Beckmann城市体系是异速生长模型的理论基础与实证分析   总被引：2，自引：0，他引：2  

陈彦光 《科技通报》2002,18(5):360-367

从基于中心地理论的Beckmann城市等级－规模模型Pm-KRS^m-1/(1-K）^m出发，导出了关于城市体系的Beckmann异速生长方程dy/dt=b(y/x)dx/dt，得到中心（最大）城市的人口规模（P1）与城市体系总人口（U）之间的几何测试关系P1∝U^b，证明了当城市规模分布的分维D≤1时，标度因子b=1；而当D＞1时，则有b＞0。从长期平均看来，b值应变化于0～1之间，即有0＜b≤1，且有b→1的变化趋势。研究发现，Beckmann异速生长方程的标度因子（b）与城市规模分布的分维（D）有一定关系，且其数值在理论上等于中心城市空间结构的广义维数（Dc）与城市体系空间结构的广义维数（Ds）之比（即有b=Dc/Ds）。以河南省城市体系（1990－1998）为实例，对理论推导结果进行了实证分析。  相似文献   

真菌趣谈     

《发明与创新》2003,(4):39-39

从远古时代以来，真菌就对生态、社会和经济产生影响。同时，真菌的多样性使其成为继昆虫之后的第二大有机体群。真菌存在于一切地方，如水中、地上、空气里（孢子）、寄生在植物上、应用于食品业和制药业、根茎周围（共生的苔癣）、草原上和森林里（蘑菇）。真菌包括任何一种有机物质腐烂时所产生的霉菌、引起农业灾害的真菌、导致皮肤病的真菌、制作面包和啤酒用的发酵剂、使乳酪具有香味的真菌以及用来制作青霉素的真菌如药用青霉。真菌的体积、颜色和形式多种多样，但有一个共同特点：缺少叶绿素或进行光合作用的色素，因此它们需要寻找…  相似文献   

种绿豆     

马路  徐亮 《小学自然教学》2007,(12):59-59

开学初,教科学的徐老师要求我们回家种绿豆,观察绿豆的生长,主要探究“绿豆芽生长需要阳光吗”“绿豆芽生长对水的需求”两个问题。我和岑瑜超觉得这个作业挺有趣,就回家试着种绿豆。  相似文献   

Potential production simulation and optimal nutrient management of two hybrid rice varieties in Jinhua,Zhejiang Province,China     

Xie WX  Wang GH  Zhang QC 《Journal of Zhejiang University. Science. B》2007,8(7):486-492

Potential growth of two widely-grown hybrid rice varieties in the Jinhua district of Zhejiang Province, Shanyou63 for mid-rice and Xieyou46 for late rice, was simulated using a crop growth model of WOFOST. Parameters of the rice growth in WOFOST were calibrated through field experiments from 1999 to 2002 in Jinhua. The potential yield simulated with WOFOST was about 12 t/ha for Shanyou63 and 10 t/ha for Xieyou46, which are in good agreement with the highest recorded yield obtained in this area. Under farmers practice, current yield is about 7.5 t/ha for Shanyou63 and 6.5 t/ha for Xieyou46. There is a gap between the actual rice yield and the potential yield for these two hybrid rice varieties grown in this area. The attainable target yields were set to 70% to 75% of their potential yields for the two varieties. A recently developed software ＂Nutrient Decision Support System （NuDSS）＂ for irrigated rice was used to optimize nutrient management for these two rice varieties. According to NuDSS, the optimal fertilizer N requirement for the target yields was about 150 kg/ha for Shanyou63 and about 120 kg/ha for Xieyou46, which were only about 70% of the fertilizer N application under current farmers＇ practice. Comparing with farmers＇ practice, there is great potential to increase actual rice yields and to reduce fertilizer N use rates by improving rice crop management practice in Jinhua.  相似文献   

Genetic analysis of fruit shape traits at different maturation stages in sponge gourd   总被引：5，自引：0，他引：5  

Zhang S  Hu J  Zhang CF  Guan YJ  Zhang Y 《Journal of Zhejiang University. Science. B》2007,8(5):338-344

The fruit shape is important quantitative trait closely related to the fruit quality. However, the genetic model of fruit shapes has not been proposed. Therefore, in the present study, analysis of genetic effects for fruit shape traits （fruit length and fruit perimeter） in sponge gourd was conducted by employing a developmental genetic model including fruit direct effects and maternal effects. Analysis approaches of unconditional and conditional variances were applied to evaluate the genetic behavior of fruit shape traits at economical and physiological maturation times. The results of variance analysis indicated that fruit length and fruit perimeter were simultaneously affected by fruit direct genetic effects and maternal effects. Fruit direct genetic effects were relatively more important for fruit shape traits at whole developmental period. The gene expression was most active at the economical maturation stage （1-12 d after flowering） for two shape traits, and the activation of gene was mostly due to direct dominance effects at physiological maturation stage （13-60 datter flowering）. The coefficients due to different genetic effects, as well as the phenotypic correlation coefficients, varied significantly between fruit shape traits themselves at various maturation stages. The results showed that it was relatively easy to improve fruit shape traits for industrial purpose by carefully selecting the parents at economical maturation stage instead of that at physiological maturation stage.  相似文献   

QTL analysis for some quantitative traits in bread wheat     

Pushpendra KG  Harindra SB  Pawan LK  Neeraj K  Ajay K  Reyazul RM  Amita M  Jitendra K 《Journal of Zhejiang University. Science. B》2007,8(11):807-814

Quantitative trait loci (QTL) analysis was conducted in bread wheat for 14 important traits utilizing data from four different mapping populations involving different approaches of QTL analysis. Analysis for grain protein content (GPC) sug- gested that the major part of genetic variation for this trait is due to environmental interactions. In contrast, pre-harvest sprouting tolerance (PHST) was controlled mainly by main effect QTL (M-QTL) with very little genetic variation due to environmental interactions; a major QTL for PHST was detected on chromosome arm 3AL. For grain weight, one QTL each was detected on chromosome arms 1AS, 2BS and 7AS. QTL for 4 growth related traits taken together detected by different methods ranged from 37 to 40; nine QTL that were detected by single-locus as well as two-locus analyses were all M-QTL. Similarly, single-locus and two-locus QTL analyses for seven yield and yield contributing traits in two populations respectively allowed detection of 25 and 50 QTL by composite interval mapping (CIM), 16 and 25 QTL by multiple-trait composite interval mapping (MCIM) and 38 and 37 QTL by two-locus analyses. These studies should prove useful in QTL cloning and wheat improvement through marker aided selection.  相似文献   

教师要有质疑精神     

李明军 《中国基础教育研究》2007,3(12):11-13

做学问要在不疑处有疑,质疑是创新的前提、学习的动力。质疑的内容是自己的教育教学工作、教师用书、教科书等;质疑的方法是发挥想象、查阅资料,联系实际观察,进行实验分析。教师有了质疑精神,可以促使教师与教师之间、教师与学生之间、教师与编者之间的交流,带动学生质疑创新,使自己心情蝓快,与新课程共同成长,为社会培养出具有创新精神的人才。  相似文献   

积累与“生长”     

储广林 《中小学教师培训》2011,(12):40-41

当前小学语文教学流派纷呈,主张林立：简单语文、深度语文、情境语文、情智语文、诗意语文等,但都离不开“语文”,归根到底还是“语文”,只不过从不同的切人点强调自己语文教学的观点。  相似文献   

诗意渗透德育，为生长提供动力     

王玉琴 《四川教育》2011,(7)

德育在我们的教育中有着举足轻重的地位。这在今天学校的日常生活中可以寻找到佐证。但从孩子的言谈举止中,我们有一个共识：德育的效果一般仅体现在孩子们的作文和表演中,没有深入到孩子的内心,化为孩子们的行为。德育教育能否像绵绵春雨,以慢慢飘洒、长时浸润的方式,鼓励孩子们去追求崇高的精神、健全的人格、美好的习惯、良好的意志品质？  相似文献   

植物世界的未解之谜     

黄双红 《聪明泉(少儿版)》2011,(4)

<正>在五光十色的植物世界中,有许多神秘莫测的自然现象。有的现象被人类破解,而有的现象至今仍是未解的谜团。植物神奇的感觉功能,植物也发生变性,植物也有血型……一个个谜诱惑着人们为之探究。1神奇的感觉功能让人不可思议的是,植物在感觉等方面与动物和人类有惊人的相似之外,还有听觉、嗅觉和触觉,而且还富有情感呢!当植物的叶子受到摧折时,它们会表现出痛感。马铃薯对气压的变化非常敏感,在两天前就能作出反应。在印度尼西亚爪哇岛上,生长着一种奇异的花,这种花平时很少见,但火山爆发前一天,会冒出来,预报火山即将爆发。植物的这些特异功能等等着人们去探究。  相似文献