全文获取类型
收费全文 | 100365篇 |
免费 | 8352篇 |
国内免费 | 3929篇 |
专业分类
电工技术 | 7777篇 |
技术理论 | 8篇 |
综合类 | 8651篇 |
化学工业 | 16248篇 |
金属工艺 | 1992篇 |
机械仪表 | 3061篇 |
建筑科学 | 13578篇 |
矿业工程 | 5137篇 |
能源动力 | 9765篇 |
轻工业 | 5331篇 |
水利工程 | 19647篇 |
石油天然气 | 8074篇 |
武器工业 | 263篇 |
无线电 | 1386篇 |
一般工业技术 | 4495篇 |
冶金工业 | 3536篇 |
原子能技术 | 1179篇 |
自动化技术 | 2518篇 |
出版年
2024年 | 346篇 |
2023年 | 1166篇 |
2022年 | 2226篇 |
2021年 | 2712篇 |
2020年 | 2970篇 |
2019年 | 2443篇 |
2018年 | 2364篇 |
2017年 | 2869篇 |
2016年 | 3312篇 |
2015年 | 3320篇 |
2014年 | 6350篇 |
2013年 | 5985篇 |
2012年 | 7579篇 |
2011年 | 7638篇 |
2010年 | 5573篇 |
2009年 | 5793篇 |
2008年 | 5122篇 |
2007年 | 6765篇 |
2006年 | 6343篇 |
2005年 | 5638篇 |
2004年 | 4485篇 |
2003年 | 4083篇 |
2002年 | 3514篇 |
2001年 | 2894篇 |
2000年 | 2429篇 |
1999年 | 1868篇 |
1998年 | 1319篇 |
1997年 | 1101篇 |
1996年 | 857篇 |
1995年 | 781篇 |
1994年 | 564篇 |
1993年 | 443篇 |
1992年 | 347篇 |
1991年 | 277篇 |
1990年 | 216篇 |
1989年 | 223篇 |
1988年 | 136篇 |
1987年 | 145篇 |
1986年 | 100篇 |
1985年 | 96篇 |
1984年 | 90篇 |
1983年 | 53篇 |
1982年 | 28篇 |
1981年 | 13篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
一级开发大柳树高坝原始库容比二级开发小观音高坝多 4 0亿m3 ,库容大带来的好处体现在 5~ 7月可多向下游增供水量 ,缓解下游河道断流 ;延长泄放清水时间 ;增加发电效益 ;满足宁蒙河段防凌要求 ;增加汛期集中泄水 ,减缓下游河道淤积萎缩 ;满足南水北调西线工程水量调节要求等。为了更好优化配置黄河水资源 ,从全局和长远利益考虑 ,应采用一级开发方案 ,修建大柳树高坝大库 相似文献
22.
23.
舰船水声隐身技术(二) 总被引:2,自引:0,他引:2
本文探讨了水声隐身性能对舰船战技术性能的影响 ,舰船水噪声的主要噪声源、水噪声的治理措施及其展望。 相似文献
24.
Shuichi Yamamoto Teruaki Morihiro Koichi Ariyoshi Turkan Aktas 《Drying Technology》2005,23(6):1319-1330
As the surface properties of the drying materials are very important not only for the drying rate but also for the quality change during drying, the effects of surface concentration on the drying behavior of liquid foods (sugar solutions) were investigated by isothermal drying experiments and by numerical calculation experiments. The isothermal drying experiments with gelled sugar solution systems (sucrose and maltodextrin) were carried out at various relative humidity (RH) values (RH = 0 to 84%). Separate experiments were carried out for determination of the desorption isotherms.
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
25.
以水资源可持续发展为出发点,探讨了一种可以同时兼顾经济发展、水资源利用和社会效益的多目标水资源宏观经济模型的建立方法,通过引入带权2-模评价函数,将多目标优化问题转变成单目标优化问题。以2002年为现状水平年,对安徽省2010年的产业结构及产业规模进行优化分析。结果表明,多目标模型求得的总用水量较单目标模型明显降低,而两模型优化的产业规模与结构差别不大,体现了高用水效率行业优先发展的要求。 相似文献
26.
卜寺沟水电站预可阶段正常蓄水位是考虑规划成果、地形、地质务件、梯级衔接、水库淹没、筑坝技术、水能资源利用等因素综合初选的.从理论角度分析,水库淹没时水库内寺庙的影响,按全部淹没进行经济补偿处理代价较小;其社会环境敏感因素对正常蓄水位的选择不应起决定性作用.但是,考虑到少数民族群众、僧侣和地方政府的要求,适当降低正常蓄水位,以减少对扎西日岗寺庙的影响,将带来较积极的社会影响. 相似文献
27.
结合兰州市的水泥标准稠度用水量方法测定 (代用法 )的实例 ,分析代用法测定标准稠度用水量的缺点 ,并对此方法提出了一些改进措施 相似文献
28.
29.
This research investigates the utility of passive microwave remote sensing instruments to accurately determine snow water equivalent (SWE) over large spatial extents. Three existing Special Sensor Microwave Imager (SSM/I) snow water equivalent algorithms produced by Chang, Tait and Goodison were evaluated for their ability to determine snow water equivalent in a snowpack containing substantial depth hoar, large faceted snow crystals. The Kuparuk River Watershed (8140 km2) test site on the North Slope of Alaska was chosen for its snowpack containing a think depth hoar layer and long history of ground truth data. A new regional snow water equivalent algorithm was developed to determine if it could produce better results than the existing algorithms in an area known to contain significant depth hoar. The four algorithms were tested to see how well they could determine snow water equivalent: (1) on a per pixel basis, (2) across swath-averaged spatial bands of approximately 850 km2, and (3) on a watershed scale. The algorithms were evaluated to see if they captured the annual spatial distribution in snow water equivalent over the watershed. Results show that the algorithms developed by Chang and from this research are generally within 3 cm of the spatially averaged snow water equivalents over the entire watershed. The algorithms produced by Chang, Tait, and in this research were able to predict the basin-wide ground measured snow water equivalent value within a percent error range from −32.4% to 24.4% in the years with a typical snowpack. None of the algorithms produce accurate results on a pixel-by-pixel scale, with errors ranging from −26% to 308%. 相似文献
30.
金沙江防洪(库容)规划的探讨 总被引:1,自引:0,他引:1
在分析长江灾害洪水特征的基础上,全面深入地研究了全沙江水库的防洪库客、防洪目标、防洪特点和调度原则,并对防洪库容的作用进行了估算和分析。从多方面比较了虎跳峡高坝方案与低坝方案,结果表明:高坝方案的效益明显高于低坝方案,而两者所需付出的代价相差不大。 相似文献