Fig. 3

Link density relationships between countries/regions and the top ten countries/regions. A The complex network of countries/ regions associations, forming four types of associations; B the four types of associations through the form of a map; C the intensity of cooperation between countries/ regions; D the top ten countries/regions. The most published papers were from the People's Republic of China (n = 776), followed by the USA (n = 151) and South Korea (n = 98)