全文获取类型
收费全文 | 6884篇 |
免费 | 519篇 |
国内免费 | 515篇 |
专业分类
测绘学 | 3049篇 |
大气科学 | 373篇 |
地球物理 | 696篇 |
地质学 | 1671篇 |
海洋学 | 292篇 |
天文学 | 14篇 |
综合类 | 927篇 |
自然地理 | 896篇 |
出版年
2024年 | 6篇 |
2023年 | 28篇 |
2022年 | 159篇 |
2021年 | 194篇 |
2020年 | 189篇 |
2019年 | 142篇 |
2018年 | 138篇 |
2017年 | 316篇 |
2016年 | 259篇 |
2015年 | 298篇 |
2014年 | 350篇 |
2013年 | 511篇 |
2012年 | 449篇 |
2011年 | 458篇 |
2010年 | 334篇 |
2009年 | 299篇 |
2008年 | 349篇 |
2007年 | 441篇 |
2006年 | 432篇 |
2005年 | 382篇 |
2004年 | 397篇 |
2003年 | 311篇 |
2002年 | 280篇 |
2001年 | 243篇 |
2000年 | 176篇 |
1999年 | 146篇 |
1998年 | 143篇 |
1997年 | 103篇 |
1996年 | 91篇 |
1995年 | 48篇 |
1994年 | 56篇 |
1993年 | 52篇 |
1992年 | 40篇 |
1991年 | 17篇 |
1990年 | 23篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有7918条查询结果,搜索用时 330 毫秒
991.
Thomas J. Pingel 《The Journal of geography》2018,117(4):153-164
Game-based Web sites and applications are changing the ways in which students learn the world map. In this study, a Web map-based digital learning tool was used as a study aid for a university-level geography course in order to examine the way in which global scale cognitive maps are constructed. A network analysis revealed that clicks were negatively correlated with familiarity, but were positively correlated with area. More significantly, well-known countries did not act as central nodes within network-based mental models, but served a more complex mediating role in structuring the space between subregions. 相似文献
992.
面积辽阔的南海是中国未来重要的能源接续区与资源基地,也是涉及国家海洋权益最为集中的区域。本文针对地理信息技术支撑下的南海岛礁研究现状,从南海岛礁现有基础数据成果、遥感手段岛礁基础地理信息提取方法及提取成果所做的岛礁分析与评价3方面,系统地回顾了国内外涉及南海岛礁资源环境研究的相关进展,评述了现有研究技术方法存在的不足,并对未来的研究进行了展望,在此基础上,提出了3个主要方向作为未来研究的重点:①促进遥感数据获取多源化,构建海量多源、多尺度南海岛礁遥感数据仓库;②加强技术协同创新,结合地理信息技术的发展,提升岛礁信息提取与监测的准确性与可靠性;③提升遥感分析智能化,研究并建立综合分析与情势推演平台及战略决策辅助支撑系统,以期为南海岛礁的进一步深入研究提供参考。 相似文献
993.
Environmental pollution, food safety and health are closely linked. A key challenge in addressing the problem of food safety and protecting public health is building an integrated knowledge base to inform policy and strengthen governance. This requires breaking down the trans-departmental information barrier across the environment, food and health domains to ensure the effective flow of data and the efficient utilization of resources, and facilitate the collaborative governance of food safety. Achieving this will be crucial for the development of health and medical care in China in the era of big data. Currently, the information resources commanded by various departments are incomplete and fragmented. Data resources are also organized in vertical silos and there is a lack of data sharing within and across policy streams. To provide the basis for more effective integrated collection and analysis of data in future, this study summarizes the information resources of various departments whose work relates to interactions between environment, food and health, and presents measures to strengthen top-down design, and establish unified data standards and a big data sharing platform. It also points to the need for increased training of data analysts with interdisciplinary expertise. 相似文献
994.
卫星资料凭着卫星遥感的全球性、连续性和高频次观测等优势,成为一种重要的非常规资料源,但卫星观测仍然存在各种各样的观测误差,其中包含由于观测偶然性所造成的统计学上的随机误差及仪器本身和辐射传输模式等造成的系统性偏差,这些误差在很大程度上影响了卫星资料的质量。文中提出了一种能有效订正卫星观测资料系统性偏差的梯度信息同化算法,该方法用一个梯度算子进行模式变量与观测变量的梯度变换,从而达到订正系统性偏差的目的。本文利用WRF(Weather Research Forecast)模式及其同化模式WRFDA(WRF Data Assimilation system),以及AIRS(Atmospheric Infrared Sounder)资料,对台风“圆规”进行了实际的数值模拟和同化试验,数值结果表明,梯度信息同化方法能明显改善台风路径的模拟,在处理可信度较低的资料时仍然适用。另外,通过同化诊断分析,发现卫星资料的系统性偏差对于台风数值模拟有较大影响,而文中提出的梯度信息同化方法能较好的解决此类问题。 相似文献
995.
Bart Kuijpers Walied Othman 《International journal of geographical information science》2017,31(9):1722-1748
Space-time prisms envelop all spatio-temporal locations that moving objects may have visited between two of their known spatio-temporal locations, given a bound on their travel speed. In this context, the known locations are often the result of observations or measurements, and they are called ‘anchor points’. The classic space-time prism, in isotropic two-dimensional space, as well as in transportation networks, assumes that the measurements of these anchor points are exact. Whereas, in many applications, we can assume that time can be measured fairly precisely, this assumption is unrealistic for the spatial components of measured locations (we think of Global Positioning System (GPS) errors, for instance). In this paper, we extend the classical prism from anchor points to circular ‘anchor regions’ that capture the uncertainty or error on their measurement. We define the notion of a space-time prism with uncertain anchor points, called uncertain prism, for short. We study the geometry of uncertain prisms in an arbitrary metric space to make this concept as widely applicable as possible. We also focus on the rims of uncertain space-time prisms, which demarcate the area that a moving object can have visited between two anchor regions (given some local speed limitations). 相似文献
996.
Shihong Du Xiaonan Wang Chen-Chieh Feng Xiuyuan Zhang 《International journal of geographical information science》2017,31(3):542-568
The exponential growth of natural language text data in social media has contributed a rich data source for geographic information. However, incorporating such data source for GIS analysis faces tremendous challenges as existing GIS data tend to be geometry based while natural language text data tend to rely on natural language spatial relation (NLSR) terms. To alleviate this problem, one critical step is to translate geometric configurations into NLSR terms, but existing methods to date (e.g. mean value or decision tree algorithm) are insufficient to obtain a precise translation. This study addresses this issue by adopting the random forest (RF) algorithm to automatically learn a robust mapping model from a large number of samples and to evaluate the importance of each variable for each NLSR term. Because the semantic similarity of the collected terms reduces the classification accuracy, different grouping schemes of NLSR terms are used, with their influences on classification results being evaluated. The experiment results demonstrate that the learned model can accurately transform geometric configurations into NLSR terms, and that recognizing different groups of terms require different sets of variables. More importantly, the results of variable importance evaluation indicate that the importance of topology types determined by the 9-intersection model is weaker than metric variables in defining NLSR terms, which contrasts to the assertion of ‘topology matters, metric refines’ in existing studies. 相似文献
997.
中国区域信息空间和人口空间的耦合关联分析 总被引:1,自引:0,他引:1
从流动空间角度出发,建立基于关系测度的空间耦合模型,采用复杂网络分析方法和灰色关联分析方法深入探讨区域信息空间和人口空间的耦合格局。研究发现信息空间和人口空间的耦合网络呈现“核心-边缘”模式,北京、上海、广东、天津、新疆和甘肃等耦合核心省市在整个省市内占据主导地位,是其他省市耦合发展所依附的核心。全国省市信息空间和人口空间耦合分布的总体布局呈现“川”型特征,分为高耦合协调型、中耦合磨合型以及低耦合发展型。信息空间和人口空间的耦合主要分为高耦合协调型、中耦合磨合型以及低耦合发展型3种,其中空间的高耦合程度一方面响应了国家加快推进互联互通建设的发展战略,另一方面也是京津冀一体化以及建设丝绸之路经济带的必然结果。 相似文献
998.
随着新型城镇化建设成为了国家战略,各地政府掀起了智慧城市建设热潮。在智慧城市建设中,公共信息平台建设是不可或缺的重要基础环节。随着平台的深入运行,逐步积累了大量的城市数据。但是,数据资源中蕴含的知识远未得到充分挖掘和应用,致使数据爆炸但知识匮乏。因此,基于数据时空和专题属性,建立科学的城市数据体系是城市管理的迫切需求;同时,基于数据体系,揭示各类数据随时空变化规律,展现城市脉动发展情况是城市决策重要的依据,也是观察和诊治"城市病"的重要技术手段。我们以中新天津生态城所建成的大数据汇聚公共平台为依托,基于数据挖掘技术手段,针对环境、能源、交通脉动进行研究并取得初步成果,科学地揭示了"城市脉动"变化规律,使平台数据发挥最大价值。脉动分析结果以可视化手段表现,反映城市各项指标脉动变化特征。 相似文献
999.
1000.