全文获取类型
收费全文 | 1272篇 |
免费 | 104篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 13篇 |
综合类 | 32篇 |
化学工业 | 91篇 |
金属工艺 | 31篇 |
机械仪表 | 49篇 |
建筑科学 | 36篇 |
矿业工程 | 4篇 |
能源动力 | 69篇 |
轻工业 | 665篇 |
水利工程 | 3篇 |
石油天然气 | 3篇 |
无线电 | 45篇 |
一般工业技术 | 220篇 |
冶金工业 | 6篇 |
原子能技术 | 4篇 |
自动化技术 | 129篇 |
出版年
2024年 | 6篇 |
2023年 | 37篇 |
2022年 | 68篇 |
2021年 | 62篇 |
2020年 | 48篇 |
2019年 | 49篇 |
2018年 | 54篇 |
2017年 | 47篇 |
2016年 | 57篇 |
2015年 | 48篇 |
2014年 | 71篇 |
2013年 | 71篇 |
2012年 | 190篇 |
2011年 | 119篇 |
2010年 | 106篇 |
2009年 | 78篇 |
2008年 | 34篇 |
2007年 | 103篇 |
2006年 | 86篇 |
2005年 | 32篇 |
2004年 | 3篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有1400条查询结果,搜索用时 31 毫秒
21.
Yanqiao Zhao Khanh Tran Margaret Brennan Charles Brennan 《International Journal of Food Science & Technology》2021,56(6):2687-2695
Polyphenols were extracted from five kinds of New Zealand grape pomace (Sauvignon Blanc, Pinot Gris, Gerwurztraminer, Merlot and Pinot Noir) at 30, 50 and 70 °C in an ultrasonic generator. The extraction kinetics for total phenol, anthocyanin and tannin were determined. The results of dynamics study showed that the extraction of total polyphenols, anthocyanin and tannin followed first-order reaction kinetics during the extraction at 30, 50 and 70 °C. The total phenolic content, anthocyanin conten, and tannin content of water–ethanol extracts from grape pomaces were compared, and the parameters in the extraction kinetics equations were determined. The extraction results showed that the Pinot Noir pomace extract had the highest total phenolic content of 59.95 mg GAE g−1 pomace and tannin content of 79.93 mg EE g−1 pomace. The anthocyanin content in Merlot pomace extract was the highest, which was 4.50 CE g−1 pomace. The results might be of great significance for the development of grape pomace or its polyphenol and/or anthocyanin components as an antioxidant source with natural and inexpensive benefits. 相似文献
22.
滚珠丝杠副是精密伺服驱动系统核心零部件,随着丝杠运行,温度升高会导致丝杠单轴伺服系统直线度误差增加。为了明确该误差及其产生规律,建立滚珠丝杠副热误差模型,分别对滚珠丝杠副的热源、温度场以及热误差模型进行了研究。根据滚珠丝杠副的结构特点,确定其内部热源及温度场分布规律,分析热误差的特性。设计实验,检定温度变化前后的直线度误差,设定5 min间隔分段运行,明确温度和直线度误差的变化过程及规律。实验结果表明,随着温度升高,丝杠直线度误差随着丝杠本身的弯曲状态会出现更为明显的弯曲,剔除丝杠自身存在的直线度误差和检定过程中斜率误差后,直线度误差增加了11.4 μm。本文得到丝杠直线度误差随温度变化的规律,可以应用于其他空间驱动系统整体几何误差的检定和补偿,具有较强的工程应用前景。 相似文献
23.
Like Yue Shixue Wang Takuto Araki Yoshio Utaka Yulin Wang 《International Journal of Hydrogen Energy》2021,46(3):2969-2977
Water management of proton exchange membrane fuel cells remains a prominent issue in research concerning fuel cells. In this study, the gas diffusion layer (GDL) of a fuel cell is partially treated with a hydrophobic agent, and the effect of GDL hydrophobicity on the water distribution in the fuel cell is examined. First, the effect of the position of the cathode GDL hydrophobic area relative to the channel on the fuel cell performance is investigated. Then, the water distribution in the fuel cell cathode GDL is observed using X-ray imaging. The experimental results indicate that when the hybrid GDL's hydrophobic area lies on the channel, water tends to accumulate under the rib, and the water content in the channel is low; this improves the fuel cell performance. When the hydrophobic area is under the rib, the water distribution is more uniform, but the performance deteriorates. 相似文献
24.
《International Journal of Hydrogen Energy》2019,44(57):30185-30195
Nowadays, energy shortage is one of the major problems in the world. Photocatalytic hydrogen production is a new type of energy technology with good application prospect. As a new type of photocatalytic semiconductor material, g-C3N4 has attracted much attention as a photocatalyst. By ultrasonic treatment of a mixed solution of g-C3N4 and bovine serum albumin, followed by adding a certain amount of silver nitrate solution and then directly hydrothermal treatment, a special dandelion-like g-C3N4/Ag (D-g-C3N4/Ag) was prepared. The scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction, Fourier transform infrared, fluorescence and physicochemical adsorption methods were used to characterize the morphology and structure of D-g-C3N4/Ag. In addition, the photocatalytic H2 production of D-g-C3N4/Ag with different Ag loadings or in different sacrificial agents and different pH conditions were investigated. The results indicated that when triethanolamine was used as sacrificial agent, photocatalytic hydrogen efficiency was the best, and the rate of photocatalytic hydrogen production reached 862 μmol g−1 h− 1 as the Ag loading was 4%. 相似文献
25.
26.
《International Journal of Hydrogen Energy》2022,47(6):4062-4074
In this work, coupling effects of water content, temperature, oxygen density, and polytetrafluoroethylene (PTFE) loading on oxygen transport through an ionomer thin film on a platinum surface in a catalyst layer of a proton exchange membrane (PEM) fuel cell are investigated using molecular dynamics approach. Taguchi orthogonal algorithm is employed to comprehensively analyze the coupling effects in a limited number of cases. It is found that the effect of operation temperature is the weakest among the four factors, which has the smallest effect index 14.4. Coupling effects including the PTFE loadings on the oxygen transfer through the ionomer thin film is uncovered. Less PTFE loadings should be beneficial for the oxygen transfer. The chemical potential gradient is considered as the major driven force for the oxygen transport through the ionomer thin film, and oxygen density is the dominating factor, significantly affecting the chemical potential in the thin film. 相似文献
27.
The effective utilization of glycerol, a by-product in the production of biodiesel, into useful chemicals is desirable from the viewpoint of green chemistry. With this in mind, a novel and highly selective route to synthesizing glycerol dimethyl ether (2,3-dimethoxy-1-propanol), a potential fuel additive, from glycerol was proposed. This route uses both glycerol and methanol as starting materials, takes epichlorohydrin as an intermediate product, and utilizes HCl as a recycling agent. Hereinto, the key step of this route is the reaction between epichlorohydrin and methanol to produce 2,3-dimethoxy-1-propanol which is identified by GC–MS, ESI-MS, IR and NMR. The thermodynamics of this reaction was analyzed and the result showed that the thermodynamics of a reaction was favorable and a high product yield was expected. The effect of various parameters such as kind of acid catalyst, molar ratio of epichlorohydrin to methanol, reaction temperature and reaction time was studied. Among various acid catalysts investigated, the acidic ionic liquid [HSO3-b-N(CH3)3]HSO4 exhibited the highest activity and selectivity: conversion of epichlorohydrin of 100% and selectivity of 2,3-dimethoxy-1-propanol of 99% at 393 K, 10 h, an initial pressure of 0.1 MPa and a molar ratio of catalyst:ECH:CH3OH of 0.01:1:5. After the reaction, [HSO3-b-N(CH3)3]HSO4 was separated by vacuum distillation and then reused for the next cycle directly. The results showed that the product selectivity remained at about 94% but the conversion of epichlorohydrin dropped to 75% after being used five times. Subsequently, a reaction mechanism for the synthesis of 2,3-dimethoxy-1-propanol from epichlorohydrin and methanol was proposed. 相似文献
28.
Shu-Lin Ma Shi Ren Yun Yang 《Journal of Inorganic and Organometallic Polymers and Materials》2010,20(1):104-109
Two new complexes, [M2(L)2(bpy)2](ClO4)2 [L = methyl salicylate, bpy = 2,2′-bipyridine, M = Cu (1) and Zn (2)] have been synthesized and structurally characterized by X-ray structure analyses. The centrosymmetric dimeric structure
consists of a binuclear unit, in which M (M = Cu or Zn) atoms are bridged by two phenol oxygen atoms as a μ
2-bridged. The neighboring binuclear units interact with each other by two kinds of weak contacts: one kind is π–π stacking
by π–σ attraction with an edge-to-face C–H···π interaction, and the second type is a H-bonding interaction, which extends
the binuclear unit into a 3D network. Magnetic measurements confirm that 1 presents a very strong intradinuclear ferromagnetic coupling between the copper(II) ions. 相似文献
29.
《Carbon》2014
Gold nanoparticle/graphene oxide hybrids (AuNP/GO) were easily fabricated by a redox reaction between GO and chloroauric acid without using any additional reductant and then used to stabilize Pickering emulsions. Factors affecting the properties of the emulsions were studied, including the HAuCl4/GO mass ratio used to prepare the AuNP/GO, the oil/water ratio, the AuNP/GO concentration, the pH value, and the type and concentration of electrolytes. The emulsions were more stable when stabilized by AuNP/GO made from HAuCl4/GO mass ratios of 0.375–0.5. High pH values and AuNP/GO concentrations that were too high or too low were unfavorable to the stability of the Pickering emulsions. Adding electrolytes to the systems improved the stability of the Pickering emulsions owing to the reduction of repulsive interactions between AuNP/GO sheets. The AuNP/GO stabilized Pickering emulsions were used to prepare AuNP/GO supported polystyrene (PS) microspheres (AuNP/GO@PS) by polymerizing the Pickering emulsion. The catalytic performance of AuNP/GO@PS for the reduction of 4-nitrophenol was then studied. 相似文献
30.