Harris (2014, p.56) argued that "nursing staff..."
In a recent study (Evans, 2015), qualifications of school-leavers were analysed...
In his autobiography (Fry, 2014)...
They are all listed
In an important study of the subject (Hill, Smith and Reid, 2014)
Cite the first name listed in the source followed by et al.
New research on health awareness by Tipton et al. (2016)...
Separate the dates of publication with a semicolon (;) with the earliest date first
In both editions (Hawksworth, 2009; 2013)...
Use the phrase no date
In an interesting survey of youth participation in sport, the authors (Harvey and Williams, no date)...
Use the title and no date
Integrated transport systems clearly work (Trends in European transport systems, no date)
Should follow the preceding guidelines - author and date where possible.
Title and date if no author
By URL if no author or title
The latest survey of health professionals (http://www.onlinehealthsurvey.org, 2015) reveals that...
You can find all those examples and more in:
Pears, R. and Shields, G.J. (2016) Cite them right: the essential referencing guide. . Basingstoke, Hampshire: Palgrave Macmillan.