科学文献中的动词时态

标题（Title）
标题通常都不是完整的句子
e.g. Cleavage of structural proteins during the assembly of the head of bacteriophage T4 [1].

在这种情况下，不需要使用动词时态。
但是，如果你想用一个完整的句子的话，用一般现在时。
e.g. CXCL12 in early mesenchymal progenitors is required for haematopoietic stem-cell maintenance [2].
e.g. Single-cell transcriptomics reveals bimodality in expression and splicing in immune cells [3].

引言（Introduction）
引言中会用到各种时态，包括现在时、现在完成时和过去时态。
现在时-用于陈述一般事实。
e.g. Today, just over half of NIH-funded clinical-research participants are women [4].
e.g. While promising, GFP-based methods rely on cellular transfection that proves to be difficult to achieve in certain primary cell types [5].

现在完成时–
用于描述过去发生的，但现在仍然相关的事情
e.g. Fluorescent polymers and green fluorescent proteins (GFPs) have recently been used for temperature mapping within a living cell [5].
e.g. Certain rigorous studies evaluating the effects of sex differences have been effective in bridging the divide between animal and human work [4].

过去式：用于讨论以前的研究或过去的事件
e.g. Earlier this year, a study demonstrated that mice with XY chromosomes in the central nervous system had   greater neurodegeneration than did those with XX chromosomes [5]; 
e.g. More than two decades ago, the US National Institutes of Health (NIH) established the Office of Research on Women’s Health (ORWH) [4].

过去式-用于陈述假设
e.g. We speculated that exchange of the methyl group at the 2-position of the phenyl ring by a carboxyl group    would reduce the hydrophobicity and unspecific binding of the fluorophore [6].
e.g. We hypothesized that miR expression would differ among patients with AML who have low vitamin D levels compared with those who have normal vitamin D levels [7].

材料与方法（Materials and Methods）
方法一节中最常用的时态是过去式，但有时需要用过去完成时和过去进行时。
过去时-用于描述研究过程中使用的材料和方法
e.g. Bacterial genomic DNA was isolated from mice faeces, amplified for V1–V4 hypervariable regions of the 16S rRNA gene, and used for pyrosequencing analysis [8].

过去完成时-用于描述一个发生在另一个动作之前的动作的时候。
e.g. As a substrate, we used degenerately doped silicon onto which a 270-nm-thick layer of SiO2 had been grown [9].
e.g. Once the temperature set in the thermostat had been reached, the system was allowed to equilibrate for 30 min [10].

过去进行时-描述一个过去正在进行的动作时使用。
e.g. Participants were asked to recall what they had been told about post-HCT QOL as they were preparing for transplant [11].
e.g. Patients with relapsed and/or refractory MM whose disease was progressing after two or more prior lines of therapy were eligible to participate [12].

结果（Results）
在结果部分中最常用的时态是过去式。然而，有时也会用到现在时态。
过去时-描述一个实验的结果时使用（在写论文之前发生的，因此使用过去时态）：
e.g. Analysis of the identified gene set revealed the induction of a broad-spectrum antipathogen response [13].

现在时-描述一个现在认为是事实的结果时使用。
e.g. Consistent with the former finding, challenge with the flagellin 51 MAMP peptide, flg22 (ref. 10), or the necrotroph Botrytis cinerea 52 11 suppresses photosynthesis-related transcripts [14].

讨论（Discussion）
与引言一样，通常科学论文的讨论部分会用到多种时态，包括过去时，现在时和将来时。
将来时-用于讨论研究的影响
e.g. Demonstrating whether forest elephants use clearings to maintain their relationships will allow us to understand how elephant social relationships vary across the wide range of ecological conditions occupied by both forest and savannah elephants [15].

在一个句子里混合使用多种时态
e.g. Males were [past] more likely to be responsible for the creation of mixed groups, despite a female bias in the visiting population, and therefore appear [present] to be more socially exploratory and less socially choosy than females, as seen in savannah elephants [15].

图例/表例（Figure/table legends）
现在时-用于引用文本中的图/表
e.g. Selected examples are shown in Table 1 and Fig. 2.

图例和表例应该是独立的，即描述性的，足以让你的读者理解，而不必阅读的主要文本。图例和表例的独立性，他们的结构有点像一个缩减了的论文，包括标题，以及方法和结果[ 16 ]的简短描述。因此，图例和表例中会用到混合时态。
e.g. Figure 1. Number of copulations per 6 h during an entire breeding attempt [title – no tense]. Data are shown [present] as median and interquartile range. (a) Pairs were caring [past continuous] for their larvae. (b) Larvae had been [past perfect] withheld and pairs were not caring [past continuous] for larvae. For statistical analysis of the time course of copulations, we divided [past] the observation period into six successive time intervals (TI1eTI6), each with a duration of 42 h [15].

References
1. Laemmli, U.K., 1970. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. nature, 227, pp.680-685.
2. Greenbaum, A., Hsu, Y.M.S., Day, R.B., Schuettpelz, L.G., Christopher, M.J., Borgerding, J.N., Nagasawa, T. and Link, D.C., 2013. CXCL12 in early mesenchymal progenitors is required for haematopoietic stem-cell maintenance.Nature, 495(7440), pp.227-230.
3. Shalek, A.K., Satija, R., Adiconis, X., Gertner, R.S., Gaublomme, J.T., Raychowdhury, R., Schwartz, S., Yosef, N., Malboeuf, C., Lu, D. and Trombetta, J.J., 2013. Single-cell transcriptomics reveals bimodality in expression and splicing in immune cells. Nature, 498(7453), pp.236-240.
4. Clayton, J.A. and Collins, F.S., 2014. NIH to balance sex in cell and animal studies. Nature, 509(7500), pp.282-283.
5. Kucsko, G., Maurer, P.C., Yao, N.Y., Kubo, M.I.C.H.A.E.L., Noh, H.J., Lo, P.K., Park, H. and Lukin, M.D., 2013. Nanometre-scale thermometry in a living cell. Nature, 500(7460), pp.54-58.
6. Lukinavičius, G., Umezawa, K., Olivier, N., Honigmann, A., Yang, G., Plass, T., Mueller, V., Reymond, L., Corrêa Jr, I.R., Luo, Z.G. and Schultz, C., 2013. A near-infrared fluorophore for live-cell super-resolution microscopy of cellular proteins. Nature chemistry, 5(2), pp.132-139.
7. Lee, H.J., Muindi, J.R., Tan, W., Hu, Q., Wang, D., Liu, S., Wilding, G.E., Ford, L.A., Sait, S.N., Block, A.W. and Adjei, A.A., 2014. Low 25 (OH) vitamin D3 levels are associated with adverse outcome in newly diagnosed, intensively treated adult acute myeloid leukemia. Cancer, 120(4), pp.521-529.
8. Yoshimoto, S., Loo, T.M., Atarashi, K., Kanda, H., Sato, S., Oyadomari, S., Iwakura, Y., Oshima, K., Morita, H., Hattori, M. and Honda, K., 2013. Obesity-induced gut microbial metabolite promotes liver cancer through senescence secretome. Nature, 499(7456), pp.97-101.
9. Lopez-Sanchez, O., Lembke, D., Kayci, M., Radenovic, A. and Kis, A., 2013. Ultrasensitive photodetectors based on monolayer MoS2. Nature nanotechnology, 8(7), pp.497-501.
10. Nielsen, M., Alberico, E., Baumann, W., Drexler, H.J., Junge, H., Gladiali, S. and Beller, M., 2013. Low-temperature aqueous-phase methanol dehydrogenation to hydrogen and carbon dioxide. Nature, 495(7439), pp.85-89.
11. Jim, H.S., Quinn, G.P., Gwede, C.K., Cases, M.G., Barata, A., Cessna, J., Christie, J., Gonzalez, L., Koskan, A. and Pidala, J., 2014. Patient education in allogeneic hematopoietic cell transplant: what patients wish they had known about quality of life. Bone marrow transplantation, 49(2), pp.299-303.
12. Badros, A.Z., Vij, R., Martin, T., Zonder, J.A., Kunkel, L., Wang, Z., Lee, S., Wong, A.F. and Niesvizky, R., 2013. Carfilzomib in multiple myeloma patients with renal impairment: pharmacokinetics and safety. Leukemia, 27(8), pp.1707-1714.
13. Ariotti, S., Hogenbirk, M.A., Dijkgraaf, F.E., Visser, L.L., Hoekstra, M.E., Song, J.Y., Jacobs, H., Haanen, J.B. and Schumacher, T.N., 2014. Skin-resident memory CD8+ T cells trigger a state of tissue-wide pathogen alert.Science, 346(6205), pp.101-105.
14. de Torres Zabala, M., Littlejohn, G., Jayaraman, S., Studholme, D., Bailey, T., Lawson, T., Tillich, M., Licht, D., Bölter, B., Delfino, L. and Truman, W., 2015. Chloroplasts play a central role in plant defence and are targeted by pathogen effectors. Nature Plants, 1(6).
15. Fishlock, V. and Lee, P.C., 2013. Forest elephants: fission–fusion and social arenas. Animal Behaviour, 85(2), pp.357-363.
16. Panter M., 2016. Writing an Effective Figure Legend. Available at: http://www.aje.com/en/arc/writing-effective-figure-legend/[Accessed 07 October, 2016]