Academic Search Premier is an excellent next step after you've search in HOLLIS, as it's a smaller universe than HOLLIS but still multidisciplinary with a range of article types.
Google Scholar searches full-text which can be an advantage for a very narrow topic, and is also helpful for seeing who cited an article after it was published. Follow these instructions to connect Google Scholar with Harvard Library.
Art
Art Full-Text covers art historical topics as well as museum design and construction, programming, exhibition spaces, visitor experiences, cultural heritage, and curation of collections.
ARTbibliographies Modern extends from artists and movements beginning with Impressionism in the late 19th century, up to the most recent works and trends in the late 20th century, including modern and contemporary art, performance and video art, computer and electronic art, body art, graffiti, artists' books, theater arts, crafts, jewelry, illustration, as well as the traditional fine arts.
The International Bibliography of Art provides the most comprehensive coverage of scholarship in the disciplines of art history and architectural history. Also included are citations to art-related book content, conference proceedings, dissertations, and exhibition catalogs.
Business/Management/Marketing
ProQuest One Business is an extensive full-text database combining scholarly journals, newspapers, dissertations, books, company/industry/country reports, and other sources relevant to research in business and management. If you're interested in museum marketing, planning, funding, or administration, this is a resource to explore.
IBISWorld provides comprehensive industry reports (including a March 2021 report on US Museums) that detail key demographic and business trends and outlooks.
Communication and Education
Communication Abstracts provides comprehensive access to communication-related publications on a world-wide scale.
ERIC[Educational Resources Information Center] is useful for topics that touch on museum education, exhibit creation, and instructional practice.
History
America: History and Life is an essential database for topics related to the U.S. and Canada. Local history is well-represented, as is scholarship on history museums more generally.
AnthroSource contains full-text of journals and newsletters published by the American Anthropological Association. Look here for discussions of cultural heritage, material culture, museums of anthropology, science, and natural history.
Social Science Premium Collection is a core resource in sociology, social planning and policy, and many related disciplines. Look here for studies of museum culture, the social experience of museums, the political dimensions of museums and collections, etc.
Natural History
History of Science, Technology, and Medicine is a good choice for topics that might involve natural history museums and science/technology-focused museum topics, particularly in their historical contexts.
Web of Science broadly searches across the sciences, social sciences, and humanities.
