全文获取类型
收费全文 | 461篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 152篇 |
金属工艺 | 46篇 |
机械仪表 | 10篇 |
建筑科学 | 4篇 |
能源动力 | 16篇 |
轻工业 | 11篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 31篇 |
一般工业技术 | 107篇 |
冶金工业 | 23篇 |
原子能技术 | 6篇 |
自动化技术 | 65篇 |
出版年
2023年 | 5篇 |
2022年 | 21篇 |
2021年 | 14篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 17篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 26篇 |
2013年 | 49篇 |
2012年 | 37篇 |
2011年 | 33篇 |
2010年 | 17篇 |
2009年 | 35篇 |
2008年 | 29篇 |
2007年 | 12篇 |
2006年 | 16篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1993年 | 5篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有476条查询结果,搜索用时 15 毫秒
31.
Iulian Riposan Stelian Stan Valentin Uta Ion Stefan 《Journal of Materials Engineering and Performance》2017,26(9):4217-4226
Inoculation is one of the most important metallurgical treatments applied to the molten cast iron immediately prior to casting, to promote solidification without excessive eutectic undercooling, which favors carbides formation usually with undesirable graphite morphologies. The paper focused on the separate addition of an inoculant enhancer alloy [S, O, oxy-sulfides forming elements] with a conventional Ca-FeSi alloy, in the production of gray and ductile cast irons. Carbides formation tendency decreased with improved graphite characteristics as an effect of the [Ca-FeSi + Enhancer] inoculation combination, when compared to other Ca/Ca, Ba/Ca, RE-FeSi alloy treatments. Adding an inoculant enhancer greatly enhances inoculation, lowers inoculant consumption up to 50% or more and avoids the need to use more costly inoculants, such as a rare earth bearing alloy. The Inoculation Specific Factor [ISF] was developed as a means to more realistically measure inoculant treatment efficiency. It compares the ratio between the improved characteristic level and total inoculant consumption for this effect. Addition of any of the commercial inoculants plus the inoculant enhancer offered outstanding inoculation power [increased ISF] even at higher solidification cooling rates, even though the total enhancer addition was at a small fraction of the amount of commercial inoculant used. 相似文献
32.
Synthesis,structural characterization,and photocatalytic properties of iron-doped TiO<Subscript>2</Subscript> aerogels 总被引:1,自引:0,他引:1
M. Popa L. Diamandescu F. Vasiliu C. M. Teodorescu V. Cosoveanu M. Baia M. Feder L. Baia V. Danciu 《Journal of Materials Science》2009,44(2):358-364
Fe(III)-doped TiO2 aerogels are prepared by acid catalyzed sol–gel method followed by supercritical drying, and then heat treatment. Raman spectra
together with X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of the iron-doped TiO2 aerogel samples revealed the existence of both anatase and brookite crystalline phases. It was found that the brookite phase
formation is favored by the increase of the iron content in the dried samples. XRD measurements show that the lattice constant
c of anatase phase decreases with the dopant addition, while the value of a remains essentially unchanged. The microstructure of the investigated samples is relatively compact with small mesopores
as revealed from transmission electron microscopy (TEM). The most enhanced photocatalytic activity was exhibited by the TiO2 aerogel sample with 1.8 at.% Fe(III) whose apparent rate constant of the salicylic acid photodegradation was found to be
of almost six times higher than that of Degussa P25. 相似文献
33.
We deposited BiFeO3 films on stainless steel substrates using a simple low-temperature wet-chemical route. Bismuth and iron nitrates were used as metal source and citric acid as chelating agent to prepare a water solution and deposit the film by dipping the steel substrate in the viscous solution. We have investigated the composition, crystallinity and structure of the BiFeO3 film on steel by X-ray diffraction, X-ray photoelectron spectroscopy, high resolution scanning electron microscopy, conventional and high resolution transmission electron microscopy, and energy dispersive spectroscopy techniques. The film deposited on the steel substrate has two sublayers: a very thin (about 100 nm) nanocrystalline layer, with crystallite size of few nanometers, and a thicker (below 1 μm) crystalline layer. 相似文献
34.
Borovic B. Lewis F.L. Agonafer D. Kolesar E.S. Hossain M.M. Popa D.O. 《Journal of microelectromechanical systems》2005,14(5):961-970
A method is presented for determining lumped dynamical models of thermal microelectromechanical systems (MEMS) devices for purposes of feedback control. As a case study, an electrothermal actuator is used. The physical properties and a set of assumptions are used to determine the basic structure of the dynamical model, which requires the development of the electrical, thermal, and mechanical dynamics. The importance of temperature-dependent parameters is emphasized for dynamical modeling for purposes of feedback control. To confront temperature dependence in a practical yet effective manner, an average temperature is introduced to preserve the energy balance inside the structure. This allows the development of a practical method that combines structure of the model, through the average body temperature, with finite element analysis (FEA) in novel way to perform system identification and identify the unknown parameters. The result is a lumped dynamical model of a MEMS device that can be used for the design of feedback control systems. We compare computer simulated results using the dynamical model with experimental behavior of the actual device to show that our procedure indeed generates an accurate model. This dynamical model is intended for further synthesis of driving signal and control system but also gives a qualitative insight into the relationship between device's geometry and its behavior. The method enables fast development of the model by conducting relatively few static FEA and is verifiable with dynamic experimental results even when temperature measurements are not available. 相似文献
35.
The interest for the primary solid tumors of the mesentery (TSPM) is justified by the difficulties of preoperative diagnosis and surgical treatment of these unusual lesions. We analyzed 68 TSPM operated in the Department of General Surgery of Fundeni Hospital between 1960-1993. In the study were included only the lymphoma presented as mesenteric masses (n = 17); the enlarged mesenteric lymph nodes were excluded. The most common malignant tumor was the fibroma (n = 8) and lipoma (n = 10). In the resection of mesenteric tumors exposure of the superior mesenteric vessels is important. The relation between tumoral and superior mesenteric vessels is the necessary criterion of resectability: in 41 cases from 43 unresectable lesions the reason of unresectability was the invasion of the superior mesenteric vein and artery; in only two cases the reason was the presence of liver metastases. The resectability was not influenced by the multiplicity of the lesions: in all cases with multiple mesenteric tumors (6 patients) the resection was performed. The distant metastases of TSPM are rare; on the contrary, the local invasion is common. 相似文献
36.
The paper reports measurements of optical transmittance and of I–V characteristic performed simultaneously on the same host mixture ChCl + LCh 74:26% molar in which was introduced another azocumilphenol derivative from paraphenetidine (Dpf). The optical and electrical measurements were interpreted by correlating them with the microstructural aspects recorded by a polarizing microscope in the same conditions of field and temperature. 相似文献
37.
Preserving mapping consistency under schema changes 总被引:1,自引:0,他引:1
Yannis?VelegrakisEmail author Renée?J.?Miller Lucian?Popa 《The VLDB Journal The International Journal on Very Large Data Bases》2004,13(3):274-293
In dynamic environments like the Web, data sources may change not only their data but also their schemas, their semantics, and their query capabilities. When a mapping is left inconsistent by a schema change, it has to be detected and updated. We present a novel framework and a tool (ToMAS) for automatically adapting (rewriting) mappings as schemas evolve. Our approach considers not only local changes to a schema but also changes that may affect and transform many components of a schema. Our algorithm detects mappings affected by structural or constraint changes and generates all the rewritings that are consistent with the semantics of the changed schemas. Our approach explicitly models mapping choices made by a user and maintains these choices, whenever possible, as the schemas and mappings evolve. When there is more than one candidate rewriting, the algorithm may rank them based on how close they are to the semantics of the existing mappings.Received: 13 January 2004, Accepted: 26 March 2004, Published online: 12 August 2004Edited by: M. Carey 相似文献
38.
Gheorghe?I.?RusuEmail author George?G.?Rusu Mihai?E.?Popa 《Materials Research Innovations》2003,7(6):372-380
The investigated compounds are some derivatives of orthotolidin-N,N-bis (4-aminobenzene-2-sulphonic) acid. The temperature dependences of the electrical conductivity and Seebeck coefficient are studied on the thin films deposited from dimethylformamide solution onto glass substrates. It is known that the investigated compounds have typical semiconducting properties. The values of some important parameters of the films (thermal activation energy of electrical conduction, concentrations and mobilities of charge carriers) have been determined. The correlations between some of these parameters and molecular structure of the respective compounds are discussed. 相似文献
39.
We prove that the Schrodinger equation, written for a closed system composed of an electron and electromagnetic field, has a solution at the classical limit if the dipole approximation is fulfilled and the magnetic potential vector enters in classical form in the Schrodinger equation. Though the above property is valid generally in the case of laser beams, its potential importance is increased for the domain of the very high intensities of the electrical field, where it is in agreement with a lot of recent classical models and experimental results from literature. This result leads to a simplified computational model for the interaction between electrons and laser beams. 相似文献
40.
Catalin Popa Yuki Okayasu Ken-ichi Katsumata Toshihiro Isobe Nobuhiro Matsushita Akira Nakajima Taisuke Kurata Kiyoshi Okada 《Journal of Materials Science》2013,48(2):941-947
Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method using rayon fibers as the pore formers. Rayon fibers of 8.1, 9.6, 16.8, and 37.6 μm in diameter were used as the pore formers and were kneaded with alumina powder, kaolin clay, China earthen clay, and water to form pastes. These pastes were extruded into cylindrical tubes, dried, and fired at 1500 °C for 4 h. The apparent porosities ranged from 45.7 to 48.2 %. The pore size distributions showed a sharp peak at 9.4, 10.0, 15.6, and 30 μm with increasing fiber diameters. The height of the capillary rise was 1780, 1670, 1320, and 950 mm with increasing fiber diameter. The maximum capillary rise is much higher than previously reported. The contact angle and effective pore radius that determine the capillary rise ability were calculated by fitting the capillary rise curves using the Fries and Dreyer’s equation. 相似文献