Two new kids on the block: How do Crossref and Dimensions compare with Google Scholar, Microsoft Academic, Scopus and the Web of Science?

In the last 3 years, several new (free) sources for academic publication and citation data have joined the now well-established Google Scholar, complementing the two traditional commercial data sources: Scopus and the Web of Science. The most important of these new data sources are Microsoft Academic (2016), Crossref (2017) and Dimensions (2018). Whereas Microsoft Academic has received some attention from the bibliometric community, there are as...