Preprint servers to enhance access to scientific knowledge

Preprint servers can enhance the access to scientific knowledge by linking indexed papers in bibliography databases to their counterpart preprint versions whenever available. The current state of connection is to link preprints to their published versions in peer-reviewed journals. Here, I suggest the opposite. That is, linking indexed journal papers to their preprint versions wherever these are posted on a preprint server. Such linking from paid version (journals' articles) to their corresponding free preprint versions would make much sense as it removes the barrier to get access to pay walled papers for free.