全文获取类型
收费全文 | 213122篇 |
免费 | 3844篇 |
国内免费 | 617篇 |
专业分类
电工技术 | 3562篇 |
综合类 | 162篇 |
化学工业 | 33962篇 |
金属工艺 | 8209篇 |
机械仪表 | 6427篇 |
建筑科学 | 5338篇 |
矿业工程 | 1325篇 |
能源动力 | 5510篇 |
轻工业 | 20512篇 |
水利工程 | 2414篇 |
石油天然气 | 4109篇 |
武器工业 | 8篇 |
无线电 | 23668篇 |
一般工业技术 | 41988篇 |
冶金工业 | 37958篇 |
原子能技术 | 5137篇 |
自动化技术 | 17294篇 |
出版年
2022年 | 1455篇 |
2021年 | 2678篇 |
2020年 | 1622篇 |
2019年 | 2018篇 |
2018年 | 3106篇 |
2017年 | 3202篇 |
2016年 | 3382篇 |
2015年 | 2286篇 |
2014年 | 3723篇 |
2013年 | 9930篇 |
2012年 | 5997篇 |
2011年 | 8071篇 |
2010年 | 6402篇 |
2009年 | 7089篇 |
2008年 | 7157篇 |
2007年 | 7163篇 |
2006年 | 6091篇 |
2005年 | 5604篇 |
2004年 | 5330篇 |
2003年 | 5191篇 |
2002年 | 4802篇 |
2001年 | 4829篇 |
2000年 | 4702篇 |
1999年 | 4871篇 |
1998年 | 11528篇 |
1997年 | 8277篇 |
1996年 | 6532篇 |
1995年 | 4771篇 |
1994年 | 4347篇 |
1993年 | 4158篇 |
1992年 | 3297篇 |
1991年 | 3130篇 |
1990年 | 2925篇 |
1989年 | 2997篇 |
1988年 | 2869篇 |
1987年 | 2434篇 |
1986年 | 2357篇 |
1985年 | 2760篇 |
1984年 | 2533篇 |
1983年 | 2373篇 |
1982年 | 2110篇 |
1981年 | 2233篇 |
1980年 | 2059篇 |
1979年 | 2149篇 |
1978年 | 2148篇 |
1977年 | 2387篇 |
1976年 | 3199篇 |
1975年 | 1846篇 |
1974年 | 1765篇 |
1973年 | 1781篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Vu Hoa T. Nguyen Manh B. Vu Tan M. Le Giang H. Pham Trang T. T. Nguyen Trinh Duy Vu Tuan A. 《Topics in Catalysis》2020,63(11-14):1046-1055
Topics in Catalysis - Nano Fe-BTC/graphene oxide (GO) composites were successfully synthesized by hydrothermal treatment with a microwave-assisted method. Samples were characterized by X-ray... 相似文献
103.
104.
105.
Maria Yousaf Lodhi Muhammad Azhar Khan Majid Niaz Akhtar Muhammad Farooq Warsi Asif Mahmood Shahid M. Ramay 《Ceramics International》2018,44(3):2968-2975
The influence of neodymium and nickel substitution on structural and dielectric parameters was investigated in strontium-barium X-type hexagonal ferrites having composition SrBaCu2?xNixNdyFe28?yO46 (x = 0, 0.2, 0.4, 0.6, 0.8, 1 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1). Sol-gel method was employed for synthesizing these hexagonal ferrites. The XRD plots of all studied materials which were annealed at 1250 °C show single phase characteristics. Lattice parameter ‘c’ increased as a consequence of larger radius of rare earth ion (Nd3+) as compared to (Fe3+), while lattice parameter ‘a’ showed very small variation. The cell volume was obtained in the range 2508.32–2523.75 (Å3). The inclusion of Nd-Ni also affected X-ray density, bulk density and porosity. The FTIR spectroscopy indicated the particular absorption peaks of hexagonal ferrites and it was performed in the range of 500–700 cm?1. On account of Nd-Ni doping, the dielectric constant, dielectric loss and AC-conductivity showed decreasing trend. The occupancy of Nd3+ ions at octahedral site impedes the valence alternation of Fe3+; therefore there was decrease in dielectric permittivity. Ac conductivity has been decreased from 9.14 to 6.49 (Ω cm)?1 at frequency of 2.7 GHz. The Cole-Cole plots of synthesized materials noticeably revealed grain boundary contribution. The appearance of single semi-circle in impedance Cole-Cole graphs confirms the exceptional role of grain boundaries in the conduction process. The considerably lower dielectric parameters of investigated nano X-type ferrites propose their feasibility for high-frequency applications (phase shifters, dielectric resonators, stealth technology etc). 相似文献
106.
Mohan B. Ponnuchamy G. Mohan Muralikrishna Venkateswara Rao Mannava G. Srinivas Reddy 《Ceramics International》2018,44(13):15019-15023
Nanocrystalline nickel oxide (NiO) was prepared from nickel hydroxide by Spark plasma sintering (SPS) and the mechanisms involved in the densification of NiO were studied. Reverse precipitated nickel hydroxide powders were SPS processed at 400, 600 and 700?°C with 70?MPa pressure. Pure NiO with 12?nm crystallite size formed after 400?°C sintering process. However NiO grains had grown to 18 and 38?nm after 600 and 700?°C sintering respectively. NiO pellets prepared using 600 and 700?°C SPS sintering schedules had relative densities of 83% and 94% respectively. Two displacement rate regimes were observed during densification of NiO in both 600 and 700?°C sintering processes. Decomposition of nickel hydroxide and particle sliding of NiO led to first displacement rate maximum while inverse Hall-Petch based plastic deformation facilitated densification during the constant second displacement rate regime. No densification occurred during sintering holding times indicating the limited role that diffusion played during densification. 相似文献
107.
H. Cherfouh O. Fellahi T. Hadjersi B. Marsan 《International Journal of Hydrogen Energy》2018,43(6):3431-3440
This work aims at developing a new composite material based on nanosized semiconducting CuInS2 (CIS) particles combined with silicon nanowires grown on a silicon substrate (SiNWs/Si) for photoelectrochemical (PEC)-splitting of water. The CIS particles were prepared via a colloidal method using N-methylimidazole (NMI) as the solvent and an annealing treatment. The SiNWs were obtained by chemical etching of silicon (100) substrates assisted by a metal. The CIS/SiNWs/Si composite material was obtained by deposition of an aliquot of a suspension of CIS particles onto the SiNWs/Si substrate, using spin coating followed by a drying step. The XRD pattern demonstrated that CuInS2 grows in the tetragonal/chalcopyrite phase, while SiNWs/Si presents a cubic structure. The SEM images show semi-spherical particles (~10 nm) distributed on the surface of silicon nanowires (~10 μm). The EIS measurements reveal n-type conductivity for CIS, SiNWs/Si and CIS/SiNWs/Si materials, which could favour the oxidation reaction of water molecules. 相似文献
108.
The cracks in the workpiece specimens can reduce the fatigue life of any machine components. Since the residual stress has a considerable amount of influence on determining crack formation over the machined surface, it is very essential to analyze the residual stress developed in any machining process. However, it is a very tedious process to compute the residual stress over the machined surface. In the present study, an endeavor has been made to measure and analyze the residual stress of machined silicon steel as a workpiece using the EDM process with different energy distribution. The nano-indentation method was used to compute the residual stress produced over the machined surface. From the experimental results, it was found that the uniform energy distribution has produced higher compressive residual stress owing to the tiny and uniform spark energy distribution. It has also been observed that the tool electrode has a considerable amount of influence on determining development of residual stress in the EDM process. 相似文献
109.
S.K. Vimala Bharathi M. Maria Leena J.A. Moses C. Anandharamakrishnan 《International Journal of Food Science & Technology》2020,55(3):1238-1245
The usage of cling wraps is emerging as an easy and cost-effective approach to protect fresh-cut fruits and vegetables from dust, whilst improving visual appeal on retail counters. This study focused on developing an alternate, protein-based packaging material as a food grade cling wrap for food packaging applications. Zein-based cling wraps were produced, and their physical and mechanical characteristics were evaluated and compared with conventionally used chitosan biopolymer films and commercial synthetic polymer films. Antioxidant potential of the prepared films was studied, and the effectiveness of the developed films as anti-browning cling wraps was evaluated using studies conducted on fresh-cut apple slices at ambient conditions. Anti-browning effects were in par with polymeric counterparts; however, zein cling wraps could better prevent weight loss in apple slices. Zein-based films can be adopted as biodegradable food grade cling wraps as an alternative to chitosan and synthetic polymeric materials. 相似文献
110.
Shchelkunov E. B. Vinogradov S. V. Shchelkunova M. E. Pronin A. I. Buravitsyn D. A. 《Russian Engineering Research》2020,40(5):367-371
Russian Engineering Research - The theoretically possible reconfigurable parallel mechanisms are classified, in terms of the layout of guides on the base. Formulas are derived for the... 相似文献