Perhaps you should try some spelling variations:
hac thuc » hoc thuc, ha thuc, thach thuc
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
cua tre » cua te, cua triet, dua tren
vat dan » va dan, van dan, vat ran
van hac » van hoc, van ha, van hai
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
cuu tre » cau tren, cau treo
dan vi » doan vi, don vi, dan va

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach y ((nang xa) or (nang ma)) hoi. hieu van hac thuc vat dan vi ((cua tre) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y ((nang xa) OR (nang ma)) hoi. hieu van hac thuc vat dan vi ((cua tre) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: su sach y ((nang xa) or (nang ma)) hoi. hieu van hac thuc vat dan vi ((cua tre) or (cuu tre))*.