Many students may find useful this definition of primary sources: "Primary sources are those with a direct link, in time and place, to the person, event, situation, or culture under study."
For example, a newspaper article on the outbreak of World War II in 1939 would be a primary source; a newspaper article reflecting on the outbreak of that war in 2014 would be considered a secondary source. A primary source, such Abraham Lincoln's "Emancipation Proclamation," issued January 1, 1863, is a primary source, but it is also a primary source when republished in 1963.
Primary:
Secondary:
As you search for research articles, you may want to consider two different approaches. Sometimes, you may already have a subject that you are interested in researching -- in this case it may be easiest to start with a search engine and keywords tied to the subject you want to research. Other times, you may not already have a subject in mind and may be in need of inspiration -- if this is the case, it might be worthwhile to pick a journal or two and start perusing the table of contents. Find something interesting but the article itself doesn't meet the presentation criteria? Look at the keywords associated with the article, and try plugging those into a search engine!