全文获取类型
收费全文 | 44125篇 |
免费 | 4920篇 |
国内免费 | 2818篇 |
专业分类
电工技术 | 1035篇 |
综合类 | 2240篇 |
化学工业 | 4994篇 |
金属工艺 | 6084篇 |
机械仪表 | 3370篇 |
建筑科学 | 610篇 |
矿业工程 | 562篇 |
能源动力 | 2395篇 |
轻工业 | 646篇 |
水利工程 | 489篇 |
石油天然气 | 708篇 |
武器工业 | 526篇 |
无线电 | 16677篇 |
一般工业技术 | 8159篇 |
冶金工业 | 856篇 |
原子能技术 | 745篇 |
自动化技术 | 1767篇 |
出版年
2024年 | 84篇 |
2023年 | 812篇 |
2022年 | 1017篇 |
2021年 | 1376篇 |
2020年 | 1378篇 |
2019年 | 1230篇 |
2018年 | 1147篇 |
2017年 | 1540篇 |
2016年 | 1435篇 |
2015年 | 1527篇 |
2014年 | 2178篇 |
2013年 | 2402篇 |
2012年 | 2851篇 |
2011年 | 3192篇 |
2010年 | 2493篇 |
2009年 | 2456篇 |
2008年 | 2631篇 |
2007年 | 3003篇 |
2006年 | 2769篇 |
2005年 | 2338篇 |
2004年 | 2128篇 |
2003年 | 1835篇 |
2002年 | 1522篇 |
2001年 | 1323篇 |
2000年 | 1112篇 |
1999年 | 944篇 |
1998年 | 812篇 |
1997年 | 754篇 |
1996年 | 683篇 |
1995年 | 629篇 |
1994年 | 547篇 |
1993年 | 462篇 |
1992年 | 352篇 |
1991年 | 318篇 |
1990年 | 217篇 |
1989年 | 112篇 |
1988年 | 82篇 |
1987年 | 30篇 |
1986年 | 27篇 |
1985年 | 28篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1975年 | 5篇 |
1959年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
61.
F.T. Munna Vidhya Selvanathan K. Sobayel Ghulam Muhammad Nilofar Asim Nowshad Amin Kamaruzzaman Sopian Md. Akhtaruzzaman 《Ceramics International》2021,47(8):11003-11009
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell. 相似文献
62.
Shannon Lee Scott L. Carnahan Georgiy Akopov Philip Yox Lin-Lin Wang Aaron J. Rossini Kui Wu Kirill Kovnir 《Advanced functional materials》2021,31(16):2010293
Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi4P4 and IrSi3P3 are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and 29Si and 31P magic angle spinning NMR. In agreement with previous report RuSi4P4 crystallizes in NCS space group P1, while IrSi3P3 is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi4P4 and IrSi3P3 to be wide bandgap (Eg) semiconductors, Eg = 1.9 and 1.8 eV, respectively. RuSi4P4 and IrSi3P3 outperform the current state-of-the-art infrared SHG material, AgGaS2, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi4P4 and IrSi3P3 are promising candidates for longer wavelength NLO materials. 相似文献
63.
Jiming Zhou Kangdi Zhong Chentong Zhao Haiming Meng Lehua Qi 《Ceramics International》2021,47(5):6597-6607
The design of an interfacial structure is particularly important for load transfer in composites. In this paper, different amounts of carbon nanotubes (CNTs) were grafted onto the carbon fiber (CF) surface by adjusting grown temperature using injection chemical vapor deposition (ICVD). The prepared CF preform grafted with CNTs (CNTs-CF) were used to reinforce magnesium alloy by squeeze casting process. The microstructures were analyzed by means of optical microscope (OM) and scanning electron microscope (SEM), and the interlaminar shear strength (ILSS) and tensile strength of the composites were determined by double-notch shear test and tensile test. The results indicated that moderate ILSS was more conducive to improving the tensile properties of carbon fiber reinforced magnesium matrix (Cf/Mg) composites. Compared with Cf/Mg, the tensile strength of composite with CNTs increased by about 80%. For Cf/Mg composites grafted with CNTs, CNTs had the effects of delaying crack propagation and increasing energy consumption by the pull-out and bridging mechanism, which were the main reasons for improving the strength. The analysis of shear fracture surface showed that the crack propagation path can be optimized by adjusting the amounts of grafted CNTs. The presence of CNTs affects the stress distribution and consequently the crack initiation as well as the crack propagation. 相似文献
64.
Wei Shao Qianqian Pan Qiaoli Chen Chongzhi Zhu Weijian Tao Haiming Zhu Huijun Song Xuelu Liu Ping-Heng Tan Guan Sheng Tulai Sun Xiaonian Li Yihan Zhu 《Advanced functional materials》2021,31(3):2006738
Metallic nanocrystals manifest themselves as fascinating light absorbers for applications in plasmon-enhanced photocatalysis and solar energy harvesting. The essential challenges lie in harvesting the full-spectrum solar light and harnessing the plasmon-induced hot carriers at the metal–acceptor interface. To this end, a cooperative overpotential and underpotential deposition strategy is proposed to mitigate both the challenges. Specifically, by utilizing both ionic additive and thiol passivator to introduce symmetry-breaking growth over gold icosahedral nanocrystals, the microscopic origin can be attributed to the site-specific nucleation of stacking faults and dislocations. By adopting asymmetric crystal shape and unique surface facets, such nanocrystals attain high activity toward photocatalytic ammonia borane hydrolysis, arising from combined broadband plasmonic properties and enhanced direct transfer of hot electrons across the metal–adsorbate interface. 相似文献
65.
Two-beam laser welding (TBLW) is an advanced process for precise, low distortion joining of cylindrical miniature parts. The process is composed of a laser source, optics and various actuators, which form a sophisticated system for control and maintenance in high volume manufacturing. A well-established method for identifying welding defects and ensuring welding quality is the monitoring of plasma light emission in TBLW. Although such monitoring systems can detect a change in process status, they are not able to diagnose the nature of the fault. The main challenge in this research was to extend the use of quality-based monitoring systems to measure additional deterioration-related parameters and to estimate system deterioration from them by using expert knowledge.This paper shows a novel condition-based maintenance (CBM) for the TBLW system, which performs condition identification using online monitoring of plasma light emission in combination with offline inspection of the seam macrographs. A combination of quality parameters derived from seam macrographs of defective parts is used to identify process deterioration, such as contamination of the optics, misalignment of the optomechanical system, or reduced laser power. The information obtained is used to make predefined process adjustments based on expert domain knowledge. The implementation of the developed CBM in high volume manufacturing of piezoelectric pressure sensors resulted in more predictable TBLW by reducing system failures as well as shorter diagnosis times. 相似文献
66.
E. Willems M. Turon-Vinas B. Camargo dos Santos B. Van Hooreweder F. Zhang B. Van Meerbeek J. Vleugels 《Journal of the European Ceramic Society》2021,41(10):5292-5306
The possibility of additive manufacturing of ceramics has been reported widely in scientific literature. This study investigates the potential of direct inkjet printing or material jetting of 3Y-TZP ceramics by assessing the microstructure and mechanical properties of the sintered printed parts. The technique allows to print in layers of 10.5 μm, with an as-printed green density of 58 % and nearly fully sintered density of 6.03 ± 0.1 g/cm3 (99.7 % TD). The dimensions of the green and sintered parts were highly accurate but showed an anisotropic roughness in function of the building direction, mainly due to the support structures. The biaxial bending and 4-point bending strength of the sintered material was found to be substantially higher in the XY direction than in the building (Z) direction. SEM and X-Ray computed tomography revealed the presence of delamination cracks, agglomerates and spherical pores, which were identified as fracture origins on fractured surfaces. 相似文献
67.
《Ceramics International》2022,48(20):29892-29899
It is very challenging for 3D printing based on the selective laser melting (SLM) technology to obtain cermet bulk materials with high density and homogeneous microstructures. In this work, the SLM process of the cermet powders was studied by both simulations and experiments using the WC-Co cemented carbides as an example. The results indicated that the evolution of the ceramic and metallic phases in the cermet particle during the heating, melting and solidification processes were all significantly inhomogeneous from atomic scale to mesoscale microstructures. As a consequence, the microstructural defects were caused intrinsically in the printed bulk material. The formation and growth of the bonding necks between the particles were mainly completed at the later stage of laser heating and the early stage of solidification. Both simulations and experiments demonstrated that thin amorphous layers formed at the ceramics/metal interfaces. This work disclosed the mechanisms for the evolution from the atomic scale to microstructure during the SLM printing of cermet powders, and discovered the origin of the defects in the printed cermet bulk materials. 相似文献
68.
Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles, which can be polymerize form the monomer of dimethoxymethane (DMM). The industrial synthesis of DMM is mainly involved two-step process: methanol is oxidized to form the formaldehyde in fixed bed reactor and then reacted with the generated formaldehyde through acetalization in continuous stirred-tank reactor. Due to huge energy consumption, this typical synthesis route of DMM needs to be upgraded and more green routes should be determined. In this review, four state-of-the-art one-step direct synthetic routes, including two upgrading routes (methanol direct oxidation and direct dehydrogenation) and two green routes (methanol diethyl ether direct oxidation and carbon oxides direct hydrogenation), have been summarized and compared. Combination with the reaction mechanism and catalytic performance on the different catalysts, the challenges and opportunities for every synthetic route are proposed. The relationships between catalyst structure and property in different synthesis strategy are also investigated and then the suggestions of the design of catalyst are given about future research directions that efforts should be made in. Hopefully, this review can bridge the gap between newly developed catalysts and synthesis technology to realize their commercial applications in the near future. 相似文献
69.
《Journal of the European Ceramic Society》2022,42(6):2957-2973
Functionally graded ceramics (FGC), which combine properties of different ceramics in one part, usually have better comprehensive function and structural efficiency. In this study, four different gradient transition Al2O3-ZrO2 FGC samples were prepared by laser directed energy deposition (LDED) method. The results show that there is an obvious interface in direct transition sample. The transition section bears tensile stress caused by difference of thermophysical properties of materials, resulting in significant longitudinal cracks. Element transition in interface region shows a step sharp transition. The direct transition sample shows intergranular fracture and the bonding strength is very low. Gradient transition mode can effectively suppress cracks, and avoid the step transition of microstructure and elements. Elements, microhardness of 25, 20 wt% FGC samples realized a nearly linear smooth transition. The interface fracture of FGC samples changed to transgranular fracture, bonding strength was significantly improved, and the maximum flexural strength reached 160.19 MPa. 相似文献
70.
Kleitos Panagi Christian J. Laycock James P. Reed Alan J. Guwy 《International Journal of Hydrogen Energy》2021,46(2):2630-2645
Biohythane is typically composed of 60/30/10 vol% CH4/CO2/H2 and can be produced via two-stage anaerobic digestion of renewable and low carbon biomass with much greater efficiency compared with CH4/CO2 biogas. This work investigates the effects of fuel variability on the electrical performance and fuel processing of a commercially available anode supported solid oxide fuel cell (SOFC) operating on biohythane mixtures at 750 °C. Cell electrical performance was characterised using current-voltage curves and electrochemical impedance spectroscopy. Fuel processing was characterised using quadrupole mass spectroscopy. It is shown that when H2/CO2 is blended with CH4 to make biohythane, the SOFC efficiency is significantly increased, high SOFC durability is achieved, and there are considerable savings in CH4 consumption. Enhanced electrical performance was due to the additional presence of H2 and promotion of CH4 dry reforming, the reverse Boudouard and reverse water-gas shift reactions. These processes alleviated carbon deposition and promoted electrochemical oxidation of H2 as the primary power production pathway. Substituting 50 vol% CH4 with 25/75 vol% H2/CO2 was shown to increase cell power output by 81.6% at 0.8 V compared with pure CH4. This corresponded to a 3.4-fold increase in the overall energy conversion efficiency and a 72% decrease in CH4 consumption. A 260 h durability test demonstrated very high cell durability when operating on a typical 60/30/10 vol% CH4/CO2/H2 biohythane mixture under high fuel utilisation due to inhibition of carbon deposition. Overall, this work suggests that decarbonising gas grids by substituting natural gas with renewably produced H2/CO2 mixtures (rather than pure H2 derived from fossil fuels), and utilising in SOFC technology, gives considerable gains in energy conversion efficiency and carbon emissions savings. 相似文献