Perhaps you should try some spelling variations:
nghien su » nghiem su, nghien cuu, nghiep sua
dao nghe » day nghe, dat nghe, nao nghe
hoach va » hoach xay, hanh va, doanh va
tu sach » thu sach, su sach, te sach
da nghe » day nghe, va nghe, dang nghe
su hoc » tu hoc, du hoc, so hoc
d hoc » du hoc, ad hoc, de hoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( tu sach ((dao nghe) OR (da nghe)) d hoc ) or ( thu hoach va nghien su hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu sach ((dao nghe) OR (da nghe)) d hoc ) OR ( thu hoach va nghien su hoc )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( tu sach ((dao nghe) OR (da nghe)) d hoc ) or ( thu hoach va nghien su hoc ))".
• Adding a wildcard symbol may retrieve word variants: (( tu sach ((dao nghe) OR (da nghe)) d hoc ) or ( thu hoach va nghien su hoc ))*.