论文写作指导：英文摘要中语态和时态的用法

 英文 摘要的字数大多数期刊规定不超过250个词， 内容 应与中文摘要对应。医学论文中，一般少用第一人称和主动语态，多用第三人称和被动语态，用以体现叙述客观事实。所用时态需与事情发生时间一致，叙述基本 规律 时可用现在时，叙述 研究 对象、 方法 和结果时，用过去时。举例如下。

　　Objective: The purpose of this study was to determine whether an in hospital transportable CT scanner can provide diagnostic brain images and to compare the quality of these images with those from a convertional fixed? platform CT scanner.

　　Subjects and Methods:Twenty seven patients with known or suspected intracranial pathology underwent imaging on a transportable scanner and a fixed? platform scanner within 1hr of each other.Images from each CT examination were evaluated independently by two neuroradiologists who were unaware of patient history.Conspicuousness of intracranial pathology and normal anatomy were rated on a 5? point scale (1 point 'optimal;5 points'poor or not visualized).Statistical comparisons were made using nonparametric tests.

　　Results:Seven CT scans were interpreted as showing normal findings and 20 scans revealed intracranial pathology on both CT scanners.Image quality was higher on the fixed scanner(average rating'2.42 points'SE=0.12)than on the transportable scanner(average rating'3.10   points'SE=0.12(p=0.001).Depiction of the cerebellum'midbrain'and supratentorial gray? white matter was better on the fixed scanner(p＜0.05＝. However 'we found no significant differences in detection of intracranial pathology between scanners.Both radiologists found images from both scanners to bediagnostic in all 27 patients.

　　Conclusion:Images of the brain on the transportable CT scanner were less clear than those on a fixed scanner.However'images from the transportable CT scanner were diagnostic in 27 consecutivepatients.The implications of this finding are important for the provision of CT services for critically ill patients who cannot be transported to the radiology department.

　　上面是AJR(美国放射学杂志)中一段完整的英文摘要，从中可以看出其特点：①用词简练、准确；②时态为过去时；③不用第一人称，多用被动语态；④方法和结果中强调统计方法及数据。对母语非 英语 的作者来说，撰写英文摘要的质量好坏直接与作者的英文水平有关，在这方面，只有多阅读英文 文献 ，才能提高英文写作水平，从而写出高质量的英文摘要。