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   6008篇
  免费   505篇
  国内免费   750篇
测绘学   511篇
大气科学   547篇
地球物理   884篇
地质学   1793篇
海洋学   353篇
天文学   1537篇
综合类   282篇
自然地理   1356篇
  2024年   22篇
  2023年   59篇
  2022年   133篇
  2021年   97篇
  2020年   161篇
  2019年   207篇
  2018年   146篇
  2017年   202篇
  2016年   193篇
  2015年   209篇
  2014年   212篇
  2013年   322篇
  2012年   201篇
  2011年   231篇
  2010年   198篇
  2009年   385篇
  2008年   451篇
  2007年   450篇
  2006年   443篇
  2005年   347篇
  2004年   318篇
  2003年   297篇
  2002年   278篇
  2001年   248篇
  2000年   209篇
  1999年   232篇
  1998年   213篇
  1997年   110篇
  1996年   93篇
  1995年   91篇
  1994年   77篇
  1993年   94篇
  1992年   64篇
  1991年   51篇
  1990年   55篇
  1989年   41篇
  1988年   40篇
  1987年   31篇
  1986年   15篇
  1985年   11篇
  1984年   5篇
  1982年   1篇
  1981年   3篇
  1980年   1篇
  1979年   2篇
  1977年   4篇
  1976年   3篇
  1975年   1篇
  1972年   1篇
  1954年   4篇
排序方式: 共有7263条查询结果,搜索用时 15 毫秒
21.
This article reconsiders the epistemic and geographic boundaries that have long separated scholarship on urban water poverty and politics in the Global North and South. We stage an encounter between the seemingly dissimilar cases of Tooleville outside of the city of Exeter in California’s Central Valley and Bommanahalli outside of Bangalore, India, to illuminate the geography of water marginalization at the fringes of urban areas, and to deepen cross-fertilization between two geographic literatures: environmental justice (EJ) and urban political ecology (UPE). We argue that there is scope for transnational learning in three arenas in particular: (1) water access, (2) state practice, and (3) political agency. In so doing, we aim to advance a genuinely post-colonial approach to theory and practice in the pressing arena of urban water politics.  相似文献   
22.
基于一般系统论和博弈论理论,对旅游产业利益相关者进行界定,分析了各利益主体对旅游产业认知差异,认为主要表现在政策、经济、社会文化、环境保护等4个方面.由于认知差异的存在,各利益主体行为对旅游产业产生了正面影响和负面影响,针对负面影响提出了相应的对策,旨在促进旅游产业发展达到一种利益均衡、责权对称的状态.  相似文献   
23.
Mega-urban agglomerations are strategic core areas for national economic development and the main regions of new urbanization. They also have important roles in shifting the global economic center of gravity to China. However, the development of mega-urban agglomerations has triggered the interactive coercion between resources and the eco-environment. The interactive coupled effects between urbanization and the eco-environment in mega-urban agglomerations represent frontier and high-priority research topics in the field of Earth system science over the next decade. In this paper, we carried out systematic theoretical analysis of the interactive coupling mechanisms and coercing effects between urbanization and the eco-environment in mega-urban agglomerations. In detail, we analyzed the nonlinear-coupled relationships and the coupling characteristics between natural and human elements in mega-urban agglomerations. We also investigated the interactive coercion intensities between internal and external elements, and the mechanisms and patterns of local couplings and telecouplings in mega-urban agglomeration systems, which are affected by key internal and external control elements. In addition, we proposed the interactive coupling theory on urbanization and the eco-environment in mega-urban agglomerations. Furthermore, we established a spatiotemporal dynamic coupling model with multi-element, multi-scale, multi-scenario, multi-module and multi-agent integrations, which can be used to develop an intelligent decision support system for sustainable development of mega-urban agglomerations. In general, our research may provide theoretical guidance and method support to solve problems related to mega-urban agglomerations and maintain their sustainable development.  相似文献   
24.
Galaxies can be classified in two broad sequences which are likely to reflect their formation mechanism. The 'main sequence', consisting of spirals, irregulars and all dwarf galaxies, is probably produced by gas settling within dark matter haloes. We show that the sizes and surface densities along this sequence are primarily determined by the distributions of the angular momentum and formation time of dark haloes. They are well reproduced by current cosmogonies provided that galaxies form late, at z  ≲ 2. In this scenario, dwarf ellipticals were small 'discs' at z  ∼ 1 and become 'ellipticals' after they fall into cluster environments. The strong clustering of dwarf ellipticals is then a natural by-product of the merging and transformation process. The number of dwarf galaxies predicted in a cluster such as Virgo is in good agreement with the observed number. On the other hand, the 'giant branch', consisting of giant ellipticals and bulges, is probably produced by the merging of disc galaxies. Based on the observed phase-space densities of galaxies, we show that the main bodies of all giant ellipticals can be produced by dissipationless mergers of high-redshift discs. However, high-redshift discs, although denser than present-day ones, are still not compact enough to produce the high central phase-space density of some low-luminosity ellipticals. Dissipation must have occurred in the central parts of these galaxies during the merger which formed them.  相似文献   
25.
A key challenge for effective, ongoing urban climate adaptation is to adapt institutions within urban governance. While an extensive foundation of empirical knowledge on urban climate adaptation has accumulated over the last decade, our image of institutional adaptation continues to be dominated by a focus on planning. Whilst understandable, this can obscure a fuller range of areas in which institutional adaptation to climate change is being pursued. Furthermore, methodological path dependency in large-N analysis via a common focus on analyzing formal planning documents risks a skewed perspective as such documents may only offer a partial view. Building on the rich range of work to date assessing climate adaptation in cities, and notwithstanding continued major gaps such as in small-medium cities, we now need to find ways to examine the diversity of institutional adaptation occurring in practice, and to comparatively draw on the situated interpretive knowledge of case experts within individual cities to do so. With this aim in mind, this paper explores institutional adaptation in a specific domain (urban water) in a sample of 96 major cities across six continents through a survey of 319 case experts, examining the diversity of institutional adaptation across contexts and exploratively probing its drivers. Findings show that multiple forms of institutional adaptation are being jointly pursued in cities across all continents, leaning towards ‘softer’ rather than ‘harder’ forms, but nonetheless revealing a wide range of activity. Patterns in drivers suggest a political explanation for institutional adaptation (e.g. involving change agents and political pressure) rather than a rational one (e.g. involving response to climate-related risks and/or extreme events). Overall, there is a need to combine parsimony with expanded interpretive sensibility in advancing large-N research on institutional adaptation diversity in comparative perspective.  相似文献   
26.
利用1976、1989、2005年三期遥感影像,运用GIS和分形理论研究干旱区典型流域——玛纳斯河流域近30年的土地利用/土地覆被变化的复杂性和稳定性。结果表明:玛纳斯河流域各时段的土地利用/土地覆被类型分布具有分形结构,土地利用/土地覆被类型形状复杂性和斑块的稳定性波动变化,1976、1989、2005年三时期的各种土地利用/土地覆被类型总平均分维值分别为1.394 0、1.363 4和1.389 9。总平均稳定性指数分别为0.606 0、0.636 6、0.610 1。三期土地利用/覆被类型平均稳定性排序为:沙地>未利用土地>居民点工矿用地>水域>林地>草地>耕地>盐碱地。耕地、林地、草地、盐碱地稳定性相对较差。通过对流域土地利用/土地覆被类型变化复杂性和稳定性的研究,可以为政府协调水土开发和调整土地利用结构提供支持。  相似文献   
27.
We present a geometric and graphic approach to studying spatial patterns of urban hierarchy in the US. The multiplicatively weighted Voronoi diagram is found to be effective for visualizing theoretical regions delineated by socio‐economic variables. The population landscape of the continental US demonstrates overall and stepwise patterns reflecting population, neighborhood and distance, with overwhelming influence from huge metropolitan areas. Stepwise exploration and cluster analysis of the spatial pattern reveal an urban hierarchy. Attributes and arrangement are the two important factors of urban hierarchy, with attribute having a stronger local influence and arrangement having a stronger global influence. The study also presents a variation of Zipf's law to visualize the rank‐size distribution from tabular and statistical space to map space.  相似文献   
28.
29.
In this paper a slightly different approach is proposed for the process of determining the functions S m and H m * of the algorithm of the canonical version of Hori method. This process will be referred to as integration theory of the mth order equation of the method. It will be shown that the ordinary differential equation with an auxiliary parameter t * as independent variable, introduced through Hori auxiliary system, can be replaced by a partial differential equation in the time t. In this way, the mth order equation of the algorithm assumes a form very similar to the one of other perturbation methods. In virtue of this new approach of the integration theory for Hori method, Lagrange's variational equations introduced by Sessin are revised. As an example, the Duffing equation is solved through this new approach.  相似文献   
30.
文章总结了以往国内学者对城市功能区域的数量化方法研究,认为在层次分析法等方法中对指标权重的确定存在主观因素过多等不足,严重影响了研究的科学性和准确性,文章为了克服上述不足,将多属性效用理论的代理价值法与博弈论的方法应用于城市功能区的布局与研究,并以深圳市南山区物流中心的选址为例,阐述了代理价值法与博弈论在城市功能区域中的具体实践操作。  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