Change how references are displayed in reference list ( 1. reference, instead of [1] reference )

Change how references are displayed in reference list ( 1. reference, instead of [1] reference )

Right now my references in the reference list look like:
[1] Alpha
[2] Bravo
[3] Charlie
I want to change them to be displayed like this:
1. Alpha
2. Bravo
3. Charlie
but so that labels in text remain [1], [2], [3]. My document starts with:
\documentclass[12pt,a4paper]{article}
\usepackage{graphicx}
\usepackage{polyglossia}
\usepackage{xltxtra}
\usepackage{xunicode}
\usepackage{units}
\usepackage{amsmath}
\usepackage{pstricks}
\usepackage{float}
\usepackage{wrapfig}
\usepackage[top=2.5cm, left=3cm, bottom=2.5cm, right=2.5cm]{geometry}
\usepackage{setspace}
\usepackage{pgfplots}
\pgfplotsset{compat=1.8}
\usepgfplotslibrary{polar}
\usepgflibrary{shapes.geometric}
\usetikzlibrary{calc}
\onehalfspacing
\setmainfont{Times New Roman}
\setdefaultlanguage{latvian}
\setotherlanguages{english, russian}
\numberwithin{equation}{subsection}
\numberwithin{figure}{subsection}
\numberwithin{table}{subsection}
\pgfplotsset{pa/.append style={axis x line=bottom, axis y line=left, xlabel={$r; \cdot 10^7 m$}, ylabel={$F_{pa}; \cdot 10^8 N$}}}
\begin{document}
And my bibliography looks like:
\begin{thebibliography}{99}
\bibitem[1]{alpha} Alpha
\bibitem[2]{bravo} Bravp
\bibitem[3]{charlie} Charlie
\bibitem[4]{delta} Delta
\end{thebibliography}
I use MiKTeX 2.9 x64, TeXnicCenter (last version). My document is compiled through XeLaTeX -> PDF.