serves as a centralized database that enables users to locate materials and identify which libraries hold them. It includes a vast array of materials, ranging from books and manuscripts to music recordings and videos. Users can search for specific titles, authors, subjects, or keywords, and WorldCat provides a list of libraries that have the desired item in their collections.

is one of the world's most voluminous search engines especially for academic web resources. BASE provides more than 300 million documents from more than 10,000 content providers. You can access the full texts of about 60% of the indexed documents for free (Open Access). BASE is operated by Bielefeld University Library.

is a free web browser extension and database that provides access to scholarly research articles that are typically behind paywalls. It is designed to help users find legal open access versions of research papers, making scholarly content more accessible to the general public.

Google Scholar
provides access to scholarly material from various publishers, universities, and scholarly societies. It indexes content from academic publishers, institutional repositories, and other websites that provide scholarly information. The search results in Google Scholar often include peer-reviewed papers, theses, dissertations, conference papers, technical reports, and other scholarly publications.

OAister is a union catalog of millions of records that represent open access resources. This catalog was built through harvesting from open access collections worldwide using the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH). Today, OAIster includes more than 50 million records that represent digital resources from more than 2,000 contributors. is the website of the CORE service, and it serves as a search engine for academic publications. It harvests research articles from various sources, including institutional repositories, subject repositories, and journals, and makes them available for users to search and access. is a comprehensive and open platform for scholarly and patent research. It provides access to a vast amount of academic and patent-related information, making it a valuable resource for researchers, inventors, and intellectual property professionals. is a tool that helps users access academic papers quickly and conveniently. It simplifies the process of obtaining research papers and articles by providing direct links to the full text of scholarly articles through a browser extension or web app. 

Scilit is a comprehensive content aggregator platform for scholarly publications. It is developed and maintained by the open access publisher MDPI AG . It is offered for free to scientists, scholars and the interested general public. Using widely automated approaches to sourcing and curating data, we cover newly published content from a variety of data sources within hours or days.