I wish to get article text by passing article ID?

Simple, supplying you delivering articles id with publish/get and taking advantage of variable "id" since it's number:

$articleId = JRequest::getInt('id');
$db =& JFactory::getDBO();

$sql = "SELECT fulltext FROM #__content WHERE id = ".intval($articleId);
$db->setQuery($sql);
$fullArticle = $db->loadResult();

if(!strlen(trim($fullArticle))) $fullArticle = "Article is empty ";

EDIT: to obtain articleId everywhere:

$articleId = (JRequest::getVar('option')==='com_content' && JRequest::getVar('view')==='article')? JRequest::getInt('id') : 0;