1. 平行结构概论
平行结构是指英语句子中用相似的语法形式来表达相似的句子成分的方法。具体说来，平行结构可以分为下面几种不同的类型：
一、连词连接两个对等的词和对等的结构
并列连词and， but， as well as， or， or else， both … and， neither … nor， either … or， not only … but （also）， rather than等以及从属连词than可连接两个对等的词和对等的结构。
1.所连接的谓语形式必须一致
例1：He went downtown， bought some books and visited his daughter.
例2：Gunpowder was discovered in the twelfth century， but not used in warfare until two hundred years later.
2.所连接的词或短语形式必须一致
例1：Your semester grade is based not only on how well you do on each test， but also on how you participate in class.
例2：We often go to the countryside as well as to factories.
例3：I would much rather go to the countryside than stay here.
3.连接的非谓语动词的形式必须一致
例1：Some find swimming more enjoyable than sitting at home reading.
例2：He was engaged in writing a letter rather than reading the newspaper.
4.所连接的句子结构必须一致
例1：She is pleased with what you have given and all that you have told him.
例2：The purpose of the research had a more different meaning for them than it did for us.
二、某些特定的固定结构。
（1）有些词后要用平行结构。
例如：
prefer sth to sth
prefer doing sth to doing sth
prefer to do sth rather than do sth
1） I prefer rice to noodles.
2）I prefer watching TV to listening to music.
3） He preferred to die rather than surrender.
（2）有些结构中要用平行结构。
例如：
would / had rather / sooner do something than do something， would / had as soon do something as do something （宁可……也不……）
1） Liu Hulan said she had rather die than give up.
2） I would as soon stay at home as go.
部分强调句
要强调句子的某一部分，可以把句子的结构改变一下，通常有两种表示强调的句式：It is / was … that …结构和What … is / was…结构。
一、It is / was … that … 结构
1.It is / was … that … 结构可以用来强调句子中几乎任何部分
例1：It was my mother that threw an egg at Mr. Li yesterday.
例2：It was Mr. Li that my mother threw an egg at yesterday.
2.被强调的部分指人时，可用who或whom
强调主语时，如果指的是人，可以不用that而用who来代替。强调宾语时，如果指点的是人，可用whom.例如：
1）It was the dean who walked by.
2）It was Mary whom the old lady missed most.
3被强调部分指物时，要用that
例如：It was an egg that my mother threw at Mr. Li yesterday.
4.被强调部分是状语时，也只能用that，不能用when或where.
例1：It is during his spare time that John has been studying a course in French.
例2：It was in the hall that the mayor held the press conference.
5.不能用It is / was … that 结构强调动词
强调动词常用do，过去式用did.例如：
1） They did study very hard yesterday.
2） He does look forward to making the acquaintance of her.
What … is / was … 结构
二、What … is / was … 结构常用来强调主语或宾语，在这种结构中，is/ was后面是强调的部分。
例如：
1）What hurts is my left leg.
2）What I like is her style.
2. 科技英语中平行结构的分类
Classification of parallelism
1) expressing similar or equivalent ideas, quantities, actions or ways
... in a way through the simultaneous use of voice, videos, image and data.
2) expressing a series of things arranged in increasing degree.
3) expressing a series of actions taking place one after another in chronological order.
4) expressing alternative actions.
eg: The purpose of life is a life of purpose.
3. 平行结构在科技英语翻译中的应用
Advantages of parallelism
1) make the statements concise.
2) show clearly the relationship between the component parts.
3) give the reader a sense of completeness.
4) impress the reader deeply.
5)make a new idea easier to be understood.
6) offer a sharp contrast between different things.