Four domains and the twenty-six fields beneath them. Field assignment is probabilistic rather than categorical — a work belongs to several fields in proportions — so these figures overlap and do not sum to the corpus.
1,728,771 works · 52% open access · 34% of all field assignments
1,245,357 works · 68% open access · 24% of all field assignments
1,192,597 works · 66% open access · 23% of all field assignments
977,615 works · 65% open access · 19% of all field assignments