全文获取类型
收费全文 | 670208篇 |
免费 | 7530篇 |
国内免费 | 1403篇 |
专业分类
电工技术 | 11698篇 |
综合类 | 2774篇 |
化学工业 | 102787篇 |
金属工艺 | 30959篇 |
机械仪表 | 23584篇 |
建筑科学 | 15060篇 |
矿业工程 | 5110篇 |
能源动力 | 15756篇 |
轻工业 | 49237篇 |
水利工程 | 8384篇 |
石油天然气 | 15700篇 |
武器工业 | 39篇 |
无线电 | 71173篇 |
一般工业技术 | 138346篇 |
冶金工业 | 100074篇 |
原子能技术 | 15164篇 |
自动化技术 | 73296篇 |
出版年
2021年 | 5507篇 |
2019年 | 5279篇 |
2018年 | 25080篇 |
2017年 | 24428篇 |
2016年 | 20460篇 |
2015年 | 6742篇 |
2014年 | 10494篇 |
2013年 | 26304篇 |
2012年 | 19445篇 |
2011年 | 32589篇 |
2010年 | 27346篇 |
2009年 | 26556篇 |
2008年 | 27808篇 |
2007年 | 29326篇 |
2006年 | 16418篇 |
2005年 | 17448篇 |
2004年 | 15945篇 |
2003年 | 15608篇 |
2002年 | 14092篇 |
2001年 | 12978篇 |
2000年 | 12571篇 |
1999年 | 12074篇 |
1998年 | 27700篇 |
1997年 | 20064篇 |
1996年 | 15673篇 |
1995年 | 12026篇 |
1994年 | 10891篇 |
1993年 | 10639篇 |
1992年 | 8356篇 |
1991年 | 8143篇 |
1990年 | 7991篇 |
1989年 | 7766篇 |
1988年 | 7492篇 |
1987年 | 6748篇 |
1986年 | 6534篇 |
1985年 | 7393篇 |
1984年 | 6701篇 |
1983年 | 6440篇 |
1982年 | 5778篇 |
1981年 | 5897篇 |
1980年 | 5632篇 |
1979年 | 5734篇 |
1978年 | 5664篇 |
1977年 | 6180篇 |
1976年 | 7687篇 |
1975年 | 5110篇 |
1974年 | 4903篇 |
1973年 | 4980篇 |
1972年 | 4279篇 |
1971年 | 4039篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
The dynamic interaction between the mechanical and electrical drive parameters when damage suddenly appears in the mechanical part of a conveyer belt is investigated. The possibility of using the change in the motor’s electrical parameters as a diagnostic signal is assessed. A model for investigating the dynamic processes in the system consisting of the grid, the induction motor, and the conveyer belt is proposed. The grid and induction motor are described by a model of fourth-order state space, whose output is the torque at the motor shaft. The moments of inertia and pliability of the links between the elements in the mechanical part of the conveyer belt are determined. By gradually identifying the elements with the minimum moment of inertia and distributing their moments of inertia and pliabilities among the adjacent elements, we obtain a three-mass system simulating the mechanical part of the conveyer belt. This dynamic model is solved by means of Matlab Simulink software. The energy characteristics of the drive are determined in dynamic processes following a mechanical accident. 相似文献
113.
Antti Voss Niko Hänninen Mohammad Pour-Ghaz Marko Vauhkonen Aku Seppänen 《Materials and Structures》2018,51(3):68
The development of visualizing tools to monitor unsaturated moisture flow in cement-based materials is of great importance, as most degradation processes in cement-based materials are connected to and take place in the presence moisture. This paper investigates the ability of electrical capacitance tomography (ECT) to image two-dimensional (2D) unsaturated moisture flow in cement-based materials. In ECT, the electrical permittivity distribution within an object is reconstructed based on measured capacitances between electrodes attached on the object’s surface. In a series of experiments, mortar specimens with and without discrete cracks were imaged with ECT during a 2D moisture ingress. The results show that ECT is able to monitor the evolution of the moisture flow, and to approximate the shape and position of the moisture front. These findings indicate that ECT is a viable method for monitoring and visualizing 2D unsaturated moisture flow in cement-based materials in the presence and absence of discrete cracks. 相似文献
114.
115.
Advanced technologies and modern high-production machines for underground mining of thick gently dipping coal demand strict adherence to technological discipline, reduction in operational loss and selection of optimized ventilation modes. The authors analyze ventilation schemes used in working areas in thick gently dipping seams in order to reveal influence exerted by the schemes, methods and parameters of ventilation on distribution of air loss in mined-out areas. 相似文献
116.
117.
Ahmed Obaid M. Alzahrani M. Sh. Abdel-wahab Meshari Alayash M. S. Aida 《Journal of Materials Science: Materials in Electronics》2018,29(19):16317-16324
In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector. 相似文献
118.
Video transmission over IEEE 802.11e wireless networks still shows poor performance for large bandwidth demand and frequently changed environments. Thus, several enhancements of IEEE 802.11e were proposed. On the other hand, big frames and simultaneous sending of adjacent frames always cause packet dropping for buffer overflow. In the past, we proposed an IEEE 802.11e enhancement named DFAA and a content aware mechanism to solve the above problems. The motivation of this paper is to find a proper way to integrate these two mechanisms. A DFAA enhancement (DFAA-E) is proposed to make up the insufficiency of content aware mechanism. Experiments results show that the combination of DFAA-E and content aware mechanism improves the video decoded quality greatly. And its performance can be further enhanced by selecting the suitable settings of certain parameters. 相似文献
119.
120.