Have previous publications without DOI with certain journals though they now provide DOIs but don't seems to be ready to link up for the provision of DOIs for previous publications. Any means to acquire that please?
To Tanvir Singh: DOIs can be generated for most of your unpublished work. As publications classified as article, book, chapter, patent, cover page, poster, and conference paper are considered to have been published elsewhere, DOIs cannot be generated for these types of research. You can, however, add an existing DOI issued by your publisher to any of your research. You should not generate a new DOI for a research item that already has one, as this will potentially lead to confusion.
More details: https://explore.researchgate.net/display/support/ResearchGate+DOIs