全文获取类型
收费全文 | 115947篇 |
免费 | 10525篇 |
国内免费 | 6169篇 |
专业分类
电工技术 | 7814篇 |
技术理论 | 8篇 |
综合类 | 7972篇 |
化学工业 | 17264篇 |
金属工艺 | 7023篇 |
机械仪表 | 7933篇 |
建筑科学 | 7230篇 |
矿业工程 | 3589篇 |
能源动力 | 3100篇 |
轻工业 | 8851篇 |
水利工程 | 2879篇 |
石油天然气 | 5247篇 |
武器工业 | 1406篇 |
无线电 | 13193篇 |
一般工业技术 | 15256篇 |
冶金工业 | 6594篇 |
原子能技术 | 1962篇 |
自动化技术 | 15320篇 |
出版年
2024年 | 543篇 |
2023年 | 1708篇 |
2022年 | 3737篇 |
2021年 | 4887篇 |
2020年 | 3693篇 |
2019年 | 3093篇 |
2018年 | 3871篇 |
2017年 | 4233篇 |
2016年 | 4091篇 |
2015年 | 4864篇 |
2014年 | 6132篇 |
2013年 | 7619篇 |
2012年 | 8281篇 |
2011年 | 8459篇 |
2010年 | 7766篇 |
2009年 | 7683篇 |
2008年 | 7520篇 |
2007年 | 7370篇 |
2006年 | 6731篇 |
2005年 | 5165篇 |
2004年 | 3820篇 |
2003年 | 2941篇 |
2002年 | 3040篇 |
2001年 | 2833篇 |
2000年 | 2545篇 |
1999年 | 1999篇 |
1998年 | 1629篇 |
1997年 | 1399篇 |
1996年 | 902篇 |
1995年 | 736篇 |
1994年 | 544篇 |
1993年 | 480篇 |
1992年 | 385篇 |
1991年 | 308篇 |
1990年 | 222篇 |
1989年 | 209篇 |
1988年 | 161篇 |
1987年 | 99篇 |
1986年 | 112篇 |
1985年 | 103篇 |
1984年 | 51篇 |
1983年 | 49篇 |
1982年 | 51篇 |
1981年 | 49篇 |
1980年 | 57篇 |
1979年 | 45篇 |
1978年 | 36篇 |
1976年 | 43篇 |
1974年 | 29篇 |
1969年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Kazantsev Yu. N. Kraftmakher G. A. Mal’tsev V. P. 《Journal of Communications Technology and Electronics》2019,64(6):550-554
Journal of Communications Technology and Electronics - Approximate formulas for calculating the coefficient of reflection from an artificial magnetic conductor (AMC) based on a capacitive lattice... 相似文献
52.
Zinov’eva I. V. Fedorov A. Ya. Milevskii N. A. Zakhodyaeva Yu. A. Voshkin A. A. 《Theoretical Foundations of Chemical Engineering》2021,55(4):663-670
Theoretical Foundations of Chemical Engineering - A choline chloride–sulfosalicylic acid deep eutectic solvent (DES) is proposed for dissolving the oxides Co(II), Cu(II), Zn(II), Fe(III),... 相似文献
53.
Chertkov Yu. B. Anikin M. N. Lebedev I. I. Naimushin A. G. Smol’nikov N. V. 《Atomic Energy》2021,131(1):42-45
Atomic Energy - The results of calculations and experimental determination of the neutronics characteristics of the IRT-T research reactor are presented. The IRT-T reactor is a pool reactor with... 相似文献
54.
Zakraoui Jezia Saleh Moutaz Al Ja’am Jihad 《Multimedia Tools and Applications》2019,78(16):22833-22859
Multimedia Tools and Applications - Text-to-picture systems attempt to facilitate high-level, user-friendly communication between humans and computers while promoting understanding of natural... 相似文献
55.
Crystallographic characteristics and microwave dielectric properties of Ni-modified MgTa2O6 ceramics
Liang Shi Xueying Wang Rui Peng Gang Wang Cheng Liu Xiaolei Shi Dainan Zhang Huaiwu Zhang 《Ceramics International》2021,47(16):22514-22521
Ni2+ modified MgTa2O6 ceramics with a trirutile phase and space group P42/mnm were obtained. The correlations between crystallographic characteristics and microwave dielectric performance of MgTa2O6 ceramics were systematically studied based on the chemistry bond theory (PVL theory) for the first time. The results indicate that the introduction of Ni2+ causes a change in polarizability and the Mg–O bond ionicity, which contributes to the variation of dielectric constant. Moreover, the lattice energy, and packing fraction, full width at half maximum of the Raman peak of Ta–O bond, as the quantitative characterization of crystallographic parameters, regulate the dielectric loss of MgTa2O6 ceramics in GHz frequency band. In addition, the study of sintering behavior shows that the densification and micromorphology are the crucial factors affecting the microwave dielectric performance. Typically, Ni2+ doping on the A-site of MgTa2O6 can effectively promote the Q × f values to 173,000 GHz (at 7.43 GHz), which ensures its applicability in 5G communication technology. 相似文献
56.
Liang Shi Dainan Zhang Rui Peng Cheng Liu Xiaolei Shi Xueying Wang Huaiwu Zhang 《Journal of the European Ceramic Society》2021,41(11):5526-5530
Mg(1-x)ZnxTa2O6 (x = 0.00?0.08) dielectric ceramics were synthesized via the traditional solid-state reaction method. We used XRD and Rietveld refinement to demonstrate that a pure Mg(1-x)ZnxTa2O6 phase with trirutile structure was formed. Zn2+ substitution helped to decrease the Raman full width at half width of the A1g mode at 703 cm?1, which resulted in an increase in the order and rigidity of the TaO6 octahedron, this in turn contributed to improving the Q×f values. Additionally, the introduction of Zn2+ significantly promoted grain growth and increased the dense, and the molecular polarizability, these factors lead to a higher permittivity. Moreover, enhanced Ta-O bond energy resulted in a more stable TaO6 octahedron in the Mg(1?x)ZnxTa2O6 system, which contributed to enhanced τf values via substitution of Zn2+ doped on the A-site. Correspondingly, the microwave dielectric properties were significantly improved for 0.04-doped samples, obtaining: εr = 27, Q × f = 185,000 GHz (at 7.47 GHz), τf =32 ppm/°C. 相似文献
57.
Byakova O. V. Stepanov G. V. Vlasov A. O. Danylyuk V. E. Semenov N. V. Berezovs’kyi O. M. Gnyloskurenko S. V. 《Strength of Materials》2019,51(5):726-734
Strength of Materials - The paper addresses the investigation of high-strain rate compressive behavior of Al foams subjected to impact at the intermediate striking velocity ranged from 40 to... 相似文献
58.
Longbang Qing Yuehua Cheng Ru Mu 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(11):2533-2543
Based on theoretical analysis and numerical simulation, the impact of steel fibres on the stress intensity factor (SIF) at the crack tip for cementitious composite was studied. The enhanced toughness of steel fibre reinforced cementitious composite (SFRC) in resisting cracks was explained by the decrement of SIF caused by steel fibre inclusions at the crack tip of the composite. The equivalent initial fracture toughness was used to characterize the crack initiation of SFRC. A simplified method for determining the of SFRC was proposed based on a linear regression method. Fracture tests were conducted on three‐point bending notched beams with different steel fibre volume fractions and specimen sizes to study the crack initiation behaviour of aligned steel fibre reinforced cementitious composite (ASFRC). of ASFRC was calculated, and the size effect of was analysed. The results showed that slightly increased with the steel fibre volume fraction and gradually became stable. For the tested specimens, whose heights varied between 40 and 100 mm, the specimen size had little impact on the . 相似文献
59.
60.
V. N. Oparin V. I. Vostrikov O. M. Usol’tseva P. A. Tsoi V. N. Semenov 《Journal of Mining Science》2015,51(3):624-633
The authors have developed a procedure and a test bench for studying evolution of various nature physical fields in modeling geomedium fracture by fluids. The test bench performs synchronous recording of macro- and micro-deformation, heat and acoustic emission induced in physical models of geomedium under loading to discontinuity. The experimental procedure has been trialed. The analysis of the synchronized test data allows a conclusion on the existence of time–space relationship between different nature physical fields induced during failure of solids. 相似文献