全文获取类型
收费全文 | 6439篇 |
免费 | 328篇 |
国内免费 | 67篇 |
专业分类
电工技术 | 53篇 |
综合类 | 291篇 |
化学工业 | 4307篇 |
金属工艺 | 28篇 |
机械仪表 | 31篇 |
建筑科学 | 379篇 |
矿业工程 | 16篇 |
能源动力 | 26篇 |
轻工业 | 305篇 |
水利工程 | 48篇 |
石油天然气 | 482篇 |
无线电 | 22篇 |
一般工业技术 | 801篇 |
冶金工业 | 14篇 |
原子能技术 | 11篇 |
自动化技术 | 20篇 |
出版年
2024年 | 15篇 |
2023年 | 41篇 |
2022年 | 91篇 |
2021年 | 111篇 |
2020年 | 108篇 |
2019年 | 109篇 |
2018年 | 106篇 |
2017年 | 177篇 |
2016年 | 154篇 |
2015年 | 169篇 |
2014年 | 220篇 |
2013年 | 303篇 |
2012年 | 407篇 |
2011年 | 403篇 |
2010年 | 299篇 |
2009年 | 340篇 |
2008年 | 349篇 |
2007年 | 469篇 |
2006年 | 521篇 |
2005年 | 403篇 |
2004年 | 390篇 |
2003年 | 353篇 |
2002年 | 285篇 |
2001年 | 264篇 |
2000年 | 158篇 |
1999年 | 132篇 |
1998年 | 76篇 |
1997年 | 54篇 |
1996年 | 50篇 |
1995年 | 61篇 |
1994年 | 49篇 |
1993年 | 32篇 |
1992年 | 35篇 |
1991年 | 22篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 11篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 13篇 |
排序方式: 共有6834条查询结果,搜索用时 15 毫秒
101.
Ensuring the geometrical stability of organic coatings is a key challenge for steel/polymer composites produced by the automotive industry to reduce the cars' weight. During the thermal treatment of painting, which exceeds the melting temperature of the organic part of the laminated film, polymer shrinkage may occur. It induces uncovered parts of the steel sheet which would present negative corrosion behavior in use. Two original and innovative experiments were presented. They enable to measure the deformation induced by the shrinkage and then to identify the microstructural mechanisms responsible for its appearance. Main results show strong influences of the macromolecular chains orientation induced by the film extrusion process and of the postheating parameters used to perform the painting curing. Raman spectroscopy and differential scanning calorimetry are used both to perform analysis of the microstructure evolution during heating treatments in terms of crystals melting, crystalline macromolecular chains disorientation, and volume damage healing. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
102.
Poly(n‐octadecyl acrylate) (PnOA) was used as an interfacial compatibilizer for improving the performance of polypropylene/alumina trihydrate (PP/ATH) composites in this study. The influences of PnOA on the properties of fire‐retardant PP/ATH composites were evaluated by tensile and impact tests, differential scanning calorimetry (DSC), scanning electron microscope (SEM) observation, thermogravimetric analysis, and mass flow rate tests. The results suggested that PnOA significantly improved the mechanical properties and rheological behavior of the PP/ATH composites. SEM observation helped formulate reasons for these differences. A pronounced difference in DSC curves was detected for the composites with and without PnOA when the temperature is near the melt temperature of PnOA. Tentative theoretical explanation was also provided based on related DSC and SEM analysis. PnOA is a promising new compatibilizer for polyolefin composites with aluminum trihydrate as a flame retardant. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
103.
以RPP为研究对象,探讨了POE物料对RPP力学性能的影响,确定了最佳的配比及工艺条件,结果表明:POE物料对RPP具有良好的增韧效果,用改性后的RPP树脂制造中低档汽车保险杠,性能可达到技术指标要求。 相似文献
104.
海南炼化聚丙烯装置采用非对称外给电子体技术生产高速BOPP膜料。利用连续自成核热分级技术对3个样品进行等规度序列分布表征,结果表明3个样品的片晶厚度分布系数为1.07~1.08,样品的Ipeak1/Ipeak2值为1.36~1.58,说明采用非对称外给电子体技术生产的高速BOPP膜料具有较宽的等规度分布,且高等规度组分含量大于低等规度组分含量。与传统的BOPP膜料相比,采用非对称电子体技术生产的高速BOPP膜料不仅具有良好的成膜性,而且还具有较高的挺度。 相似文献
105.
106.
Morphologically dependent alternating‐current and direct‐current breakdown strength in silica–polypropylene nanocomposites 下载免费PDF全文
Timothy Krentz Mohammad M. Khani Michael Bell Brian C. Benicewicz J. Keith Nelson Su Zhao Henrik Hillborg Linda S. Schadler 《应用聚合物科学杂志》2017,134(1)
In this article, we report the synthesis of a new bimodal surface ligand morphology on silica nanoparticles. Combining grafting‐to and grafting‐from approaches, in this study, we demonstrated the efficacy of anthracene surface modification for improving the dielectric breakdown strength (DBS) under alternating‐current and direct‐current conditions and that of a matrix‐compatible polymer brush for controlling the nanofiller (NF) dispersion. Ligand‐modified spherical colloidal SiO2 nanoparticles (~14 nm in diameter) were mixed into polypropylene, and the resulting dispersion was improved over the unmodified particles, as shown with transmission electron microscopy. The results suggest that the electronic structure of the anthracene‐modified particle surface was critical to the improvement in DBS. In addition, the DBS of the composite was shown to depend on the dispersion state of the filler and the mode of stress; this indicated that the individually dispersed nanoparticles were not necessarily the optimal morphology for all stress conditions. Additionally, the precise nature of the matrix‐compatible brush was less important than the NF dispersion it produced. The bimodal grafted architectural design has provided a promising solution for the control of the dispersion and surface properties, especially for high‐molecular‐weight polymer matrices. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44347. 相似文献
107.
Glass fiber reinforced Polypropylene (GFR-PP) is used in manufacturing industries like bicycles, auto bodies, aircraft, and civil applications due to superior properties. Machining of fiber-reinforced plastics is problematic especially when drilling due to their inherent in-homogeneity, anisotropy and limited plastic deformation. Drilling is often required to facilitate the assembly of the parts to get the final products. Surface quality in drilled composites is an essential design characteristic in many situations, such as accurate fits, aesthetic requirements, etc. The present work deals with detailed investigation on the influence of tool materials and machining parameters during drilling of GFR-PP composite material. The study mainly focused on machined surface quality such as surface roughness of the drilled hole and dimensional inaccuracies such as oversize of the hole. The better dimensional and surface quality of drilled hole is observed from solid carbide drill with a spindle speed of 2500?rpm and a feed rate of 0.05?mm/rev. Regression model is developed using experimental data for estimating the surface roughness and oversize. The developed model has high R-sq value which shows the strong relationship between the model and the response variables. The effect of drilling process parameters and associated interactions are discussed in detail. 相似文献
108.
In this article, the equilibrium morphology of a typical polypropylene (PP) impact copolymer (ICP) system is investigated by numerical self-consistent field simulations. The ICP was fractionated using temperature rising elution fractionation (TREF) to obtain the data necessary to define the simulation parameters. The results demonstrated the formation of a stratified droplet structure, in which ethylene content decreases from the center of the droplet toward the PP interface. This structure is shown to be in accordance with observations from transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. The components are confined to a narrow layer whose position is primarily determined by its ethylene content. Leakage into a neighboring layer occurs to a degree that is determined by the component molecular weight and the difference in ethylene content between the layers. Simulations for a range of droplet sizes enable calculation of the interfacial tension. A typical drawback of TREF involves the inability to fractionate the amorphous part, leading to a large difference in ethylene content between the matrix and its neighboring layers. Although this effect is shown not to have a significant influence on the stratified structure, it is shown to have a significant influence on the derived interfacial tension. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
109.
Jian Kang Feng Yang Tong Wu Huilin Li Dongming Liu Ya Cao Ming Xiang 《应用聚合物科学杂志》2012,125(4):3076-3083
Two isotactic polypropylene (iPP) samples (PP-A and PP-B) were obtained by utilizing two different heterogeneous Ziegler–Natta catalysts in a given polymerization system. The molecular structure and conformational behavior of the samples were studied. The results of determination of xylene soluble material (XS) and 13C NMR showed that the average isotacticity of the samples were nearly same. However, the results of high-resolution high-temperature 13C NMR (HRHT 13C NMR) and successive self-nucleation and annealing (SSA) fractionation revealed that the amount of high isotacticity of PP-B was lower than that of PP-A, and the amount of relative medium and low isotacticity of PP-B was higher than PP-A, indicating that the stereodefect distribution of PP-B was more uniform than PP-A. The calculation of average meso sequence length from SSA was found to be in good agreement with that calculated from the results of HRHT 13C NMR. Moreover, Fourier transformation infrared was utilized to study the influence of stereodefect distribution on the conformational behavior of iPP. The result suggested that the molecular conformation of the PP-B was more disordered than PP-A, the regularity of molecular structure for PP-B was lower than that of PP-A. The related action mechanism and the influences of which on crystallization behavior were discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
110.
The toughness of conventional injection-molded isotactic polypropylene bars has been investigated with respect to the notch location and β-nucleating agent. Superior toughness is achieved in the β-nucleated bars with notches near the gate, but is absent in the near-gate bars without β-nucleating agent or in the β-nucleated ones far from the gate. With detailed structural analysis across the sample thickness, it is indicated that in these tough bars, extensive flow close to the surface suppresses the formation of β-form to a large extent but favors the generation of oriented α-form, whereas toward inner region, an opposite tendency is presented with the decay of flow strength and the activation of β-nucleating agent. Allowing that this peculiar hierarchical structure is absent in other two kinds of bars, it is deduced that the cooperative effect of molecular orientation of α-form in the skin layer and rich β-form in the inner region is responsible for the significant toughness enhancement in the β-nucleated bars near the gate. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献