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951.
Flash pyrolysis, which combines conventional pyrolysis with flash sintering, was first conducted to produce polymer derived SiC-TiC nanocomposites. Pre-pyrolysis at 800℃ allows the conversion from titanium isopropoxide (TTIP) modified polysiloxane to an amorphous SiTiOC ceramic. The subsequent application of an electric field gives rise to the formation of turbostratic carbon and creates Joule heating to obtain a sample internal temperature of ~1400℃. The precipitation of β-SiC, TiC, as well as titanium oxides is realized upon carbothermal reduction of extensively phase separated SiO2 and TiO2 with carbon. Increasing TTIP content embodies the nanocomposites with prominent electrical percolation behaviors. The electrical transport of the synthesized ceramics follows an amorphous semiconductor mechanism. High thermal stability in air is guaranteed, thanks to the in-situ formed TiC nanocrystals and preferentially reduced amorphous carbon. Flash pyrolyzed nanocomposite with a Ti:Si molar ratio of 0.20 exhibits the highest electrical conductivity (0.696 S/cm) and minimum mass change (~2%) at 1000℃, serving as a competitive candidate for electro-discharge machining (EDM) applications or self-standing conducting devices that must withstand high temperature conditions. 相似文献
952.
Katy S. Gerace John C. Mauro Clive A. Randall 《Journal of the American Ceramic Society》2021,104(5):1915-1944
Piezoelectric materials have coupled mechanical and electrical energies and have long been used in devices for actuators, sensors, energy harvesters, frequency filters, and various additional applications. Piezoelectricity requires a non-centrosymmetric crystal structure and is therefore confined to materials that possess a periodic crystalline structure. Due to the non-crystalline nature of glass, piezoelectricity is fundamentally forbidden. However, one way to exploit piezoelectric properties in a glassy matrix is by developing glass-ceramics that possess controlled growth of a crystalline phase. Growth and orientation of piezoelectric crystals in a glassy matrix is a non-trivial process that has long been explored to combine the formability of glass with the thermal and mechanical resilience of glass-ceramics. While extensive work has been done in the field of functional glass-ceramics, the results are presented in isolated articles and a comprehensive review pertaining to symmetry breaking methods to exploit anisotropic properties in glass-ceramics has been absent from the literature. Here, we present a global review of the fundamental symmetry requirements for piezoelectricity, the development of polar, piezoelectric glass-ceramic compositions (specifically those with LiNbO3 and fresnoite-based crystal phases), and various crystal growth and orientation mechanisms, including relevant kinetic and thermodynamic driving forces. Lastly, we discuss the challenges associated with implementing gradients to drive oriented crystal growth to develop non-centrosymmetry, and the need for future modeling work to produce adequate time-temperature-transformation (TTT) diagrams that take into account kinetic and thermodynamic driving forces for oriented crystal growth. Going beyond technical challenges, we conclude with an examination of current and potential applications for piezoelectric glass-ceramics that combine the formability of glass with the symmetry-dependent properties of ceramics. 相似文献
953.
Xiao-Qiang Song Wen Lei Fei Wang Tao Chen Shi-Wo Ta Zhen-Xiao Fu Wen-Zhong Lu 《Journal of the American Ceramic Society》2021,104(4):1740-1749
A gillespite-structured MCuSi4O10 (M = Ba1-xSrx, Sr1-xCax) ceramics with tetrahedral structure (P4/ncc) were prepared by solid-state reaction method. X-ray diffraction and thermogravimetry with differential scanning calorimetry (TG-DSC) were employed to study the phase synthesis process of BaCuSi4O10. Pure BaCuSi4O10 phase was obtained at 1075°C and decomposed into BaSiO3, BaCuSi2O6, and SiO2 when calcined at 1200°C. The relationships between the crystal structure and microwave dielectric properties of MCuSi4O10 ceramics were revealed based on the Rietveld refinement and P-V-L complex chemical bond theory. The dielectric constant (εr) decreased linearly with decreasing total bond susceptibility and ionic polarizability. Quality factor (Q × f) was closely dependent on bond strength and lattice energy. The temperature coefficient of resonant frequency (τf) was controlled by the stability of [CuO4]6− plane in MCuSi4O10. Optimum microwave dielectric properties were obtained for SrCuSi4O10 when sintered at 1100°C for 3 hours with a εr of 5.59, a Q × f value of 82 252 GHz, and a τf of −41.34 ppm/°C. Thus, SrCuSi4O10 is a good candidate for millimeter-wave devices. 相似文献
954.
Qin Du Wenli Wang Zhiguang Wang Wei Su Zhiyuan Deng Jingen Wu Ming Ma Zhongqiang Hu Ziyao Zhou Ming Liu 《Journal of the American Ceramic Society》2021,104(2):896-902
Perovskite materials with compositions in the vicinity of the steep morphotropic phase boundary (MPB) exhibit various intriguing properties including giant piezoelectricity and large dielectric constant. Aside from composition, the phase configuration of the perovskites is also strongly related to the ambient temperature. Here, we report a giant piezoelectricity of 10 980 pm/V at 93°C in the 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystals which is more than five times larger than that at room temperature. The enhanced piezoelectricity can be attributed to the instability of the thermally induced tetragonal phase which can be converted to the orthorhombic phase by the external electric field in the <011> oriented single crystal. The transverse piezoelectricity has been investigated by measuring the electric-field-dependent ferromagnetic resonance (FMR) field in the CoFeB/PMN-PT magnetoelectric (ME) heterostructures. The ME coupling coefficient has been increased from 49.3 to 476 Oe cm/kV as temperature increased from 25 to 90°C. The findings reveal that both longitudinal and transverse piezoelectricity in the PMN-PT single crystals can be greatly enhanced by proper setting of ambient temperature, indicating an effective route for the design of strain-mediated tunable devices with ultralow driving voltage. 相似文献
955.
Huahai Shen Menglu Li Pengcheng Li Haiyan Xiao Haibin Zhang Xiaotao Zu 《Journal of the American Ceramic Society》2021,104(5):2301-2312
In the past decades, pyrochlores, such as Gd2Zr2O7, have demonstrated great potential to immobilize nuclear wastes such as Pu, which results in the production of Pu2Zr2O7. Due to the high radioactivity of Pu, it is difficult to investigate the radiation response behavior of Pu2Zr2O7 and its physical properties of the damaged state experimentally. Consequently, few related data have been reported in the literature thus far. In this study, first-principles calculations have been carried out to investigate the defect formation and its effect on the thermodynamic properties of Pu2Zr2O7. It reveals that PuZr antisite and O8a interstitial defects are very easy to form in Pu2Zr2O7. In particular, the O8a interstitial defect can be formed spontaneously, while it is mechanically unstable. When vacancy, interstitial or antisite defects are formed in Pu2Zr2O7, and the elastic moduli and Debye temperature are decreased. Besides, better ductility is resulted. As compared with other zirconate pyrochlores, such as Gd2Zr2O7, the Pu2Zr2O7 is suggested to be less resistant to radiation-induced amorphization. This study demonstrates that the created defects due to self-radiation from actinide decay have remarkable influences on the thermophysical properties of Pu2Zr2O7. 相似文献
956.
Haiming Zhang Biao Zhao Huimin Xiang Fu-Zhi Dai Zhili Zhang Yanchun Zhou 《Journal of the American Ceramic Society》2021,104(5):2213-2224
The electromagnetic (EM) wave absorbing properties of Cr2AlB2 powders and those after high-temperature oxidation were investigated. Coupling of magnetic and dielectric loss enables Cr2AlB2 with good absorption properties. The minimum reflection loss (RL) value is −44.9 dB at 8.5 GHz with a thickness of 2.7 mm, and the optimized effective absorption bandwidth (EAB) is 4.4 GHz (13.0-17.4 GHz) with a thickness of 1.6 mm. After oxidation at 750, 900, and 1000°C for 2 h, the minimum RL values, respectively, are −23.9 dB (17.5 GHz, 1.5 mm), −41.4 dB (16.5 GHz, 1.5 mm), and −39.5 dB (8.0 GHz, 3.0 mm); and the corresponding EAB values, respectively, are 3.8 GHz (13.6-17.4 GHz, 1.7 mm), 4.1 GHz (13.5-17.6 GHz, 1.6 mm), and 4.4 GHz (13.0-17.4 GHz, 1.7 mm). With an absorber thickness of 1.5-4.0 mm, the EAB with a RL value of less than −10 dB can be tuned in a broad-frequency range 5.0-18.0 GHz, which basically covers C (4-8 GHz), X (8-12 GHz), and Ku (12-18 GHz) bands. These results demonstrate that Cr2AlB2, as a high-efficient and oxidation-resistant absorber, is a promising candidate for microwave absorption applications and can retain good EM wave absorbing properties after high-temperature oxidation. 相似文献
957.
Fang Guan Yiquan Wu Iva Milisavljevic Xin Cheng Shifeng Huang 《Journal of the American Ceramic Society》2021,104(10):5148-5156
Spinel-structured NiMn2O4 ceramics, with different valence Ni sources, were originally prepared using Ni2O3 and NiO as raw materials, and the effects of different valence Ni sources on their electrical properties were first investigated. XRD patterns show that both Ni2O3-based and NiO-based NiMn2O4 ceramics are single cubic spinel structures. SEM/EDS images indicate that the NiMn2O4 ceramics exhibited high density at the experiment-determined sintering temperatures. XPS results and Raman drifts prove that the Ni valence-induced changes in Mn ions at B sites played a significant role in the electrical properties and thermal stability of NiMn2O4 ceramics. Compared with NiO-based NiMn2O4, the resistivity at 25°C (ρ25°C) of Ni2O3-based NiMn2O4 increased dramatically from 3109 to 106958 Ω cm, the thermal constant (B25/50) increased from 3264 to 4473 K, and the resistance shifts after annealing for 1000 h at 150°C decreased from 0.80% to 0.74%. The investigation of the relationship between the material properties and valence of Ni sources has provided a new and effective way for designing the spinel-structured negative temperature coefficient (NTC) materials by modulating the valence of ions at A sites in the raw materials. 相似文献
958.
Erhan Kilinc Anthony M. T. Bell Paul A. Bingham Russell J. Hand 《Journal of the American Ceramic Society》2021,104(8):3921-3946
Crystallization, mechanical properties, and workability are all important for the commercialization and optimization of silicate glass compositions. However, the inter-relations of these properties as a function of glass composition have received little investigation. Soda-lime-silica glasses with Na2O-MgO-CaO-Al2O3-SiO2 compositions relevant to commercial glass manufacture were experimentally studied and multiple liquidus temperature and viscosity models were used to complement the experimental results. Liquidus temperatures of the fabricated glasses were measured by the temperature gradient technique, and Rietveld refinements were applied to X-Ray powder diffraction (XRD) data for devitrified glasses, enabling quantitative determination of the crystalline and amorphous fractions and the nature of the crystals. Structural properties were investigated by Raman spectroscopy. Acoustic echography, micro-Vicker's indentation, and single-edge-notched bend testing methods were used to measure Young's moduli, hardness, and fracture toughness, respectively. It is shown that it is possible to design lower-melting soda-lime-silica glass compositions without compromising their mechanical and crystallization properties. Unlike Young's modulus, brittleness is highly responsive to the composition in soda-lime-silica glasses, and notably low brittleness values can be obtained in glasses with compositions in the wollastonite primary phase field: an effect that is more pronounced in the silica primary phase field. The measured bulk crystal fractions of the glasses subjected to devitrification at the lowest possible industrial conditioning temperatures indicate that soda-lime-silica glass melts can be conditioned close to their liquidus temperatures within the compositional ranges of the primary phase fields of cristobalite, wollastonite, or their combinations. 相似文献
959.
Nisha Sheth Carl Greenley Raul Bermejo John C. Mauro Carlo G. Pantano Seong H. Kim 《Journal of the American Ceramic Society》2021,104(9):4550-4558
Water or acid soaking surface treatments have been shown to increase the mechanical strength of soda-lime silicate (SLS) glasses. This increase in strength has traditionally been attributed to effects related to residual stress or changes in fracture resistance. In this work, we report experimental data that cannot be explained based on the existing knowledge of glass surface mechanics. In dry environments, annealed and acid-leached SLS surfaces have comparable crack initiation stress and fracture stress as measured by Hertzian indentation and biaxial bending tests, respectively. Yet, in the presence of humidity, acid-leached surfaces have higher failure stress than the annealed surfaces. This apparent enhancement in the crack resistance of the acid-leached surface of SLS glass in humid environments supports the hypothesis that acid-leached surface chemistry can lower the transport kinetics of molecular water to critical flaws. 相似文献
960.
Pengyu Xu Hao Wang Lu Ren Bingtian Tu Weimin Wang Zhengyi Fu 《Journal of the American Ceramic Society》2021,104(12):6455-6466
Knowledge on the mechanical and thermophysical properties of ZnO·nAl2O3 is essential for practical applications. Based on the first-principles calculations and the bond valence method, the disordered spinel-type structure of ZnO·nAl2O3 (n = 1–4) was constructed to investigate the composition-dependent mechanical and thermophysical properties. The effects of cation substitution on the hardness, elastic modulus, thermal expansion, and thermal conductivity were revealed from the insights into the chemical bonds. At a higher n, the tetrahedral bond is stronger, manifested as its higher hardness and bulk modulus as well as smaller thermal expansion coefficient. Meanwhile, the octahedral bond is weaker, leading to the lower hardness and bulk modulus, along with the larger expansion coefficient. In consequence, the hardness and elastic moduli of ZnO·nAl2O3 are improved moderately while the expansion coefficient is decreased with the rise of n. Due to the different vibration characteristics of ZnIV and AlIV, the cation disorder in the 8a site provides the primary source of phonon scattering, resulting in the dramatic reduction of thermal conductivity as n increases. The understanding offers guidance on the application-oriented design of new oxide spinels. 相似文献