Microsoft Academic

Microsoft Academic is a free public web search engine for academic publications and literature, developed by Microsoft Research. Re-launched in 2016, the tool features an entirely new data structure and search engine using semantic search technologies. It currently indexes over 220 million publications, 88 million of which are journal articles. 
The Academic Knowledge API offers information retrieval from the underlying database using REST endpoints for advanced research purposes. The search engine provides not only search results and access to sources but also citation information that include the number of sources, "g"-index, and "h"-index. Aside from academic publications, it is also used to find websites that contain state and local records.
The service replaces the earlier Microsoft research project, Microsoft Academic Search, which ended development in 2012. The platform was developed in 2009 of the Microsoft Research branch in Asia and the project was headed by Zaiqing Nie.
Preliminary reviews by bibliometricians suggest the new Microsoft Academic Search is a competitor to Google Scholar, Web of Science, and Scopus for academic research purposes as well as citation analysis. 