<?php
//I want the 'delimX' to be included as well:
$str = "It seems entirely 1 (b natural b) to us that there are teams of scientists in universities and other institutions around the world, attempting to 2 (b discover b) the way the world works. However, it hasn't always been that 3 (b way b) . Although the scientific method is now four or five hundred years old, the ancient Greeks, for example, believed that they could work out the 4 (b causes b) of natural events just by the power of thought.";
$result = preg_split ('~([0-9 ]\(b.*?b\))~',$str ,-1, PREG_SPLIT_DELIM_CAPTURE);
var_dump($result);
array(9) {
[0]=>
string(19) "It seems entirely 1"
[1]=>
string(14) " (b natural b)"
[2]=>
string(114) " to us that there are teams of scientists in universities and other institutions around the world, attempting to 2"
[3]=>
string(15) " (b discover b)"
[4]=>
string(63) " the way the world works. However, it hasn't always been that 3"
[5]=>
string(10) " (b way b)"
[6]=>
string(145) " . Although the scientific method is now four or five hundred years old, the ancient Greeks, for example, believed that they could work out the 4"
[7]=>
string(13) " (b causes b)"
[8]=>
string(48) " of natural events just by the power of thought."
}