The national portal NARCIS contains open access scholarly publications from universities, higher professional education institutions, KNAW, NWO and other scientific institutes.
In addition to more than 780,000 open access publications, the portal also includes "restricted" or "closed" access publications. However, a number of these publications are freely available elsewhere. To find these publications, DANS integrated Unpaywall in NARCIS. Each DOI - Digital Object Identifier - (to be found at the bottom of the record) has the Unpaywall logo. If the logo is green, the publication is available elsewhere as an open access publication. By clicking on the DOI, one has access to the open access publication, in another portal. If the logo is gray-green, Unpaywall has also found the publication elsewhere as "closed access".
See for example a closed access publication from TU/e, which can be found elsewhere as open access: How Acceptable Is This? How User Experience Factors Can Broaden our Understanding of The Acceptance of Privacy Trade-offs. Via Unpaywell (see the logo at the bottom of the record) this publication can be found as open access publication in ScienceDirect.
Dutch National website providing information for academics about the advantages of open access to publicly financed research