全文获取类型
收费全文 | 69214篇 |
免费 | 6123篇 |
国内免费 | 3601篇 |
专业分类
电工技术 | 4479篇 |
技术理论 | 3篇 |
综合类 | 5228篇 |
化学工业 | 10976篇 |
金属工艺 | 3764篇 |
机械仪表 | 4141篇 |
建筑科学 | 5809篇 |
矿业工程 | 1892篇 |
能源动力 | 1774篇 |
轻工业 | 5266篇 |
水利工程 | 1313篇 |
石油天然气 | 3844篇 |
武器工业 | 556篇 |
无线电 | 7855篇 |
一般工业技术 | 7977篇 |
冶金工业 | 3458篇 |
原子能技术 | 776篇 |
自动化技术 | 9827篇 |
出版年
2024年 | 291篇 |
2023年 | 1123篇 |
2022年 | 1864篇 |
2021年 | 2669篇 |
2020年 | 2098篇 |
2019年 | 1732篇 |
2018年 | 1866篇 |
2017年 | 2188篇 |
2016年 | 1956篇 |
2015年 | 2689篇 |
2014年 | 3450篇 |
2013年 | 4148篇 |
2012年 | 4310篇 |
2011年 | 4759篇 |
2010年 | 4367篇 |
2009年 | 4055篇 |
2008年 | 4240篇 |
2007年 | 4056篇 |
2006年 | 3965篇 |
2005年 | 3210篇 |
2004年 | 2438篇 |
2003年 | 2224篇 |
2002年 | 2495篇 |
2001年 | 2164篇 |
2000年 | 1711篇 |
1999年 | 1642篇 |
1998年 | 1252篇 |
1997年 | 1105篇 |
1996年 | 1055篇 |
1995年 | 825篇 |
1994年 | 675篇 |
1993年 | 453篇 |
1992年 | 420篇 |
1991年 | 307篇 |
1990年 | 226篇 |
1989年 | 202篇 |
1988年 | 165篇 |
1987年 | 119篇 |
1986年 | 91篇 |
1985年 | 58篇 |
1984年 | 59篇 |
1983年 | 31篇 |
1982年 | 41篇 |
1981年 | 32篇 |
1980年 | 42篇 |
1979年 | 15篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
3.
讨论了在VMI管理思想下对具有随机需求特性的多客户库存分配问题 ,重点论述了有效近似算法的设计过程 ,最后基于一组模拟数据给出了一个算例。 相似文献
4.
5.
贴片机脱机编程的快捷方法 总被引:7,自引:4,他引:3
SMT生产线中的大多数加工设备均为数控设备。它们编程所需要的大多数特征数据均可从CAD设计系统中得到。文章介绍了如何从CAD设计系统中导出X、Y坐标数据,并转换成贴片数据的方法和思路,以期引起更多的同行加入到这方面的研究中。 相似文献
6.
7.
Disciplinary and linguistic considerations for academic Web linking: An exploratory hyperlink mediated study with Mainland China and Taiwan 总被引:4,自引:0,他引:4
The Web has become an important means of academic information exchange and can be used to give new insights into patterns
of informal scholarly communication. This study develops new methods to examine patterns of university Web linking, focusing
on Mainland China and Taiwan, and including language considerations. Multiple exploratory investigations into Web links were
conducted between universities in these two places. Firstly, inlinks were counted to each university Web site from its national
peers using four alternative Web document models. The results were shown to correlate significantly with research productivity
in Taiwan but not in the Mainland, although in the latter case less reliable institutional data could have been the cause.
For Taiwan, this is the first evidence of a scholarly association with academic linking for a non-English speaking region.
It was then ascertained that the same link counts associated more strongly with scientific than social scientific research
productivity in Taiwan. This confirms the general assumption of greater Web use by the hard sciences. We then investigated
Taiwan-Mainland university cross-links, and found that although English is extensively used on the Web, there was no evidence
that it was the language of preference for informal scholarly communication between the two areas.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
10.
Ching-Wen Tang Chi-Yang Chang 《Electronics letters》2002,38(15):801-803
A novel chip-type ceramic balun designed in the 2.4 GHz ISM band frequency is presented. A buried capacitor is included in the balun, so that the length of the coupled transmission lines can be reduced and can be designed very easily. A meander or spiral broadside coupled-line is adopted to realise the proposed LTCC multi-layer balun. The measured performances of phase and amplitude balance for this LTCC-MLC balun show a good match with computer simulation 相似文献