4.4 摘要的时态

写作摘要时需要交替使用多种时态，总的原则是：在说明、描写、解释、刻画某事或物的特点，或描述现在发生的情况时用现在时；叙述过去发生的过程或结果时用过去时。在把握这个原则的基础上，我们再来具体看摘要的几个主要部分写作时的时态使用情况。

（1）Background（研究背景）：为了突出所在研究领域的现状，用现在进行时、现在完成时或一般现在时来表达。

情况1：现在进行时

As global temperatures rise, large amounts of carbon sequestered in permafrost are becoming available for microbial degradation.（Woodcroft et al.,2018）

情况2：现在完成时

Microcracking has been suspected of influencing the transport properties and durability of concrete structures, but the nature and extent of this influence is unclear.（Wu et al.,2015）

情况3：一般现在时

Dysregulated NLRP3 inflammasome activity results in uncontrolled inflammation, which underlies many chronic diseases.（Zhong et al.,2018）

（2）Topic（研究话题）：介绍论文目的用一般现在时，叙述研究目的或方法用一般过去时。

情况1：介绍论文目的，类似于说明文中的说明性语句

This paper investigates the effect of low confining pressure on transport properties of cement-based materials and establishes if it can be used to study the influence of microcracks on transport.（Wu et al.,2014）

情况2：叙述研究目的或方法，类似于叙述文中的叙述性语句

The aim of the present investigation was to clarify whether the K-i 67 nuclear antigen is restricted in its expression to certain phases of the cell cycle.（Gerdes, et al.,1984）

（3）Methods（研究方法）：叙述过去的事情（调查或试验）发生的过程用一般过去时，描述或说明方法的流程用一般现在时。被动语态和主动语态均可以，但被动语态用得更多。

情况1：一般过去时

Microcracks were quantified using fluorescence microscopy and image analysis.（Wu et al.,2014）

Here we use metagenomic sequencing of 214 samples from a permafrost thaw gradient to recover 1,529 metagenome-assembled genomes, including many from phyla with poor genomic representation.（Woodcroft et al.,2018）

注：Here是指in this paper。

情况2：一般现在时，数值建模类论文用得较多

The approach is based on finite-element method and adopts aligned meshing to improve computational efficiency.The mesostructure of concrete is represented by aggregate particles that are surface meshed by triangulation and porous cement paste matrix that arediscretised with tetrahedral elements.（Abyaneh et al.,2016）

（4）Results（研究结果）：说明或描述结果状态用一般现在时，叙述过去产生的结果用一般过去时。被动语态和主动语态均可以，但被动语态用得更多。

情况1：说明或描述结果状态

Results show for the first time that there is a significant size effect on microcracks and transport properties.（Wu et al.,2015）

情况2：叙述过去产生的结果

Samples with smaller t/MSA had more severe microcracking and higher gas permeability.（Wu et al.,2015）

图4.5展示了一个完整的具有代表性的摘要的时态使用情况。