Perhaps you should try some spelling variations:
sach thu » sach thue, sach tham, cach thuc
tinh vai » tinh va, tinh hai, tinh bai
cua viet » ca viet, hoa viet, cua vat
va tinh » may tinh
vai cua » dai cua, hai cua, lai cua
ve hoc » te hoc, va hoc, de hoc
vi hoc » li hoc, va hoc
x hoi » xa hoi, o hoi, x ho
nuoc » quoc, duoc, ngoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: te ((sach thu) or (sach thieu)) nang x hoi. hieu ((ve hoc) OR (vi hoc)) nuoc va tinh vai cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach thu) OR (sach thieu)) nang x hoi. hieu ((ve hoc) OR (vi hoc)) nuoc va tinh vai cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach thu) or (sach thieu)) nang x hoi. hieu ((ve hoc) OR (vi hoc)) nuoc va tinh vai cua viet".
• Adding a wildcard symbol may retrieve word variants: te ((sach thu) or (sach thieu)) nang x hoi. hieu ((ve hoc) OR (vi hoc)) nuoc va tinh vai cua viet*.