全文获取类型
收费全文 | 13833篇 |
免费 | 879篇 |
国内免费 | 880篇 |
专业分类
电工技术 | 219篇 |
综合类 | 874篇 |
化学工业 | 1776篇 |
金属工艺 | 1587篇 |
机械仪表 | 1132篇 |
建筑科学 | 278篇 |
矿业工程 | 105篇 |
能源动力 | 309篇 |
轻工业 | 236篇 |
水利工程 | 77篇 |
石油天然气 | 116篇 |
武器工业 | 52篇 |
无线电 | 3698篇 |
一般工业技术 | 4037篇 |
冶金工业 | 272篇 |
原子能技术 | 199篇 |
自动化技术 | 625篇 |
出版年
2024年 | 16篇 |
2023年 | 136篇 |
2022年 | 190篇 |
2021年 | 229篇 |
2020年 | 309篇 |
2019年 | 240篇 |
2018年 | 262篇 |
2017年 | 418篇 |
2016年 | 338篇 |
2015年 | 398篇 |
2014年 | 587篇 |
2013年 | 861篇 |
2012年 | 851篇 |
2011年 | 1272篇 |
2010年 | 901篇 |
2009年 | 1030篇 |
2008年 | 975篇 |
2007年 | 909篇 |
2006年 | 751篇 |
2005年 | 745篇 |
2004年 | 661篇 |
2003年 | 629篇 |
2002年 | 528篇 |
2001年 | 322篇 |
2000年 | 322篇 |
1999年 | 257篇 |
1998年 | 220篇 |
1997年 | 188篇 |
1996年 | 160篇 |
1995年 | 122篇 |
1994年 | 137篇 |
1993年 | 123篇 |
1992年 | 102篇 |
1991年 | 91篇 |
1990年 | 89篇 |
1989年 | 57篇 |
1988年 | 33篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
《Ceramics International》2020,46(12):20415-20422
Boron nitride nanosheets (BNNS) with thickness 5–11 nm were successfully produced when pure boron powder (1–2 μm) interacted with ammonia gas in chemical vapour deposition set up. Under the optimized parameters, at 1200 °C and for uninterrupted 1 h of reaction duration, 2D BNNS with thickness of ca.11 nm were synthesized. BNNS were characterized by X-ray diffraction (XRD) for crystal structure, scanning electron microscopy for dimensions and morphology, energy dispersive X-ray analysis for chemical composition and Fourier transform infrared spectroscopy for sp2 BN bond detection. The thickness of BNNS determined from both XRD data (using Scherrer equation) and atomic force microscopic analysis confirmed the stated product thickness. The BNNS obtained at 1200 °C had high crystallinity, purity and yield. 相似文献
32.
Konstantinos Spyrou Matteo Calvaresi Evmorfia K. Diamanti Theodoros Tsoufis Dimitrios Gournis Petra Rudolf Francesco Zerbetto 《Advanced functional materials》2015,25(2):263-269
Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”. 相似文献
33.
The visible light driven Bi2MoO6 photocatalyst doped with different contents of Ag nanoparticles was successfully synthesized by a combination of hydrothermal and sonochemical methods. The as-synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy (SEM and TEM) and UV–visible spectroscopy to investigate crystalline structure, morphology, composition and photocatalytic properties. XRD patterns and TEM images of the samples revealed pure phase orthorhombic Bi2MoO6 nanoplates without any detection of Ag dopant due to its low concentration and very tiny particle size. TEM images showed that Ag nanoparticles with the size of 10–15 nm were dispersed randomly on the surface of Bi2MoO6. The XPS analysis of Ag/Bi2MoO6 nanocomposites revealed the presence of additional metallic Ag. Photocatalytic activities of the Ag/Bi2MoO6 nanocomposites were evaluated by determining the degradation of rhodamine B (RhB) under visible light radiation. In this research, the 10 wt% Ag/Bi2MoO6 nanocomposites showed the best photocatalytic activity. The results suggest that the dispersion of Ag nanoparticles on the surface of Bi2MoO6 significantly enhances its photocatalytic activity. 相似文献
34.
In this article, two novel kinds of focusing elements as reflectors are analyzed and compared. One is the grooved Fresnel zone plate reflector with continuous phase‐correcting. The other called subzone paraboloid reflector, has the profile that consists of a series of paraboloids. Their diffraction efficiencies and bandwidths are described. The two elements still preserve the advantages of Fresnel zone plates, namely, low profile, high efficiency, and simple fabrication. Two dual‐reflector antennas using the proposed focusing elements as the main reflectors are simulated and the results show that these antennas have good radiation performances. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:101–108, 2015. 相似文献
35.
《Ceramics International》2020,46(10):15889-15896
UO2-Mo composites with a core-shell structure have been considered candidates for the thermal conductivity (TC)-enhanced UO2 pellets and have demonstrated commercial potential for use in novel high-level safety reactors. Nevertheless, UO2-Mo composites tend to form micro-cracks that are caused by the presence of residual stress (RS) during manufacturing. In this work, neutron diffraction measurements were employed to analyse the RS in UO2-Mo core-shell structured composites fabricated by spark plasma sintering (SPS) for the first time. It was found that in the UO2-Mo composites, the RS state present in the UO2 matrix was tensile in nature. The RS in the UO2 matrix increased with increaseing Mo content. There was a maximum value of 148 ± 15 MPa in the UO2-10 vol% Mo composite. The micro-cracks produced in the high-Mo content composites were explained by the results of the neutron diffraction measurements. These results could provide significant guidance for the manufacturing and improvement of the operational performance of UO2-Mo composites as next-generation fuels. 相似文献
36.
Based on column approximation (CA) assumption, many-beam Schaeublin–Stadelmann diffraction equations are employed for simulating the transmission electron microscopy (TEM) diffraction image contrast of dislocation loops within thin TEM foil of finite thickness, and two beam and many beam diffraction conditions are compared. Moreover, the effects of materials anisotropy and free surface relaxation induced elastic fields distortion of dislocation loops on the black-white image contrast are specially focused. It is found that anisotropy has a remarkable impact on the TEM image contrast of dislocation loop, and free surface relaxation induced image forces can change the black-white contrast features when dislocation loops are near TEM foil free surfaces. Thus, in order to make reliable judgment on the nature of defects, effects of free surface and anisotropy should be included when analysing irradiation induced dislocation loops and other type of defects in in-situ electron, proton, heavy-ion irradiation experiments under TEM environments. 相似文献
37.
《Journal of the European Ceramic Society》2020,40(3):672-681
Promising piezoelectric properties have been reported in potassium sodium niobate-based ceramics by introducing Bi0.5(Na0.82K0.18)0.5ZrO3 (BNKZ) into K0.48Na0.52Nb0.95Sb0.05O3 (KNNS) solid solutions in order to control the polymorphic phase transformation temperatures. In the present study, synchrotron x-ray powder diffraction (SXPD) was employed in combination with dielectric and ferroelectric measurements in order to clarify the influence of BNKZ on the phase transition temperatures of (1-x)KNNS-(x)BNKZ ceramics (with x = 0 to 0.05). The results, presented in terms of temperature-dependent SXPD patterns, dielectric permittivity and thermal depolarisation characteristics, confirmed that polymorphic phase transformation temperatures all shifted in a systematic manner with increasing BNKZ content. Broadening of the phase transition regions was also observed with increasing BNKZ content, leading to improvements in thermal stability of the ferroelectric properties. Microstructural examination of the KNNS-BNKZ ceramics revealed the presence of core-shell microstructures; this was correlated with the presence of weak shoulders on the diffraction peaks. 相似文献
38.
Effect of Fe doping on structure,magnetic and electrical properties La0.7Ca0.3Mn0.5Fe0.5O3 manganite
N.T. Dang V.S. Zakhvalinskii D.P. Kozlenko The-Long Phan S.E. Kichanov S.V. Trukhanov A.V. Trukhanov Yu.S. Nekrasova S.V. Taran S.V. Ovsyannikov S.H. Jabarov E.L. Trukhanova 《Ceramics International》2018,44(13):14974-14979
The crystal and magnetic structures of La0.7Ca0.3Mn0.5Fe0.5O3 compound have been studied by neutron powder diffraction in the temperature range of 10–300 К. The magnetization and electrical resistivity measurements have been also performed in the temperature range of 5–300?K in magnetic fields up to 1?T. These experimental results indicate a formation of a complex magnetic state in which the long-range antiferromagnetic G-type phase coexists with the short-range ferromagnetic clusters. The electrical conductivity of La0.7Ca0.3Mn0.5Fe0.5O3 demonstrates an anomalous temperature behavior suggesting a switching between different states. The origin of the unconventional magnetic state, the mechanisms of the electrical conductivity, and correlation between magnetic and transport properties in this manganite have been discussed. 相似文献
39.
Yang Luo Shi-li Zheng Shu-hua Ma Chun-li Liu Xiao-hui Wang 《Journal of the European Ceramic Society》2018,38(16):5282-5293
A novel mullite-bonded SiC-whisker-reinforced SiC matrix composite (SiCw/SiC, SiC whisker-to-SiC powder mass ratio of 1:9) was designed and successfully prepared. Before preparing the composite, the inexpensive lab-made SiCw was first modified by an oxidation/leaching process and then coated with Al2O3. The kinetics results indicate that the oxidation process can be described by improved shrinking-cylinder models. The aspect ratio of SiCw improved after modification. Subsequently, raw materials with a SiC–SiO2–Al2O3 triple-layered structure were obtained after the Al2O3-coating process and used as feedstocks during the subsequent hot-pressing sintering. Finally, the characterization of the composites indicates that the mullite-bonded sample performs better (relative density of 93.8?±?1.4%, flexural strength of 533.3?±?18.2?MPa, fracture toughness of 13.6?±?2.1?MPa?m1/2, and Vickers hardness of 20.6?±?2.5?GPa) than the reference sample without the mullite interface. The improved toughness could essentially be attributed to the moderately strong interface bonding and effective load transfer effects of the mullite interface. 相似文献
40.
Pavel P. Fedorov Vera Y. Proydakova Sergey V. Kuznetsov Valery V. Voronov Alexandr A. Pynenkov Konstantin N. Nishchev 《Journal of the American Ceramic Society》2020,103(5):3390-3400
The thermal analysis and X-ray powder diffraction studies of the Li2SO4–Na2SO4 system, including the high-temperature X-ray diffraction technique, have elucidated four phases of variable composition: three solid solutions based on the α-Li2SO4, α-Na2SO4, and α-LiNaSO4 high-temperature polymorphs, and a low-temperature β-LiNaSO4 phase. α-Na2SO4-Base solid solution disintegrates into two phases via a monotectoid phase transformation. It is quite probable that the monotectoid process is related to the conversion of the second-order phase transition to the first-order phase transition. 相似文献