Public Library of Science (PLOS)
Provides two APIs:
1) PLOS Search API enables developers to query the content of PLOS journals and integrate the data into applications for the web, desktop or mobile devices. Search API FAQ.
2) PLOS Article-Level Metrics (ALM) API gives developers access to data collected by the PLOS Article-Level Metrics application for every article published in a PLOS journal, including usage statistics (e.g., page views, downloads), citation counts, mentions in Wikipedia, activity on social networks and blog coverage. See the ALM API FAQ.
The PLOS API Display Policy specifies how data extracted using the PLOS APIs may be displayed.