全文获取类型
收费全文 | 102879篇 |
免费 | 1345篇 |
国内免费 | 1230篇 |
专业分类
电工技术 | 1924篇 |
综合类 | 138篇 |
化学工业 | 10489篇 |
金属工艺 | 5456篇 |
机械仪表 | 3186篇 |
建筑科学 | 2033篇 |
矿业工程 | 159篇 |
能源动力 | 2959篇 |
轻工业 | 6059篇 |
水利工程 | 704篇 |
石油天然气 | 668篇 |
武器工业 | 15篇 |
无线电 | 15941篇 |
一般工业技术 | 21755篇 |
冶金工业 | 25245篇 |
原子能技术 | 1382篇 |
自动化技术 | 7341篇 |
出版年
2022年 | 452篇 |
2021年 | 698篇 |
2020年 | 522篇 |
2019年 | 676篇 |
2018年 | 1129篇 |
2017年 | 1093篇 |
2016年 | 1173篇 |
2015年 | 924篇 |
2014年 | 1489篇 |
2013年 | 4667篇 |
2012年 | 2569篇 |
2011年 | 3840篇 |
2010年 | 3097篇 |
2009年 | 3718篇 |
2008年 | 3893篇 |
2007年 | 4079篇 |
2006年 | 3689篇 |
2005年 | 3325篇 |
2004年 | 3177篇 |
2003年 | 3024篇 |
2002年 | 2670篇 |
2001年 | 2970篇 |
2000年 | 2718篇 |
1999年 | 3075篇 |
1998年 | 9437篇 |
1997年 | 6153篇 |
1996年 | 4761篇 |
1995年 | 3162篇 |
1994年 | 2787篇 |
1993年 | 2723篇 |
1992年 | 1628篇 |
1991年 | 1593篇 |
1990年 | 1518篇 |
1989年 | 1322篇 |
1988年 | 1171篇 |
1987年 | 861篇 |
1986年 | 887篇 |
1985年 | 916篇 |
1984年 | 803篇 |
1983年 | 698篇 |
1982年 | 699篇 |
1981年 | 681篇 |
1980年 | 567篇 |
1979年 | 476篇 |
1978年 | 414篇 |
1977年 | 533篇 |
1976年 | 958篇 |
1975年 | 299篇 |
1974年 | 276篇 |
1973年 | 256篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
M. Takahashi H. Sofue T. Iguchi M. Matsumoto F. Huang Y. Pramono T. Matsuzawa S. Uchida 《Progress in Nuclear Energy》2005,47(1-4):553-560
For the development of 45w%Pb-55w%Bi cooled direct contact boiling water small fast reactor (PBWFR), experimental study on Pb-Bi-water direct contact boiling two-phase flow has been performed using Pb-Bi-water direct contact boiling two-phase flow loop. For stable start-up of the boiling flow operation, Pb-Bi single-phase natural circulation must be realized in a Pb-Bi flow system of the loop before water injection into Pb-Bi. The Pb-Bi flow system consists of a four-heater-pin bundle, a chimney, an upper plenum, a level meter tank, a cooler, and an electromagnetic flow meter. A stable Pb-Bi single-phase natural circulation was realized in the range of flow rate from 1.5 l/min to 4.8 l/min by heating Pb-Bi in the heater-pin bundle with a power up to 7.7 kW. The inlet and outlet temperatures of the heater bundle were in the ranges from 243°C to 278°C, and from 251°C to 278°C, respectively. The natural circulation flow was simulated analytically using one-dimensional flow model including frictional, form and drag forces. Total hydraulic head through the loop were calculated from Pb-Bi densities at measured Pb-Bi temperatures in the loop. It was found that the calculated flow rate agreed well with the measured ones, which indicated the validity of the analytical models. 相似文献
942.
A refined beam theory based on the refined plate theory 总被引:5,自引:0,他引:5
Summary Based on the refined plate theory, a refined theory of rectangular beams is derived by using the Papkovich-Neuber solution and Lur’e method without ad hoc assumptions. It is shown that the displacements and stresses of the beam can be represented by the angle of rotation and the deflection of the neutral surface. The solutions based on the new theory are the same as the exact solutions of elasticity theory. In three examples it is shown that the new theory provides as good or better results than Levinson’s beam theory when compared to those obtained from the linear theory of elasticity. 相似文献
943.
Atomic force microscope analysis, with a resolution of /spl lsim/1.1 nm, shows that peak-to-peak surface roughness (/spl Delta/h/sub p-p/) of amorphous silicon films thinner than /spl ap/50 nm on silicon dioxide can be controlled to better than 5 nm. Low-pressure, chemically-vapor-deposited silicon films on silicon dioxide initially show an approximately linear increase in the surface roughness due to growing nuclei as the deposition progresses, followed by a decrease in the surface roughness as growth nuclei coalesce. A simple model based on random nucleation and nuclei growth displays similar trends. Films deposited on rougher substrates show more surface roughness. Surface treatment during the predeposition cleaning process does not significantly affect /spl Delta/h/sub p-p/. As a means of producing smooth surfaces, films thinner than about 20 nm are first deposited more thickly than needed, and then etched back to the desired dimension; the use of a binary HNO/sub 3/ and HF etching process improves roughness control. Boron-ion implanted and subsequently crystallized 45-nm-thick Si films show significant smoothing with /spl Delta/h/sub p-p//spl ap/2.2 nm. Thin amorphous silicon films deposited by source evaporation are attractive because they can be deposited at room temperature, and have smoother surfaces (/spl Delta/h/sub p-p//spl ap/2.5 nm) than comparable films produced by chemical vapor deposition. 相似文献
944.
945.
946.
947.
948.
949.
950.