段落的结构与组织

写得好的段落并不是将句子任意堆放在一起，而是有逻辑地进行组织与安排。每个段落中有两个非常重要的位置：段首句和段尾句。通常，段首句介绍段落主题，而段尾句用于总结、得出结论或强调某些重要性。

主题句一般都位于段首是因为这个位置的影响力最大。有些段落可能不止有一个主题句。如果主题句位于段尾，它可能被赋予了更重要的使命，既用于介绍下一个段落的主题，又作为本段的概要和总结。写得好的论文都将主题句放在最有影响力的位置，读者通过简单地浏览这些主题句就可以了解论文内容，不必完整地阅读全文。

段落的中间部分的组织和撰写取决于段落所要达到的目的：既可以按照信息的重要性从小到大或从大到小排列，也可以按照发表顺序或时间顺序排列。有的段落还可以按照比较与对比、提出问题与解决问题的方式来组织。

例：Volatile organic compounds (VOCs)are emitted from a variety of manmade and natural sources. Manmade sourcesinclude motor vehicles, chemical plants, refineries, factories, consumer andcommercial products, and other industrial sources. Natural sources responsiblefor biogenic VOC emissions include oak, citrus, eucalyptus, pine, spruce,maple, hickory, fir, and cottonwood. The overall relative contributions ofmanmade versus natural sources of VOCs have not been clearly established, butthe relative contributions of these source groups vary depending on geography.

 这段话的主题是 “VOCs”。段落的结构方式，即其余句子的排列顺序不是任意的，而是按照先“manmade”后“natural”的顺序行进。

练习

1 该段文字是关于谷氨酸受体。虽然段落有主题句，但是其余的句子并没有按照与主题句的逻辑关系依次推进。在主题句后加入一个符合读者期望的句子。（看了主题句后读者会期望了解什么呢？）改写第二句，使其与第三句平行。

1 Ionotropic glutamate receptors fall into twogeneral categories (7, 8). 2 WhenNMDA receptors are activated by N-methyl-D-aspartate (MNDA), ion channels areopened, allowing ions to rush into the cell and thus cause an excitatorypostsynaptic potential. 3 non NMDAreceptors like PCP bind to kainate and quisqualate only and prevent ion flowand an excitatory postsynaptic potential, even in the presence of NMDA.

2 该段文字是关于鲑鱼的迁徙。虽然第一句和第二句描述了鲑鱼的迁徙可能利用的两种方法，但段落缺少主题句。补充主题句，概括出整个段落的主题（鲑鱼在秋季返回途中所利用的不同的方法）。以主题作为主题句的主语。此外，让第二句和第三句平行。

1 Salmon may use a magnetic or sun compass toorient themselves. 2 As described byBrown et al. (15), olfactory cues learned as smelts any also help salmon tofind the river and tributary of their birth .3 Salmo may reenter fresh water inspring, summer, or fall, but spawning occurs in the fall, and the life cycle ofthe salmon begins anew.

3 检查该段文字中单词的位置，保持叙述角度一致(保持每个句子的主语一致); 在第三句的句首增加过渡词，指明第三句与第四句的逻辑关系; 用正确的平行结构表达相对应的思想。

1 InterlecukinⅠ(IL-I) is a mediator produced byactivated macrophages and many other cell types (1). 2 IL-I initiates inflammation and thus stimulates various cells. 3 InT-cell activation, one of the co signals is IL-I. 4 IL-I plays a role in activation B cells and the production ofacute phase proteins, muscle catabolism, bone resorption, and fever isstimulated by ILI.

参考答案

      1.

1. Ionotropicglutamate receptors fall into two general categories (7, 8). 1’Thesereceptors are NMDA receptors or non-NMDA receptors. 2NMDA receptors areactivated by N-methyl-D-aspartate (NMDA). 2’Upon activation, ion channels are opened, allowing ions to rushinto the cell and thus cause an excitatory postsynaptic potential (Fig. 1). 3In contrast, non-NMDA receptors like PCP bind to kainate andquisqualate only and prevent ion flow and an excitatory postsynaptic potential,even in the presence of NMDA. 4 Thus,PCP acts as a strong noncompetitive antagonist of NMDA.

主题句是有关glutamate receptor的两个分类, 读完第一句后, 读者期望找到是哪两个类别. 句1’满足了主题句制造的期望. 句2修改为与句3平行. 句2也分为两个部分, 把两个不同的思想分为两个句子表达.

2.

1’Salmon use different methods to find theirway during their homeward journey in the fall. 1 Salmon may use a magnetic or sun compass to orient themselves. 2 As described by Brown et al. (15), they may also use olfactory cues learned assmelts to find the river and tributary of their birth. 3 Salmon may reenter fresh water in spring, summer, or fall, but spawningoccurs in the fall, and the life cycle of the salmon begins anew.

主题句指出了句子的信息, “the different methods salmon use to findtheir way during their homeward journey in the fall.” 主题是各句的主语, 从而使得整个段落观点具一致性. 第2句与第1句平行.

3.

1 lnterleukin I (IL-I) is a mediator produced byactivated macrophages and many other cell types (1). 2 IL-I initiatesinflammation and thus stimulates various cells. 3 IL-I is a co-signal in T-cell activation. 4 Furthermore, IL-I playsa role in activating B cells and instimulating the production of acute phase proteins, muscle catabolism, boneresorption, and fever.

观点贯穿整个段落. 第4句的开始加了一个转接词以指出与第3句的逻辑关系, 并且平等的思想以正确的平行句式表达(第4句: in stimulating).

摘编自《科技写作与交流》(任胜利等译. 科学出版社,2012年出版)