Bookends 4+

Bookends is the reference management app you've been looking for.

The basic version offers:

• Search online sites directly (arXiv, Google Books, Google Scholar, JSTOR, the Library of Congress, PubMed, PubMed Central, and Semantic Scholar) or use the built-in browser (EZProxy-compliant) to download PDFs and reference metadata (requires access privileges). Searches can return a maximum of 20 references, and only 50 references can be stored in your personal database.
• Use unique identifiers such as DOI, PMID, ISBN, or arXiv id to autofill references.
• See PDF annotation in a note stream, and create your own with our powerful PDF markup engine.
• Barcode scanning, one per day.
• And many more features designed to help you discover, organize, and use reference information.

Standard, one-time purchase ($14.99):

• No limit on searches or importing.

Pro Features Yearly Subscription ($14.99). Requires a Standard purchase.

• Cloud sync with all your iOS devices and Bookends for Mac (separate purchase)
• Share onlnine libraries with colleagues
• Create multiple libraries
• Unlimited barcode scanning
• Extract PDF annotations with deep links to annotations and text
• View PDF notes in a note stream
• Automate your actions

Subscription is for one year and has an auto-renew option. The subscription can be managed in iOS -> Settings > [your name] > Subscriptions. A subscription may renew if it isn't canceled at least 24 hours before the renewal date.
If the subscription is not renewed, Pro Features will be disabled but Standard features will continue to work.
No cancellation of the current subscription is allowed during the active subscription period.