全文获取类型
收费全文 | 4023篇 |
免费 | 371篇 |
国内免费 | 398篇 |
专业分类
测绘学 | 1237篇 |
大气科学 | 495篇 |
地球物理 | 301篇 |
地质学 | 893篇 |
海洋学 | 647篇 |
天文学 | 26篇 |
综合类 | 424篇 |
自然地理 | 769篇 |
出版年
2024年 | 17篇 |
2023年 | 60篇 |
2022年 | 149篇 |
2021年 | 178篇 |
2020年 | 182篇 |
2019年 | 251篇 |
2018年 | 125篇 |
2017年 | 243篇 |
2016年 | 219篇 |
2015年 | 238篇 |
2014年 | 262篇 |
2013年 | 281篇 |
2012年 | 317篇 |
2011年 | 288篇 |
2010年 | 213篇 |
2009年 | 183篇 |
2008年 | 211篇 |
2007年 | 194篇 |
2006年 | 195篇 |
2005年 | 137篇 |
2004年 | 134篇 |
2003年 | 106篇 |
2002年 | 102篇 |
2001年 | 76篇 |
2000年 | 62篇 |
1999年 | 53篇 |
1998年 | 49篇 |
1997年 | 50篇 |
1996年 | 53篇 |
1995年 | 31篇 |
1994年 | 31篇 |
1993年 | 27篇 |
1992年 | 16篇 |
1991年 | 17篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有4792条查询结果,搜索用时 15 毫秒
51.
According to the initial vision of "digital earth" (DE), the public should constitute a significant proportion of its users. However, to date, most of the studies and applications have focused on science, the private sector and government. A DE-supported online oceanic educational public service and popularization system, iOcean, is studied. First, the vision for the public’s engagement with "digital ocean" is described: an analysis is presented from four aspects, i.e., the space dimension, the time dimension, the state dimension and its relationship with human beings. Second, the technical framework of iOcean is discussed, including data updating and model computing, the data, the function, and the application layers. Third, two key technologies are studied in detail that will enable the construction of iOcean. More than half a million public viewers have used the current version’s website. Practical demonstrations show that iOcean can bring virtual oceans to web browsers and desktops and construct a bridge between government departments and the general public. 相似文献
52.
文中论述了海洋环境移动平台观测技术发展现状,强调移动平台观测技术的重要性。通过剖析移动平台观测技术谱系,从顶层设计、关键技术创新、平台载体系统集成及应用技术等方面,分析了未来技术发展趋势,提出了加强我国海洋环境移动平台观测技术的发展建议。 相似文献
53.
以三类内孤立波理论(Kd V、e Kd V和MCC)的适用性条件为依据,采用Morison和傅汝德-克雷洛夫公式分别计算Spar平台内孤立波水平力和垂向力,结合时域有限位移运动方程,建立了有限深两层流体中内孤立波与带分段式系泊索Spar平台相互作用的理论模型。以东沙群岛某海域实测内孤立波为对象,数值分析了在内孤立波作用下某经典式Spar平台的内孤立波动态载荷、运动响应及其系泊张力的变化特性。研究表明,内孤立波不仅会对Spar平台产生突发性冲击载荷,使其产生大幅度水平漂移运动,而且还会使其系泊张力显著增大。因此,在Spar平台等深海平台的设计应用中,内孤立波的影响不可忽视。 相似文献
54.
55.
Monitoring offshore platforms, long span bridges, high rise buildings, TV towers and other similar structures is essential for ensuring their safety in service. Continuous monitoring assumes even greater significance in the case of offshore platforms, which are highly susceptible to damage due to the corrosive environment and the continuous action of waves. Also, since a major part of the structure is under water and covered by marine growth, even a trained diver cannot easily detect damage in the structure. In the present work, vibration criterion is adopted for structural monitoring of jacket platforms. Artificial excitation of these structures is not always practicable and ambient excitation due to wind and waves may not be sufficient for collecting the required vibration data. Alternate methods can be adopted for the same purpose, for example, the application of an impact or a sudden relaxation of an applied force for exciting the structure. For jacket platforms, impact can be applied by gently pushing the structure at the fender while relaxation can be accomplished by pulling the structure and then suddenly releasing it using a tug or a supply vessel in both cases. The present study is an experimental investigation on a laboratory model of a jacket platform, for exploring the feasibility of adapting vibration responses due to impulse and relaxation, for structural monitoring. Effects of damage in six members of the platform as well as changes in deck masses were studied. A finite element model of the structure was used to analyze all the cases for comparison of the results as well as system identification. A data acquisition and analysis procedure for obtaining the response signatures of the platform due to the impulse and relaxation procedure was also developed for possible adoption in on-line monitoring of offshore platforms. From the study, it has been concluded that both impulse and relaxation responses are useful tools for monitoring offshore jacket platforms. The present work forms the basis for the development of an automated, on-line monitoring system for offshore platforms, using neural networks. 相似文献
56.
57.
南美洲成矿区带划分及其地质特征 总被引:2,自引:1,他引:2
南美洲是全球成矿规律研究的热点地区,区内优势矿产资源铜、铁、铝土矿、锡、铌、锂、金、银等在世界上占有重要地位,也是全球矿产勘查投资的重点地区。根据大地构造单元划分,结合实际矿床(点)空间分布、主要成矿类型及其成矿背景,对南美洲开展了三级成矿区带划分,共划分出2个Ⅰ级成矿区,9个Ⅱ级成矿省和42个Ⅲ级成矿带。阐述了南美洲成矿区带划分原则、命名规则、优势矿种、主要成矿时代等。以圭亚那地盾成矿省(Ⅱ-1)泛亚马孙成矿带(Ⅲ-2)为例,概述了Ⅲ级成矿带的优势矿种、矿床类型、赋矿岩系、控矿因素等,总结了区域构造演化、变质作用、岩浆活动等与成矿的关系。 相似文献
58.
空间位置服务平台的构架设计与服务接口实现 总被引:1,自引:0,他引:1
通过空间位置服务平台对位置服务领域中众多复杂的空间信息数据进行有效地整合和资源共享, 可以为用户提供综合性的位置应用和服务.利用基于空间信息网格(spatial information grid, SIG) 的分布式思想对空间位置服务平台的架构进行了模型设计和技术实现, 完成了地图数据和定位查询的分布式存储和检索.平台服务接口满足开放位置服务(openlocation service, OpenLS) 规范, 利用XML进行信息编码, 通过HTTP进行数据传输, 介绍了相应的接口内容和调用示例.针对定位信息的更新和传递提出了一种新的基于Push的主动通知机制, 提供与各种定位接口的数据转换和消息处理能力, 高效地实现了位置应用和服务平台之间的消息传递.最后结合MAPGIS平台和CDMA手机定位技术进行了原型系统的实现, 验证了平台理论模型和服务接口的可用性. 相似文献
59.
60.
Carbonate sediments of mid-Cretaceous platforms on Allison and Resolution Guyots, Mid-Pacific Mountains (ODP Leg 143, Sites 865, 866, 867 and 868) and those of upper Oligocene to Pliocene reefs of the Kita-daito-jima Borehole were studied. The mid-Cretaceous platforms abound with abiotic (?) precipitates (ooids) and microbial carbonate grains/sediments (oncoids and ‘algal’ laminites), whereas the Cenozoic reefs consist mainly of coral and non-geniculate coralline algae, major frame-builders, benthic foraminifers and codiacean alga (Halimeda). There exists a remarkable difference in a mode of calcification between the mid-Cretaceous platforms and Cenozoic reefs. The major reef-builders of Cenozoic reefs precipitated carbonates within closed to semiclosed spaces within their bodies. In contrast, the mid-Cretaceous platforms contain abundant grains/sediments formed by chemical (?) precipitations and biotic extracellular calcification. This contrasting feature reflects different modes of biogeochemical cycles between the mid-Cretaceous and Cenozoic. Increased CO2 (degassed by active volcanism) and resultant high temperature and intensive weathering may have brought high concentration of Ca2+ and HCO3? into the mid-Cretaceous sea, which enhanced abiotic and extracellular calcification. Inverse processes are true for the Cenozoic. 相似文献