Perhaps you should try some spelling variations:
"su sach ki thuat co khi" » "su sach ki thuat o khi", "so sach ki thuat co khi", "vu sach ki thuat co khi", "su sach kinh thuat co khi", "su sach bai thuat co khi", "su sach kem thuat co khi", "su cach ki thuat co khi", "su xach ki thuat co khi"
"su sac ky thuat do thi" » "su sac ky thuat o thi", "su cac ky thuat do thi", "su xac ky thuat do thi"
"su sai ky thuat do thi" » "su sai ky thuat o thi", "su tai ky thuat do thi", "su hai ky thuat do thi", "su dai ky thuat do thi"

Try widening your search to All Fields.

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 ki thuat co khi") or ((("su sac ky thuat do thi") OR ("su sai ky thuat do thi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("su sach ki thuat co khi") OR ((("su sac ky thuat do thi") OR ("su sai ky thuat do thi")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"su sach ki thuat co khi\") or (((\"su sac ky thuat do thi\") OR (\"su sai ky thuat do thi\"))))".
• Removing quotes may allow a broader search: (( su sach ki thuat co khi ) or ((( su sac ky thuat do thi ) OR ( su sai ky thuat do thi )))).
• Adding a wildcard symbol may retrieve word variants: (("su sach ki thuat co khi") or ((("su sac ky thuat do thi") OR ("su sai ky thuat do thi"))))*.