本研究在系统功能语言学视角下，以机械工程英语教科书和期刊论文为语料，系统讨论工科英语的基本特点及其体现方式。

工科英语属于科学话语的范围。作为知识的主要建构手段，科学话语一直是学者们关注的焦点。以往关于科学话语的研究主要从专门用途英语、语用学、教育社会学和系统功能语言学等视角展开。科学话语研究在不同理论的影响下取得了较大发展，但仍然存在一些问题，主要表现为：（一）注重大类学科之间的特征对比，但对具体学科的专门性特征关注不够；（二）关注不同符号资源的意义建构方式，但对符号之间的协同和转换机制缺乏系统的描写和阐释；（三）系统功能语言学视角下的科学英语特点研究为后续研究提供了参考框架，但相关研究还只是初步探讨，尚未对相应的词汇语法体现进行深入、系统分析；（四）目前工科英语的相关研究大多局限于对词汇句法翻译策略、语篇阅读技巧等的探讨，相关语料库途径的词块对比研究以及个别语言特点分析的目的都是为学术写作或词汇教学等教学实践服务的，没有探究特定语言现象与学科内容或知识建构之间的关系；我们发现，工学英语语篇大多体现为多符号结构、以及由此产生的语义扩展关系。为此，本研究以机械工程学科为例，选取西方主流权威英文教科书和核心期刊论文为语料，系统探究工科英语的基本特点及其体现方式。

本研究采用了语料库工具UAM Corpus Tool 3.3自建语料库。首先，我们将PDF格式的教科书和期刊论文转换为TXT纯文本格式，将语料库软件无法识别的公式和符号人工转换为文字标记，再用文本整理器对它们进行批量整理和清洁，将由此获取的文本导入语料库工具，并在该工具内自动完成词性赋码；然后，在语料库工具中打开文本进行手动标注分析，并同步建立标注体系；最后，对所标注的特点进行归纳、概括和分类，并在语料库软件内完成检索和结果统计。

本研究的主要发现如下：总体来看，工科英语具有其他科学英语的基本特点，即连锁定义、专门分类、特殊表达、词汇密度、句法模糊性、语义非连续性和语法隐喻，但也有自身的特点，如符号隐喻。通过和科学英语语篇的比较，我们发现，工科英语的特点表现出多种形式的语法体现方式；其中有些是和科学英语共有的，有些是工科英语特有的。具体来说，机械工程英语术语通常采用四种方式建构连锁定义，即名词词组或其复合体、“名词词组或其复合体 + x”结构、小句和小句复合体。与Halliday发现的科学英语的专门分类相比，机械工程英语中的术语，除运用上下义关系和组成关系建构专门分类外，还通过语义成分关系建构术语之间的联系，每个类别又包括多种子类。机械工程英语中的特殊表达集中体现在两方面：一是相关术语体现为从高度专业化的特殊表达、到半专业以及特殊的非专业表达；二是不同符号资源共同表征和建构意义。就语义非连续性而言，机械工程英语和科学英语的体现方式基本相同，主要表现为两个方面：一是语篇中首次被提及的新信息，可能被预设为已知信息，作为论证下一步内容的起点；二是经语法隐喻方式识解的小句未能明确其中的逻辑语义关系。前者包括两个子类：一是作者将专业知识作为背景知识，产生语义跳跃，形成语义非连续性；二是首次提到的信息和前文有某种隐性关联，需要读者根据相关内容进行推导和补足。机械工程英语中的词汇密度和句法模糊性均是“语法隐喻综合征”的体现，而本研究中的语法隐喻包括序列到构型、序列到事物、构型到事物、成分到成分四个类别，共54个子类，既有级转移隐喻，也有类转移隐喻。语法隐喻在机械工程英语中具有两类功能：建构术语及其专门分类；生成语篇的衔接、连贯及其科学性。机械工程英语中的符号隐喻主要由英语和数理符号、以及英语和化学符号体现，包括成分到序列、成分到表达式、成分到运算过程、成分到级转移表达式、成分到反应过程五类，28个子类。符号隐喻在构建语篇衔接和推动论证展开方面具有重要作用。

本研究具有以下意义：以系统功能语言学理论为指导、对机械工程英语的特点及其体现形式进行了系统描写和解释，相关研究发现拓展了科学话语研究的广度和深度，尤其是对符号隐喻类别及其体现方式的系统阐释，在一定程度上弥补了符号隐喻实证研究的不足；研究中详尽的特点分类和丰富的实例引述，可为后续系统开展其他学科英语特点的对比研究提供参照基础，为机械工程英语的内容教学直接提供参考。

From the perspective of Systemic Functional Linguistics (hereafter, SFL), this study, taking the discipline of mechanical engineering as an example, systematically discusses features of engineering English with English textbooks and research articles as the corpus.

Engineering English belongs to the scope of scientific discourse. As the main means of knowledge construction, scientific discourse has long been a focus of scholars. Previous studies in this area are mainly conducted from perspectives of English for Specific Purposes, Pragmatics, Educational Sociology and SFL. Though scientific discourse research has made great progress under the influence of different theories and from various perspectives, there are still some problems, which can be summarized into the following aspects: (1) the relevant studies focus on feature comparison between general disciplines such as natural science and social science, without paying enough attention to the speciality of specific disciplines; (2) they look at the meaning construction of different semiotic resources, but explain less the cooperation and transformation mechanisms between different semiotics; (3) the study on the features of scientific English from the perspective of SFL can provide framework reference for subsequent research, but the relevant studies are only preliminary discussions and have not yet been explored in-depth and systematically in terms of their lexicogrammatical realizations; and (4) the current research of engineering English is mostly restricted to the discussions of lexical and syntactic translation strategies and discourse reading skills. Those contrastive studies of lexical bundles based on corpus and examination of particular linguistic features are only carried out for vocabulary teaching and academic writing, they do not investigate the relationship between particular language phenomenon and disciplinary content or knowledge. We find that engineering English discourse is characterized with multisemiotic constructions and the resultant semantic expansion. To comprehensively examine the features of engineering English, this study, taking the discipline of mechanical engineering as an example, selecting both English textbooks and research articles as the corpus, investigates systematically features of engineering English and their realizations.

This study self-builds a corpus with UAM Corpus Tool 3.3. First of all, the PDF textbook chapters and research articles are transformed into TXT format, in which, the mathematical equations and symbols which cannot be identified by the corpus tool are manually replaced with linguistic expressions or markers, then the texts are batch cleaned by TextEditor 5.0. After that, the resultant texts are added into the Corpus Tool, the POS tagging is automatically completed by this tool. Then, the texts are manually annotated with an annotation layer coming into being synchronously in this process. Finally, the annotated features are summarized and classified into different categories, their retrieval and statistics can be carried out in the corpus tool.

The major findings of the present study are summarized as follows. Generally speaking, engineering English shares the basic features, namely interlocking definitions, technical taxonomies, special expressions, lexical density, syntactic ambiguity, semantic discontinuity and grammatical metaphor, with other scientific English, but it has its unique features as well, such as semiotic metaphor. By comparing with scientific English discourse, we find that the basic features in engineering English discourse show more grammatical realizations of various forms, some of which are common with scientific English, some of which are unique to the engineering discipline. Specifically, there are four ways to construct interlocking definitions for mechanical engineering English, namely nominal group or its complex, “nominal group or its complex + x” structure, clause and clause complex. Compared with the technical taxonomies discovered by Halliday in scientific English, technical terms in mechanical engineering English not only use hyponymy and “part-whole” relations to construct classification, but also use semantic component relations, each of which further includes various sub-types. Special expressions in mechanical engineering English are mainly embodied in two aspects: first, the relevant terms are organized into highly specialized special expressions, semi specialized expressions and non-specialized special expressions; second, engineering meanings are jointly constructed by different semiotics. As for semantic discontinuity, mechanical engineering English and scientific English show basically the same linguistic realizations, which is summarized into two aspects: the new information mentioned for the first time in the text may be presupposed as known information, serving as the starting point of the next clause for the argumentation; the clauses construed by grammatical metaphor fail to clarify their logical semantic relations. The former includes two cases: the first case is that the author takes professional knowledge as the background knowledge, without explaining it the first time mentioned, thus resulting in semantic discontinuity caused by the resultant semantic leaps; the second case is that the information mentioned for the first time has some implicit relationship with the previous content, requiring the reader to deduce according to the context. Lexical density and syntactic ambiguity in mechanical engineering are found to be “syndromes of grammatical metaphor”, and grammatical metaphors in this study are found to have four categories, namely sequence to figure, sequence to thing, figure to thing and component to component, each being further specified into various types, altogether 54 types, including both rank shift and class shift. Grammatical metaphor has two main functions in mechanical engineering English: constructing technical terms and their technical taxonomies, and generating discourse cohesion, coherence and scientificity. Last, semiotic metaphors in mechanical engineering English, which are mainly expressed by English and mathematical-physical symbols, English and chemical formulas, are divided into five categories: component to sequence, component to statement, component to operative process, component to expression, and component to reactive process, altogether 28 types. Semiotic metaphor plays an important role in the construction of discourse cohesion and the promotion of argumentation.

The study is of significance in the following aspects: under the guidance of the theory of SFL, the basic features of mechanical engineering English and their realizations are systematically described and interpreted, which expands the scope and depth of the study of scientific discourse; particularly, the systematic description and explanation of categories and realizations of semiotic metaphor, to some extent, can make up for the deficiencies of semiotic metaphor’s empirical exploration; the detailed feature classifications and abundant examples in this study can provide a reference basis for systematic conduction of comparative studies of features of other disciplinary Englishes in the future, and a direct reference for content teaching of mechanical engineering English.