Articles that appear in journals are generally written by scholars or experts in an academic or professional field. The articles may report original research or cover highly specialized topics; usually long, they provide in-depth analyses and bibliographies of references used in preparing the article or resources for further study.
Scholarly journals may have graphs and charts, but usually don't have glossy advertisements. Their titles often include terms like journal, quarterly, studies, bulletin or review, but not always. In the case of Nature, Cell and Lancet, you would need to look through them in order to determine that they are all journals.
Use journals when you need: