排序方式： 共有89条查询结果，搜索用时 31 毫秒
21.
回归分析是统计分析中常用的方法之一。传统的回归模型不具备全域分析能力,而变量场之间的关系多采用SVD（Singular Value Decomposition）进行分析,与传统的回归分析有所脱节。更为广义的线性回归模型是传统线性回归模型的延拓,在标量情况下,该模型可转化为传统线性回归模型。该模型的基本特征包含乘法不可互易性、等价于传统线性回归（因子项为标量时）、可分析性、延拓性、降维特征及容错性等。该模型解决了传统的线性回归模型不具备全域分析能力及模型表达能力受限于模型维数的现实问题。本文采用了NCEP（National Centers for Environmental Prediction）降水、高度场、风场月平均资料及国家气候中心西太平洋副热带高压指数资料,利用该模型和传统回归方案进行对比分析,分析结果表明,该模型具有一定的实用参考价值。 相似文献
22.
Neuropeptide Y(NPY) is a 36-amino acid peptide of the neuropeptide Y family that plays key roles in the regulation of food intake. In this study,we focused on NPY m RNA expression changes around feeding time and during food deprivation in olive flounder. The olive flounder NPY m RNA levels were analyzed in different tissues and a high level of expression was detected in the brain. We also demonstrated a correlation between NPY expression levels in the brain and feeding schedule. NPY expression levels in olive flounder maintained on a daily scheduled feeding regimen increased shortly before feeding and decreased after the scheduled feeding time. Compared with the-1 h group before feeding,NPY expression in the 3 h group after feeding decreased significantly( P <0.05). Food deprivation led to an 81.7% decrease in NPY m RNA levels in the 24 h fasted group(P <0.05) and a 91.7% decrease in the 48 h fasted group(P <0.05). Therefore,our study demonstrates that NPY expression is associated with food intake in olive flounder. This result reveals the function of NPY in regulating food intake and its potential importance in olive flounder aquaculture. 相似文献
23.
区域双核结构模式是一种重要的经济地理现象。基于新经济地理学的研究视角和分析框架,论文构建模型,分析了规模经济和对外贸易推动区域双核结构模式的生成过程和经济机理。模型研究表明,规模经济和对外贸易是塑造区域双核结构模式的基本力量:规模经济的增强放大了本地市场效应,导致了区域核心城市的出现;对外贸易影响着沿海地区的经济地理优势,决定着港口区位核心城市和内陆地区核心城市的并存。山东半岛济南—青岛双核结构模式生成过程的实证研究也表明,双核结构模式是制造业活动完成由以手工业为主导向现代化大生产为主导转变、区域发展环境完成由相对封闭向相对开放转变之后才产生的经济地理现象。 相似文献
24.
基于DEA和Malmquist指数模型的中国资源型城市效率及其变化(英文) 总被引：1，自引：0，他引：1
Employing DEA model and Malmquist productivity index, this paper probes into the urban efficiencies of 24 typical resources-based cities in China and their changes from 2000 to 2008. The research finds that the overall efficiencies of the resources-based cities are just at a general level, and only a few of them reach the optimal level. The scale efficiency is the major determining factor of the achievement of overall efficiency, the effect of which, never-theless, is reducing. From the perspective of classification characteristics, the re-sources-based cities in northeastern region have been in the front rank in terms of overall efficiency, pure technical efficiency and scale efficiency. There is a certain positive correlation between urban population scale and urban efficiency. The analysis of urban efficiency changes shows that the changes in overall efficiency of resources-based cities from 2000 to 2008 had a weak improving tendency. Both the technical change index and productivity change index decreased, indicating that the urban efficiency did not improve during this pe-riod, and the tendency of technical recession and productivity decline was obvious. In terms of the classification of urban efficiency changes, the urban overall efficiency improved in each of the four regions from 2000 to 2008, among which western region witnessed the greatest increase. Cities with different resource types have improved their urban overall efficiencies except steel-based cities. The urban overall efficiency increased in resources-based cities of different scales, with greater improvement in small and medium-sized cities than in big cities. 相似文献
25.
人文与经济地理学的传承与创新：青年学者的责任 总被引：2，自引：2，他引：0
陈明星 周素红 何深静 叶超 汪明峰 孙威 王开泳 刘艳军 朱晟君 马海涛 姚华松 马仁锋 张华 余建辉 吴康 王丰龙 黄耿志 赵荣钦 郝庆 刘春腊 郑捷 刘海猛 《地理研究》2018,37(3):449-472
2018年1月27-28日,人文与经济地理学青年论坛暨第二届中国科学院区域可持续发展分析与模拟重点实验室青年论坛在北京国家会议中心成功举办。青年论坛以“人文与经济地理学的传承与创新：青年学者的责任与行动”为主题。莅临会场的院士、前辈和主管部门领导纷纷表示鼓励、支持和关怀青年人才的更快更好的成长。在这样的背景下,以这次青年论坛主题为题,在新时代传承和创新人文与经济地理学,青年学者责无旁贷,追寻地理学家的精神,集中探讨青年学者的责任与行动,展示人文与经济地理青年学者的思考和风采。 相似文献
26.
City growth patterns are attracting more attention in urban geography studies. This paper examines how cities develop and grow in the upper tail of size distribution in a large-scale economy based on a theoretical model under new economic geography framework and the empirical evidence from the US. The results show that cities grow in a sequential pattern. Cities with the best economic conditions are the first to grow fastest until they reach a critical size, then their growth rates slow down and the smaller cities farther down in the urban hierarchy become the fastest-growing ones in sequence. This paper also reveals three related features of urban system. First, the city size distribution evolves from low-level balanced to primate and finally high-level balanced pattern in an inverted U-shaped path. Second, there exist persistent discontinuities, or gaps, between city size classes. Third, city size in the upper tail exhibits conditional convergence characteristics. This paper could not only contribute to enhancing the understanding of urbanization process and city size distribution dynamics, but also be widely used in making effective policies and scientific urban planning. 相似文献
27.
要解决行星引潮力与太阳活动的关系问题,首先要解决计算方法不同引致的引潮力结果差异的问题.本文从引潮力的计算方法着手分析了不同的计算方法所得出的引潮力的异同,发现过去的引潮力计算方法只能显示出行星公转周期或者会合周期,却反映不出对应于行星公转或者会和半周期的引潮力变化.利用引力与太阳绕转惯性离心力之差计算出来的引潮力,比过去常规的引力之差计算出来的引潮力大两个数量级,并且其引起的太阳潮汐变化相位也大不相同,为重新理解引潮力与太阳活动之间的关系提供了新的视角.利用绕转惯性离心力和引潮力共同解释太阳活动变化特征,比传统引潮力单一因子的解释更有说服力,太阳活动是行星引潮力、太阳绕转惯性离心力等多个因子共同作用的结果. 相似文献
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采用液相还原法制备纳米铁粒子,粒径约为50 nm,主要成分为ɑ-Fe。实验研究了纳米铁还原高浓度硝基苯的效果及反应动力学。结果表明:自制的纳米铁具有很高的活性,短时间内能将高浓度硝基苯彻底还原,效果远优于普通铁粉。当摩尔比满足n纳米铁∶n硝基苯=4∶1时,纳米铁还原硝基苯属于一级反应动力学,反应速率常数和半衰期分别为0.159 3 h-1和4.351 2 h。整个实验过程中,ρ(DO)在0.5 mg/L以下,pH值约为9.0,体系呈弱碱性的厌氧环境,有利于厌氧微生物的生长。纳米铁反应后的产物为Fe6(OH)12CO3和MgFe3O4,且以Fe6(OH)12CO3为主。纳米铁反应后较以前比粒径变化不大,分散性较好,但表面被严重腐蚀。 相似文献
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利用北京市2012年竞争型投入产出表,构建了敏感度模型,定量分析了最终使用变动1%对某一产业增加值和就业的影响程度。研究表明：① 根据经济敏感度系数,北京应该优先疏解金属制品、机械和设备修理服务等8个产业部门。假设上述产业部门全部疏解,对北京市产业增加值的影响为1.06%,对应的产业增加值减少186.4亿元。② 根据就业敏感度系数,北京应该优先疏解木材加工品和家具、纺织品等8个产业部门。假设上述产业部门全部疏解,对北京市就业人口的影响为1.31%,对应的就业人数减少12.0万人。③ 根据综合敏感度系数和首都核心功能定位,北京应该疏解的产业部门依次是批发和零售、化学产品、食品和烟草、金属冶炼和压延加工品、煤炭采选产品等19个产业部门。 相似文献
30.
本地居民对居住地景观的审美感知水平对于区域大尺度景观的保护与持续利用具有重要影响,这在相对欠发达但具有较高审美价值景观资源的地区意义更为重大。本文以云南省怒江傈僳族自治州为例,基于620份针对当地居民的调查问卷与现场调研,通过构建Logistic回归模型,分析了怒江州本地居民对居住地景观的审美感知状况及相关影响因素。结果表明,怒江州本地居民对于居住地景观的审美感知水平较高,有75．81％的受访者认为居住地周边景观是美的。对这一审美感知具有影响的因素共有8项,在直接影响因素中,是否在保护区内、行政村周边高程标准差具有正向影响;行政村到最近县城距离、是否认为近年生态环境恶化、是否认为旅游开发存在不好的影响、是否希望进入城市生活具有负向影响。在间接影响因素中,包括住房类型和家中是否有电视都具有正向影响。本文据此尝试提出提高怒江州居民对居住地景观审美感知水平、促进当地景观保护与持续利用的相关政策建议。 相似文献