In this study, scholarly communication systems provided by commercial services and open access systems are examined on the basis of the comprehensiveness and uniqueness of their coverage. Commercial databases (Web of Science and Scopus) are compared with search engine (Google Scholar), aggregate institutional repositories (OAIster and OpenDOAR), and the open access system for physics research (arXiv). Retrievals were conducted from the six databases or systems, and the output at each location was compared with that at the others. Journal articles published by Nobel laureates in physics from 2001 to 2013 were selected as samples in this study. The study reveals that search engine tend to provide more resources than do commercial databases but also that commercial databases have better coverage than institutional repositories. Institutional repositories showed a zero percentage of uniqueness when compared with Google Scholar. The results of the present study may provide suggestions to researchers, thereby enabling them to select better information and reference sources for scholarly assessment of individual research productivity and influence; consequently, their international visibility and diffusion may be enhanced.