全文获取类型
收费全文 | 4013篇 |
免费 | 740篇 |
国内免费 | 618篇 |
专业分类
测绘学 | 40篇 |
大气科学 | 291篇 |
地球物理 | 1623篇 |
地质学 | 1332篇 |
海洋学 | 672篇 |
天文学 | 603篇 |
综合类 | 336篇 |
自然地理 | 474篇 |
出版年
2024年 | 13篇 |
2023年 | 40篇 |
2022年 | 108篇 |
2021年 | 135篇 |
2020年 | 132篇 |
2019年 | 147篇 |
2018年 | 140篇 |
2017年 | 145篇 |
2016年 | 139篇 |
2015年 | 144篇 |
2014年 | 199篇 |
2013年 | 219篇 |
2012年 | 204篇 |
2011年 | 179篇 |
2010年 | 211篇 |
2009年 | 302篇 |
2008年 | 262篇 |
2007年 | 286篇 |
2006年 | 229篇 |
2005年 | 208篇 |
2004年 | 214篇 |
2003年 | 191篇 |
2002年 | 160篇 |
2001年 | 146篇 |
2000年 | 191篇 |
1999年 | 166篇 |
1998年 | 168篇 |
1997年 | 122篇 |
1996年 | 114篇 |
1995年 | 95篇 |
1994年 | 79篇 |
1993年 | 59篇 |
1992年 | 63篇 |
1991年 | 41篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有5371条查询结果,搜索用时 0 毫秒
131.
从若干方面的研究结果揭示了黄河流域水循环发生的巨大变化.水循环是水资源科学评价与合理开发利用的基本依据.水循环主要要素的变化取决于气候条件的变化与人类活动的影响.对前者宜采用适应性对策,在研究气候变化的基础上,分析水循环变动的规律并预测其趋势,制定相应的适应性措施;对于后者则应加强水资源开发利用的科学管理,以维持流域天然水资源的可更新(可再生)性. 相似文献
132.
133.
134.
山西大同-阳高地震活动背景 总被引:2,自引:1,他引:2
通过对大同盆地历史地震活动及大同盆地历史地震活动与华北地震区、山西地震带强震活动的关系的研究,得出山西大同-阳高1989年6.1级地震活动是这一地区历史地震的延续,是华北北部中强地震活动的重要组成部分,具有广义前震的重要意义,其后对应发生的河北张北6.2级地震。标志着华北地震区的地震活动期已进入尾声。 相似文献
135.
136.
Hege Fonneland-Jorgensen Harald Furnes Karlis Muehlenbachs Yildirim Dilek 《Island Arc》2005,14(4):517-541
Abstract The Solund‐Stavfjord ophiolite complex (SSOC) in western Norway represents a remnant of the Late Ordovician oceanic lithosphere, which developed in an intermediate‐ to fast‐spreading Caledonian back‐arc basin. The internal architecture and magmatic features of its crustal component suggest that the SSOC has a complex, multistage sea floor spreading history in a supra‐subduction zone environment. The youngest crustal section associated with the propagating rift tectonics consists of a relatively complete ophiolite pseudostratigraphy, including basaltic volcanic rocks, a transition zone between the sheeted dyke complex and the extrusive sequence, sheeted dykes, and high‐level isotropic gabbros. Large‐scale variations in major and trace element distributions indicate significant remobilization far beyond that which would result from magmatic processes, as a result of the hydrothermal alteration of crustal rocks. Whereas K2O is strongly enriched in volcanic rocks of the extrusive sequence, Cu and Zn show the largest enrichment in the dyke complex near the dyke–volcanic transition zone or within this transition zone. The δ18O values of the whole‐rock samples show a general depletion structurally downwards in the ophiolite, with the largest and smallest variations observed in volcanic rocks and the transition zone, respectively. δ18O values of epidote–quartz mineral pairs indicate 260–290°C for volcanic rocks, 420°C for the transition zone, 280–345°C for the sheeted dyke complex and 290–475°C for the gabbros. The 87Sr/86Sr isotope ratios show the widest range and highest values in the extrusive rocks (0.70316–0.70495), and generally the lowest values and the narrowest range in the sheeted dyke complex (0.70338–0.70377). The minimum water/rock ratios calculated show the largest variations in volcanic rocks and gabbros (approximately 0–14), and generally the lowest values and range in the sheeted dyke complex (approximately 1–3). The δD values of epidote (?1 to ?12‰), together with the δ18O calculated for Ordovician seawater, are similar to those of present‐day seawater. Volcanic rocks experienced both cold and warm water circulation, resulting in the observed K2O‐enrichment and the largest scatter in the δ18O values. As a result of metal leaching in the hot reaction zone above a magma chamber, Zn is strongly depleted in the gabbros but enriched in the sheeted dyke complex because of precipitation from upwelling of discharged hydrothermal fluids. The present study demonstrates that the near intact effect of ocean floor hydrothermal activity is preserved in the upper part of the SSOC crust, despite the influence of regional lower greenschist facies metamorphism. 相似文献
137.
138.
The swing of the main channel of the Qiantang River is controlled by the high-water and low-water changes in the river, as well as the impact of large-scale reclamation of tidal flats. Its evolution in modern times is the result of the combined functions of natural and man-made factors. This paper analyzes the cause of the formation of the South Channel and Xisan Tidal Furrow and proposes the regulation principle of “To regulate the river and reclaim tidal flats by taking the advantage of local topography”. It is suggested to cut off the South Channel and Xisan Tidal Furrow completely to restrict the swing of the main channel and to increase the reclamation area of the tidal flat at the same time. 相似文献
139.
140.