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   2039篇
  免费   127篇
  国内免费   75篇
测绘学   492篇
大气科学   86篇
地球物理   82篇
地质学   392篇
海洋学   196篇
天文学   3篇
综合类   163篇
自然地理   827篇
  2024年   4篇
  2023年   19篇
  2022年   68篇
  2021年   71篇
  2020年   58篇
  2019年   94篇
  2018年   44篇
  2017年   106篇
  2016年   99篇
  2015年   86篇
  2014年   115篇
  2013年   170篇
  2012年   121篇
  2011年   107篇
  2010年   91篇
  2009年   77篇
  2008年   118篇
  2007年   102篇
  2006年   99篇
  2005年   87篇
  2004年   63篇
  2003年   61篇
  2002年   59篇
  2001年   48篇
  2000年   51篇
  1999年   42篇
  1998年   36篇
  1997年   23篇
  1996年   12篇
  1995年   11篇
  1994年   10篇
  1993年   16篇
  1992年   5篇
  1991年   10篇
  1990年   7篇
  1989年   5篇
  1988年   12篇
  1987年   6篇
  1986年   6篇
  1985年   7篇
  1984年   10篇
  1983年   1篇
  1982年   3篇
  1980年   1篇
排序方式: 共有2241条查询结果,搜索用时 671 毫秒
371.
Adaptation to climate change is about planning for the future while responding to current pressures and challenges. Adaptation scientists are increasingly using future visioning exercises embedded in co-production and co-development techniques to assist stakeholders in imagining futures in a changing climate. Even if these exercises are growing in popularity, surprisingly little scrutiny has been placed on understanding the fundamental assumptions and choices in scenario approaches, timeframes, scales, or methods, and whether they result in meaningful changes in how adaptation is being thought about. Here, we unpack key insights and experiences across 62 case studies that specifically report on using future visioning exercises to engage stakeholders in climate change adaptation. We focus on three key areas: 1) Stakeholder diversity and scales; 2) Tools, methods, and data, and 3) Practical constraints, enablers, and outcomes. Our results show that most studies focus on the regional scale (n = 32; 52%), involve mainly formal decision makers and employ vast array of different methods, tools, and data. Interestingly, most exercises adopt either predictive (what will happen) and explorative (what could happen) scenarios while only a fraction use the more normative (what should happen) scenarios that could enable more transformative thinking. Reported positive outcomes include demonstrated increases in climate change literacy and support for climate change adaptation planning. Unintended and unexpected outcomes include increased anxiety in cases where introduced timeframes go beyond an individual’s expected life span and decreased perceived necessity for undertaking adaptation at all. Key agreed factors that underpin co-production and equal representation, such as gender, age, and diversity, are not well reported, and most case studies do not use reflective processes to harness participant feedback that could enable more robust methodology development. This is a missed opportunity in developing a more fundamental understanding of how these exercises can effectively shift individual and collective mindsets and advance the inclusion of different viewpoints as a pathway for more equitable and just climate adaptation.  相似文献   
372.
Wars are frequent and can affect land use substantially, but the effects of wars can vary greatly depending on their characteristics, such as intensity or duration. Furthermore, the spatial scale of the effects can differ. The effects of wars may be localized and thus close to conflict locations if direct mechanisms matter most (e.g., abandonment because active fighting precludes farming), or wide-ranging, e.g., farther away from conflict locations, if indirect mechanisms predominate (e.g., no access to agricultural inputs). Our goal was to quantify how the very different wars in the Caucasus region during post-Soviet times most likely affected agricultural abandonment at different scales. We analyzed data on conflict locations plus Landsat-derived land-cover data from 1987 to 2015, and applied matching statistics, difference-in-differences estimators, and logistic panel regressions. We examined the localized versus wide-ranging effects of the different wars on permanent agricultural abandonment and inferred to direct and indirect mechanisms that may have resulted in agricultural abandonment. While permanent agricultural abandonment was overall surprisingly limited across the Caucasus, up to one third of abandonment was most likely related to the wars. Among the wars, the war in Chechnya was by far the most intense and longest, but its effect on abandonment was similar to the less intense and relatively short war in Abkhazia. 47 % and 45 % of agricultural abandonment was related to each war, respectively. The reason was that the effect of the war in Chechnya was more localized, and abandonment occurred near conflict locations, in contrast to Abkhazia, where the effect was wide-ranging and abandonment occurred farther away from conflict locations. In contrast, the war in South Ossetia showed no significant effect on abandonment, and the war in Nagorno-Karabakh had the surprising pattern that abandonment was higher where no war had occurred. For each of the wars, abandonment was predominately related to the nearest conflict locations, but in Abkhazia additional conflict locations within 10 km further increased the probability of abandonment. We infer that the direct mechanisms of the war such as bombing, and active fighting most likely resulted in a localized effect close to conflict locations in Chechnya and in Nagorno-Karabakh. However, in Nagorno-Karabakh subsidies for new settlers after the war, (i.e., a positive wide-ranging effect), potentially reduced the amount of abandonment there. In contrast, negative wide-ranging effects such as refugee movements and post-war restrictions on their return is related to broad-scale abandonment in Abkhazia. In summary, permanent agricultural abandonment was not necessarily higher in a war with a high overall intensity. Instead, the effect of a given war varied in scale, and was related to the relative importance of direct and localized versus indirect and wide-ranging mechanisms, including postwar events and policies, which is likely the case for other wars, too.  相似文献   
373.
建议隐伏矿矿区采用行、排剖面网法布置勘探线和钻孔,利于多方位编制研究性勘探线剖面图,研究和确定深部矿体产状。对隐伏构造蚀变岩型、石英脉—蚀变岩型钼矿333类型资源/储量的圈定与外推分七种情况作了叙述,对米.百分值工程矿体的圈定和外推分五种情况作了叙述。低品位矿应圈定矿体与估算资源/储量。  相似文献   
374.
镇江市矿产资源规划数据库建设创新探讨   总被引:1,自引:0,他引:1       下载免费PDF全文
唐海燕  朱映  杨婷 《江苏地质》2012,36(4):379-383
在MapGIS平台,采用关系数据库模型,建设镇江市矿产资源规划数据库,形成较为完整的矿产资源规划数据库的图层内容、属性结构、属性内容、属性字段,为江苏全面开展各市县矿产资源规划数据库建设起到指导示范作用。  相似文献   
375.
生态型土地整治规划设计模式分析   总被引:3,自引:0,他引:3  
针对中国农村土地利用存在的问题和新农村生态景观建设需求,从生态型土地整治的涵义以及研究的意义入手,对生态型土地整治规划设计的特点和基本原则进行了论述,提出了生态型设计的四种基本模式,探讨了合肥地区生态型土地整治规划设计的三种重点区域模式及主要内容。  相似文献   
376.
数字旅游规划管理信息系统研究   总被引:1,自引:0,他引:1  
赵俊兰  赵洪岩 《测绘科学》2011,36(1):187-189
本文采用VB.NET与Super Objects的编程语言,研究了旅游规划管理信息系统的设计与实现,探讨了旅游空间数据库和属性数据库的设计,提供一种加快旅游业信息进程的方式,力求改变传统的规划管理模式,并以通海县兴蒙乡为例开发了适合政府规划管理部门应用的旅游规划管理信息系统.  相似文献   
377.
城市化进程的快速发展对城市规划管理观念、方法和手段提出了更高的要求,通过科学技术手段尤其是信息化手段改进城市规划管理,提高城市规划水平已成为必然。本文以GIS为核心技术,采用SOA面向服务的体系结构设计思想,介绍了昆明市规划管理信息系统的逻辑框架、技术路线、数据库的设计和各个功能模块的实现,最后重点阐述了系统的关键技术及应用后可能取得的社会、经济效益。  相似文献   
378.
针对我国500 m球面射电望远镜天线(FAST),提出了一体化天文轨迹规划;给出了详细的数学模型及推导分析。相对于当前采用的FAST轨迹规划,该方法使得馈源位置和反射面位置的控制误差可以相互补偿。指出当馈源系统和反射面系统具有相同的测控延迟误差时,并不影响FAST天线的性能。  相似文献   
379.
针对规划公示信息的多层次公众认知需求,利用本体思想解析土地利用规划信息,构建有向图为框架的信息重构模型;设计模型要素的关系数据结构,实现基于图遍历的信息检索与语义表达算法。以海南省昌江黎族自治县土地利用总体规划成果(2006~2020年)为实例,验证了模型的有效性。  相似文献   
380.
城市区域土地规划信息系统设计与实现   总被引:1,自引:0,他引:1  
从系统的总体技术体系、软件架构、关键技术问题的解决方案等方面介绍了基于GIS开发城市区域土地规划信息系统——杨春湖城市副中心土地规划信息系统的经验。本系统通过引入GIS思想和技术,提高了土地规划业务工作的效率,简化了业务工作流程。土地规划信息支持系统的建立,不仅解决了业务工作中存在的问题,而且为下一步建设土地规划的辅助...  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