全文获取类型
收费全文 | 2220篇 |
免费 | 355篇 |
国内免费 | 77篇 |
专业分类
电工技术 | 11篇 |
综合类 | 236篇 |
化学工业 | 778篇 |
金属工艺 | 24篇 |
机械仪表 | 45篇 |
建筑科学 | 141篇 |
矿业工程 | 29篇 |
能源动力 | 16篇 |
轻工业 | 36篇 |
水利工程 | 30篇 |
石油天然气 | 24篇 |
武器工业 | 5篇 |
无线电 | 51篇 |
一般工业技术 | 144篇 |
冶金工业 | 541篇 |
原子能技术 | 9篇 |
自动化技术 | 532篇 |
出版年
2023年 | 16篇 |
2022年 | 19篇 |
2021年 | 20篇 |
2020年 | 32篇 |
2019年 | 29篇 |
2018年 | 43篇 |
2017年 | 60篇 |
2016年 | 116篇 |
2015年 | 128篇 |
2014年 | 149篇 |
2013年 | 183篇 |
2012年 | 102篇 |
2011年 | 153篇 |
2010年 | 140篇 |
2009年 | 156篇 |
2008年 | 148篇 |
2007年 | 140篇 |
2006年 | 165篇 |
2005年 | 132篇 |
2004年 | 131篇 |
2003年 | 118篇 |
2002年 | 72篇 |
2001年 | 69篇 |
2000年 | 34篇 |
1999年 | 22篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 11篇 |
1993年 | 18篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1966年 | 3篇 |
1962年 | 4篇 |
1959年 | 8篇 |
1958年 | 6篇 |
1957年 | 8篇 |
1956年 | 7篇 |
1955年 | 4篇 |
1954年 | 5篇 |
排序方式: 共有2652条查询结果,搜索用时 31 毫秒
81.
A straightforward method, which is termed novel handspinning, is reported for producing uniaxially aligned sPP nanofibers. As demonstrated by SEM analysis, the morphologies of handspun sPP nanofibers are strongly dependent upon the processing conditions such as spinning method and solvent system. Compared to the normal electrospun sPP nanofibers, the handspun sPP nanofibers show smoother morphologies. FT‐IR analysis demonstrates a significant difference in polymer chain conformation between the handspun and electrospun sPP nanofibers. Moreover, interestingly, the handspun sPP single nanofibers show higher Young's modulus and tensile strength than electrospun sPP single nanofibers.
82.
杨金榜 《重庆理工大学学报(自然科学版)》2014,(12):18-21
以实质蕴涵和逻辑蕴涵为对象,通过对郁慕镛教授和袁正校教授的观点进行比较,对逻辑学里的一个非常重要的概念——蕴涵进行了分析和讨论,澄清关于实质蕴涵和逻辑蕴涵的若干误解。 相似文献
83.
The structure and properties of HDPE/UHMWPE blends prepared through a pan‐milling reactor in solid state at ambient temperature were compared with the blends made by melt mixing. The changes of structure and properties of the blends were investigated by FTIR, melt flow index, mechanical properties, dynamic rheological measurement, DSC, and WAXD. DSC measurement illustrated that after pan‐milling treatment, the half‐width of the melting temperature became smaller. The more content of UHMWPE added in the blend, the more evident change was observed. Combined with the dynamic rheological analysis, it was proved that, the pan‐milling treatment can improve the compatibility of the HDPE/UHMWPE blends. X‐ray diffraction analysis showed that after pan‐milling treatment some ordered structure could be induced, but after heat treatment, the induced crystalline structure disappeared. The tensile properties of pan‐milled HDPE/UHMWPE blends also achieved improvement after pan milling treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39916. 相似文献
84.
85.
Investigation on the morphology and tensile behavior of β‐nucleated isotactic polypropylene with different stereo‐defect distribution 下载免费PDF全文
Hongmei Peng Bin Wang Jinggang Gai Jinyao Chen Feng Yang Ya Cao Huilin Li Jian Kang Ming Xiang 《应用聚合物科学杂志》2014,131(6)
Large amount of work has been published on the tacticity‐properties relationship of isotactic polypropylene (iPP). However, the stereo‐defect distribution dependence of morphology and mechanical properties of β‐nucleated iPP (β‐iPP) is still not clear. In this study, two different iPP resins (PP‐A and PP‐B) with similar average isotacticity but different uniformities of stereo‐defect distribution were selected, their β‐iPP injection molding specimens were prepared, and the morphology evolution and tensile behaviors were studied by means of differential scanning calorimetry (DSC), 2D wide‐angle X‐ray diffraction (2D‐WAXD) and scanning electron microscope (SEM). DSC results showed that with the same concentration of β‐nucleating agent (0.3 wt % WBG‐II), PP‐B with more uniform stereo‐defect distribution exhibited more amount of β‐phase than that of PP‐A with less uniform stereo‐defect distribution, indicating that PP‐B is more favorable for the formation of β‐phase. SEM results showed that PP‐B formed more amount of β‐crystals with relatively high structural perfection, while in PP‐A a mixed morphology of α‐ and β‐phase with obviously higher amount of structural imperfection emerges. The results of room‐temperature tensile test indicated that the yield peak width of PP‐B was obviously wider, and the elongation at break of PP‐B was higher than that of PP‐A, showing a better ductile of PP‐B. The morphology evolution results of SEM, 2D‐WAXD and DSC suggest that, a combination of lamellar deformation and amorphous deformation occurred in PP‐A, while only amorphous deformation mainly took place in PP‐B, which was thought to be the reason for the different tensile behaviors of the samples. In the production of β‐PP products via injection molding, the uniformity of stereo‐defect distribution was found to be an important factor. PP with more uniform distribution of stereo‐defect favors the formation of large amount of β‐phase with high perfection, which exhibit superior ductile property. The related mechanism was discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40027. 相似文献
86.
In situ biaxial stretching for the platelet formation of an ethylene–vinyl alcohol copolymer through multistage stretching extrusion and its effect on the gas‐barrier properties of polyethylene 下载免费PDF全文
The morphological evolution of ethylene–vinyl alcohol copolymer (EVOH) and its effect on the gas‐barrier properties of high‐density polyethylene (HDPE) were investigated. HDPE/EVOH blends were prepared through a multistage stretching extrusion, which combined an assembly of force‐assembling elements (FAEs) with an extruder. Scanning electron microscopy confirmed that with an increasing number of FAEs, the biaxial‐stretching field existing in each FAE transformed the dispersed EVOH phase into well‐defined platelets along the flowing plane. Dynamic rheological results further revealed that the formation of the platelets enlarged the interfaces between the dispersed barrier phase and the matrix; this not only led to the decline of the complex viscosity but also created more tortuous paths for the diffusion of gas molecules. Compared with that of the non‐FAE specimen blended with 25 wt % EVOH, the oxygen permeability coefficient decreased more than one order of magnitude when one FAE was applied. The structural model for permeability indicated that the enhanced barrier resulted from the increased tortuosity of the diffusion pathway, which was provided by the aligned high‐aspect‐ratio platelets. Compared with the previous biaxial‐stretching method, multistage stretching extrusion provided a simple and economical way to generate a laminar structure of the dispersed phase in the matrix phase without the application of an external stretching force. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40221. 相似文献
87.
《Journal of the European Ceramic Society》2014,34(2):533-539
Equilibrium phase relations in the system CaO·SiO2Na2O·SiO2Na2O·Al2O3·6SiO2 at 40–80 wt% Na2O·Al2O3·6SiO2 composition range have been experimentally studied at temperatures between 800 °C and 1200 °C. The liquidus temperature was determined with differential scanning calorimetry. The equilibrated samples were quenched with pressurized nitrogen, and examined with electron probe X-ray microanalysis and X-ray diffraction for identification of microstructure and phase relations. Five primary phase fields, CaO·SiO2, Na2O·SiO2, Na2O·2CaO·3SiO2, 2Na2O·CaO·3SiO2 and Na2O·Al2O3·6SiO2 were established. The ternary eutectic point of CaO·SiO2, Na2O·2CaO·3SiO2 and Na2O·Al2O3·6SiO2 was determined to be at 1030 °C with the composition of 29.0 wt% CaO·SiO2, 12.0 wt% Na2O·SiO2 and 59.0 wt% Na2O·Al2O3·6SiO2. Peritectic reaction of Na2O·2CaO·3SiO2, 2Na2O·CaO·3SiO2 and Na2O·Al2O3·6SiO2 occurred at 930 °C with the composition of 13.0 wt% CaO·SiO2, 29.0 wt% Na2O·SiO2 and 58.0 wt% Na2O·Al2O3·6SiO2. The liquidus surface projection of the ternary system has been constructed in the composition region important for the bottom ash application. 相似文献
88.
Structure and mechanical properties of crosslinked glycidyl azide polymers via click chemistry as potential binder of solid propellant 下载免费PDF全文
Depending upon the advantages of high efficiency, insensitivity to humidity and so on, the reaction of azide groups in glycidyl azide polymers (GAP) with alkynyl compounds has been used as a substitute of the urethane curing strategy to develop GAP‐based binder for solid propellant. In this work, an alkynyl compound of dimethyl 2,2‐di(prop‐2‐ynyl)malonate (DDPM) reacted with GAP to produce new crosslinked materials under the catalysis of Cu(I)Cl at ambient temperature, and showed great potential as a binder in composite propellant. As the feeding molar ratio of DDPM vs. GAP increased from 1 : 1 to 5 : 1, the crosslinking densities of as‐prepared materials gradually increased, together with simultaneous enhancement of Young's modulus and tensile strength. The breaking elongation showed the maximum value of ca. 82% when the feeding molar ratio of DDPM vs. GAP was 3 : 1. In addition, with an increase of the crosslinking densities, the glass transition temperatures of as‐prepared materials significantly increased from ?43.9°C to ?5.1°C while the mechanical loss peaks also gradually broadened and shifted up to high temperature, and even presented two peaks at the feeding molar ratio of DDPM vs. GAP higher than 4 : 1. It indicated that the formation of triazole‐based network resulted in structural heterogeneity in the as‐prepared materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40636. 相似文献
89.
EDTA and pH‐sensitive crosslinking polymerization of acrylic acid, 2‐acrylamidoglycolic acid,and 2‐acrylamide‐2‐methyl‐1‐propanesulfonic acid 下载免费PDF全文
Network formation was monitored by shear storage modulus (G′) during free radical crosslinking polymerization to investigate the effects of pH and ethylenediaminetetraacetic acid (EDTA; a complex agent). Three types of acrylic monomers, acrylic acid (AAc), 2‐acrylamidoglycolic acid (AmGc), and 2‐acrylamido‐2‐methyl propanesulfonic acid (AmPS), were polymerized in the presence of a crosslinking agent. The ratio of crosslinking agent (methylene bis‐acrylamide; MBAAm) to monomer was varied as: 0.583 × 10?3, 1.169 × 10?3, 1.753 × 10?3, and 2.338 × 10?3. G′ of the hydrogel in crosslinking polymerizations of AAc and AmPS was effectively increased by addition of EDTA, which was not the case for the crosslinking polymerization of AmGc. The order of magnitude of G′ differed based on the acidity of monomer. The maximum values of G′ in crosslinking polymerizations of AAc, AmGc, and AmPS were ~20,000 Pa, 6000 Pa, and 400 Pa, respectively. G′ varied linearly with the molecular weight between crosslinks (Mwc). pH and EDTA‐complex affected the rate of intramolecular propagation during crosslinking polymerization. Our results indicated that G′ was primarily affected by the following factors in the order: (1) acidity of monomer, (2) Mwc, and (3) physical interactions induced by pH and EDTA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41026. 相似文献
90.
Processing behavior and mechanical properties of autopolymerizing hypoallergenic denture base polymers 下载免费PDF全文
Driven by the phenomenon of increasing irritations and allergic reactions of dental prosthesis carriers preferably due to residual methyl methacrylate monomer in conventional dental materials, autopolymerizing hypoallergenic denture base polymers were prepared as two‐component materials in the shape of paste/paste‐ or powder/liquid systems. The processing behavior of these materials was investigated regarding the processing and solidification times also in dependence on the polymerization catalyst concentration, whereas the whole processing and curing characteristics and the final polymer properties were evaluated by dynamic mechanical analysis in shear mode in the temperature range from ?145°C to 200°C. The mechanical properties of the hypoallergenic denture base polymers were validated regarding stiffness (flexural modulus E') and fracture toughness (maximum factor of loading intensity , total work of fracture ) and the effects of monomer composition, kind of resin powder, impact modification by the liquid component, and water immersion on these properties were investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41378. 相似文献