Journals, sometimes called periodicals or serials, are scholarly magazines with each issue comprising several journal articles written by different authors. Journals are subject specific with an expert editorial board of academics reviewing each article is submitted for publication.
Primo (the Library Catalogue) can search across the hundreds of journal that the Library subscribes to. You may prefer to search these subject specific journal publisher collections instead of Primo for a more focused search. However, remember the Library may not have purchased every journal from these publisher so not all hits will be full text. Always check Primo to determine the library's holdings of a journal.
Library Skills Guide: peer review and journal tutorials
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Scopus and Web of Science are competitor product databases which search across selected journals from many different publishers and provide advanced features for analysing results to see trends in the literature. They can be useful for identifying review papers, highly cited papers and for searching by author. They are most useful at final project stage and for Masters and Post Graduate Researchers. You could use both or choose one which you prefer - the journal coverage is slightly different so see which one is a best fit for your project although many of the same journals are indexed by both tools.
A 'thesis' in the UK refers normally to Doctoral/ PhD level research work, while a 'dissertation' refers to Undergraduate/Postgraduate Taught level original work of a shorter length.
Theses and dissertations are not peer-reviewed but a PhD Thesis will be a very high-level piece of in-depth work and would only 'pass' after a successful defence of the thesis by the author in front of a panel of academics. (If you find a useful PhD thesis, it is worth checking Scopus or Web of Science for an author profile as it is quite common for authors to publish articles arising from the thesis.)