The core-periphery structure of the global scientific/technological system

Studies on global inequality in scientific/technological system have mainly examined how countries are positioned across fields, while paying less attention to inequality within fields. We define the core and periphery of a field as its high-quality and low-quality subfields, respectively, and seek to investigate if there are universal patterns of scientific/technological development between fields and between core and periphery of those fields. The results show that the core of one field is often related more to the core of other fields than to the periphery of the same field. Two big clusters in relatedness networks are detected: one with mainly core subfields and the other including mainly periphery subfields. Tracing the evolution of national scientific/technological portfolios reveals that for countries, entering new core subfields relies on their existing advantages in other core subfields rather than their advantages in peripheries. For scientific/technological independence, lagging countries need to focus on general resources.