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41.
《Ceramics International》2019,45(16):19879-19887
We report the structure, magnetic domain state and spin dynamics of biphasic Co nanoparticles embedded in amorphous carbon matrix. Two types of samples were synthesized by heating the precursors (Co-acetylacetonate and toluene) from RT to the pyrolysis reaction temperature (800 °C) at two different heating rates, viz. ∼ 3 °C/min and ∼20 °C/min. We observe that the sample prepared at higher heating rate (∼20 °C/min) predominantly contains fcc-phase of Co in the Co-nanoparticles, whereas the sample synthesized at lower heating rate exhibits higher amount of the hcp-phase-content in the Co-nanoparticles. The Co-nanoparticles are surrounded by graphitic carbon layers forming core-shell type morphology. The hcp-phase of Co is characterized by a higher saturation magnetization and coercivity (higher magnetic hardness) than the fcc-phase. The nature of the measured hysteresis loop in combination with the estimated critical size for the particles to be in a single magnetic domain state suggest that both hcp and fcc-phases of Co coexist in the same particle and most of the particles are multidomain-particles. Furthermore, our results reveal that the dynamics of the spins present at the grain boundaries are the slowest followed by those in the fcc-phase and hcp-phase of Co. The dynamics of the spins present at the domain walls are slower than those inside the magnetic domains. The responsive nature of the spins on the domain walls in comparison to those inside the domains leads to the so called domain wall enhancement effect. 相似文献
42.
低频脉冲磁化对刀具性能的影响 总被引:1,自引:0,他引:1
介绍了国内外提高刀具性能的方法,提出了低频脉冲磁化处理的方法,并阐述其工作原理,通过摩擦系数的测定试验和抗冲击试验,对经过低频脉冲磁化处理的切削刀具和未经过处理的刀具的性能进行了比较,分析了磁化处理对切削刀具性能的影响。 相似文献
43.
44.
大型汽轮发电机近年来事故原因及防范对策 总被引:8,自引:2,他引:6
章重点对近期国产300MW汽轮发电机定子事故及故障原因作了分析,提出防止发电机内冷水系统与大轴磁化故障的建议。 相似文献
45.
Xavier Ravalec Nathalie Le Tallec François Carré Jacques D. de Certaines Elisabeth Le Rumeur 《Magma (New York, N.Y.)》1999,9(1-2):52-58
Kinetics of phosphoryl transfers from PCr to γ-ATP and from β-ATP to β-ADP were measured by magnetization transfer in an in
vivo31P NMR experiment in working rat skeletal hind leg muscles. Two groups were examined. One group was submitted to a 6-week training
program of treadmill running. The other group was composed of sedentary animals. Metabolic oxidative capacity and mechanical
performance were improved greatly by training as shown previously. Phosphoryl transfer of PCr→γ-ATP or β-ATP→β-ADP total fluxes
were identical in resting trained and untrained muscles. Under stimulation, the flux of creatine kinase transfer was significantly
inhibited by 23% compared with resting level in untrained muscles; by contrast, it was not inhibited and maintained at the
high resting level in trained muscles. Thus physiological changes probably linked to a decrease of the production of anions,
which could inhibit creatine kinase, were able to maintain creatine kinase flux. The flux of β-ATP to β-ADP transfer were
enhanced largely in working muscles from 1.4±0.8 and 2±0.8 at rest to 4±1.6 and 6.6±2.7 mM s−1 for untrained and trained muscles respectively; the effect was more pronounced in trained than in untrained muscles. These
results showed an acceleration of phosphoryl turnover in working muscles after training, which could contribute to improve
oxidative and mechanical performances. Such kinetic measurements of phosphoryl conversion may provide information on ATP turnover
in pathophysiologic situations where ADP accumulates because of impaired ATP synthesis (mitochondrial myopathies, lower perfusion
level). 相似文献
46.
47.
A series of L10 Fe63Pt37 films with controlled thickness (tFM) were deposited on MgO(100) substrates for microstructure and magnetization reversal mechanism study. X-ray diffraction measurements show that face-centered tetragonal (200) peak also exists in addition to face-centered tetragonal (002) one, and becomes weak for thick films. High resolution electron microscopy study reveals the existence of periodic misfit dislocations at the FePt/MgO interface and other types of defects such as twins and antiphase boundary inside the film. Out-of-plane initial magnetization shows a slow increase responding to the external magnetic field and then follows a steep increase. The out-of-plane coercivity HC at room temperature decreases with increasing tFM and increases when the angle θH between the external magnetic field and the film normal direction increases. HC at θH = 0 changes as a linear function of temperature for individual samples and the slope decreases with increasing tFM. In addition, magnetic viscosity measurements show that the fluctuation field at room temperature decreases with increasing tFM. These phenomena indicate that the magnetization reversal in the L10 FePt films should be realized by the motion of weakly pinned domain wall and thus governed by the thermal activation model. The magnetization reversal thermal activation volume and corresponding energy increase with increasing tFM, as a result of the interactions between domain walls and structural defects can be attributed to the sample microstructural characteristic evolution with tFM. 相似文献
48.
Bimetallic Ni-x%Pt/SiO2 nanoclusters at different initial platinum contents (x = 0, 2, 9, 15, 25, 35, 85 and 95 at %) are synthesized at room temperature by the radiolytic process. According to the Pt amount, the structural studies (XRD, TEM and SAED) reveal the presence after irradiation of NiSi and Ni3Pt or NiPt3 nanoalloyed clusters on amorphous silica. The Ni-Pt nanoparticles have a fcc solid solution structure and a narrow cluster size distribution. The radiation-induced nanoparticles exhibit an enhancement of the magnetization at low temperature. Moreover, unlike Ni-Pt bulk alloys, the magnetization increases with the Pt content. In the ultra divided state, platinum seems to play a major role by enhancing the nickel ion reduction and protecting Ni against corrosion during the synthesis. 相似文献
49.
Polycrystalline samples of Ho doped BiFeO3 were prepared by solid state reaction method and effect of partial substitution of Ho on dielectric, magnetic and ferroelectric properties was studied. High temperature dielectric results show two dielectric anomalies both in ? and tan δ, out of which, anomaly at higher temperature (∼400 °C) could be ascribed to antiferromagnetic Néel temperature which, is a signature of magnetoelectric coupling. The magnetic moment is greatly improved and the maximum magnetization was found to be 0.736 emu/g. Saturated ferroelectric hysteresis loops were observed for Bi0.95Ho0.05FeO3 with remnant polarization (Pr) = 1.59 μC/cm2, maximum polarization (Pmax) = 2.56 μC/cm2 and coercivity (Ec) = 5.45 kV/cm. We have conducted comprehensive magnetoelectric and magnetodielectric properties at room temperature. Magnetic field induced ferroelectric hysteresis loop observed in Bi0.95Ho0.05FeO3 is of prime importance. 相似文献
50.
根据楞次定律,在高速漏磁检测过程中钢管与轴向磁化线圈发生轴向相对运动时将产生涡流效应。涡流磁场与原磁化场叠加后影响钢管磁化状态,最终影响到高速漏磁检测结果的一致性。为分析高速漏磁检测中涡流效应对钢管全长磁化的影响,将原磁化场矢量分解轴向分量和径向分量并根据楞次定律建立钢管内部涡流分布方程,并获得感应涡流磁场在钢管中的空间分布。分析涡流磁场叠加于原磁化场之后对管头、管体和管尾处磁化状态的影响,发现管头涡流磁场与原磁化场方向相反,涡流效应具有抑制钢管磁化作用;管尾处两者方向相同,涡流效应具有增强磁化作用;涡流效应对管体磁化基本没有影响。通过有限元法分析钢管运行速度与涡流密度的关系,并进一步研究涡流效应对钢管管头、管体和管尾磁化状态的影响,为钢管全长一致性评价提供参考依据。 相似文献