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   594篇
  免费   27篇
  国内免费   40篇
测绘学   171篇
大气科学   67篇
地球物理   81篇
地质学   75篇
海洋学   143篇
天文学   2篇
综合类   61篇
自然地理   61篇
  2023年   1篇
  2022年   11篇
  2021年   7篇
  2020年   29篇
  2019年   15篇
  2018年   14篇
  2017年   47篇
  2016年   44篇
  2015年   29篇
  2014年   42篇
  2013年   60篇
  2012年   16篇
  2011年   56篇
  2010年   32篇
  2009年   29篇
  2008年   36篇
  2007年   30篇
  2006年   38篇
  2005年   21篇
  2004年   16篇
  2003年   12篇
  2002年   19篇
  2001年   10篇
  2000年   14篇
  1999年   7篇
  1998年   4篇
  1997年   4篇
  1996年   1篇
  1995年   3篇
  1994年   4篇
  1993年   3篇
  1992年   2篇
  1991年   1篇
  1989年   2篇
  1983年   2篇
排序方式: 共有661条查询结果,搜索用时 78 毫秒
51.
地图网站是地理空间信息面向公众发布的最好形式。以湖南地图网(www.dzmap.cn)为例,介绍了基于SuperMap IS.NET的地图网站的服务定位、地图数据分析与处理,并讨论了网络地图发布平台架构、网络地图功能与属性数据库设计、数据更新等方面的设计与实现。  相似文献   
52.
面对Internet应用模式的变化和Web海量信息的冲击,Web信息个性化、智能化的研究不断深入.语义Web规划对当前的万维网进行扩展,期望用加入信息中的语义内容导航信息资源检索并提高网络服务的智能化,使机器自动与人协同工作.目前,虽然语义Web还是个理想模型,但将语义Web融入现有Web结构进行信息智能开发的初步努力已经展开.特别是随着对本体技术研究的日渐深入,OWL本体理论探索和应用开发逐渐受到广泛重视.  相似文献   
53.
Derek Hall 《Geoforum》2010,41(5):826-835
The years since 2000 have seen a constant stream of high-profile scandals relating to food safety and food labeling in Japan. One response of Japan’s Ministry of Agriculture, Forestry and Fisheries (MAFF) has been to promote food traceability as a mechanism to improve food safety and to provide reliable information to consumers about their food. MAFF’s main approach to traceability promotion, however, has not involved making traceability mandatory (as has been done in the EU) but encouraging private companies to adopt it. These actions constitute, I argue, an example of the public promotion of private governance. When viewed against the literature on the private governance of food safety and quality, MAFF’s traceability activities are surprising for three reasons: their forms and extent, the relative lack of interest the Ministry has shown in third-party certification, and the way MAFF has responded to concerns about the safety of imported food by focusing almost entirely on domestic traceability. I also argue, however, that looking at the literature from a Japanese perspective suggests that public encouragement is more central to the rise of private governance in the global agri-food system than is usually appreciated.  相似文献   
54.
While some non-profits have suffered under the political and economic pressures of neoliberal urban governance reform, others have emerged as important institutional players in local governance regimes. This article highlights how non-profits food banks in Chicago have commercialized in order to respond to increased demand, enhance their institutional independence from government, and reassert their local dominance in emergency food service delivery. From a food bank member agency perspective, the consolidation of food bank institutional power has produced new bureaucratic limitations, user fees, and increased competition. These shifts reveal the rise of metropolitan food banks as important players in neoliberal urban governance regimes, as they control the conceptualization of hunger, management of poverty, and organization of food distribution systems.  相似文献   
55.
Selenium like any other element can both be essential and toxic depending upon the concentration at which it occurs in human diet. This paper assessed the level of this trace element in twenty different (20) types of locally produced food items around Abeokuta town and the blood obtained from the antecubital fossa vein of eighty-eight (88) healthy adults resident in Abeokuta.  相似文献   
56.
杨仕勇 《山东地质》2010,(11):46-51
通过分析借鉴当今服务链技术与工作流技术研究成果,充分考虑地理信息数据量大、数据源异构性的特点,对适于地理信息服务链的过程建模方法、过程定义语言、建模工具以及工作流引擎的体系结构、调度算法、应用框架进行重新设计,实现了地理信息服务的可视化组合建模和服务链的自动执行。  相似文献   
57.
Regularly monitoring the amount of food produced in food insecure, isolated, subsistence farming areas can be used to help identify households or communities who may be in need of additional food resources. Measuring seasonal food production in developing countries, particularly at a sub-national level, is complicated by lack of data. In this study we use high resolution remotely sensed data to calculate cultivated area in two different growing areas, during two different seasons in Kenya. The results of the research support the usefulness of this approach for agricultural monitoring in the developing world and suggest that monitoring cultivated area requires attention to the specific growing characteristics of an area.  相似文献   
58.
Geo-folksonomies link social web users to geographic places through the tags users choose to label the places with. These tags can be a valuable source of information about the user’s perception of place and can reflect their experiences and activities in the places they label. By analysing the associations between users, places and tags, an understanding of a place and its relationships with other places can be drawn. This place characterisation is unique, dynamic and reflects the perception of a particular user community that generated the geo-folksonomy. In this work, an approach is proposed to analysing geo-folksonomies that builds on and extends existing statistical methods by considering specific concepts of relevance to geographic place resources, namely, place types and place-related activities, and by building a place ontology to encode those concepts and relationships. The folksonomy analysis and evaluation are demonstrated using a realistic geo-folksonomy data set. The resulting ontology is used to build user profiles from the folksonomy. The derived profiles reflect the association between users and the specific places they tag as well as other places with relevant associated place type and activities. The methods proposed here provide the potential for many interesting and useful applications, including the harvesting of useful insight on geographic space and employing the derived user profiles to enhance the search experience and to identify similarities between users based on their association to geographic places.  相似文献   
59.
海洋传感观测服务柔性开发技术研究   总被引:1,自引:0,他引:1  
海洋传感观测服务能够实现多个海洋观测系统间的数据共享与集成,支持大范围、多学科的海洋科学研究。在软件开发过程中,由于不同观测系统的数据库异构互异,导致传感器观测服务软件难以复用,开发效率低。本文针对数据库结构的相似性进行分析,提出海洋传感观测服务的柔性开发模型,设计可适配于异构数据库的服务构件。该构件通过配置观测数据在具体数据库的存储结构,实现了数据库结构向服务模式定义的映射;服务构件根据配置信息生成数据库查询语句,实现观测数据的自动提取,避免了数据库异构导致的重复开发的问题。通过将服务构件应用在实际开发中,验证了该模型的有效性与可行性。  相似文献   
60.
Increasing attention by consumers to the social and environmental dimensions of the food they eat has generated many different responses, including certification programs, watch lists and local/slow food movements. This article examines the more recent entry of seafood into these consumer social movements. Although a concern with the family farm—as well as tendency to equate national security with food security—has long connected terrestrial food production with other cultural concerns, fisheries have tended to be regarded more as natural resources. Considering seafood as part of the “food system” would enhance the management of fisheries, while the long engagement in fisheries with co- and adaptive management and the politics of knowledge would enrich the debate in the agri-foods literature. The article also offers suggestions on how fisheries management could better govern for sustainable food systems, and provides further ideas about food, sustainability and governance.  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