全文获取类型
收费全文 | 1810篇 |
免费 | 4篇 |
国内免费 | 56篇 |
专业分类
电工技术 | 58篇 |
综合类 | 3篇 |
化学工业 | 541篇 |
金属工艺 | 47篇 |
机械仪表 | 9篇 |
建筑科学 | 236篇 |
能源动力 | 82篇 |
轻工业 | 457篇 |
水利工程 | 55篇 |
石油天然气 | 26篇 |
武器工业 | 1篇 |
无线电 | 18篇 |
一般工业技术 | 171篇 |
冶金工业 | 102篇 |
自动化技术 | 64篇 |
出版年
2022年 | 1篇 |
2019年 | 1370篇 |
2018年 | 333篇 |
2017年 | 83篇 |
2015年 | 1篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 1篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 17篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1870条查询结果,搜索用时 15 毫秒
981.
Hans Georg Gemünden Patrick Lehner Alexander Kock 《International Journal of Project Management》2018,36(1):147-160
This paper presents a new conceptualization of the project-oriented organization. The project-oriented organization is conceptualized as an entrepreneurial, future- and stakeholder-oriented innovating organization, which uses projects as temporary, task-focused organizations, to define, develop, and implement its strategies, to transform its structure, culture and behavior, and to define and develop new products, services, and business models. The concept of the project-oriented organization consists of the three segments (1) values, (2) structures, and (3) people. For each segment three important areas are described, which characterize a project-oriented organization. The model is theoretically based on a wide spectrum of management disciplines: (1) The orientations in the value segment have been developed in entrepreneurship, strategic management and technology and innovation management; (2) The foundations for the design of the socio-technical artefacts in the structure segment of derived from organizational design, planning and controlling, and ICT systems theory; (3) The foundations for the elements of the human side come from organizational behavior, human resource management, and knowledge management theories. Our model shows a clear linkage to these theories, references key articles, and gives special consideration to empirical studies in the realm of projects, programs, project portfolios, and project-based or project-oriented organizations. Thus, our assumption that the elements of our model are supposed to increase project success, innovation success, and business success is based on empirical evidence. 相似文献
982.
The thickness of the base plays a crucial role in the stability of pavements and the lack of availability of good quality aggregates is a major concern in India and other countries. Loading on top of the base plays a crucial role in the design of pavements. Usually, the design of the pavement is done for standard axle load, however, in the field, in some of the cases, the vehicles are overloaded which results in a higher wheel load on the pavements. The current paper examines the performance of geogrid reinforced unpaved sections at higher stresses with the primary objective of reducing the thickness of base layer required in the field. Experimental studies were carried out using repeated plate load tests to obtain the optimum depth of placing the geogrid in granular base layer to achieve maximum reduction in rutting of pavement. Resilient deformation behavior of both reinforced and unreinforced sections are obtained and these values are utilized to predict the resilient modulus of the base sections. The paper also discusses the reduction in permanent deformation by the introduction of geogrid. Rut depth reduction studies were carried out in order to compare the performance of reinforced and unreinforced sections. The role played by the reinforcement in reducing the strains on top of the subgrade is studied in detail. A comparison is also carried out to understand the pressure distribution along the base layer and role played by the geogrids in reducing the pressure on the subgrade. Further, values of stress distribution angles were obtained for reinforced and unreinforced sections. It is evident from the studies that geogrids contributed to improved performance as well as reduction in thickness of the aggregate layer. 相似文献
983.
MgAl2O4 bulk samples were fabricated by two different approaches to investigate the effect of slip casting and sintering temperature on their transparency. Three MgAl2O4 samples containing 1 wt% LiF, as the sintering aid, were prepared by the spark plasma sintering process (SPS) at 1400 °C and 1500 °C, under 100 MPa, for 15 min. Also, another MgAl2O4 sample was prepared by slip casting followed by SPS under similar conditions. It was observed that utilizing slip casting led to more transparency (10% in the visible region and 20% in the IR region) due to the more homogeneous structure. It was also observed that by reducing the SPS temperature from 1500 °C to 1400 °C, the transparency increased (20% in the IR region) because of the lower grain growth rate at the lower temperature. 相似文献
984.
The influence of CuO and B2O3 addition on the sintering behavior, microstructure and microwave dielectric properties of Ti1?xCux/3Nb2x/3O2 (TCN, x = 0.23) ceramic have been investigated. It was found that the addition of CuO and B2O3 successfully reduced the sintering temperature of TCN ceramics from 950 to 875 °C. X-ray diffraction studies showed that addition of CuO-B2O3 has no effect on the phase composition. The TCN ceramics with 0.5 wt% CuO-B2O3 addition showed a high dielectric constant of 95.63, τf value of + 329 ppm/°C and a good Q × f value of 8700 GHz after sintered at 875 °C for 5 h, cofirable with silver electrode. 相似文献
985.
S.A.V. Prasad M. Deepty P.N. Ramesh G. Prasad K. Srinivasarao Ch. Srinivas K. Vijaya Babu E. Ranjith Kumar N. Krisha Mohan D.L. Sastry 《Ceramics International》2018,44(9):10517-10524
Structural, elastic and electron magnetic resonance investigations of spinel ferrites with the formula MFe2O4 (M = Mg2+, Zn2+, Mn2+) synthesized by the sol-gel auto-combustion method are reported here. XRD patterns revealed the co-existence of secondary phases along with the ferrite phase. The lattice parameter (8.301?Å, 8.366?Å and 8.434?Å) was found to be varying according to the ionic radii of cations. As determined by scanning electron microscopy (SEM), ZnFe2O4 has a comparatively narrow distribution of grain sizes (1.3–3.8?µm) compared to those in MnFe2O4 (0.8–4.3?µm) and MgFe2O4 (0.3–4.8?µm). The estimated values of average crystallite sizes (17.5?nm, 21.3?nm and 23.3?nm) determined from the X-ray diffraction peaks are considerably less than the average grain sizes (1.3?µm, 1.6?µm and 2.7?µm) estimated from the SEM histograms. The vibrational frequencies in FTIR spectra are in the conformity with the cubic spinel structure and their variation supports the variation of lattice parameter. Equal values of Poission's ratio (0.35) were obtained for the three systems which represent the isotropic behaviour of spinel ferrite systems. The exceptional low value of Lande's g-parameter for ZnFe2O4 indicates the dominance of Fe3+–O–Fe3+ superexchange interaction. Though cation redistribution is possible in the present ferrite systems, the secondary phases existed in these ferrite systems are predominantly influencing the structural, elastic and electron magnetic resonance properties. 相似文献
986.
(Li, Ce, and Nd)-multidoped CaBi2Nb2O9 (CBN) Aurivillius phase ceramics were prepared via a conventional solid-state sintering route. The crystal structure including bond lengths and bond angles, microstructure, dielectric constant, DC resistivity, and piezoelectric properties were systematically investigated. Rietveld-refinements of X-ray results indicated that small quantity of (Li, Ce, Nd) doping (< 2.5 mol%) increases orthorhombic distortion, because of the smaller ionic radii of doping ions. However, orthorhombic distortion obviously decreased with increasing (Li, Ce, Nd) doping concentration from 5 to 25 mol%. The replacement of asymmetric A-site Bi3+ with 6s2 lone pair electrons by symmetric Li+, Ce3+ and Nd3+ ions decreased the orthorhombic distortion. The morphologies and electrical properties of sintered ceramics were tailored by the introducing (Li, Ce, Nd) multi-dopants. The improvement of piezoelectric properties of modified-CBN ceramics were attributed to decreasing grain sizes and morphotropic phase boundary (MPB). Ca0.85(Li0.5Ce0.25Nd0.25)0.15Bi2Nb2O9 (CBNLCN-15) ceramics had optimum properties, and d33 and Tc values were found to be ~ 13.1 pC/N and ~ 900 °C, respectively. 相似文献
987.
Throughout the intense research of anodic TiO2 nanotubes (ATNTs), the effect of ambient pressure is usually ignored. In this article, Ti foils were potentiostatically anodized both under atmospheric pressure (0.1 MPa) and in vacuum (0.005 MPa). The anodizing current and nanotube length in vacuum are larger than those under atmospheric pressure, which cannot be explained by field-assisted dissolution theory. According to the oxygen bubble mould and Nernst equation, we attribute the higher current in vacuum to the faster gas evolution and oxide growth under narrower electrochemical potential gaps. By mathematically separating the total current into ionic and electronic parts, the faster oxide growth is further confirmed. The different nanotube lengths are due to various electric charge transported during anodization. 相似文献
988.
989.
Jarosław Kaszewski Jarosław Olszewski Julita Rosowska Bartłomiej Witkowski Łukasz Wachnicki Karolina Wenelska Ewa Mijowska Zdzisław Gajewski Marek Godlewski Michał M. Godlewski 《中国稀土学报(英文版)》2019,37(11):1176-1182
Europium doped hafnium dioxide nanoparticles were crystallized using biologically friendly microwave hydrothermal method and employed in observation of small rodents tissues.Main solvent in synthesis is water,in consequence nanoparticles are found surrounded by thin hydroxide layer.Size of the nanoparticles is controlled by temperature of calcination.1200℃heating causes drop of luminescence intensity,explained as damage of high symmetry surface emission centers in the nanocrystals.On the other hand,growth of crystallites increases intensity of X-ray and electron beam excited luminescence.This makes them promising activator in photodynamic therapy. 相似文献
990.
The crystallization behavior of a CaO-SiO2-MgO-Al2O3 slag system with varying Al2O3/SiO2 mass ratios from 0.03 to 1.10 has been investigated using a confocal laser scanning microscopy (CLSM). The resulting continuous cooling transformation (CCT) and time-temperature-transformation (TTT) curves showed that the initial crystallization temperature increased and the incubation time for crystallization slightly decreased with increasing Al2O3/SiO2 ratio. The crystal growth rate first increased and then decreased with decreasing isothermal temperature. X-ray diffraction (XRD) analysis suggested that Ca2MgSi2O7 or Ca3MgSi2O8 precipitated as the primary phase at lower Al2O3/SiO2 ratios, while the Ca2Al2SiO7 phase was preferred at higher Al2O3/SiO2 ratios. The observed crystalline phases correlated well with the expected thermodynamic predictions from FactSage. In addition, structural analysis using 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR) microscopy of the as-quenched slags indicated the presence of a higher ratio of tetrahedral [AlO4]5-structural units with increasing Al2O3/SiO2 ratio, which enhanced the polymerization of tetrahedral [AlO4]5- and [SiO4]4- structural units to form Ca2Al2SiO7. 相似文献