EDITORIAL NOTE 2015101201 - There are 2 pages of Description which are not page numbered A laboratory test-tube rack Technical field This utility model involves a laboratory test-tube rack. Background technology Currently, test-tube rack used in the process of experiment and teaching by most scientific research institutes and colleges and universities is fixed test-tube rack. Generally, test tubes of multiple specifications such as 5ml, 10ml, 20ml and 25ml can be placed. As pore diameter is relatively fixed, such test-tube rack cannot hold test tubes of different specifications simultaneously, thus causing inconvenient operation and use in the process of experiment. In addition, test tubes placed on the existing test-tube rack have a great gap. The space of test-tube rack cannot be utilized completely rationally. Great waste of use space is caused. Invention content (I) Technical problem to be solved To solve the problem above, this utility model puts forward a laboratory test-tube rack which has a simple structure, reasonable design, low production cost and greatly increased use space. (II) Technical proposal A laboratory test-tube rack of this utility model includes base, four support rods in four directions on the top of the base, frame body on four support rods and big and small plastic circles within the frame body. A groove is set up on the top of the base, which is opposite to the frame body. There are four rows of big plastic circles and three rows of small plastic circles. Small plastic circles are placed within the gap of each two rows of big plastic circles and big and small plastic circles are connected closely. Further, the base is columned and the frame body is hexagonal prisms. Further, the diameter of big plastic circles is greater than that of small plastic circles. There are 20 and more big plastic circles and 17 and more small plastic circles. Further, the undersurface of the groove is hexagonal. (III) Beneficial effect Compared to the existing technology, this utility model has the following beneficial effect: in this utility model, small plastic circles are placed within the gap of two rows of big plastic circles so that big and small plastic circles are connected closely, space is utilized better and the quantity of test tubes placed on this test-tube rack increases. It has a simple structure, reasonable design, low production cost and greatly increased use space. Descriptions of the attached figure Fig.1 is the front view of laboratory test-tube rack in this utility model; Fig.2 is the top view of laboratory test-tube rack in this utility model; 1-base; 2-frame body; 3-support rod; 4-big plastic circle; 5-small plastic circle; 6-groove. Detailed implementation way As shown in fig.1 and fig.2, a laboratory test-tube rack in this utility model includes base 1, four support rods 3 in four directions on the top of the base 1, frame body 2 on four support rods 3 and big 4 and small plastic circles 5 within the frame body 2. A groove 6 is set up on the top of the base 1, which is opposite to the frame body 2. There are four rows of big plastic circles 4 and three rows of small plastic circles 5. Small plastic circles 5 are placed within the gap of each two rows of big plastic circles 4 and big 4 and small plastic circles 5 are connected closely. The base 1 is columned and the frame body 2 is hexagonal prisms. The diameter of big plastic circles 4 is greater than that of small plastic circles 5. There are 20 and more big plastic circles 4 and 17 and more small plastic circles 5. In this implementation example, there are 20 big plastic circles 4 and 17 small plastic circles. The whole frame body 2 of hexagonal prisms can be filled. Test tubes of different specifications can be placed within big plastic circles 4 and small plastic circles 5. The undersurface of the groove 6 is hexagonal. The bottom of test tubes placed within big plastic circles 4 and small plastic circles 5 is placed within the groove 6. Compared to the existing technology, this utility model has the following beneficial effect: in this utility model, small plastic circles are placed within the gap of two rows of big plastic circles so that big and small plastic circles are connected closely, space is utilized better and the quantity of test tubes placed on this test-tube rack increases. It has a simple structure, reasonable design, low production cost and greatly increased use space. The implementation example mentioned above is only descriptions about the optimized implementation way of this utility model rather than limitations on its design and scope. Under the premise of not deviating from the design idea of this utility model, various modifications and improvements of the technical proposal of this utility model made by ordinary persons in this field shall fall into the protection scope of this utility model. Technical contents of this utility model required for protection have been recorded in the claim.