全文获取类型
收费全文 | 27446篇 |
免费 | 2434篇 |
国内免费 | 1083篇 |
专业分类
电工技术 | 1529篇 |
技术理论 | 1篇 |
综合类 | 1648篇 |
化学工业 | 4616篇 |
金属工艺 | 1647篇 |
机械仪表 | 1628篇 |
建筑科学 | 2215篇 |
矿业工程 | 892篇 |
能源动力 | 806篇 |
轻工业 | 2033篇 |
水利工程 | 507篇 |
石油天然气 | 1400篇 |
武器工业 | 220篇 |
无线电 | 2967篇 |
一般工业技术 | 3527篇 |
冶金工业 | 1301篇 |
原子能技术 | 366篇 |
自动化技术 | 3660篇 |
出版年
2024年 | 77篇 |
2023年 | 521篇 |
2022年 | 784篇 |
2021年 | 1212篇 |
2020年 | 985篇 |
2019年 | 756篇 |
2018年 | 834篇 |
2017年 | 1028篇 |
2016年 | 881篇 |
2015年 | 1144篇 |
2014年 | 1338篇 |
2013年 | 1656篇 |
2012年 | 1689篇 |
2011年 | 1857篇 |
2010年 | 1586篇 |
2009年 | 1515篇 |
2008年 | 1445篇 |
2007年 | 1358篇 |
2006年 | 1317篇 |
2005年 | 1267篇 |
2004年 | 815篇 |
2003年 | 706篇 |
2002年 | 625篇 |
2001年 | 539篇 |
2000年 | 571篇 |
1999年 | 682篇 |
1998年 | 630篇 |
1997年 | 504篇 |
1996年 | 535篇 |
1995年 | 437篇 |
1994年 | 387篇 |
1993年 | 275篇 |
1992年 | 218篇 |
1991年 | 176篇 |
1990年 | 137篇 |
1989年 | 108篇 |
1988年 | 104篇 |
1987年 | 67篇 |
1986年 | 45篇 |
1985年 | 33篇 |
1984年 | 33篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1972年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
31.
32.
33.
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
34.
35.
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
36.
37.
The strategies for nanosol from metal alkoxide have enabled production of ultratransparent and mechanically robust polymer nanocomposites at extremely high loading. Herein, a simple approach to fabricate high‐performance polyurethane‐based nanocomposites via unmodified boehmite nanoparticles is reported. Evaluating their physical properties, the uniform dispersion of boehmite in the matrix caused nanocomposites retains ultrahigh transparency. Hydrogen bonding and intermolecular entanglement between boehmite and polyurethane brings about the mechanical properties of the nanocomposites material enhanced, i.e., strength, stiffness, and toughness. Optimized strength, stiffness, and toughness of Boehmite/Cationic waterborne polyurethane at 40 wt% (BNC40) are up to 58.1 MPa, 1096.7 MPa, 249.5 MJ m?3, respectively. Furthermore, the feasibility and mechanism of polymer strengthening and toughening by inorganic rigid nanoparticles is explored from the aspects of crystallinity and micromorphology. 相似文献
38.
Zhao Hongliang Lu Tingting Liu Fengqin Yin Pan Wang Sen 《JOM Journal of the Minerals, Metals and Materials Society》2019,71(5):1643-1649
JOM - The Isa/Ausmelt smelting technology with a top submerged lance (TSL) has been extensively used in copper smelting processes. However, the TSL is extremely vulnerable to damage and failure... 相似文献
39.
Xiangyang Chen Dongfeng Xu Hua Zhang Xinxing Feng Jianping Deng Kai Pan 《应用聚合物科学杂志》2020,137(20):48687
A novel halogen-free flame retardant copolyamide 6,6 (FR-PA66) was prepared successfully by in situ polymerizing with adipic acid hexamethylene salt and 2-carboxy ethyl (phenyl) phosphinic acid (CEPPA). The elemental composition and chemical structure of FR-PA66 were characterized by energy dispersive X-ray spectroscopy, Fourier transform infrared spectrometer and 13C Nuclear magnetic resonance spectrometer. The flame retardancy, thermal stability, and morphology of char residues were also investigated by the limiting oxygen index (LOI), UL 94 test, thermogravimetric analysis, and scanning electron microscopy. The results showed that FR-PA66 samples had much better flame retardancy and char formation ability than pure PA66 after the flame retardant modification. The LOI values were increased from 24.0 to 28.0% by adding 6 wt % of CEPPA and all FR-PA66 samples were rated as V-0 rating in UL-94 test. Furthermore, the thermal stability analysis indicated that in situ polymerization with CEPPA effectively decreased the initial decomposition temperature and increased the amount of char residue. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48687. 相似文献
40.