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   7757篇
  免费   652篇
  国内免费   645篇
测绘学   1827篇
大气科学   482篇
地球物理   512篇
地质学   1560篇
海洋学   193篇
天文学   17篇
综合类   935篇
自然地理   3528篇
  2024年   28篇
  2023年   77篇
  2022年   260篇
  2021年   332篇
  2020年   310篇
  2019年   347篇
  2018年   266篇
  2017年   373篇
  2016年   383篇
  2015年   384篇
  2014年   449篇
  2013年   565篇
  2012年   518篇
  2011年   538篇
  2010年   453篇
  2009年   389篇
  2008年   405篇
  2007年   405篇
  2006年   403篇
  2005年   346篇
  2004年   333篇
  2003年   278篇
  2002年   248篇
  2001年   221篇
  2000年   167篇
  1999年   124篇
  1998年   107篇
  1997年   97篇
  1996年   53篇
  1995年   43篇
  1994年   35篇
  1993年   29篇
  1992年   17篇
  1991年   11篇
  1990年   14篇
  1989年   7篇
  1988年   6篇
  1987年   9篇
  1986年   8篇
  1985年   6篇
  1984年   5篇
  1983年   3篇
  1982年   2篇
排序方式: 共有9054条查询结果,搜索用时 15 毫秒
81.
干旱区坎儿井与山前凹陷地下水库   总被引:2,自引:0,他引:2       下载免费PDF全文
邓铭江 《水科学进展》2010,21(6):748-756
在分析研究坎儿井主要技术特点的基础上,结合河流冲洪积扇地形地貌特征、储水构造以及水资源转化特点,提出了建设山前凹陷带"横坎儿井式"地下水库的具体思路,并以台兰河地下水库示范工程为例,对构筑"横坎儿井式"地下水库的可行性及其"引渗回补"调蓄系统、"横坎儿井"集水系统、"自流虹吸"输水系统三大工程组成部分的结构设计原理进行了初步的探讨.山前凹陷地下水库是非常理想的应急抗旱水源工程,其研究和示范工程,为干旱区内陆河流域地表水与地下水联合调度、水资源高效利用探索出了一种新模式.  相似文献   
82.
Models of land use change are useful tools for un-derstanding the analysis of the cause and conse-quences of land use changes, assessing the impacts of land use system on ecological system and supporting land use planning and policy[1,2]. Modeling land use scenario changes and its potential impacts on the structure and function of the ecosystem in the typical regions are regarded as one of the good ways to un-derstand the interactive mechanism between land use system and ecological system[3―10…  相似文献   
83.
ABSTRACT

Researchers are continually finding new applications of satellite images because of the growing number of high-resolution images with wide spatial coverage. However, the cost of these images is sometimes high, and their temporal resolution is relatively coarse. Crowdsourcing is an increasingly common source of data that takes advantage of local stakeholder knowledge and that provides a higher frequency of data. The complementarity of these two data sources suggests there is great potential for mutually beneficial integration. Unfortunately, there are still important gaps in crowdsourced satellite image analysis by means of crowdsourcing in areas such as land cover classification and emergency management. In this paper, we summarize recent efforts, and discuss the challenges and prospects of satellite image analysis for geospatial applications using crowdsourcing. Crowdsourcing can be used to improve satellite image analysis and satellite images can be used to organize crowdsourced efforts for collaborative mapping.  相似文献   
84.
为了进一步查清城市土地的权属、位置、面积、用途等基本情况,掌握真实的土地基础数据,建立和完善城市土地调查、土地统计和土地登记制度,实现土地资源信息的社会化服务,为建立科学的城市国土资源管理与评价体系提供详实的基础数据,需要开展3维地籍数据库更新与维护,以保证地籍数据库的真实性、现势性,满足城市国土资源管理工作和经济社会发展的需要。  相似文献   
85.
上海地下水环境容量评价及在地面沉降控制中的应用   总被引:1,自引:1,他引:0  
在分析地下水水环境容量内涵及地下水资源开发利用产生的环境效应基础上,探讨了地下水环境容量的概念,认为地下水环境容量是用来表征一定目标约束下,地下水系统对自然或人类活动影响所能承受能力的最大阙值,并以上海市为例,采用地下水临界水位、地面沉降量、地下水质作为评价指标对地下水环境容量进行了评价,并将其应用于上海市地面沉降防治工作中,剖析了地下水资源管理和地面沉降控制的工作机制。升,第四承压含水层向弹性变形态势转变,土体表现为微量回弹。  相似文献   
86.
镇赉县土地利用结构调整   总被引:1,自引:0,他引:1  
基于遥感与GIS进行吉林省镇赉县土地利用现状调查与生态适宜性评价, 通过分析二者差异提出土地利用调整方向及对策, 进一步优化土地利用结构。研究结果显示, 镇赉县宜林地和宜牧地的利用现状主要是盐碱地, 其次为耕地, 很少用于林地与草地; 宜农地和宜农、林、牧地利用格局单一, 耕林草比例不合理; 土地利用结构调整方向为盐碱地治理、退耕还林还草与土地利用格局优化。结合自然环境特点分析, 调整后的土地利用模式有农林复合、林草复合及开发水田等3种, 农、林、牧用地比例接近3∶1∶1, 空间格局交替安排。  相似文献   
87.
在土地资源紧缺等"城市病"问题愈发突出的背景下,提高土地集约利用效率是国土资源管理的重点研究方向。为支撑城市土地空间资源集约利用研究,本文在深入研究城市土地利用评价及空间演化模拟技术的基础上,基于C#.NET开发平台,结合ArcGIS Engine组件技术,研发了城市土地空间利用评价预警调控系统,实现土地空间利用评价、预警及政策仿真调控等功能,作为科学管理土地的辅助工具。本文对系统的总体需求、系统结构及主要功能设计与实现进行了阐述,以期为土地资源管理研究及相关软件研发提供参考。  相似文献   
88.
Open space of metropolitan suburbs in mountain region, has been increasingly becoming the coupling mosaic structure of industrial actions and landscape behaviors. However, the local governments, when making land use planning, often aim at economic development, and rarely refer to the coordination of compatibilities and conflicts between industrial actions and landscape behaviors in the mosaic structure. In this study land use in the Jinyun Mountain and its surrounding area, Chongqing is adjusted by gray multi-objective programming approach and local-level decision-making process to cope with conflicts between objectives for human welfare and objectives for landscape conservation. The results indicate that: 1) the compatibilities and conflicts among different behavior characters and different landscape types result in the compatibilities of landscape to human behavior; 2) a land use planning in the study area is produced based on the sustainable land use and social-eco development, which pays more attention to the resources and environment constraints and economic objectives, and follows the distribution law of rare resources; 3) in the study area, cultivated land of 1,207.27 ha can meet the demands for food and byproducts by the residents there, orchard land and forestland of 632.55 ha, 2,276.61 ha, respectively can provide enough spaee for the local people to improve their living structure and meet their demands for reereational activities, and urban residential land, rural residential land, mining land and transportation land of 1107.60 ha, 120.27 ha, 162.48 ha, 100.91 ha, respeetively can satisfy the resident's eeonomie development and infrastructures; 4) the equilibrium among industrial actions, landscape accessibility and ecological conservation can be obtained by analyzing the possible impaets of human activities on landscape eeologieal proeess in open spaee of metropolitan suburbs in mountain areas.  相似文献   
89.
土地质量是土地管理、农业发展和环境保护的前提,土地质量评估是打造现代农业,保护生态环境,实现土地“质量型、生态型”管理的项基础性地质调查工作。本文根据上海地区现有工作程度,详细介绍了全市、典型县区土地质量评估工作,结合正在开展的乡镇级土地质量评估工作,分析了不同工作比例尺土地质量地球化学评估工作中评估单元、评估指标、评估标准等的异同,为进步开展相关工作奠定基础。  相似文献   
90.
Three-River Headwaters(TRH) region involved in this paper refers to the source region of the Changjiang(Yangtze) River,the Huanghe(Yellow) River and the Lancang River in China.Taking the TRH region of the Qinghai-Tibet Plateau as a case,the annual evapotranspiration(ET) model developed by Zhang et al.(2001) was applied to evaluate mean annual ET in the alpine area,and the response of annual ET to land use change was analyzed.The plant-available water coefficient(w) of Zhang’s model was revised by using vegetation-temperature condition index(VTCI) before annual ET was calculated in alpine area.The future land use scenario,an input of ET model,was spatially simulated by using the conversion of land use and its effects at small regional extent(CLUE-S) to study the response of ET to land use change.Results show that the relative errors between the simulated ET and that calculated by using water balance equation were 3.81% and the index of agreement was 0.69.This indicates that Zhang’s ET model based on revised plant-available water coefficient is a scientific and practical tool to estimate the annual ET in the alpine area.The annual ET in 2000 in the study area was 221.2 mm,11.6 mm more than that in 1980.Average annual ET decreased from southeast to northwest,but the change of annual ET between 1980 and 2000 increased from southeast to northwest.As a vast and sparsely populated area,the population in the TRH region was extremely unbalanced and land use change was concentrated in very small regions.Thus,land use change had little effect on total annual ET in the study area but a great impact on its spatial distribution,and the effect of land use change on ET decreased with increasing precipitation.ET was most sensitive to the interconversion between forest and unused land,and was least sensitive to the interconversion between cropland and low-covered grassland.  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