There are many different corpora for the English language:
- Google Books ngram database is freely accessible and covers publications indexed in Google Books from the 16th century; words are tagged by part-of-speech (more info here).
- The Corpus of Contemporary American English is a large and balanced corpus of American English, including not only books but also magazines, newspapers and spoken English.
- The British National Corpus is a similar enterprise for British English, both spoken and written.
However, one may want to do an analysis of the evolution of English as used in written academic works (theses, journal articles, etc.). This came apparent to me while I was trying to research usage of passive vs. active voice for this question.
So, are there any available corpora of academic works in English language?
- corpus: collections of written or spoken material in machine-readable form, assembled for the purpose of studying linguistic structures, frequencies, etc. [New Oxford American Dictionary]