全文获取类型
收费全文 | 137754篇 |
免费 | 13908篇 |
国内免费 | 7718篇 |
专业分类
电工技术 | 9886篇 |
技术理论 | 15篇 |
综合类 | 10285篇 |
化学工业 | 21054篇 |
金属工艺 | 7670篇 |
机械仪表 | 8822篇 |
建筑科学 | 11327篇 |
矿业工程 | 4260篇 |
能源动力 | 4009篇 |
轻工业 | 10312篇 |
水利工程 | 3057篇 |
石油天然气 | 6861篇 |
武器工业 | 1439篇 |
无线电 | 17193篇 |
一般工业技术 | 15360篇 |
冶金工业 | 5828篇 |
原子能技术 | 1722篇 |
自动化技术 | 20280篇 |
出版年
2024年 | 615篇 |
2023年 | 2370篇 |
2022年 | 4697篇 |
2021年 | 6728篇 |
2020年 | 5024篇 |
2019年 | 3863篇 |
2018年 | 4379篇 |
2017年 | 4720篇 |
2016年 | 4326篇 |
2015年 | 6228篇 |
2014年 | 7864篇 |
2013年 | 9073篇 |
2012年 | 10548篇 |
2011年 | 11149篇 |
2010年 | 9638篇 |
2009年 | 9018篇 |
2008年 | 8702篇 |
2007年 | 7903篇 |
2006年 | 7057篇 |
2005年 | 5883篇 |
2004年 | 4105篇 |
2003年 | 3181篇 |
2002年 | 2894篇 |
2001年 | 2438篇 |
2000年 | 2435篇 |
1999年 | 2643篇 |
1998年 | 2108篇 |
1997年 | 1747篇 |
1996年 | 1686篇 |
1995年 | 1408篇 |
1994年 | 1198篇 |
1993年 | 835篇 |
1992年 | 640篇 |
1991年 | 481篇 |
1990年 | 398篇 |
1989年 | 347篇 |
1988年 | 261篇 |
1987年 | 171篇 |
1986年 | 125篇 |
1985年 | 85篇 |
1984年 | 63篇 |
1983年 | 44篇 |
1982年 | 60篇 |
1981年 | 43篇 |
1980年 | 52篇 |
1979年 | 29篇 |
1976年 | 15篇 |
1974年 | 11篇 |
1959年 | 15篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
71.
Haitang Yang Zilong Lu Bixiong Bie Zeyu Fu Jianling Yue Xiaozhong Huang 《Ceramics International》2019,45(9):11395-11402
SiCf/PyC/SiC and SiCf/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapor deposited PyC or BN interface layers are fabricated. The microstructure evolutions of the mini-composite samples as the oxidation temperature increases (oxidation at 1000, 1200, 1400, and 1600?°C in air for 2?h) are observed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction characterization methods. The damage evolution for each component of the as-fabricated SiCf/SiC composites (SiC fibre, PyC/BN interface, SiC matrix, and mesophase) is mapped as a three-dimensional (3D) image and quantified with X-ray computed tomography. The mechanical performance of the composites is investigated via tensile tests.The results reveal that tensile failure occurs after the delamination and fibre pull-out in the SiCf/PyC/SiC composites due to the volatilization of the PyC interface at high temperatures in the air environment. Meanwhile, the gaps between the fibres and matrix lead to rapid oxidation and crack propagation from the SiC matrix to SiC fibre, resulting in the failure of the SiCf/PyC/SiC composites as the oxidation temperature increases to 1600?°C. On the other hand, the oxidation products of B2O3 molten compounds (reacted from the BN interface) fill up the fracture, cracks, and voids in the SiC matrix, providing excellent strength retention at elevated oxidation temperatures. Moreover, under the protection of B2O3, the SiCf/BN/SiC mini-composites show a nearly intact microstructure of the SiC fibre, a low void growth rate from the matrix to fibre, and inhibition of new void formation and the SiO2 grain growth from room to high temperatures. This work provides guidance for predicting the service life of SiCf/PyC/SiC and SiCf/BN/SiC composite materials, and is fundamental for establishing multiscale damage models on a local scale. 相似文献
72.
Sumeng Wei Yuling Yang Xiao Feng Shanshan Li Lei Zhou Jingyu Wang Xiaozhi Tang 《International Journal of Food Science & Technology》2020,55(7):2691-2699
Structures and properties of myofibrillar protein gel prepared at different power (300–800 W) were evaluated. Amino acid analysis demonstrated that changes in microwave power did not alter primary structure of gel. However, an increase in microwave power could change higher structures of gel. As microwave power increased, α-helix content decreased and β-sheet content increased. Increased microwave power probably facilitated protein to unfold and expose the internal groups, causing surface hydrophobicity and the formation of disulphide bonds were enhanced, which indicated changes in tertiary and quaternary structures of protein. At 500 W, gel had the best ultrastructure where surface morphology, springiness and water holding capacity reached the optimum. Our findings suggested that microwave at an appropriate power (500 W) could change higher structures of myofibrillar protein gel to achieve desired processing and quality protein gel characteristics. 相似文献
73.
74.
Li Lei Limin Li Shasha Wang Gaoyang Zhao Yoshifumi Oshima Yang Ren Lei Zhao Lihua Jin Yao Wang Chengshan Li Pingxiang Zhang 《Journal of the European Ceramic Society》2018,38(14):4694-4700
Highly (100)-oriented Ce1-x(Y0.2Zr0.8)xOδ (CYZO) films were prepared on biaxially textured NiW substrates by a chemical solution deposition approach using metal inorganic salts as starting materials. It has been found that both the preferential orientation and surface roughness of CYZO films decrease gradually with increasing of the doping percentage of Y3+ and Zr4+ ions. The epitaxial growth relationship of (220)CYZO//(200)NiW and [00?l]CYZO//[001]NiW was demonstrated by XRD texture measurement as well as atomic resolution STEM observation. XRD, Raman and XPS spectra results indicate that Y3+ and Zr4+ ions were indeed introduced into CeO2 lattice to substitute Ce4+ ions and form cubic fluorite CYZO solid solution. Moreover, CeO2 buffer layer can be endowed a strong enough capability to prevent element diffusion through co-doping of yttrium and zirconium, provided that an optimal doping ratio of them is adopted. This will provide a new approach to fabricating strong-barrier single buffer layer for coated conductor. 相似文献
75.
Peng Jiang Jiafeng Lu Kun Li Xiquan Chen Ruiqi Dan 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(5):381-386
AbstractPreparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe3O4/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe3O4/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe3O4 nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe3O4 nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe3O4/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has been enhanced. 相似文献
77.
78.
Han Yan Gu Yi Chen Lei Li Bing Liu Xiang Ming Chen 《International Journal of Applied Ceramic Technology》2020,17(2):790-796
SrLa[Ga1−x(R0.5Ti0.5)x]O4 (R = Mg, Zn) ceramics were prepared by a standard solid state sintering method. The single-phase ceramics with K2NiF4-type layered perovskite structure and I4/mmm space group were obtained, indicating that SrLa(R0.5Ti0.5) and SrLaGaO4 can form the unlimited solid solutions. With increasing x for R = Mg and Zn, εr increases monotonously, the Qf value first increases and then decreases, while τf increases from a negative to a positive value. The optimized microwave dielectric properties were obtained as following: εr = 23.3, Qf = 89 400 GHz, τf = −0.8 ppm/°C for SrLa[Ga0.6(Mg0.5Ti0.5)0.4]O4 and εr = 23.3, Qf = 76 200 GHz, τf = 0.2 ppm/°C for SrLa[Ga0.7(Zn0.5Ti0.5)0.3]O4, indicating that the present solid solution ceramics are the promising candidates as microwave resonator materials for the telecommunication applications. 相似文献
79.
Design and Fabrication of Concentration‐Gradient Generators with Two and Three Inlets in Microfluidic Chips
下载免费PDF全文
![点击此处可从《化学工程与技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A simple and low‐cost method for designing and fabricating concentration‐gradient generators with two and three inlets is proposed which can generate different concentration gradients at varying flow velocities. The microchannel structure was designed in S‐shape and left‐right symmetry. The concentration‐gradient generator was simulated based on the finite element method. The microchannels were processed on a computer numerical control (CNC) engraving and milling machine on poly(methylmethacrylate) substrate, and then two concentration‐gradient generators were fabricated by hot bonding technology. The results of experiment and simulation were compared to prove the feasibility of the method. Flow velocity was an important factor for generating different concentration gradients. The concentration‐gradient profiles of the generators with two and three inlets present approximately linear and quadratic curves. 相似文献
80.
Zdeněk Slanina Filip Uhlík Lipiao Bao Takeshi Akasaka Xing Lu Ludwik Adamowicz 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(7):565-570
AbstractRelative populations of four energy-lowest IPR (isolated-pentagon-rule) isomers of Eu@C86 are computed using the Gibbs energy based on characteristics from density functional theory calculations (M06-2X/3-21G?~?SDD entropy term, M06-2X/6-31G*~SDD or B2PLYP(D)/6-31G*~SDD energetics). The calculations confirm that the recently isolated Eu@C1(7)-C86 species is a major isomer in a relevant temperature region. Relationship to the empty C86 cages is discussed, too. 相似文献