If you are citing something from a web page, it is always a good idea to make a copy of it. Maybe save it as a PDF for your files. The lifespan of a web page is surprising short. It can be changed or even deleted, leaving little evidence behind.
A better idea might be to save the web page at the date and time of access into the Wayback Machine. The page, and outlinks, can be captured and added to Internet Archive, providing a link to how it appeared at the time. There is the added benefit of being able to compare the page at a later date to see any changes.
Internet Archive is one of the largest digital libraries in the world. They began with the Wayback Machine but it is now just one of the ways that they are preserving our digital history and making knowledge accessible to everyone.
When it comes to evaluating scientific papers, citation counts are mentioned more often than not. A paper can be cited for a variety of reasons but it is generally agreed that citations are one of many indicators of impact. There are a number of resources that are either free or subscribed to by the Library for looking up citing references, such as Google Scholar, Scopus, and Web of Science.
The authors of The Wisdom of Citing Scientists discuss the limitations of citing references for assessing the usefulness of papers. For example, one cannot assume that a paper with few citations has been widely read and critiqued. It is possible that the paper was not found by others or that it did have some influence on future writings. They argue that cited references in a paper tell a more complete story, revealing a scientist’s preference for particular journals and theoretical approaches, and his/her ability to identify relevant, current, and high quality publications. As librarians we are always stressing the importance of examining the reference list of a paper so it was quite nice to see this articulated.