全文获取类型
收费全文 | 86195篇 |
免费 | 8586篇 |
国内免费 | 4346篇 |
专业分类
电工技术 | 5494篇 |
技术理论 | 3篇 |
综合类 | 5995篇 |
化学工业 | 13823篇 |
金属工艺 | 5190篇 |
机械仪表 | 5747篇 |
建筑科学 | 7166篇 |
矿业工程 | 2644篇 |
能源动力 | 2391篇 |
轻工业 | 6094篇 |
水利工程 | 1856篇 |
石油天然气 | 4365篇 |
武器工业 | 822篇 |
无线电 | 10427篇 |
一般工业技术 | 10024篇 |
冶金工业 | 3852篇 |
原子能技术 | 1065篇 |
自动化技术 | 12169篇 |
出版年
2024年 | 431篇 |
2023年 | 1641篇 |
2022年 | 3048篇 |
2021年 | 4086篇 |
2020年 | 3159篇 |
2019年 | 2474篇 |
2018年 | 2603篇 |
2017年 | 3169篇 |
2016年 | 2772篇 |
2015年 | 3897篇 |
2014年 | 4749篇 |
2013年 | 5679篇 |
2012年 | 5973篇 |
2011年 | 6618篇 |
2010年 | 5728篇 |
2009年 | 5521篇 |
2008年 | 5371篇 |
2007年 | 4820篇 |
2006年 | 4506篇 |
2005年 | 3828篇 |
2004年 | 2441篇 |
2003年 | 1994篇 |
2002年 | 1848篇 |
2001年 | 1644篇 |
2000年 | 1494篇 |
1999年 | 1588篇 |
1998年 | 1374篇 |
1997年 | 1116篇 |
1996年 | 1114篇 |
1995年 | 968篇 |
1994年 | 787篇 |
1993年 | 615篇 |
1992年 | 444篇 |
1991年 | 387篇 |
1990年 | 269篇 |
1989年 | 219篇 |
1988年 | 195篇 |
1987年 | 124篇 |
1986年 | 98篇 |
1985年 | 65篇 |
1984年 | 54篇 |
1983年 | 42篇 |
1982年 | 33篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 21篇 |
1976年 | 9篇 |
1972年 | 6篇 |
1959年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
为研究古建筑木结构透榫节点的M-θ力学模型,在分析透榫节点构造特征与受力机理的基础上,建立其数值模型,用透榫节点的试验数据验证了该数值模型的正确性,并分析了节点缝隙、木材横纹弹性模量和大榫头长度对透榫节点受弯承载力的影响。根据受力分析结果,建立以弹性点、屈服点与极限点为特征点的三折线多参数M-θ力学模型,其结果与多数的试验结果基本吻合,并将该力学模型应用于木构架的受力分析。研究结果表明:透榫节点的滞回耗能能力强,节点的变形主要集中在榫头处。当榫头与卯口之间的缝隙增大时,节点的受弯承载力降低。随木材横纹弹性模量的提高和大榫头长度的增加,节点的受弯承载力有一定提高。文章建立的M-θ力学模型能较好反映透榫节点的受力过程,适用于木构架的受力分析,其荷载 位移骨架曲线与试验结果基本吻合。研究成果可为古建筑木结构的维修与保护提供参考。 相似文献
65.
66.
Qiang Xia Tao Feng Xiaowei Lou Ying Wang Yangying Sun Daodong Pan Jinxuan Cao 《International Journal of Food Science & Technology》2020,55(2):669-680
As a decisive attribute, flavour could be influenced by HP treatments through multiple physical and chemical pathways within the high pressure (HP)-assisted meat curing process. This investigation aimed to identify the major pathway influencing volatile flavour patterns of two representative vinasse-cured duck (VCD) products with HP treatments (150–300 MPa/15 min), including wet and dry types, by employing headspace fingerprinting as an untargeted approach. Results suggested that HP treatments greatly lowered moisture contents and increased Warner-Bratzler shear force and thiobarbituric acid reactive substances of the cured samples. According to multivariate models, the volatile flavour patterns of the HP-processed VCD could be clearly separated from the unprocessed samples, but the VCD pressurised at different intensities represented similar volatile fingerprinting, which was validated by e-nose analysis. The discriminant analysis (OPLS-DA) model outlined vinasse-derived ethanol, acetic acid, 3-methyl-1-butanol, 2-methyl-1-butanol, phenethyl alcohol and 2-methyl-3-octanone as the major discriminant aromas across the unpressurised and pressurised samples. 相似文献
67.
68.
Timothy Zurrer Kenneth Wong Jonathan Horlyck Emma C. Lovell Joshua Wright Nicholas M. Bedford Zhaojun Han Kang Liang Jason Scott Rose Amal 《Advanced functional materials》2021,31(9):2007624
The vast chemical and structural tunability of metal–organic frameworks (MOFs) are beginning to be harnessed as functional supports for catalytic nanoparticles spanning a range of applications. However, a lack of straightforward methods for producing nanoparticle-encapsulated MOFs as efficient heterogeneous catalysts limits their usage. Herein, a mixed-metal MOF, NiMg-MOF-74, is utilized as a template to disperse small Ni nanoclusters throughout the parent MOF. By exploiting the difference in Ni O and Mg O coordination bond strength, Ni2+ is selectively reduced to form highly dispersed Ni nanoclusters constrained by the parent MOF pore diameter, while Mg2+ remains coordinated in the framework. By varying the ratio of Ni to Mg in the parent MOF, accessible surface area and crystallinity can be tuned upon thermal treatment, influencing CO2 adsorption capacity and hydrogenation selectivity. The resulting Ni nanoclusters prove to be an active catalyst for CO2 methanation and are examined using extended X-ray absorption fine structure and X-ray photoelectron spectroscopy. By preserving a segment of the Mg2+-containing MOF framework, the composite system retains a portion of its CO2 adsorption capacity while continuing to deliver catalytic activity. The approach is thus critical for designing materials that can bridge the gap between carbon capture and CO2 utilization. 相似文献
69.
A facile and effective method was proposed to prepare the molecularly imprinted fluorescence sensor with carbon quantum dots, which were modified vinyl groups by acrylic acid on the surface. The obtained fluorescence composite material was investigated by transmission electron microscope and Fourier transform infrared spectra. After the experimental conditions were optimized, a linear range of 1.0–60 μmol L−1 was obtained and the detection limit was 0.17 μmol L−1. The novel fluorescence sensor can be successfully used to detect tetracycline in real samples. This study provides a convenient strategy for selective recognition and rapid detection of tetracycline in the complex environment. 相似文献
70.
Hechun Cao Hui Zheng Lining Fan Zifeng Cheng Jianwei Zhou Qiong Wu Peng Zheng Liang Zheng Yang Zhang 《International Journal of Applied Ceramic Technology》2020,17(2):813-822
In this study, yttrium iron garnet co-doped with Zn and Zr atoms with a chemical formula Y3ZnxZrxFe(5−2x)O12 (x = 0.0-0.3) has been successfully prepared by the solid-state reaction method. The effects of doping concentration on the microstructure, crystal structure, magnetic properties, and dielectric properties of Y3ZnxZrxFe(5−2x)O12 were investigated. The microstructure analysis indicates that co-doping of YIG with Zn and Zr can effectively reduce the grain size of the ceramic. The crystal structure results reveal that the doping concentration of Zn–Zr has substantial influence on the lattice parameters of YIG, such as, increases the lattice constant, crystal cell size, and interplanar spacing. However, the second phase of ZrO2 appears once x ≥ 0.15. Additionally, the dielectric properties of YIG ferrite can be regulated using this Zn–Zr co-doping method. Zn–Zr co-doping can improve the dielectric stability and reduce the dielectric loss at high temperature. The magnetization measurement shows that the saturation magnetization is stabilized at x < 0.15, and the magnetic loss is decreased with the increase in the doping concentration. Overall, the findings show that the ceramic with x = 0.1 exhibits better properties included high saturation magnetization (24.607 emu/g), low magnetic loss (0.0025 @ 1 MHz), and relatively low dielectric loss (496 @ 400°C). 相似文献