What is this line supposed to do:
$url =~ s/&/=/g ;
Are you sure that you want to replace all & in your URL with =? If I remove that line, and much other unnecessary cruft, I see the complete HTML and especially also the relevant META tags:
use strict;
use LWP::Simple;
#Parsing the http file for the required fields
my $url = 'http://content.karger.com/ProdukteDB/produkte.asp?Aktion=Sh
+owAbstract&ArtikelNr=6735&Ausgabe=224691&ProduktNr=223832';
#$url =~ s/&/=/g ;
#my @url_mod = split('=', $url);
#checking for url and increasing article no.
warn "Downloading $url";
my $html = get $url;
print $html;