Can I cite a URL only instead of author, title, etc. in a research paper?
No, it's not OK to cite URLs because firstly, you are citing ONLY the URL! The URL could change at any given time without notice. Also, you are assuming that everyone is reading your paper electronically and has access to the internet.

You NEED to give the name of the paper, the author(s), the Journal it was published in and the year it was published.