全文获取类型
收费全文 | 7322篇 |
免费 | 1118篇 |
国内免费 | 502篇 |
专业分类
电工技术 | 2045篇 |
综合类 | 473篇 |
化学工业 | 1158篇 |
金属工艺 | 867篇 |
机械仪表 | 271篇 |
建筑科学 | 193篇 |
矿业工程 | 72篇 |
能源动力 | 497篇 |
轻工业 | 81篇 |
水利工程 | 57篇 |
石油天然气 | 427篇 |
武器工业 | 43篇 |
无线电 | 1239篇 |
一般工业技术 | 820篇 |
冶金工业 | 135篇 |
原子能技术 | 65篇 |
自动化技术 | 499篇 |
出版年
2024年 | 44篇 |
2023年 | 149篇 |
2022年 | 218篇 |
2021年 | 242篇 |
2020年 | 285篇 |
2019年 | 261篇 |
2018年 | 239篇 |
2017年 | 319篇 |
2016年 | 339篇 |
2015年 | 329篇 |
2014年 | 420篇 |
2013年 | 402篇 |
2012年 | 510篇 |
2011年 | 669篇 |
2010年 | 485篇 |
2009年 | 470篇 |
2008年 | 487篇 |
2007年 | 521篇 |
2006年 | 450篇 |
2005年 | 310篇 |
2004年 | 332篇 |
2003年 | 257篇 |
2002年 | 230篇 |
2001年 | 167篇 |
2000年 | 162篇 |
1999年 | 118篇 |
1998年 | 97篇 |
1997年 | 92篇 |
1996年 | 60篇 |
1995年 | 63篇 |
1994年 | 49篇 |
1993年 | 45篇 |
1992年 | 41篇 |
1991年 | 27篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有8942条查询结果,搜索用时 31 毫秒
81.
化学镀Ni-P-Cr2O3和Ni-P-SiO2复合镀层的研究 总被引:2,自引:0,他引:2
KARTHIKEYAN S SRINIVASAN K N VASUDEVAN T JOHN S 《电镀与涂饰》2007,26(1):1-6
本文对化学镀镍及化学镀镍磷基质中SiO2与Cr2O3的共沉积进行了研究.微粒在不断生长的膜层中共沉积引起了新的化学复合镀层的出现,这些复合镀层许多都具有优异的耐磨及耐蚀性能.通过选取镀层合金/复合微粒/金属基体的组分可改进镀层,获得所需的性能,以满足特别的需求.在对这些复合镀层的应用需求正在迫近与增长的同时,其市场正在迅速扩张.本文开发出了一种合适的复合化学镀镍液,并通过维氏硬度法对化学复合镀镍层进行了表征.采用动电位极化及交流阻抗法测定了镀层的Taber耐磨性能及耐蚀性能.采用SEM及XRD对复合镀层的表面形貌进行了分析. 相似文献
82.
In the present study, different types of 75% Cr3C2-25% NiCr coatings were applied on a steel substrate by means of high velocity oxygen fuel spraying (HVOF), and studied using ac and dc electrochemical measurements in an aerated and unstirred 0.5 M H2SO4 solution. Structural characterization was determined before and after electrochemical tests. Differences between all sprayed systems are related to the gun transverse speed and number of deposited layers, which strongly affected the electrochemical characteristics of the coated steels. The coating obtained with a higher torch speed showed better resistance against corrosion. The electrochemical impedance results were analyzed using an equivalent circuit where porosity of the coatings and substrate oxidation were considered. 相似文献
83.
A.H Moreira A.V BenedettiP.T.A Sumodjo J.A GarridoP.L Cabot 《Electrochimica acta》2002,47(17):2823-2831
The electrochemical corrosion and passivation of Al5Zn1.7Mg0.23Cu0.053Nb alloys, submitted to different heat treatments (cold-rolled, annealed, quenched and aged, and quenched in two steps and aged), in sulphate-containing chloride solutions, has been studied by means of cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The cyclic polarization curves showed that sulphate addition to the chloride solution produced a poor reproducible shift of the breakdown potential to more positive potentials. The repassivation potentials, much more reproducible, and practically separating the passive from the pitting potential region, were slightly displaced in the negative direction with that addition. When the alloys were potentiodynamically polarized in the passive potential region, sulphate was incorporated in the oxide film, thus precluding chloride ingress. In addition, Zn depletion was favoured, whereas Mg losses were avoided. Different equivalent circuits corresponding to different alloys and potentials in the passive and pitting regions were employed to account for the electrochemical processes taking place in each condition. This work shows that sulphate makes these alloys more sensitive to corrosion, increasing the fracture properties of the surface layer and favouring the pitting attack over greater areas than chloride alone. 相似文献
84.
Dynamic surface control-backstepping based impedance control for 5-DOF flexible joint robots 总被引:1,自引:0,他引:1
A new impedance controller based on the dynamic surface control-backstepping technique to actualize the anticipant dynamic
relationship between the motion of end-effector and the external torques was presented. Comparing with the traditional backstepping
method that has “explosion of terms” problem, the new proposed control system is a combination of the dynamic surface control
technique and the backstepping. The dynamic surface control (DSC) technique can resolve the “explosion of terms” problem that
is caused by differential coefficient calculation in the model, and the problem can bring a complexity that will cause the
backstepping method hardly to be applied to the practical application, especially to the multi-joint robot. Finally, the validity
of the method was proved in the laboratory environment that was set up on the 5-DOF (degree of freedom) flexible joint robot.
Tracking errors of DSC-backstepping impedance control that were 2.0 and 1.5 mm are better than those of backstepping impedance
control which were 3.5 and 2.5 mm in directions X, Y in free space, respectively. And the anticipant Cartesian impedance behavior and compliant behavior were achieved successfully
as depicted theoretically. 相似文献
85.
利用Advanced Design System(ADS)完成了L波段低噪声放大器(LNA)的设计。分析了实际电路可能产生的非连续性、寄生参数效应等因素对电路各个性能指标的影响,并针对这些因素利用ADS进行了电磁仿真计算,最后给出了放大器的仿真结果和最终电路及测试结果。采用ATF-35143器件设计,达到了预定的技术指标,工作频率1.21GHz,增益G大于14dB,噪声系数NF小于0.5 dB,输入1dB压缩点大于5dbm。 相似文献
86.
张杰 《山东电力高等专科学校学报》2010,13(4):21-24
发电机误上电保护是发电机变压器组保护中逻辑判据较为复杂的一种保护类型,在测试过程中有一定的难度。本文通过对发电机误上电保护的调试和检测,总结出实用的逻辑电路并提供相应的测试方法。对有类似微机保护装置的发电厂、变电站、电力职业院校及电力培训中心也有一定借鉴意义。 相似文献
87.
Calcium phosphate film was prepared by electrochemical deposition technology. Subsequently, the alkaline treatment process
of calcium phosphate film in 0.1 mol/L NaOH solution was monitored on real time by the piezoelectric quartz crystal impedance
(PQCI) technique. The variations of morphology and composition for the alkaline treatment products were characterized by scanning
electron microscopy (SEM), Fourier transform infrared (FT-IR) and X-ray diffraction (XRD), respectively. The dynamic variations
of calcium phosphate can be characterized by the change of equivalent circuit parameters. The results show that the forming
process of hydroxyapatite (HA) is composed of three stages: (1) acidic calcium phosphate dissolution; (2) phase transformation;
and (3) HA formation. Furthermore, the correlative kinetic equations and parameters are obtained by fitting the static capacitance
(C
s)—time curves.
Foundation item: Project(2005CB623901) supported by the Major State Basic Research and Development Program of China 相似文献
88.
由于各向异性介质电磁参数为张量形式,使得各向异性介质涂覆导体目标的电磁散射建模和精确计算相当复杂和困难.引入高阶张量阻抗边界条件,可以大大简化建模过程,提高计算效率.论文针对各向异性介质涂覆曲面导体目标,采用基于平面近似的高阶张量阻抗边界条件,将一维二阶张量阻抗边界条件应用于柱面涂覆目标,二维二阶张量阻抗边界条件应用于三维曲面涂覆目标上,建立二者的高阶张量阻抗边界条件解.设计算例仿真,并与精确解/矩量法解比较.通过仿真,研究了各向异性介质涂覆目标电尺寸、涂覆厚度以及目标形状对高阶张量阻抗边界条件解的精度的影响. 相似文献
89.
针对柔性注压锚杆解析及实验比较困难,采用有限元方法,模拟研究其锚固段阻抗摩擦应力的分布规律。数值模拟显示:沿锚杆环向呈近似正弦或余弦函数的循环分布形态;沿锚杆轴向应力分布可划分成波浪段、平台段以及突降段3个阶段。柔性注压锚杆锚固段最大阻抗摩擦应力沿轴向分布近似是均匀的,可实现真正的全长锚固。 相似文献
90.
沈园云 《上海轻工业高等专科学校学报》2010,(1):52-54
通过对SEL-351A的零(负)序方向元件分别在接地方向、相间故障方向及三相短路故障方向的理论分析,结合电测试数据阐述了对SEL-351A继电器方向元件的认识。 相似文献