Perhaps you should try some spelling variations:
danh kien » dinh kien, danh viet, linh kien
danh dien » dinh dien, danh lien, nganh dien
cau tren » cu tren, dau tren, ca tren
hac thuc » hoc thuc, ha thuc, thach thuc
hieu van » hieu va, thien van, lieu va
thuc va » thuc vat, thuc dan, thuc day
so sach » so sanh, bo sach, co sach
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
van hac » van hoc, van ha, van hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach y ((nang xa) or (nang ma)) hoi. hieu van hac thuc va ((danh dien) OR (danh kien)) cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y ((nang xa) OR (nang ma)) hoi. hieu van hac thuc va ((danh dien) OR (danh kien)) cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y ((nang xa) or (nang ma)) hoi. hieu van hac thuc va ((danh dien) OR (danh kien)) cau tren".
• Adding a wildcard symbol may retrieve word variants: so sach y ((nang xa) or (nang ma)) hoi. hieu van hac thuc va ((danh dien) OR (danh kien)) cau tren*.