Figures:

Fig. 1 Publication output performance during 1991–2018.
Fig. 2 The collaboration of the top 20 countries/territories and institutions: (a) network mapping of countries/territories; (b) network mapping of institutions.
Fig. 3 Main co-cited authors for publications.
Fig. 4 Dual-map overlay of scientific publications between 1991 and 2018.
Fig. 5 Keyword co-occurrence map of publications.
Fig. 6 A cluster view of the co-citation network.
Fig. 7 A timeline visualization of the top 10 clusters.