Application for drawing professional scientific diagrams

hello,
do you know of a good program(s) to drawing professional scientific diagrams (chemistry, physics, biology,…), … Specially diagram as available in notes, … is there any plug-in for microsoft word for doing this. cuz its really difficult doing it in words
or do you a good method that could be used to draw them.
Answer #1
-Smartdraw
-ConceptDraw
-Microsoft Visio
Answer #2
thanks. tried checking them on youtube and google but have not yet downloaded.
are there good for scientific diagrams, … . when i checked, they were used for flowcharts and drawing networks. and can they be easily used with microsoft word??
thanks
Answer #3
any one???