To search for the string and output just that line with the search string:
for i in $(find /path/of/target/directory -type f); do grep -i "the string to look for" "$i"; done
e.g.:
for i in $(find /usr/share/applications -type f); \
do grep -i "web browser" "$i"; done
To display filename containing the search string:
for i in $(find /path/of/target/directory -type f); do if grep -i "the string to look for" "$i" > /dev/null; then echo "$i"; fi; done;
e.g.:
for i in $(find /usr/share/applications -type f); \
do if grep -i "web browser" "$i" > /dev/null; then echo "$i"; \
fi; done;