全文获取类型
收费全文 | 122972篇 |
免费 | 10836篇 |
国内免费 | 6965篇 |
专业分类
电工技术 | 6684篇 |
技术理论 | 10篇 |
综合类 | 14291篇 |
化学工业 | 14483篇 |
金属工艺 | 7431篇 |
机械仪表 | 7988篇 |
建筑科学 | 21833篇 |
矿业工程 | 4602篇 |
能源动力 | 2927篇 |
轻工业 | 7930篇 |
水利工程 | 3277篇 |
石油天然气 | 5081篇 |
武器工业 | 1419篇 |
无线电 | 8257篇 |
一般工业技术 | 11782篇 |
冶金工业 | 4974篇 |
原子能技术 | 845篇 |
自动化技术 | 16959篇 |
出版年
2024年 | 213篇 |
2023年 | 1470篇 |
2022年 | 2802篇 |
2021年 | 3407篇 |
2020年 | 3481篇 |
2019年 | 2695篇 |
2018年 | 2554篇 |
2017年 | 3314篇 |
2016年 | 3542篇 |
2015年 | 4028篇 |
2014年 | 7589篇 |
2013年 | 6445篇 |
2012年 | 8736篇 |
2011年 | 9609篇 |
2010年 | 7493篇 |
2009年 | 7994篇 |
2008年 | 7418篇 |
2007年 | 8874篇 |
2006年 | 7938篇 |
2005年 | 6939篇 |
2004年 | 5745篇 |
2003年 | 5134篇 |
2002年 | 4248篇 |
2001年 | 3581篇 |
2000年 | 2938篇 |
1999年 | 2427篇 |
1998年 | 1828篇 |
1997年 | 1582篇 |
1996年 | 1226篇 |
1995年 | 1065篇 |
1994年 | 985篇 |
1993年 | 662篇 |
1992年 | 617篇 |
1991年 | 479篇 |
1990年 | 382篇 |
1989年 | 293篇 |
1988年 | 225篇 |
1987年 | 127篇 |
1986年 | 96篇 |
1985年 | 96篇 |
1984年 | 79篇 |
1983年 | 71篇 |
1982年 | 78篇 |
1981年 | 30篇 |
1980年 | 71篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
β(1,3)-glucans are a component of fungal and plant cell walls. The β-glucan of pathogens is recognized as a non-self-component in the host defense system. Long β-glucan chains are capable of forming a triple helix structure, and the tertiary structure may profoundly affect the interaction with β-glucan-binding proteins. Although the atomic details of β-glucan binding and signaling of cognate receptors remain mostly unclear, X-ray crystallography and NMR analyses have revealed some aspects of β-glucan structure and interaction. Here, we will review three-dimensional (3D) structural characteristics of β-glucans and the modes of interaction with β-glucan-binding proteins. 相似文献
82.
83.
Bakhtiar Ul Haq S. AlFaify Thamraa Alshahrani R. Ahmed Q. Mahmood S.A. Tahir Hala H. Alhashim A. Laref 《Ceramics International》2021,47(3):3380-3388
The development of materials in two-dimensions has been established as an effective approach to improve their thermoelectric performance for renewable energy production. In this article, we generated monolayers of the orthorhombic structured lead-chalcogenides PbX (X = S, Se, and Te) for room-temperature thermoelectric applications. The Density functional theory and semiclassical Boltzmann transport theory-based computational approaches have been adopted to carry out this study. The band structures of PbX monolayers exhibited narrow indirect bandgaps with a large density of states corresponding to their bandgap edges. Accordingly, substantial electrical conductivities and Seebeck coefficients have been obtained at moderate level doping that has caused significant thermoelectric power factors (PFs) and figures-of-merit (zT) ~1. The single-layered PbX showed anisotropic dispersion of electronic states in the band structure. A relatively lighter effective mass of charge carriers has been extrapolated from the bands oriented in the y-direction than that of the x-direction. As a result, the electrical conductivities and PFs have been observed larger in the y-direction. The optimum PFs recorded for single-layered PbS, PbSe, and PbTe in y-direction amounts to 9.90 × 1010 W/mK2s at 1.0 eV, 10.40 × 1010 W/mK2s at 0.82 eV, and 10.80 × 1010 W/mK2s 0.66 eV respectively. Moreover, a slight increase in p-type doping is found to improve the x-component of the PF, whereas n-type doping has led to improvement in the y-component of PF. Our results show an improved thermoelectric response of PbX monolayer (PbTe in particular) than their bulk counterparts reported in the literature, which indicates the promise of PbX monolayers for nanoscale thermoelectric applications at room temperature. 相似文献
84.
为国民身体素质、探索具有中国特色的现代食育之路,必须深入分析与探索中国饮食文化中的食育理念。文章以传统饮食文化为出发点和落脚点,概括出医食同源、饮食有节、饮食有礼等先进的食育观点。分析传统饮食与现代食育的关系,认为食育是弘扬传统饮食文化的重要途径,传统饮食文化是发展现代食育的基础。但探索现代食育仍面临着西方快餐文化冲击和国民食育进程缓慢等困境,必须采取强化国民食育意识、加强食育法制建设、健全食育教育体系、推进食育试点工作等措施促进中国传统饮食文化融入食育体系建设,真正探索具有中国特色的食育之路。 相似文献
85.
86.
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
87.
With this contribution,as a comment to the publication in Journal of Mate rials Science&Technology 44(2020)54,reporting giant dielectric response,structural characterization and numerical simulations in Sr_(1-1.5 x)Bi_xTiO3ceramics,we show that the re ported results are rather contradicting and not well analysed,while the suggested mechanism for the giant permittivity response is not valid or doubtful and has to be reconsidered.Moreover,many details and data are missing making impossible not only to call the obtained results very suitable for practical application but even to reproduce them. 相似文献
88.
《中国有色金属学会会刊》2021,31(9):2861-2870
AsSb alloy (0.70–95.81 wt.% As) was prepared by electrodeposition in As(III) and Sb(III) contained electrolytes. The influence of electrolyte composition, hydrochloric acid concentration, and temperature on the composition and structure of AsSb deposits was studied. The electroreduction mechanism of As(III) and Sb(III) in hydrochloric acid solution was revealed via thermodynamic analysis. The results show that the increase of H+ concentration promotes the reduction of As(III), while the increase of Cl− concentration significantly inhibits the reduction of Sb(III). As a result, the As content in deposits increases gradually with the increase of hydrochloric acid concentration. Simultaneously, the phase structure of AsSb deposits evolves from crystalline to amorphous. When the As content is 24.55–33.75 wt.%, AsSb mixed crystal is obtained. The electrolysis temperature has little effect on the deposits composition, but the structure of deposits evolves from crystalline to amorphous with decreasing the temperature. 相似文献
89.
Yi Chen Weijian Sun Haonan Zheng Changhao Li Bo Zhang Baoxiang Wang Chuncheng Hao 《Ceramics International》2021,47(17):24080-24091
In this paper, a novel H2Ti2O5@MoS2@SiO2 ternary composite material was prepared by a combination of dual hydrothermal method and controlled hydrolysis method, in which H2Ti2O5 nanotubes are tightly combined with hierarchical molybdenum disulfide, and the unique structure of titanate nano whiskers, including the loosely bound alkali metal ions between the titanate layers with high dielectric constant and the large aspect ratio, which induce active response to the electric field. Flower-like molybdenum disulfide provides electrical conductivity, and silicon dioxide as a insulative coating layer can suppress excessive the electrical conductivity of the two-dimensional material. The morphological evolution was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results of showed that the sheet-shaped molybdenum disulfide coated with curved H2Ti2O5 nanotubes showed a honeycomb structure with uniform size. Silicon oxide acts as a cladding layer to increase the thickness of the flakes. The existence of H2Ti2O5, molybdenum disulfide and silicon dioxide is confirmed by X-ray powder diffractometer (XRD) and Fourier transform infrared spectroscopy (FT-IR). The prepared product was confirmed by XPS, BET test and electrorheological rheometer. Core/shell nanoparticles not only exert the active response characteristics of titanate nanoparticles and molybdenum disulfide to electric field, but also inherit the excellent characteristics of a core-shell structure produced by the interface polarization and the synergistic effect of the polar groups on the surface of the two-dimensional material further enhance the electrorheological effect. 相似文献
90.
Polymers containing a certain amount of long-chain-branching (LCB) structure are expected to possess improved mechanical properties over those of the linear structure counterpart. However, fundamental knowledge on the structure–property relationship in LCB containing polypropylene (PP) is still illusive. In the present study, a set of model PP systems containing an increasing molar fraction of LCB (5–19 mol%) were prepared by reactive extrusion to determine how LCB content may influence the scratch behavior of PP. It is shown that with only 5 mol% of LCB content in PP can improve resistance against scratch-induced fish-scale formation by over 25%. The improvement of scratch resistance is attributed to the increases in entanglement density in LCB-containing PPs, which is evidenced by their creep-recovery behavior. The present study demonstrates that the incorporation of LCB in PP leads to higher viscoelastic recovery and increased tensile strength, which account for the observed improvement in scratch performance. The usefulness of LCB in polymers for improving scratch performance is discussed. 相似文献