全文获取类型
收费全文 | 53731篇 |
免费 | 4392篇 |
国内免费 | 2659篇 |
专业分类
电工技术 | 726篇 |
技术理论 | 1篇 |
综合类 | 3135篇 |
化学工业 | 19825篇 |
金属工艺 | 2797篇 |
机械仪表 | 2063篇 |
建筑科学 | 615篇 |
矿业工程 | 450篇 |
能源动力 | 755篇 |
轻工业 | 4434篇 |
水利工程 | 90篇 |
石油天然气 | 1976篇 |
武器工业 | 492篇 |
无线电 | 4943篇 |
一般工业技术 | 6471篇 |
冶金工业 | 1168篇 |
原子能技术 | 272篇 |
自动化技术 | 10569篇 |
出版年
2024年 | 159篇 |
2023年 | 690篇 |
2022年 | 997篇 |
2021年 | 1360篇 |
2020年 | 1363篇 |
2019年 | 1174篇 |
2018年 | 1219篇 |
2017年 | 1488篇 |
2016年 | 1798篇 |
2015年 | 1781篇 |
2014年 | 2772篇 |
2013年 | 2774篇 |
2012年 | 3272篇 |
2011年 | 4003篇 |
2010年 | 3060篇 |
2009年 | 3299篇 |
2008年 | 2989篇 |
2007年 | 3727篇 |
2006年 | 3380篇 |
2005年 | 3083篇 |
2004年 | 2614篇 |
2003年 | 2393篇 |
2002年 | 2083篇 |
2001年 | 1665篇 |
2000年 | 1460篇 |
1999年 | 1189篇 |
1998年 | 1026篇 |
1997年 | 778篇 |
1996年 | 634篇 |
1995年 | 531篇 |
1994年 | 439篇 |
1993年 | 349篇 |
1992年 | 272篇 |
1991年 | 179篇 |
1990年 | 170篇 |
1989年 | 101篇 |
1988年 | 83篇 |
1987年 | 51篇 |
1986年 | 48篇 |
1985年 | 59篇 |
1984年 | 53篇 |
1983年 | 51篇 |
1982年 | 33篇 |
1981年 | 36篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 7篇 |
1973年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
二苯并-18-冠-6的合成条件的优化 总被引:3,自引:0,他引:3
通过改变溶剂的极性、离子性、离去基团的活性及反应温度等方法,对传统的Pedersen冠醚合成法进行了优化,使目标产物的最高产率达到71%以上.产物通过IR、1H NMR及元素分析等方法进行结构表征. 相似文献
102.
Inverse surface design problems from light transport behavior specification usually represent extremely complex and costly processes, but their importance is well known. In particular, they are very interesting for lighting and luminaire design, in which it is usually difficult to test design decisions on a physical model in order to avoid costly mistakes. In this survey, we present the main ideas behind these kinds of problems, characterize them, and summarize existing work in the area, revealing problems that remain open and possible areas of further research. 相似文献
103.
104.
The texture effect on visual colour difference evaluation was investigated in this study. Five colour centers were selected and textured colour pairs were generated using scanned textile woven fabrics and colour‐mapping technique. The textured and solid colour pairs were then displayed on a characterized cathode ray tube (CRT) monitor for colour difference evaluation. The colour difference values for the pairs with texture patterns are equal to 5.0 CIELAB units in lightness direction. The texture level was represented by the half‐width of histogram, which is called texture strength in this study. High correlation was found between texture strength and visual colour difference for textured colour pairs, which indicates that an increasing of 10 units of texture strength in luminance would cause a decreasing of 0.25 units visual difference for the five colour centers. The ratio of visual difference between textured and solid colour pairs also indicates a high parametric effect of texture. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 341–347, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col. 相似文献
105.
Mohammad Ziabari Vahid Mottaghitalab Scott T. McGovern A. K. Haghi 《Nanoscale research letters》2007,2(12):597-600
In this paper, a new image analysis based method for electrospun nanofiber diameter measurement has been presented. The method
was tested by a simulated image with known characteristics and a real web. Mean (M) and standard deviation (STD) of fiber
diameter obtained using this method for the simulated image were 15.02 and 4.80 pixels respectively, compared to the true
values of 15.35 and 4.47 pixels. For the real web, applying the method resulted in M and STD of 324 and 50.4 nm which are
extremely close to the values of 319 and 42 nm obtained using manual method. The results show that this approach is successful
in making fast, accurate automated measurements of electrospun fiber diameters. 相似文献
106.
107.
Porous NiTi shape memory alloy (SMA) is a novel biomedical material used for human hard tissue implant .The influence of elemental titanium powder characteristics such as powder morphology, particle size and specific surface area( SSA) on the minimal ignition temperature ,combustion temperature and final product of porous Ni-Ti SMA fabricated by combustion synthesis method was investigated in this paper by scanning electron microscopy (SEM) and laser diffraction.The preliminary data indicated that the titanium powder characteristics had a strong effect on combustion synthesis of porous NiTi SMA. 相似文献
108.
Wenhui MA Gang XIE Hua WANGFaculty of Materials Metallurgical Engineering Kunming University of Science Technology Kunming China Manuscript received January in revised form May 《材料科学技术学报》2002,18(3):286-287
The thermal expansion behavior of La1-xSrxMn1-yCoyO3-δ (x=0.2-0.4, y=0.1-0.3) perovskites in air has been investigated. The average linear thermal expansion coefficients increased with increasing Sr content up to 40 mole fraction or Co content up to 30 mole fraction. The expansion is generally attributed to an increase in the average cation radius as some of the cations in the perovskite are reduced in valence when oxygen ions are removed from the structure. 相似文献
109.
110.
以溴和苯基取代的对苯二甲酰氯及2,2′-二甲基联苯-4,4′-二甲酰氯作为单体,分别与甲基、叔丁基、苯基取代的对苯二酚经熔融缩聚反应,合成一类具有刚性棒状结构的全芳香液晶聚酯。聚酯的热性质以TGA、DSC,热台偏光显微镜研究。所有的聚酯均为热致性液晶,它们具有相对较低的转变温度,在普通的有机溶剂中具有较好的溶解性质。 相似文献