排序方式： 共有107条查询结果，搜索用时 31 毫秒
91.
气候变化背景下辽宁省气候资源变化特征分析 总被引：11，自引：0，他引：11
采用辽宁省54个气象台站建站以来的气温、降水、积温、风速、日照、蒸发等9个气象要素年资料,分析了近半个世纪辽宁省气候资源变化的空间、时间特征,以及其变化对农业和气象能源的影响.结果表明:辽宁省各地的气温、积温普遍为增高趋势,降水、风速、日照、蒸发普遍为减少倾向;气温、积温、日照、蒸发等均具有突变性和阶段性特征,风速、最低气温无显著突变性,而是存在明显的趋势性;从长远看,气候资源变化对辽宁省农业生产和生态环境的影响是弊大于利;虽然观测表明风速有下降趋势,但不能说明风能资源蕴藏量有下降趋势,需要今后进一步关注,但太阳能资源有一定的减少倾向;辽西地区易发展太阳能资源开发利用项目. 相似文献
92.
This study introduces a multi-step methodology for analyzing social media data during the post-disaster recovery phase of Hurricane Sandy. Its outputs include identification of the people who experienced the disaster, estimates of their physical location, assessments of the topics they discussed post-disaster, analysis of the tract-level relationships between the topics people discussed and tract-level internal attributes, and a comparison of these outputs to those of people who did not experience the disaster. Faith-based, community, assets, and financial topics emerged as major topics of discussion within the context of the disaster experience. The differences between predictors of these topics compared to those of people who did not experience the disaster were investigated in depth, revealing considerable differences among vulnerable populations. The use of this methodology as a new Machine Learning Algorithm to analyze large volumes of social media data is advocated in the conclusion. 相似文献
93.
建筑业是中国最大的钢铁消费领域,动态分析建筑中的钢铁存量的变化特征,有助于把握其二次资源回收潜力,为铁资源的循环利用及相关管理提供科学支撑。本研究以动态物质流分析结合生命周期分布函数,测算了1949—2016年中国房屋建筑中的钢铁存量。结果显示：经过缓慢增长期、稳定增长期和快速增长期三个阶段后,中国房屋建筑中钢铁存量从1949年的10.0万t增长到2016年的28.1亿t,房屋建筑中人均钢铁存量也从0.2kg/人增加到2029kg/人;受工业化和城镇化进程影响,中国四大经济区域房屋建筑中人均钢铁存量差别明显,2016年东部地区房屋建筑中人均钢铁存量最大为2526kg/人,其次是东北地区2128kg/人、中部地区1732kg/人和西部地区1605kg/人;受城镇和农村的生活环境、经济水平差异影响,中国城乡房屋建筑中人均钢铁存量差异显著,2016年中国房屋建筑中城镇人均钢铁存量达3145kg/人,农村为530kg/人。 相似文献
94.
在工业经济支撑下,河南省巩义市于上世纪80年代跻身于全国百强县的行列。但是,随着村域经济的发展,村域主体(企业、农户等)间的竞争日趋激烈,资源短缺,配置效率低,能源紧张问题突出,恶性竞争时有发生,已成为制约该市村域经济增长的瓶颈。本文在简述国内外学者研究的基础上,指出借用生态学研究村域经济发展具有优越性,并结合ArcGIS技术对1994年～2006年间巩义市292个村域生态经济位的时空演化进行分析,认为村域经济在稳步向前发展的同时,呈现动态波动特征。针对村域经济发展过程中存在的产业结构重构、恶性竞争、资源要素配置不合理等问题,提出3点调控措施：实施错位经营战略;共同进化代替竞争排斥;开拓潜在生态位。 相似文献
95.
松嫩平原西部草地的时空变化特征 总被引：11，自引：0，他引：11
本文以遥感信息作为主要数据源，以地理信息系统为主要手段，首次对松嫩平原西部地区不同覆盖度的草地资源以及草地内部结构的时空变化进行了深入分析，得出了1989年～2001年间高、中、低覆盖草地之间以及与其它土地利用类型之间的相互转化数量和特征。结果表明，12年间研究区3种草地类型的面积均有不同程度的减少，其中，它们转化为旱田的比例分别占转移总面积的77.78%、70.13%和36.57%，说明人类对草地的持续开发是造成草地面积减少的主要原因。从与盐碱地之间的相互转化关系来看，3种草地类型转化为盐碱地的面积比例随着草地覆盖率的减少而增大，比例分别为0%、4.62%和32.81%，可见植被覆盖率对于草地盐碱化的发生起决定作用。从草地内部结构的动态变化来看，呈现高覆盖向中覆盖再向低覆盖的逐级退化特征，而且这种演替规律在当前人类活动下基本上为不可逆过程，草地的退化在空间上主要集中在镇赉县的北部、洮南市的南部、通榆县的北部以及乾安县的西部。本文最后从合理利用研究区现有的草地资源、综合进行草地盐碱化的治理出发，提出了生态环境修复和草地可持续发展的对策。 相似文献
96.
Joe Nandhakumar 《The Information Society》2002,18(4):251-262
This article reports an ethnographic study that investigates the ways in which time was experienced and managed in an information systems (IS) development project. The study is based on 6 months of intensive overt participant observation of the development of Executive Information Systems in a large multinational company. Drawing on time geography, this article discusses a social perspective of time and social dynamics of time management in IS development project teams and outlines its implications for formal approaches to time management. 相似文献
97.
Prior research has demonstrated that achievement goals for teaching matter for student learning and teacher experiences. While previous studies have primarily focused on how goals differ between individuals, educational theorists and practitioners have proposed that investigating variation within individuals may be more suitable for explaining their daily experiences. To investigate the magnitude of within-person variation in goals, we distinguished between temporal variability and context specificity and tested their relevance for differences in emotional experiences when teaching. One-hundred-and-eight higher education teachers participated with 213 courses and 949 consecutive course sessions across an average of five weeks. Before each session, they reported their current achievement goals, and directly afterwards, the emotions they experienced throughout the respective session. We used multilevel analyses to investigate sources of variation in these constructs. Results indicated that between half and two thirds of the variability in goal pursuit could be attributed to a stable-general fraction (between-level: different teachers), and that goal pursuit also had substantial amounts of variable-general (different semester weeks of the teachers), stable-specific (different courses of the teachers), and variable-specific (remaining session variance) fractions. Variability in emotions could also be attributed to these four fractions to a substantial extent, with the stable-general fraction being lower than for the goals. Further, emotions were systematically related to achievement goals, with different effects being observable for the different levels. Taken together, these findings contribute to a better understanding of how to conceptualize and assess achievement goals for teaching and how they are intertwined with emotions. 相似文献
98.
基于五螺旋理论,评价2008—2019年中国30个省份绿色创新系统耦合协调时空分布规律。运用空间杜宾模型探讨影响绿色创新系统耦合协调的主要因素。研究发现中国各省份绿色创新系统耦合协调度呈逐年上升态势,绿色创新系统耦合协调度呈现东部>中部>西部>东北的特征;在直接效应层面,市场化水平、对外开放水平、城镇化水平能有效促进绿色创新系统耦合协调水平上升,产业结构高级化则抑制绿色创新系统耦合协调水平提升,财政自主度未对绿色创新系统耦合协调水平产生影响。基于此,提出提升中国绿色创新系统耦合协调水平的政策建议。 相似文献
99.
研究目的：创新要点：研究方法：重要结论：采用广义估计方程模型对存在时间相关件的事故频次数据进行建模,并与传统广义线性模型的估计效果进行对比。
通过广义估计方程来考虑事故频次建模中数据的时间相关性,从而提高参数估计准确度以及模型预测精度。基于4年高速公路交通事故频次数据,建立考虑时间相关性的广义估计方程以及传统的广义线性模型,并采用统计指标对模型效果进行对比。1．事故频次数据样本最对预测精度影响很大;2．广义估引方程能够有效考虑事故频次数据中存住的时间相关性;3．广义估计方程的参数估计比传统广义线性模型史准确,且精度更高。 相似文献
100.
Extensible Markup Language (XML) documents are associated with time in two ways: (1) XML documents evolve over time and (2) XML documents contain temporal information. The efficient management of the temporal and multi-versioned XML documents requires optimized use of storage and efficient processing of complex historical queries. This paper provides a comparative analysis of the various schemes available to efficiently store and query the temporal and multi-versioned XML documents based on temporal, change management, versioning, and querying support. Firstly, the paper studies the multi-versioning control schemes to detect, manage, and query change in dynamic XML documents. Secondly, it describes the storage structures used to efficiently store and retrieve XML documents. Thirdly, it provides a comparative analysis of the various commercial tools based on change management, versioning, collaborative editing, and validation support. Finally, the paper presents some future research and development directions for the multi-versioned XML documents. 相似文献