This is my collection of Calibre recipes for downloading recent articles from academic journals in ePub format, for offline reading (e.g., on a Kindle).
You will need to have access to the journals (e.g., via your university) to download the articles.
So far, I have recipe templates for journals hosted by Oxford, Springer, Taylor and Francis, and Wiley. I have no idea whether or not these templates will work reliably for all journals, but they have worked fairly well for the journals I have tried.
Improvements to the templates welcome, as are templates for other publishers, and additional recipes.