全文获取类型
收费全文 | 6485篇 |
免费 | 286篇 |
国内免费 | 296篇 |
专业分类
电工技术 | 92篇 |
综合类 | 457篇 |
化学工业 | 571篇 |
金属工艺 | 1479篇 |
机械仪表 | 1443篇 |
建筑科学 | 137篇 |
矿业工程 | 428篇 |
能源动力 | 49篇 |
轻工业 | 526篇 |
水利工程 | 36篇 |
石油天然气 | 118篇 |
武器工业 | 63篇 |
无线电 | 360篇 |
一般工业技术 | 827篇 |
冶金工业 | 204篇 |
原子能技术 | 63篇 |
自动化技术 | 214篇 |
出版年
2024年 | 14篇 |
2023年 | 56篇 |
2022年 | 80篇 |
2021年 | 89篇 |
2020年 | 126篇 |
2019年 | 85篇 |
2018年 | 105篇 |
2017年 | 175篇 |
2016年 | 149篇 |
2015年 | 189篇 |
2014年 | 330篇 |
2013年 | 295篇 |
2012年 | 368篇 |
2011年 | 476篇 |
2010年 | 342篇 |
2009年 | 395篇 |
2008年 | 310篇 |
2007年 | 449篇 |
2006年 | 428篇 |
2005年 | 421篇 |
2004年 | 326篇 |
2003年 | 314篇 |
2002年 | 265篇 |
2001年 | 239篇 |
2000年 | 206篇 |
1999年 | 167篇 |
1998年 | 124篇 |
1997年 | 130篇 |
1996年 | 114篇 |
1995年 | 98篇 |
1994年 | 53篇 |
1993年 | 54篇 |
1992年 | 34篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有7067条查询结果,搜索用时 484 毫秒
41.
Patricia Muñoz-Escalona Shreyes Melkote Kai Liu 《Journal of Materials Engineering and Performance》2005,14(5):582-590
In recent years, the finite element method (FEM) has become the main tool for simulating the metal cutting process because
research based on trial and error is time consuming and requires high investment. Early studies were done by different investigators.
In this research AISI 52100, hardened steel (62 HRC) was selected for an orthogonal machining process as well as metal cutting
simulation using the software DEFORM-2D. This software is based on a forging process and has been adapted to an orthogonal
machining process. The results of simulated cutting forces were compared with experimental cutting force data to validate
the orthogonal cut simulation. Also, the surface roughness was measured, and the influence of the stress, strain, and temperature
on the surface roughness was studied. 相似文献
42.
金刚石颗粒在锯切石材过程中磨损形态的研究 总被引:1,自引:1,他引:1
本文分析和归纳了锯切花岗石过程中金刚石颗粒的五种磨损形态和三个磨损阶段,探讨了金铡石颗粒磨损形态对金刚石锯片锯切性能的影响。 相似文献
43.
Manuel Belmonte Vitor A. Silva Antonio José Fernandes Florinda Costa Rui Silva 《Journal of the American Ceramic Society》2003,86(5):749-754
The efficiency of different surface pretreatments (four standard chemical etchings and four diamond powder abrasive procedures) on silicon nitride (Si3 N4 ) substrates for chemical vapor deposition (CVD) of diamond has been systematically investigated. Blank Si3 N4 samples were polished with colloidal silica (∼0.25 μm). Diamond nucleation and growth runs were conducted in a microwave plasma chemical vapor deposition apparatus for 10 min and 6 h, respectively. Superior results concerning nucleation density ( N d ∼ 1010 cm−2 after 10 min), film uniformity, and grain size (below 2 μm after 6 h) were obtained for the mechanically microflawed samples, revealing that chemical etchings (hot and cold strong acids, molten base or CF4 plasma) are not crucial for good CVD diamond quality on Si3 N4 . 相似文献
44.
K HondaM Yoshimura R UchikadoT Kondo Tata N Rao D.A TrykA Fujishima M WatanabeK Yasui H Masuda 《Electrochimica acta》2002,47(27):4373-4385
Electrochemical characteristics for several redox systems at diamond films with highly ordered nanometer-scale cylindrical pores (‘nano-honeycombs’) were examined with cyclic voltammetry (CV) and electrochemical impedance measurements. The cyclic voltammetric anodic-cathodic peak separations for these nano-honeycomb electrodes were in the same range as those for polished polycrystalline diamond films, indicating that the involvement of the oxygen-terminated surface of the nano-pore walls, which should give rise to large peak separations for certain redox couples was only slight. Moreover, the peak currents in the CV were not enhanced to the extent expected on the basis of the roughness factors of the nano-honeycomb films. Ac impedance plots results indicated the existence of a concentration gradient of the reactant in the nano-pores, which is in agreement with theoretical predictions for charge transfer reactions in porous electrodes. The average concentration of the reactant (Fe2+/3+) inside the nano-pores was a factor of ca. 80 lower than that in the bulk electrolyte. The results of the impedance analysis also indicated an increase in the reaction resistances with decreasing pore diameters. 相似文献
45.
Shingo Kanehira Soshu Kirihara Yoshinari Miyamoto Kazuaki Sakoda Mitsuo Wada Takeda 《Journal of the American Ceramic Society》2003,86(10):1691-1694
Photonic crystals with a diamond structure of epoxy lattices in which TiO2 -based ceramic particles are dispersed were fabricated by stereolithography. The periodicity of the lattice was designed to reflect electromagnetic waves in the gigahertz range. The volume fraction (β) of the dielectric lattice medium was modified from 14% to 33% by changing the rod diameter of the lattice. The photonic band gap was observed along Γ-L 〈111〉, Γ-X 〈100〉, and Γ-K 〈110〉 directions and the complete photonic band gap was formed at over β= 20%. The width of the forbidden gap increased gradually when the β increased over 14%, and reached 2.4 GHz at β= 33%. These results agreed with the band calculation using the plane wave expansion method. 相似文献
46.
47.
48.
介绍了含硼T641石墨炭源合成耐热性高、抗氧化性好与化学惰性强的金刚石及其性质。讨论了含硼金刚石高耐热性的形成及其氧化机理。指出了进一步提高质量、耐热性、抗氧化性与化学惰性金刚石的合成途径及方法。 相似文献
49.
Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode 总被引:1,自引:0,他引:1
Enric Brillas Birame Boye José Antonio Garrido Conchita Arias Christos Comninellis 《Electrochimica acta》2004,49(25):4487-4496
The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe2+ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe2+ and H2O2 electrogenerated at the O2-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl−, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe3+-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated. 相似文献
50.
C. Tuve' R. Potenza M. Chiorboli M.G. Grimaldi F. La Rosa F. Raimondo M. Marinelli E. Milani A. Tucciarone G. Verona Rinati M. Donato G. Faggio G. Messina S. Santangelo G. Pucella 《Diamond and Related Materials》2006,15(11-12):1986
Polycrystalline (pCVD) and single crystal (scCVD) diamond films grown from Chemical Vapour Deposition (CVD), if sufficiently pure at Raman analysis, are very good materials for beam or flux monitors inside accelerators or nuclear reactors. This is because they are very hard to damage in high radiation fields and very resistant to high temperatures. Films of pCVD diamond are, however, not so good as spectroscopy detectors due to inhomogeneities induced by their growth in grains with the consequent presence of grain boundaries which worsen their energy resolution. The latter can be significantly improved by growing scCVD diamond films onto HPHT synthetic diamond substrates. We have shown that it is possible to measure the density of defects inside diamond specimens using as probes suitable penetrating nuclear radiations. With the preliminary results reported here we'll show that, bombarding CVD diamond films grown at Roma “Tor Vergata” with energetic protons and 4He, 6Li and 12C ions produced in the accelerators of Catania laboratories, the pulse height defects are higher than those in silicon detectors and likewise well described by a power law in the deposited energy. Furthermore, we'll show that pulse heights for the same particles seem to depend on the duration of the measurement, thus exhibiting a sort of depolarization of the insulator when exposed to the electric voltage which makes it a particle detector. 相似文献