全文获取类型
收费全文 | 314284篇 |
免费 | 33012篇 |
国内免费 | 26100篇 |
专业分类
电工技术 | 26889篇 |
技术理论 | 9篇 |
综合类 | 33611篇 |
化学工业 | 39806篇 |
金属工艺 | 23577篇 |
机械仪表 | 21596篇 |
建筑科学 | 23186篇 |
矿业工程 | 10978篇 |
能源动力 | 7875篇 |
轻工业 | 30511篇 |
水利工程 | 9731篇 |
石油天然气 | 13576篇 |
武器工业 | 4124篇 |
无线电 | 34691篇 |
一般工业技术 | 27962篇 |
冶金工业 | 11849篇 |
原子能技术 | 5817篇 |
自动化技术 | 47608篇 |
出版年
2024年 | 1152篇 |
2023年 | 4596篇 |
2022年 | 10431篇 |
2021年 | 13889篇 |
2020年 | 9932篇 |
2019年 | 7380篇 |
2018年 | 8014篇 |
2017年 | 8823篇 |
2016年 | 8026篇 |
2015年 | 12435篇 |
2014年 | 16113篇 |
2013年 | 18948篇 |
2012年 | 23232篇 |
2011年 | 28051篇 |
2010年 | 24571篇 |
2009年 | 22656篇 |
2008年 | 23022篇 |
2007年 | 22141篇 |
2006年 | 20106篇 |
2005年 | 16601篇 |
2004年 | 15068篇 |
2003年 | 9937篇 |
2002年 | 9639篇 |
2001年 | 7874篇 |
2000年 | 6312篇 |
1999年 | 4603篇 |
1998年 | 2803篇 |
1997年 | 2473篇 |
1996年 | 1794篇 |
1995年 | 1405篇 |
1994年 | 1116篇 |
1993年 | 2377篇 |
1992年 | 1860篇 |
1991年 | 1290篇 |
1990年 | 1188篇 |
1989年 | 945篇 |
1988年 | 665篇 |
1987年 | 404篇 |
1986年 | 285篇 |
1985年 | 186篇 |
1984年 | 118篇 |
1983年 | 101篇 |
1982年 | 75篇 |
1981年 | 64篇 |
1980年 | 128篇 |
1979年 | 111篇 |
1976年 | 39篇 |
1965年 | 62篇 |
1959年 | 63篇 |
1951年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
1.
Pengfei Liang Jie Zhu Di Wu Hui Peng Xiaolian Chao Zupei Yang 《Journal of the American Ceramic Society》2021,104(6):2702-2710
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics. 相似文献
2.
为探索生物活性未知的双对苯醌(2,7-dihydroxy-3,6,9-trimethyl-9H-xanthene-1,4,5,8-tetraone,DTXT)的抗氧化活性,并提高其发酵产量,考察DTXT的还原力以及对超氧阴离子自由基、羟自由基、1,1-二苯基-2-三硝基苯肼(1,1-diphenyl-2-picrylhydrazyl,DPPH)自由基的清除效果,在单因素试验基础上,采用响应面法优化了DTXT产生菌瓶生顶孢霉(Acremonium cavaraeanum)CA022菌株的固体发酵培养基。结果表明:在200 μg/mL质量浓度下,DTXT的还原力与芦丁差异不显著,高于VE和2,6-二叔丁基-4甲基苯酚,对超氧阴离子自由基清除率达到67.00%,对羟自由基清除率达到78.83%,对DPPH自由基清除率达到76.53%。通过响应面试验,得到最佳培养基配方为葡萄糖0.773%、硝酸钠0.185%、H3BO3 0.032%、VB1 100 μg/100 g,在此条件下实际获得的DTXT产量为4 150.8 mg/kg,是优化前产量的(2 864.83 mg/kg)1.45 倍。 相似文献
3.
4.
6.
随着食品和膳食补充剂的市场变得越来越全球化,食品和膳食补充剂的安全性、质量和功效引起人们的高度关注。近年来,食品和膳食补充剂中被检测出兴奋剂阳性的事件屡见不鲜。运动员在误服误用被兴奋剂污染的食品和膳食补充剂后,会导致兴奋剂检测呈阳性,这对运动员和国家都造成了重大损失。由于摄入受污染的食品或膳食补充剂会导致严重的健康损害或意外违反反兴奋剂规定,因此准确了解食品和膳食补充剂中兴奋剂污染种类是十分有必要的。本文主要从食品和膳食补充剂中兴奋剂污染的来源和种类以及常用的检测方法等方面进行简要概述,以提高运动员对高风险食品的警惕和防范,避免因误服被兴奋剂污染的食品、膳食补充剂而导致的不良分析结果。 相似文献
8.
Peng Wang Yan Li Yujiao Qu Baowei Wang Jingxin Sun Chunwei Miao Ming Huang He Huang Congxiang Zhang 《International Journal of Food Science & Technology》2022,57(6):3428-3439
The effects of cellulose microfibres (CMFs, Average size: 100 ± 5 μm) and cellulose nanofibres (CNFs, Average size: 60 ± 3 nm) on the properties of myofibrillar protein (MP) gels from duck breast meat were studied. The results demonstrated that CMFs and CNFs were mostly connected to MP by non-covalent bonds, the diffusion and cross-linking of MP molecules was promoted, and a denser and more complete gel network was formed. With the increases of CMFs and CNFs concentration (0–10%), the hardness was increased by 13.15% and 19.78% for CMFs10% and CNFs10% gels, respectively, and the elasticity was increased by 40% and 80%, respectively. At the same concentration (0–10%), the increase in gel hardness, viscoelasticity and immobilised water content was greater in the CNFs-MP group than in the CMFs-MP group. The CNFs-MP group had a tighter gel network, and CNFs had a better potential to improve the gelation performance of MP. 相似文献
9.
Xin Li Yurui Wang Minxuan Xu Yueqin Shi Hemiao Wang Xin Yang Haoting Ying Qi Zhang 《应用聚合物科学杂志》2021,138(19):50406
Polymer electrets have revealed great potential application in electromechanical devices because of the low weight, large quasi-piezoelectric sensitivity, and excellent flexibility. For an electret, a permanent and macroscopic electric field exists on the surface, principally led by a macroscopic electrostatic charge on the surface or a net orientation of polar groups inside the object. Here, progress in the development of polymer electrets is reviewed. After a brief retrospect of the research courses and those typical polymer electrets that are classified into fluorine polymer and nonfluorine polymer, we present a survey on the charging methods, including corona, soft X-ray, contact, thermal and monoenergetic particle beams. The latest representative applications (i.e., power harvesting, sensors, field effect transistors, and biomedicine) based on polymer electrets are also summarized. Finally, we complete this review with a discussion on perspectives and challenges in this field. 相似文献
10.
Fan Deng-Ping Huang Ziling Zheng Peng Liu Hong Qin Xuebin Van Gool Luc 《国际自动化与计算杂志》2022,19(4):257-287
Machine Intelligence Research - This paper aims to conduct a comprehensive study on facial-sketch synthesis (FSS). However, due to the high cost of obtaining hand-drawn sketch datasets, there is a... 相似文献