文章不知道使用什么时态，快来看看JAMA子刊是如何做的
正确地使用动词时态是英文写作的基本功，如不能正确选用时态，就会出现“broken English”，影响期刊编辑、评审专家和读者的理解。
梅斯学术今天将以JAMA子刊上发表的“Effect of Sleep Extension on Objectively Assessed Energy Intake Among Adults With Overweight in Real-life Settings A RandomizedClinical Trial”，从一篇英文学术论文的Abstract、Introduction、Materials and Methods 、Results、Discussion和Conclusion 六个部分分别阐明学术论文写作中的时态问题，旨在帮助刚开始撰写英文学术论文的读者更好的选择动词的时态。
Abstract
Abstract通常包括Background、Method、Results、Conclusions和Keywords（不需要句子）。一般采用现在完成式阐述已有的研究现状，采用一般过去式指出自己研究的实施。如：
Short sleep duration has been recognized asa risk factor for obesity. Whether
extending sleep duration may mitigate thisrisk remains unknown.
Participants were adults aged 21 to 40 yearswith a body mass index (calculated as weight in kilograms divided by height inmeters squared) between 25.0 and 29.9 and had habitual sleep duration of lessthan 6.5 hours per night.
但要注意的是Conclusions部分如果要进行展望时，通常使用一般现在时。
Introduction
Introduction通常需要说明如下3方面内容：（1）研究背景，突出该科学问题的重要性。比如某种疾病的疾病负担有多重、某种疾病目前普遍认可的危险因素和风险因素；（2）综述该科学问题在同领域的研究现状；（3）提出自己研究的科学假说及简要阐明预期达到的目的。这个时候，通常应采用现在式时态。如：
Obesity is a major public healthconcern. The obesity epidemic appears to coincide with a pattern of sleepingless that has been observed in society over the past several decades.
Substantial evidence suggests thatsleeping less than 7 hours per night on a regular basis is associated with adversehealth consequences.
注意在上述（2）中，如果想表述类似的研究已经被广泛开展等意思时，需要用到现在完成时。如：
Short term experimental laboratorystudies have found that sleep restriction in healthy individuals is associatedwith an increased mean energy intake of about 250 to 350 kcal/d with minimal tono change in energy expenditure.
Materials and Methods
方法学部分用于阐明本研究中的样本来源，实验或调查的实施，以及统计分析的方法。通常采用过去时态来表示本研究如何开展。例如：
After a 2-week habitual sleep period at baseline, participants were randomized to either 2-week sleep extension (sleep extension group) or 2-week continued habitual sleep (control group)
In secondary analyses, mixed models that adjusted for sex or menstrualcycle were also fit; these covariates were chosen because of the knowninfluence of menstrual cycle on short term changes in weight.
注意图和表的引用通常采用现在时态， 助解释你做了什么，用现在时态引用该图形或图表。
Figure 2 illustrates the mean nightlysleep duration by actigraphy in each group throughout the 4-week study.
Results
在描述结果部分，使用过去时态来详细说明你获得的结果。例如：
One participant in the control group revealed adhering to a weight loss
regimen and thus did not meet the study inclusion criteria and was deemedineligible after randomization.
Energy intakewas statistically significantly decreased in the sleep extension group comparedwith the control group (−270.4 kcal/d; 95% CI, −393.4 to −147.4 kcal/d; P <.001).
如果文章中提到图形、表格和图表时，通常使用现在时态。
Figure 3A through D illustrates thechanges from baseline in
energy intake and the changes frombaseline in sleep duration in individual participants.
Discussion
通常使用过去式表示研究的主要发现，结合现在式突出本研究在同领域研究中的意义。如：
In this RCT of adults with overweight who habitually curtailed their sleep duration, sleep extension reduced energy intake and resulted in a negative energy balance (ie, energy intake that is less than energy expenditure) in real-life settings.
To our knowledge, this study provides the first evidence of the beneficial effects of extending sleep to a healthy duration on objectively assessed energy intake and body weight in participants who continued to live in their home environment.
Conclusion
总结本研究的主要发现和研究展望。这时，我们通常采用一般过去式阐述研究主要发现，用一般现在式对研究做出展望。
This RCT found that short-term sleep extension reduced objectively measured energy intake and resulted in a negative energybalance in real-life settings in adults with overweight who habitually curtailedtheir sleep duration.
The findings highlighted the importance of improving and maintaining adequate sleep duration as a public health target for obesity prevention and increasing awareness about the benefits of adequate sleep duration for healthy weight maintenance.
需要强调的是，不同领域和研究者往往会有不同的写作习惯和范式。因此本文只是简要阐明进行英文学术论文撰写时选择时态的一般做法。更多写作范式需要多阅读高质量的文献，做好积累。
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