全文获取类型
收费全文 | 1568篇 |
免费 | 36篇 |
国内免费 | 49篇 |
专业分类
电工技术 | 39篇 |
综合类 | 21篇 |
化学工业 | 207篇 |
金属工艺 | 374篇 |
机械仪表 | 108篇 |
建筑科学 | 27篇 |
矿业工程 | 10篇 |
能源动力 | 86篇 |
轻工业 | 71篇 |
水利工程 | 6篇 |
石油天然气 | 23篇 |
武器工业 | 3篇 |
无线电 | 184篇 |
一般工业技术 | 212篇 |
冶金工业 | 42篇 |
原子能技术 | 47篇 |
自动化技术 | 193篇 |
出版年
2024年 | 4篇 |
2023年 | 43篇 |
2022年 | 45篇 |
2021年 | 56篇 |
2020年 | 45篇 |
2019年 | 34篇 |
2018年 | 23篇 |
2017年 | 47篇 |
2016年 | 28篇 |
2015年 | 41篇 |
2014年 | 58篇 |
2013年 | 65篇 |
2012年 | 90篇 |
2011年 | 108篇 |
2010年 | 75篇 |
2009年 | 94篇 |
2008年 | 76篇 |
2007年 | 84篇 |
2006年 | 98篇 |
2005年 | 75篇 |
2004年 | 67篇 |
2003年 | 54篇 |
2002年 | 51篇 |
2001年 | 46篇 |
2000年 | 49篇 |
1999年 | 47篇 |
1998年 | 32篇 |
1997年 | 17篇 |
1996年 | 22篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1653条查询结果,搜索用时 0 毫秒
71.
介绍了阴极电泳涂装中常出现的缺陷类型,主要有粗糙、针孔、缩孔、杂质和气泡等.分别分析了其出现的原因,提出了相应的解决方法.为开展阴极电泳研究及解决实际生产中出现的缺陷问题提供了参考. 相似文献
72.
73.
Young Hyun Nam 《Journal of Mechanical Science and Technology》1999,13(2):158-167
Ultrasonic testing uses the directivity of the ultrasonic wave, which propagates in one direction. The directivity is expressed
as the relationship between the propagation direction and its sound pressure. The directivity of an ultrasonic wave is related
to the choice of probe arrangement, testing sensitivity and scanning pitch, and correct measurement of defect size and location.
This paper investigated the directivity of ultrasonic waves, which are scattered from a slit defect located in simulated butt
weld joint using a visualization method. When the defect size was smaller than the wavelengths, clear directivity in the reflected
wave was observed. When the ratio of defect size to wavelength is greater than 1.5, measured directivities almost agree with
the theoretical directivity. The directivity of shear waves scattered from the slit defect varied according to probe direction
(Far defect, Near defect). The angle of reflection wave became similar to angle of incidence as the height of excess metal
in welded joint increased. 相似文献
74.
在中国国家自然科学基金重点项目《特大件成形制造技术基础研究》、国家科技支撑计划课题《大型轧机共性技术》、国家重点基础研究发展计划(973计划)前期研究专项《大型零件热态成形制造虚拟技术基础研究》,以及中国河北省科技攻关项目《大型轧机共性技术》和《特大件成形制造技术基础研究》共同资助下,以大型锻钢轧辊(辊身直径超过1 000 mm或质量大于100 t)为对象,通过宏观 微观强耦合建模,解决铸造缺陷信息遗传、孔洞锻合条件、形变焊合条件、材料断裂准则构建,以及热 力 微观组织耦合建模等关键技术问题,建立以淬硬层深度数值预测技术为核心的热处理工艺分析与优化系统,提出基于非均质轧辊辊间接触力学模型的轧辊强度设计方法,构建起大型锻钢轧辊热态成形制造与服役评估的多学科耦合决策支持理论体系,提出理论研究报告。针对缩孔和气孔等大型铸钢锭铸造中的孔洞缺陷控制,以大锻件内部孔洞锻造闭合过程为科学问题,以大锻件内部有效锻合区域数值预测为目标,将有限元方法与人工神经网络技术相结合,利用神经网络的非线性映射能力,描述材料变形抗力、温度、应力应变与孔洞闭合程度之间的复杂关系,将孔洞锻合过程有限元模拟结果作为神经网络训练样本,建立起温度、应力和变形等多场耦合作用下的孔洞锻合条件模型(VCCM)。针对孔洞形变焊合机理与物理模拟模型一致性问题,以消除大锻件心部残留微孔隙,实现物理闭合状态下的锻合孔洞缺陷的真正冶金结合为目标,基于临界闭合孔洞界面接触力学原型和原子高温扩散理论,以界面接触应变和高温环境作为孔洞焊合的驱动力,利用高温和大变形对闭合孔洞界面扩散焊合的有利影响,提出适用于大锻件在锻造成形阶段的内部孔洞缺陷形变的形变焊合方法,通过物理模拟实 相似文献
75.
76.
Fang Xu Wang-lin Li Zhan-lei Liu Bo-fan Zhang Bing-yu Zhang 《Geotextiles and Geomembranes》2017,45(3):178-183
In studies on the geomembrane air expansion in plain reservoirs, the forced deformation of a geomembrane is generally simplified as geomembrane air expansion deformation under ring-restrained conditions. In this study, a test apparatus was developed to measure geomembrane air expansion deformation, and a number of factors that can affect geomembrane air expansion deformation were investigated, including the test apparatus diameter, loading rate, and geomembrane defects. The results of this study show that under ring-restrained conditions, as the test apparatus diameter increases, the burst pressure decreases, and the burst crown height increases. Moreover, the burst pressure and the burst crown height gradually increase as the loading rate increases. Geomembrane defects, such as holes, folds, and scratches, decrease both the burst pressure and the burst crown height. 相似文献
77.
Metal magnetic memory (MMM) technique can evaluate early damages of ferromagnets and search possible defect locations, while just classifies the defect types roughly. To promote study in this area, the magnetic gradient tensor (MGT) of the self-magnetic leakage field (SMLF) on the fracture zone of crack and stress concentration was measured using a tri-axis magnetometer. From measured results, both the plane and the vertical characteristics of SMLF distributions were discussed. To remove the influence of the measuring direction on experimental results, a new parameter of the analytical signal of magnetic gradient tensor (AMGT) was introduced to determine the location and boundary of the defect. Then, the vertical features were acquired by measuring the plane distributions of AMGT under different lift offs. Through analyzing the vertical features, it was concluded that change rule of the maximum AMGT can be used to predict the defect type. At last, the explanation of the relationship between the vertical feature and the defect type was discussed, which can give some useful inspirations to researchers on magnetic leakage field testing. 相似文献
78.
《International Journal of Hydrogen Energy》2020,45(31):15571-15577
Here, the storage sites of hydrogen in FeCr alloy, namely (H, He)–V nano-clusters with open volume, have been investigated by first-principles calculations and positron annihilation spectroscopy. The positron lifetimes in the nano-clusters obtained by theoretical calculations and experiments were compared. These results suggest that positron is sensitive to the relative position of the gas atoms decorating the open volume; and a helium atom forms a more repulsive ion core than a hydrogen atom when it occupies the vacancy, resulting in a decrease in positron lifetime. Interpretation of the PAS data was successfully combined with theoretical calculations, and allowed us to determine the defect status in specimens after H/He irradiation with different implantation patterns. The speculated kinds of hydrogen storage sites formed after irradiation are summarized. For the He-ions pre-implanted situation, the helium-vacancy clusters or bubbles forming in advance may recombine with H atoms to form stable He–H–V complex. 相似文献
79.
《International Journal of Hydrogen Energy》2019,44(54):28556-28565
NiFe layered double hydroxides (LDHs) is considered to be one of the LDHs electrocatalyst materials with the best electrocatalytic oxygen evolution properties. However, its poor conductivity and inherently poor electrocatalytic activity are considered to be the limiting factors inhibiting the electrocatalytic properties for oxygen evolution reaction (OER). The amorphous NiFeAl-LDHs electrocatalysts were prepared by electrodeposition with nickel foam as the support, and the D-NiFeAl-LDHs electrocatalyst with defect sites was then obtained by alkali etching. The mechanism of catalysts with defect sites in OER was analyzed. The ingenious defects can selectively accelerate the adsorption of OH−, thus enhancing the electrochemical activity. The D-NiFeAl-LDHs electrocatalyst had higher OER electrocatalytic activity than NiFe-LDHs electrocatalyst: its accelerated OER kinetics were mainly due to the introduction of iron and nickel defects in NiFeAl-LDHs nanosheets, which effectively adjusted the surface electronic structure and improved OER electrocatalytic performance. There was only a low overpotential of 262 mV with the current density of 10 mA cm−2, and the Tafel slope was as low as 41.67 mV dec−1. The OER electrocatalytic performance of D-NiFeAl-LDHs was even better than those of most of the reported NiFe-LDHs electrocatalysts. 相似文献
80.
纵波探伤是检测中厚钢板内部质量的主要方式。探伤钢板按不同标准、不同级别进行检测判定。对于钢板内部存在的缺陷,有些是标准允许的,有些则是纵波探伤技术性问题而无法检测出来。目前对缺陷的定性、定量技术,还不能完全满足科研人员了解产品内部缺陷详细情况的要求。为此笔者阐述了探伤合格钢板存在缺陷的原因,及缺陷定性、定量的不确定性问题。 相似文献