至于Introduction字数，一般SCI该部分控制在450字以内，以300-400 words为宜。

通常分2-4个自然段，切记不要详述众所周知的问题。

Tip 3

引证代表/权威文献

Introduction写作中的参考文献的应用，数量上在15篇以内比较合理，选用的文献应是领域具有代表性的，尽量选取顶级期刊（NEJM, LANCET, JAMA等）发表的文献，引证的一些数字，具有权威性，同时给读者或Reviewer一个初印象。

第二，比较重要的，在引证参考文献时，应是作者亲自阅读过的文献，不能完全套（chao)用(xi）原文中的sentence，毕竟编辑会对稿件查重！正确的做法是，是在理解的基础上，对引证文献中的内容，抓住核心论点或结论，紧密结合自己要说明的问题。

第三，值得注意的是，在引用文献时，尽量避免作者姓名的使用，尤其当投级别较高的期刊时（Review类文章或特殊情况下除外），像“XXX ，et al find that/ reported in their study that ....”一类的话尽量不要出现。

Tip 4

明确结果写引言

至于何时写Introduction合适，这个因人而异。很多时候，作者会先撰写引言，再开始后面部分的写作，好像是不写完前言，后面就无法开展。这可能是每个人的习惯。那么什么时候写比较合适呢？一个小Tip是在完成Materials and Methods和Results部分后，再返回写Introduction。因为在明确study design 和main results or finding后，写引言会顺畅，同时也会和整体论文相协调，相呼应，而不至于引言与后续部分脱节。

介绍这么多，这里便以最近发在顶刊JAMA上的文献为例，解析下SCI论文中的引言写作。

2019年8月13在顶刊JAMA上在线发表的题为“Association between long-term exposure to ambient air pollution and change in quantitatively assessed emphysema and lung function”。

以下是Paper的引言原文：

原文链接：

https://jamanetwork.com/journals/jama/article-abstract/2747669

INTRODUCTION

Chronic lower respiratory disease is the fourth leading cause of death in the United States and third leading cause of death worldwide.1,2Most of this mortality is due to chronic obstructive pulmonary disease (COPD), defined by persistent airflow limitation, measured via spirometry, and pulmonary emphysema, defined by destruction of the lung parenchyma.3 Emphysema can be measured quantitatively on computed tomographic (CT) imaging and can be observed without spirometric COPD.4,5 (PS:简述研究领域的背景材料，也就是回顾历史。引言撰写的首几句，一般可从疾病的定义，流行病学，病因学，诊疗手段，预后等方面入手；用一到两句话简介，并过渡到后文）The percentage of emphysema-like lung on CT scans (“percent emphysema”) is associated with the degree of lung function impairment and symptoms as well as mortality in patients with COPD.6 Percent emphysema is also associated with dyspnea and disease exacerbations independent of lung function among smokers7 and with incident COPD and all cause mortality among individuals without COPD in the general population.4,8（PS：通过研究报道，简介疾病的监测指标，阐明立题依据。常见的分析指标包括：biochemistry index, angiographic indices; gene or protein等）

Ambient air pollution is a major risk factor for poor health worldwide.9 The relationship of air pollution exposures with respiratory morbidity and mortality has been documented in the short-term10 and, by a more limited number of prospective cohorts, in the long-term.11,12(PS: 通过引证之前的文献，过渡到本研究关心的主题，建立研究方向和目标疾病的逻辑关联。)There is elevated risk of death associated with ozone (O3) and fine particulate matter less than 2.5 microns in aerodynamic diameter (PM2.5) exposure in patients with COPD11 and a faster decline in lung function associated with long-term exposure to traffic-related air pollutants in healthy populations.13（PS：承接前文，具体阐述某种指标/因素在特定疾病/健康状况发挥的作用; 给出前人研究工作的已得结论，是开展本研究的理论基础。）No longitudinal studies of air pollution and emphysema progression on CT scan, to our knowledge, have been reported.(PS: 文段最后一句，通常提出目前尚未解决的问题或急需解决的问题，从而引出自己的研究动机和意义。常用的概括主要不足的sentence还有如：However, evidence for the relationship between ....was still limited /scarce in the developing country/ China.../; However, few XX study has been performed to assess.../ 当然，我们在叙述前人工作的欠缺时，来强调自己研究的创新和亮点时，应慎重语言, 最好写的留有余地，最多见的表达：To our best knowledge, we find this was the first XXX study .../ )

This cohort study examined the hypothesis(阐述自己研究的目的，常用表达语：This study was aimed to investigate/ explore/ exam.. / In this study ,the aim was to...) that long term exposure to air pollutants is associated with progression of percent emphysema shown on CT imaging, as well asdecline in lung function (PS:as well as 后面常表达次要性质), in a well-characterized, multiethnic cohort of adults (PS: 1.在Introduction部分的结尾需明确提出本研究的范围：(1)时间尺度；（2）目标对象；（3）区域尺度；如果本研究对其他研究有什么帮助，可以总结性的来一句：This study will fill the knowledge gap of .... 2. 我们在写SCI过程中，如果研究的Aim有多个，可以采用一二三几个方面来描述，显的目标很明确，思路很清晰。对于SCI后文的写作有铺垫作用:eg : The first aim of our study was.., the second ... Finally ...)

附1：JAMA引言部分文献

图2. JAMA例证文章中Introduction部分参考文献

JAMA这篇文献的引言文献数量为13篇，基本都是该领域代表性的期刊，包括：2篇Lancet, 6篇AJRCCM，1篇Thorax，Ann intern Med, Int J Chron Obstruct Pulmon Dis，PLOS ONE各一篇，以及美国国家健康统计中心数据（图2）。引证文献权威，说服力强。

附2：常用语小扩展

对于文末阐述研究目标的方式有很多种，问题，检验假设和使用不定式是比较常见的几种，以下给出几种：

问题式：

Finally , do those genes in rice display any tissue or organ-specific expression pattern? We further examined this question using/by .....

检验假设：

In present study ,we test the hypotheses that....Consider the priority of ....., we honored this opportunity to investigate.....

不定式（最多见）：

1. Thus/ Therefore, we aimed to investigate/explore/ evaluate/assess the association.....

2. We conducted a XXX study to investigate whether.....

3. Therefore, the purpose/ aim of the present study was to determine...

4. A major goal of this report is to extend the utilization of recently developed procedure for the .....

5. To better understand the mechanism, we tried to ....

6. Further studies are still necessary.....

总结一下，本文以JAMA最新文献为例，向大家介绍了如何写好SCI论文中的Introduction，相信初学者只要掌握技巧，勤奋多练，一定会能写出令人称颂的优质前言！

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