一般情况下，研究背景，实验目的，论文结论，采用一般现在时。实验方法，结果及发现，采用过去时。
举几个栗子：
研究背景：A method to select non-responders as early as possible isessential for preventing unnecessary toxicity.
实验方法：Human breast cancer cells were injected into nude rats.
实验结果：A new in vivo breast cancer model was successfully established.
论文结论：The present study suggests that …
有些杂志也会专门有些比较“特别”的要求，比如Cell，要求Abstract全部使用一般现在时。
这部分用到的时态很多变，不能一概而论。
以作者为主语，阐述曾经的研究结果，如果该研究结果仍然正确，则谓语动词用过去时，从句中仍使用一般现在时。
比如：Poliseno et al. recently proposed that the high sequence homologyenables pseudogenes to compete with their parental genes for a shared pool of common miRNAs.
研究背景描述的如果是经典原理，事实，或目前为止最前沿的结果，作者写论文时仍认为是正确的（即使是曾经发生的），用一般现在时。
比如：CircRNAs are recently identified as a naturally occurring family of noncoding RNAs that is highly represented in the eukaryotic transcriptome.
描述已经完成的事，强调 “曾经”，目前为止对此持肯定态度，用现在完成时。
比如：A large number of circRNAs have been successfully identified in various cell lines and across different species.
曾经的研究，其结果现在为止仍然正确，则一句话中可以既有完成时，也有一般现在时。
比如：Recent studies have shown that exon circularization is facilitated by complementary sequences and regulated by specific protein factors.
曾经的研究，但已经过时或失效，作者怀疑其正确性，或要否定其正确性时，用过去时或过去完成时。
比如：Nevertheless, these species had generally been considered to be of low abundance and likely representing errors in splicing.
比如：The proliferation of Huh-7, HCT-116, HeLa cells was tested by CCK-8 kit.
这部分一般时态变化比较少，没什么争议。
比如：In total, 67,358 distinct circRNA candidates were found in these tissues and 27,296 of these circRNAs contained at least two unique back-spliced reads.
但是，单纯描述结果呈现形式（图或表），或直接用图或表作为主语时，因为是写作当时发生的事，所以使用一般现在时。
比如：A detailed summary for each sample is provided in Supplementary Table 1.
Figure 1 shows the mean spectra for the original data.
比如：In this study, we identified lincRNA-p21 as a key regulator of cell proliferation and apoptosis.
对Results部分的结果描述进行更深入的分析和讨论,阐述结果的意义，用一般现在时。
比如：However, certain circRNAs are predominately expressed in one gene locus and present at substantial levels that suggest these species arepurposefully produced.
比如，In conclusion, our study provided a portrayal of circRNAs in different human normal and cancerous tissues.
阐述自己研究成果的意义用一般现在时。
比如，Taken together, these lines of evidence reveal a new level of diversity in the transcriptome and their regulation in human cells.
提出研究前景或将来的研究方向用将来时，这部分也可能出现在Discussion中。
比如，It will be interesting to explore whether lincRNA-p21 can interact with epigenetic factors