One of the main goals of the Open Science movement is to leverage scientific collaboration through, among others, promoting the sharing and reuse of research outputs, such as publications, data and software. Sharing is enabled by public and accessible scientific repositories where these outputs are managed throughout their lifecycle. In this context, finding these digital artifacts has become a key problem. Semantic search mechanisms have risen as a means to solve this issue. However, implementing and integrating them into scientific repositories presents many challenges. This article presents a systematic literature review of research efforts on mechanisms for supporting search for scientific papers, data and processes. Our investigation is based on extracting and analyzing the entire contents of nine digital libraries using the associated search engines – in alphabetical order: ACM Digital Library, arXiV, Engineering Village, IEEE Xplore, SBC OpenLib, Springer Link, Scopus, Wiley Online Library and Web of Science. After retrieving a combined amount of 5012 documents, we identified 2054 unique papers that were used as a basis for our analysis. Our findings provide, among others, a new categorization of literature on search and discuss unexplored gaps, thereby contributing to advancing research on semantic search mechanisms to support Open Science.