全文获取类型
收费全文 | 24394篇 |
免费 | 2103篇 |
国内免费 | 1203篇 |
专业分类
电工技术 | 1144篇 |
综合类 | 1309篇 |
化学工业 | 4300篇 |
金属工艺 | 582篇 |
机械仪表 | 1350篇 |
建筑科学 | 1453篇 |
矿业工程 | 280篇 |
能源动力 | 1067篇 |
轻工业 | 1528篇 |
水利工程 | 115篇 |
石油天然气 | 1205篇 |
武器工业 | 130篇 |
无线电 | 7247篇 |
一般工业技术 | 3730篇 |
冶金工业 | 472篇 |
原子能技术 | 292篇 |
自动化技术 | 1496篇 |
出版年
2024年 | 87篇 |
2023年 | 359篇 |
2022年 | 571篇 |
2021年 | 816篇 |
2020年 | 765篇 |
2019年 | 748篇 |
2018年 | 634篇 |
2017年 | 981篇 |
2016年 | 1015篇 |
2015年 | 1019篇 |
2014年 | 1679篇 |
2013年 | 1437篇 |
2012年 | 1638篇 |
2011年 | 1846篇 |
2010年 | 1483篇 |
2009年 | 1549篇 |
2008年 | 1387篇 |
2007年 | 1452篇 |
2006年 | 1283篇 |
2005年 | 1092篇 |
2004年 | 941篇 |
2003年 | 864篇 |
2002年 | 634篇 |
2001年 | 554篇 |
2000年 | 548篇 |
1999年 | 416篇 |
1998年 | 331篇 |
1997年 | 293篇 |
1996年 | 233篇 |
1995年 | 175篇 |
1994年 | 202篇 |
1993年 | 157篇 |
1992年 | 97篇 |
1991年 | 84篇 |
1990年 | 69篇 |
1989年 | 43篇 |
1988年 | 41篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 29篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1959年 | 3篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Determination of assimilable organic carbon (aoc) in ozonated water with acinetobacter calcoaceticus
The effect of ozone application in drinking water on the production of assimilable organic carbon (AOC) was evaluated. The typical procedure to determine AOC is suggested by van der Kooij, which is the method of bacterial growth measurement by colony‐forming units using the strain P17 and/or NOX. The bacterial indicator species used for this study is Acinetobacter calcoaceticus which was isolated and identified while ozonating Nakdong river water. This strain could never be isolated from the raw water, but this strain was the predominant isolate in the ozonated water. Within a short incubation time, this organism was found to replicate well on acetate and oxalate as the sole carbon sources. The yield coefficients of this organism for acetate and oxalate are the same order of magnitude as the value of P17 and NOX. With full‐scale experiments, A. calcoaceticus concentration was found to increase after ozonation, but did not decrease upon chlorination. In laboratory‐scale experiments with Yongsan river water, aldehyes were found to be produced in proportion to the ozone dose. The raw water contains low concentrations of aldehydes, but has a high AOC concentration. A correlation between aldehyde production and AOC production was observed in the tested water with ozonation. 相似文献
62.
由于器件的快速退化,101.5小时似乎成了Znse基蓝绿色半导体激光器难于逾越的寿命极限。分析退化机制,发现在强电流注入的半导体激光器中,热退化具有重要影响。研究表明,用作载流子限制层的宽带Ⅱ-Ⅵ族四元合金(如ZnMgSSe)只能对ZnSe中的电子有效地限制,无法对空穴很好地限制;而对BeTe,却只能对空穴进行有效的限制,无法对电子很好地限制。这导致ZnSe(或BeTe)活性层空穴(或电子)漏电发热,引起退化。本文提出以ZnSe/BeTe超晶格为蓝绿发光层,并用包络函数理论具体计算了阱宽、垒宽对载流子能级的不同影响,考察了ZnSe、BeTe厚度比和超晶格周期对带隙、载流子限制能力的调节。为研制新型长寿命蓝绿色半导体激光器提供了一条新的途径。 相似文献
63.
近几年来,由于超辐射发光二极管在光纤陀螺和光时域反射仪等方面的重要应用,已引起了人们的极大关注,许多国家都在竞相研制和开发.本文综述了目前超辐射发光二极管的主要结构和特性及其应用前景. 相似文献
64.
65.
自发参量下转换光场的实验研究进展综述 总被引:1,自引:0,他引:1
自发参量下转换(spontaneous parametric down-conversion,SPDC)光场是基于单色泵浦光子流和量子真空噪声对非线性晶体的综合作用而产生的,它固有的量子起源决定了在非经典光场研究中的重要地位和作用.对SPDC光场的相干特性和它在绝对测量光电探测器量子效率中的应用进行了深入而细致的研究和探讨. 相似文献
66.
An Arctangent Unwrapping Technique of Photoelasticity Using Linearly Polarized Light at Three Wavelengths 总被引:2,自引:0,他引:2
Abstract: In the automatic measurements of the principal stress directions ψ and the total relative phase retardation ρ tol , ψ and ρ tol can be easily obtained by the phase unwrapping method using the arctangent function. However, only some published works exist on the measurements of ψ and ρ tol by photoelastic techniques using a linearly polarised incident light source. This paper presents the technique of applying an unwrapping by means of the arctangent function to photoelasticity. The technique overcomes the error associated with the quarter-wave plate by using an incident light of different wavelength and does not need an interpolation for the determination of ψ . The technique is validated by determining ψ and ρ tol for the well-known circular disk subjected to a diametral compressive load model. 相似文献
67.
定电流对LED的重要性 总被引:2,自引:0,他引:2
高功率超高亮度LED已经开始大量应用.要实际体现LED(尤其是高功率超高亮度LED)的优点,采用定电流驱动方式必要条件之一. 相似文献
68.
The process of mechanoluminescence transformation of a pulse pressure sensor is considered. The process consists in excitation
of emission under the action of mechanical loading. An algorithm for use in processing the output optical signal of the sensor
that makes it possible to determine an input shock pulse is presented.
__________
Translated from Izmeritel’naya Tekhnika, No. 10, pp. 28–31, October, 2007. 相似文献
69.
70.
Power devices with high capability have been developed. 8‐kV/3.5‐kA‐class light‐triggered thyristors have the highest capability among power devices. These devices are used in the Kii Channel HVDC transmission system in Japan. In this paper, we report the extracted problems of conventional testing methods of 8‐kV/3.5‐kA‐class light‐triggered thyristors among manufacturers, and the proposed unified testing methods on the basis of element characteristics and operating conditions in the Kii Channel HVDC system. Furthermore, we propose a figure of merit for power devices for the practical use, and try to extract elements used at the Kii Channel HVDC system with small margins and low withstand capabilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 61–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10024 相似文献