How do I get a citation dataset with full text articles in PDF format? I am doing research in text mining. For that I need a dataset which contain full text PDFs of research paper articles, and all articles should be related with each other in terms of citing. There are citation network datasets available which contain only metadata of papers, but with this I also want those full text articles in PDF format.

What should I do to get such dataset?
An alternative to arXiv mentioned in another response could be PubMed Central, specially if you are interested on text mining of papers in biomedical and life sciences research.