Perhaps you should try some spelling variations:
thuoc sach » hoc sach, nuoc sach, thuat sach
tinh ven » trinh ven, tinh yen, sinh vien
hieu van » hieu va, thien van, lieu va
truc va » thuc va, thuc vat, trung va
tinh ve » trinh ve, dinh ve, tinh va
van cau » van dau, van hau, van chat
ty hang » ly hang, thi hang, thu hang
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: thuoc sach ((ty hang) or (ty xang)) ma hoa. hieu van cau truc va ((tinh ve) OR (tinh ven)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuoc sach ((ty hang) OR (ty xang)) ma hoa. hieu van cau truc va ((tinh ve) OR (tinh ven)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuoc sach ((ty hang) or (ty xang)) ma hoa. hieu van cau truc va ((tinh ve) OR (tinh ven)) cua tre".
• Adding a wildcard symbol may retrieve word variants: thuoc sach ((ty hang) or (ty xang)) ma hoa. hieu van cau truc va ((tinh ve) OR (tinh ven)) cua tre*.