全文获取类型
收费全文 | 1005篇 |
免费 | 41篇 |
国内免费 | 31篇 |
专业分类
电工技术 | 13篇 |
综合类 | 41篇 |
化学工业 | 497篇 |
金属工艺 | 31篇 |
机械仪表 | 44篇 |
建筑科学 | 16篇 |
矿业工程 | 4篇 |
能源动力 | 25篇 |
轻工业 | 1篇 |
石油天然气 | 3篇 |
武器工业 | 9篇 |
无线电 | 99篇 |
一般工业技术 | 257篇 |
冶金工业 | 8篇 |
原子能技术 | 15篇 |
自动化技术 | 14篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 27篇 |
2016年 | 38篇 |
2015年 | 24篇 |
2014年 | 43篇 |
2013年 | 86篇 |
2012年 | 76篇 |
2011年 | 87篇 |
2010年 | 53篇 |
2009年 | 73篇 |
2008年 | 63篇 |
2007年 | 58篇 |
2006年 | 69篇 |
2005年 | 49篇 |
2004年 | 43篇 |
2003年 | 28篇 |
2002年 | 36篇 |
2001年 | 24篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1989年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有1077条查询结果,搜索用时 171 毫秒
81.
A series of poly(methyl methacrylate-co-methacrylamide-co-tricyclodecyl methacrylate) (PMMA-co-PMAAM-co-PTCM) copolymers possessing high glass transition temperatures and high transparency are prepared. By incorporating the aliphatic tricyclodecyl methacrylate moiety into the PMMA-co-PMAA main chain results in high glass transition temperature and high transparency of PMMA-based polymeric material. The TCM content affects the fraction of hydrogen bonding in these terpolymers, small content of TCM does not sacrifice the fraction of hydrogen-bonded association in and does not cause Tg decrease. The extent of free amide group plays the major role in dictating moisture absorption of terpolymers. The incorporation of TCM significantly reduces the moisture absorption of terpolymers due to its hydrophobic and bulky tricyclodecyl group. In addition, the TCM plays the role of inert diluent to convert portion of the strong self-associated hydrogen bonded amide groups into inter-associated hydrogen bonding between carbonyl groups of ester units and MAAM. 相似文献
82.
本文研究了激光诱导的周期性表面结构(LIPSS)在聚甲基丙烯酸甲酯(PMMA)薄膜表面的形成过程。在导电玻璃衬底上制备得到PMMA薄膜,经p偏振的XeCl准分子激光照射后形成周期性的褶皱结构。用原子力显微镜(AFM)观察发现,形成的褶皱结构周期具有纳米量级,且当引入外加电场时,褶皱形成所需的激光脉冲数减少到2。当外加电压增加到30V时,褶皱的周期间隔明显减小,LIPSS变得不可控,出现了柱状的自组织结构。与直接用准分子激光照射的薄膜样品相比,外加辅助电压的引入改变了PMMA样品表面褶皱结构形成的时间和周期大小,褶皱形成的内部驱动力也发生了变化。 相似文献
83.
介绍了聚甲基丙烯酸甲酯(PMMA)液体现场浇筑膜的概念和性能,对其特点、应用前景和注意事项等进行了讨论. 相似文献
84.
《International Journal of Hydrogen Energy》2023,48(32):11899-11913
The development of sustainable processes for the recycling of plastic is a major environmental issue to reduce the pollution by this kind of waste. The electro-oxidation of plastic wastes in electrolysers powered by renewable energies is a promising option to produce hydrogen at low temperature while diminishing the energy demand compared to Oxygen Evolution Reaction (OER). Poly (methyl-methacrylate) (PMMA) particles, a widely used polymer, were dissolved (0.1–2% wt.) in an isopropanol(IPA)/H2O binary solvent and electro-oxidized on Pt/C-based electrodes in a liquid batch electrochemical cell at 70 °C in acidic media. Despite the dissolution strategy, polymer macromolecules partially block the accessibility of the active sites of a commercial electrode and strongly degrades its electrochemical performances mainly linked to IPA electro-oxidation. The preparation of a more porous electrode supported on carbon paper was found to strongly hinder this deactivation. Furthermore, the electrooxidation of PMMA or PMMA-derived molecules can be performed during cyclic voltammetries up to 1.4 V and chrono-amperometries at 1.4 V. 相似文献
85.
Although well studied, there are still interesting features about the ignition and steady burning rate behaviour of PMMA when heated by thermal radiation. In this contribution, the dependence on external heat flux of ignition delay time and steady mass flux of PMMA are investigated numerically. Ignition is modelled by the critical mass flux criterion. The heat transfer model includes effects of heat lost by out gassing, change of volume during degradation and absorption of radiation in both condensed and gaseous phases. Model results are compared to experimental data for both ignition delay time and quasi-steady mass flux across a range of heat fluxes from 20 to 210 kW m−2 and the importance of both gas-phase and condensed-phase radiation absorption effects are discussed. 相似文献
86.
Djahida Lerari Sophie Peeterbroeck Samira Benali Ahmed Benaboura Philippe Dubois 《Polymer International》2010,59(1):71-77
Nanocomposites of poly(methyl methacrylate) (PMMA) filled with 3 wt% of modified natural Algerian clay (AC; montmorillonite type) were prepared by either in situ polymerization of methyl methacrylate initiated by 2,2′‐azobisisobutyronitrile or a melt‐mixing process with preformed PMMA via twin‐screw extrusion. The organo‐modification of the AC montmorillonite was achieved by ion exchange of Na+ with octadecyldimethylhydroxyethylammonium bromide. Up to now, this AC montmorillonite has found applications only in the petroleum industry as a rheological additive for drilling muds and in water purification processes; its use as reinforcement in polymer matrices has not been reported yet. The modified clay was characterized using X‐ray diffraction (XRD), which showed an important shift of the interlayer spacing after organo‐modification. The degree of dispersion of the clay in the polymer matrix and the resulting morphology of nanocomposites were evaluated using XRD and transmission electron microscopy. The resulting intercalated PMMA nanocomposites were analysed using thermogravimetric analysis and differential scanning calorimetry. The glass transition temperature of the nanocomposites was not significantly influenced by the presence of the modified clay while the thermal stability was considerably improved compared to unfilled PMMA. This Algerian natural montmorillonite can serve as reinforcing nanofiller for polymer matrices and is of real interest for the fabrication of nanocomposite materials with improved properties. Copyright © 2009 Society of Chemical Industry 相似文献
87.
S. M. Sayyah M. A. EI-Ahdal Z. A. El-Shafiey M. El-Sockary U. F. Kandil 《Journal of Polymer Research》2000,7(2):97-106
Anionic solution polmerization studies of benzylidene malononitrile, benzylidene ethyl cyanoacetate and their para chloro
derivtives in dimethyl formamide (DMF) as a reaction medium using pipridene as initiator under nitrogen atmosphere at 100
°C were carried out. Infrared, 1H NMR and ultraviolet-visible (UV-Vis) spectroscopic studies for the obtained polymers were investigated. The effect of γ-irradiation
on PMMA films doped with 1 % of the benzylidene polymers was investigated by uv-vis spectroscopy. A change in the intensity
of absorption bands with increasing irradiation dose was recorded. It is suggested that PMMA films doped with this type of
benzylidene polymer can be used as dosimeter. 相似文献
88.
The effect of changing environmental conditions on the coupling efficiency of a prism–film coupler is studied for polymer waveguides. A large shift of the coupling efficiency is observed subject to environmental changes. Two processes, change of water content and loss of residual solvent in the polymer waveguides, lead to the efficiency change of the prism coupler. Experimental results show that the index change in the waveguide film is the dominant reason behind the efficiency change. Variation of water content in polymer material is the key contribution to the index change. 相似文献
89.
A fluorescence method was adapted to measure moisture‐uptake kinetics in films of poly(methyl methacrylate), and data were interpreted in the context of a Fickian diffusion model. The films, 2–60 μm thick, were supported on acid‐etched microscope slides. They were compared with several freestanding slabs about 1 mm thick. The moisture diffusion in the slabs was Fickian with a diffusivity of 3.2 × 10?9 cm2/s. The apparent Fickian diffusivity in the films decreased substantially with decreasing film thickness; however, a careful examination revealed that the initial moisture uptake was governed by a thickness‐independent diffusivity for a wide range of film thicknesses. This suggested that the appearance of non‐Fickian behavior originated within about a micrometer of the buried interface, possibly as a result of water accumulation beneath the film or slight thickness variations. Moisture uptake in the thickest films was more rapid than in the slabs, most likely because of residual thermal stresses. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2463–2471, 2002 相似文献
90.
Tatsuki Kitayama Nobutaka Fujimoto Takatsune Yanagida Koichi Hatada 《Polymer International》1994,33(2):165-170
Polymerization of methyl methacrylate (MMA) by isotactic poly(methyl methacrylate) (PMMA) living anion, prepared with t-C4H9MgBr in toluene at ?60°C, was carried out at ?78°C in the presence of trialkylaluminiums (R3Al; R = CH3, C2H5, and n-C4H9) to obtain a stereoblock PMMA, isotactic PMMA-block-syndiotactic PMMA. Among the R3Als, (CH3)3Al gave most effectively the steroblock PMMA with narrow molecular weight distribution. The fraction of rr triad in the syndiotactic PMMA block increased with increase in the ratio of Al/Mg and reached about 76% at a ratio of Al/Mg ≥ 6. The method was also used to prepare stereoblock copolymer comprising isotactic PMMA block and syndiotactic block of butyl methacrylate. Stereocomplex formation and solution viscosity of the stereoblock PMMA were also studied. 相似文献