Perhaps you should try some spelling variations:
"so sai ky thuat dong khi" » "so sai ky thuat song khi", "so sai ky thuat cong khi", "so sai ky thuat tong khi", "so sai ky thuat duong khi", "so sai ky thuat dong thi", "so sai ky thuat ong khi", "so sai kmy thuat dong khi", "so sai kkxy thuat dong khi", "so sai kki thuat dong khi", "so dai ky thuat dong khi", "so hai ky thuat dong khi", "do sai ky thuat dong khi", "so sac ky thuat dong khi"
"bo sach ky thuat oc khi" » "bo sach ky thuat doc khi", "bo sach ky thuat o khi", "bo sach ky thuat quoc khi", "co sach ky thuat oc khi", "hoc sach ky thuat oc khi", "bo sac ky thuat oc khi", "bo sach ty thuat oc khi", "bo sach kem thuat oc khi", "bo sach kmy thuat oc khi", "bo sach kkxy thuat oc khi", "bo sach kki thuat oc khi", "bo sach ky thuat hoc khi", "bo sach ky thuat hoc khoi", "bo sach ky thuat hoc khia"
"te sach y thuat do thi" » "te sach y thuat o thi", "toc sach y thuat do thi", "te sach my thuat do thi", "te sach kxy thuat do thi", "te sach ki thuat do thi"

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

• Performing a fuzzy search may retrieve terms with similar spellings: (((("bo sach ky thuat oc khi") or ("so sai ky thuat dong khi"))) or ("te sach y thuat do thi"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("bo sach ky thuat oc khi") OR ("so sai ky thuat dong khi"))) OR ("te sach y thuat do thi")).
• Removing quotes may allow a broader search: (((( bo sach ky thuat oc khi ) or ( so sai ky thuat dong khi ))) or ( te sach y thuat do thi )).
• Adding a wildcard symbol may retrieve word variants: (((("bo sach ky thuat oc khi") or ("so sai ky thuat dong khi"))) or ("te sach y thuat do thi"))*.