首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
This paper examines the spatial-temporal evolution of urban spatial structure across 269 Chinese prefectural cities from 2002 to 2019. Our analysis identifies a consistent trend toward a more polycentric configuration in the 25 Chinese mega-cities during this period, primarily due to population growth and a supportive policy environment. However, the evolutionary pathways of small- and medium-sized cities unfolded in a rather complex and diverse manner, with some becoming more polycentric while the majority adhering to a monocentric trajectory. In these cases, population growth is usually associated with a more monocentric pattern, characterized by rapid expansion of the urban core, while polycentric development is primarily attributed to specific spatial policies that support the emergence of subcenters. We conclude that polycentric development, while potentially suitable for mega-cities to alleviate diseconomies of scale, may be less appropriate for small- and medium-sized cities as it may constrain growth associated with agglomeration economies. We suggest that the development and implementation of regional spatial policy should be considerate of local historical paths and contextual factors. Finally, we propose a stylized framework to more accurately reflect the diverse and complex nature of urban spatial structure evolution in Chinese prefectural cities.  相似文献   

2.
Aiming at domestic garbage aerobic compost and town sludge anaerobic treatment, on the basis of reactor TISTD (the integrated of sludge thickening and digestion)which is developed by the authors’ team, a TIDGTS (the integrated of domestic garbage and town sludge)reactor is designed.The reactor is made up of garbage and sludge chambers.Aerobic compost is adopted in the garbage chamber, while anaerobic fermentation is used in the sludge chamber, thus garbage and sludge can be treated in the same reactor.32~36 ℃ of sludge digestion can be ensured by the heat from sludge digestion, and 20 L sludge and 15 kg garbage can be treated per day.While inlet sludge moisture content is 97.2%~99.8% and VS/TS is 0.45~0.69, the discharged sludge moisture content is 92.7%~96.1% and VS/TS is 0.28~0.42.When the inlet garbage moisture content is 73.5% and VS/TS is 0.65~0.88, the discharged garbage moisture content is 48.6% and VS/TS is 0.32~0.44.The results show that the efficiency of concentration and digestion is near to TISTD which is heated by heating wire.  相似文献   

3.
Zenith luminance converting factor is the characteristic parameter of sky luminance distribution,which is not related to regions.The fractal dimension value of the change process of zenith luminance converting factor shows that the sky can be divided into four types as CIE standard clear sky,pseudo- clear sky,pseudo- overcast sky and CIEstandard overcast sky.This is more suitable for the study of sky lumimance distribution with the exception of a few particular weather conditions.  相似文献   

4.
节水农作制度综合效益评价的研究   总被引:2,自引:1,他引:1  
不同的自然以及社会经济条件是形成各种节水农作制度的基础。文章主要从自然生态、经济、社会三个方面探讨节水农作制度形成的影响因素,将所涵盖的因素又具体细分为几类,从理化机制方面以及国内外实践经验出发,科学地分析了各种因素对节水农作制度形成与发展的制约形式,建立我国旱作地区节水农作制度形成机制的基本理论框架,并提出节水农作制度综合效益评价的构想。  相似文献   

5.
Products in enterprises are various in specifications. In order to get better benefits, it is essential for the managers of these enterprises to make right decisions for adjusting the stock structure of products. This paper develops a new modil system, which includes a series of interactive models, such as quatitative analysis, balance and evaluation models etc, and provides a frame for using these models to support the decision-making of product structure adjust.  相似文献   

6.
Three aspects of integrated disease management are considered. The first is the epidemiological synergism that can be derived through combining management tactics, and through disease management at regional scales. Field studies with potato late blight are used to demonstrate epidemiological impacts of integrating host resistance, fungicides, host density, and host genetic diversity. The importance of considering spatial scale and regional disease management are demonstrated with examples of cultivar mixtures in three different pathosystems. The second aspect is the potential for integrated management to increase the durability of resistance, e.g., through reduction of pathogen population size and imposition of disruptive selection. At this point in time, most information on this topic is limited to arguments of logic and to the results of mathematical models; empirical data are largely lacking. We suggest that current theoretical approaches need to be supplemented with inclusion of more complex processes, such as the effect of fitness modifiers in pathogen populations and the influence of quantitative adaptation of pathogens to their hosts. The third aspect is integration of resistance into overall crop management, including factors such as the balance between yield potential and disease resistance and the management of genotype x environment interaction. Such integration will increase the likelihood that farmers will utilize durable resistance, and will be demonstrated with examples from wheat production in the Pacific Northwest region of the USA. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

7.
城市模型反射率测量方法与运用   总被引:1,自引:0,他引:1  
介绍了一种测试城市模型反射率的试验方法。制作10个条形和十字形的城市模型进行测试,观测路面不同反射率对城市反射率的影响,并将实测模型反射率与ASTM E1918-06规范计算结果进行对比。研究发现:瞬时太阳辐射强度变化值在规范允许范围内,模型计算的反射率与ASTM E1918-06测量值的误差在0~0.1之间。当峡谷纵横比(建筑物高度与路面宽度之比)为1.0时,路面反射率从0.15提高到0.65,城市峡谷反射率增幅在0~0.30之间;提高路面反射率并不能有效提高城市峡谷反射率,尤其是纵横比较大的深峡谷。城市峡谷中的多重反射抑制城市反射率的提高。同时,反射路面将给行人增加额外的辐射通量,可能带来热不适感和眩光刺眼等问题。因此,应谨慎看待反射路面作为一个缓解城市热岛效应策略。  相似文献   

8.
邓明学 《中国农学通报》2009,25(23):358-363
以控制木虱木虱为重点的柑桔黄龙病综合防治理论已在广西柑桔主产区大面积推广应用,并取得了显著的防治效果,为了更好地理解和推广应用该理论,加速该理论在柑桔黄龙病区的推广应用,本文报道了该理论的形成过程、事实和理论依据以及技术要点。  相似文献   

9.
福寿螺综合防治研究进展   总被引:9,自引:0,他引:9  
摘 要:福寿螺作为入侵生物,已经在农业生产、生态环境和寄生虫病传播等方面产生了一系列严重的危害。目前在亚洲、北美和南美洲都有福寿螺为害的规模暴发。本文综述了近些年来,福寿螺的危害性及其综合防治的研究进展,同时简要的分析了在福寿螺的防治过程中存在的一些问题和当前研究的热点。  相似文献   

10.
Based on the network model of integrated service chains and evaluation index of candidate service resources, optimizing integrated service chain can be formally defined as a multi objective global optimization model with multiple constraints. We propose a multi objective global optimization algorithm based on improved multi objective genetic algorithms. The proposed algorithm uses a distance based nonparametric population diversity measurement operator, and diversity control is involved in the process of adaptive value assignment, elitist maintaining and selection operation. The proposed algorithm can optimize multiple objectives at the same time on the premise of meeting the constraints, and finally get a constrained Pareto optimum solution set which satisfy decision makers’ prefers. The simulation experiments indicate that the proposed algorithms can achieve global convergence and has better solution quality and distribution, which efficiently solve the problem of integrated service chain multi objective global optimization.  相似文献   

11.
高温高湿地区奶牛热应激综合控制技术体系研究   总被引:3,自引:1,他引:2  
摘要:根据南方高温高湿气候条件和中国荷斯坦牛生物学特性,利用分子生物、遗传育种、营养调控及环境控制技术,建立了包括新型实用防暑降温散栏式奶牛舍、新型实用散栏式奶牛场环境小气候智能化控制系统、奶牛抗热应激营养调控剂以及培育奶牛耐热新品系等高温高湿地区奶牛热应激综合控制技术体系。  相似文献   

12.
City residential structure is the main aspect of city spatial structure and in western countries it has been experienced three phases: centripetal collection, centrifugal pervasion and organic collection.From the viewpoint of historical development, the evolvement of residential structure in China can be summarized in three phases: archaic city, neoteric city and modern city.The character of city residential structure is different at different times.However, the residential sub-urbanization and the residential redistribution are the two central forms of the evolvement of residential structure in the modern city.  相似文献   

13.
Urban land-lease becomes an important way of paid land use,but the study of this way seems weak. This essay concentrates on three major issues: the Connotation,Rights Structure and Measure of Land Rent.The author clarifies the meaning,scope and forms of the urban land-lease,which differs from the lease of the land use right,specifies the rights structure especially the rights of the tenant and analyzes the principles,standards and ways of the land rent.In all,this essay puts forward a practical analysis for bettering the urban land-lease.  相似文献   

14.
鱼腥草主要病虫害调查方法与综合防治标准操作规程   总被引:2,自引:0,他引:2  
摘 要:该文简述了鱼腥草主要病虫害种类,形态和症状及识别方法,提出了相应的调查取样方法和分级标准。根据鱼腥草主要病虫害的发生规律,参照《国家绿色食品A级农药施用标准》和《中药材生产质量管理规范(试行)》等条例的规定,归纳了一套鱼腥草病虫害防治标准操作规程,为鱼腥草GAP标准化生产提供了保障。  相似文献   

15.
Today the information globalization is the trend of society development. The information technology has great influence not only on the mode of life and production, but also on the urban social and economic structure. In order to fit in with the change in this regard, the urban land-use distribution, residential mode, traffic pattern and so on should be changed correspondingly. Therefore, this change will lead to the development and evolution of whole urban spatial structure. In this paper, the development tendency of urban spatial structure in the information age is analyzed and some proposals on city planning and construction are put forward.  相似文献   

16.
Crack propagation of control fissures in perilous rock under loads is a key process in the failure of perilous rock. Based on the loading mechanism, the control fissures are classified into compression shear and tension shear types. By introducing a model of seepage stress, the calculating principle of the stress intensity factor and the propagation orientation of control fissure under seepage stress are put forward using fracture mechanics methods. Using Shoulishan perilous rock in the Wanzhou district of Chongqing, P. R. China, as an example, the calculated results show that there is an obvious increase of the stress intensity factor. The influence of hydrostatic pressure and hydrodynamic pressure also are analyzed.  相似文献   

17.
水稻白叶枯病再流行原因分析与防控对策研究   总被引:1,自引:0,他引:1  
为分析水稻白叶枯病历史演变与流行原因,研讨综合防治技术,对中国1960—2014年和浙江省温州市1971—2015年水稻白叶枯病的发生情况进行调查统计和分析。结果发现20世纪70—90年代初期为该病重发流行阶段,90年代中后期为间歇流行阶段,进入21世纪后病害发生减轻,但近年又趋上升态势。2014、2015年浙江省晚稻白叶枯病发病点多面广,浙江省东南沿海和沿江沿溪部分稻区发病较为严重,造成水稻产量较大损失。对该病在浙江省的发生动态及其影响流行的相关因子解析表明感病品种的种植与抗性退化、台风暴雨频繁、病原菌的累积和栽培管理措施不当是导致近年病害再度上升流行的主因;提出了新的耕作栽培条件下病害的防控对策,集成了一套以监测预警预报、选用抗(耐)病良种为基础,杜绝病菌来源为前提,秧田防治为重点,健身栽培和合理肥水、本田适期施药预防保护的综合防治技术,在生产上示范推广应用,有效控制该病的发生和流行。  相似文献   

18.
叶片可直接反映玉米植株的营养状况,是光合作用的主要场所,与干物质积累和产量形成密切相关。本研究以郑单958 (ZD958)为试验材料,以T1代表农民习惯处理; T2代表在T1的基础上,增加种植密度,推迟收获,降低施肥量,并优化施肥时期; T3代表在T2的基础上进一步增加种植密度和施肥量; T4代表在T3的基础上,降低种植密度和施肥量;N代表施氮量处理,设N0、N1、N2和N3分别为0、129.0、184.5和300.0kgNhm~(–2),研究综合农艺管理对夏玉米叶片生长及内源激素的调控作用。综合农艺管理措施包括优化耕作方式、种植密度、施肥量、施肥时期和收获时间等。结果表明,施氮量不足导致IAA、ZR和GA_3含量降低, ABA含量升高,叶片SPAD值、叶面积指数(LAI)及比叶重均显著降低;随施氮量的增加,叶片IAA、ZR和GA_3含量增加,ABA含量降低,LAI、SPAD和干物质积累量均显著增加。综合农艺管理处理可调节叶片内源激素含量,其中T4处理IAA、ZR和GA_3含量较T1处理分别高23.1%、9.8%和14.7%;ABA含量降低12.4%;叶片LAI适宜, SPAD值增加4.2%,最终单株干物质积累量增加12.6%。综合农艺管理在降低施氮量,配合最佳的农艺管理方式下,可调节内源激素含量,增加叶片SPAD和比叶重,有利于单株干物质积累,这可能是促进夏玉米产量增加的重要原因之一。  相似文献   

19.
STEVE(Screening Tool for Estate Environment Evaluation)is a statistical model through regression analysis. It can predict the air temperature by climate and urban morphology predictors for Singapore estate, while it hasn't been proved valid in other areas. Consequently, three groups of validation tests in Guangzhou area were conducted, one using the original data in the literature and the other two using experimental data from the field measurement. It is shown that STEVE tool can meet the engineering accuracy and can be used as a simple temperature prediction model tool in urban planning and design process in Guangzhou area and other cities with similar climate conditions. Besides, the STEVE tool can be optimized further to expand its applicable scope.  相似文献   

20.
Summary Horizontal, uniform, race-non-specific or stable resistance can be discerned according to Van der Plank, from vertical, differential, race-specific or unstable resistance by a test in which a number of host genotypes (cultivars or clones) are tested against a number of pathogen genetypes traces of isolatest. If the total non-environmental variance in levels of resistance is due to main effects only differences between cultivars and differences between isolates) the resistance and the pathogen many (in the broad sense) are horizontal in nature. Vertical resistance and pathogenicity are characterized by the interaction between host and pathogen showing up as a variance compenent in this test due to interaction between cultivars and isolates.A host and pathogen model was made in which resistance and pathogenicity are governed by live polygenic loci. Within the host the resistance genes show additivity. Two models were investigated in model I resistance and pathogenicity genes operate in an additive way as envisaged by Van der Plank in his horizontal resistance. Model II is characterized by a gene-for-gene action between the polygenes of the host and those of the pathogen.The cultivar isolate test in model I showed only main effect variance. Surprisingly, the variance in model II was also largely due to main effects. The contribution of the interaction to the variance uppeared so small, that it would be difficult to discern it from a normal error variance.So-called horizontal resistance can therefore be explained by a polygenic resistance, where the individual genes are vertical and operating on a gene-for-gene basis with virulence genes in the pathogen. The data reported so far support the idea that model II rather than model I is the realistic one.The two models also revealed that populations with a polygenic resistance based on the gene-for-gene action have an increased level of resistance compared with the addition model, while its stability as far as mutability of the pathogen is concerned, is higher compared to those with an additive gene action. Mathematical studies of Mode too support the gene-for-gene concept.The operation of all resistance and virulence genes in a natural population is therefore seen as one integrated system. All genes for true resistance in the host population, whether they are major or minor genes are considered to interact in a gene-for-gene way with virulence genes either major or minor, in the pathogen population.The models revealed other important aspects. Populations with a polygenic resistance based on a gene-for-gene action have an increased level of resistance compared to populations following the addition model. The stability, as far as mutability of the pathogen is concerned, is higher in the interaction model than in the addition model.The effect of a resistance gene on the level of resistance of the population consists of its effect on a single plant times its gene frequency in the population. Due to the adaptive forces in both the host and the pathogen population and the gene-for-gene nature of the gene action an equilibrium develops that allows all resistance genes to remain effective although their corresponding virulence genes are present. The frequencies of the resistance and virulence genes are such that the effective frequencies of resistance genes tend to be negatively related to the magnitude of the gene effect. This explains why major genes often occur at low frequencies, while minor genes appear to be frequent. It is in this way that the host and the pathogen, both as extremely variable and vigorous populations, can co-exist.Horizontal and vertical resistance as meant by Van der Plank therefore do not represent different kinds of resistances, they represent merely polygenic and oligogenic resistances resp. In both situations the individual host genes interact specifically with virulence genes in the pathogen. Van der Plank's test for horizontal resistance appears to be a simple and sound way to test for polygenic inheritance of resistance.The practical considerations have been discussed. The agro-ecosystems should be made as diverse as possible. Multilines, polygenic resistance, tolerance, gene deployment and other measures should be employed, if possible in combination.  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