Fetch academic papers from Sci-Hub given a DOI. Automatically downloads PDFs and saves them to research/papers/ with clean filenames. Use when the user provides a DOI or requests a paper from PubMed.

根据DOI从Sci-Hub获取学术论文，自动下载PDF并保存至research/papers/目录下，文件名简洁清晰。当用户提供DOI或请求从PubMed获取论文时使用。