Here we provide a list of most common AI (artificial intelligence) tools that may be useful in supplementary literature searches of which some are limited in the free version and others are completely free : 

Semantic Scholar is a free AI-powered research tool for scientific literature.

Undermind AI allows to access papers based mainly on Semantic Scholar (www.semanticscholar.org) 

Scite is an AI-powered platform that allows to search papers. It shows whether studies support or contradict a claim. Data come from several sources including partnership with publishers.  

Consensus is an AI-powered academic search engine. It allows access to papers using Semantic Scholar (www.sematicscholar.org) and potentially other sources. 

PubMed AI provided a free AI-powered search in the contents of PubMed.