string <- '<a href="/Archiv-Suche/!344002&s=&SuchRahmen=Print/" ratiourl-ressource="344002"'
pattern = "!(\\d+)&"
res <- unlist(regmatches(string,regexec(pattern,string)))
res[2]
c3RyaW5nIDwtICc8YSBocmVmPSIvQXJjaGl2LVN1Y2hlLyEzNDQwMDImYW1wO3M9JmFtcDtTdWNoUmFobWVuPVByaW50LyIgcmF0aW91cmwtcmVzc291cmNlPSIzNDQwMDIiJwpwYXR0ZXJuID0gIiEoXFxkKykmYW1wOyIKcmVzIDwtIHVubGlzdChyZWdtYXRjaGVzKHN0cmluZyxyZWdleGVjKHBhdHRlcm4sc3RyaW5nKSkpCnJlc1syXQ==