全文获取类型
收费全文 | 24375篇 |
免费 | 2578篇 |
国内免费 | 1577篇 |
专业分类
电工技术 | 852篇 |
技术理论 | 2篇 |
综合类 | 3596篇 |
化学工业 | 3738篇 |
金属工艺 | 2184篇 |
机械仪表 | 1427篇 |
建筑科学 | 1301篇 |
矿业工程 | 166篇 |
能源动力 | 1789篇 |
轻工业 | 1600篇 |
水利工程 | 179篇 |
石油天然气 | 123篇 |
武器工业 | 300篇 |
无线电 | 2068篇 |
一般工业技术 | 3866篇 |
冶金工业 | 396篇 |
原子能技术 | 589篇 |
自动化技术 | 4354篇 |
出版年
2024年 | 90篇 |
2023年 | 856篇 |
2022年 | 916篇 |
2021年 | 946篇 |
2020年 | 1146篇 |
2019年 | 1035篇 |
2018年 | 810篇 |
2017年 | 1151篇 |
2016年 | 1192篇 |
2015年 | 1350篇 |
2014年 | 2064篇 |
2013年 | 1930篇 |
2012年 | 2459篇 |
2011年 | 2328篇 |
2010年 | 1776篇 |
2009年 | 1955篇 |
2008年 | 1146篇 |
2007年 | 1567篇 |
2006年 | 1134篇 |
2005年 | 543篇 |
2004年 | 216篇 |
2003年 | 242篇 |
2002年 | 255篇 |
2001年 | 232篇 |
2000年 | 244篇 |
1999年 | 228篇 |
1998年 | 126篇 |
1997年 | 68篇 |
1996年 | 98篇 |
1995年 | 78篇 |
1994年 | 56篇 |
1993年 | 56篇 |
1992年 | 55篇 |
1991年 | 46篇 |
1990年 | 55篇 |
1989年 | 34篇 |
1988年 | 16篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1959年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
In order to develop a basic electrode with low fume and good usability, a uew slag system has been designed after analyzing several basic electrode slag systems. Then in view of uniform design method, arranging the experiment points by it, the influenced laws of the uew system coating compouents on the arc stability had been searched. In the formula, niue coating compouents were taken as independent variables and they were divided into six levels in all twenty-four experiments. The arc stability was taken as function and taken down the data when welding and then put them into the computer to be processed statistically. The analysis results give the mathematical model and trend diagrams between independent variables and the function. They indicate that the effects of many coating compouents on the arc stability are in the mutual form. The mutual effects between CaCO3 and BaF2, BaF2 and BaCO3 , increases the arc stability separately. While the mutual effects between CaF2 and iron powder, the square item of iron powder itself decreases the arc stability separately. 相似文献
73.
《钢铁研究学报(英文版)》2006
Being a new permanent magnets(PMs) arrangement, the Halbach array could approve the magnetic flux density effectively, through weakening the magnetic flux density in one side of the PMs array, meanwhile strengthening the magnetic flux density in the other side. In the disk coreless PM synchronous motor (PMSM), the magnetic flux density is required to be sine wave and the peak value should be as high as possible. The paper deals with the application of the 90° Halbach array in the disk coreless PMSM, adopting NdFeB PMs. For the thickness of PMs influences the magnetic flux density in the air gap, the thickness variation technology is adopted. Through altering the adjacent PMs thickness, nine different PMs thickness combination is analyzed by FEM methods. And the conclusion is that when the thickness of tangential magnetization PMs is great than that of the radial magnetization PMs, the magnetic flux density wave is closer to sine wave than when the thickness of the tangential magnetization PMs is smaller than that of the radial magnetization PMs. Furthermore, when the thickness of the tangential magnetization PMs is great than that of the radial magnetization PMs, keeping the thickness of the tangential magnetization PMs being 0.006 m and the thickness of the radial magnetization PMs variation from 0.0048 m to 0.006 m, the magnetic flux density in the air gap will become closer to sine wave gradually, and then it becomes nonsinusoidal again. And when the thickness of radial magnetization PMs is 0.0054 m and 0.0055 m, the waves of magnetic flux density in the air gap are better than others. 相似文献
74.
《International Journal of Heat and Mass Transfer》2007,50(15-16):3250-3263
75.
《Materials Letters》2007,61(4-5):1109-1113
We report the synthesis of a nanostructured γ-LiAlO2 network in an Al-based metal matrix composite (MMC) by arc-melting a powder compact of Al–15 wt.%Li2O. During synthesis, chemical reactions between Al and Li2O occurred, and a two-phase Al-γ-LiAlO2 MMC was produced. The γ-LiAlO2 was in the form of nano-network extended evenly in the Al matrix. The apparent density and Vickers' hardness number of the MMC were determined to be 2.31 gcm− 3 and 143, respectively, and having a relative density of 0.87. The MMC was made nano-porous by etching away Al with a 2 M NaOH solution. The sizes of pores were about 150 nm and the width of the branches in the γ-LiAlO2 network was about 90 nm. Atomic force microscopy revealed that the branches were composed of fine grains of 50 nm in diameter. Microstructure of the network was not altered even after prolonged etching, and this suggested that γ-LiAlO2 was chemically inert to NaOH corrosion. Specific surface area of the γ-LiAlO2 nano-network was measured to be 79 m2/g, and its porosity was determined to be 43.7%. 相似文献
76.
《Cement and Concrete Composites》2007,29(4):330-336
The relatively simple to measure ‘time constant’ is presented as an index for characterizing the level of corrosion experienced by steel in concrete. This communication, largely in the form of a technical note, explicitly illustrates that the time constant determined from electrochemical testing has significant merit for monitoring corrosion of steel in concrete, and appears to be insensitive to the area of electrode being probed. In this work, the time constant, κ, is determined following a galvanostatic excitation signal, revealing a good correlation between the value of κ and corrosion status across specimens of widely varying geometry. Although this notion has been suggested in the past, this work presents both a survey and consolidated review to indicate the utility of the parameter as an index to corrosion rate on-site. 相似文献
77.
78.
79.
80.
《Journal of power sources》2006,158(1):169-176
A fuel cell is a device that can convert chemical energy into electricity directly. Among various types of fuel cells, both polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) can work at low temperature (<80 °C). Therefore, they can be used to supply power for commercial portable electronics such as laptop computers, digital cameras, PDAs and cell phones. The focus of this paper is to investigate the performance of a miniaturized DMFC device using a micropump to deliver fuel. The core of this micropump is a piezoelectric ring-type bending actuator and the associated nozzle/diffuser for directing fuel flow. Based on the experimental measurements, it is found that the performance of the fuel cell can be significantly improved if enough fuel flow is induced by the micropump at anode. Three factors may contribute to the performance enhancement including replenishment of methanol, decrease of diffusion resistance and removal of carbon dioxide. In comparison with conventional mini pumps, the size of the piezoelectric micropump is much smaller and the energy consumption is much lower. Thus, it is very viable and effective to use a piezoelectric valveless micropump for fuel delivery in miniaturized DMFC power systems. 相似文献