全文获取类型
收费全文 | 5006篇 |
免费 | 570篇 |
国内免费 | 352篇 |
专业分类
电工技术 | 47篇 |
综合类 | 249篇 |
化学工业 | 1886篇 |
金属工艺 | 561篇 |
机械仪表 | 145篇 |
建筑科学 | 183篇 |
矿业工程 | 45篇 |
能源动力 | 192篇 |
轻工业 | 173篇 |
水利工程 | 10篇 |
石油天然气 | 368篇 |
武器工业 | 9篇 |
无线电 | 346篇 |
一般工业技术 | 1109篇 |
冶金工业 | 288篇 |
原子能技术 | 60篇 |
自动化技术 | 257篇 |
出版年
2024年 | 12篇 |
2023年 | 97篇 |
2022年 | 151篇 |
2021年 | 165篇 |
2020年 | 201篇 |
2019年 | 181篇 |
2018年 | 167篇 |
2017年 | 201篇 |
2016年 | 251篇 |
2015年 | 226篇 |
2014年 | 324篇 |
2013年 | 313篇 |
2012年 | 412篇 |
2011年 | 427篇 |
2010年 | 297篇 |
2009年 | 366篇 |
2008年 | 355篇 |
2007年 | 320篇 |
2006年 | 301篇 |
2005年 | 225篇 |
2004年 | 154篇 |
2003年 | 128篇 |
2002年 | 124篇 |
2001年 | 84篇 |
2000年 | 64篇 |
1999年 | 65篇 |
1998年 | 51篇 |
1997年 | 32篇 |
1996年 | 39篇 |
1995年 | 39篇 |
1994年 | 23篇 |
1993年 | 14篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有5928条查询结果,搜索用时 15 毫秒
1.
2.
Hideaki Kaneto Tomohiko Kimura Atsushi Obata Masashi Shimoda Kohei Kaku 《International journal of molecular sciences》2021,22(5)
While there are various kinds of drugs for type 2 diabetes mellitus at present, in this review article, we focus on metformin which is an insulin sensitizer and is often used as a first-choice drug worldwide. Metformin mainly activates adenosine monophosphate-activated protein kinase (AMPK) in the liver which leads to suppression of fatty acid synthesis and gluconeogenesis. Metformin activates AMPK in skeletal muscle as well, which increases translocation of glucose transporter 4 to the cell membrane and thereby increases glucose uptake. Further, metformin suppresses glucagon signaling in the liver by suppressing adenylate cyclase which leads to suppression of gluconeogenesis. In addition, metformin reduces autophagy failure observed in pancreatic β-cells under diabetic conditions. Furthermore, it is known that metformin alters the gut microbiome and facilitates the transport of glucose from the circulation into excrement. It is also known that metformin reduces food intake and lowers body weight by increasing circulating levels of the peptide hormone growth/differentiation factor 15 (GDF15). Furthermore, much attention has been drawn to the fact that the frequency of various cancers is lower in subjects taking metformin. Metformin suppresses the mechanistic target of rapamycin (mTOR) by activating AMPK in pre-neoplastic cells, which leads to suppression of cell growth and an increase in apoptosis in pre-neoplastic cells. It has been shown recently that metformin consumption potentially influences the mortality in patients with type 2 diabetes mellitus and coronavirus infectious disease (COVID-19). Taken together, metformin is an old drug, but multifaceted mechanisms of action of metformin have been unraveled one after another in its long history. 相似文献
3.
4.
Covalent triazine frameworks (CTFs) have been recently employed for visible light-driven photocatalysis due to their unique optical and electronic properties. However, the usually highly hydrophobic nature of CTFs, which originates from their overall aromatic backbone, leads to limitations of CTFs for applications in aqueous media. In this study, we aim to extend the range of the application media of CTFs and design hybrid material of a CTF and mesoporous silica (SBA-15) for efficient photocatalysis in aqueous medium. A thiophene-containing CTF was directly synthesized in mesopores of SBA-15. Due to the high surface area and the added hydrophilic properties by silica, the hybrid material demonstrated excellent adsorption of organic molecules in water. This leads not only to high photocatalytic performance of the hybrid material for the degradation of organic dyes in water, but also for efficient photocatalysis in solvent-free and solid state. Furthermore, the reusability, stability and easy recovery of the hybrid material offers promising metal-free heterogeneous photocatalyst for broader applications in different reaction media. 相似文献
5.
6.
7.
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
8.
9.
合成了具有介孔-大孔双模型分级结构的无定形硅-铝催化剂,利用硅和铝核的固体魔角核磁共振谱,考察了合成样品中硅和铝结构上的原子特征. 相似文献
10.
We determine the exact power of two-prover interactive proof systems introduced by Ben-Or, Goldwasser, Kilian, and Wigderson (1988). In this system, two all-powerful noncommunicating provers convince a randomizing polynomial time verifier in polynomial time that the inputx belongs to the languageL. We show that the class of languages having tow-prover interactive proof systems is nondeterministic exponential time.We also show that to prove membership in languages inEXP, the honest provers need the power ofEXP only.The first part of the proof of the main result extends recent techniques of polynomial extrapolation used in the single prover case by Lund, Fortnow, Karloff, Nisan, and Shamir.The second part is averification scheme for multilinearity of a function in several variables held by an oracle and can be viewed as an independent result onprogram verification. Its proof rests on combinatorial techniques employing a simple isoperimetric inequality for certain graphs: 相似文献