The phrase "scientific leaders" refers to individuals who are highly respected and knowledgeable in their field of science. They are experts who guide and influence others in scientific research and advancements. Full definition
The highly capable students of today are likely to become the intellectual, cultural, technological, financial, social, and scientific leaders of tomorrow. (aagc.ssri.duke.edu)
And by the way, both religious and scientific leaders thought the earth was flat. (religion.blogs.cnn.com)
How does a lab deal with the loss of an intellectually vibrant scientific leader and move on? (sciencemag.org)