Perhaps you should try some spelling variations:
greatest challenges » greatest challenge, treatment challenges, related challenges
challenges finding » challenges facing, challenges during, challenges arising
finding among » funding among, bonding among, singing among
1.1 greatest » 100 greatest, _ greatest, its greatest
deng era » qing era, deal era, peng er
among di » among hiv, among idp, among _
nan yan » nan ya, wang yan, qian yan
ng era » 5g era, qing era
yang » lang, wang

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 di))((ng era) OR (deng era)) 1.1 greatest challenges finding among di ;~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((nan yan) or (yang di))((ng era) OR (deng era)) 1.1 greatest challenges finding among di ;~".
• Adding a wildcard symbol may retrieve word variants: ((nan yan) or (yang di))((ng era) OR (deng era)) 1.1 greatest challenges finding among di ;*.