全文获取类型
收费全文 | 145423篇 |
免费 | 13490篇 |
国内免费 | 7283篇 |
专业分类
电工技术 | 9563篇 |
技术理论 | 8篇 |
综合类 | 10737篇 |
化学工业 | 23949篇 |
金属工艺 | 8664篇 |
机械仪表 | 9151篇 |
建筑科学 | 12510篇 |
矿业工程 | 4415篇 |
能源动力 | 4077篇 |
轻工业 | 11243篇 |
水利工程 | 2949篇 |
石油天然气 | 7664篇 |
武器工业 | 1379篇 |
无线电 | 15991篇 |
一般工业技术 | 15938篇 |
冶金工业 | 6451篇 |
原子能技术 | 1595篇 |
自动化技术 | 19912篇 |
出版年
2024年 | 802篇 |
2023年 | 2849篇 |
2022年 | 5162篇 |
2021年 | 6819篇 |
2020年 | 5036篇 |
2019年 | 4049篇 |
2018年 | 4515篇 |
2017年 | 4965篇 |
2016年 | 4276篇 |
2015年 | 6041篇 |
2014年 | 7468篇 |
2013年 | 8627篇 |
2012年 | 9973篇 |
2011年 | 10448篇 |
2010年 | 8956篇 |
2009年 | 8738篇 |
2008年 | 8337篇 |
2007年 | 7852篇 |
2006年 | 7720篇 |
2005年 | 6683篇 |
2004年 | 4642篇 |
2003年 | 4099篇 |
2002年 | 4086篇 |
2001年 | 3493篇 |
2000年 | 3231篇 |
1999年 | 3322篇 |
1998年 | 2538篇 |
1997年 | 2080篇 |
1996年 | 2055篇 |
1995年 | 1686篇 |
1994年 | 1379篇 |
1993年 | 994篇 |
1992年 | 796篇 |
1991年 | 624篇 |
1990年 | 454篇 |
1989年 | 365篇 |
1988年 | 300篇 |
1987年 | 209篇 |
1986年 | 148篇 |
1985年 | 99篇 |
1984年 | 63篇 |
1983年 | 41篇 |
1982年 | 58篇 |
1981年 | 43篇 |
1980年 | 44篇 |
1979年 | 15篇 |
1978年 | 2篇 |
1965年 | 2篇 |
1959年 | 2篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
74.
Longjie Zhou A. Zimmermann Yu-Ping Zeng F. Aldinger 《Journal of Materials Science》2004,39(8):2675-2681
The bipolar electric fatigue behaviour of antiferroelectric ceramics with the composition of Pb0.88Ba0.10La0.02(Zr0.55Sn0.35Ti0.10)O3 was investigated under various cycling fields. The material exhibits a degradation in the maximum field induced strain, a diffuse AFE-FE phase transition and an enhancement in the diffusion character of the FE-AFE phase transition due to electric cycling. Those variations increase with cycle number, indicating a logarithmic fatigue up to 108 cycles. There is no indication for the variations to be recovered, and the symmetry of the negative and positive parts of the strain hysteresis loops still remains. Higher cycling field results in a stronger deterioration of the maximum field induced strain and a larger extent of diffusion in AFE-FE and FE-AFE phase transitions. The normalized maximum strain shows nearly the same scale of degradation when the materials are cycled at various electric fields. After a heat treatment at 500°C for 1 h, the variations in the AFE-FE and FE-AFE phase transition due to cycling disappear, whereas the maximum strain resumes almost to its original value. Electrochemical variations are considered to contribute to the main fatigue mechanism for the material under investigation. 相似文献
75.
Colour is the most widely used attribute in image retrieval and object recognition. A technique known as histogram intersection has been widely studied and is considered to be effective for color‐image indexing. The key issue of this algorithm is the selection of an appropriate color space and optimal quantization of the selected color space. The goal of this article is to measure the model performance in predicting human judgment in similarity measurement for various images, to explore the capability of the model with a wide set of color spaces, and to find the optimal quantization of the selected color spaces. Six color spaces and twelve quantization levels are involved in evaluating the performance of histogram intersection. The categorical judgment and rank order experiments were conducted to measure image similarity. The CIELAB color space was found to perform at least as good as or better than the other color spaces tested, and the ability to predict image similarity increased with the number of bins used in the histograms, for up to 512 bins (8 per channel). With more than 512 bins, further improvement was negligible for the image datasets used in this study. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 265–274, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20122 相似文献
76.
近年新疆能源工业回顾与展望 总被引:5,自引:0,他引:5
新疆是我国的能源资源富集区,“九大煤田”、“十八条大河”、“三大油田”、“九大风区”资源储量丰富,品质优良,是新疆的优势资源之一,不但为新疆的开发建设提供了雄厚的物质基础,同时也将是我国重要的能源开发接替地。 相似文献
77.
A. Carpinteri S. Valente F. P. Zhou G. Ferrara G. Melchiorri 《Materials and Structures》1997,30(5):269-276
Three series of novel tensile and flexural creep tests on partially-damaged concrete specimens were carried out in order to gain some insight into creep crack growth and failure of strain-softening materials. In the tests, each specimen was initially loaded to a given point in the descending branch and thus had a lower load-carrying capacity than that at the peak-point. Then, the specimen was unloaded and reloaded to sustain a load which was from 70% to 95% of its current load-carrying capacity. Experimental creep curves display a three-stage process, consisting of primary, secondary and tertiary stages, with a decreasing, constant and increasing creep rate, respectively. The secondary stage dominates the whole failure lifetime, whereas both the secondary and tertiary stages are important in terms of creep deformation. Failure life-time seems to be more sensitive to the change of load level in flexural tests rather than in tensile tests. The decrease in load-carrying capacity due to damage tends to result in a shorter failure lifetime and a lower critical load level for creep rupture. The descending branch of the static load-deflection or load-CMOD curve may be used as an envelope criterion for creep fracture. 相似文献
78.
烧成及热处理工艺对钛酸锶铅基热敏材料性能及显微结构的影响 总被引:3,自引:0,他引:3
研究了烧成及热处理工艺对钛酸锶铅基热敏材料的阻温特性及显微结构的影响。通过扫描电镜(SEM)和能量分散仪(EDAX)分析了材料的显微结构及不同形貌晶粒的成份。通过对组成、烧成及热处理工艺的控制,可得到具有V型PTCR特性的热敏材料。 相似文献
79.
用保形样条方法求解非定常对流扩散方程 总被引:1,自引:0,他引:1
在欧拉-拉格朗日分裂方法的基础上,本文发展了一种固定网格上的欧拉-拉格朗日分裂方法.保形样条方法(SPSM)被用来解决倒特征线插值问题.通过求解几个有精确解的例子,说明SPSM方法的解是单调无振荡的,并且数值耗散也是比较小的. 相似文献
80.
正交双频光栅CCD系统剪切干涉测量二维温度场 总被引:1,自引:1,他引:0
以半导体激光器为光源,利用正交双频光栅(ODFG)CCD系统剪切干涉对带平板边界的半圆柱体热源的二维温度场进行实时诊断,分析剪切干涉图时,用柱函数系作为拟合基底,给出二维自然对流温度场的定量分布。 相似文献