Proctor, A. (2019) ‘Student paramedics' views on placements in general practice as part of a degree', Journal of Paramedic Practice, 11(12), pp. 519-525.
Lowe, A., Littlewood, C. and McLean, S. (2018) ‘Understanding physical activity promotion in physiotherapy practice: a qualitative study’, Musculoskeletal Science and Practice, 35, pp. 1-7.
Toomey, E.C. et al. (2021) 'Extended use or reuse of single-use surgical masks and filtering face-piece respirators during the coronavirus disease 2019 (COVID-19) pandemic: A rapid systematic review', Infection Control & Hospital Epidemiology, 42(1), pp. 75-83.
Nightingale, J. (2015) ‘Radiography research as a global community’, Radiography, 21(2), pp. 108-109. doi:10.1016/j.radi.2015.03.006.
Including a doi (digital object identifier) is usually optional, just be consistent. It is not needed in the example above but not wrong to add it. It is, however, needed when you are using an online-only journal that has no page numbers. In that case the doi is used in place of page numbers or other missing information in your reference.
An example is provided below: