全文获取类型
收费全文 | 4561篇 |
免费 | 986篇 |
国内免费 | 1328篇 |
专业分类
测绘学 | 384篇 |
大气科学 | 936篇 |
地球物理 | 992篇 |
地质学 | 2491篇 |
海洋学 | 741篇 |
天文学 | 161篇 |
综合类 | 478篇 |
自然地理 | 692篇 |
出版年
2024年 | 23篇 |
2023年 | 85篇 |
2022年 | 255篇 |
2021年 | 254篇 |
2020年 | 241篇 |
2019年 | 272篇 |
2018年 | 313篇 |
2017年 | 257篇 |
2016年 | 311篇 |
2015年 | 274篇 |
2014年 | 326篇 |
2013年 | 291篇 |
2012年 | 299篇 |
2011年 | 317篇 |
2010年 | 325篇 |
2009年 | 337篇 |
2008年 | 296篇 |
2007年 | 243篇 |
2006年 | 197篇 |
2005年 | 190篇 |
2004年 | 149篇 |
2003年 | 142篇 |
2002年 | 154篇 |
2001年 | 147篇 |
2000年 | 145篇 |
1999年 | 170篇 |
1998年 | 133篇 |
1997年 | 121篇 |
1996年 | 99篇 |
1995年 | 92篇 |
1994年 | 70篇 |
1993年 | 76篇 |
1992年 | 52篇 |
1991年 | 40篇 |
1990年 | 27篇 |
1989年 | 34篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1958年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有6875条查询结果,搜索用时 16 毫秒
111.
112.
沿贺兰山台褶带北部西缘深大断裂带分布的小松山超基性杂岩体属岩浆结晶分异形成的似层状含铬岩体,岩组分析表明岩体中橄榄石具有高度的定向性。笔者通过研究认为,这种定向性系岩浆上侵过程中的流动分异作用影响造成,反映了小松山岩体系构造动荡环境下的产物。 相似文献
113.
邛崃地震发生后,成都市地震局很快做出反应,及时开展了地震考察并做出了正确的震后趋势判断,取得了较好的社会效益。 相似文献
114.
115.
This paper proposes a simple lattice model for collapse analysis of RC bridges subjected to earthquakes by using the extended distinct element method (EDEM). In the model, a concrete element consists of lumped masses connected to one another by springs, and a reinforcement bar is represented by a discrete model or an integrated model. The proposed lattice model is simple but its parameters are reasonably defined. It has fewer element nodes and connecting springs, which will be of benefit by shortening the CPU time. The processes to determine the initial stiffness of concrete and steel springs, the parameters of the constitutive model and the fracture criteria for springs are described. A re‐contact spring model is also proposed to simulate the re‐contact of the concrete after fracture of springs; and a general grid searching method is used to decrease the CPU time for judging re‐contact after fracture. The lattice model is assessed by numerical simulations and experiments. As an application, a damaged single‐column pier subjected to the Kobe Earthquake in 1995 is analysed by EDEM with the proposed model. The simulation results indicate that the proposed model predicts well qualitatively the collapse process of RC bridges. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
116.
117.
118.
Cretaceous deformation history of the middle Tan-Lu fault zone in Shandong Province, eastern China 总被引:13,自引:0,他引:13
Based on field analysis of fault-slip data from different rock units of the Cretaceous basins along the middle part of the Tan-Lu fault zone (Shandong Province, eastern China), we document polyphase tectonic stress fields and address the changes in sense of motion of the Tan-Lu fault zone during the Cretaceous. The Cretaceous deformation history of the Tan-Lu fault zone can be divided into four main stages. The first stage, during the earliest Cretaceous, was dominated by N-S extension responsible for the formation of the Jiaolai basin. We interpret this extension to be related to dextral strike-slip pull-apart opening guided by the Tan-Lu fault zone. The second stage, during the middle Early Cretaceous, was overwhelmingly rift-dominated and characterized by widespread silicic to intermediate volcanism, normal faulting and basin subsidence. It was at this stage that the Tan-Lu-parallel Yi-Shu Rift was initiated by E-W to WNW-ESE extension. The tectonic regime then changed during the late Early Cretaceous to NW-SE-oriented transpression, causing inversion of the Early Cretaceous rift basin and sinistral slip along the Tan-Lu fault zone. During the Late Cretaceous, dextral activation of the Tan-Lu fault zone resulted in pull-apart opening of the Zhucheng basin, which was subsequently deformed by NE-SW compression. This deformation chronology of the Tan-Lu fault zone and the associated Cretaceous basins allow us to constrain the regional kinematic models as related to subduction along the eastern margin of Asia, or related to collision in the Tibet region. 相似文献
119.
北极涛动(Arctic Oscillation,简称AO)和南极涛动(Antarctic Oscillation,简称AAO)分别用于描述北半球和南半球热带外气候变率的主要模态,它们分别是北半球和南半球中纬度和高纬度之间气压变化的跷跷板结构.作者利用1958年1月~1999年12月的NCEP/NCAR全球再分析月平均资料、北极涛动指数IAO和南极涛动指数IAAO来研究AO和AAO的年变化特征以及AO和AAO与纬向平均的月平均各要素场的相关系数随纬度和月份的变化规律. 相似文献
120.