全文获取类型
收费全文 | 254篇 |
免费 | 34篇 |
国内免费 | 30篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 22篇 |
地球物理 | 9篇 |
地质学 | 61篇 |
海洋学 | 74篇 |
天文学 | 1篇 |
综合类 | 42篇 |
自然地理 | 77篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 29篇 |
2013年 | 20篇 |
2012年 | 10篇 |
2011年 | 14篇 |
2010年 | 16篇 |
2009年 | 27篇 |
2008年 | 21篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 9篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 12篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 14篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有318条查询结果,搜索用时 93 毫秒
41.
Simplified equations of fluid mud motion, which is described as Bingham-Plastic model under waves and currents, are presented by order analysis. The simplified equations are non-linear ordinary differential equations which are solved by hybrid numerical-analytical technique. As the computational cost is very low, the effects of wave current parameters and fluid mud properties on the transportation velocity of the fluid mud are studied systematically. It is found that the fluid mud can move toward one direction even if the shear stress acting on the fluid mud bed is much smaller than the fluid mud yield stress under the condition of wave and current coexistence. Experiments of the fluid mud motion under current with fluctuation water surface are carried out. The fluid mud transportation velocity predicted by the presented mathematical model can roughly match that measured in experiments. 相似文献
42.
On the basis of field observations, microscopic thin-sections and laboratory data analysis of ten faults in Xuanhan County area, northeastern Sichuan Basin, central China, the internal and megascopic structures and tectonite development characteristics are mainly controlled by the geomechanical quality in brittle formation of the Changxing-Feixianguan Formation. The fluid transportation performance difference between the faults formed by different geomechanics or different structural parts of the same fault are controlled by the mcgascopic structure and tectonite development characteristics. For instance, the extension fault structure consists of a tectonite breccia zone and an extension fracture zone. Good fluid transportation performance zones are the extension fracture zone adjacent to the tectonite breccia zone and the breccia zone formed at the early evolutionary stage. The typical compression fault structure consists of a boulder-clay zone or zones of grinding gravel rock, compression foliation, tectonite lens, and dense fracture development. The dense fracture development zone is the best fluid transporting area at a certain scale of the compression fault, and then the lens, grinding gravel rock zone and compression foliation zones are the worst areas for hydrocarbon migration. The typical tensor-shear fault with a certain scale can be divided into boulder-clay or grinding gravel rock zones of the fault, as well as a pinnate fractures zone and a derivative fractures zone. The grinding gravel rock zone is the worst one for fluid transportation. Because of the fracture mesh connectivity and better penetration ability, the pinnate fractures zone provides the dominant pathway for hydrocarbon vertical migration along the tensor-shear fault. 相似文献
43.
基于GIS的广东省综合运输体系规划信息平台构建研究 总被引:1,自引:0,他引:1
广东省交通运输厅从2012年起,组织分期研究开发基于地理信息系统的广东省综合运输体系规划信息平台(简称"平台"),旨在建立健全统一的全省交通运输业数据采集、发布标准及技术管理规范,分别构建5大类运输方式线网及重要的运输枢纽站场节点的多级图层,叠加形成全省综合运输体系布局规划"一张图"。"平台"采用4层设计,依托后台管理、应用分析和综合展示3大子系统,搭建了基础地理信息、经济社会、交通运输现状、综合运输体系规划成果及其他共5大类数据库,"平台(一期)"于2014年3月26日通过验收,实现了多维度、多视角展示和查询交通运输业数据成果的预期功能。研究实践将力促综合运输体系规划研究和决策方式实行根本性变革。 相似文献
44.
Carrying Capacity of Marine Region in Liaoning Province 总被引:1,自引:1,他引:1
Carrying capacity is one of important studies on coordinating development of population,resources,and environment.At present,the researches on it mainly concentrate on the carrying capacity for population and economy,such as the water resources carrying capacity,the land resources carrying capacity,the environment carrying capacity,etc.Based on the related theories and methods,this paper creatively proposed the concept and meaning of carrying capacity of marine region,and formed the appraisal system.According to the developing situation of marine economy of Liaoning Province in recent years,and by employing the method of the state space,this paper also measured the carrying capacity and carrying state of marine region and discussed the sustainable problems of marine economy of Liaoning.The research results show that the carrying state of marine region of Liaoning is in the state of overloading at present,but taking a favorable turn. 相似文献
45.
46.
47.
中国煤炭资源供应格局演变及流动路径分析 总被引:1,自引:0,他引:1
利用1949—2008年的相关统计数据,分析中国煤炭资源供应格局和流动路径,结果表明:(1)国家政策变动对中国煤炭资源消费规模影响深刻,每一次政策变化都会造成能源消费规模的波动,近年来强烈的能源需求使得我国煤炭供应不得不面临进口的现实;(2)受能源需求和资源禀赋的双重压力,大规模、跨区域、长距离的煤炭运输成为我国能源运输体系的重要特征;(3)尽管煤炭运输方式在向铁路、水路和公路组合并用的多元化发展,但仍然不能满足旺盛的能源需求,煤炭运输瓶颈始终存在,变输煤为输电是缓解当前煤炭运输困难的一个途径。 相似文献
48.
The characteristics of moisture transport and budget of widespread heavy
rain and local heavy rain events in Northeast China are studied using the
NCEP--NCAR reanalysis 6-hourly and daily data and daily precipitation data
of 200 stations in Northeast China from 1961--2005. The results demonstrate
that during periods with widespread heavy rain in Northeast China, the Asian
monsoon is very active and the monsoonal northward moisture transport is
strengthened significantly. The widespread heavy rainfall obtains enhanced
water vapor supply from large regions where the water vapor mainly
originates from the Asian monsoon areas, which include the East Asian
subtropical monsoon area, the South China Sea, and the southeast
and southwest tropical monsoon regions. There are several branches of
monsoonal moisture current converging on East China and its coastal areas,
where they are strengthened and then continue northward into Northeast
China. Thus, the enhanced northward monsoonal moisture transport is the key
to the widespread heavy rain in Northeast China. In contrast, local heavy
rainfall in Northeast China derives water vapor from limited areas,
transported by the westerlies. Local evaporation also plays an important
role in the water vapor supply and local recycling process of moisture. In
short, the widespread heavy rains of Northeast China are mainly caused by
water vapor advection brought by the Asian monsoon, whereas local heavy
rainfall is mainly caused by the convergence of the westerly wind field. 相似文献
49.
The origin of the Ryukyu Current(RC) and the formation of its subsurface velocity core were investigated using a 23-year(1993–2015) global Hybrid Coordinate Ocean Model(HYCOM) dataset. The volume transport of the RC comes from the Kuroshio eastward branch(KEB) east of Taiwan and part of the North Pacific Subtropical Gyre(pNPSG). From the surface to 2 000 m depth, the KEB(p-NPSG) transport contributes 41.5%(58.5%) to the mean total RC transport. The KEB originally forms the subsurface velocity core of the RC east of Taiwan due to blockage of the subsurface Kuroshio by the Ilan Ridge(sill depth: 700 m). Above 700 m, the Kuroshio can enter the East China Sea(ECS) over the Ilan Ridge, meanwhile, the blocked Kuroshio below 700 m turns to the right and flows along the Ryukyu Islands. With the RC flowing northeastward, the p-NPSG contribution strengthens the subsurface maximum structure of the RC owing to the blockage of the Ryukyu Ridge. In the surface layer, the pNPSG cannot form a stable northeastward current due to frequent disturbance by mesoscale eddies and water exchange through the gaps(with net volume transport into ECS) between the Ryukyu Islands. 相似文献
50.
铁路是综合运输体系的重要组成部分之一,合理高效的铁路运输系统有利于发挥交通运输的支撑引领作用,运输效率问题的探讨显得尤为重要。以铁路局为研究单元,使用超效率SBM-Malmquist指数方法,对2005-2013年中国铁路运输效率的时空演化特征及影响机理进行了分析。研究表明:① 中国铁路运输效率呈波动上升趋势,但总体水平不高,规模效率是造成这两种现象的主要原因。② 铁路运输效率呈现东部高于中部,中部高于西部的空间分布格局。与此同时,高、中、低值区内部运输效率的空间分布存在差异,各铁路局效率演化的类型也不尽相同。③ 通过对研究期内大规模建设高铁的铁路局运输效率演化进行分析,发现近些年大规模高速铁路的建设并没有引起运输效率和生产率的较大变动。④ 从地域空间视角,区位条件、资源势差、地形条件以及城镇格局与城镇化水平等外部因素对运输效率空间格局及其演化产生着重要作用。 相似文献