三、非限定动词。
　　如前所述，科技文章要求行文简练，结构紧凑，为此，往往使用分词短语代替定语从句或状语从句；使用分词独立结构代替状语从句或并列分句；使用不定式短语代替各种从句；介词十动名词短语代替定语从句或状语从句。这样可缩短句子，又比较醒目。试比较下列各组句子。
　　A direct current is a current flowing always in the same direction.
　　直流电是一种总是沿同一方向流动的电流。
　　Radiating from the earth, heat causes air currents to rise.
　　热量由地球辐射出来时，使得气流上升。
　　A body can more uniformly and in a straight line,there being no cause to change that motion.
　　如果没有改变物体运动的原因，那么物体将作匀速直线运动。
　　Vibrating objects produce sound waves ,each vibration producing one sound wave.
　　振动着的物体产生声波，每一次振动产生一个声波。
　　In communications, the problem of electronics is how to convey information from one place to another.
　　在通讯系统中，电子学要解决的问题是如何把信息从一个地方传递到另一个地方。
　　Materials to be used for structural purposes are chosen so as to behave elastically in the environmental conditions.
　　结构材料的选择应使其在外界条件中保持其弹性。
　　There are different ways of changing energy from one form into another.
　　将能量从一种形式转变成另一种形式有各种不同的方法。
　　In making the radio waves correspond to each sound in turn ,messages are carried from a broadcasting station to a receiving set.
　　使无线电波依次对每一个声音作出相应变化时，信息就由广播电台传递到接收机。

　　四、后置定语
　　大量使用后置定语也是科技文章的特点之一。常见的结构不以下五种：
　　1、介词短语
　　The forces due to friction are called frictional forces.
　　由于摩擦而产生的力称之为摩擦力。
　　A call for paper is now being issued .
　　征集论文的通知现正陆续发出。

　　2、形容词及形容词短语。
　　In this factory the only fuel available is coal.
　　该厂唯一可用的燃料是煤。
　　In radiation ,thermal energy is transformed into radiant energy ,similar in nature to light.
　　热能在辐射时，转换成性质与光相似的辐射能。

　　3、副词
　　The air outside pressed the side in .
　　外面的空气将桶壁压得凹进去了。
　　The force upward equals the force downward so that the balloon stays at the level.
　　向上的力与向下的力相等，所以气球就保持在这一高度。

　　4、单个分词，但仍保持校强的动词意义。
　　The results obtained must be cheeked .
　　获得的结果必须加以校核
　　The heat produced is equal to the electrical energy wasted.
　　产生的热量等于浪费了的电能。

　　5、定语从句
　　During construction, problems often arise which require design changes.
　　在施工过程中，常会出现需要改变设计的问题。
　　The molecules exert forces upon each other, which depend upon the distance between them.
　　分子相互间都存在着力的作用，该力的大小取决于它们之间的距离。
　　Very wonderful changes in matter take place before our eyes every day to which we pay little attention.
　　我们几乎没有注意的很奇异的物质变化每天都在眼前发生。
　　To make an atomic bomb we have to use uranium 235,in which all the atoms are available for fission.
　　制造原子弹，我们必须用铀235，因为轴的所有原子都会裂变。

　　五、常用句型
　　科技文章中经常使用若干特定的句型，从而形成科技文体区别于其他文体的标志。例如It---that---结构句型；被动态结构句型；结构句型，分词短语结构句型，省略句结构句型等。举例如下：
　　It is evident that a well lubricated bearing turns more easily than a dry one .
　　显然，润滑好的轴承，比不润滑的轴承容易转动。
　　It seems that these two branches of science are mutually dependent and interacting .
　　看来这两个科学分支是相互依存，相互作用的。
　　It has been proved that induced voltage causes a current to flow in opposition to the force producing it.
　　已经证明，感应电压使电流的方向与产生电流的磁场力方向相反。
　　It was not until the 19th century that heat was considered as a form of energy.
　　直到十九世纪人们才认识到热是能量的一种形式。
　　Computers may be classified as analog and digital.
　　计算机可分为模拟计算机和数字计算机两种。
　　The switching time of the new-type transistor is shortened three times .
　　新型晶体管的开关时间缩短了三分之二。（或---缩短为三分之一。）
　　This steel

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