Different types of scientific literature exist, normally referred to as the …, secondary, tertiary and grey literature. 

The ablest undergraduates are actively involved into … work.

Those … who entered the Institute get an opportunity to major in almost all branches of mathematics as they are obligatory subjects in this specialization.

The secondary literature… publications that rely on primary sources for information.

It is important to note that the form that a publication takes no guide to its classification as primary, secondary or … literature.