全文获取类型
收费全文 | 516141篇 |
免费 | 8067篇 |
国内免费 | 1441篇 |
专业分类
电工技术 | 9430篇 |
综合类 | 513篇 |
化学工业 | 74175篇 |
金属工艺 | 19810篇 |
机械仪表 | 14995篇 |
建筑科学 | 12291篇 |
矿业工程 | 2266篇 |
能源动力 | 14365篇 |
轻工业 | 45992篇 |
水利工程 | 5184篇 |
石油天然气 | 9267篇 |
武器工业 | 37篇 |
无线电 | 59615篇 |
一般工业技术 | 100765篇 |
冶金工业 | 103503篇 |
原子能技术 | 10557篇 |
自动化技术 | 42884篇 |
出版年
2021年 | 4657篇 |
2020年 | 3475篇 |
2019年 | 4553篇 |
2018年 | 7810篇 |
2017年 | 7610篇 |
2016年 | 7930篇 |
2015年 | 5561篇 |
2014年 | 9244篇 |
2013年 | 24067篇 |
2012年 | 14632篇 |
2011年 | 20143篇 |
2010年 | 15804篇 |
2009年 | 17697篇 |
2008年 | 18096篇 |
2007年 | 17777篇 |
2006年 | 15508篇 |
2005年 | 14209篇 |
2004年 | 13599篇 |
2003年 | 13397篇 |
2002年 | 12227篇 |
2001年 | 12085篇 |
2000年 | 10920篇 |
1999年 | 11837篇 |
1998年 | 32144篇 |
1997年 | 22259篇 |
1996年 | 16813篇 |
1995年 | 12927篇 |
1994年 | 11162篇 |
1993年 | 10883篇 |
1992年 | 7811篇 |
1991年 | 7313篇 |
1990年 | 7196篇 |
1989年 | 6884篇 |
1988年 | 6370篇 |
1987年 | 5663篇 |
1986年 | 5578篇 |
1985年 | 6186篇 |
1984年 | 5827篇 |
1983年 | 5098篇 |
1982年 | 4819篇 |
1981年 | 4906篇 |
1980年 | 4654篇 |
1979年 | 4555篇 |
1978年 | 4356篇 |
1977年 | 5284篇 |
1976年 | 6914篇 |
1975年 | 3748篇 |
1974年 | 3503篇 |
1973年 | 3631篇 |
1972年 | 2956篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Francisca Holgado Gloria Márquez-Ruiz María Victoria Ruiz-Méndez Joaquín Velasco 《International Journal of Food Science & Technology》2019,54(8):2520-2528
The influence of the drying method, freeze-drying and spray-drying, on the oxidative stability of microencapsulated sunflower oil depended on the type of encapsulation matrix. For a dairy-type matrix, formed by sodium caseinate and lactose, greater losses of tocopherols were detected during spray-drying, but both the free and encapsulated oil fractions were more stable against lipid oxidation than their freeze-dried counterparts. Results suggested that the free oil was also constituted by droplets that preserved their interfacial membrane and were protected by the matrix. Therefore, the free oil was not necessarily the non-encapsulated fraction. For a matrix constituted by gelatine, maltodextrin and sucrose, the emulsion showed low stability and a great destabilisation during spray-drying. No significant effect of the drying method on the oxidative stability of the encapsulated fraction was found with this matrix, but the free oil of the spray-dried sample oxidised faster, probably due to the emulsion destabilisation observed, which gave rise to a great amount of oil on the particle surface as a consequence of large droplets poorly stabilised. 相似文献
992.
Tamara G. Oberti Diego Larsen M. Susana Cortizo 《Polymer-Plastics Technology and Engineering》2019,58(4):443-453
New copolymers of dioctyl fumarate (DOF) and styrene (S) were synthetized by radical polymerization and used to modify bitumen. The poly(dioctyl fumarate-co-styrene) copolymers, PFS, were characterized by 1H-NMR and FTIR spectroscopies and size exclusion chromatography (SEC) in order to determine their monomer composition and weight average molecular weights, respectively. The polymer-bitumen blending conditions were optimized and the samples analyzed by different methodologies. Fluorescence microscopy, rotational viscosity and differential scanning calorimetry (DSC) were used to study the morphological changes of blends during their manufacturing and the rheological and thermal behavior, respectively. All modified bitumen (MB) exhibited higher viscosity than the based bitumen (BB) under studied conditions and this effect was more evident for the MB containing the higher molecular weight polymer. The addition of polymers to BB enhances the bitumen viscosity and thus increased the energy required for the flowing (activation energy calculated by Arrhenius equation). Thermal and morphological analysis showed that all MB exhibited good polymer- bitumen compatibility, which could be consider as a good starting point for a potential applications of this new material in road engineering. 相似文献
993.
A.R. Jayakrishnan Kevin V. Alex Athul Thomas J.P.B. Silva K. Kamakshi Navneet Dabra K.C. Sekhar J. Agostinho Moreira M.J.M. Gomes 《Ceramics International》2019,45(5):5808-5818
This work reports the composition dependent microstructure, dielectric, ferroelectric and energy storage properties, and the phase transitions sequence of lead free xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 [xBZT-(1-x)BCT] ceramics, with x?=?0.4, 0.5 and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results confirm the coexistence of rhombohedral and tetragonal phases at room temperature (RT). The temperature dependence of Raman scattering spectra, dielectric permittivity and polarization points a first phase transition from ferroelectric rhombohedral phase to ferroelectric tetragonal phase at a temperature (TR-T) of 40?°C and a second phase transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a temperature (TT-C) of 110?°C. The dielectric analysis suggests that the phase transition at TT-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric materials. The composition induced variation in the temperature dependence of dielectric losses was correlated with full width half maxima (FWHM) of A1, E(LO) Raman mode. The saturation polarization (Ps) ≈8.3?μC/cm2 and coercive fields ≈2.9?kV/cm were found to be optimum at composition x?=?0.6 and is attributed to grain size effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 105 cycles. The effect of a.c. electric field amplitude and temperature on energy storage density and storage efficiency is also discussed. The presence of high TT-C (110?°C), a high dielectric constant (εr ≈?12,285) with low dielectric loss (0.03), good polarization (Ps ≈?8.3?μC/cm2) and large recoverable energy density (W?=?121?mJ/cm3) with an energy storage efficiency (η) of 70% at an electric field of 25?kV/cm in 0.6BZT-0.4BCT ceramics make them suitable candidates for energy storage capacitor applications. 相似文献
994.
Xiao Y. Luo Xiao Y. Lv Gui L. Shi Qin Meng Hao R. Li Cong M. Wang 《American Institute of Chemical Engineers》2019,65(1):230-238
Generally, amine group captures CO2 according to 2:1 or 1:1 stoichiometry. Here, we report a kind of improved carbon capture using amino-functionalized ionic liquids (ILs) through 1:2 stoichiometry. A serial of amino-functionalized ILs various with basicity and steric hindrance of anion were designed, prepared, and applied in CO2 capture. Through a combination of absorption experiment, quantum chemical calculation, spectroscopic investigation and calorimetric method, the results indicated that one amine group could bind two CO2 through proton transfer (PT) process and intramolecular hydrogen bond formation, which leading to enhanced capacity that breaks through equimolar. The basicity and steric hindrance of anion play a significant role in promoting amine group to capture two CO2. [P66614]2[Asp] with dual anion was further designed and synthesized to promote PT process, which showed high capacity of 1.96 mol/mol IL at 30°C and 1 atm as well as excellent reversibility. © 2018 American Institute of Chemical Engineers AIChE J, 65: 230–238, 2019 相似文献
995.
David Kok Devinder Yadav Emanuele Sortino Scott J. McCormack Kuo-Pin Tseng Waltraud M. Kriven Rishi Raj Martha L. Mecartney 《Journal of the American Ceramic Society》2019,102(2):644-653
In situ X-ray diffraction measurements at the Advanced Photon Source show that α-Al2O3 and MgAl2O4 react nearly instantaneously and completely, and nearly completely to form single-phase high-alumina spinel during voltage-to-current type of flash sintering experiments. The initial sample was constituted from powders of α-Al2O3, MgAl2O4 spinel, and cubic 8 mol% Y2O3-stabilized ZrO2 (8YSZ) mixed in equal volume fractions, the spinel to alumina molar ratio being 1:1.5. Specimen temperature was measured by thermal expansion of the platinum standard. These measurements correlated well with a black-body radiation model, using appropriate values for the emissivity of the constituents. Temperatures of 1600-1736°C were reached during the flash, which promoted the formation of alumina-rich spinel. In a second set of experiments, the flash was induced in a current-rate method where the current flowing through the specimen is controlled and increased at a constant rate. In these experiments, we observed the formation of two different compositions of spinel, MgO•3Al2O3 and MgO•1.5Al2O3, which evolved into a single composition of MgO•2.5Al2O3 as the current continued to increase. In summary, flash sintering is an expedient way to create single-phase, alumina-rich spinel. 相似文献
996.
The adhesion of a punch to a linear elastic, confined layer is investigated. Numerical analysis is performed to determine the equivalent elastic modulus in terms of layer confinement. The size of the layer relative to the punch radius and its Poisson’s ratio are found to affect the layer stiffness. The results reveal that the equivalent modulus of a highly confined layer depends on its Poisson’s ratio, whereas, in contrast, an unconfined layer is only sensitive to the extent of the elastic film. The solutions of the equivalent modulus obtained from the simulations are fitted by an analytical function that, subsequently, is utilized to deduce the energy release rate for detachment of the punch via linear elastic fracture mechanics. The energy release rate strongly varies with layer confinement. Regimes for stable and unstable crack growth can be identified that, in turn, are correlated to interfacial stress distributions to distinguish between different detachment mechanisms. 相似文献
997.
998.
Binbin Chen Nicolas Gauquelin Daen Jannis Daniel M. Cunha Ufuk Halisdemir Cinthia Piamonteze Jin Hong Lee Jamal Belhadi Felix Eltes Stefan Abel Zoran Jovanović Matjaž Spreitzer Jean Fompeyrine Johan Verbeeck Manuel Bibes Mark Huijben Guus Rijnders Gertjan Koster 《Advanced materials (Deerfield Beach, Fla.)》2020,32(50):2004995
999.
Svitsiankou I. E. Pavlovskii V. N. Muravitskaya E. V. Lutsenko E. V. Yablonskii G. P. Borodavchenko O. M. Zhivulko V. D. Mudry A. V. Yakushev M. V. Kognovitckii S. O. 《Semiconductors》2020,54(10):1247-1253
Semiconductors - The emission spectra of thin nanocrystalline films of Cu(In1 – xGax)(SySe1 – y)2 (CIGSSe) direct-gap solid solutions in the structure of solar cells, recorded upon... 相似文献
1000.
Mustafa Mohammed Abdalla G. M. T. Manimurugan S. Alharbi Adel R. 《The Journal of supercomputing》2020,76(8):5899-5922
The Journal of Supercomputing - Auscultation, the listening process for lung sound using acoustic stethoscope, is the first physical examination used to detect any disorder in heartbeat system.... 相似文献