\documentclass{standalone}
\usepackage{tikz,pgfplots}
\usepackage{pgfplotstable}
\usepgfplotslibrary{dateplot}
\begin{document}
\begin{tikzpicture}
\begin{semilogyaxis}[
axis background/.style = {shade,top color=gray,bottom color=white},
width = \textwidth,
height = 9cm,
enlargelimits=false,
ymin=1E-6, ymax=1E-4,
ylabel = {y-Achse},
date coordinates in = x,
date ZERO = 2014-01-01 00,
xmax = 2014-12-31 23:59,
xtick = {2014-01-01, 2014-02-01, 2014-03-01, 2014-04-01, 2014-05-01, 2014-06-01, 2014-07-01, 2014-08-01, 2014-09-01, 2014-10-01, 2014-11-01, 2014-12-01},
xticklabel={\pgfcalendar{tickcal}{\tick}{\tick}{\pgfcalendarshorthand{m}{.}}},
xticklabel style = {anchor=north},
xticklabel style = {xshift=15pt}
]
% Data
\addplot+[const plot, color=blue, fill, blue, mark=] coordinates {
(2014-01-01 00:00, 2.06E-06)
(2014-01-01 00:00, 3.56E-06)
(2014-01-09 11:53, 6.76E-06)
(2014-01-09 13:21, 3.56E-06)
(2014-01-13 09:26, 3.56E-06)
(2014-01-13 09:55, 2.06E-06)
(2014-02-14 09:05, 2.90E-06)
(2014-02-14 09:56, 2.06E-06)
(2014-03-05 07:32, 3.85E-06)
(2014-03-05 11:04, 2.06E-06)
(2014-03-06 15:22, 3.85E-06)
(2014-03-06 16:52, 2.06E-06)
(2014-03-07 08:06, 2.10E-06)
(2014-03-07 11:34, 2.06E-06)
(2014-03-09 01:50, 3.71E-06)