共查询到20条相似文献，搜索用时 31 毫秒
1.
区域人口迁移流的规模不仅取决于迁出地与目的地的“双边”要素,也与前期迁移流和周边迁移流息息相关。传统重力模型揭示了区域人口迁移过程的“推-拉”机制,但受制于对时空维度的忽视,无法有效表达迁移流之间的时空依赖关系,因而难以度量区域要素变化对迁移流产生的时空溢出效应。本文引入多种形式的时空依赖结构,构建迁移流时空重力模型,并采用贝叶斯马尔可夫链蒙特卡洛（MCMC）方法进行估计。在此基础上,结合时空效应框架量化区域要素对迁移流的影响,定量分析人口迁移过程的时空溢出效应与动力机制。本文以1985-2015年中国省际人口迁移为例,通过与非空间的动态重力模型估计结果比较,初步表明时间依赖、空间依赖以及时空扩散依赖在区域人口迁移过程中不容忽视;时空维度上,区域要素变化在初期对迁移网络的溢出效应超过对该区域迁移流的直接影响;逐渐衰减的时空溢出效应维持了区域人口迁移规模发展的相对稳定,与动态重力模型估计结果形成了鲜明对比。区域人口规模、人均GDP水平及其时空溢出效应共同驱动中国省际人口迁移系统的发展。耦合时空维度依赖关系的时空重力模型能更好地理解区域人口迁移过程的演化特征,为促进区域人口均衡发展提供科学的决策依据。 相似文献
2.
Han Jinfen Nan Fangru Feng Jia Lü Junping Liu Qi Liu Xudong Xie Shulian 《中国海洋湖沼学报》2022,40(2):729-744
Journal of Oceanology and Limnology - The genus Sheathia consists of over 20 species primarily distributed in Asia, Europe, Oceania, North America, and Africa. However, the origin and evolution of... 相似文献
3.
The recession and revitalization of old industrial cities concerns urban industrial evolution and its characteristics. Based on the theory of evolutionary resilience, we developed an analytical framework for the industrial structure evolution of old industrial cities, and applied the framework to a case study in Shenyang. The following conclusions are drawn. First, since 1978, Shenyang's industrial growth capacity has shown fluctuation between ‘contraction-expansion'. As the secondary industry has a much stronger expansionary and contractionary capacity for growth, this results in lacking stability leading to industrial structure transformation. Second, since 1999, the orientation towards a high-end manufacturing industry in Shenyang has weakened, and the evolution of the new and old growth path is characterized by low-end orientation. Third, since 2007, Shenyang's industrial innovation output capacity has dropped sharply which has been significantly affected by scientific and technological personnel and enterprise-owed science and technology institutions and to a less extent by RD expenditure. We applied the resilience theory to study the industrial evolution of an old industrial city, explored new study perspectives on industrial evolution and verified the applicability of the resilience theory. This paper provides a scientific reference for understanding the recent deceleration in economic growth in the Northeast old industrial base, and for exploring new paths toward revitalization. 相似文献
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恐龙化石对研究地球演化、生物进化、地层对比、地质年代、古环境、古地理、古气候等方面具有重要的科学价值。但恐龙化石发掘后面临着严重的风化问题,许多化石发掘后十几年甚至几年内就迅速遭受风化破坏。为深入研究探索恐龙化石地质遗迹的深层次风化原因和机理,该文采用TM（温度和应力）耦合分析方法,对山东诸城恐龙化石风化规律进行深入分析研究。根据化石与围岩间膨胀的不协调性,探索在温度变化情况下化石与围岩间的相互作用规律及对风化造成的影响。结果揭示了温度作用下化石风化的初步原因和规律,可为化石保护提供参考科学依据。 相似文献
5.
TheSouthChinaSea(SCS)islocatalinthejunCti0noftheEurasian,PacificandIndodeustralianPlates,andisoneofthebiggestrnarginalseasinthewesternPadfic~n.Uyeda(l977)regardedtheSCS'soriginasoneofthebasicprobboincompletelyre-solvedbytheTheoryofPlateTeCtoniesrv).Heaskedfl.Whydoesanarcriseup(theoriginofarcmountains)?2.Whyisthestressinthebackurcbasinregionextensional(theoriginofbackurcbasin)?3.Whyisthernantleintheinnerurcbelthot(theoriginofvohanismandhighgcothermalflow)?Therewermanyviewnointsontheori… 相似文献
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Meteorites are the extraterrestrial rocks, which provide insights into the origin and evolution of the solar system. During the past half century, a great number of meteorites has been discovered on the Antarctic Ice Sheet, confirming that the Antarctica is the most important meteorite concentration area on the earth. Since the first four Antarctic meteorites were found in Grove Mountains in 1998, a total of 9834 meteorites have been collected by four subsequent expeditions. It opens a new field of meteorite study in China, and also accumulates a great deal of scientific samples for China. Recently, classification of Grove Mountains meteorites has been carried out for 6 years, and made following progresses: (1) 2433 meteorites, which include many special meteorites, e.g. Martian meteorites, ureilites and carbonaceous chondrites, have been classified. (2) the Antarctic meteorite curation and the sample sharing system are set up preliminarily. (3) the classification procedure, the management of meteorite samples, and the application procedure for the Antarctic meteorites are completed after the systematic classification during these years. (4) young generation researchers on meteorite are trained through the cooperation of many universities and institutes on meteorite classification. 相似文献
7.
一、引言关于地球上生命的起源问题,人类为之探索和争论早在亚里士多德(公元前384—322年)那个时代就已经开始,至今已逾几千年,可是,仍然是当代科学面临的重大课题。1985年,美国《科学文摘》杂志载文谈“二十世纪尚待解决的二十个重大课题”时将生命起源列为第一个重大课题。近些年来,有关研究虽已取得一些主要进展,但问题并没有真正解决,生命起源的奥秘还远未揭开。目前,有关生命起源的学说甚多,归纳起来,大体上可分为两大类, 相似文献
8.
华北平原水资源紧缺情势与因源 总被引：15，自引：0，他引：15
基于水资源可持续利用理念,从水资源承载能力演化周期性、经济社会需用水规模难变性和未来水资源供需关系入手,介绍近60年以来华北平原水资源情势,特别是该平原水资源量、实际用水量和地下水开采量变化特征,并结合未来10到30年区域经济社会发展需用水量趋势,识别和诊断华北平原水资源紧缺因源.结果表明:由于降水量减少导致华北平原缺... 相似文献
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Xiaopei Yan 《中国地理科学(英文版)》1995,6(1):1-14
This paper focuses on the evolution and characteristics of the export labour service in China since the modern time especially
since the reform of economic system in 1978. Historically the contract workers, central to the goal of making a living, were
the main body of the international migration. And Guangdong and Fujian provinces were the main origin places of the migration
but the destination of the migrants varied. Both pull and push forces for driving the migration were identified. Then analysis
is turned to the characteristics of export labour service of China since the reform of economic system in 1978. 1) The export
labour has increased rapidly despite a small quantity. 2) The export labour service is planned and organized. 3) The export
workers are considered temporary migrants. 4) The dominant ways of export labour service are project contracts and pure labour
export. And 5) the destinations of export labour are scattered over the world. Thirdly, the impact of the export labour service
on the origin places and the emerging problems and contradictions were examined. In China, export labour service has alleviated
the employment contradiction and gradually become one of sources of gaining foreign currency on the one hand, and China, through
the service, has learnt the advanced technology and management experiences of other countries. However, some problems in the
service such as small number, unsatisfactory quality of the export labour, and the weak link between the service and employment
are emerging, which need to be solved. Finally, the prospects for China as a large country of export labour was discussed. 相似文献
11.
References： 《东北亚地学研究》2007,10(1):17-21
Eyl has the unique desultory-weak or gap seismic reflection structure as its one of the most important characteristics. It is very important to clarify sedimentary characteristics and its origin for Yitong Graben and its sedimentary facies and tectonic evolution. On the basis of the research of core analyses, well logging data analyses, sedimentary facies analyses and seismic reflection structure analyses, the authors have concluded the sedimentary characteristics of Eyl, and have carried out Eyl sedimentary environments and its origin. The result shows that Eyl desultory-weak or gap seismic reflection may be a series of small scale secondary sediment fans superimposition. 相似文献
12.
Many observations show that in the Yellow Sea internal tidal waves (ITWs) possess the remarkable characteristics of internal Kelvin wave, and in the South Yellow Sea (SYS) the nonlinear evolution of internal tidal waves is one of the mechanisms producing internal solitary waves (ISWs), which is different from the generation mechanism in the case where the semidiurnal tidal current flows over topographic drops. In this paper, the model of internal Kelvin wave with continuous stratification is given, and an elementary numerical study of nonlinear evolution of ITWs is made for the SYS, using the generalized KdV model (GKdV model for short) for a continuous stratified ocean, in which the different effects of background barotropic ebb and flood currents are considered. Moreover, the parameterization of vertical turbulent mixing caused by ITWs and ISWs in the SYS is studied, using a parameterization scheme which was applied to numerical experiments on the breaking of ISWs by Vlasenko and Hutter in 2002. It is found that the vertical turbulent mixing caused by internal waves is very strong within the upper layer with depth less than about 30m, and the vertical turbulent mixing caused by ISWs is stronger than that by ITWs. 相似文献
13.
地震模式受制于学术思想和科技水平,并随时间演化。研究了从“弹性回跳说”以来的演化轨跡：仅考虑震源区（断层段）→震源区和周围构造相互作用→地壳上部脆性层和深部韧性层与上地幔间的耦合→将地震视为现今大陆变形动力系统自组织演化过程的一种行为。百年演化总趋势是从震源到“动力系统”。特征为：模式时空域扩大、维数上升|从还原论、机械论到整体论、演化论|从经典力学到复杂系统理论及非线性动力学|新模式包容并超越已有模式,向大自然的本性逐渐接近。受益于地震大地测量学观测成就,关联性强的跨学科新地震模式正在探索与成长中。 相似文献
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Changwei CHEN Linfu XUE Hongbing DAI Jian WANG Xingke XU Qinglong MENG College of Earth Sciences Jilin University Changchun China 《东北亚地学研究》2007,(1)
Ey1 has the unique desultory-weak or gap seismic reflection structure as its one of the most important characteristics.It is very important to clarify sedimentary characteristics and its origin for Yitong Graben and its sedimentary facies and tectonic evolution.On the basis of the research of core analyses,well logging data analyses,sedimentary facies analyses and seismic reflection structure analyses,the authors have concluded the sedimentary characteristics of Ey1,and have carried out Ey1 sedimentary environments and its origin.The result shows that Ey1 desultory-weak or gap seismic reflection may be a series of small scale secondary sediment fans superimposition. 相似文献
16.
Ey1 has the unique desultory-weak or gap seismic reflection structure as its one of the most important characteristics. It is very important to clarify sedimentary characteristics and its origin for Yitong Graben and its sedimentary facies and tectonic evolution. On the basis of the research of core analyses, well logging data analyses, sedimentary facies analyses and seismic reflection structure analyses, the authors have concluded the sedimentary characteristics of Ey1, and have carried out Ey1 sedimentary environments and its origin. The result shows that Ey1 desultory-weak or gap seismic reflection may be a series of small scale secondary sediment fans superimposition. 相似文献
17.
罗艳 《成都信息工程学院学报》2010,25(1):50-55
三维数据场可视化中的体绘制技术是科学计算可视化领域最重要的一项技术。由于体绘制技术需要处理的数据量十分庞大,生成图像算法又比较复杂,常常需要使用高端图形工作站和特殊硬件来实现。近年来计算机性能的大幅提高,特别是可编程GPU的顶点和片段处理器的快速发展,为普通Pc机上实现实时体绘制技术提供了硬件加速的支持。介绍了科学计算可视化和可编程GPU的概况,在普通PC机上实现了基于GPU的三维纹理映射的体绘制算法,实验表明,在不损失图像绘制质量的情况下,加快了绘制的速度。 相似文献
18.
阎小培 《中国地理科学(英文版)》1996,(1)
ＳＯＭＥＡＳＰＥＣＴＳＯＦＥＸＰＯＲＴＬＡＢＯＵＲＳＥＲＶＩＣＥＩＮＣＨＩＮＡ阎小培ＳＯＭＥＡＳＰＥＣＴＳＯＦＥＸＰＯＲＴＬＡＢＯＵＲＳＥＲＶＩＣＥＩＮＣＨＩＮＡ￥ＹａｎＸｉａｏｐｅｉ（ＣｅｎｔｒｅｆｏｒＵｒｂａｎ＆ＲｅｇｉｏｎａｌＳｔｕｄｉｅｓ，Ｚ... 相似文献
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张虎才 《中国地理科学(英文版)》1998,8(4):377-382
ＧｅｏｌｏｇｉｃａｌｒｅｃｏｒｄｓｒｅｖｅａｌｅｄｔｈａｔｔｈｅＨｏｌｏｃｅｎｅｅｎｖｉｒｏｎｍｅｎｔｓｈａｄｅｘｐｅｒｉｅｎｃｅｄｄｒａｓｔｉｃｃｈａｎｇｅｓ,ｗｈｉｃｈｗａｓｃｌｏｓｅｌｙｒｅｌａｔｅｄｔｏｈｕｍａｎｅｖｏｌｕｔｉｏｎａｎｄｆｉｎ... 相似文献