Elicit is purpose-built for exactly this kind of academic research task, letting you upload or search papers, extract key findings, and generate structured summaries across a set of sources all in one workflow. It understands research methodology language and can organize papers by theme, intervention, or outcome, which maps directly onto what a thesis literature review requires. NotebookLM is a strong free alternative if you want to upload your own PDFs and ask questions across them in a conversational way. Perplexity works well when you need to discover new papers and get cited, web-grounded summaries before you have a fixed reading list. Claude Sonnet is worth considering if you want a capable general-purpose model to help draft synthesis paragraphs or restructure notes once your sources are already gathered.