For example (just as rough proof of concept)
Research articles: Pretty much any academic library website for published stuff, arxiv.org for white papers in computer science and math, pubmed for biosciences
audio equipment: gearspace.com
Encyclopedia: Wikipedia
Thesaurus: Wordhippo.com
The idea is to avoid needing to visit a search engine. Might be a high idea.
For German-speakers, one such directory is lila.schike.de.
Für Leute, die Deutsch sprechen, gibt es u.a. das Verzeichnis lila.schike.de.