全文获取类型
收费全文 | 69446篇 |
免费 | 8008篇 |
国内免费 | 2722篇 |
专业分类
电工技术 | 1179篇 |
技术理论 | 1篇 |
综合类 | 3031篇 |
化学工业 | 25233篇 |
金属工艺 | 10055篇 |
机械仪表 | 1379篇 |
建筑科学 | 2096篇 |
矿业工程 | 971篇 |
能源动力 | 1380篇 |
轻工业 | 9142篇 |
水利工程 | 472篇 |
石油天然气 | 1144篇 |
武器工业 | 383篇 |
无线电 | 2797篇 |
一般工业技术 | 16296篇 |
冶金工业 | 2928篇 |
原子能技术 | 272篇 |
自动化技术 | 1417篇 |
出版年
2024年 | 285篇 |
2023年 | 1631篇 |
2022年 | 2290篇 |
2021年 | 3168篇 |
2020年 | 2943篇 |
2019年 | 2520篇 |
2018年 | 2803篇 |
2017年 | 3161篇 |
2016年 | 3210篇 |
2015年 | 3338篇 |
2014年 | 4003篇 |
2013年 | 5088篇 |
2012年 | 4538篇 |
2011年 | 5614篇 |
2010年 | 3800篇 |
2009年 | 4119篇 |
2008年 | 3415篇 |
2007年 | 3759篇 |
2006年 | 3588篇 |
2005年 | 2786篇 |
2004年 | 2710篇 |
2003年 | 2310篇 |
2002年 | 1851篇 |
2001年 | 1232篇 |
2000年 | 1027篇 |
1999年 | 781篇 |
1998年 | 665篇 |
1997年 | 584篇 |
1996年 | 482篇 |
1995年 | 456篇 |
1994年 | 333篇 |
1993年 | 238篇 |
1992年 | 248篇 |
1991年 | 201篇 |
1990年 | 244篇 |
1989年 | 230篇 |
1988年 | 86篇 |
1987年 | 58篇 |
1986年 | 59篇 |
1985年 | 71篇 |
1984年 | 67篇 |
1983年 | 33篇 |
1982年 | 58篇 |
1981年 | 7篇 |
1980年 | 36篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
31.
Jianrong Xia Hanyu Xue Renjin Gao Yuchi Zhang Qi Lin 《Polymer Engineering and Science》2021,61(2):489-496
The over-exploitation of finite fossil resources and/or the increased environmental and sustainable awareness inspire scientists and technologists to search for inexpensive alternatives from renewable chemicals. Phenol formaldehyde (PF) resins, the oldest type of synthetic polymers with good mechanical properties and heat resistance, are widely used in the production of coatings, laminates, molding compositions, and glues. Here, biobased urushiol-derived PF resins were synthesized from the alkali-catalyzed reaction between urushiol and formaldehyde. The chemical compositions and molecular structures of resole resins were characterized by carbon-13 nuclear magnetic resonance and Fourier transform infrared spectroscopy, and their curing behaviors were studied by differential scanning calorimetry. The as-prepared urushiol-derived resole resins had methylol (Ph−CH2OH), ortho- and para-hemiformal groups (Ph−CH2OCH2OH), and the para−para/ortho−para/ortho−ortho links of methylene groups (Ph−CH2−Ph), whereas the resole resins had low curing temperatures at about 100–113°C. Additionally, given the long side alkyl group moiety on the aromatic rings of urushiol, the films of cured urushiol-derived resole resins had low glass transition temperatures of 132 ± 2°C. Furthermore, the as-prepared urushiol-derived coatings exhibited excellent physical and mechanical properties. 相似文献
32.
《中国有色金属学会会刊》2021,31(10):3063-3074
The transient liquid phase (TLP) bonding of CoCuFeMnNi high entropy alloy (HEA) was studied. The TLP bonding was performed using AWS BNi-2 interlayer at 1050 °C with the TLP bonding time of 20, 60, 180 and 240 min. The effect of bonding time on the joint microstructure was characterized by SEM and EDS. Microstructural results confirmed that complete isothermal solidification occurred approximately at 240 min of bonding time. For samples bonded at 20, 60 and 180 min, athermal solidification zone was formed in the bonding area which included Cr-rich boride and Mn3Si intermetallic compound. For all samples, the γ solid solution was formed in the isothermal solidification zone of the bonding zone. To evaluate the effect of TLP bonding time on mechanical properties of joints, the shear strength and micro-hardness of joints were measured. The results indicated a decrement of micro-hardness in the bonding zone and an increment of micro-hardness in the adjacent zone of joints. The minimum and maximum values of shear strength were 100 and 180 MPa for joints with the bonding time of 20 and 240 min, respectively. 相似文献
33.
《Ceramics International》2021,47(23):32641-32647
Multi-components and equimolar rare earth monosilicates, (Y1/3Dy1/3Er1/3)2SiO5, (Y1/3Dy1/3Lu1/3)2SiO5, (Y1/4Dy1/4Ho1/4Er1/4)2SiO5 and (Yb1/4Dy1/4Ho1/4Er1/4)2SiO5, were prepared by solid-state reactions and the following hot-pressing. Dense microstructures with uniform elemental distributions were obtained for all samples. These investigated multi-components monosilicates exhibit low thermal conductivities and similar coefficients of thermal expansion with SiC. Moreover, they exhibit high corrosion resistances in 1400 °C water vapor, especially, four-components (Y1/4Dy1/4Ho1/4Er1/4)2SiO5 and (Yb1/4Dy1/4Ho1/4Er1/4)2SiO5 experienced almost invariable weights after small weight losses during the initial 0.5 h. All those results indicate that multi-components rare earth monosilicates are promising candidates of environmental barrier coatings for SiC/SiC composites. 相似文献
34.
Pengfei Liang Jie Zhu Di Wu Hui Peng Xiaolian Chao Zupei Yang 《Journal of the American Ceramic Society》2021,104(6):2702-2710
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics. 相似文献
35.
Ewa Olewnik-Kruszkowska Magdalena Gierszewska Sylwia Grabska-Zieliska Joanna Skopiska-Winiewska Ewelina Jakubowska 《International journal of molecular sciences》2021,22(7)
Hydrogels based on chitosan are very versatile materials which can be used for tissue engineering as well as in controlled drug delivery systems. One of the methods for obtaining a chitosan-based hydrogel is crosslinking by applying different components. The objective of the present study was to obtain a series of new crosslinked chitosan-based films by means of solvent casting method. Squaric acid—3,4-dihydroxy-3-cyclobutene-1,2-dione—was used as a safe crosslinking agent. The effect of the squaric acid on the structural, mechanical, thermal, and swelling properties of the formed films was determined. It was established that the addition of the squaric acid significantly improved Young’s modulus, tensile strength, and thermal stability of the obtained materials. Moreover, it should be stressed that the samples consisting of chitosan and squaric acid were characterized by a higher swelling than pure chitosan. The detailed characterization proved that squaric acid could be used as a new effective crosslinking agent. 相似文献
36.
Lun Feng William G. Fahrenholtz Gregory E. Hilmas Frédéric Monteverde 《Journal of the European Ceramic Society》2021,41(1):92-100
Dense high-entropy (Hf,Zr,Ti,Ta,Nb)B2 ceramics with Nb contents ranging from 0 to 20 at% were produced by a two-step spark plasma sintering process. X-ray diffraction indicated that a single-phase with hexagonal structure was detected in the composition without Nb. In contrast, two phases with the same hexagonal structure, but slightly different lattice parameters were present in compositions containing Nb. The addition of Nb resulted in the presence of a Nb-rich second phase and the amount of the second phase increased as the Nb content increased. The relative densities were all >99.5 %, but decreased from ~100 % to ~99.5 % as the Nb content increased from 0 to 20 at%. The average grain size decreased from 13.9 ± 5.5 μm for the composition without Nb additions to 5.2 ± 2.0 μm for the composition containing 20 at% Nb. The reduction of grain size with increasing Nb content was due to the suppression of grain growth by the Nb-rich second phase. The addition of Nb increased Young’s modulus and Vickers hardness, but decreased shear modulus. While some Nb dissolved into the main phase, a Nb-rich second phase was formed in all Nb-containing compositions. 相似文献
37.
Lingping Kong Jue Gong Qingyang Hu Francesco Capitani Anna Celeste Takanori Hattori Asami Sano-Furukawa Nana Li Wenge Yang Gang Liu Ho-kwang Mao 《Advanced functional materials》2021,31(9):2009131
The soft nature of organic–inorganic halide perovskites renders their lattice particularly tunable to external stimuli such as pressure, undoubtedly offering an effective way to modify their structure for extraordinary optoelectronic properties. Here, using the methylammonium lead iodide as a representative exploratory platform, it is observed that the pressure-driven lattice disorder can be significantly suppressed via hydrogen isotope effect, which is crucial for better optical and mechanical properties previously unattainable. By a comprehensive in situ neutron/synchrotron-based analysis and optical characterizations, a remarkable photoluminescence (PL) enhancement by threefold is convinced in deuterated CD3ND3PbI3, which also shows much greater structural robustness with retainable PL after high peak-pressure compression–decompression cycle. With the first-principles calculations, an atomic level understanding of the strong correlation among the organic sublattice and lead iodide octahedral framework and structural photonics is proposed, where the less dynamic CD3ND3+ cations are vital to maintain the long-range crystalline order through steric and Coulombic interactions. These results also show that CD3ND3PbI3-based solar cell has comparable photovoltaic performance as CH3NH3PbI3-based device but exhibits considerably slower degradation behavior, thus representing a paradigm by suggesting isotope-functionalized perovskite materials for better materials-by-design and more stable photovoltaic application. 相似文献
38.
《Ceramics International》2022,48(4):5312-5320
Ce3+ and Pr3+ co?doped Lu3Al5O12 phosphors were synthesized by the sol–gel process, and their crystal structure, photoluminescence (PL) properties, and energy transfer (ET) from the Ce3+ to Pr3+ were studied. The Lu2.94?yAl5O12:0.06Ce3+, yPr3+ phosphors (0.002 ≤ y ≤ 0.008) showed the green?yellow emission from the 2D3/2 → 2F5/2, 7/2 transition of Ce3+ and the red emission at 610 and 637 nm, which were caused by the 1D2→3H4 and 3P0→3H5 transitions of Pr3+, respectively. The optimal concentration of Pr3+ for efficient ET was found to be x = 0.006. The electric quadrupole?quadrupole interaction was responsible for the concentration quenching in the Lu2.94?yAl5O12:0.06Ce3+, yPr3+ phosphors, based on Dexter's theory. The incorporation of Pr3+ for Lu3+ enhanced the red PL intensity in the Lu2.94Al5O12:0.06Ce3+ phosphor. 相似文献
39.
40.
《Journal of the European Ceramic Society》2022,42(11):4479-4492
ZrB2-MeC and ZrB2-19 vol% SiC-MexCy where Me=Cr, Mo, W were obtained by pressureless sintering. The capability to promote densification of ZrB2 and ZrB2-SiC matrices is the highest for WC and lowest for Cr3C2. The interaction between the components results in the formation of new phases, such as MeB (MoB, CrB, WB), a solid solution based on ZrC, and a solid solution based on ZrB2. The addition of Cr3C2 decreases the mechanical properties. On the other hand, the addition of Mo2C or WC to ZrB2-19 vol% SiC composite ceramics leads increased mechanical properties. Long-term oxidation of ceramics at 1500 °C for 50 h showed that, in binary ZrB2-MexCy, a protective oxide scale does not form on the surface thus leading to the destruction of the composite. On the contrary, triple composites showed high oxidation resistance, due to the formation of dense oxide scale on the surface, with ZrB2-SiC-Mo2C displaying the best performance. 相似文献