Although there are standards with regard to the classification of scientific fields (UNESCO, 1978), these standards do not seem to have gained acceptance when it comes to compile corpora of academic discourse.
the French SCIENTEXT corpus is divided in ten scientific domains (Tutin and Kraif, 2016), Coxhead (2000) distinguishes four big scientific areas (Arts, Commerce, Law, and Science) in turn subdivided into 27 subareas, Paquot (2010) draws a big divide between hard and soft sciences and further breaks down the former into four sections and the latter into six, etc.