Many of the fundamental skills of a scientist are seldom taught. Instead, one is expected to pick them up through intuition, informal conversations, or trial-and-error. One of these essential skills is how to search the literature for journal articles related to a particular topic.

This is a challenging task with severe consequences for failure. Just ask any Ph.D. student who discovered that his thesis was focused on a problem that had already been solved. Or anybody who left grad school because of the overwhelming task of grasping and keeping up with the scientific literature related to his thesis topic.

Why

The purpose of a literature search is not merely to become aware of what results are already known. Rather, a good literature search provides a map of the scientific terrain, indicating the general layout of a research area:

• What are the main goals of research in this area?
• What kind of advances are considered significant, and why?
• What are the recognized open questions, and what impact would their answers have?
• What other research areas are most closely connected to this one?
• Are there other research areas with connections to this one that have not been recognized?
• How is this research area viewed by those who focus on related, competing topics?

How

With these goals in mind, how does one conduct an effective literature search? Here are some techniques that have served me well:

• Ask for help. You have a network of collaborators (or at least an advisor!) who each know some part of the literature much better than you. If you're starting research in a new topic where they have expertise, ask them for the most significant work on that topic. Ask their opinion of new papers that seem significant to you. Ask them for the right keywords, authors, and review articles to start with. Because they can make connections that a search engine never would, they are your most valuable resource.
• Use Google Scholar. Yes, there are countless databases and search tools out there for looking at a articles from a particular discipline or publisher. But I have yet to find one as effective as Scholar. I'm convinced that its coverage is much broader than any of the commercial academic databases available. For instance, few other databases cover the ArXiv, which is an essential source in some fields.
• Link forward through the literature. Every paper has a list of references to the works that it cites. But since you're mostly interested in learning about the state-of-the-art, it's usually more helpful to obtain a list of papers that cite the one you have. This is another major advantage of Google Scholar, which allows you to do so easily. Each search result includes a link to a list of all the articles that cite it.
• Learn how to do effective keyword searches. This skill has become incredibly valuable in the internet age, and nowhere more so than in searching for journal articles. When learning about a new topic, it can be hard to know which keywords to search for, and you should ask for help (see above). Once you know the right words, it can be very important whether search for A and B, A or B, A since year X, B authored by Y, and so forth. Learn how to refine your searches in this way.
• Learn to rapidly evaluate article titles and abstracts. You can't hope to read all the articles, or even all the abstracts published in your field. Your ability to find the most relevant ones is directly proportional to how quickly you can eliminate the irrelevant. I'm convinced that this skill can only be obtained by experience, but you can accelerate it by noticing articles that you thought would be useful but turned out not to be, as well as becoming aware of who the key authors are in an area.
• Check for articles in review journals. Most fields have some journals that publish only review articles. Such articles provide a broad overview of a topic along with a detailed bibliography; they are invaluable when starting research on a new topic. In my field, the most relevant are Acta Numerica and SIAM Review. Review articles tend to rank high in search engines because they are heavily cited, but it can be worth searching for them specifically or even browsing review journals that publish a low volume (like the two just mentioned).
• Check the websites of key authors. You can often find their preprints there long before the published article becomes available. Of course, you don't have time to do this on a large scale, so you have to be selective.

I'm planning a future post that will discuss what to do with all the relevant and significant articles you find.