首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6766篇
  免费   739篇
  国内免费   494篇
测绘学   1460篇
大气科学   374篇
地球物理   941篇
地质学   2054篇
海洋学   1639篇
天文学   16篇
综合类   607篇
自然地理   908篇
  2024年   19篇
  2023年   41篇
  2022年   128篇
  2021年   184篇
  2020年   223篇
  2019年   246篇
  2018年   174篇
  2017年   352篇
  2016年   279篇
  2015年   334篇
  2014年   404篇
  2013年   466篇
  2012年   440篇
  2011年   446篇
  2010年   370篇
  2009年   373篇
  2008年   438篇
  2007年   417篇
  2006年   412篇
  2005年   333篇
  2004年   299篇
  2003年   230篇
  2002年   243篇
  2001年   201篇
  2000年   151篇
  1999年   172篇
  1998年   112篇
  1997年   110篇
  1996年   81篇
  1995年   66篇
  1994年   57篇
  1993年   50篇
  1992年   29篇
  1991年   23篇
  1990年   21篇
  1989年   17篇
  1988年   17篇
  1987年   10篇
  1986年   6篇
  1985年   8篇
  1984年   9篇
  1983年   3篇
  1982年   3篇
  1981年   1篇
  1971年   1篇
排序方式: 共有7999条查询结果,搜索用时 15 毫秒
991.
A digital earth platform for sustainability   总被引:1,自引:1,他引:0  
ABSTRACT

Based on the experience of the International Society for Digital Earth (ISDE), this paper describes some challenges foreseen in order to develop a Digital Earth platform that can support the implementation of the Sustainable Development Goals. The use of ready-to-use derived geospatial information is essential. Future Earth’s methodology of ‘co-design’ aims to bring together natural, social scientists and decision makers to plan and carry out research for sustainability. Sustainability implies transdisciplinary research, but in order for scientists of different disciplines to work together, they will need to be able to share, access and use common data. This is by far not simple! While the good will to share data might exist, the associated technological, ethical and privacy issues are difficult to solve. An adequate e-infrastructure will be required. ISDE could consider to use the SDGs is the basis to develop the desired Digital Earth platform. This paper, by no means, covers everything for a Digital Earth platform, it aims to trigger research discussions and to have a good view about a starting point.  相似文献   
992.
对高速公路车速进行有效监控与管理,是抑制违章超速行驶、减少高速公路交通事故的重要手段。现有的基于点速度和区间平均速度的高速公路车速监控方法,难以准确反应出车辆的实际行驶状态,实施效果有限,可靠性较差。文中提出基于GPS和地图匹配技术的高速公路车速全程监控和管理方法,建立相关算法的数学模型。经过理论分析和实例验证,车速监控与管理方法能实现高速公路车速的全程监控,极大地提高车速安全监控和管理的可靠性、准确性和有效性。  相似文献   
993.
针对航空遥感惯性稳定平台中所受到的不平衡力矩等所引起的成像载荷不稳定导致无法获取高分辨率遥感数据的问题,提出了在平台控制系统中应用基于模型参考的自适应比例-积分-微分控制方法。根据需求设计出参考模型,将参考系统输出与实际系统输出之间的误差输入到自适应PID调节器,实时调整PID参数,对误差进行实时校正,以达到抑制不平衡力矩扰动、提高稳定平台稳定精度的目的。对所提出的模型参考自适应控制方法进行了仿真验证,结果表明:相对传统PID方法,模型参考自适应控制器对偏心力矩等主要干扰具有很好的抑制作用,系统输出能够很好地跟踪姿态变化,系统稳定精度得到显著提高。  相似文献   
994.
“多规合一”信息平台架构设计——以南京市为例   总被引:3,自引:0,他引:3  
孙玉婷  吴掠桅  秦萧 《测绘通报》2017,(12):117-121
"多规合一"是党和国家近年来积极推进的改革措施,是推进城市治理体系和治理能力现代化的有力抓手。"多规合一"信息平台是科学开展"多规合一"工作,促进部门规划数据共享共建、加强各规划编制过程衔接的重要技术支撑。在当今智慧城市建设如火如荼,"天地图""互联网+政务服务"等政府改革措施大力推进的背景下,"多规合一"信息平台应当如何构建,如何有效衔接既有智慧城市成果,是一项需要综合考虑的问题。本文以南京市为例,在深入梳理国内典型城市"多规合一"信息平台建设经验的基础上,从数据架构、业务架构、应用架构、技术架构4个方面全面开展"多规合一"信息平台架构设计,以期为后续其他城市信息平台的建设实施提供指导。  相似文献   
995.
目前,我国正处于城市人口剧增的城镇化加速发展时期,同时,也面对交通堵塞、环境污染、能源紧缺等来自各方面的挑战。那么,如何破解城市发展所带来的诸多难题,实现城市可持续发展呢?建设智慧城市已成为当今世界城市发展不可逆转的历史潮流。目前,我国已有154个城市提出建设智慧城市。然而,在智慧城市建设过程中出现了值得重视的问题,即一些城市对基础地理数据、空间信息以及基础地理信息共享平台的建设认识不明确,重视不够。搭建地理信息共享平台是智慧城市建设的基础,是城市转型发展、生态文明建设、新型城镇化和治理现代化的需求,是推进“互联网+”行动和促进电子政务协调发展等方面的要求。因此,必须按照先进性、现势性、完备性、实用性等原则搭建地理信息共享平台。  相似文献   
996.
针对城市交通部门事故管理系统中存在道路数据不独立以及发布的事故信息易读性差导致应急部队无法准确定位事故地点进行救援的问题,基于公路的线性特征,结合GIS对地理数据的多样操作功能,提出路段名+特征参考点的一维定位表达方法。将线性参照系理论应用到以综合车道为公路模型的空间数据管理模式中,建立基于线性参照系的城市公路事故信息发布系统,实现二维坐标向一维坐标转换、降低数据冗余、实现事故地点的快速定位以及对定位的事故信息进行发布。  相似文献   
997.
对多源遥感影像进行几何校正是遥感影像应用的重要环节,以往的遥感影像利用人工或半自动的方式进行几何校正时,存在校正结果难以预料,控制点精度不可控,二次校正过程中控制点利用效率较低等问题。本文基于以上问题,利用华浩超算平台,对资源一号02C卫星10 m多光谱影像和2.36 m全色影像进行几何校正。试验证明华浩超算平台的实时几何校正模块,可以对每一个精校正后控制点的精度进行实时控制,并有效地解决了控制点利用效率低的问题。  相似文献   
998.
Community forest management has been identified as a win-win option for reducing deforestation while improving the welfare of rural communities in developing countries. Despite considerable investment in community forestry globally, systematic evaluations of the impact of these policies at appropriate scales are lacking. We assessed the extent to which deforestation has been avoided as a result of the Indonesian government’s community forestry scheme, Hutan Desa (Village Forest). We used annual data on deforestation rates between 2012 and 2016 from two rapidly developing islands: Sumatra and Kalimantan. The total area of Hutan Desa increased from 750 km2 in 2012 to 2500 km2 in 2016. We applied a spatial matching approach to account for biophysical variables affecting deforestation and Hutan Desa selection criteria. Performance was assessed relative to a counterfactual likelihood of deforestation in the absence of Hutan Desa tenure. We found that Hutan Desa management has successfully achieved avoided deforestation overall, but performance has been increasingly variable through time. Hutan Desa performance was influenced by anthropogenic and climatic factors, as well as land use history. Hutan Desa allocated on watershed protection forest or limited production forest typically led to a less avoided deforestation regardless of location. Conversely, Hutan Desa granted on permanent or convertible production forest had variable performance across different years and locations. The amount of rainfall during the dry season in any given year was an important climatic factor influencing performance. Extremely dry conditions during drought years pose additional challenges to Hutan Desa management, particularly on peatland, due to increased vulnerability to fire outbreaks. This study demonstrates how the performance of Hutan Desa in avoiding deforestation is fundamentally affected by biophysical and anthropogenic circumstances over time and space. Our study improves understanding on where and when the policy is most effective with respect to deforestation, and helps identify opportunities to improve policy implementation. This provides an important first step towards evaluating the overall effectiveness of this policy in achieving both social and environmental goals.  相似文献   
999.
1000.
The estimation of total evaporation is fundamental for water accounting, considering its influence on water availability. Moreover, the current increase in water consumption (e.g. in sub-Saharan Africa and the world over), land cover/use changes, deteriorating water quality and the climate change projections in most regions of the world underscore the need to understand water loss. So far, different approaches have been developed and implemented in estimating the variations of total evaporation, with varying accuracies. The aim of this work was therefore, to provide a review of these different approaches for estimating total evaporation, as well as a detailed discussion of their strengths and weaknesses. Findings from this review have shown that total evaporation estimates derived, using ground-based meteorological and micro-meteorological methods are inadequate for representing its large-scale spatial variations. On the other hand, remote sensing technology, which acquires data at different resolutions (i.e. radiometric, spectral, spatial and temporal), provides timely, up-to-date and relatively accurate spatial estimates of total evaporation over large geographic coverage, for sustainable and effective water accounting, which is key for well-informed and improved management of water resources at both catchment and regional scales. In this regard, more details on the remote sensing-based methods of estimating total evaporation are provided, especially considering the robust technological advancements and its potential in characterizing earth features over time and space. This work has also managed to identify research gaps and challenges in the accurate estimation of total evaporation, using remote sensing, especially with the emergence of more advanced sensors and the characteristics of the landscape.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号