全文获取类型
收费全文 | 20284篇 |
免费 | 548篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 256篇 |
综合类 | 11篇 |
化学工业 | 4235篇 |
金属工艺 | 351篇 |
机械仪表 | 358篇 |
建筑科学 | 1179篇 |
矿业工程 | 114篇 |
能源动力 | 568篇 |
轻工业 | 1575篇 |
水利工程 | 169篇 |
石油天然气 | 195篇 |
武器工业 | 1篇 |
无线电 | 1267篇 |
一般工业技术 | 3335篇 |
冶金工业 | 4265篇 |
原子能技术 | 198篇 |
自动化技术 | 2779篇 |
出版年
2022年 | 167篇 |
2021年 | 260篇 |
2020年 | 194篇 |
2019年 | 249篇 |
2018年 | 307篇 |
2017年 | 310篇 |
2016年 | 366篇 |
2015年 | 273篇 |
2014年 | 451篇 |
2013年 | 1232篇 |
2012年 | 790篇 |
2011年 | 1029篇 |
2010年 | 787篇 |
2009年 | 785篇 |
2008年 | 994篇 |
2007年 | 978篇 |
2006年 | 797篇 |
2005年 | 797篇 |
2004年 | 627篇 |
2003年 | 630篇 |
2002年 | 587篇 |
2001年 | 370篇 |
2000年 | 340篇 |
1999年 | 334篇 |
1998年 | 351篇 |
1997年 | 338篇 |
1996年 | 329篇 |
1995年 | 363篇 |
1994年 | 292篇 |
1993年 | 333篇 |
1992年 | 288篇 |
1991年 | 183篇 |
1990年 | 258篇 |
1989年 | 301篇 |
1988年 | 221篇 |
1987年 | 228篇 |
1986年 | 226篇 |
1985年 | 278篇 |
1984年 | 274篇 |
1983年 | 242篇 |
1982年 | 232篇 |
1981年 | 231篇 |
1980年 | 183篇 |
1979年 | 203篇 |
1978年 | 190篇 |
1977年 | 183篇 |
1976年 | 163篇 |
1975年 | 188篇 |
1974年 | 173篇 |
1973年 | 140篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Catalysis, the turntable for a clean future 总被引:1,自引:0,他引:1
Upgrading the bottom of the barrel for clean fuel production, developing new engines with optimized catalytic posttreatments, implementing clean catalytic combustion technologies, improving the overall CO2 balance via catalytic processes and, lastly, developing new water purification techniques represent major upheavals in catalysis linked to refining and environmental protection. This paper, thus, will focus on the determining contribution of catalysis to the most recent achievements in these domains. A technico-economic approach will follow, underlining their main incentives and drawbacks within the framework of future environmental constraints. 相似文献
112.
The United States has historically excelled in the design of products, processes and new technologies. Capitalizing on this historical strength to teach applied mathematics and science has many positive implications on education. First, engineering design can be used as a vehicle for addressing deficiencies in mathematics and science education. Second, as achievement in mathematics and science is enhanced, a greater number of students at an earlier age will be exposed to technical career opportunities. Third, enhancing elementary and secondary curricula with engineering design can attract underrepresented populations, such as minorities and females, to engineering as a profession. This paper describes a new and innovative engineering design curriculum, under development in the Austin Independent School District (AISD) in Austin, TX. The philosophic goals upon which the curriculum is based include: integrating the design problem-solving process into elementary schools, demonstrating the relationship of technical concepts to daily life, availing teachers with instructional strategies for teaching applied (as opposed to purely theoretical) science and mathematics, and teaching teamwork skills that are so greatly needed in industry and everyday life. Based on these goals, kindergarten, first grade, and second grade engineering design lessons have been piloted in AISD, in conjunction with a University of Texas program for teacher enhancement and preparation. 相似文献
113.
114.
115.
116.
Richard L. Lehman 《Journal of the American Ceramic Society》1992,75(8):2194-2199
Sodium-calcium-lead silicate glass compositions were prepared over a wide compositional range by conventional glass-melting methods. The acid chemical stability of the glass structure was studied by corroding samples of glass in 4% acetic acid solution at 22°C for periods up to 24 h. Lead corrosion stability was evaluated by measuring lead concentrations in the corrosion solution. At short times, parabolic time dependence was observed and the parabolic time coefficients were regressed against composition, yielding a simple additive relationship. A similar model was fitted to 24-h release data, which showed compositional effects similar to the 2-h data. Of the oxides studied, sodium was the most detrimental to durability, and the coefficients of the oxides decreased in the series: Na2 O, PbO, CaO, SiO2 . The effects of the oxides could be partially explained by the number of nonbridging oxygens expected in the glass structure, and the residual effect was attributed to cation characteristics. Small phosphate additions to the glass greatly increased the lead-ion stability under nearly all experimental conditions examined. 相似文献
117.
Combined-Stage Sintering Model 总被引:8,自引:0,他引:8
James D. Hansen Richard P. Rusin Mao-Hua Teng D. Lynn Johnson 《Journal of the American Ceramic Society》1992,75(5):1129-1135
By focusing on the similarities between the three stages of sintering, a single equation is derived that quantifies sintering as a continuous process from beginning to end. The microstructure is characterized by two separate parameters representing geometry and scale. The dimensionless geometry parameter, denoted T, comprises five scaling factors that relate specific microstructural featuers (e.g., surface curvature) to the scale (grain diameter). Calculations of T from experimental data show (a) agreement with computer simulations of initial-stage sintering, (b) the effect of surface diffusion on T, and (c) changes in T with microstructural evolution during sintering. Application of the model to the design of firing schedules and the study of microstructural geometry effects on sintering is discussed. 相似文献
118.
119.
Avants S. Kelly; Margolin Arthur; Kosten Thomas R.; Rounsaville Bruce J.; Schottenfeld Richard S. 《Canadian Metallurgical Quarterly》1998,66(6):924
In response to a need to match drug users to the most appropriate and cost-effective level of care, it was hypothesized that socially anxious methadone-maintained patients would attain greater benefit from coping skills training provided in the context of a low-intensity enhanced standard methadone maintenance intervention (E-STD) than in the context of a high-intensity, socially demanding day treatment program (DTP). Social anxiety was assessed in 307 methadone-maintained patients using the Social Anxiety and Distress Scale prior to randomization to either E-STD or DTP. The hypothesis was supported: Socially anxious patients were drug free longer during treatment, were more likely to be abstinent at treatment completion, and had greater reductions in HIV risk behaviors if assigned to the lower intensity intervention, which was provided at ? the cost of the DTP. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
120.