全文获取类型
收费全文 | 25250篇 |
免费 | 2989篇 |
国内免费 | 1653篇 |
专业分类
电工技术 | 1606篇 |
技术理论 | 2篇 |
综合类 | 2886篇 |
化学工业 | 3292篇 |
金属工艺 | 1746篇 |
机械仪表 | 992篇 |
建筑科学 | 2602篇 |
矿业工程 | 1199篇 |
能源动力 | 748篇 |
轻工业 | 1855篇 |
水利工程 | 1632篇 |
石油天然气 | 1460篇 |
武器工业 | 250篇 |
无线电 | 1777篇 |
一般工业技术 | 3206篇 |
冶金工业 | 1302篇 |
原子能技术 | 108篇 |
自动化技术 | 3229篇 |
出版年
2024年 | 53篇 |
2023年 | 390篇 |
2022年 | 693篇 |
2021年 | 818篇 |
2020年 | 914篇 |
2019年 | 830篇 |
2018年 | 792篇 |
2017年 | 957篇 |
2016年 | 1090篇 |
2015年 | 1100篇 |
2014年 | 1554篇 |
2013年 | 1667篇 |
2012年 | 1848篇 |
2011年 | 2033篇 |
2010年 | 1464篇 |
2009年 | 1418篇 |
2008年 | 1384篇 |
2007年 | 1643篇 |
2006年 | 1506篇 |
2005年 | 1282篇 |
2004年 | 1043篇 |
2003年 | 894篇 |
2002年 | 732篇 |
2001年 | 626篇 |
2000年 | 489篇 |
1999年 | 457篇 |
1998年 | 361篇 |
1997年 | 308篇 |
1996年 | 277篇 |
1995年 | 264篇 |
1994年 | 213篇 |
1993年 | 159篇 |
1992年 | 118篇 |
1991年 | 124篇 |
1990年 | 117篇 |
1989年 | 77篇 |
1988年 | 58篇 |
1987年 | 26篇 |
1986年 | 32篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1975年 | 2篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
81.
《全球能源互联网(英文)》2020,3(4):303-312
Given the increasing uncertainties in power supply and load, this paper proposes the concept of power source and grid coordination uniformity planning. In this approach, the standard deviation of the transmission line load rate is considered as the uniformity evaluation index for power source and grid planning. A multi-stage and multi-objective optimization model of the power source and grid expansion planning is established to minimize the comprehensive cost of the entire planning cycle. In this study, the improved particle swarm optimization algorithm and genetic algorithm are combined to solve the model, thus improving the efficiency and accuracy of the solution. The analysis of a simple IEEE Garver’s 6-node system shows that the model and solution method are effective and feasible. Moreover, they are suitable for the coordinated planning of the power source and grid under a diversified nature of power supply and load. 相似文献
82.
83.
84.
In this paper, a novel systematic and integrated methodology to assess gas supply reliability is proposed based on the Monte Carlo method, statistical analysis, mathematical-probabilistic analysis, and hydraulic simulation. The method proposed has two stages. In the first stage, typical scenarios are determined. In the second stage, hydraulic simulation is conducted to calculate the flow rate in each typical scenario. The result of the gas pipeline system calculated is the average gas supply reliability in each typical scenario. To verify the feasibility, the method proposed is applied for a real natural gas pipelines network system. The comparison of the results calculated and the actual gas supply reliability based on the filed data in the evaluation period suggests the assessment results of the method proposed agree well with the filed data. Besides, the effect of different components on gas supply reliability is investigated, and the most critical component is identified. For example, the 48th unit is the most critical component for the SH terminal station, while the 119th typical scenario results in the most severe consequence which causes the loss of 175.61×104 m3 gas when the 119th scenario happens. This paper provides a set of scientific and reasonable gas supply reliability indexes which can evaluate the gas supply reliability from two dimensions of quantity and time. 相似文献
85.
Zuo‐Yu Sun 《国际能源研究杂志》2018,42(8):2845-2858
In the present article, series of experiments were conducted to study the structure characteristics of premixed flames in turbulent rich hydrogen‐air mixtures within a constant‐volume turbulent combustion system, 7 equivalence ratios (1.2, 1.4, 1.6, 1.8, 2.0, 2.2, and 2.5), and 5 turbulent intensity (0, 0.494, 0.742, 1.080, and 1.309 m/s) were studied. With the increase of turbulent intensity, the cellularity degree was obviously enhanced for turbulence promoted the formation and the development of initial cracks by wrinkling flame‐front; furthermore, the enhanced hydrodynamic instability was also one important reason. Turbulence would change the linear growth of critical radius to equivalence ratio into nonlinear, but the variation extents had limitation. The wrinkling index of flame‐front would rise as flame expanded, and the wrinkling index on flames with similar size would be increased with the increase of turbulence once the turbulent intensity was sufficiently high. From the variations of the root mean square of related oscillation on flame‐front, it could be found that the partial amount of oscillation induced by sole turbulence was declined as flame expanded for the breakup of large eddies. 相似文献
86.
《Ceramics International》2020,46(14):22230-22238
Polycrystalline cubic boron nitride (PCBN) tool materials with NbN binder without additives and PCBN with Al2O3 or Si3N4 micropowder and whisker additives were manufactured and compared. PCBN materials with Si3N4 whisker reinforcement have the best mechanical properties of all the evaluated materials. Composites reinforced with Al2O3 whiskers have the lowest fracture toughness. However, Al2O3 whisker-reinforced tools outperform both commercial and Si3N4 reinforced tools when machining hardened steel. Thus Al2O3 whisker-reinforced PCBN materials are promising for industrial applications, likely due to their higher resistance to oxidation and diffusional wear mechanisms during cutting operations. 相似文献
87.
《Journal of the European Ceramic Society》2020,40(8):3057-3064
In the present study an advanced pillar splitting method is used to determine the fracture toughness of a garnet-type Li7La3Zr2O12 (LLZO) electrolyte. The obtained results are compared to data derived on the basis of conventional Vickers indentation. Furthermore, potential micro-pillar size effects are investigated. The estimated fracture toughness values for single grains and polycrystalline LLZO material obtained via both methods are in good agreement, yielding ∼ 1 MPa m0.5, hence the data indicate that LLZO exhibits relatively low fracture toughness and has a brittle behavior. 相似文献
88.
《Ceramics International》2020,46(5):6300-6310
Metallic binder is a key factor affecting the microstructure and mechanical properties of Ti(C,N)-based cermets. To optimize the overall performances, cermets with various weight ratios of Ni/(Co + Ni) ranging from 0 to 1 were fabricated by gas pressure sintering. Microstructure, phase formation, interface structure and related mechanical properties of the sintered cermets were investigated. With the increase of the Ni/(Co + Ni) ratios, the black cores became smaller and grains of Ti(C,N) dispersed uniformly. Compared to the pure Ni or Co, Ni–Co binders accelerated the formation of rim phases, and avoided the nonuniform dispersed binder pools. When the ratio was 0.5, the cermets showed fine grains, uniformly dispersed binders and small lattice misfit of the core-rim interface, exhibiting the optimal mechanical properties, i.e. satisfactory Vickers hardness of 1670 (HV30) Kgf/mm2, bending strength of 1970 MPa and Fracture toughness of 8.94 MPa m0.5. This work sheds light on constructing the relationship between the microstructure, mechanical performance of Ti(C,N)-based cermets and the Ni/Co-based binders. 相似文献
89.
《Ceramics International》2020,46(12):20068-20080
In this study, Al2O3–TiC composites synergistically reinforced with multi-walled carbon nanotubes (MWCNTs) and graphene nanoplates (GNPs) were prepared via spark plasma sintering (SPS). The effects of the MWCNT and GNP contents on the phase composition, mechanical properties, fracture mode, and toughening mechanism of the composites were systematically investigated. The experimental results indicated that the composite grains became more refined with the addition of MWCNTs and GNPs. The nanocomposites presented high compactness and excellent mechanical properties. The composite with 0.8 wt% MWCNTs and 0.2 wt% GNPs presented the best properties of all analysed specimens, and its relative density, hardness, and fracture toughness were 97.3%, 18.38 ± 0.6 GPa, and 9.40 ± 1.6 MPa m1/2, respectively. The crack deflection, bridging, branching, and drawing effects of MWCNTs and GNPs were the main toughening mechanisms of Al2O3–TiC composites synergistically reinforced with MWCNTs and GNPs. 相似文献
90.
《Ceramics International》2020,46(11):19092-19102
In previous works, it was found hard to synthesize “phase pure” ζ-Ta4C3-z at relatively low temperatures even by prolonged heating, though ζ-Ta4C3-z was believed stable till decomposition at ~2130°C. When the samples were subjected to TEM, vast richness of locally disordered structures in close relation with stacking of the close-pacted Ta-atom planes was observed. Although kinetic factors including diffusion of C atoms/vacancies and re-stacking of the Ta-atom planes explain the densely disordered structures, the richness of local disorders is a scenario that shows cohabitant of the cubic, rhombohedral, and hexagonal structures in a single grain, i.e. formation of a “hybrid grain” consisted of the three symmetries, indicating a transitional or intermediate stage before complete formation of the final phase of rhombohedral ζ-Ta4C3-z. This time tantalum carbide ceramics TaCx with C:Ta atomic ratios x = 0.66 and 0.7 were prepared by reaction hot pressing of TaC and Ta powder mixtures. 5–30 mol% Cu/Ag additives and heat treatments were used to reproduce “hybrid grains” to facilitate further TEM and HRTEM observations on the disordered hybrid grains to argue for the transitional/intermediate stage. The cohabitant cubic, rhombohedral, and hexagonal structures in single grains may also help explain the difficulty in identification of the various phases by XRD in the transitional/intermediate stage of ζ-Ta4C3-z reaction. Microstructural evolution and fracture toughness of the composites were also investigated. 相似文献