The General Index consists of 3 tables derived from 107,233,728 journal articles. A table of n-grams, ranging from unigrams to 5-grams, is extracted using SpaCy. Each of the 355,279,820,087 rows of the n-gram table consists of an n-gram coupled with a journal article id. A second table is constructed using Yake and consists of 19,740,906,314 rows, each with a keywords and an article id. A third table associates an article id with metadata.
See:
https://archive.org/details/GeneralIndex