include a php variable in php string

So you want to construct the string by using .

stripos($_SERVER['REQUEST_URI'],'/'.$thisproduct['alias'].'/')

or double quotes evaluate variables

stripos($_SERVER['REQUEST_URI'],"/{$thisproduct['alias']}/")

Since you're using Single Quotes, your variable is being treated as a string instead of the value the variable actually contains.

Make sense?

$array = array('foo' => 'bar);

echo $array;            //array()
echo $array['foo'];     //bar
echo '$array[\'foo\']'; //array['foo']
echo "{$array['foo']}"; //bar

etc

Best handled by this if you aren't specifically looking for /alias/ and instead just looking for alias

// were $thisproduct['alias'] is now treated as a variable, not a string
if (FALSE !== stripos($_SERVER['REQUEST_URI'], $thisproduct['alias'])) 
{
    echo 'This page content';
}

Otherwise

if (FALSE !== stripos($_SERVER['REQUEST_URI'], "/{$thisproduct['alias']}/")) 
{
    echo 'This page content';
}

If you want /alias/

try the below :

"this is a text and this is a $variable " ; // using double quotes or 
"this is a test and this is a {$variable} "; // or 
"this is a test and this is a ". $variable ; 

So for your case you can do this :

<?php if (stripos($_SERVER['REQUEST_URI'], "/{$thisproduct['alias']}/") !== false) {echo 'This page content';} ?>

The below is from : http://php.net/manual/en/language.types.string.php

<?php
// Show all errors
error_reporting(E_ALL);

$great = 'fantastic';

// Won't work, outputs: This is { fantastic}
echo "This is { $great}";

// Works, outputs: This is fantastic
echo "This is {$great}";
echo "This is ${great}";

// Works
echo "This square is {$square->width}00 centimeters broad."; 


// Works, quoted keys only work using the curly brace syntax
echo "This works: {$arr['key']}";


// Works
echo "This works: {$arr[4][3]}";

// This is wrong for the same reason as $foo[bar] is wrong  outside a string.
// In other words, it will still work, but only because PHP first looks for a
// constant named foo; an error of level E_NOTICE (undefined constant) will be
// thrown.
echo "This is wrong: {$arr[foo][3]}"; 

// Works. When using multi-dimensional arrays, always use braces around arrays
// when inside of strings
echo "This works: {$arr['foo'][3]}";

// Works.
echo "This works: " . $arr['foo'][3];

echo "This works too: {$obj->values[3]->name}";

echo "This is the value of the var named $name: {${$name}}";

echo "This is the value of the var named by the return value of getName(): {${getName()}}";

echo "This is the value of the var named by the return value of \$object->getName(): {${$object->getName()}}";

// Won't work, outputs: This is the return value of getName(): {getName()}
echo "This is the return value of getName(): {getName()}";
?>