Perhaps you should try some spelling variations:
thi nghiem » thuc nghiem
ha nghiem » khao nghiem, thu nghiem, van nghiem
tu sach » thu sach, su sach, te sach
sach da » sach dao, sach dat, sach dau
da nghe » day nghe, va nghe, dang nghe
de hoc » te hoc, du hoc, dien hoc
su hoc » tu hoc, du hoc, so hoc
d hoc » du hoc, ad hoc, y 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 da nghe ((d hoc) or (de hoc)) ) or ( thu hoach ((ha nghiem) OR (thi nghiem)) su hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu sach da nghe ((d hoc) OR (de hoc)) ) OR ( thu hoach ((ha nghiem) OR (thi nghiem)) su hoc )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( tu sach da nghe ((d hoc) or (de hoc)) ) or ( thu hoach ((ha nghiem) OR (thi nghiem)) su hoc ))".
• Adding a wildcard symbol may retrieve word variants: (( tu sach da nghe ((d hoc) or (de hoc)) ) or ( thu hoach ((ha nghiem) OR (thi nghiem)) su hoc ))*.