篇 |
2019年 | 74篇 |
2018年 | 60篇 |
2017年 | 83篇 |
2016年 | 96篇 |
2015年 | 122篇 |
2014年 | 129篇 |
2013年 | 103篇 |
2012年 | 102篇 |
2011年 | 112篇 |
2010年 | 100篇 |
2009年 | 140篇 |
2008年 | 141篇 |
2007年 | 163篇 |
2006年 | 135篇 |
2005年 | 149篇 |
2004年 | 124篇 |
2003年 | 97篇 |
2002年 | 93篇 |
2001年 | 69篇 |
2000年 | 79篇 |
1999年 | 67篇 |
1998年 | 42篇 |
1997年 | 43篇 |
1996年 | 44篇 |
1995年 | 45篇 |
1994年 | 44篇 |
1993年 | 26篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 17篇 |
1989年 | 23篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1978年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有2863条查询结果,搜索用时 390 毫秒
261.
We have carried out systematic surveys for small bright-rimmed clouds associated with IRAS point sources in/around HII regions. They are candidate sites for star formation due to radiation-driven implosion. 相似文献
262.
V. A. Dogiel A. V. Gurevich Ya. N. Istomin K. P. Zybin 《Astrophysics and Space Science》2005,297(1-4):201-211
Acceleration of charged particles by neutral gas turbulence in giant molecular clouds is considered. The gamma-ray emission
from these clouds is estimated. It is shown that molecular clouds can be the counterparts of some of unidentified sources. 相似文献
263.
We report first evidence for a new unidentified and variable MeV source, located near the galactic plane at (l,b)∼(284.5°,
2.5°). The source, GRO J1036-55, is found at a significance level of ∼5.6σ by COMPTEL in its 3–10 MeV band. The energy spectrum indicates a spectral maximum at 3–4.3 MeV with a steep slope at higher
energies. Since the COMPTEL 3–4.3 MeV data contain contamination by an instrumental background line, we performed several
consistency checks, which all are consistent with an astrophysical nature of this emission feature. 相似文献
264.
Saikia D. J. Shastri P. Cornwell T. J. Junor W. Muxlow T. W. B. 《Journal of Astrophysics and Astronomy》1989,10(2):203-235
As part of our study to understand the nature of extragalactic radio sources which are very asymmetric in the surface brightness
of the two lobes, often with radio emission on only one side of the nucleus, we have observed a large number of them with
high angular resolution and good surface brightness sensitivity at radio frequencies. In this paper we present VLA and MERLIN
observations of 15 such sources. We discuss their observed structures and spectra, and possible explanations for their morphologies.
We report evidence of a possible correlation between the hot-spot brightness ratio and the degree of core prominence, used
as a Statistical measure of source orientation, suggesting that relativistic beaming of the hot-spot emission does play a
significant role in the observed brightness asymmetry. To explain the apparently one-sided sources within the relativistic
beaming framework, the velocities required are in the range of 0.2 to 0.8c. We discuss the possibility that the lobe which is seen to the south of the jet in 3C273 is the counter-lobe seen in projection.
We also draw-attention to a number of one-sided sources with very weak cores, and discuss their possible nature. 相似文献
265.
266.
在浙西北双溪坞群和上墅组火山岩系获得较可靠的Sm-Nd同位素年龄的基础上,本文进一步做了Nd、Sr同位素地球化学研究。∈Nd(T)和∈Sr(T)示踪判别了该区前震旦纪火山岩浆源区特征及其物质来源。同时,Nd同位素模式年龄为该区存在更古老基底提供了重要的地质年代信息。 相似文献
267.
Zhi-qiang Shen Tong-shan Wan Xiao-yu Hong Dong-rong Jiang Shi-guang Liang 《Chinese Astronomy and Astrophysics》1996,20(4):415-425
This paper describes a 5 GHz VLBI survey in the southern hemisphere. The first observation of 23 extragalactic radio sources was conducted in November 1992. Twenty VLBI images were obtained, of which 15 sources show core-jet structure, one has a two-sided jet, and three sources are unresolved. No compact double source was found. Eleven of the 16 sources with core-jet (including a two-aided jet) show evidence of jet bending. In addition, four sources appear to be superluminal, of which three sources are new. 相似文献
268.
能谱仅反映了高能天体辐射的部分性质,而高能X射线辐射的时变可以反映致密天体的动态性质。因此,在构造高能辐射的理论模型时,既要考虑X辐射的能谱性质,也要考虑其时变性质。特别对高能天体X辐射的快速光变,一般认为其发生在致密天体附近,致密天体快速光变的研究可以揭示出致密天体附近的物理性质,因此,时变可以对X辐射模型给以很强的限制。X射线源不同能量光子到达观测者的时间差称为X射线辐射的时延。介绍了高能X辐射时变中的时延分析方法及其最新发展,综述了致密双星系统中黑洞侯选林和中子星的时延现象,并简单介绍了为解释这些现象所发展的模型,以及时延对模型的限制。 相似文献
269.
K. A. Postnov 《Astronomy Letters》2003,29(6):372-373
The empirically found universal power-law form of the X-ray luminosity function for a population of high-mass X-ray binaries in galaxies can be explained by the fundamental mass-luminosity and mass-radius relations for massive stars. 相似文献
270.
We have reinvestigated the reported tendency for the extended radio structures associated with bright elliptical galaxies
to be oriented preferentially along the optical minor axes. It is found that such a tendency exists only for those galaxies
in which the compact radio cores coincident with their nuclei are quite prominent. If the galaxies are divided into two groups
according to whether their cores account for less than or greater than 10 per cent of the total flux density at 2.7 GHz, the
angle Φ (between the radio axis and the optical minor axis) appears to be uniformly distributed between 0‡ and 90‡ for the
former, but is nearly always < 30‡ for the latter group. One possible explanation is that the radio emission from compact
cores suffers thermal absorption by ionized gas that is distributed differently in the two groups. 相似文献