Perhaps you should try some spelling variations:
greatest challenge » greatest challenges, great challenge, treatment challenges
challenge funding » challenge finding, challenges finding, challenge facing
funding among » bonding among, building among, jumping among
2.1 greatest » 2.1 pretest, 2.1 treatment, _ greatest
among di » among hiv, among idp, among _
nan yan » nan ya, wang yan, qian yan
yang xi » yang di, yang yi, yang jui
era 2.1 » era 3.1
ng era » 5g era, qing era, deng era

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: ((nan yan) OR (yang xi))ng era 2.1 greatest challenge funding among di ;~.
• Adding a wildcard symbol may retrieve word variants: ((nan yan) or (yang xi))ng era 2.1 greatest challenge funding among di ;*.