Bibliographic Databases
OpenAlex
OpenAlex is an open, nonprofit index of scholarly works, authors, institutions, journals, and research topics, developed by OurResearch as a free alternative to proprietary databases like Scopus and Web of Science. It aggregates metadata from sources such as Crossref, DataCite, PubMed, ORCID, ROR, DOAJ, Unpaywall, Microsoft Academic Graph, and open repositories like arXiv and Zenodo. These records are cleaned, linked, and disambiguated to create a structured graph of the global research ecosystem. Licensed under CC0, OpenAlex provides open access via an API and downloadable datasets, supporting open science, reproducibility, and equitable access to bibliographic data.
Lens.org Scholar
Lens.org Scholar is a free, open research-metadata platform maintained by Cambia that integrates global scholarly literature with patent data to show how research connects to innovation. Drawing from Crossref, PubMed, OpenAlex, Microsoft Academic, and open-access sources like Unpaywall and CORE, Lens offers over 200 million records searchable through a rich interface and API. By linking scholarly and patent citations, Lens enables exploration of research influence, institutional collaboration, and knowledge transfer, advancing transparency and accessibility in the research and innovation landscape.
Google Scholar
Google Scholar is a free academic search engine developed by Google that indexes scholarly literature across a wide range of disciplines and publication types, including journal articles, theses, books, conference papers, and preprints. Unlike curated databases such as Scopus or Web of Science, Google Scholar uses automated web crawling to discover content from publishers, repositories, and university websites, making its coverage broad but non-transparent and unverified. Its exact size is unknown, but estimates in the scholarly literature suggest it may index between 300–400 million records, making it the largest academic search tool in scope. However, Google does not disclose its data sources, update frequency, or inclusion criteria, and its automated indexing can sometimes include non-scholarly or duplicate materials. Google Scholar does not provide an open API and actively restricts large-scale web crawling, limiting its use for bibliometric or data-driven research. Additionally, it lacks structured metadata and advanced search functionality, offering only basic keyword-based queries. Despite these limitations, Google Scholar remains one of the most widely used academic discovery tools due to its accessibility, broad coverage, and integration with citation tracking and researcher profiles (Google Scholar Citations).
Scopus
Scopus is a subscription-based bibliographic database operated by Elsevier, offering comprehensive coverage of peer-reviewed literature across science, technology, medicine, social sciences, and the arts and humanities. It indexes over 90 million records from more than 27,000 journals, conference proceedings, and book series, sourced from verified academic publishers. Scopus provides citation tracking, author and institutional profiles, and analytics tools for measuring research impact and collaboration. Its inclusion criteria are guided by an independent Content Selection and Advisory Board (CSAB) to maintain quality and relevance, and its structured metadata powers tools like SciVal and Scopus AI for bibliometric and trend analyses.
Dimensions Plus
Dimensions is a research information system developed by Digital Science that integrates publications, datasets, grants, patents, and clinical trials into a unified, linked database. It combines data from sources like Crossref, PubMed, and numerous funder databases to enable discovery across the full research lifecycle. Dimensions includes over 140 million publications and offers citation metrics, altmetrics, and collaboration mapping. Available in both free and subscription versions, it supports advanced analytics, policy monitoring, and research evaluation, providing a transparent and interconnected alternative to traditional citation databases.
Web of Science from Clarivate Analytics
Web of Science is a curated citation index maintained by Clarivate, widely used for bibliometric research and research assessment. It provides structured metadata and citation data for over 85 million records across more than 21,000 journals, conference proceedings, and books. Web of Science is known for its rigorous journal selection process and long-standing citation data continuity, dating back to the Science Citation Index founded by Eugene Garfield in the 1960s. It supports citation tracking, impact metrics (such as the Journal Impact Factor), and research analytics through tools like InCites and Web of Science Analytics, serving as a benchmark in global scholarly indexing.