全文获取类型
收费全文 | 770095篇 |
免费 | 124445篇 |
国内免费 | 87262篇 |
专业分类
电工技术 | 76902篇 |
技术理论 | 3篇 |
综合类 | 85208篇 |
化学工业 | 97061篇 |
金属工艺 | 63679篇 |
机械仪表 | 49944篇 |
建筑科学 | 58104篇 |
矿业工程 | 36363篇 |
能源动力 | 22798篇 |
轻工业 | 80258篇 |
水利工程 | 26538篇 |
石油天然气 | 33514篇 |
武器工业 | 11597篇 |
无线电 | 89378篇 |
一般工业技术 | 75647篇 |
冶金工业 | 30398篇 |
原子能技术 | 10688篇 |
自动化技术 | 133722篇 |
出版年
2024年 | 4887篇 |
2023年 | 12647篇 |
2022年 | 26381篇 |
2021年 | 33660篇 |
2020年 | 27769篇 |
2019年 | 28059篇 |
2018年 | 30177篇 |
2017年 | 33801篇 |
2016年 | 31932篇 |
2015年 | 41358篇 |
2014年 | 48237篇 |
2013年 | 53741篇 |
2012年 | 64097篇 |
2011年 | 63726篇 |
2010年 | 60427篇 |
2009年 | 56156篇 |
2008年 | 55971篇 |
2007年 | 54136篇 |
2006年 | 46961篇 |
2005年 | 38622篇 |
2004年 | 32023篇 |
2003年 | 23440篇 |
2002年 | 23444篇 |
2001年 | 20811篇 |
2000年 | 16561篇 |
1999年 | 9722篇 |
1998年 | 6060篇 |
1997年 | 5250篇 |
1996年 | 4791篇 |
1995年 | 4624篇 |
1994年 | 3753篇 |
1993年 | 3347篇 |
1992年 | 3090篇 |
1991年 | 2335篇 |
1990年 | 1852篇 |
1989年 | 1706篇 |
1988年 | 1263篇 |
1987年 | 502篇 |
1986年 | 420篇 |
1985年 | 308篇 |
1984年 | 230篇 |
1983年 | 184篇 |
1982年 | 213篇 |
1981年 | 269篇 |
1980年 | 259篇 |
1979年 | 157篇 |
1976年 | 315篇 |
1975年 | 209篇 |
1972年 | 237篇 |
1960年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
212.
Mani Balamurugan Hui‐Yun Jeong Venkata Surya Kumar Choutipalli Jung Sug Hong Hongmin Seo Natarajan Saravanan Jun Ho Jang Kang‐Gyu Lee Yoon Ho Lee Sang Won Im Venkatesan Subramanian Sun Hee Kim Ki Tae Nam 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(25)
The electrochemical reduction of carbon dioxide (CO2) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO2 to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO2 to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO2 in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions. 相似文献
214.
据不完全统计,从1998年葛锐诉郑州铁路分局至今10余年,铁路部门因公益诉讼站在被告席的次数已不少于10次。这些诉讼在一定程度上推动了中国法治建设的进程。但深究诉讼中原、被告博弈的过程,其中折射出的经济学、社会学及法学问题不容小觑。随着我国改革的全面深化,培育法治信仰、优化法治环境,方能实现法治"中国梦"、促进经济社会和谐发展。 相似文献
215.
Hong Wei Li Li Ya‐Li Ma Ru‐Xue Liu Shuang‐Yan Meng Li‐Tong Niu Zhe Zhang Zhi‐Wang Yang 《火与材料》2019,43(7):868-879
Through the simple precipitation of palygorskite (PGS) by zinc borate (ZB) (to make PGS@ZB) and the decoration of PGS@ZB by dodecylamine (N), a novel organic‐inorganic@inorganic hybrid flame retardant of PGS@ZB‐N was prepared and was incorporated with ethylene vinyl acetate copolymer (EVA) to improve its flame retardance. The structure and morphology of PGS@ZB‐N were characterized by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), and scanning electron microscopy (SEM), and it was confirmed that the PGS@ZB‐N hybrid had been successfully prepared. The flame retardancy and burning behavior of EVA/PGS@ZB‐N/EG (EG = expandable graphite) composite were studied through thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL‐94 (by the vertical burning test), and cone calorimeter test (CCT) characterizations. The prepared EVA/PGS@ZB‐N/EG composite obtained an LOI value of 41.2% with the addition of 30 wt% PGS@ZB‐N/EG. It was found that EVA/PGS@ZB‐N/EG was protected through a gas phase and condensed phase alternating synergistic effect mechanism. 相似文献
216.
The red grape berry pigments, anthocyanins, were characterized in the early 20th century, but investigations of wine pigments were stymied during that era. The question of their identity was a major challenge for wine chemists. A number of techniques showed that the pigments were polymeric in nature. Some structures were postulated by mid-century based on reactions between anthocyanins and condensed tannin, and later postulated wine pigments were observed in model reactions. Some related compounds were then observed in wine. By the end of the 20th century, the ionization of non-volatiles for mass spectrometry opened the door to these compounds. In addition, a new class of compounds was observed, the pyranoanthocyanins, a product of fermentation and aging metabolites with anthocyanins. These compounds possess the pigment stability to SO2 and pH change that is characteristic of aged red wine. Aging experiments show a dynamic situation with shifts in the population of pigment classes over time. The very large number of diverse pigments explains why it has been so difficult to answer the century-old question of the structure of wine pigments. Our current understanding is founded on the use of mass spectral analysis using electrospray and related ionization techniques over the last 25 years. Future progress will rely on more sophisticated analysis of this very complex mixture of substances. © 2019 Society of Chemical Industry 相似文献
217.
218.
Sowoon Seo Yunjeong Song Sun Mi Gu Hyun Kyu Min Jin Tae Hong Hye Jin Cha Jaesuk Yun 《International journal of molecular sciences》2020,21(23)
Background: Epilepsy is a chronic neurological disorder characterized by the recurrence of seizures. One-third of patients with epilepsy may not respond to antiseizure drugs. Purpose: We aimed to examine whether D-limonene, a cyclic monoterpene, exhibited any antiseizure activity in the pentylenetetrazole (PTZ)-induced kindling mouse model and in vitro. Methods: PTZ kindling mouse model was established by administering PTZ (30 mg/kg) intraperitoneally to mice once every 48 h. We performed immunoblot blots, immunohistochemistry (IHC), and high-performance liquid chromatography (HPLC) analysis after the behavioral study. Results: An acute injection of PTZ (60 mg/kg) induced seizure in mice, while pretreatment with D-limonene inhibited PTZ-induced seizure. Repeated administration of PTZ (30 mg/kg) increased the seizure score gradually in mice, which was reduced in D-limonene (10 mg/kg)-pretreated group. In addition, D-limonene treatment increased glutamate decarboxylase-67 (GAD-67) expression in the hippocampus. Axonal sprouting of hippocampal neurons after kindling was inhibited by D-limonene pretreatment. Moreover, D-limonene reduced the expression levels of Neuronal PAS Domain Protein 4 (Npas4)-induced by PTZ. Furthermore, the adenosine A2A antagonist and ZM241385 inhibited anticonvulsant activity and gamma-aminobutyric acid (GABA)ergic neurotransmission-induced by D-limonene. Conclusion: These results suggest that D-limonene exhibits anticonvulsant activity through modulation of adenosine A2A receptors on GABAergic neuronal function. SCH58261相似文献
219.
紫砂壶以造型为基本的载体,通过形神兼备的造型表现出深厚的文化情感,它将自然万物融汇其中,将各种不同的生命、思想和个性呈现其上,使人观壶如同与人交流,产生深刻的情感、精神共鸣,感受到内心的平静,这十分有益于舒缓当代人的精神心理压力,让人们通过泡茶品茗这种生活方式来获得暂时的悠闲,并通过对紫砂壶的把玩来感悟其中的文化内蕴,从而获得自由淡泊的心态,更好地面对生活。本文以紫砂壶“知竹”为例,浅谈其文化意境。 相似文献
220.