It wouldn't take much to significantly improve things. We don't even have full-text search for paywalled articles. The paid search engines like Web of Science

It wouldn't take much to significantly improve things. We don't even have full-text search for paywalled articles. The paid search engines like Web of Science just do title, keywords, and abstract. Even considering the subset of open access articles, Google Scholar and Semantic Scholar do ok but don't offer much in the way of search refinement (e.g., "DTAF" NEAR "collagen"). They're good at finding _something_ related to your query but not good for systematic review.