A new bibliometric method is proposed for representing links between subfields as defined by a classification scheme. The frequency of co-occurrence of articles from different subfields in selected journals is used for measuring the degree of relatedness between these subfields. The results of such quantitative analysis could be compared to the tree topology of the classification network established in a qualitative analysis. The method is applied to describe the internal links within the field of condensed matter physics using the 1984 Physics Abstracts database. A distinction is made between experimental and theoretical links on the basis of treatment codes assigned to journal articles. The links described by cluster analysis are matched against the cross-reference network of the International Classification for Physics.