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951.
任平 《武汉理工大学学报(材料科学英文版)》2009,24(6):927-930
Spinel zinc ferrites ZnFe2O4, prepared by co-precipitation method using the zinc nitrate Zn(NO3)2·6H2O and ferric nitrate Fe(NO3)3·2H2O as the raw materials, were characterized by the thermo gravimetric analysis (TG) and differential scanning calorimeter (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The influence of synthesis conditions, such as Zn/Fe molar ratio, pH value, the sintering temperature and time, on the microstructures was detailedly investigated. The relationships between the microstructures and the synthesis conditions were discussed. The results show that the pure spinel zinc ferrites ZnFe2O4 are formed when the Zn/Fe molar ratio is 1.05:2 at pH=8.5 or Zn/Fe molar ratio is 1:2 at Ph=9-10, and the precursors are sintered at 1100 °C for 4 h. Especially no other phases are observed when the Zn/Fe molar ratio is 1:2 at pH=10 and the precursor is sintered above 700 for 4 °C h. The higher sintering temperature and longer sintering time contribute to grain growth. 相似文献
952.
何庆复 《武汉理工大学学报(材料科学英文版)》2009,24(3):428-431
Behaviour of hardening and serration yield of a Fe-Ni-Cr alloy under isothermal cycling (ISC) and out-phase TMF was studied
on the basis of varied hysteresis loops. Cycling hardening and serrated yielding for ISC depend on the temperature and the
total strain range, stronger hardening with serrated yielding at higher strain range under ISC at 600 °C, but no hardening
and serrated yielding occurred under ISC at 800 °C. Stronger hardening with stress serration occurred at the thermal path
going to the lowest temperature, no stress serration occurred at the highest temperature under the out-phase. The hardening
also depends on the total strain range, higher total strain range with lower cycling temperature resulted in a stronger hardening
and remarkable serration yielding behavior. Weaker hardening without serrated yielding occurred at near 800 °C may due to
an obvious cycling stress drop under out-phase TMF. Change in the shape of the hysteresis loops also expresses the degree
of the damage of the tested alloy under out-phase and ISC. 相似文献
953.
章桥新 《武汉理工大学学报(材料科学英文版)》2009,24(6):871-874
Silver powder was fabricated by spray pyrolysis, using 2%–20% AgNO3 solution, 336–500 mL/h flux of AgNO3 solution, 0.28–0.32 MPa flux of carrier gas and in the 620–820 °C temperature range. The effects of furnace set temperature,
concentration of AgNO3 aqueous solution, flux of AgNO3 aqueous solution as well as carrier gas on the morphology and particle size distribution of silver powder, were investigated.
The experimental results showed that with the high concentration of AgNO3 aqueous solution, the average grain size of silver decreased with the increasing of furnace set temperature. But the gain
size distribution was not homogenous, the discontinuous grain growth occurred. With the low concentration of AgNO3 aqueous solution, the higher furnace set temperature made the nano sliver grains sintered together to grow. Nano silver powder
about 100 nm was fabricated by spray pyrolysis, using 2wt% AgNO3 solutions, 336 mL/h flux of AgNO3 aqueous solution, 0.32 MPa flux of carrier gas at 720 °C furnace set temperature. 相似文献
954.
Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and paramagenetic ferromagnetic-transitions as well as colossal magnetoresistance is due to the formation of ferromagnetic clusters in the paramagnetic background. The transition to metallic state is resulted from percolation of ferromagnetic metallic clusters, while the colossal magnetoresistance is due to the application of magnetic field, which accelerates the growth of ferromagnetic metallic clusters and causes the shift of the onset temperature for the metallic percolation to higher temperature. Based on the random resistor network model, the zero-field resistivity versus temperature dependence is simulated by using experimental parameters, and experimental data well agree with those in whole temperature range, giving a strong support to our approach. 相似文献
955.
贺海燕 《武汉理工大学学报(材料科学英文版)》2009,24(3):359-362
Fatigue-free Bi3.2La0.8Ti3O12 ferroelectric thin films were successfully prepared on p-Si (100) substrates using metalorganic solution deposition process. The orientation and formation of 5-layers thin films
were studied under different processing conditions using XRD. Experimental results indicate that increase in annealing time
at 700 °C after preannealing for 10 min at 400 °C can remarkably increase (200)-orientation of the films derived from the
precursor solutions with two contents of citric acid. Meanwhile, high content of citric acid increases the film thickness
and is conducive to the a-orientation of the films with the preannealing, and low concentration of the solution is conducive to the c-orientation of
the films without the preannealing. 相似文献
956.
A series of dimer acid-based polyamides were synthesized by melt-polycondensation of dimer acid and various aromatic diamines,
and were characterized by Fourier transform infrared spectrum (FT-IR) and nuclear magnetic resonance (1H NMR). The physical properties of the polyamides, such as glass transition temperature, melting temperature, decomposition
temperature and mechanical properties were also investigated. The polyamides’ intrinsic viscosity ranges from 1.8 dL·g−1 to 2.2 dL·g−1, and the melting temperature ranges from 140 °C to 181 °C. The glass transition temperatures, observed from dynamic mechanical
analysis, fall in the range of 34.8–48.2 °C. The physical and mechanical properties of the resultant polyamides are similar
to those of the PA1212. The heat resistance and mechanical properties of poly (4, 4′-diphenylsulfone dimeramide) (PSD) and
poly(4, 4′-diphenyl dimeramide) (PPDI) are comparable to those of PA1212. 相似文献
957.
艾桃桃 《武汉理工大学学报(材料科学英文版)》2009,24(5):732-735
Al2O3/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al TiO2 and Nb2O5, and the microstructure and mechanical properties were investigated. The results indicate the fine Al2O3 particles tend to disperse on the grain boundaries. The grain size of TiAl matrix decreases and the hardness increases with increasing Nb2O5 content. The bending strength and fracture toughness reach to a maximum when Nb2O5 content is 6 wt%, under 642 MPa and 6.69 MPa·m1/2, respectively. Based on the fractography and the observation of crack propagation path, it is concluded that the strengthening and toughening of such composites at room temperature can be attributed to the refinement of the TiAl matrix, the deflection behavior in the crack propagation and the dispersion of Al2O3 particles. 相似文献
958.
Fe-Ni-Al mixtures as hot-pressing sintering additive to Titanium diboride (TiB2) were studied. It is found that liquid alloy formed under high temperature hardly has effects on the densification behaviors
of TiB2-independent. Fe-Ni-Al additive just works as filler between TiB2 particles and does not change the TiB2-independent sintering behaviors. Pressing mode has a great effect on the liquid flowing between TiB2 particles. Multiple-steps pressing mode will give more time and space for the liquid flowing and improve the relative density
of TiB2-Fe-Ni-Al cermet. 相似文献
959.
潜器Stewart平台动力学仿真 总被引:1,自引:0,他引:1
建立了Stewart平台的动力学模型,对潜器的动力学特征进行分析,对其运动进行动力学仿真研究.以Stewart平台的任意支腿为研究对象,考虑各支腿的重力和惯性力,利用牛顿-欧拉方法建立了支腿及动平台的力和力矩平衡方程,推导出了Stewart平台的动力学方程及支腿所受的支反力.以潜艇模拟器并联机构为例,运用动力学模型进行了实际计算并绘制了支腿驱动力的变化曲线,将驱动力与支腿运动速度相乘得到支腿功率输出的变化曲线,为液压油缸的功率设计提供了依据,也为潜器的精确动力学解耦奠定了基础. 相似文献
960.
为制备高性能析氧电极,采用热分解法在400℃温度下制备Ti/RuO2(x)-Co3O4(1-x)(0≤x≤1,x为Ru的摩尔分数)复合氧化物电极,通过电极开路电压、循环伏安曲线及极化曲线等分析其在1.0mol/LKOH溶液中的析氧催化活性及析氧动力学.结果表明,摩尔分数为10%的RuO2使电极催化活性急剧变化,摩尔分数为50%的RuO2复合氧化物电极具有最大的伏安电荷(429.63mC.cm-2)、最高的表面粗糙度(1786),其析氧性能最佳;Ti/Co3O4在高、低过电位区域电极对OH-的反应级数分别近似为1.0和2.0,含RuO2电极反应级数均为1.0. 相似文献