Finding Reference Identifiers

Identifiers like DOI, PubMed ID, and ISBN let Auto-Cite fetch complete reference data automatically. This guide helps you find these identifiers for your sources.

DOI (Digital Object Identifier)

DOIs uniquely identify scholarly content. They start with 10. followed by a prefix and suffix.

Example: 10.1038/nature12373

Where to Find DOIs

On the article webpage:

• Near the title or abstract
• In the footer or sidebar
• In the “Cite this article” section

In the PDF:

• First page, often below the title
• In the header or footer
• Near author information

In Google Scholar:

1. Search for the article
2. Click “Cite” (quotation marks icon)
3. Look at the bottom for the DOI

Using CrossRef:

1. Visit search.crossref.org
2. Enter title and author
3. Find your article and copy the DOI

DOI Tips

• Always include the full DOI (starts with 10.)
• You can use either format:
• Not all articles have DOIs (older ones especially)

PubMed ID (PMID)

PubMed IDs are unique numbers assigned to biomedical literature in the NCBI database.

Example: 23831764

Where to Find PMIDs

On PubMed:

1. Search pubmed.ncbi.nlm.nih.gov
2. Open the article
3. PMID appears below the title

In the URL: pubmed.ncbi.nlm.nih.gov/23831764 (the number is the PMID)

On journal websites: Look for “PubMed” or “PMID” links/badges.

PMID Tips

• PMIDs are numeric only (no letters)
• One article can have both DOI and PMID
• PMID gives access to PubMed’s rich metadata

ISBN (International Standard Book Number)

ISBNs identify books. They come in 10-digit (older) and 13-digit (current) formats.

Examples:

• ISBN-10: 0-13-468599-1
• ISBN-13: 978-0-13-468599-1

Where to Find ISBNs

On the book:

• Copyright page (inside front cover)
• Back cover (usually with barcode)
• Inside the dust jacket

Online:

• Publisher website
• Amazon, Google Books, or bookstores
• Library catalogs

For eBooks:

• eBooks have their own ISBNs
• Check the copyright/title page in the eBook

ISBN Tips

• Enter with or without hyphens (both work)
• Use the ISBN-13 when both are available
• Some academic books have limited data in ISBN databases

arXiv ID

arXiv hosts preprints in physics, mathematics, computer science, and related fields.

Example: 2103.00020

Where to Find arXiv IDs

On arXiv:

1. Visit arxiv.org
2. Search for the paper
3. ID appears in the URL: arxiv.org/abs/2103.00020

In the PDF:

• First page header or footer
• Marked as “arXiv:2103.00020”

In citations: Papers often cite arXiv versions with the ID.

arXiv Tips

• Format: YYMM.NNNNN (year-month.number)
• Old format: category/YYMMNNN (still works)
• Many arXiv papers later get DOIs when published

bioRxiv ID

bioRxiv hosts biology preprints.

Example: 2021.01.15.426789

Where to Find bioRxiv IDs

On bioRxiv:

1. Visit biorxiv.org
2. Find the paper
3. ID in URL: biorxiv.org/content/10.1101/2021.01.15.426789

In the PDF: Listed as “bioRxiv preprint doi: https://doi.org/10.1101/…”

bioRxiv Tips

• bioRxiv uses DOI-like identifiers
• The number after 10.1101/ is what you need
• Similar format to medRxiv (medical preprints)

ORCID

ORCID is an author identifier, not a publication identifier. Use it to find all works by an author.

Example: 0000-0002-1825-0097

Where to Find ORCIDs

On the author’s profile:

• Author websites often display ORCID
• Look for the green ORCID icon

On publications:

• Author list may link to ORCIDs
• Acknowledgment or author bio sections

On ORCID.org: Search by author name to find their ORCID and publication list.

ORCID Tips

• Format: Four groups of four digits
• Using ORCID imports all of an author’s publications
• Useful for adding multiple works by a researcher

When No Identifier Exists

Some sources don’t have standard identifiers:

Older publications:

• Pre-digital articles may lack DOIs
• Use manual entry with title/author search in databases

Non-academic sources:

• News articles, blog posts: use URL
• Books without ISBN: use manual entry

Unpublished works:

• Dissertations: check ProQuest or institutional repository
• Working papers: check SSRN, NBER, or author website

Using URLs

When no identifier exists, Auto-Cite can extract metadata from URLs:

Best results from:

• News sites with good metadata
• Academic blogs
• Publisher websites
• Organizational reports

Limited results from:

• Social media
• Paywalled content
• Dynamically generated pages

Search Strategies

Can’t Find the DOI?

1. Search Google Scholar for the exact title
2. Check the publisher’s website
3. Use CrossRef search (search.crossref.org)
4. Check Unpaywall (unpaywall.org)

Wrong Results from Identifier?

• Verify you copied the identifier correctly
• Some identifiers are reused or reassigned
• Old DOIs may point to different content

Multiple Versions?

• Preprints vs. published versions have different identifiers
• Use the identifier for the version you’re citing
• Note which version in your citation if needed

Quick Reference

Identifier	Format	Where to Find
DOI	10.xxxx/xxxxx	Article page, PDF, Google Scholar
PMID	Numeric (e.g., 12345678)	PubMed URL or page
ISBN	10 or 13 digits	Book cover, copyright page
arXiv	YYMM.NNNNN	arXiv URL
bioRxiv	YYYY.MM.DD.NNNNNN	bioRxiv URL/DOI
ORCID	0000-0000-0000-0000	Author profiles

Next Steps

• Auto-Cite – Use identifiers to fetch references
• Manual Entry – When identifiers aren’t available