I think there are two ways of citing sources in an article: links distributed in the article body, or links listed at the end of the article.
Example with links in the article:
This is some text that will have links here and there, wherever they are relevant. This style is commonly used in blogs and news sites. It seems very common. I guess it's not bad for SEO at all, or nobody would be using it. However links in the body might sometimes be distracting, making visitors feel curious, click, land on a different site, and get sidetracked.
Example with links at the end:
This is some text that will only list the sources (1) at the end, at the bottom of the article. This style is commonly used in more formal documents (2), like research papers, books, etc. The links (3) won't be evenly distributed inside the article (4), there will just be a list of links at the end, one after the other, and I wonder if Google (5) likes that.
I don't think there are any other common and sensible styles to cite sources. Wikipedia seems to use both at the same time: links in the body for internal content, and a list of links at the bottom for external sources.
What I'm asking is: how does that affect SEO? Are there pros and cons for each style? How many links are going to be too many? I might have to write articles that will require citing a lot of sources. The more sources I have, the longer the article text will be, so I don't think I'd have problems with link density or link/text ratio. The problem is that I'm not sure Google might like lots of links listed one after the other at the end. A possible solution to play it safe might be to just list the URLs without actually linking them with an anchor tag, although I'm not sure how good this idea is (will Google not like that anyway? Will users find it annoying they can't click directly on a source?)