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   955篇
  免费   52篇
  国内免费   63篇
测绘学   292篇
大气科学   46篇
地球物理   85篇
地质学   237篇
海洋学   36篇
天文学   15篇
综合类   126篇
自然地理   233篇
  2024年   1篇
  2023年   4篇
  2022年   15篇
  2021年   16篇
  2020年   31篇
  2019年   31篇
  2018年   20篇
  2017年   41篇
  2016年   33篇
  2015年   30篇
  2014年   35篇
  2013年   73篇
  2012年   51篇
  2011年   46篇
  2010年   33篇
  2009年   39篇
  2008年   61篇
  2007年   71篇
  2006年   57篇
  2005年   39篇
  2004年   45篇
  2003年   55篇
  2002年   40篇
  2001年   33篇
  2000年   27篇
  1999年   24篇
  1998年   28篇
  1997年   11篇
  1996年   15篇
  1995年   13篇
  1994年   8篇
  1993年   12篇
  1992年   9篇
  1991年   7篇
  1990年   5篇
  1989年   5篇
  1988年   3篇
  1987年   1篇
  1979年   1篇
  1978年   1篇
排序方式: 共有1070条查询结果,搜索用时 656 毫秒
241.
《The Journal of geography》2012,111(6):233-242
Abstract

Concern about the health of American democracy mounts as a result of the large body of literature documenting chronically low levels of voter turnout among young people in particular. A volunteer, nonprofit organization called “Kids Voting, USA” was formed in the late 1980s to try to tackle the specific problem of encouraging young adults to vote. In cooperation with school districts, the program includes some grade-specific curricula and culminates on Election Day with kids voting in polling booths set up alongside official ones. Existing assessments of the program's impact have been very positive. Particularly hopeful is one study that concludes that the program's strongest effects are found in mobilizing those least advantaged in terms of the customary correlates of political participation. Our ecological analysis, based on the actual turnout rates in the Kids Voting elections for participating schools in Erie County, NY (N = 222), suggests that such conclusions are perhaps overly optimistic. Patterns in the geography and social ecology of participation in Kids Voting elections unfortunately look quite similar to those related to variations in the official electoral process. Although Kids Voting programs may have a salutary effect stimulating political involvement among the young, further reforms seem necessary if they are to reach their full potential.  相似文献   
242.
Abstract

A Learning Support System (LSS) that emphasizes experiential research in natural environments using the cutting-edge technologies of GIS and multimedia has been developed for teaching environmental literacy to undergraduate students at the University of Georgia. Computers are used as cognitive tools to create a context in which students become interns in an ecological research center. Students are instructed to conduct research in the form of two field laboratories (the stream and forest laboratories). They accomplish their tasks by collecting data in the field (the State Botanical Garden of Georgia near the campus). They enter the data in the Learning Support System (LSS), and are guided to formulate hypotheses relating to stream water quality and human impact on forest succession for testing. Students also interact with the Environmental Research Support Site (ERSS) within the LSS for explanations to their findings. A specially customized Arc View GIS program within the LSS provides a tool to students for spatial analysis in the case of the forest laboratory. Students and faculty evaluations as well as final examination results confirmed the receptiveness of students to the LSS approach and its effectiveness in the learning of environmental literacy.  相似文献   
243.
《The Journal of geography》2012,111(6):255-266
Abstract

This study investigated the effects of using a long-duration, project-based science professional development model on the acquisition of declarative knowledge and basic terminology associated with the use of geographic information technologies (GIT), teachers' self-assessed confidence in using GIT skills, and the implementation of GIT in participants' classrooms. Results suggest that a long-duration, project-based science model was effective in teaching GIT declarative knowledge and raising teachers' self-confidence in using GIT tools. The academy was funded through a grant from the US Department of Education with additional support from Environmental Science Resources Institute (ESRI), Inc., and members of the New Mexico Geographic Information Council.  相似文献   
244.
Abstract

Over the next decade or so, the National Assessment for Educational Progress in Geography and the Geographic Education Standards Project promise to give geography a new definition as a school subject. This will challenge the educational community to re-examine how geography is taught and learned across all the grade levels, K-12. If geography is to be perceived as an essential subject in preparing students for citizenship as adults, not only must its image change, but its content and the pedagogy that delivers it must be modified as well. To achieve those ends, new curricular models grounded in cogent and applicable research must develop through partnerships of teachers, teacher educators, learning theorists, and professional geographers.  相似文献   
245.
Genetic techniques are increasingly employed in the field of conservation biology; our understanding of sea turtle biology, and particularly of sea turtle migrations and population structures, has increased through genetic analyses that ‘match’ turtles found in various and often widely distributed habitats (e.g. nesting beaches, foraging grounds, migratory corridors). This relatively recent technological development has implications for how sea turtles are conceived, both as resources and as objects of conservation. Traditionally, sea turtle populations have been identified with nesting beaches, and most conservation efforts have been focused on these discrete geographic locations and undertaken by the state. The more complete understanding of relationships among turtles found in geographically disparate areas, achieved via genetic analysis, can take conservation beyond the beaches and territorial waters of individual states; foraging populations can now be linked to nesting populations sometimes hundreds of kilometers distant. In this paper, we explore the implications of genetic analysis for sea turtle conservation, the scale at which it is undertaken, and the variety of actors with competing interests in it. We focus on the case of hawksbill sea turtles in the Caribbean, where genetic data are invoked in conservation conflicts. We are particularly interested in the way genetic data can support the scaling-up of sea turtle conservation, creating new ‘conservation territories,’ and we draw on political ecology and common pool resource theory to explore the implications thereof.  相似文献   
246.
地理信息系统的应用现状及发展趋势   总被引:3,自引:0,他引:3       下载免费PDF全文
地理信息系统(GIS)是近年发展起来的综合处理和分析空间数据的一种技术系统,文章重点对地理信息系统在地质找矿,矿产资源预测评价,土地整治,自然资源管理,区域规划,国情研究,城市建设,各种灾害的评估和防治,农作物估产和耕地动态变化等方面的应用现状和发展趋势进行了综述。  相似文献   
247.
A geographic information system (GIS) raster technique has been developed and used interactively with remediation designers to evaluate the optimum extent of excavating soil contaminated by chlorinated solvents. The technique and the results of its application are presented. The site was a former chemical storage plant for acids and solvents. Two distinct solvent plumes were detected within the ground using a photo-ionisation detector. The solvents were found to be dissolved in the groundwater and migrating in the general direction of groundwater flow. A remediation strategy was proposed involving the localised excavation of contamination ‘hot spots’ followed by the implementation of a groundwater remediation system. A number of excavation options were discussed and the GIS raster technique was developed to evaluate these options in terms of contaminant removed and excavation cost.

The plumes were initially mapped using a triangular irregular network (TIN). These TIN models were rasterised to produce a regular grid of rectangular cells, each cell having a value relating to the concentration of contaminant at that spatial point. The proposed excavation zones were then overlaid on to the raster models as masks. The relationship between the value of contaminant concentration of cells within the mask (or excavation zone) and the total value of contaminant concentration of cells within the solvent plume was used to determine the efficiency of the excavation.

The excavation options were compared taking into account the percentage of the contaminant plume removed, the excavation area (soil volumes) and related costs. Once the GIS raster technique had been developed, it proved very quick to rerun the analysis for the other excavation zones. The optimum excavation zone, based upon cost and contaminant recovery, was found for the site. The technique helped by targeting the worst area of contamination and provided the client with a cost-benefit analysis of the different remediation options.  相似文献   

248.
地理模型库系统的研究与建立   总被引:2,自引:0,他引:2  
孙亚梅  张犁 《测绘学报》1993,22(2):94-102
  相似文献   
249.
GIS空间分析的应用领域   总被引:7,自引:0,他引:7  
姜亚莉  张延辉 《四川测绘》2004,27(3):99-102
随着地理信息系统的不断发展,对于空间数据结构的研究也日趋成熟,作为该系统的核心——空间分析也相应成为人们倍加关注的热点。本文从空间分析的定义、目的出发,进一步概括了GIS空间分析的具体应用领域,并结合参与的项目着重分析了空间分析在水污染监测中的应用情况。  相似文献   
250.
基于面向对象编程原理,对数字地图的符号按面向对象的分类方法进行分类,详细说明了各类数字地图符号在计算机上的绘制方法,并在对线状符号的处理上改进了以往的传统做法,提出了新的思路,使程序实现更为方便,提高了程序执行效率。  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