引言是科技论文正文的起始部分，也是读者最关注的部分之一，其主要任务是向读者介绍研究背景、研究现状、存在的问题以及问题的解决方法（创新点）。好的引言可以吸引读者的阅读兴趣，对正文起到提纲掣领的作用。那么，究竟该如何写好论文中这最让人头疼同时也至关重要的部分呢？让我们从下文中寻找答案吧。
引言结构 三“步”曲
第一步：介绍研究背景（已知的）
先通过介绍大家熟知的背景以强调自己研究内容的重要性；然后由大到小引入到自己的具体研究方向/内容上来，并进一步概括该方向的研究进展，即其他学者在该方向已经做了哪些工作。
注意：背景切记要点题，不要写得太“大”！
第二步：总结研究差距（未知的）。
基于前人的研究，总结得出目前未知的内容/待开展的工作。
第三步：开展研究创新（填补空白）。
根据上述的研究差距（即Why，为什么开展这项研究），引出自己的研究目标/假设（即What，研究什么科学问题）和研究方法（即How，拟如何开展研究）。
此外，在引言的写作过程中，一定要牢记前呼后应（Based on important results），即根据自己后续的重要数据和结论来构架引言的逻辑、选择写作的侧重点。倘若你的部分结果并不能证明某一问题，而你却在引言里面详细叙述这一方面的内容，一方面会偏题，另一方面会引起读者对你文章的质疑。
如果引言里面包含有专业术语或缩写词，务必解释以帮助读者阅读与理解。例如，The increased As uptake is attributed to selenate-enhanced activities of glutathione peroxidase (GPX), which reduces As-induced production of reactive oxygen species H2O2。
叙述前人工作的欠缺以强调自己研究的创新时，应慎重且留有余地（勿“过谦/自夸”、慎重使用“首次提出”、“重大发现”等词汇）。
引言部分参考文献的注意事项：
（1）除非是经典文献或者无其他相关文献，否则尽量阅读并引用优质期刊的文献（≥2区）；
（2）务必客观引用“最相关”的文献（相关性、权威性、时效性、易获取性）
（3）引言写作之前，应收集、整理自己已阅读过的相关文献；
（4）阅读拟投稿的期刊近2~3年发表的论文的目录，从中找出与本文相关的文献，并仔细阅读，适当加以引用；
（5）选择与本文内容相关的国际上知名学者的论文进行引用；
（6）同一篇论文如果同时在会议论文集和期刊中发表，原则上只列出发表在期刊上的论文；
浙江大学马奇英教授：“Last sentences should be a statement of objectives”
实例分享
下面以南京大学历红波老师发表在EST的一篇文章Childhood Lead Exposure in an Industrial Town in China: Coupling Stable Isotope Ratios with Bioaccessible Lead（“中国某工业城镇儿童铅暴露：稳定同位素比值与生物可给铅的耦合”）为例。
第一步：介绍大的研究背景——儿童铅暴露的危害。
Lead (Pb) exposure is a serious hazard for children, adversely affecting their cognitive and behavioral development.
大的研究背景一般比较笼统，有时读起来会显得比较“大”和“空”。因此，可以利用举例（权威机构和知名学者的研究结果）和“量化数据”的方式，使其更直观和具体化并令人信服。
Recent reports suggest that neurological damage occurs in children at low blood lead levels (BLLs; 2–10 μg dL–1), indicating there are no “safe” BLLs.
然后由大到小引入到自己的具体研究方向/内容上——作者研究的是“中国某工业城镇儿童铅暴露”。因此，这里由大背景转到了小方向，即工业活动导致的中国儿童铅暴露。并且，进一步强调了该研究内容的重要性（虽然含铅汽油被逐步淘汰，但工业活动对儿童铅暴露的贡献同样不容忽视）。
Although a dramatic decline in BLLs is observed worldwide after leaded gasoline has been phased out, children’s exposure to Pb is still common in China because of industrial expansion.
继续向自己的研究方向递进——工业区儿童铅暴露的主要途径、准确识别主要暴露途径的重要性。
To reduce exposure to Pb for children living near industrial areas, it is important to identify predominant Pb exposure pathways, which include both nondietary (ingestion of dust/soil and inhalation of particulates) and dietary pathways (consumption of food and drinking water).
继续向自己的研究方向递进——识别儿童铅暴露的有效手段：铅同位素技术
However, identifying major exposure pathways is often compromised by the lack of paired data of blood Pb with environmental Pb for a given cohort.
Fingerprinting based on stable Pb isotope ratios (207Pb/206Pb and 208Pb/206Pb) of environmental and blood samples helps to identify Pb exposure pathways.
并简单介绍了铅同位素技术识别儿童铅暴露途径的主要原理
In general, natural sources of Pb have ratios lower than those of anthropogenic sources. As a result, when environmental Pb sources are isotopically distinct from one another, Pb exposure pathways may be identified by comparing the isotopic composition of blood Pb with environmental Pb.
然后进一步概括介绍铅同位素技术识别儿童铅暴露途径的研究进展，即其他学者在该方向已经发表了哪些工作
Over the years, this technique has been successful in identifying pathways of childhood Pb exposure. For example, by comparing the 208Pb/206Pb isotope ratio in environmental media (e.g., soil, dust, paint, air particulates, and gasoline) with that in blood samples of children having elevated BLLs (28–43 μg dL–1), Yaffe et al. found that blood isotope ratios were close to those of soil and housedust, suggesting ingestion of soil and housedust was the source of blood Pb. Liang et al. found that the Pb isotopic composition of children’s blood in Shanghai, China, matched those in PM10 and coal combustion ash, suggesting inhalation of air particulates contaminated with coal combustion ash was an important blood Pb contributor. Cao et al. found close agreement between Pb isotope ratios of children’s blood and vegetables, wheat, drinking water, and air particulates, while blood Pb ratios were different from those of soil and housedust, suggesting that dietary and inhalation pathways were the most likely sources of children’s blood Pb. Similarly, Gulson et al. and Delves and Campbell successfully used Pb isotopes to identify housedust and drinking water as predominant blood Pb sources in children.
第二步：研究背景介绍完之后，作者开始总结现有研究的不足及其原因
However, there have also been studies that failed to identify blood Pb sources in humans. Manton et al. suggested that the success rate of blood Pb source identification using Pb isotopes in the United States is ∼20%. One reason is the overlap of isotopic compositions of different environment samples with one another. For example, Soto-Jiménez and Flegal found that the Pb isotope ratios of dust, soil, and aerosols from a smelting area of México were indistinguishable from each other, all being similar to blood Pb ratios. Another issue associated with previous Pb isotope studies is that isotope ratios are usually determined for total Pb in environmental media. However, it is recognized that following ingestion or inhalation of soil, dust, air, and food matrices, only the bioavailable fraction of Pb is absorbed into the systemic circulation. Conceivably, comparison of Pb isotope ratios for blood and total Pb in environmental matrices may not provide an accurate estimate of exposure sources when isotope ratios of bioavailable Pb and nonbioavailable Pb differ.
研究差距：铅同位素技术在识别儿童铅暴露过程中并不是无往不利的，有时并不能准确鉴定来源（注意，作者这里巧妙引用文献，量化数据，使得该研究差距更加直观可信——在美国，使用铅同位素进行血液铅源鉴定的成功率为～20%）。
作者总结的原因包括两个：
一为已知的原因（文献报道，作者这里引用了文献，使其更加可信）：不同环境指纹样品与人血的同位素组成相互重叠，难以区分；
二为推测的原因（目前未知，为作者总结推测，也相当于作者总结出来的科学问题，这是目前未知的内容，也是作者拟开展的研究）：之前的研究测定的是环境介质总铅的同位素组成，而人体摄入体内的铅主要为生物可利用铅，当总铅和生物可利用铅的同位素组成存在差异时，总铅的同位素组成可能无法准确识别血铅来源。
第三步：基于上述的研究背景和研究差距，作者引出了自己的研究目标和研究方法
In this study, BLLs were assessed in a cohort of children who resided in Zhuhang, China, a town characterized by intensive wire rope production. Potential Pb exposure sources were assessed by determining total and bioaccessible Pb concentrations, and stable Pb isotope ratios in children’s blood and environmental media. We hypothesized that comparing Pb isotopic data between children’s blood and bioaccessible Pb in environmental media would provide an approach for identifying Pb exposure pathways more robust than total Pb determinations, especially when isotope ratios vary significantly between total and bioaccessible Pb.
研究目标（我们假设，当总铅和生物可给铅的同位素组成差异较大时，生物可给铅的铅同位素组成比总铅的同位素组成更能准确识别儿童血铅来源）和研究方法（通过测定中国某工业城镇儿童血液和环境介质中的总铅和生物可给铅浓度及二者的铅同位素组成来评估潜在的铅暴露源）。
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