Many university libraries offer DRM-protected PDF downloads of the 2013 edition to authorized students/faculty.
provides the data (ephemerides) for a specific year, the Supplement explains the mathematical models
A community-uploaded version of the 394-page supplement can be viewed or downloaded with a subscription.
Explanatory Supplement to the Astronomical Almanac - NASA ADS
The Explanatory Supplement to the Astronomical Almanac is an essential technical resource explaining how almanac values are derived and implemented. For accurate, current information, obtain the official edition PDF from publisher or institutional sources, verify edition/metadata, respect copyright, and consult supporting datasets and errata when implementing algorithms.
