主题句讲述了一个段落的主要观点：它是这段话的一个小主题/中心思想。你可以把主题句看作是你给读者设定的一个路牌，用于提醒读者这个段落中最重要的要点。当你按顺序阅读论文时，论文里的所有主题句可以提供文章论点的梗概。因此，主题句不仅可以引导读者理解你的论文，也可以帮助你提高论文的质量，让你更容易地发现论文中的漏洞。

主题句通常出现在段落的开头。在下面的《Anatomy of Criticism》的例子中:

The tragic hero is typically on top of the wheel of fortune, half-way between human society on the ground and the something greater in the sky（主题句）. Prometheus, Adam, and Christ hang between heaven and earth, between a world of paradisal freedom and a world of bondage. Tragic heroes are so much the highest points in their human landscape that they seem the inevitable conductors of the power about them, great trees more likely to be struck by lightning than a clump of grass. Conductors may of course be instruments as well as victims of the divine lightning: Milton’s Samson destroys the Philistine temple with himself, and Hamlet nearly exterminates the Danish court in his own fall.

这个段落的结构简单而有力：第一句主题句提出一个抽象的观点，段落的其余部分使用具体的例子作为证据来阐述这个观点。

主题句在开头是比较常见的！

不一定，有时在主题句前会出现一两个过渡句之后，例如:

We found in comedy that the term bomolochos or buffoon need not be restricted to farce, but could be extended to cover comic characters who are primarily entertainers, with the function of increasing or focusing the comic mood. The corresponding contrasting type is the suppliant, the character, often female, who presents a picture of unmitigated helplessness and destitution（主题句）. Such a figure is pathetic, and pathos, though it seems a gentler and more relaxed mood than tragedy, is even more terrifying. Its basis is the exclusion of an individual from the group; hence it attacks the deepest fear in ourselves that we possess—a fear much deeper than the relatively cosy and sociable bogey of hell. In the suppliant pity and terror are brought to the highest possible pitch of intensity, and the awful consequences of rejecting the suppliant for all concerned is a central theme of Greek tragedy.

这个段落的第一句话用于过渡的：它为主题句做准备。第二句才是这个段落的主题句。过渡句通常是在上一个段落和当前段落之间的桥梁。

当然，有时作者会在某一段结尾留一个主题句。

主题句放在哪里，这可能需要根据具体需要和个人习惯。

• 主题句和SCI论文紧密的联系在一起，可以帮助加强论文的连贯性。

• 主题句应该是推进论文向前发展的。

• 如果SCI论文的introduction中包含了一个主题句，那么主题句中最好加入keyword关键词。

• 如果一个主题句重述一个主题，那么它是多余的，你最好重写这个主题句。

• 如果多个主题句重述一个主题，即使这些主题句使用不同的词语，那么它也是重复的。

虽然主题句很好用，但大家切忌重复使用主题句！接下来笔者说说什么时候使用主题句！

• 如果一个段落与前一个段落具有相同的观点，那么这个段落的主题句可以省略。

• 如果一个段落中的论据可以表明作者的观点，或者隐含主题句，那么这个段落的主题句也可以省略。

• 如果你不确定是否使用主题句，那么你最好还是写一个主题句。

笔者小经验：建议大家可以先写论文每一段的主题句，相当于论文的大纲。最后根据主题句，去丰富论文内容！