As people use multiple devices like desktop/laptop/tablet, the need for access to our files has led to popularization of cloud storage sharing tools like Dropbox and also cloud applications like Google apps. However for research purposes Zotero is a special free add-on to Firefox and other browsers, that helps to maintain your own card catalogue , have it portable through cloud and also lets you stories copies of the important articles for offline use.
I became aware of this tool recently through Shyamal, an avid wikipedia contributor who trained a batch of young wikipedians, on how they can take its help to improve Wikipedia citations. I started using it and It has become an essential tool for me. Do give it a try, if you have not tried this category of applications that can simplify you research/study work.