"Extensive research" refers to a thorough and in-depth investigation that involves gathering a significant amount of information and analyzing it to gain a comprehensive understanding of a particular topic or subject. Full definition
A dissertation is an academic document which is based on extensive research on a topic and is written by a student for a university degree or diploma. (instantassignmenthelp.com)
He or she should be familiar with the topic of the thesis and must be capable of doing extensive research on that subject. (professionalthesiswriters.com)
It has conducted extensive research into the barriers to adoption and implementation of technology in schools, with a specific focus on mobile technology and 1:1 provision. (educationbusinessuk.net)