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排序方式: 共有489条查询结果,搜索用时 15 毫秒
71.
数学教学的核心是学生的再创造,让学生经历知识的再创造过程,培养了学生的创造性思维。学生从教师的教转向主动地学,在教师的指导下去建构数学知识,为学生能够顺利地用数学知识解决实际问题奠定了良好的知识基础。 相似文献
72.
Elastomeric pad bearings are widely applied in short- to medium-span girder bridges in China, with the superstructure restrained by reinforced concrete (RC) shear keys in the transverse direction. Field investigations after the 2008 Wenchuan earthquake reveal that bearing systems had suffered the most serious damage, such as span falling, bearing displaced, and shear key failure, while the piers and foundations underwent minor damage. As part of a major study on damage mechanism and displacement control method for short- to medium-span bridges suffered in Wenchuan earthquake, a 1:4 scale, two-span bridge model supported on elastomeric pad bearings were recently tested on shake tables at Tongji University, Shanghai. The bridge model was subjected to increasing levels of four seismic excitations possessing different spectral characteristics. Two restraint systems with and without the restraint of RC shear keys were tested. A comprehensive analytical modeling of the test systems was also performed using OpenSees. The experimental results confirmed that for the typical bridges on elastomeric pad bearings without RC shear keys, the sliding effect of the elastomeric pad bearings plays an important role in isolation of ground motions and, however, lead to lager bearing displacement that consequently increases the seismic risk of fall of span, especially under earthquakes that contain significant mid-period contents or velocity pulse components. It is suggested from the test results that RC shear keys should be elaborately designed in order to achieve a balance between isolation efficiency and bearing displacement. Good correlation between the analytical and the experimental data indicates that the analytical models for the bearing and RC shear key as well as other modeling assumptions were appropriate. 相似文献
73.
Gang Meng G. Brent Hall Mary E. Thompson Patrick Seliske 《The Canadian geographer》2013,57(2):154-172
This study assesses the overall spatial variations and neighbourhood‐level “hot spots” of low birth weight and preterm birth incidence within three public health units in Ontario, Canada. The analysis uses a stepwise approach of intra‐class correlation analysis, a spatial scan statistic, and multilevel spatial modeling. Results show that neighbourhood level variation accounts for only 2–3 percent of the total variation of adverse birth outcomes in the study area. However, strong spatial autocorrelation is observed at the neighbourhood level, and spatial clusters of relatively high adverse birth outcome rates exist in areas that are associated with environmental risks, including pollution sources and proximity to highways. Thus, although estimated neighbourhood impacts on adverse birth outcomes are small compared with those of individual‐level risks, local high potential environmental risk areas are identifiable. Environmental surveillance and spatial statistical analysis should be conducted regularly by local health authorities to identify and monitor the impact of environmental changes on health in general and on birth outcomes in particular. Specific community‐oriented health interventions may be required to reduce observed local health impacts. 相似文献
74.
Evidence for a Neolithic Age fire-irrigation paddy cultivation system in the lower Yangtze River Delta,China 总被引:1,自引:0,他引:1
Linchao Hu Zhihong Chao Min Gu Fuchun Li Lina Chen Bending Liu Xia Li Zhaoqin Huang Yuanyuan Li Baoshan Xing Jingyu Dai 《Journal of archaeological science》2013
Establishing stable cropping systems was vital in antiquity, assuring certain yields and enabling ancient people to settle, thus possibly causing various modern food habits and culture to form around the world, especially in cereal-cultivation-dominated countries. China, one of the most famous ancient agricultural countries, has a long history of rice planting, and the fire-irrigation paddy cultivation system is prevalent in the lower Yangtze region, which is considered a rice domestication center. However, its origin and cultivation pattern remain unclear. We studied a famous agricultural vestige, the Chuodun site, involved in rice planting in the lower Yangtze River Delta in eastern China, during the Neolithic Age. Clear evidence from archaeology, paleobiology, pedology and biogeochemistry suggest both that the rice fire-irrigation cultivation system formed during the Neolithic Age and that ancient peoples lived there steadily. Under this extensive cultivation system, soil structures and properties changed significantly; in particular, it left more black carbon in the soil and increased the organic carbon soil stability, which can be used to reconstruct prehistoric environments. Meanwhile, the prevalent fire-irrigation paddy cultivation system used by farmers in this area, though for a different purpose than ancient people, may be inherited from the Neolithic Age. 相似文献
75.
Gang Li 《Alcheringa: An Australasian Journal of Paleontology》2013,37(3):305-316
Two spinicaudatan species, Triglypta eedemtensis Li sp. nov. and Dundgobiestheria mandalgobiensis Li gen. et sp. nov., are described on the basis of scanning electron microscopy (SEM) imaging of newly collected specimens from paper-thin laminated black shale of the Eedemt Formation exposed at the Eedemt locality in the Khootiin Khotgor coal mine region of Dundgobi Province in southeast Mongolia. Triglypta eedemtensis is ornamented mainly with puncta and a punctate fine reticulum; radial lirae occur only on two or three growth bands near the venter. The small spinicaudatan Triglypta is a common component of the Middle Jurassic Euestheria ziliujingensis fauna and Sinokontikia fauna, and is a typical taxon in the Middle Jurassic lacustrine sequences of northern Hebei and the Junggar and Turpan basins of the Xinjiang Autonomous District of China; however, it does not occur in stratigraphically higher units elsewhere. Therefore, the age of the Eedemt Formation should be considered Middle Jurassic rather than Early Cretaceous. The Eedemt Formation is much older than the Early Cretaceous Shinekhudag Formation in the Shine Khudag area of southeast Mongolia. 相似文献
76.
大云山江都王陵10号墓是江都王陵内最为重要的一座陪葬墓。通过文献资料的梳理与相关汉墓材料的对比研究可知,10号墓墓主人为文献记载中的淖姬。这一信息的确认将为西汉诸侯王陪葬墓的研究提供身份明确的墓葬资料,学术意义重大。 相似文献
77.
Di Hu 《Journal of Archaeological Research》2013,21(4):371-402
Recently, interest in the archaeology of ethnogenesis has surged. This renewed interest stems from innovations in the historical study of ethnogenesis, theoretical shifts favoring multidirectional agency, and relevant contemporary sociopolitical debates. Theoretical problems surrounding the appropriateness of the social science concept of “ethnicity,” however, have made the comparative study of ethnogenesis difficult. Drawing from past and emergent perspectives adds renewed vigor to comparative studies of ethnogenesis. A methodology that integrates the different types of theory can resolve the theoretical tensions in the archaeological study of ethnogenesis. 相似文献
78.
黑河流域居民生活质量研究 总被引:1,自引:0,他引:1
以《Calvert-Henderson生活质量指标》一书为理论指导构建了生活质量评价指标体系,通过开展生活质量问卷调查及查找相关统计资料,运用主成分分析法确定指标的权重,研究了我国西北地区第二大内陆河流域-黑河流域城乡居民2004年的生活质量。具体的评价结果是:黑河流域城镇居民生活质量明显高于农村;黑河流域城市居民生活质量表现出中游高于上游和下游;黑河流域农村居民生活质量以乡镇为单位计算差异显著;黑河流域农村居民生活质量中游略好于上游、下游;影响黑河流域城乡居民生活质量的主要因素是收入、教育和住房。 相似文献
79.
本文在分析三门峡秦人墓中洞室墓各型式的基础上,对各型式墓葬的年代分别进行了讨论,进而认为,三门峡秦人墓中的洞室墓最早出现于战国晚期,并一直延续到西汉中期. 相似文献