全文获取类型
收费全文 | 107376篇 |
免费 | 10905篇 |
国内免费 | 6093篇 |
专业分类
电工技术 | 7559篇 |
技术理论 | 5篇 |
综合类 | 8903篇 |
化学工业 | 16649篇 |
金属工艺 | 5912篇 |
机械仪表 | 7156篇 |
建筑科学 | 8672篇 |
矿业工程 | 3184篇 |
能源动力 | 3023篇 |
轻工业 | 8790篇 |
水利工程 | 2445篇 |
石油天然气 | 5436篇 |
武器工业 | 1116篇 |
无线电 | 12215篇 |
一般工业技术 | 11625篇 |
冶金工业 | 4348篇 |
原子能技术 | 1508篇 |
自动化技术 | 15828篇 |
出版年
2024年 | 469篇 |
2023年 | 1793篇 |
2022年 | 3543篇 |
2021年 | 4829篇 |
2020年 | 3638篇 |
2019年 | 2871篇 |
2018年 | 3200篇 |
2017年 | 3614篇 |
2016年 | 3186篇 |
2015年 | 4471篇 |
2014年 | 5908篇 |
2013年 | 6917篇 |
2012年 | 7735篇 |
2011年 | 8174篇 |
2010年 | 7489篇 |
2009年 | 6954篇 |
2008年 | 6866篇 |
2007年 | 6565篇 |
2006年 | 6065篇 |
2005年 | 4966篇 |
2004年 | 3592篇 |
2003年 | 3151篇 |
2002年 | 3313篇 |
2001年 | 2786篇 |
2000年 | 2340篇 |
1999年 | 2142篇 |
1998年 | 1390篇 |
1997年 | 1210篇 |
1996年 | 1183篇 |
1995年 | 920篇 |
1994年 | 762篇 |
1993年 | 588篇 |
1992年 | 410篇 |
1991年 | 309篇 |
1990年 | 226篇 |
1989年 | 210篇 |
1988年 | 194篇 |
1987年 | 110篇 |
1986年 | 68篇 |
1985年 | 38篇 |
1984年 | 37篇 |
1983年 | 19篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1976年 | 2篇 |
1971年 | 2篇 |
1959年 | 8篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
51.
52.
Crystallographic characteristics and microwave dielectric properties of Ni-modified MgTa2O6 ceramics
Liang Shi Xueying Wang Rui Peng Gang Wang Cheng Liu Xiaolei Shi Dainan Zhang Huaiwu Zhang 《Ceramics International》2021,47(16):22514-22521
Ni2+ modified MgTa2O6 ceramics with a trirutile phase and space group P42/mnm were obtained. The correlations between crystallographic characteristics and microwave dielectric performance of MgTa2O6 ceramics were systematically studied based on the chemistry bond theory (PVL theory) for the first time. The results indicate that the introduction of Ni2+ causes a change in polarizability and the Mg–O bond ionicity, which contributes to the variation of dielectric constant. Moreover, the lattice energy, and packing fraction, full width at half maximum of the Raman peak of Ta–O bond, as the quantitative characterization of crystallographic parameters, regulate the dielectric loss of MgTa2O6 ceramics in GHz frequency band. In addition, the study of sintering behavior shows that the densification and micromorphology are the crucial factors affecting the microwave dielectric performance. Typically, Ni2+ doping on the A-site of MgTa2O6 can effectively promote the Q × f values to 173,000 GHz (at 7.43 GHz), which ensures its applicability in 5G communication technology. 相似文献
53.
Liang Shi Dainan Zhang Rui Peng Cheng Liu Xiaolei Shi Xueying Wang Huaiwu Zhang 《Journal of the European Ceramic Society》2021,41(11):5526-5530
Mg(1-x)ZnxTa2O6 (x = 0.00?0.08) dielectric ceramics were synthesized via the traditional solid-state reaction method. We used XRD and Rietveld refinement to demonstrate that a pure Mg(1-x)ZnxTa2O6 phase with trirutile structure was formed. Zn2+ substitution helped to decrease the Raman full width at half width of the A1g mode at 703 cm?1, which resulted in an increase in the order and rigidity of the TaO6 octahedron, this in turn contributed to improving the Q×f values. Additionally, the introduction of Zn2+ significantly promoted grain growth and increased the dense, and the molecular polarizability, these factors lead to a higher permittivity. Moreover, enhanced Ta-O bond energy resulted in a more stable TaO6 octahedron in the Mg(1?x)ZnxTa2O6 system, which contributed to enhanced τf values via substitution of Zn2+ doped on the A-site. Correspondingly, the microwave dielectric properties were significantly improved for 0.04-doped samples, obtaining: εr = 27, Q × f = 185,000 GHz (at 7.47 GHz), τf =32 ppm/°C. 相似文献
54.
就经典分水岭图像分割算法中存在的过分割问题,提出一种结合位图切割和区域合并的彩色图像分割算法。对原始彩色图像通过空域梯度算子求其梯度图像,并利用位图切割重建梯度图像;对新梯度图像进行分水岭预分割;对预分割图像基于异质性最小原则进行区域合并,并获得最终分割结果。相比于现有的同类方法,该算法引入位图切割,抑制噪声对分割结果的影响,在边缘模糊处分割准确,得到符合人类视觉的较小分割区域数目,同时在运行效率上提高。 相似文献
55.
56.
Neural Computing and Applications - Traffic identification is currently an important challenge for network management and security. In this paper, we propose a novel application identification... 相似文献
57.
58.
59.
Shensong Wang Zheng Wu Jie Chen Jiangping Ma Jingshi Ying Shouchen Cui Shigang Yu Yongming Hu Jinhe Zhao Yanmin Jia 《Ceramics International》2019,45(9):11703-11708
In this work, the hydrothermally-synthesized sodium niobate nanowires were used to decompose Rhodamine B dye solution through the piezo-catalytic effect. With the sodium niobate catalyst, a high piezo-catalytic degradation ratio of ~80% was achieved under the excitation of vibration for the Rhodamine B dye solution (~5?mg/l). These active species in the catalytic process, hydroxyl radicals and superoxide radicals with the strong oxidation ability, were also observed, which confirmed the key role of piezoelectric effect for piezo-catalysis. The piezo-catalysis of sodium niobate nanowires provides a high-efficiency and reusable tool in application in depredating the dye wastewater. 相似文献
60.