Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
van pham » san pham, van phan, van phat
ky tang » ky nang, ky dang, kho tang
tang xa » trang xa, tang ma, lang xa
va tinh » may tinh
tinh di » tinh doi, trinh di, tinh da
cuu tre » cau tren, cau treo
cua tre » cua te, cua triet, dua tren

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu cac) or (thu sach)) ky tang xa hoi. hieu van pham duc va tinh di ((cuu tre) OR (cua tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu cac) OR (thu sach)) ky tang xa hoi. hieu van pham duc va tinh di ((cuu tre) OR (cua tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu cac) or (thu sach)) ky tang xa hoi. hieu van pham duc va tinh di ((cuu tre) OR (cua tre))".
• Adding a wildcard symbol may retrieve word variants: ((tu cac) or (thu sach)) ky tang xa hoi. hieu van pham duc va tinh di ((cuu tre) OR (cua tre))*.