The best way to keep track of source materials is to save a copy of each potential source as you conduct your research. Many database services will allow you to e-mail, save, or print citations or full texts of articles, and you can easily download, copy, or take screen shots of information from the Web.
Working with photocopies, printouts, and electronic files—as opposed to relying on memory or hastily written notes—has several benefits. You can highlight key passages, perhaps even color-coding them to reflect topics in your outline. You can get a head start on note taking. Finally, you reduce the chances of unintentional plagiarism since you will be able to compare your use of a source in your paper with the actual source, not just with your notes. (See also the chart "Information to collect for a working bibliography" in 51a.)