Search providers worth to integrate?

Just a unsorted list of search providers, may one or the other is worth to have a look or implement an engine.

• https://www.persee.fr/
• https://base-search.net/
• https://science.gov/
• https://www.bioline.org.br/
• https://link.springer.com/
• https://marginalia-search.com/ --> https://github.com/searxng/searxng/issues/3034
• https://www.refseek.com/
• https://gallica.bnf.fr/
• https://search.creativecommons.org/
• https://arxiv.org/
• https://archive.org/
• label:"engine request"

Feel free to add your suggestions and comments ...