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   7624篇
  免费   697篇
  国内免费   792篇
测绘学   465篇
大气科学   464篇
地球物理   432篇
地质学   2511篇
海洋学   850篇
天文学   13篇
综合类   721篇
自然地理   3657篇
  2024年   23篇
  2023年   81篇
  2022年   272篇
  2021年   271篇
  2020年   249篇
  2019年   269篇
  2018年   200篇
  2017年   240篇
  2016年   255篇
  2015年   259篇
  2014年   345篇
  2013年   449篇
  2012年   429篇
  2011年   379篇
  2010年   336篇
  2009年   368篇
  2008年   366篇
  2007年   404篇
  2006年   442篇
  2005年   393篇
  2004年   390篇
  2003年   345篇
  2002年   347篇
  2001年   357篇
  2000年   375篇
  1999年   313篇
  1998年   227篇
  1997年   190篇
  1996年   130篇
  1995年   85篇
  1994年   69篇
  1993年   62篇
  1992年   42篇
  1991年   37篇
  1990年   24篇
  1989年   14篇
  1988年   22篇
  1987年   16篇
  1986年   10篇
  1985年   7篇
  1984年   8篇
  1983年   4篇
  1982年   6篇
  1981年   1篇
  1980年   1篇
  1977年   1篇
排序方式: 共有9113条查询结果,搜索用时 15 毫秒
941.
The city of Vitoria‐Gasteiz in Spain is considered a “healthy city” and has implemented sustainable actions to increase the mobility of its healthcare professionals. The objectives of this study are firstly to account for the use of bicycles at work as a strategy for a healthy city and secondly to propose a conceptual framework for analyzing this network and its capacity to spread their practices The paradigm proposed is that of social networks, within which sharing between contacts is explained by means of two models: the “threshold model” and “opinion leaders”.  相似文献   
942.
Recent debates about the state of geography raise valuable questions about how the discipline can and should change in response to shifting institutional realities. Focusing on the breadth and interdisciplinarity of geography, these discussions often overlook the role of pedagogy—particularly graduate training—in adapting the discipline to new institutional landscapes. Drawing on experiences as current and recent geography doctoral students, we identify institutional seedlings of opportunity that can be cultivated toward a spectrum of alternative doctoral training models. These alternatives offer significant opportunities to better prepare early-career geographers for success and to solidify geography's position as a leader in interdisciplinary research.  相似文献   
943.
During the last quarter-century, global demand for energy has increased by more than 60%, and a similar increase is anticipated to occur by 2030 (Raymond, Deming, & Nichols, 2007). In the U.S., oil and gas development is projected to continue across western states within sage-grouse habitat. Greater sage-grouse, recently a candidate species for protection under the Endangered Species Act (ESA), have well documented negative responses to oil and gas disturbance. In this study, we create spatially-explicit oil and gas future development scenarios, baseline and high, and link them to sage-grouse population and habitat maps to quantify future exposure risk within Western Association of Fish and Wildlife Agencies (WAFWA) sage-grouse management zones (MZ) I and II. We then analyze recent land use decisions from the Bureau of Land Management (BLM) along with enacted policy from the State of Wyoming to estimate how these management actions might minimize the exposure risk of sage-grouse to oil and gas development into the future. Our results show that BLM and Wyoming conservation plans could reduce the exposure of sage-grouse to oil and gas development from 15-27% to 11–17% (31–37% reduction) in MZ I and from 15-27% to 5–9% (64–68% reduction) in MZ II. Our estimates of exposure to future oil and gas development, and conservation measures designed to ameliorate those threats, represent the upper and lower extents of potential impacts within scenarios. Our work demonstrates how spatial modeling and GIS visualization can be used by managers to assess likely outcomes of conservation decisions.  相似文献   
944.
In 2013, it was announced that Timor‐Leste's Oecussi enclave would become the site of a special economic zone. Arid, and inhabited mostly by semi‐subsistence farmers from West Timor's Meto ethno‐linguistic group, the plan entails remaking the enclave as an industrial, transport and tourism hub. To facilitate this, in mid‐2015 the authorities began the process of clearing hundreds of indigenous gardens and homes from land slated for mega‐projects intended to make the region attractive to foreign investors. In this paper, I describe how, for many Meto, land tends to be experienced as a spiritually mediated ‘geography of affect’ (Lea & Woodward, 2010) in which questions of place, belonging, spirituality and personal fortune cannot easily be divided, a reality that raises questions about the suitability of the plan's vision of globalized and investment driven ‘development’. Drawing on Scott, I argue that in Oecussi, spirits associated with the land are not apolitical, but are sometimes perceived as acting to protect locals against powerful outsiders – a characteristically Meto ‘weapon of the weak’ that is in keeping with their previous encounters with colonial regimes.  相似文献   
945.
Though relationships between urbanization and tree cover are generally well studied, the effect of redevelopment on urban trees, at the scale of the individual property, is not well understood. Developing knowledge in this area is important in order to limit tree loss during redevelopment and thus, ensure sustained ecosystem services. Here, we explore the removal or retention of trees adjacent to building demolition in Christchurch, New Zealand. We mapped the presence or absence of individual trees on 123 properties prior to, and following, building demolition. Using a classification tree (CT) analysis, the presence or absence of 1209 trees was modelled as a function of: tree-related variables, property-related variables, and economic variables. The CT model estimated tree presence/absence with overall accuracy of 80.4%. Results show that 21.6% of all trees were removed as a consequence of building demolition, resulting in a tree canopy cover reduction of 19.7% across all 123 properties. The CT showed that tree crown area was the most important variable for predicting the presence/absence of trees, whereby trees with small crown areas (<7.9 m2) were most frequently removed, especially if they were within 0.7 m of a demolished building. Land value was also an important determinant of tree presence/absence, such that tree removal was more prevalent on properties with higher land value ($/m2). The results provide important new insights into some of the reasons for tree removal or retention during redevelopment at the scale of the individual property where most tree-related decisions are made.  相似文献   
946.
947.
The notion of the “urban experiment” has become increasingly prevalent and popular as a guiding concept and trope used by both scholars and policymakers, as well as by corporate actors with a stake in the future of the city. In this paper, we critically engage with this emerging focus on “urban experiments”, and with its articulation through the associated concepts of “living labs”, “future labs”, “urban labs” and the like. A critical engagement with the notion of urban experimentation is now not only useful, but a necessity: we introduce seven specific areas that need critical attention when considering urban experiments: these are focused on normativity, crisis discourses, the definition of “experimental subjects”, boundaries and boundedness, historical precedents, “dark” experiments and non-human experimental agency.  相似文献   
948.
论乡村重构   总被引:91,自引:18,他引:73  
龙花楼  屠爽爽 《地理学报》2017,72(4):563-576
快速城镇化进程驱动中国乡村地域发生巨大变化。乡村重构,即为适应乡村内部要素和外部调控的变化,通过优化配置和有效管理影响乡村发展的物质和非物质要素,重构乡村社会经济形态和优化地域空间格局,以实现乡村地域系统内部结构优化、功能提升以及城乡地域系统之间结构协调、功能互补的过程。本文在界定乡村重构的概念内涵,构建基于“要素—结构—功能”演变助推乡村重构的理论框架基础上,从空间重构、经济重构、社会重构视角探讨了乡村重构的实现路径,并着眼于服务当前国家重大战略需求和解决城乡转型发展进程中乡村地域系统面临的现实困境,提出了未来中国乡村重构研究需重点关注的内容。最后,就现有旨在促进乡村社会经济发展的重大引导性战略和政府干预性政策及其在实践操作中引发的一系列问题,展开批判性分析和讨论。  相似文献   
949.
都市区空间结构与经济发展的互动关系研究   总被引:5,自引:3,他引:2  
张婷麟  孙斌栋 《地理科学》2017,37(4):512-518
文章采用结构方程模型实证检验空间结构与经济发展的互动关系。研究发现,中国都市区已经进入多中心分散阶段,空间结构与经济发展存在因果关系,即经济发展水平的提高会扩大人口规模,规模增加则导致集聚不经济上升,并促进空间结构多中心化。多中心化后的空间结构由于降低了集聚不经济而进一步提高生产率。因而,传统地理学中关于两者互动发展的描述得到实证支持;同时明确了多中心化的直接动力是人口规模的增加,而不是经济发展水平的提高。这些发现对于优化当前中国的城市与区域空间战略具有重要的启示。  相似文献   
950.
以广东省的市域为经济单元,利用空间自相关分析和密度分析法,对1994—2015年广东省产业结构发展水平空间格局进行了研究。结果表明:广东省逐渐形成了以广州、深圳、东莞为中心的第三产业圈,周边城市为第二产业外圈,并逐渐向四周扩散的圈层式空间格局。珠三角地区产业结构发展水平较高,其他地区相对落后。全省的全局空间自相关性比较高,产业发展水平的空间聚集特征明显,高-高区域集中在珠三角地区,低-低区域主要分布在其他地区,有较明显的两极分化异质性。  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