全文获取类型
收费全文 | 20727篇 |
免费 | 1161篇 |
国内免费 | 495篇 |
专业分类
电工技术 | 512篇 |
综合类 | 1059篇 |
化学工业 | 12465篇 |
金属工艺 | 813篇 |
机械仪表 | 314篇 |
建筑科学 | 654篇 |
矿业工程 | 257篇 |
能源动力 | 81篇 |
轻工业 | 1601篇 |
水利工程 | 96篇 |
石油天然气 | 816篇 |
武器工业 | 51篇 |
无线电 | 280篇 |
一般工业技术 | 2800篇 |
冶金工业 | 354篇 |
原子能技术 | 196篇 |
自动化技术 | 34篇 |
出版年
2024年 | 55篇 |
2023年 | 110篇 |
2022年 | 260篇 |
2021年 | 345篇 |
2020年 | 363篇 |
2019年 | 331篇 |
2018年 | 337篇 |
2017年 | 438篇 |
2016年 | 505篇 |
2015年 | 609篇 |
2014年 | 888篇 |
2013年 | 1241篇 |
2012年 | 1619篇 |
2011年 | 1463篇 |
2010年 | 1144篇 |
2009年 | 1226篇 |
2008年 | 1047篇 |
2007年 | 1382篇 |
2006年 | 1472篇 |
2005年 | 1176篇 |
2004年 | 998篇 |
2003年 | 922篇 |
2002年 | 803篇 |
2001年 | 673篇 |
2000年 | 537篇 |
1999年 | 495篇 |
1998年 | 392篇 |
1997年 | 260篇 |
1996年 | 258篇 |
1995年 | 214篇 |
1994年 | 187篇 |
1993年 | 160篇 |
1992年 | 139篇 |
1991年 | 71篇 |
1990年 | 50篇 |
1989年 | 50篇 |
1988年 | 24篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 25篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 20篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1959年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A new method to improve the stability,tensile strength,and heat resistant properties of shape‐memory epoxy resins: Two‐stages curing 下载免费PDF全文
In this article, we design a new thermal curing method: two‐stage curing. The purpose of using this approach is to maintain the excellent shape‐memory property of epoxy resin system after first stage curing, and the material can be folded in small size to storage or transportation and recovery its original shape commodiously by heating temperature. Then, after second stage curing, the stability, glass transition temperature(Tg), and tensile strength of material can be improved effectively. For this aim, a series of mixtures have been prepared. Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), tensile test, scanning electron microscope (SEM), dynamic mechanical analysis (DMA), and fold‐deploy shape‐memory test have been used to characterize the feasibility of two‐stage curing process, curing degree, tensile strength, morphology, thermodynamic properties, and shape‐memory performance of these polymers. DSC results show that two independent curing stages can be achieved successfully. Tensile tests and DMA results suggest that tensile strength and heat resistance have been improved after the second curing stage. SEM results reveal that the addition of latent curing agent do not change the fracture mechanism. Furthermore, the fold‐deploy shape‐memory tests prove that the composites after first stage curing possess eximious shape‐memory property. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39882. 相似文献
82.
Thermosetting systems based on DGEBA epoxy resin and poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (EPE) triblock copolymer were prepared and investigated. Different mixtures were obtained by using different contents of EPE block copolymer in order to study the influence of the modifier on the properties of the final materials. All thermosetting systems were prepared without using any solvent and were cured at ambient temperature, taking into account the lower critical solution temperature (LCST) behavior of the block copolymer. DSC results indicated that the addition of block copolymer affected to the curing reaction time and to the glass transition temperature of the mixtures and also the miscibility of EPE triblock copolymer in the epoxy resin was proved. The morphologies studied by AFM and TEM showed clear nanostructuration up to 25 wt % EPE content. The addition of 5 and 15 wt % of EPE block copolymer led to a considerable improvement in the toughness of the materials. When EPE block copolymer was added to the epoxy resin, the surface became more hydrophilic and the UV–vis transmittance decreased slightly maintaining a high level of transparency. 相似文献
83.
J. Vanerek A. Benesova P. Rovnanik R. Drochytka 《Journal of Adhesion Science and Technology》2014,28(14-15):1405-1417
This article describes the evaluation of the durability of joints composed of wood adherends with a bonded layer of fibre-reinforced polymer (FRP) fabric. Carbon and glass fibres in an epoxy matrix were studied. The main purpose of FRP usage with timber in the construction industry is generally to improve the stiffness/strength of reinforced members without any influence on their service-life or any environmental impact. From the perspective of the timber reinforcement process, optimal dimensional stability during moisture changes in wood should be one of the most important criteria for such joints. Therefore, FRP/wood joints were evaluated with regard to the influence of real external environmental conditions on the bondline over a period of 40?months. During exposure to these conditions, specimen failures and defects were continuously visually evaluated. The decisive factor in this evaluation was bond integrity, verified by the tensile shear strength of the FRP/wood joint. After the experimental study, it was noted that the first 20?months have a significant effect on bondline failure occurrences, which involve decreases in tensile shear strength. In the next 20?months, the FRP/wood bondlines resist other severe hygrothermal stresses without significant strength decreases. An additional observed parameter was the percentage of wood failure in the bonded area of single lap joints, which characterises the mode of failure of the bonded joint. To determine the influence of ageing on adhesive due to ultraviolet radiation and varying temperature, infrared absorption spectroscopy analysis was performed to reveal changes in the macromolecular structure of the epoxy adhesive. Findings showed that UV radiation had a significant influence on the degradation of the adhesive structure. 相似文献
84.
85.
86.
In this work, a modified alkyd resin (basic alkyd resin) was synthesized using maleic anhydride (MAH) to replace part of phthalic anhydride (PA) to achieve the target product acrylate-grafted-alkyd hybrid resin. The resin was then dispersed in water to form water-reducible emulsion. The properties were examined, including the extent of neutralization of final emulsion, ratio of MAH/PA in basic alkyd resin, mole ratio of basic alkyd resin to modified vinyl monomers, mole ratio of vinyl monomers (MMA/St/AA) on water dispersion stability of emulsion, particle size, drying time and mechanical properties. The optimal synthesis conditions produced a final emulsion particle size of 81.1 nm with good storage stability, hydrolytic stability and shorter drying time. The optimized synthesis conditions were identified as 80% neutralization, 1:0.8 mole ratio of basic alkyd resin to modified monomers, 4:3:2 modified monomers MMA/St/AA and 0.18 mole ratio of MAH/PA. 相似文献
87.
为了降低传统脲醛树脂中甲醛的危害,采用了果糖代替甲醛与尿素合成了环保型果糖/尿素树脂,并用合成出的树脂与芦苇纤维复合制备了芦苇纤维板,考察了树脂合成过程中果糖/尿素物质的量之比、反应温度、反应时间、催化剂种类等工艺参数对树脂及芦苇纤维板性能的影响,得到了果糖/尿素树脂的最佳合成工艺,即果糖/尿素/催化剂盐酸的物质的量之比为2.5/1/0.13、反应温度为91℃、反应时间为3 h。在此最佳合成工艺下合成的树脂固含量为65.57%、黏度为73 m Pa·s,由此树脂制备的芦苇纤维板的静曲强度为26.19 MPa,弹性模量为6.13 GPa,完全满足国家标准GB/T 11718–2009的要求。 相似文献
88.
89.
90.