This template provides link to PubMed Central, a free digital database of full-text scientific literature in biomedical and life sciences.
It takes a single parameter of the PMC article number:
Hence: {{PMC|137841}} Gives: PMC 137841
Alternatively Diberri's Wikipedia template filling tool can generate a fully populated {{cite journal}} markup using the PMC article number. https://citation-template-filling.toolforge.org/cgi-bin/index.cgi