Google's search engine for scientific publications
Go to Google Scholar
Google Scholar is a search engine that indexes the content of scholarly material published on the Web and in electronic books and journals.
Google Library Link
Click on GetIt@Leiden and to check whether a book or article is accessible through the Leiden University's network. If not, search the catalogue for the printed version. For the GetIt@Leiden to appear off-campus you need to configure your personal Library Links settings in Google Scholar. See the demo in Youtube.
Help pages from Google Scholar.