全文获取类型
| 收费全文 | 51605篇 |
| 免费 | 9233篇 |
| 国内免费 | 11325篇 |
专业分类
| 测绘学 | 4359篇 |
| 大气科学 | 5920篇 |
| 地球物理 | 11140篇 |
| 地质学 | 30109篇 |
| 海洋学 | 5333篇 |
| 天文学 | 3425篇 |
| 综合类 | 3606篇 |
| 自然地理 | 8271篇 |
出版年
| 2024年 | 174篇 |
| 2023年 | 500篇 |
| 2022年 | 1331篇 |
| 2021年 | 1564篇 |
| 2020年 | 1649篇 |
| 2019年 | 2030篇 |
| 2018年 | 1599篇 |
| 2017年 | 1826篇 |
| 2016年 | 1994篇 |
| 2015年 | 2191篇 |
| 2014年 | 2724篇 |
| 2013年 | 2712篇 |
| 2012年 | 3016篇 |
| 2011年 | 3269篇 |
| 2010年 | 2787篇 |
| 2009年 | 3386篇 |
| 2008年 | 3342篇 |
| 2007年 | 3774篇 |
| 2006年 | 3610篇 |
| 2005年 | 3129篇 |
| 2004年 | 2956篇 |
| 2003年 | 2831篇 |
| 2002年 | 2488篇 |
| 2001年 | 2176篇 |
| 2000年 | 2048篇 |
| 1999年 | 1926篇 |
| 1998年 | 1695篇 |
| 1997年 | 1490篇 |
| 1996年 | 1391篇 |
| 1995年 | 1160篇 |
| 1994年 | 1154篇 |
| 1993年 | 992篇 |
| 1992年 | 790篇 |
| 1991年 | 554篇 |
| 1990年 | 502篇 |
| 1989年 | 386篇 |
| 1988年 | 303篇 |
| 1987年 | 194篇 |
| 1986年 | 140篇 |
| 1985年 | 87篇 |
| 1984年 | 40篇 |
| 1983年 | 30篇 |
| 1982年 | 34篇 |
| 1981年 | 22篇 |
| 1980年 | 26篇 |
| 1979年 | 33篇 |
| 1978年 | 39篇 |
| 1977年 | 25篇 |
| 1975年 | 4篇 |
| 1954年 | 26篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
51.
52.
53.
The study of the chemical stability of vitreous material in aqueous media is well‐established. There has to date been little consideration of the implications of variations in the chemical durability of tephra in Quaternary tephrochronology. Chemical alteration can take the form of cationic leaching from the matrix, or complete destruction of the silica network, either of which could constrain the ability to chemically identify distal tephra. Here we apply established models of vitreous durability to the published chemical analyses of a large number of Icelandic tephras in order to predict their relative durabilities under equivalent conditions. This suggests that some important tephras have relatively poor chemical stability, and that rhyolitic tephras are, in general, more stable than basaltic. We conclude that tephras should be expected to show predictable differential chemical stability in the post‐depositional environment. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
54.
55.
56.
Hong-Qi Zhang Xing-Ming Bao Yin Zhang Ji-Hong Liu Shu-Dong Bao Yuan-Yong Deng Wei Li Jie Chen Jin-Ping Dun Jiang-Tao Su Juan Guo Xiao-Fan Wang Ke-Liang Hu Gang-Hua Lin Dong-Guang WangNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(6):491-494
We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle. 相似文献
57.
在常规照相天体测量工作中 ,对暗天体的定位是采用逐级定标星过渡的方法实现的。由于星表系统差和局部差的存在 ,最终定位结果可能包含难以把握的误差积累。在CCD小视场观测情况下时常难以找到足够数量的定标星。鉴于此 ,推导了CCD观测联合平差方法的严格矢量表达式 ,以期通过共同星的过渡 ,实现大天区统一平差。原理上此方法可实现相对于河外天体的定位 ,以削弱星表系统差和局部差对定位结果的影响。讨论了CCD联合平差方法实现中的问题 ,包括底片常数模型选择、切点位置改正、共同星的较差改正和法方程解算方法等 ,并分析了具体的处理措施。用实例初步检验了CCD联合平差方法的效果 ,表明通过对多张CCD观测的联合平差 ,可以削弱单张CCD观测参考星数目过少、单张CCD观测参考星分布不均、个别参考星存在位置偏差和局部区域参考星存在系统性位置偏差等不利因素对归算结果的影响 ,进而达到扩大视场和提高归算精度的目的 相似文献
58.
59.
60.
We study morphology and luminosity segregation of galaxies in groups. We analyze the two catalogs of (∼2×400) groups which
have been identified in the Nearby Optical Galaxy sample, by means of hierarchical and percolation `friends-of-friends' methods.
We find that earlier-type (brighter) galaxies are more clustered and lie closer to the group centers, both in position and
in velocity, than later-type (fainter) galaxies. Spatial segregations are stronger than kinematical segregations. These effects
are generally detected at the ≳3-sigma level, with the exception of morphological segregation in velocity, which is the weakest
effect. Our main results are confirmed by the analysis of statistically more reliable groups (with at least five members),
and are strengthened by the detection of segregation in both hierarchical and percolation catalogs. Luminosity segregation
is shown to be independent of morphology segregation. Our conclusions agree with a continuum of segregation properties of
galaxies in systems, from low-mass groups to massive clusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献