Sci-Hub is a web service that provides free access to research articles and latest research information, the website uses donated library credentials of contributors to circumvent publishers’ paywalls and thus downloads large parts of their collections. In 2016 Sci-Hub released data on ~28 million downloads done through the service and in 2017 Sci-Hub released the list of ~ 62 million Digital Object Identifiers (DOIs) of the content they have stored.

A recent publication DOI describes a detailed analysis of Sci-Hub usage and as you can see in the plot below taken from the article chemistry journals (shown in red) are particularly popular.