Perhaps you should try some spelling variations:
"dan cua cong san" » "dan cua cong tac" (Expand Search), "ban cua cong san" (Expand Search), "dan cu cong san" (Expand Search), "dan luan cong san" (Expand Search)
"van cua cong so" » "ban cua cong so" (Expand Search), "han cua cong so" (Expand Search), "nhan cua cong so" (Expand Search), "van cua cong son" (Expand Search), "van cua cong o" (Expand Search), "van cua cong hoa" (Expand Search)
"dan ca cong so" » "dan ca cong son" (Expand Search), "dan ca cong o" (Expand Search), "dan ca cong hoa" (Expand Search), "dan cac cong so" (Expand Search), "dan cap cong so" (Expand Search), "dan cau cong so" (Expand Search)

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: (("van cua cong so") OR ((("dan cua cong san") OR ("dan ca cong so"))))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"van cua cong so\") OR (((\"dan cua cong san\") OR (\"dan ca cong so\"))))".
• Removing quotes may allow a broader search: (( van cua cong so ) OR ((( dan cua cong san ) OR ( dan ca cong so )))).
• Adding a wildcard symbol may retrieve word variants: (("van cua cong so") OR ((("dan cua cong san") OR ("dan ca cong so"))))*.