全文获取类型
收费全文 | 44013篇 |
免费 | 4597篇 |
国内免费 | 2592篇 |
专业分类
电工技术 | 2999篇 |
技术理论 | 4篇 |
综合类 | 3641篇 |
化学工业 | 7039篇 |
金属工艺 | 2283篇 |
机械仪表 | 2451篇 |
建筑科学 | 3808篇 |
矿业工程 | 1246篇 |
能源动力 | 1237篇 |
轻工业 | 3736篇 |
水利工程 | 961篇 |
石油天然气 | 2289篇 |
武器工业 | 391篇 |
无线电 | 5327篇 |
一般工业技术 | 5421篇 |
冶金工业 | 1763篇 |
原子能技术 | 483篇 |
自动化技术 | 6123篇 |
出版年
2024年 | 261篇 |
2023年 | 1019篇 |
2022年 | 1757篇 |
2021年 | 2473篇 |
2020年 | 1688篇 |
2019年 | 1423篇 |
2018年 | 1533篇 |
2017年 | 1596篇 |
2016年 | 1357篇 |
2015年 | 1886篇 |
2014年 | 2385篇 |
2013年 | 2695篇 |
2012年 | 2944篇 |
2011年 | 3051篇 |
2010年 | 2593篇 |
2009年 | 2560篇 |
2008年 | 2468篇 |
2007年 | 2338篇 |
2006年 | 2261篇 |
2005年 | 1928篇 |
2004年 | 1362篇 |
2003年 | 1330篇 |
2002年 | 1319篇 |
2001年 | 1161篇 |
2000年 | 954篇 |
1999年 | 895篇 |
1998年 | 718篇 |
1997年 | 619篇 |
1996年 | 546篇 |
1995年 | 471篇 |
1994年 | 366篇 |
1993年 | 274篇 |
1992年 | 220篇 |
1991年 | 145篇 |
1990年 | 141篇 |
1989年 | 141篇 |
1988年 | 90篇 |
1987年 | 46篇 |
1986年 | 46篇 |
1985年 | 27篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 11篇 |
1980年 | 18篇 |
1979年 | 7篇 |
1976年 | 5篇 |
1970年 | 4篇 |
1959年 | 5篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Haitang Yang Zilong Lu Bixiong Bie Zeyu Fu Jianling Yue Xiaozhong Huang 《Ceramics International》2019,45(9):11395-11402
SiCf/PyC/SiC and SiCf/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapor deposited PyC or BN interface layers are fabricated. The microstructure evolutions of the mini-composite samples as the oxidation temperature increases (oxidation at 1000, 1200, 1400, and 1600?°C in air for 2?h) are observed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction characterization methods. The damage evolution for each component of the as-fabricated SiCf/SiC composites (SiC fibre, PyC/BN interface, SiC matrix, and mesophase) is mapped as a three-dimensional (3D) image and quantified with X-ray computed tomography. The mechanical performance of the composites is investigated via tensile tests.The results reveal that tensile failure occurs after the delamination and fibre pull-out in the SiCf/PyC/SiC composites due to the volatilization of the PyC interface at high temperatures in the air environment. Meanwhile, the gaps between the fibres and matrix lead to rapid oxidation and crack propagation from the SiC matrix to SiC fibre, resulting in the failure of the SiCf/PyC/SiC composites as the oxidation temperature increases to 1600?°C. On the other hand, the oxidation products of B2O3 molten compounds (reacted from the BN interface) fill up the fracture, cracks, and voids in the SiC matrix, providing excellent strength retention at elevated oxidation temperatures. Moreover, under the protection of B2O3, the SiCf/BN/SiC mini-composites show a nearly intact microstructure of the SiC fibre, a low void growth rate from the matrix to fibre, and inhibition of new void formation and the SiO2 grain growth from room to high temperatures. This work provides guidance for predicting the service life of SiCf/PyC/SiC and SiCf/BN/SiC composite materials, and is fundamental for establishing multiscale damage models on a local scale. 相似文献
32.
34.
35.
Xiaopeng Yue Yongjian Xu Nina Gou Hongkui Li 《Polymer-Plastics Technology and Engineering》2015,54(6):639-646
A long fatty side chain was introduced into the macromolecule of hydroxyethyl cellulose (HEC) via esterification reaction. The hydrophobicity of hydroxyethyl cellulose lauric acid ester (HECLAE) was enhanced in comparison with HEC. The obtained HECLAE was used as macromolecular coupling agent in poly (butylene succinate)/wood flour composites and exhibited a positive influence on improving the mechanical performance of composites. Besides, HECLAE plays a role as a hydrophobic agent in composites. A significant increase in storage modulus (E’) was observed upon the incorporation of treated wood flour. SEM images showed that the dispersion of treated wood flour in PBS matrix was improved. 相似文献
36.
37.
Yu Zhang Xiaofei Dai Haonan Jin Chaoxin Man Yujun Jiang 《Journal of dairy science》2021,104(4):4023-4032
This study aimed to predict the optimal carbon source for higher production of exopolysaccharides (EPS) by Lactobacillus paracasei TD 062, and to evaluate the effect of this carbon source on the production and monosaccharide composition of EPS. We evaluated the EPS production capacity of 20 strains of L. paracasei under the same conditions. We further investigated L. paracasei TD 062, which showed the highest EPS-producing activity (0.609 g/L), by examining the associated biosynthesis pathways for EPS. Genomics revealed that fructose, mannose, trehalose, glucose, galactose, and lactose were carbon sources that L. paracasei TD 062 could use to produce EPS. We identified an EPS synthesis gene cluster that could participate in transport, export, and sugar chain synthesis, and generate 6 sugar nucleotides. Experimental results showed that the sugar content of the EPS produced using fermentation with the optimized carbon source (fructose, mannose, trehalose, glucose, galactose, and lactose) increased by 115%. Furthermore, use of the optimized carbon source changed the monosaccharide content of the associated EPS. The results of enzyme activity measurements showed significant increases in the activity of 2 key enzymes involved in the glycoside synthesis pathway. Our study revealed that optimizing the carbon source provided for fermentation not only increased the production of EPS, but also affected the composition of the monosaccharides by increasing enzyme activity in the underlying synthesis pathways, suggesting an important role for carbon source in the production of EPS by L. paracasei TD 062. 相似文献
38.
39.
40.
Porous polyimide (PI) films with low dielectric constants and excellent thermal properties have been a pressing demand for the next generation of high-performance, miniature, and ultrathin microelectronic devices. A series of novel porous PI films containing fluorenyl-adamantane groups were prepared successfully via thermolysis of poly(ethylene glycol) (PEG) added in the PI matrix. The cross-sectional morphologies of porous PI films showed closed pores with diameters ranging from 135 to 158 nm, which were uniform and regular in shape without interconnectivity. These porous PI films exhibited excellent thermal properties with a glass-transition temperature at 376 °C whereas the 5% weight loss temperature in air excess of 405 °C due to enhanced rigidity afforded by fluorenyl-adamantane groups. Accompanied by thermolysis content of PEG increasing from 0 to 20 wt %, the density of porous PI films decreased, and the corresponding porosity grew significantly from 0 to 11.48%. Depending on porosity, the dielectric constant and dielectric loss of porous PI films significantly declined from 2.89 to 2.37 and from 0.050 to 0.021, respectively. These excellent properties benefit the as-prepared porous PI films for application as interlayer dielectrics, integrated circuit chips, or multichip modules in microelectronic fields. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47313. 相似文献