全文获取类型
收费全文 | 4983篇 |
免费 | 375篇 |
国内免费 | 262篇 |
专业分类
电工技术 | 191篇 |
综合类 | 473篇 |
化学工业 | 387篇 |
金属工艺 | 583篇 |
机械仪表 | 1066篇 |
建筑科学 | 275篇 |
矿业工程 | 586篇 |
能源动力 | 61篇 |
轻工业 | 176篇 |
水利工程 | 70篇 |
石油天然气 | 113篇 |
武器工业 | 57篇 |
无线电 | 338篇 |
一般工业技术 | 446篇 |
冶金工业 | 274篇 |
原子能技术 | 33篇 |
自动化技术 | 491篇 |
出版年
2024年 | 16篇 |
2023年 | 50篇 |
2022年 | 105篇 |
2021年 | 136篇 |
2020年 | 133篇 |
2019年 | 101篇 |
2018年 | 96篇 |
2017年 | 155篇 |
2016年 | 143篇 |
2015年 | 167篇 |
2014年 | 286篇 |
2013年 | 300篇 |
2012年 | 373篇 |
2011年 | 346篇 |
2010年 | 274篇 |
2009年 | 301篇 |
2008年 | 231篇 |
2007年 | 334篇 |
2006年 | 319篇 |
2005年 | 285篇 |
2004年 | 224篇 |
2003年 | 230篇 |
2002年 | 180篇 |
2001年 | 165篇 |
2000年 | 159篇 |
1999年 | 88篇 |
1998年 | 89篇 |
1997年 | 75篇 |
1996年 | 58篇 |
1995年 | 57篇 |
1994年 | 32篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有5620条查询结果,搜索用时 140 毫秒
1.
To realize ultimately efficient signal processing, it is necessary to replace electrical signal processing circuits with optical ones. The optical micro-resonator, which localizes light at a certain spot, is an essential component in optical signal processing. Single-crystal calcium fluoride (CaF2) is the most suitable material for a highly efficient optical micro-resonator. The CaF2 resonator can only be manufactured by ultra-precision machining processes, because its crystal anisotropy does not allow the application of chemical etching. However, the optical micro-resonator's performance depends definitely on the surface integrity.This study investigated the relationship between surface quality after ultra-precision machining and crystal anisotropy. Firstly, crack initiation was investigated on the (1 0 0), (1 1 0), and (1 1 1) planes using the micro-Vickers hardness test. Secondly, brittle-ductile transition was investigated by orthogonal cutting tests. Finally, cutting performance of cylindrical turning was evaluated, which could be a suitable method for manufacturing the CaF2 resonator. The most difficult point in cylindrical turning of CaF2 is that the crystalline plane and cutting direction vary continuously. In order to manufacture the CaF2 optical micro-resonator more efficiently, analysis was conducted on crack initiation and surface quality of all crystallographic orientations from the perspective of slip system and cleavage. 相似文献
2.
Hasrul Abdi Hasibuan Azis Boing Sitanggang Nuri Andarwulan Purwiyatno Hariyadi 《International Journal of Food Science & Technology》2021,56(9):4549-4558
This research aimed to produce triacylglycerols fraction rich in palmitic acid (PA) at the sn-2 position from hard palm stearin (HPS) through acetone fractionation. Fractionations were done at HPS-to-acetone ratios of 1:3, 1:5 and 1:7 (w/v) and at temperatures of 25, 30 and 35 °C for 3 h. Triacylglycerols with PA at the sn-2 position, such as tripalmitoylglycerol (PPP) and dipalmitoyl-stearoyl-glycerol (PPS), were concentrated in the solid fraction, obtained after separation by filtration. The optimal fractionation conditions were at a HPS-to-acetone ratio of 1:5 (w/v) and 30 °C. The total PPP and PPS content was more than 91%, with a corresponding yield of more than 59%. Triacylglycerols obtained were composed of more than 91% PA in which 88% were at the sn-2 position. Conclusively, the solvent fractionation is a suited alternative method for the preparation of triacylglycerols used for the enzymatic synthesis of 1,3-dioleoyl-2-palmitoylglycerol which is the main triacylglycerol for human milk fat substitute. 相似文献
3.
4.
5.
Ratnabali Biswas Kaushik Chowdhury Dharma P. Agrawal 《International Journal of Wireless Information Networks》2006,13(4):303-315
Wireless sensor network is an emerging technology that enables remote monitoring of large geographical regions. In this paper, we address the problem of distributing attributes over such a large-scale sensor network so that the cost of data retrieval is minimized. The proposed scheme is a data-centric storage scheme where the attributes are distributed over the network depending on the correlations between them. The problem addressed here is similar to the Allocation Problem of distributed databases. In this paper, we have defined the Allocation Problem in the context of sensor networks and have proposed a scheme for finding a good distribution of attributes to the sensor network. We also propose an architecture for query processing given such a distribution of attributes. We analytically determine the conditions under which the proposed architecture is beneficial and present simulation results to demonstrate the same. To the best of our knowledge, this is the first attempt to determine an allocation of attributes over a sensor network based on the correlations between attributes. 相似文献
6.
7.
于金辉 《计算机辅助设计与图形学学报》1994,6(3):181-185
本文提出一个用于计算机动画的转头模型。它利用头部的正面和侧面形象来构造出头的三维结构形象,然后按指定的旋转轴旋转该结构,经过边缘轮廓提取及隐线消除,最终得到正确的转头过程序列画面。 相似文献
8.
林苗 《电气电子教学学报》2002,24(1):43-45
阐述了我校使用“面向21世纪”电工学课程系列教材的实践与探索过程,以及对我校电工学教学所产生的转折性影响和积极的导向作用,最后对教材提出了几点建议。 相似文献
9.
以入世为契机,进一步推进电力科研院所企业化转制 总被引:1,自引:1,他引:0
我国入世和融入经济全球化,将给中国经济运行的大环境带来深刻变化,科技事业也面临着全新挑战。电力科研所实行企业化转制,与国际接轨,按照国际规则办事势在必行。作者作为电力科研单位的一把手就电力科研院所的企业化转制阐述了个人的观点。转制必须有利于回忆科技创新和高新技术产品的开发;必须有利于抓紧培养和造就复合型人才队伍;必须有利于更好地为电网、为发供电企业提供规范化、制度化、长期化和现代化的全方位服务。 相似文献
10.
Effects of storage period on hydroxymethylfurfural, pH and colour were studied in white hard grape pekmez (Zile pekmezi), a Turkish traditional product. Pekmez samples were stored at 20 °C for 8 months. Analysis of variance revealed significant differences in hydroxymethylfurfural, pH, L, a and b values (P<0.01) based on storage time. 相似文献