请讲一讲同位语的方方面面。
两个或两个以上同一层次的语言单位,如果它们所指相同,句法功能也相同,我们就把这种结构叫做同位结构,而把后项叫做前项的同位语。例如:
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Coal, petroleum and electricity, the important sources of energy, are now being widely used in our country. 煤、石油和电这些重要的能源目前在我国正得到广泛的应用。
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The result is carbon steel, one of the most important and useful of all alloys. 产品是碳钢，即所有合金中最重要和最有用的合金之一。
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The passenger plane of the 1980s, (namely) the supersonic jet, will transform relations between peoples of the world. 八十年代的客机即超音速喷气式飞机将会改变世界各国人民的关系。
就语义关系而论,同位语常常用于表示事物的另一说法,指出本位语的具体内容或者列举、突出本位语的一部分内容。例如:
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An important form of energy is atomic energy, or nuclear energy. (换个说法) 能量的很重要的一种形式是原子能即核子能。
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On October 17, 1831, Faraday succeeded in making one of the greatest discoveries in the field of electricity — the electromagnetic induction. (指出 one of the discoveries in the field of electricity 的具体内容) 法拉第于 1831 年 10 月 17 日成功地作出了电学领域中的一项最伟大的发现——电磁感应。
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The hydrogen atom is made up of two electric particles, a proton and an electron. (指出 two electric particles 的具体内容) 氢原子由两个带电粒子, 即一个质子和一个电子所组成。
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Sound waves can travel only through a medium, as air or water. (列举 a medium 的部分内容) 声波只有通过介质, 如空气或水, 才能传播。
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Some solid fuels, such as wood and coal, are chiefly composed of carbon, hydrogen and oxygen. (列举 solid fuels 的部分内容) 某些固体燃料,例如木材和煤,主要是由碳、氢和氧组成的。
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Heat, like other forms of energy, has its effects upon substances, including expansion and change of state. (指出 its effects 的部分内容) 热, 像其它形式的能量一样, 对物质会产生效应, 这种效应包括膨胀和状态的变化。
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Most liquids, particularly solutions in liquids, are good conductors. (突出 liquids 的部分内容) 大多数液体, 特别是溶液, 都是良导体。
根据本位语的形式特点,可将同位语分为名词的同位语、形容词的同位语、动词的同位语、介词短语的同位语、分句的同位语、句子部分内容的同位语、整个句子的同位语等等。例如:
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... we flew to Guilin, a place favored by artists over the centuries. (Hillary, Living History) (名词的同位语) ……我们飞到桂林, 这是许多世纪以来一直受艺术家们钟爱的地方。
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The decimal, or ten-scale, system is used for scientific purposes throughout the world. (形容词的同位语) 全世界都使用十进制进行科学活动。
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Transistor is off, or non-conducting. (副词的同位语) 晶体管 断开, 或者说不导通。
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These materials can be used to conduct, or lead, electricity from place to place. (动词的同位语) 这些材料能将电流从一处传导(或者说引导)到另一处。
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When the closed circuit is broken at any point — that is, when the path of conducting material is interrupted — there will be no current. (从句的同位语) 当闭合电路在任一点上断开，也就是说，当导电材料的通路中断时，就不会有电流。
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The electronic computer can multiply two 10-digit numbers in 1/1,000 second, a problem that would take a person five minutes to do with pencil and paper. (句子部分内容的同位语) 电子计算机在千分之一秒的时间里就可以算出两个十位数的乘积, 而一个人用铅笔和纸来做这样一道题, 就得用上五分钟。
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Atomic nucleus has positive charges exactly balancing the negative ones possessed by the electrons, a fact discovered by Rutherford in 1911. (整个句子的同位语) 原子核的正电荷恰好可以完全抵消电子的负电荷;这一事实是卢瑟福于1911年发现的。
根据同位语本身的形式特点,可将同位语分为名词型同位语、形容词型同位语、动词型同位语、介词短语型同位语、从句型同位语和句子型同位语。例如：
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Their(electrons') orbits, or paths, form concentric shells, or layers, somewhat like the layers of an onion. (名词型同位语) 电子的轨道(即轨迹)形成一些同心的壳(即同心层),有点像洋葱的皮层。
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Everything in the world is constantly changing. These changes are of two kinds: physical changes and chemical changes. (名词短语型同位语) 世界上的一切物质都在不断地变化着。这些变化有两种: 物理变化和化学变化。
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He drew a quadrilateral, i. e. foursided, geometric figure. (形容词型同位语) 他画了一个四角形, 即四边形。
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In a transformer, current alternates, or repeatedly changes directions, in the primary winding. (动词型同位语) 在变压器中，电流在初级绕组内交变，即反复改变方向。
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He always spoke so — (namely) slowly but energetically. (副词型同位语) 他总是这样说话——缓慢地但是有力地。
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Exobiology is the study of life outside the earth — on other planets and celestial bodies. (介词短语型同位语) 外层空间生物学是研究地球以外的即其它行星和天体上的生命的科学。
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Everything that we learned from photographs and from rocket landings on the moon has confirmed our belief that the moon's crust is similar to the earth's. (从句型同位语) 我们拍摄的月球照片及收集的火箭登月资料证实了我们的想法: 月球的地壳和地球的地壳是相似的。
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Some elements possess molecules of more than a single atom, e.g. atmospheric oxygen exists in pairs of atoms. (句子型同位语) 有些元素的分子不止包含一个原子,例如,大气中的氧是以原子对的形式存在的。