Most issues focus on specific subject categories subtitled: Series A, Arts and humanities, Series B, Social sciences, Series C, Mathematical sciences, engineering and technology, Series D, Life and natural sciences, and Series E, Agricultural sciences, all within a single numbering system. Volumes 20 (2011) and 21 (2010) published out of chronological order. Description based on: Vol. 18 (2010); title from cover. Latest issue consulted: Vol. 20 (2011).