敦煌盛唐佛寺建築推測性建構與研究 :以172窟北壁《觀無量壽經變圖》為例 = A conjectual construction and research on the architecture of buddhist temples in Dunhuang and HighTang Dynasty :taking the "Guan Wu Liang Shou Jing Bian Tu " on the north wall of Dunhuang cave 172 for example