Ok, so this is the whole code:

#!"E:\xamp\perl\bin\perl.exe" -T

use 5.010;
use CGI;

use strict;
use warnings;

use LWP::UserAgent;
use LWP::Simple;


use HTML::TreeBuilder;


    my $q = CGI->new();
    my $userag = LWP::UserAgent->new(timeout=>30); #it's illegal :(   
+           p.s. to make what they say, delete argument from "new"    
+"agent => 'MyApp/0.1'"
        say $q->header(), $q->start_html();
        my $addressdio = "";

            #getting the address from form
            for my $param ($q->param()) {
                    my $safe_param = $q->escapeHTML($param);

                    say "<p><strong>$safe_param</strong>: ";

                    for my $value ($q->param($param)) {
                    
                            say $q->escapeHTML($value);
                       $addressdio = $q->escapeHTML($value);
                }

                    say '</p>';
            }

        
        #the whole process of getting xml from site and giving it into
+ the string variable
        #my $dioaddress = "http://dx.doi.org/10.1016/j.nuclphysa.2015.
+05.005"; 
        my $reqforxml = new HTTP::Request GET => $addressdio;
        my $res = $userag->request($reqforxml);
        my $content = $res->content;
    #    my $content = get("$addressdio");    

            


    #    my $html = get("http://dx.doi.org/10.1007/s00601-015-1012-x")
    #      or die "Couldn't fetch the Perl Cookbook's page.";
    #    print "$html";

        #opening the file to write string with xml
        open my $overwrite, '>', 'overwrite.xml' or die "error trying 
+to overwrite: $!";
        #writing string with xml to the file
        say $overwrite "$content";

        

        #A little system just to get the title
        #($title) = $content =~ <h1 class="svTitle" id="ti0010">(.*?)<
+/h1>;
        #print "Title of article: $title";

        #my $tree = HTML::TreeBuilder->new;
        #$tree ->parse_file("overwrite.txt");
        
        #foreach my $h1 ($tree->find('h1')){
        #print $h1->as_text, "<br />";
        #}
        
        close $overwrite;








        say "<h1>And here's the site:</h1>";
        print "$content"; #string with our site



say $q->end_html();
[download]

I got the XML from ScienceDirect thanks to this: agent => 'MyApp/0.1', but even when I give this paramater to agent while connecting to Link Springer, then the situation is the same like I explained in the first post.