全文获取类型
收费全文 | 8907篇 |
免费 | 2197篇 |
国内免费 | 640篇 |
专业分类
测绘学 | 39篇 |
大气科学 | 20篇 |
地球物理 | 7144篇 |
地质学 | 2781篇 |
海洋学 | 417篇 |
天文学 | 25篇 |
综合类 | 410篇 |
自然地理 | 908篇 |
出版年
2024年 | 5篇 |
2023年 | 65篇 |
2022年 | 209篇 |
2021年 | 273篇 |
2020年 | 333篇 |
2019年 | 395篇 |
2018年 | 316篇 |
2017年 | 288篇 |
2016年 | 260篇 |
2015年 | 333篇 |
2014年 | 421篇 |
2013年 | 454篇 |
2012年 | 506篇 |
2011年 | 543篇 |
2010年 | 440篇 |
2009年 | 504篇 |
2008年 | 526篇 |
2007年 | 651篇 |
2006年 | 677篇 |
2005年 | 555篇 |
2004年 | 568篇 |
2003年 | 492篇 |
2002年 | 408篇 |
2001年 | 299篇 |
2000年 | 303篇 |
1999年 | 257篇 |
1998年 | 247篇 |
1997年 | 207篇 |
1996年 | 233篇 |
1995年 | 203篇 |
1994年 | 193篇 |
1993年 | 173篇 |
1992年 | 108篇 |
1991年 | 68篇 |
1990年 | 47篇 |
1989年 | 51篇 |
1988年 | 43篇 |
1987年 | 29篇 |
1986年 | 23篇 |
1985年 | 7篇 |
1984年 | 1篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 16篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
Seismic and drilling well data were used to examine the occurrence of multiple stratigraphic unconformities in the Tarim Basin, NW China. The Early Cambrian, the Late Ordovician and the late Middle Devonian unconformities constitute three important tectonic sequence boundaries within the Palaeozoic succession. In the Tazhong, Tabei, Tadong uplifts and the southwestern Tarim palaeo‐uplift, unconformities obviously belong to superimposed unconformities. A superimposed unconformity is formed by superimposition of unconformities of multiple periods. Areas where superimposed unconformities develop are shown as composite belts of multiple tectonic unconformities, and as higher uplift areas of palaeo‐uplifts in palaeogeomorphologic units. The contact relationship of unconformities in the lower uplift areas is indicative of truncation‐overlap. A slope belt is located below the uplift areas, and the main and secondary unconformities are characterized by local onlap reflection on seismic profiles. The regional dynamics controlled the palaeotectonic setting of the Palaeozoic rocks in the Tarim Basin and the origin and evolution of the basin constrained deposition. From the Sinian to the Cambrian, the Tarim landmass and its surrounding areas belonged to an extensional tectonic setting. Since the Late Ordovician, the neighbouring north Kunlun Ocean and Altyn Ocean was transformed from a spreading ocean basin to a closed compressional setting. The maximum compression was attained in the Late Ordovician. The formation of a tectonic palaeogeomorphologic evolution succession from a cratonic margin aulacogen depression to a peripheral foreland basin in the Early Caledonian cycle controlled the deposition of platform, platform margin, and deep‐water basin. Tectonic uplift during the Late Ordovician resulted in a shallower basin which was followed by substantial erosion. Subsequently, a cratonic depression and peripheral or back‐arc foreland basin began their development in the Silurian to Early–Middle Devonian interval. In this period, the Tabei Uplift, the Northern Depression and the southern Tarim palaeo‐uplift showed obvious control on depositional systems, including onshore slope, shelf and deep‐water basin. The southern Tarim Plate was in a continuous continental compressional setting after collision, whereas the southern Tianshan Ocean began to close in the Early Ordovician and was completely closed by the Middle Devonian. At the same time, further compression from peripheral tectonic units in the eastern and southern parts of the Tarim Basin led to the expansion of palaeo‐uplift in the Late Devonian–Early Carboniferous interval, and the connection of the Tabei Uplift and Tadong Uplift, thus controlling onshore, fluvial delta, clastic coast, lagoon‐bay and shallow marine deposition. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
94.
基于四川防震减灾信息网以及中国地震台网中心、中国地震信息网、国家地震科学数据共享中心提供的汶川8.0级地震目录资料,对2008年S月12日至2010年3月1日共1613次3.0级及以上余震的地震序列进行了时空分布分析。结果表明:汶川8.0级地震的余震大致可分为7个阶段,主震后18天应列为大地震强余震发生的警戒时间;地震序列的b值为0.751,印证了在类型相同的情况下主震震级越大b值越高的观点;地震序列的P值为1.117,与全球地震衰减速率相当;汶川地震的余震分布主要沿龙门山断裂走向北东向扩展,且具有明显分区性,自南向北分为南、中、北3区段,南区为地震起始破裂段,地震后期余震则主要分布在北区;震源深度分布在10~40km,集中在10~20km,表明龙门山断裂主要发生在中上地壳,且震源深度由南向北呈现逐渐变浅的趋势;震源深度扩展,南区呈明显脉冲状,中区主要是依次由15、30、25km深度向深、浅层同时扩展,北区余震深度分布呈“乙”字型,最后稳定在15km左右。 相似文献
95.
96.
97.
98.
介绍了时间域拉东正反变换的基本原理及该项技术在地震数据处理中的应用。以Ng和Perz的算法为基础,以开发地震勘探处理与解释系统为实例,解决了实验中遇到的拉东正变换时收敛精度、反变换数据无损还原和截断信号引起的能量扩散、低信噪比情况下的滤波等问题,进一步研究了改进算法在其他地形下应用问题。 相似文献
99.
100.