全文获取类型
收费全文 | 91943篇 |
免费 | 11455篇 |
国内免费 | 7735篇 |
专业分类
电工技术 | 8500篇 |
综合类 | 10193篇 |
化学工业 | 11223篇 |
金属工艺 | 6687篇 |
机械仪表 | 6605篇 |
建筑科学 | 7060篇 |
矿业工程 | 4403篇 |
能源动力 | 2365篇 |
轻工业 | 9977篇 |
水利工程 | 2996篇 |
石油天然气 | 3487篇 |
武器工业 | 1596篇 |
无线电 | 9199篇 |
一般工业技术 | 7762篇 |
冶金工业 | 3730篇 |
原子能技术 | 1643篇 |
自动化技术 | 13707篇 |
出版年
2024年 | 264篇 |
2023年 | 1619篇 |
2022年 | 3857篇 |
2021年 | 4902篇 |
2020年 | 3532篇 |
2019年 | 2559篇 |
2018年 | 2584篇 |
2017年 | 2937篇 |
2016年 | 2552篇 |
2015年 | 4330篇 |
2014年 | 5221篇 |
2013年 | 6192篇 |
2012年 | 7912篇 |
2011年 | 8124篇 |
2010年 | 7680篇 |
2009年 | 7245篇 |
2008年 | 7393篇 |
2007年 | 7151篇 |
2006年 | 6104篇 |
2005年 | 4845篇 |
2004年 | 3613篇 |
2003年 | 2461篇 |
2002年 | 2375篇 |
2001年 | 2123篇 |
2000年 | 1651篇 |
1999年 | 646篇 |
1998年 | 212篇 |
1997年 | 185篇 |
1996年 | 146篇 |
1995年 | 106篇 |
1994年 | 81篇 |
1993年 | 83篇 |
1992年 | 76篇 |
1991年 | 58篇 |
1990年 | 43篇 |
1989年 | 34篇 |
1988年 | 42篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 24篇 |
1979年 | 14篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1959年 | 16篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Tao TIAN Chao-lan ZHANG Feng ZHU Shan-xin YUAN Ying GUO Sheng-guo XUE 《中国有色金属学会会刊》2021,31(5):1484-1495
A column experiment was conducted to investigate the effect of phosphogypsum (PG) on the saline- alkalinity, and aggregate stability of bauxite residue. Results showed that: with increasing leaching time, the concentrations of saline-alkali ions decreased while the concentration increased in bauxite residue leachate; compared with CK (control group) treatment, pH, electric conductivity (EC), exchangeable sodium percentage (ESP), sodium absorption ratio (SAR), and exchangeable Na+ content of bauxite residue were reduced following PG treatment; average particle sizes in aggregates following CK and PG treatments were determined to be 155 and 193 nm, respectively. SR-μCT test results also confirmed that bauxite residue following PG treatment acquired larger aggregates and larger pore diameter. These results indicate that the PG treatment could significantly modulate the saline-alkalinity, and simultaneously enhance aggregate stability of bauxite residue, which provides a facile approach to reclaim bauxite residue disposal areas. 相似文献
4.
5.
4,6-二氯嘧啶是一种重要的化工中间体.研究了反应温度、溶剂种类、催化剂种类、催化剂用量和反应物投料配比在4,6-二氯嘧啶合成过程中对反应的影响.结果 表明,在以邻硝基甲苯为溶剂,苄基三乙基氯化铵为催化剂,且催化剂用量为4,6-二羟基嘧啶质量的2%,n(4,6-二羟基嘧啶):n(三光气)=1∶0.8,反应温度为100~110℃的最佳条件下,产品收率可以达到93.4%. 相似文献
6.
添加不同含量的乳酸钠、双乙酸钠或柠檬酸钠,按照标准配方制作熟火腿.制备后,一部分产品直接进行感官分析,另一部分煮熟、切碎、均匀接种L monocytogenes和L curvatus,真空包装后在4℃储存.与对照组相比,添加2.5%~3.3%的乳酸钠抑制了L monocytogenes和L curvatus的生长.添加0.2%的双乙酸钠对火腿的口感和气味有负面影响.0.1%和0.2%的双乙酸钠对L curvatus没有抑制作用.另一方面,添加1%的缓冲柠檬酸钠可以促进L monocytogenes的生长. 相似文献
7.
Kyle L. Covington Alexander K. Goroncy Teresa E. Lehmann Zuhao Kou Heng Wang Vladimir Alvarado 《American Institute of Chemical Engineers》2021,67(2):e17074
Microtomography (μCT) and nuclear magnetic resonance (NMR) have been used to characterize porous media for decades. Magnetic resonance imaging (MRI) enables direct visualization of pore architecture and many pulse sequences exist. In this work, we tested the MRI pulse sequence Zero Echo Time (ZTE) to study sandstone and carbonate for its ability to address short relaxation times. We aimed at resolving two fluid conduit scales, that is, pores and fractures. In this research, we study tighter porous systems than those previously reported using ZTE. Additionally, pore cluster analysis (PCA), combined with ZTE, can be used to analyze pore-fracture connectivity of relatively large core plugs. We show that ZTE can resolve two-scale pore systems simultaneously, that is, fractures and pores. By combining time-domain NMR pore-size analysis and PCA, we show that careful selection of resolution is necessary to understand transport in porous media. 相似文献
8.
Chuncheng Wei Zhen Liu Yun Wu Yeqing Liu Heng Zhang Peng Wang Qiyan Sun Lijuan Zhou 《Ceramics International》2021,47(13):18693-18698
Laminated Si3N4/SiCw ceramics were successfully prepared by tape casting and hot-pressing. Its mechanical properties were measured and the impact resistance was discussed. The toughness of the laminated Si3N4/SiCw ceramics was 13.5 MPa m1/2, which was almost 1.6 times that of Si3N4/SiCw composite ceramics, namely 8.5 MPa m1/2. Moreover, the indentation strength of laminated Si3N4/SiCw ceramics was not sensitive to increasing indentation loads and exhibited a rising R-curve behaviour, indicating that the laminated Si3N4/SiCw ceramics had excellent impact resistance. The improved toughness and impact resistance of laminated Si3N4/SiCw ceramics was attributed to the residual stress caused by a thermal expansion coefficient mismatch between the different layers, resulting in crack deflection and bridging of SiC whiskers in the interface layer, thus consuming a large amount of fracture work. 相似文献
9.
双锥-平面线栅结构的水平极化辐射波天线对辐射场半宽影响较小且架设方便、易于维护,掌握该型天线场分布规律是确定模拟器场均匀区、开展电磁脉冲效应实验的前提。利用天线理论研究双锥-平面线栅天线的场分布规律,结合数值模拟和实际天线试验对理论分析结果进行验证。结果表明:在天线结构和激励电压确定的条件下,双锥中心正下方辐射电场极化分量仅与测点到源的距离相关,二者呈反比;Oxz平面内以双锥中心为圆心的圆弧上任意一点辐射电场极化分量的幅值相等,并在同一时刻达到峰值;Oxz平面内同一水平线上的测点总辐射场幅值相等,方向沿测点所在圆弧的切线方向;各辐射场分量关于Oxz平面和Oyz平面对称分布;对于实际模拟器,地面反射会使辐射场波形下降沿陡降,导致地面附近辐射场半宽变小;线栅极板会影响附近的场分布,且极板外侧4个角点处的反射相对较强,其他位置辐射场分布与理论分析一致。 相似文献
10.
Bin Feng Xin Jiang Guisheng Zou Wengan Wang Tianming Sun Heng Yang Guanlei Zhao Mingye Dong Yu Xiao Hongwei Zhu Lei Liu 《Advanced functional materials》2021,31(29):2102359
The realization of liquid metal-based wearable systems will be a milestone toward high-performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal-based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre-inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as “bricks” and strain-sensitive Ag film as “mortar” is developed, which breaks the long-standing sensitivity bottleneck of liquid metal-based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal-based strain sensors rival the state-of-art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut-through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid-metal paths and create crack-free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal-based electronic skins, and reveals a pathway for sensor development via crack engineering. 相似文献