全文获取类型
| 收费全文 | 73637篇 |
| 免费 | 12687篇 |
| 国内免费 | 16930篇 |
专业分类
| 测绘学 | 5997篇 |
| 大气科学 | 9924篇 |
| 地球物理 | 15757篇 |
| 地质学 | 39762篇 |
| 海洋学 | 8294篇 |
| 天文学 | 7688篇 |
| 综合类 | 4982篇 |
| 自然地理 | 10850篇 |
出版年
| 2024年 | 201篇 |
| 2023年 | 601篇 |
| 2022年 | 1643篇 |
| 2021年 | 1956篇 |
| 2020年 | 2072篇 |
| 2019年 | 2349篇 |
| 2018年 | 2097篇 |
| 2017年 | 2336篇 |
| 2016年 | 2470篇 |
| 2015年 | 2739篇 |
| 2014年 | 3651篇 |
| 2013年 | 3927篇 |
| 2012年 | 4043篇 |
| 2011年 | 4303篇 |
| 2010年 | 3909篇 |
| 2009年 | 4778篇 |
| 2008年 | 4807篇 |
| 2007年 | 5375篇 |
| 2006年 | 5246篇 |
| 2005年 | 4863篇 |
| 2004年 | 4559篇 |
| 2003年 | 4155篇 |
| 2002年 | 3722篇 |
| 2001年 | 3323篇 |
| 2000年 | 3120篇 |
| 1999年 | 3094篇 |
| 1998年 | 2856篇 |
| 1997年 | 2288篇 |
| 1996年 | 2163篇 |
| 1995年 | 1849篇 |
| 1994年 | 1768篇 |
| 1993年 | 1691篇 |
| 1992年 | 1330篇 |
| 1991年 | 1005篇 |
| 1990年 | 787篇 |
| 1989年 | 573篇 |
| 1988年 | 451篇 |
| 1987年 | 267篇 |
| 1986年 | 163篇 |
| 1985年 | 151篇 |
| 1984年 | 84篇 |
| 1983年 | 88篇 |
| 1982年 | 74篇 |
| 1981年 | 45篇 |
| 1980年 | 54篇 |
| 1979年 | 48篇 |
| 1978年 | 50篇 |
| 1977年 | 42篇 |
| 1976年 | 17篇 |
| 1954年 | 18篇 |
排序方式： 共有10000条查询结果，搜索用时 234 毫秒
141.
142.
143.
144.
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
145.
146.
1 IntroductionAnicecoreobtainedfrom polarglaciersoricesheetsisoneofthemostimportantarchivestoreconstructpaleoclimaticandpaleoatmosphericcondition .Informationonpale o environmentcanbeextractedfromicecoresaschemicaland/orphysicalsignals.Amongthechemicalsignals,heavymetalsarenotedassignalsofterrestrialenvironmentalchangeandanthropogenicpollution (e.g .Murozumietal.1 969;NgandPatterson 1 981 ;Hongetal.1 994) .SinceconcentrationsofmostofthemetalsinpolarsnowincentralGreen landareatorbelowthepptl… 相似文献
147.
A. S. Oliveira J. E. Steiner D. Cieslinski 《Monthly notices of the Royal Astronomical Society》2003,346(3):963-967
The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is Pphot = 0.227(±14) d , while radial velocities suggest a period of P spec = 0.204(±13) d . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
148.
149.
150.
昆仑山口大地震与地形变异常的讨论 总被引：7，自引：5，他引：2
针对昆仑山口大地震，总结了多种地形变（大地测量）手段所显示的异常变化及其时空分布，结果显示：8．1级大震前存在空间尺度大，时间尺度的地形变前兆异常，简要介绍了相关的异常图像，给出了初步解释，并对未来震情的发展进行了探讨，认为近期内强震活动向华北迁移的可能性不大。 相似文献