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   610篇
  免费   36篇
  国内免费   22篇
测绘学   58篇
大气科学   46篇
地球物理   8篇
地质学   84篇
海洋学   30篇
天文学   9篇
综合类   48篇
自然地理   385篇
  2024年   1篇
  2023年   8篇
  2022年   47篇
  2021年   44篇
  2020年   43篇
  2019年   38篇
  2018年   27篇
  2017年   35篇
  2016年   48篇
  2015年   26篇
  2014年   34篇
  2013年   39篇
  2012年   35篇
  2011年   16篇
  2010年   21篇
  2009年   17篇
  2008年   21篇
  2007年   18篇
  2006年   21篇
  2005年   19篇
  2004年   18篇
  2003年   17篇
  2002年   23篇
  2001年   25篇
  2000年   13篇
  1999年   8篇
  1998年   5篇
  1987年   1篇
排序方式: 共有668条查询结果,搜索用时 15 毫秒
571.
旅游厕所作为旅游活动中不可缺少的基本要素,既是一个民族的文明窗口,更是一个国家和地区综合实力的体现,已成为当前生态文明建设背景下中国旅游发展过程中亟待解决的重要课题。本文以苏州市为例,构建了旅游厕所满意度影响因素结构方程模型,基于游客满意度,深入分析旅游厕所建设影响因素,并提出旅游厕所创新发展机制。主要结论为:①规划布局、基本功能、细节设计、厕所文化、环保特征和管理工作与满意度之间存在正向关系,如厕教育与满意度之间存在负向关系;②影响旅游厕所建设主要表现在7个维度,其中规划布局对旅游厕所建设影响最大,其次是管理工作和基本功能,而环保特征对旅游厕所建设影响最小;③构建了集供需层、理念层、规划层和目标层于一体的旅游厕所创新发展机制,以期促进旅游厕所科学合理发展,为建设生态文明社会提供有益参考。  相似文献   
572.
The sustainable science-based management of natural resources requires knowledge exchange between scientists and environmental decision-makers; however, evidence suggests that information flow is inhibited by a range of barriers. To date, our understanding of the range and importance of factors limiting knowledge exchange between scientists and decision-makers is based primarily on the perceptions of decision-makers, while the perceptions of scientists have been largely overlooked. This study addresses this knowledge gap by quantitatively assessing the perceptions of scientists, represented by a sample of 78 Australian marine scientists, regarding (i) the role and importance of engaging with environmental decision-makers on a personal level, (ii) the role and importance of engaging with environmental decision-makers at the institutional level, (iii) current barriers to engaging with environmental decision-makers and (iv) options for overcoming barriers to engaging with environmental decision-makers. Survey results suggest that Australian marine scientists feel that they have an obligation to engage decision-makers in their science, and that engaging with and communicating to environmental decision-makers is important on a personal level. This study also identifies a range of barriers that impede engagement activities, including inadequate measures of science impact that do not account for engagement activities, a lack of organisational support for engagement activities, insufficient time to conduct engagement activities in addition to other responsibilities and a lack of funding to support engagement activities. To overcome these barriers, participants identified the need for institutional innovation by research institutions, research funders and decision-making agencies alike to promote a culture whereby knowledge exchange activities are legitimised as core business for research scientists, and recognised and rewarded appropriately. Although difficulties exist in implementing such institutional innovations, doing so will improve two-way knowledge exchange among scientists and decision-makers and improve the likely success of environmental management.  相似文献   
573.
几种最优滤波方法的分析和比较   总被引:1,自引:0,他引:1  
解决状态或信号最优估计问题的方法有很多,主要有Wiener滤波、经典Kalman滤波及以白噪声估计理论为基础的现代时间序列分析方法。系统总结了3种主要滤波方法的基本思想、适用条件,并结合算例进行了分析和比较。结果表明,经典Kalman滤波虽然能处理时变系统,但是求解Riccati方程要求较大的计算量,而现代时间序列分析方法则通过构造ARMA信息模型来代替求解Riccati方程,虽减少了计算量,但该方法仅仅适用于处理时不变系统。  相似文献   
574.
Energy and climate policies may have significant economy-wide impacts, which are regularly assessed based on quantitative energy-environment-economy models. These tend to vary in their conclusions on the scale and direction of the likely macroeconomic impacts of a low-carbon transition. This paper traces the characteristic discrepancies in models’ outcomes to their origins in different macro-economic theories, most importantly their treatment of technological innovation and finance. We comprehensively analyse the relevant branches of macro-innovation theory and group them into two classes: ‘Equilibrium’ and ‘Non-equilibrium’. While both approaches are rigorous and self-consistent, they frequently yield opposite conclusions for the economic impacts of low-carbon policies. We show that model outcomes are mainly determined by their representations of monetary and finance dimensions, and their interactions with investment, innovation and technological change. Improving these in all modelling approaches is crucial for strengthening the evidence base for policy making and gaining a more consistent picture of the macroeconomic impacts of achieving emissions reductions objectives. The paper contributes towards the ongoing effort of enhancing the transparency and understanding of sophisticated model mechanisms applied to energy and climate policy analysis. It helps tackle the overall ‘black box’ critique, much-cited in policy circles and elsewhere.

Key policy insights

  • Quantitative models commissioned by policy-makers to assess the macroeconomic impacts of climate policy generate contradictory outcomes and interpretations.

  • The source of the differences in model outcomes originates primarily from assumptions on the workings of the financial sector and the nature of money, and of how these interact with processes of low-carbon energy innovation and technological change.

  • Representations of innovation and technological change are incomplete in energy-economy-environment models, leading to limitations in the assessment of the impacts of climate-related policies.

  • All modelling studies should state clearly their underpinning theoretical school and their treatment of finance and innovation.

  • A strong recommendation is given for modellers of energy-economy systems to improve their representations of money and finance.

  相似文献   
575.
The existence of outliers can seriously influence the analysis of variational data assimilation. Quality control allows us to effectively eliminate or absorb these outliers to produce better analysis fields. In particular, variational quality control(VarQC) can process gray zone outliers and is thus broadly used in variational data assimilation systems. In this study,governing equations are derived for two VarQC algorithms that utilize different contaminated Gaussian distributions(CGDs): Gaussian plus flat distribution and Huber norm distribution. As such, these VarQC algorithms can handle outliers that have non-Gaussian innovations. Then, these VarQC algorithms are implemented in the Global/Regional Assimilation and PrEdiction System(GRAPES) model-level three-dimensional variational data assimilation(m3 DVAR) system. Tests using artificial observations indicate that the VarQC method using the Huber distribution has stronger robustness for including outliers to improve posterior analysis than the VarQC method using the Gaussian plus flat distribution. Furthermore,real observation experiments show that the distribution of observation analysis weights conform well with theory,indicating that the application of VarQC is effective in the GRAPES m3 DVAR system. Subsequent case study and longperiod data assimilation experiments show that the spatial distribution and amplitude of the observation analysis weights are related to the analysis increments of the mass field(geopotential height and temperature). Compared to the control experiment, VarQC experiments have noticeably better posterior mass fields. Finally, the VarQC method using the Huber distribution is superior to the VarQC method using the Gaussian plus flat distribution, especially at the middle and lower levels.  相似文献   
576.
我国油气对外依存度不断攀升,通过传统意义上的创新难以满足油气勘探开发大幅增产降本的要求,必须通过革命性、颠覆性的创新来破困突围。在页岩气革命中,基于第一性原理思维法,围绕提高控制储量和降低开发成本两大目标,创新了井工厂钻井、一趟钻钻井、超长水平段水平井钻井等颠覆性创新技术,使钻井周期和作业成本大幅降低,实现了我国首个大型页岩气田——涪陵页岩气田的高效开发。最后,笔者展望了第一性原理思维法在缝洞型碳酸盐岩油气藏和干热岩地热资源开发领域的创新应用,并指出运用第一性原理思维法是未来石油工程技术实现颠覆性创新的重要途径和方法。  相似文献   
577.
实践教学在GIS专业人才培养过程中发挥着重要作用,对于应用技术型大学的GIS专业人才培养,实践教学体系的构建更加重要。分析应用技术型大学GIS实践教学的作用,阐述实践教学体系内容设计原则、实践教学体系构成,并给出GIS专业实践教学体系设计实例,探讨实践教学应注意的具体问题。  相似文献   
578.
城市地图集综合性强,涉及领域广泛,能够全方位展示城市风貌。在编制城市地图集时结合创新主题展示城市发展现状具有重要意义。深圳市被誉为创新之都,以新版《深圳市地图集》的创新发展图组为例,介绍其如何结合深圳市创新特色进行内容结构建立和可视化表达,为同类地图集、图册的编制提供参考。  相似文献   
579.
本文在叙述了“数字地球”的产生背景的基础上,着重分析了“数字地球”的科学内涵、“数字地球”给地球科学带来的新契机和我们应有的对策.笔者认为,“数字地球”是国家利益和现代科学技术的综合产物;“数字地球”的科学内涵可分为宏观战略层、技术实现层和应用层三个层面;“数字地球”是一个战略,并不能代替相关的学科和技术领域,现有的科学技术水平也不能完全满足“数字地球”的要求;“数字地球”的兴起给地球科学带来了大好机遇,使地球科学在对地球整体性认识、数字虚拟、对地球复杂巨系统的研究等方面都大大深化;面临“数字地球”的挑战,我们应该采取的策略是积极借鉴数字地球的思想,在继续大力发展现有的相关学科和技术领域的同时,努力进行自主创新,力求通过“中国数字地球”或“数字中国”的建设来占领制高点.  相似文献   
580.
中国城镇非密集地区城乡发展的空间创新研究   总被引:1,自引:0,他引:1  
余斌  曾菊新  罗静 《地理科学》2007,27(3):296-303
经济全球化加剧了中国城镇非密集地区的"边缘化";城乡互动发展模式是城镇非密集地区城乡发展的理性选择;通过空间结构创新能够有效推动城乡互动发展。空间福利经济学研究空间消费形态与空间效用分配之间的关系;基于空间福利经济学的区域空间结构创新意在寻求区域空间结构的形态优化和层次提升,以实现空间公平与总体效率兼容发展。在中国城镇非密集地区城乡发展的空间创新过程中,政府的空间安排塑造区域空间结构的基本架构,企业的区位选择构成区域空间结构创新的基本推动力量。  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