全文获取类型
收费全文 | 4287篇 |
免费 | 845篇 |
国内免费 | 1044篇 |
专业分类
测绘学 | 297篇 |
大气科学 | 842篇 |
地球物理 | 1253篇 |
地质学 | 2173篇 |
海洋学 | 523篇 |
天文学 | 152篇 |
综合类 | 428篇 |
自然地理 | 508篇 |
出版年
2024年 | 22篇 |
2023年 | 83篇 |
2022年 | 183篇 |
2021年 | 244篇 |
2020年 | 157篇 |
2019年 | 193篇 |
2018年 | 205篇 |
2017年 | 224篇 |
2016年 | 244篇 |
2015年 | 208篇 |
2014年 | 263篇 |
2013年 | 242篇 |
2012年 | 230篇 |
2011年 | 214篇 |
2010年 | 206篇 |
2009年 | 236篇 |
2008年 | 232篇 |
2007年 | 201篇 |
2006年 | 139篇 |
2005年 | 121篇 |
2004年 | 141篇 |
2003年 | 189篇 |
2002年 | 206篇 |
2001年 | 177篇 |
2000年 | 195篇 |
1999年 | 211篇 |
1998年 | 146篇 |
1997年 | 163篇 |
1996年 | 164篇 |
1995年 | 135篇 |
1994年 | 103篇 |
1993年 | 102篇 |
1992年 | 79篇 |
1991年 | 59篇 |
1990年 | 60篇 |
1989年 | 43篇 |
1988年 | 35篇 |
1987年 | 23篇 |
1986年 | 20篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1962年 | 4篇 |
1958年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有6176条查询结果,搜索用时 0 毫秒
961.
Nonsmooth dynamics prediction of measured bridge response involving deck‐abutment pounding 下载免费PDF全文
Earthquake‐induced deck‐abutment contact alters the boundary conditions at the deck level and might activate a different mechanical system than the one assumed during the design of the bridge. Occasionally this discrepancy between the assumed and the actual seismic behavior has detrimental consequences, for example, pier damage, deck unseating, or even collapse. Recently, an insightful shake‐table testing of a scaled deck‐abutment bridge model 1 , showed unexpected in‐plane rotations even though the deck was straight. These contact‐induced rotations produced significant residual displacements and damage to the piers and the bents. The present paper utilizes that experimental data to examine the validity and the limitations of a proposed nonsmooth dynamic analysis framework. The results show that the proposed approach satisfactorily captures the planar rigid‐body dynamics of the deck which is characterized by deck‐abutment contact. The analysis brings forward the role of friction on the physical mechanism behind the rotation of the deck, and underlines the importance of considering the frictional contact forces during deck‐abutment interaction even for straight bridges, which typically are neglected. Finally, the paper investigates the sensitivity of the rotation with respect to macroscopic contact parameters (i.e., the coefficient of friction and the coefficient of restitution). Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
962.
针对无人值守地震台因供电故障造成的观测数据质量问题,现阶段GPRS在地震台站的应用大多以手机短信呈现,无良好的可视化操作界面,设计开发一种底层基于STM32单片机,以GPRS为数据传输方式,Android手机APP为监控界面的智能电源控制系统。通过在河北省地震局石家庄中心台下属的深州郭家庄地震台进行应用,证明该电源控制系统能够保证观测设备的稳定运行,并为设备维护提供了保障和依据。 相似文献
963.
Natural Hazards - Coastal inundation due to storm tides is computed using ADvanced CIRCulation (ADCIRC) model along the east coast of India. Inland inundation due to storm tides is calculated every... 相似文献
964.
965.
Xianwu Shi Jufei Qiu Bingrui Chen Xiaojie Zhang Haoshuang Guo Jun Wang Zhuyuan Bei 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(5):627-640
Stochastic Environmental Research and Risk Assessment - Storm surges, which may cause considerable casualties and economic losses, are among the most serious natural disasters that threaten the... 相似文献
966.
“黄苔”是丝状绿藻大量增殖并漂浮聚集在水面的一种藻类水华,是乌梁素海面临的重大水环境问题之一。本研究基于文献数据整合和Landsat TM/OLI系列卫星影像反演,追溯了乌梁素海近35年(1986—2021年)的水质变化和“黄苔”暴发历程,通过相关性分析和多元线性回归等方法,分析了乌梁素海“黄苔”暴发的年际影响因子。乌梁素海水体化学需氧量、总氮(TN)、总磷(TP)浓度在年尺度上呈下降趋势,但仍处于富营养状态(TLI(∑)>50)。相关性分析结果表明,乌梁素海“黄苔”暴发面积与TP、TN、氨氮、气温呈显著正相关,与出水量、风速、沉水植被面积、入水量呈显著负相关;多元线性回归结果表明,沉水植被面积和出水量是影响乌梁素海“黄苔”暴发面积的主要因子。生态补水工程的实施增加了乌梁素海出入水量,降低了水体TP、TN浓度,也造成沉水植被退化,使“黄苔”暴发的扩张趋势得以遏制。然而,乌梁素海现有营养条件、基质条件仍适宜附着藻生长和“黄苔”暴发。在全球气候变化背景下,气温升高和风力减弱可能会加剧这一现象。建议采取多种措施以防控乌梁素海“黄苔”暴发,如生态补水、外源营养盐管控、沉水植被调控、引水活... 相似文献
967.
Developing land use scenario dynamics model by the integration of system dynamics model and cellular automata model 总被引:8,自引:1,他引:8
HE Chunyang SHI Peijun CHEN Jin Li Xiaobing PAN Yaozhong LI Jing LI Yuechen & LI Jinggang Key Laboratory of Environmental Change Natural Disaster Ministry of Education of China Beijing Normal University College of Resources Science & Technology Beijing Normal University Beijing China 《中国科学D辑(英文版)》2005,48(11):1979-1989
Models of land use change are useful tools for un-derstanding the analysis of the cause and conse-quences of land use changes, assessing the impacts of land use system on ecological system and supporting land use planning and policy[1,2]. Modeling land use scenario changes and its potential impacts on the structure and function of the ecosystem in the typical regions are regarded as one of the good ways to un-derstand the interactive mechanism between land use system and ecological system[3―10… 相似文献
968.
Channel change to regulated flows along large lowland rivers with cohesive bank materials has been investigated on the lower Welsh Dee, including the tidally influenced reach. Reduction of channel width has involved the formation of a 5–40m wide discontinuous bench, often linking ‘point’ and ‘concave’ locations. Map evidence shows that wide benches occur where historically the channel had migrated laterally; narrow benches were found at stable channel locations. Auger cores of the bench deposits clearly differentiated the two contrasting depositional environments within meandering rivers: ‘point bench’ and ‘concave bench’. Around an individual bend a morphologically continuous bench showed a gradient in sediment characteristics from coarser sediments (point locations) to finer organic deposits (concave locations); it also showed a topographic gradient, gaining 0.5m in elevation around the bend suggesting that bench accretion at concave locations is faster than at point locations in fluvially dominated reaches. Such patterns are suggested to have important implications for riparian ecosystems. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
969.
本文探讨了利用地震矩反演断裂形变带运动学参数的基本理论和方法,将其初步应用于鲜水河断裂形变带变形分析和运动机制的研究。结果表明,鲜水河断裂带呈现出走向拉伸、倾向压缩的形变格局,由地震矩反演的断裂带剪切形变速率(10.9mm/a)与用地质学估算方法(17mm/a)和现今地壳形变测量(8mm/a)的结果相当。同时,反演出的应变主方向能解释鲜水河断裂现今活动分段性特征以及多种滑动方式共存的现状,从而证明该方法是目前研究区域运动学问题切实有效的手段之一。 相似文献
970.