同位语的结构

同位语使用频率较高是科技英语的一个特点。同位语按照其本身和它所说明部分（在本文中称之为本位语）两者的结构可分成为简单同位语和复杂同位语两种。

1. 简单同位语

1-1此类同位语一般是由一个名词或几个并列的名词表示；本位语通常是一个名词，但偶尔也可以是一个词组或整个句子：

(1) Water, a compound, can be decomposed into the gaseous elements hydrogen and oxygen.

水是一种化合物，它能分解为气体元素氢和氧。

(2) Color television, breaks down, the pictures into three colors——red, green and blue.

彩色电视把图像分解为三种颜色——红、绿、蓝。

(3) A rhythmic narrowing and widening of the pupil, or hippus, is of slighter diagnostic value.

瞳孔有节律地收缩和放大，或谓虹膜震荡，其诊断价值较小。

（4）Air rushes in through the nose and mouth filling the lungs——inspiration.

空气经鼻和口进入而充满肺，这就是吸气。

1 - 2有时第二个同位语是说明第一个同位语或是对本位语作进一步说明：

(5) The substance，tumor necrosis factor，or TNF, is a protein produced in the immune system by macrophages.

肿瘤坏死因子（TNF）这一种物质是巨噬细胞在免疫系统中产生的一种蛋白质。

(6) The cuticular structure undergoes change during ecdysis，or molting——a process characteristic of arthropods.

蜕壳（或蜕皮）是节肢动物的一个特征性过程，在此过程中角质层结构会发生变化。

1 - 3在少数的情况下是同位语在前，本位语在后：

(7) The father of the heart-lung machine， he researched and worked on its problems for nearly twenty years.

他对这方面的问题已进行了将近20年的研究，是心肺机之父。

(8) The marvel of the machine age, the electronic computer has been in use only since 1946.

电子计算机这一机器时代的奇迹只是从1946年才开始投入使用的。

1 - 4在同位语前除了可用引导词that is，or，namely，for example等引出外，有时还可用and引出：

(9) Cell inclusions are frequently storage products, for example fat.

细胞内涵物常常是贮存物，例如脂肪。

(10) Man's first real invention, and one of the most important inventions in history，was the Wheel.

车轮是人类第一个真正的发明，同时也是人类历史上最重要的发明之一。

2. 复杂同位语

2 - 1复杂的同位语其复杂性表现在两个方面：（1）同位语的后面跟有一个定语或定语从句；（2）本位语往往是一个词组或整个句子，一个单词的甚为少见。这类同位语的作用是对本位语进行解释或作进一步的说明：

(11) Within a 5-year period, 75 to 80 percent of patients with benign gastric ulcer will have recurrent morbidity, and 3 to 4 percent will die from complications of the ulcer, a figure comparable to the mortality rate of gastric resection for benign ulcer.

在5年时间内75 ~ 80%的良性胃溃疡病人有复发，3 ~ 4%的病人死于溃疡的并发症，后一数字相当于良性育溃疡切除手术的死亡率。

(12) The baby eels are carried by the Gulf Stream to Europe, a journey which takes two and a half years.

幼鳗被墨西哥湾水流带往欧洲，这一游程需要历时2年半。

(13) Sclerotization，a process that occurs only in the exocuticle, is not reversible and its extent varies greatly among arthropod types.

硬化（这一过程只发生于外表皮）是不可逆的，而硬化的程度在节肢动物间有很大的差异。

2 - 2复杂同位语中的同位语本身可有如下的三种表达方法：（1）重复本位语，（2）用代词one（ones），that（these），something等，（3）用一概括性较强的词以起到提示的作用。

（14）“It's an accounting error——an error that's certainly very uncommon，” a space agency spokesman said.

太空署的发言人说，“这是一种计算上的错误，这种错误肯定是非常少见的。”

（15）Crude oil，oil that has not yet been refined，is an extremely important raw material.

石油（未精炼过的原油）是一种十分重要的原料。

(16) Humans have pauses during their speech，and animals——even ones that generally produce sounds continuously——have p8uses in their communication.

人在讲话时有停顿，动物，甚至连那些通常是不断发声的动物在相互沟通时也会有停顿。

(17) To achieve the necessary resolution a large image must be projected onto the retinas of the principal eyes, one that touches as much photoreceptors as possible.

为了获得必要的分辨力，必须有大的图像投射到主眼的视网膜上，这就能触及到尽可能多的光感受器。

(18) Many doctors are working on chronic diseases, those that last a long time or cannot be cared.

许多医师正在对慢性病进行研究，所谓慢性病是指病程长或不能治愈的疾病。

(19) If one's heart doesn't work well, it can be replaced, something which wouldn't have been thought possible a few years ago.

假如现在我们的心脏功能不正常就可以把它换掉，这在几年前是不能想象的。

(20) Some studies indicate that beta-carotene，a substance the body converts to vitamin A, may be the chief protective substance. （本句中在the body前省去用作宾语的关系代词that)

某些研究表明，B - 胡萝卜素（在体内可被转化成为维生素A）可能是一种主要的保护物质。

（21）Normally a zinc-deficient animal makes fewer lymphocytes and macrophages——cells important to immune function.

在一般情况下，缺锌的动物其生成的淋巴细胞和巨噬细胞（这两种细胞对免疫功能有重要的作用）数量减少。