Manually Entered
You can quickly add items to your library if you already know their ISBN, DOI, PubMed ID, or arXiv ID. To add an item via one of these identifiers, click the “Add Item by Identifier” button (
) at the top of the center column of the Zotero pane, type or paste in the identifier, and press Enter/Return. To enter multiple identifiers at one time, type the first identifier, then press Shift+Enter/Return, then type the remaining identifiers (one on each line). Once you've typed all the identifiers, press Shift+Enter/Return to import all the items at once. You can also paste a list of multiple identifiers (each on a separate line), then press Shift+Enter/Return to finish.
Zotero uses the following databases for looking up item metadata: Library of Congress and WorldCat for ISBNs, CrossRef and other registries for DOIs, NCBI PubMed for PubMed IDs, and arXiv.org for arXiv IDs.