题目内容
设顶层柱的柱顶截面按荷载效应标准组合后的N=320kN、M=90kN·m，设截面的纵向受拉钢筋为4φ20，钢筋的相对黏结特性系数v=1.0，c=30mm，则最后按荷载效应的标准组合计算的纵向受拉钢筋的等效应力σsk最接近()项数值。
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若过梁采用砖砌过梁，则其弯曲抗拉及抗剪承载力与()项数值最为接近。
某一级公路设计行车速度v=100km/h。双向六车道，汽车荷载采用公路-I级。其公路上有一座计算跨径为40m的预应力混凝土箱形简支梁桥，采用上、下双幅分离式横断面行驶。混凝土强度等级为C50。横断面布置如下图所示。
提示：按《公路桥涵设计通用规范》(JTG D60—2004)和《公路钢筋混凝土及预应力混凝土桥涵设计规范》(JTG D62—2004)进行计算。
试问，该桥在计算汽车设计车道荷载时，其设计车道数应按下列()项取用。
对α1受体有选择性阻滞作用的药物是
Archaeology has long been an accepted tool for studying prehistoric cultures. Relatively recently the same techniques have been systematically applied to studies of the more immediate past. This has been called "historical archaeology", a term that is used in the United States to refer to any archaeological investigation into North American sites that postdate the arrival of Europeans.
Back in the 1930's and 1940's, when building restoration was popular, historical archaeology was primarily a tool of architectural reconstruction. The role of archaeologists was to find the foundations of historic buildings and then take a back seat to architects.
The mania for reconstruction had largely subsided by the 1950's and 1960's. Most people entering historical archaeology during this period came out of university anthropology departments where they had studied prehistoric cultures. They were, by training, social scientists, not historians, and their work tended to reflect this bias. The questions they framed and the techniques they used were designed to help them understand, as scientists, how people behaved. But because they were treading(踩,踏) on historical ground for which there was often extensive written documentation and because their own knowledge of these periods was usually limited, their contributions to American history remained circumscribed. Their reports, highly technical and sometimes poorly written, went unread.
More recently, professional archaeologists have taken over. These researchers have sought to demonstrate that their work can be a valuable tool not only of science but also of history, providing fresh insights into the daily lives of ordinary people whose existences might nt otherwise be so well documented. This newer emphasis on archaeology as social history has shown great promise, and indeed work done in this area has led to a reinterpretation of the United States' past.
In Kingston, New York, for example, evidence has been uncovered that indicates that English goods were being smuggled into that city at a time when the Dutch supposedly controlled trading in the area. And in Sacramento an excavation at the site of a fashionable nineteenth-century hotel revealed that garbage had been stashed(存放) in the building' s basement despite sanitation laws to the contrary.
What is the main topic of the passage？
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