全文获取类型
收费全文 | 17772篇 |
免费 | 156篇 |
国内免费 | 375篇 |
专业分类
电工技术 | 157篇 |
综合类 | 81篇 |
化学工业 | 1474篇 |
金属工艺 | 328篇 |
机械仪表 | 748篇 |
建筑科学 | 718篇 |
矿业工程 | 374篇 |
能源动力 | 61篇 |
轻工业 | 3376篇 |
水利工程 | 205篇 |
石油天然气 | 215篇 |
武器工业 | 33篇 |
无线电 | 4470篇 |
一般工业技术 | 4963篇 |
冶金工业 | 227篇 |
原子能技术 | 147篇 |
自动化技术 | 726篇 |
出版年
2015年 | 65篇 |
2014年 | 162篇 |
2013年 | 107篇 |
2012年 | 1688篇 |
2011年 | 1962篇 |
2010年 | 367篇 |
2009年 | 369篇 |
2008年 | 1449篇 |
2007年 | 1288篇 |
2006年 | 1116篇 |
2005年 | 970篇 |
2004年 | 771篇 |
2003年 | 648篇 |
2002年 | 546篇 |
2001年 | 451篇 |
2000年 | 447篇 |
1999年 | 273篇 |
1998年 | 167篇 |
1997年 | 139篇 |
1996年 | 149篇 |
1995年 | 116篇 |
1994年 | 101篇 |
1993年 | 89篇 |
1992年 | 119篇 |
1991年 | 110篇 |
1990年 | 91篇 |
1989年 | 120篇 |
1988年 | 124篇 |
1987年 | 136篇 |
1986年 | 127篇 |
1985年 | 151篇 |
1984年 | 118篇 |
1983年 | 134篇 |
1982年 | 116篇 |
1981年 | 98篇 |
1980年 | 106篇 |
1979年 | 97篇 |
1978年 | 79篇 |
1977年 | 234篇 |
1976年 | 229篇 |
1975年 | 269篇 |
1974年 | 270篇 |
1973年 | 173篇 |
1972年 | 264篇 |
1971年 | 267篇 |
1970年 | 256篇 |
1968年 | 191篇 |
1967年 | 345篇 |
1965年 | 266篇 |
1964年 | 117篇 |
排序方式: 共有10000条查询结果,搜索用时 643 毫秒
61.
Very high interest in making a low-loss fiber for the infrared has been stimulated by important applications in optical communication, surgery, cutting, welding, and heat treatment. The leaky waveguide is one of the most promising types of future fiber in the infrared region where low-loss materials are not available or not suitable for making fibers (i.e., CO2 laser light lambda = 10.6 microm). In this paper a comparative model of a He-Ne laser beam and an oxide glass leaky hollow fiber for a CO2 laser light beam and a chalcogenide glass leaky hollow fiber are studied. Measurements of attenuation, dependence of output power on diameter and angle, and the angular dependence of output angle vs input angle were made. The experimental data were compared with theoretical calculations, and the critical value of the wall thickness for minimum attenuation is given. 相似文献
62.
63.
64.
65.
66.
Matsuda N 《Behaviormetrika》1986,13(19):41-53
"Multidimensional scaling technique was applied to the Brazilian migration matrix in order to identify the functional regions of the nation, using the 1970 census data for males. The results obtained from three types of proximity matrices confirmed the key roles of Minas Gerais and Mato Grosso as the core states in addition to Rio de Janeiro and Sao Paulo. Substantial circulation of migrants among the core states runs counter to the popular notion about the Northeastern states as the major source of labor in Rio de Janeiro and Sao Paulo. The Northeast [was] found to consist of three groups of states: Maranhao, Piaui and Ceara showed a stable clustering, but peripherally located, in all configurations; and, the other two groups failed to form persistent regions across configurations. Though limited in scope, the observed attraction of Espirito Santo and Goias violated the widely held negative effect of distance and deserves further investigation." 相似文献
67.
An intensive computer keyboard training course, based on an information processing model of man, was tested on a variety of personnel in work. Over a one or two week period, 241 adult subjects were trained. Subjects achieved mean speeds of 7.1 words per minute (WPM) after the second and 13.7 WPM after the ninth lesson. Significant decreases in errors per minute (EPM) occurred from 2.67 to 1.78. Previous experience with a keyboard and being female were factors associated with enhanced keyboard operating performance. Compressing the ten lessons from two into one week reduced the effectiveness of the programme. 相似文献
68.
"In this paper we trace and interpret changes in the geographical pattern and city-size distribution of the world's largest cities in the twentieth century. Since 1900 the geographical distribution of these cities has become increasingly dispersed; their city-size distribution by rank was nearly linear in 1900 and 1940, and convex in 1980. We interpret the convex distribution which emerged following World War 2 as reflecting an economically integrated but politically and demographically partitioned global urban system. Our interpretation of changes in size distribution of cities emphasizes demographic considerations, largely neglected in previous investigations, including migration and relative rates of population change." 相似文献
69.
70.
高温钎料PdCu-Ti在氧化铝陶瓷上的润湿性及界面反应 总被引:7,自引:0,他引:7
本文采用座滴法试验研究了合金系统PdCu-Ti在Al2O3上润湿性的变化规律,探讨了界面冶金及结合等行为,运用热力学理论对结果进行了分析,随Ti含量的增加及Pd含量的减少润湿角逐渐降低,Ti的加入使界面发生了一个双重变化;液相侧富氧,钛吸收层的生成及随后的固相侧氧化钛的生成,只有界面上生成一氧化钛,才能有较好的润湿行为和较强的结合力。 相似文献