Types of identifiers as standard.

The unique identifier is really important. Today the most popular identifiers are used:

• DOIs – assigned to individual articles at the point of publication, and by platforms such as figshare and Dryad to other outputs (including datasets, images, and more);
• Handle.net identifiers – often used in institutional repositories
• PubMedID – typically associated with health sciences research
• arXiv ID – Physics, Mathematics & Computer Sciences
• ADS ID – Astrophysics data system
• SSRN ID – Social Sciences outputs
• RePEC ID – economics research
• URN (Uniform Resource Name) identifiers
• ISBNs – books hosted on publisher domains and google books

USEFUL online journal for all published articles issue DOI and Handle identifiers.