全文获取类型
收费全文 | 362220篇 |
免费 | 27613篇 |
国内免费 | 13951篇 |
专业分类
电工技术 | 19991篇 |
技术理论 | 59篇 |
综合类 | 22000篇 |
化学工业 | 61029篇 |
金属工艺 | 20147篇 |
机械仪表 | 23234篇 |
建筑科学 | 28021篇 |
矿业工程 | 11815篇 |
能源动力 | 10640篇 |
轻工业 | 20752篇 |
水利工程 | 5903篇 |
石油天然气 | 24749篇 |
武器工业 | 2930篇 |
无线电 | 40284篇 |
一般工业技术 | 42911篇 |
冶金工业 | 19352篇 |
原子能技术 | 3557篇 |
自动化技术 | 46410篇 |
出版年
2024年 | 1182篇 |
2023年 | 5456篇 |
2022年 | 9269篇 |
2021年 | 13853篇 |
2020年 | 10678篇 |
2019年 | 8622篇 |
2018年 | 9977篇 |
2017年 | 11257篇 |
2016年 | 10018篇 |
2015年 | 13438篇 |
2014年 | 17529篇 |
2013年 | 21034篇 |
2012年 | 22417篇 |
2011年 | 24930篇 |
2010年 | 21470篇 |
2009年 | 20182篇 |
2008年 | 19993篇 |
2007年 | 19191篇 |
2006年 | 20002篇 |
2005年 | 17618篇 |
2004年 | 11336篇 |
2003年 | 9948篇 |
2002年 | 8935篇 |
2001年 | 8182篇 |
2000年 | 8720篇 |
1999年 | 10433篇 |
1998年 | 8756篇 |
1997年 | 7214篇 |
1996年 | 6800篇 |
1995年 | 5713篇 |
1994年 | 4674篇 |
1993年 | 3290篇 |
1992年 | 2677篇 |
1991年 | 2096篇 |
1990年 | 1594篇 |
1989年 | 1304篇 |
1988年 | 1069篇 |
1987年 | 680篇 |
1986年 | 548篇 |
1985年 | 354篇 |
1984年 | 251篇 |
1983年 | 215篇 |
1982年 | 213篇 |
1981年 | 143篇 |
1980年 | 143篇 |
1979年 | 79篇 |
1978年 | 43篇 |
1977年 | 48篇 |
1976年 | 61篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
11.
12.
13.
针对颗粒滚动摩擦作用对筒仓中玉米颗粒的力链空间分布进行研究,通过EDEM离散元软件建立筒仓模型与仿真玉米颗粒模型进行卸粮仿真模拟,并与筒仓卸料实验作流态对比,验证模型与仿真结果的准确性。通过对模拟仓进行切片观察和数据处理,对比分析了不同摩擦情况下力链的细观参数随时间演化规律。模拟结果表明:颗粒间摩擦系数越大,卸粮完成的最终时间越长;颗粒间滚动摩擦系数越小,颗粒由整体流转变为管状流的时间越早。对于有漏斗的筒仓来说,减小颗粒间摩擦会改变整体流和管状流之间的极限,从而增加产生管状流的面积。标准滚动摩擦系数下玉米颗粒在卸料过程中会出现起拱-塌陷效应;减小滚动摩擦,玉米颗粒卸料较稳定,未出现起拱的应力突增、以及拱塌陷的应力衰减;增大颗粒间滚动摩擦不但会增加拱效应,且出现成拱高度距离漏斗口更高。 相似文献
14.
Zhang Nan Zhao Man Liu Guangfa Wang Jiaoyang Chen Yunzhi Zhang Zhengjian 《Journal of Materials Science》2022,57(19):8687-8700
Journal of Materials Science - A green modification method for effectively enhancing toughness of PLA was established. Herein, alkaline lignin (LG) was firstly alkylated with dodecane, and then... 相似文献
15.
Wang Chen Bao Chun-Hui Wu Wan-Yu Hsu Chia-Hsun Zhao Ming-Jie Zhang Xiao-Ying Lien Shui-Yang Zhu Wen-Zhang 《Journal of Materials Science》2022,57(26):12341-12355
Journal of Materials Science - Molybdenum oxide (MoOx) films had been grown by using plasma-enhanced atomic layer deposition (PEALD) with Mo(CO)6 precursor and O2 plasma reactant in a substrate... 相似文献
17.
Jinfeng Zeng Zhiting Liu Hanbo Zou Wei Yang Haosen Fan Haijun Yu Shengzhou Chen 《金属学报(英文版)》2021,34(8):1153-1162
A appropriate size with three-dimension(3 D) channels for lithium diffusion plays an important role in constructing highperforming LiNi_(0.5)Mn_(1.5)O_4(LNMO) cathode materials, as it can not only reduce the transport path of lithium ions and electrons, but also reduce the side effects and withstand the structural strain in the process of repetitive Li~+ intercalation/deintercalation. In this work, an e fficient method for designing the hollow LNMO microsphere with 3 D channels structure by using polyethylene oxide(PEO) as soft template agent assisted solvothermal method is proposed. Experimental results indicate that PEO can make the reagents mingle evenly and nucleate slowly in the solvothermal process, thus obtaining a homogeneous distribution of carbonate precursors. In the final LNMO products, the hollow 3 D channels structure obtained by the decomposition of PEO and carbonate precursor in the calcination can provide abundant electroactive zones and electron/ion transport paths during the charge/discharge process, which benefits to improve the cycling performance and rate capability. The LNMO prepared by adding 1 g PEO possesses the most outstanding electrochemical performance, which presented an excellent discharge capacity of 143.1 mAh g~(-1) at 0.1 C and with a capacity retention of 92.2% after 100 cycles at 1 C. The superior performance attributed to the 3 D channels structure of hollow microspheres, which provide uninterrupted conductive systems and therefore achieve the stable transfer for electron/ion. 相似文献
18.
Hui Liu Yaohui Fu Jinhai Yuan Lei Yu Zhefei Wang Quan Liu Bo Wei Xuhong Wang 《Ceramics International》2021,47(12):16570-16578
To provide a basis for the high-temperature oxidation of ultra-high temperature ceramics (UHTCs), the oxidation behavior of Zr3[Al(Si)]4C6 and a novel Zr3[Al(Si)]4C6-ZrB2-SiC composite at 1500 °C were investigated for the first time. From the calculation results, the oxidation kinetics of the two specimens follow the oxidation dynamic parabolic law. Zr3[Al(Si)]4C6 exhibited a thinner oxide scale and lower oxidation rate than those of the composite under the same conditions. The oxide scale of Zr3[Al(Si)]4C6 exhibited a two-layer structure, while that of the composite exhibited a three-layer structure. Owing to the volatilization of B2O3 and the active oxidation of SiC, a porous oxide layer formed in the oxide scale of the composite, resulting in the degradation of its oxidation performance. Furthermore, the cracks and defects in the oxide scale of the composite indicate that the reliability of the oxide scale was poor. The results support the service temperature of the obtained ceramics. 相似文献
19.
Yarn-dyed fabric is often woven from warp and weft yarns in the same color depth to ensure a uniform color appearance. The difference in color depth between warp and weft tends to result in the uneven color of the yarn-dyed fabric. This article aims to establish a color tolerance for yarn-dyed fabric that can be woven with a qualified color appearance but from the warp and weft yarns in different color depths. A total of 27 yarn-dyed fabric samples in three color series (red, yellow, and blue) were evaluated by using the yarn-dyed fabric from warp and weft yarns in the same color depth of 2% (on weight of fabric, owf) as the standard. Visual assessment and instrumental measurement of color were carried out to establish the color tolerance ellipse that was defined as CMC (Color Measurement Committee) color differences (2:1) of no more than 1.00. It was found that the color strengths (K/S) and color differences (ΔECMC(2:1)) of these fabric samples for each color series had linear relationships with the color depths of warp and weft yarns. The color tolerance ellipses indicated that, even though the warp and weft yarns had an apparent color difference, they could be woven in fabrics with relatively uniform color appearance and meet the requirements for yarn-dyed fabric. This work provided valuable insight into the production of qualified yarn-dyed fabrics from unqualified dyed yarns. 相似文献
20.