全文获取类型
收费全文 | 114011篇 |
免费 | 11620篇 |
国内免费 | 6196篇 |
专业分类
电工技术 | 7970篇 |
技术理论 | 9篇 |
综合类 | 9056篇 |
化学工业 | 17765篇 |
金属工艺 | 6618篇 |
机械仪表 | 7515篇 |
建筑科学 | 8690篇 |
矿业工程 | 3633篇 |
能源动力 | 3185篇 |
轻工业 | 9713篇 |
水利工程 | 2464篇 |
石油天然气 | 5571篇 |
武器工业 | 1242篇 |
无线电 | 13016篇 |
一般工业技术 | 12635篇 |
冶金工业 | 5038篇 |
原子能技术 | 1639篇 |
自动化技术 | 16068篇 |
出版年
2024年 | 647篇 |
2023年 | 2144篇 |
2022年 | 4066篇 |
2021年 | 5402篇 |
2020年 | 4102篇 |
2019年 | 3165篇 |
2018年 | 3604篇 |
2017年 | 4145篇 |
2016年 | 3611篇 |
2015年 | 5041篇 |
2014年 | 6571篇 |
2013年 | 7659篇 |
2012年 | 8529篇 |
2011年 | 8885篇 |
2010年 | 8035篇 |
2009年 | 7463篇 |
2008年 | 7333篇 |
2007年 | 7025篇 |
2006年 | 6276篇 |
2005年 | 5195篇 |
2004年 | 3685篇 |
2003年 | 2861篇 |
2002年 | 2748篇 |
2001年 | 2280篇 |
2000年 | 2186篇 |
1999年 | 1914篇 |
1998年 | 1357篇 |
1997年 | 1172篇 |
1996年 | 1087篇 |
1995年 | 838篇 |
1994年 | 683篇 |
1993年 | 479篇 |
1992年 | 373篇 |
1991年 | 282篇 |
1990年 | 223篇 |
1989年 | 197篇 |
1988年 | 156篇 |
1987年 | 78篇 |
1986年 | 80篇 |
1985年 | 41篇 |
1984年 | 45篇 |
1983年 | 32篇 |
1982年 | 29篇 |
1981年 | 26篇 |
1980年 | 26篇 |
1979年 | 14篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1959年 | 10篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
为了提升高校实验数据处理水平,高校实验室的相关建设工作已经步入正轨,但层出不穷的信息安全问题也向高校实验室计算机网络维护工作提出了新的挑战。文章从现阶段高校实验室计算机网络的相关建设工作出发,简要论述引发网络故障的具体原因,并对其诊断技术进行探讨。 相似文献
32.
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
33.
In this article, the silver-plated polyamide fabrics (SPPAFs) with high electroconductibility and shielding effectiveness were fabricated by using in situ reduction of polydopamine and chemical silvering. The effects of SPPAFs dopamine (C8H11O2N) and silver nitrate (AgNO3) concentration on surface resistivity and electromagnetic interference shielding effectiveness were studied. The results showed that the surface resistivity of SPPAFs can reach a minimum value of 0.06 ± 0.014 Ω cm−1, when C8H11O2N concentration is 4 g L−1 and the AgNO3 concentration is 120 g L−1. The shielding effectiveness of SPPAFs in the wide frequency range of 10–3000 MHz increases with the increase in the concentration of AgNO3, and increases first and stabilizes afterward with increasing C8H11O2N concentration. When the concentration of C8H11O2N and AgNO3 is 3 and 120 g L−1, respectively, mean shielding effectiveness values in the low-, medium-, and high-frequency bands are 71.3, 73.8, and 76.1 dB, respectively. Moreover, the mean shielding effectiveness values is 83.79 dB in the frequency range of 1.2–2.3 GHz. The dominant shielding mechanism of SPPAFs is the reflected electromagnetic waves and the absorption shielding effectiveness is less than 2 dB. The average electromagnetic shielding values of SPPAFs are above 67 dB after 16 weeks of storage, when C8H11O2N concentration is 4 g L−1 and the AgNO3 concentration is 80 and 100 g L−1. The prepared SPPAFs show promising applications in military textiles and smart wearable clothing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48227. 相似文献
34.
35.
介绍了尿素装置中3起液位仪表失真案例,分析了故障现象和设备工况,确定失真原因,采取了相应的处理措施,解决了仪表故障。 相似文献
36.
37.
38.
The effect of Li2O on the crystallization properties of CaO-Al2O3-SiO2-Li2O-Ce2O3 slags was investigated. With increasing the Li2O content, LiAlO2 and CaCeAlO4 were the main crystalline phases. LiAlO2 formed for the charge compensating of Li+ ions to [AlO45?]-tetrahedrons, and CaCeAlO4 formed as a result of the charge balance of Ce3+ ions, Ca2+ ions, and [AlO69?]-octahedrons. Increasing the content of Li2O to 10%, the crystallization temperature was the highest, and the incubation time was the shortest. The crystallization ability was strong due to the three factors of strengthening the interaction between ions and ion groups, decreasing the polymerization degree, and increasing the melting temperature. Further increasing the content of Li2O, the crystallization performance was obviously suppressed, because the melting temperature and the force between the cations and the anion groups decreased. 相似文献
40.
Journal of Computer Science and Technology - DOACROSS loops are significant parts in many important scientific and engineering applications, which are generally exploited pipeline/wave-front... 相似文献