全文获取类型
收费全文 | 26308篇 |
免费 | 3165篇 |
国内免费 | 2100篇 |
专业分类
电工技术 | 1586篇 |
综合类 | 2050篇 |
化学工业 | 2386篇 |
金属工艺 | 578篇 |
机械仪表 | 2749篇 |
建筑科学 | 377篇 |
矿业工程 | 199篇 |
能源动力 | 293篇 |
轻工业 | 365篇 |
水利工程 | 174篇 |
石油天然气 | 379篇 |
武器工业 | 211篇 |
无线电 | 12781篇 |
一般工业技术 | 3976篇 |
冶金工业 | 367篇 |
原子能技术 | 438篇 |
自动化技术 | 2664篇 |
出版年
2024年 | 38篇 |
2023年 | 387篇 |
2022年 | 505篇 |
2021年 | 715篇 |
2020年 | 824篇 |
2019年 | 640篇 |
2018年 | 693篇 |
2017年 | 1002篇 |
2016年 | 952篇 |
2015年 | 1151篇 |
2014年 | 1573篇 |
2013年 | 1802篇 |
2012年 | 1969篇 |
2011年 | 1922篇 |
2010年 | 1388篇 |
2009年 | 1403篇 |
2008年 | 1448篇 |
2007年 | 1740篇 |
2006年 | 1644篇 |
2005年 | 1481篇 |
2004年 | 1223篇 |
2003年 | 1245篇 |
2002年 | 923篇 |
2001年 | 982篇 |
2000年 | 755篇 |
1999年 | 547篇 |
1998年 | 426篇 |
1997年 | 356篇 |
1996年 | 336篇 |
1995年 | 246篇 |
1994年 | 240篇 |
1993年 | 230篇 |
1992年 | 181篇 |
1991年 | 156篇 |
1990年 | 134篇 |
1989年 | 108篇 |
1988年 | 45篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 35篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 7篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Tunable‐focus microlenses are urgently required for compact optical products to replace digital zoom and obtain high‐quality images. An electrically controllable tunable‐focus negative microlens is proposed, which is based on an electroactive poly(vinyl chloride) gel plasticized by ecofriendly dioctyl terephthalate. The anode and cathode of the microlens are simply assembled on the same side of the electrorheological elastomer, which greatly saves space and allows the thickness of the proposed microlens to be less than 1 mm. By applying voltages ranging from 0 to 1000 V, the stable focus of the microlens is interestingly able to vary as wide as from –∞ to ?21.3 mm correspondingly. The proposed microlens is simple and thin but is flexible and stable and has a wide range of the focus variation, showing promising applications in minielectric and optical devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46136. 相似文献
82.
Nano crystalline pure and Mg doped ceriaparticles were synthesized by simple chemical co-precipitation method using cerium nitrate hexahydrate as a source material and magnesium nitrate as doping precursor at room temperature. The effect of doping were investigated by X-ray diffraction pattern(XRD), FT-Raman,fourier transform infrared spectroscopy(FTIR), Ultraviolet spectroscopy(UV), photoluminescence spectroscopy(PL), field emission scanning electron microscope(FESEM) and high resolution transmission electron microscopy with energy dispersive spectroscopy (HRTEM &EDS). The X-ray diffraction pattern and FT-Raman studies showed that the prepared samples were nano particulates with cubic fluorite structure. The XRD pattern analysis showed that the size of the particles ranged from 13 to 20?nm, however 4?wt% Mg doping results in reduction of particle size compared with other doping concentrations. The effects of Mg concentration on various structural parameters of the prepared samples were also determined. The slight blue shift observed upon doping in UV–Vis absorption region around 330–360nmrecorded for reduction in particle size. The FTIR unveils the presence of Metal oxygen bonds below 700?cm?1in the prepared samples. All samples showed a broad emission band at 430?nm with linearly increasing intensity with respect to dopant concentrations. The Spherical morphology with weak agglomeration was identified through FESEM and HRTEM analysis. The elemental analysis of Ce, O and Mg were confirmed through EDS analysis. 相似文献
83.
Polymers beyond standard optical fibres – fabrication of microstructured polymer optical fibres 下载免费PDF全文
Eneko Arrospide Gaizka Durana Mikel Azkune Gotzon Aldabaldetreku Iñaki Bikandi Leire Ruiz‐Rubio Joseba Zubia 《Polymer International》2018,67(9):1155-1163
This paper reports the overall fabrication process of microstructured polymer optical fibres (mPOFs). mPOF fabrication involves a two‐step process: on the one hand, the design and creation of a preform containing a large‐scale version of the desired fibre and, on the other, the precise heating and drawing of the preform to the final fibre. The preforms are produced either by an improved drilling technique or by capillary stacking. For a correct and accurate drawing of the fibre, a controlled and precise heating unit has to be designed, an issue that will be explained in detail in this work. The quality and optical performance of the final mPOF depends strongly on key factors such as the preform annealing, the accuracy of the technique selected for the creation of the preform structure, the heating stage, as well as on the drawing parameters. All of them are analysed in detail and some drawn mPOFs of interest are reported as well. © 2018 Society of Chemical Industry 相似文献
84.
Yingnan Zhu Jiamin Zhang Jiayin Song Jing Yang Zheng Du Weiqiang Zhao Hongshuang Guo Chiyu Wen Qingsi Li Xiaojie Sui Lei Zhang 《Advanced functional materials》2020,30(6)
Diabetic ulcer is the most common kind of chronic wound worldwide. Though great efforts have been devoted, diabetic ulcer still remains as a challenge that requires constant monitoring and management. In this work, a multifunctional zwitterionic hydrogel is developed to simultaneously detect two fluctuant wound parameters, pH and glucose level, to monitor the diabetic wound status. A pH indicator dye (phenol red) and two glucose sensing enzymes, glucose oxidase (GOx) and horseradish peroxidase (HRP), are encapsulated in the anti‐biofouling and biocompatible zwitterionic poly‐carboxybetaine (PCB) hydrogel matrix. The visible images are collected by a smartphone and transformed into RGB signals to quantify the wound parameters. Results show that the activity and stability of both two enzymes are improved within PCB hydrogel, and the Kcat/Km value of PCB‐HRP is ≈5.5 fold of free HRP in artificial wound exudate. This novel wound dressing can successfully monitor the pH range of 4–8 and glucose level of 0.1–10 × 10?3 m . Meanwhile, it also provides a moist healing environment that can promote diabetic wound healing. This multifunctional wound dressing may open vistas in chronic wound management and guide the diabetes treatment in clinical applications. 相似文献
85.
采用阴极充氢和真空拉伸方法,研究了硼含量对氢原子在有序态Ni_3Fe合金中扩散的影响。结果表明,当合金中硼含量C_B≤0.06%(质量分数)时,氢原子在有序态Ni_3Fe合金中的扩散系数随C_B的增加而逐渐降低,而扩散激活能逐渐增大。当C_B0.06%后,氢原子的扩散系数随C_B的增加而变化很小,而扩散激活能略有减小。原子探针层析方法证实了硼原子在有序态Ni_3Fe合金中晶界处发生偏聚。对比研究硼含量对有序态Ni_3Fe合金中氢扩散系数及对合金在氢气环境中氢脆因子的作用,确认硼原子降低有序态Ni_3Fe合金在氢气环境中的氢脆敏感性的机理,是硼原子降低了氢原子在合金中的沿晶扩散系数。 相似文献
86.
Mengting Guo Chongyun Shao Yang Zhang Jingbo Yu Yan Jiao Malgorzata Guzik Georges Boulon Jinjun Ren Lili Hu 《Journal of the American Ceramic Society》2020,103(8):4275-4285
The homogeneous Yb3+/Al3+/B3+-co-doped silica glasses were prepared via a sol-gel method. The impact of B2O3 addition on the physical and optical properties and network structure was systematically studied. The network structure was investigated by the Fourier Transform Infrared (FT-IR), Raman spectra, and Solid State Nuclear Magnetic Resonance (SSNMR). Herein, B2O3 addition can continuously decrease the refractive index and density. When B2O3 is lower than 2 mol%, B2O3 addition can obviously decrease the scalar crystal field parameters, Yb3+ asymmetry degree, Yb3+ cross-sections, due to the generation of Yb–O–B bonds at the cost of partial Yb–O–Al/Si ones. When B2O3 is more than 2 mol%, FT-IR, Raman spectra, and SSNMR results indicate that further increased B atoms prefer to connect with Si and Al rather than Yb. Consequently, the above parameters are basically unchanged. Based on the results, an intuitive model of structure and properties evolution during the substitution of SiO2 by B2O3 has been established. 相似文献
87.
Guoqiang Yi Bingchu Mei Weiwei Li Jinghong Song Zuodong Liu Zhiwei Zhou Liangbi Su 《Journal of the American Ceramic Society》2020,103(1):279-286
Pr3+, Gd3+ co-doped SrF2 transparent ceramic, as the potential material for visible luminescent applications, was prepared by hot-pressing of precursor nanopowders. The microstructure, phase compositions, and in-line transmittance, as well as the photoluminescence properties were investigated systematically. Highly optical quality Pr,Gd:SrF2 transparent ceramic with nearly pore-free microstructure was obtained at 800°C for 1.5 hours. The average in-line transmittance of the x at.% Pr, 6 at.% Gd:SrF2 (x = 0.2, 0.5, 1.0, 2.0) transparent ceramics reached to 87.3 % in the infrared region. The photoluminescence spectra presented intense visible light emissions under the excitation of 444 nm, the main intrinsic emission bands located at 483 and 605 nm, which were attributed to the transitions of Pr3+: 3P0 → 3H4 and 1D2 → 3H4, respectively. With the co-doping of Gd3+ ions, the emission intensity of the Pr:SrF2 transparent ceramic was greatly enhanced. All the emission bands of x at.% Pr, 6 at.% Gd:SrF2 transparent ceramics exhibited the highest luminescence intensity with the 1.0 at.% Pr3+ doping concentrations, whereas the lifetimes decreased dramatically with the Pr3+ doping contents increasing from 0.2 to 2.0 at.% due to its intense concentration quenching effect. The 1 at.% Pr, 6 at.% Gd:SrF2 transparent ceramic is a promising material for visible luminescent device applications. 相似文献
88.
George L. Burton Sandrine Ricote Brendan J. Foran David R. Diercks Brian P. Gorman 《Journal of the American Ceramic Society》2020,103(5):3217-3230
Dual phase oxide membranes have shown promising hydrogen permeation fluxes in syngas applications due to their high mixed proton electron conduction (MPEC). However, the conductivity of grain boundaries can be many orders of magnitude lower than that of the bulk and so limits the total conductivity and hydrogen permeation. In this study, the three-dimensional nanoscale oxygen and cation distributions around grain and phase boundaries in a BaCe0.8Y0.2O3-δ-Ce0.8Y0.2O2-δ (BCY-YDC) membrane were quantified by atom probe tomography (APT) and related to average grain boundary conductivity measured by electrochemical impedance spectroscopy (EIS). Segregation varied among the general high-angle grain boundaries analyzed, but no trend from orientation analysis was determined. Correlative APT and electron energy loss spectroscopy (EELS) of one YDC grain boundary revealed composition and cerium valence information, respectively, allowing for the determination of vacancies at the grain boundary. While a specific MPEC membrane is characterized, the results are relevant to proton and electron conduction in a number of technologically important ceramics. 相似文献
89.
Alex Gansen Martin Řehoř Clemens Sill Patrycja Polińska Stephan Westermann Jean Dheur Jack S. Hale Jörg Baller 《应用聚合物科学杂志》2020,137(24):48806
An optical method allowing the characterization of melt flow instabilities typically occurring during an extrusion process of polymers and polymer compounds is presented. It is based on a camera-acquired image of the extruded compound with a reference length scale. Application of image processing and transformation of the calibrated image to the frequency domain yields the magnitude spectrum of the instability. The effectiveness of the before mentioned approach is shown on Styrene-butadiene rubber (SBR) compounds, covering a wide range of silica filler content, extruded through a Göttfert capillary rheometer. The results of the image-based analysis are compared with the results from the sharkskin option, a series of highly sensitive pressure transducers installed inside the rheometer. A simplified version of the code used to produce the optical analysis results is included as supplementary material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48806. 相似文献
90.
Although many preparation approaches have been developed, it remains a huge challenge to achieve ultraviolet (UV)-protection films that combine high transparency, excellent UV-shielding, and mechanical properties. Herein, we demonstrate a facile and eco-friendly process for fabricating strong, flexible, and transparent UV-protective poly(vinyl alcohol) (PVA) films by exploiting silicomolybdic acid (SiMoA) as UV absorber and reinforcing phase. Fourier-transform infrared analysis confirms the formation of strong hydrogen-bonding interactions between PVA and SiMoA. The glass-transition temperature, mechanical properties, and UV-shielding stability of the UV-protective PVA composite films obviously increase with increasing the content of SiMoA. By incorporation of only 2 wt % SiMoA, the UV-protective PVA composite film can block more than 90% of UV light in the entire UV regions and retain high visible light transparency (up to 95%). Simultaneously, the UV-protective PVA composite film presents excellent mechanical properties with a tensile strength of 65.2 MPa and an elongation at break of 172.6%, which are 72.0 and 69.5% higher than that of pristine PVA films. This work provides a simple but effective approach for creating strong, flexible, and transparent UV-blocking polymeric materials via hydrogen-bonding assembly, which are expected to have wide application prospects in UV-protection field. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48813. 相似文献