本文基于JDEST语料库，探讨特征性句干的型式结构与话语功能的分布特征。研究表明，特征性句干是学术写作的构建基石，具有一定程度的规约性，可包括7类主要型式结构，人称主语结构、非人称主语结构、It前置结构、存在句式、As前置结构、Wh词结构、以及其他；实施26类典型学术话语功能，其中语篇导向功能15类、参与者导向功能6类及研究导向功能5类。此外，特征性句干的使用高度依赖于局部文本环境，由环境内各种不同性质的共选合力生成，是形式、意义与语境的制衡结果。

Based on the JDEST corpus data, this paper investigates the distributions of patterns and functions of the characteristic Sentence Stems (CSSs) in academic texts. It is argued that CSSs show strong features of contextual conventionality and are frame expressions to build a skeletal academic text. CSSs fall into seven major structural categories: personal subject, impersonal subject, dummy-it construction, existential construction, as-introduced structure, wh-question structure, and others; they are also closely connected with 26 main categories of academic discourse functions, which consist of 15 text-oriented functions, six participant-oriented functions and five research-oriented functions. It is also found that the use of CSSs depends largely on the local textual environment in which they occur, and they are the place where co-selections of various types are engineered to allow meanings to take shape. CSSs are the co-selection result of form, meaning and context.