function bloqueaCaja(evt){ 
    if(window.event){
        keynum = evt.keyCode;
    }else{
        keynum = evt.which;
    }
    if(keynum>47 && keynum<58){
        return false;
    }else{
        return false;
    }
}

function soloNumeros(evt){
    if(window.event){
        keynum = evt.keyCode;
    }else{
        keynum = evt.which;
    }
    if((keynum>47 && keynum<58) || keynum==46 || keynum==8){
        return true;
    }else{
        return false;
    }
}