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61.
一种可在线确定电压稳定运行范围的方法 总被引:8,自引:0,他引:8
文中根据节点的戴维南等值电路,提出了一种确定静态电压稳定临界运行状态及其运行范围的方法。通过理论分析认为:节点的最大输出功率与戴维南等值电势的平方成正比、与戴维南等值阻抗成反比,与节点负荷的阻抗角成单调递减变化;节点的临界电压与戴维南等值电势成正比,与节点负荷的阻抗角成单调递减变化。采用广域测量系统,该方法间接地避免了潮流方程的Jacobian矩阵在临界点奇异而带来的不收敛问题,弥补了传统方法在线应用中存在的系统规模过大、非线性模型不准确、数据多且更新不及时、速度慢等缺陷。通过仿真计算表明该方法可行,可以在线快速确定电压稳定临界状态。 相似文献
62.
A comparative dielectric relaxation study of PMN–PT and PMN–PZ ceramics using impedance spectroscopy
Surya M. Gupta Pragya Pandit Pankaj Patro Ajit R. Kulkarni Vinod K. Wadhawan 《Materials Science and Engineering: B》2005,120(1-3):194-198
AC-impedance spectroscopic studies in the temperature range of 30–400 °C are carried out on solid solutions of lead magnesium niobate (PMN) with lead titanate (PT) and lead zirconate (PZ), both of them in the 65/35 atomic ratio. For PMN–PT this corresponds to the morphotropic phase boundary composition (with normal ferroelectric behaviour), and for PMN–PZ it is near the phase boundary between normal ferroelectric and relaxor ferroelectric compositions. The variation of dielectric permittivity with temperature at different frequencies shows normal ferroelectric and relaxor-like dependence for PMN–PT and PMN–PZ, respectively. Temperature-dependent spectroscopic modulus plots reveal a much broader peak for PMN–PZ compared to that for PMN–PT, which is consistent with the dielectric behaviour. PMN–PT shows nearly ideal Debye behaviour below Tm (the temperature of the permittivity maximum) and the behaviour departs from ideality above Tm, whereas non-ideal Debye behaviour is seen both below and above Tm for PMN–PZ. Complex modulus plots fit well with two depressed semicircles and three depressed semicircles, respectively, for PMN–PT and PMN–PZ. The relaxation observed in the spectroscopic plots around 1 MHz for PMN–PT has been assigned to polarisation relaxation expected for normal-sized domains. No such relaxation could be observed for PMN–PZ around 1 MHz because of the mesoscopic domain sizes. 相似文献
63.
Xiao-Yan Chang Xin-Hai Li Long Zhang Hua-Jun Guo Wen-Jie Peng 《Materials Research Bulletin》2005,40(9):1513-1520
Pure and carbon-containing olivine LiMn0.7Fe0.3O4 were synthesized at 600 °C by the method of solid-state reaction. Structure, surface morphology and charge/discharge performance of LiMn0.7Fe0.3O4 were characterized by X-ray diffraction, scanning electron microscopy, and electrochemical measurement, respectively. The prepared materials with and without carbon both show the single olivine structure. The morphologies of primary particles are greatly affected by the addition of carbon. Large particles (500-1000 nm) and densely sintered blocks were observed in pure LiMn0.7Fe0.3PO4, which made the insertion and extraction of lithium ions difficult. Battery made from this sample can not charge and discharge effectively. The carbon-containing LiMn0.7Fe0.3PO4 has a small particle size (100-200 nm) and a regular appearance. This material demonstrates high reversible capacity of about 120 mAh g−1, perfect cycling performance, and excellent rate capability. It is obvious that the addition of carbon plays an important role in restricting the particle size of the material, which helps to prepare LiMn0.7Fe0.3PO4 with excellent electrochemical performance. The electrochemical reaction resistance is much lower in the partly discharged state than in the fully charged or fully discharged state by the measurement of ac impedance for carbon-containing LiMn0.7Fe0.3PO4. It is indicated that the mixed-valence of Fe3+/Fe2+ or Mn3+/Mn2+ is beneficial to the transfer of electron which happens between the interface. 相似文献
64.
Schottky barrier diode devices were fabricated in a sandwich configuration with a blend film consisting of a conducting polymer, poly(2,5-dimethoxyaniline), PDMA in an insulating matrix, polyethylene oxide (PEO). The influence of two different dopants, sulphate anion (SA) or methane sulfonate anion (MSA), in the electronic properties of the device was followed using the devices: ITO/PDMA (SA)-PEO/Al and ITO/PDMA (MSA)-PEO/Al. Current (I)-Voltage (V) characteristics were recorded for making a comparative evaluation of the electronic and junction properties of the devices. The junction and electronic parameters were analyzed and compared in the light of differences in the electronic state, morphology and transport of carriers. The device turn on voltage was found to be higher for Al/ PEO-PDMA (MSA)/ITO (∼3.0 V) in comparison to Al/ PEO-PDMA (SA)/ITO (∼2.85 V). The electronic states of PDMA doped with SA or MSA dopant were ascertained by optical UV-Visible spectroscopy. AC-impedance measurements were made for the devices and the values of bulk resistance (Rc), depletion resistance (Rd) and depletion layer width (W) were deduced through a proposed equivalent circuit. W for the device with PEO-PDMA (MSA) is more (∼24 nm) than the device with PEO-PDMA (SA) (∼8.5 nm). The observed higher ΦB for PDMA-PEO (MSA) is consistent with this observation. 相似文献
65.
计算机高速数字电路设计技术 总被引:1,自引:0,他引:1
胡怀湘 《计算机工程与应用》2003,39(17):128-132
介绍了电源分布系统和传输线阻抗对高速电路设计的影响,并根据实践经验对如何处理高速电路电源系统的问题和注意事项提出一些指导意见,该文将对越来越多的设计者涉足高速电路的设计提供很好的帮助。 相似文献
66.
本文通过阻抗频率特性仿真,分析了变压器漏抗对滤波效果的影响,并从理论上提出了解决上述问题的方法. 相似文献
67.
用于TCSC阻抗控制的积分投切式PID控制方法 总被引:4,自引:4,他引:4
可控串补(TCSC)的阻抗控制是整个串补装置成功与否的关键。文中分析了常规比例积分微分(PID)控制在命令阻抗从不同阻抗阶跃到同一阻抗时鲁棒性不好的原因,得出了常规PID控制的效果主要与接到阻抗阶跃命令后命令阻抗和测量阻抗所包围的第一块面积有关的结论,并据此提出了一种实用的积分投切式PID阻抗控制方法。该方法在接到阻抗阶跃命令后切除积分环节,而在测量阻抗第一次超越命令阻抗时才投入积分环节。与常规PID控制的仿真结果比较表明,该方法在响应各种阻抗阶跃命令时具有较强的鲁棒性、良好的动态和静态性能,能满足工程要求。 相似文献
68.
介绍了阻抗Z*k不同的几台变压器并联运行达到最大出力时,各变压器分接头位置如何选择的计算方法,并给出了计算公工和程序框图。 相似文献
69.
70.
星形延边三角形接线平衡变压器的阻抗匹配与数学模型 总被引:17,自引:5,他引:17
星形延边三角形接线平衡变压器是应用于我国电气化铁道的一种新型三相一两相平衡变压器。针对其特殊的接线形式,提出了以磁势平衡方程、绕组连接方程、端口输出方程和电压传递方程为基础的多绕组变压器系统化分析方法。根据理想平衡变压器的技术条件提出了基于绕组之间短路阻抗的阻抗匹配关系式,推广了以前的有关结论。讨论了星形延边三角形接线平衡变压器的等值模型、两相等值电路和中性点不接地运行等问题。给出了星形延边三角形接线平衡变压器在相坐标下的节点导纳矩阵,以便与电力系统其它部分接口进行有关分析。 相似文献