全文获取类型
收费全文 | 280823篇 |
免费 | 7044篇 |
国内免费 | 2501篇 |
专业分类
电工技术 | 6328篇 |
技术理论 | 2篇 |
综合类 | 2271篇 |
化学工业 | 41693篇 |
金属工艺 | 9680篇 |
机械仪表 | 9244篇 |
建筑科学 | 9769篇 |
矿业工程 | 1347篇 |
能源动力 | 8048篇 |
轻工业 | 31015篇 |
水利工程 | 2649篇 |
石油天然气 | 3174篇 |
武器工业 | 237篇 |
无线电 | 36963篇 |
一般工业技术 | 49548篇 |
冶金工业 | 47555篇 |
原子能技术 | 3763篇 |
自动化技术 | 27082篇 |
出版年
2022年 | 1832篇 |
2021年 | 3201篇 |
2020年 | 2349篇 |
2019年 | 2490篇 |
2018年 | 3450篇 |
2017年 | 3576篇 |
2016年 | 3794篇 |
2015年 | 3319篇 |
2014年 | 5182篇 |
2013年 | 13717篇 |
2012年 | 8744篇 |
2011年 | 11769篇 |
2010年 | 9426篇 |
2009年 | 10250篇 |
2008年 | 10633篇 |
2007年 | 10543篇 |
2006年 | 9833篇 |
2005年 | 8813篇 |
2004年 | 8084篇 |
2003年 | 7907篇 |
2002年 | 7396篇 |
2001年 | 7744篇 |
2000年 | 6983篇 |
1999年 | 7506篇 |
1998年 | 16851篇 |
1997年 | 11825篇 |
1996年 | 9033篇 |
1995年 | 6899篇 |
1994年 | 6007篇 |
1993年 | 5767篇 |
1992年 | 4151篇 |
1991年 | 3880篇 |
1990年 | 3629篇 |
1989年 | 3446篇 |
1988年 | 3338篇 |
1987年 | 2629篇 |
1986年 | 2509篇 |
1985年 | 3174篇 |
1984年 | 2808篇 |
1983年 | 2568篇 |
1982年 | 2355篇 |
1981年 | 2398篇 |
1980年 | 2210篇 |
1979年 | 2058篇 |
1978年 | 1880篇 |
1977年 | 2180篇 |
1976年 | 2724篇 |
1975年 | 1585篇 |
1974年 | 1489篇 |
1973年 | 1558篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Bing Yang Yu Zhou Wenjie Yu Song Zhang Hongxiang Chen Ju Ye 《Polymer International》2019,68(4):675-683
In order to improve the dispersity and stability of the nano‐SiO2 aqueous system with high solid content, a kind of polyacrylic acid dispersant with methoxysilicon end groups (KH590‐PAA) was synthesized by photopolymerization of acrylic acid (AA) initiated with (3‐mercaptopropyl)trimethoxysilane (KH590). After adding KH590‐PAA into the nano‐SiO2 aqueous dispersion system (20 wt% solid content), the viscosity and the curing time of the system were measured with a rotational viscometer and the inverted bottle method. Moreover, the dispersion mechanism of KH590‐PAA for the nano‐SiO2 aqueous system was researched by measuring the adsorption capacity, the particle size and the zeta potential of the nanoparticles with a conductivity meter, dynamic light scattering, SEM and TEM, respectively. The results showed that the methoxysilicon groups in KH590‐PAA could react with hydroxyl groups on the surface of nano‐SiO2 in the process of stirring, which enhanced the adsorption capacity of the dispersant and then increased the surface charge of the particles. Therefore, electrostatic repulsion and steric hindrance effects between the SiO2 nanoparticles could be further enhanced by adding the KH590‐PAA dispersant, and then the nano‐SiO2 aqueous system exhibited better dispersity and stability. Besides, the dispersion properties of SiO2 nanoparticles in water were closely related to the addition amount and the molecular weight of the KH590‐PAA dispersant. © 2018 Society of Chemical Industry 相似文献
62.
Marcela Stoia Cornelia Păcurariu Ciprian Mihali Iosif Mălăescu Cătălin Nicolae Marin Aylin Căpraru 《Ceramics International》2019,45(2):2725-2735
Magnetic MnFe2O4 nanopowders were synthesized by an original solvothermal method in the absence and in the presence of tetra-n-butylammonium bromide (TBAB) and Tween 80 (TW) as surfactants. Manganese ferrite/polyaniline (PANI) hybrid materials were synthesized by in situ polymerization of aniline on the surface of MnFe2O4 using ammonium persulfate as oxidant. The purpose of the study was to investigate the influence of the two surfactants on the properties of the MnFe2O4 powders and of their composites with PANI. The specific surface area, the cumulative surface area of pores and the cumulative volume of pores are influenced by the nature of surfactant in case of MnFe2O4 powders and are higher by comparison to those of the MnFe2O4/PANI hybrid materials. The values of saturation magnetization in case of MnFe2O4 powders are higher than those of the hybrid materials and are not influenced by the surfactant nature. These features revealed that MnFe2O4 powders can be efficiently used as adsorbents for the purification of wastewaters. The values of the electrical conductivity of the composites exhibit a significant increase in comparison to the MnFe2O4 powders and depend on the surfactant nature. The highest value of electrical conductivity was achieved by the composite obtained using Tween 80 as surfactant (σDC = 54.5·10?5S?m?1) which was close to that of PANI (σDC = 61.2·10?5 S?m?1). The fact that the magnetic and electric properties of the synthesized MnFe2O4/PANI composites can be changed by design, demonstrate the high potential of these materials to be used in magneto-electric applications. 相似文献
63.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity. 相似文献
64.
65.
66.
67.
68.
69.
70.