全文获取类型
收费全文 | 181202篇 |
免费 | 27541篇 |
国内免费 | 8055篇 |
专业分类
电工技术 | 11428篇 |
技术理论 | 8篇 |
综合类 | 11374篇 |
化学工业 | 38577篇 |
金属工艺 | 9223篇 |
机械仪表 | 10404篇 |
建筑科学 | 13246篇 |
矿业工程 | 4371篇 |
能源动力 | 5511篇 |
轻工业 | 16591篇 |
水利工程 | 3607篇 |
石油天然气 | 8219篇 |
武器工业 | 1553篇 |
无线电 | 22979篇 |
一般工业技术 | 26564篇 |
冶金工业 | 7215篇 |
原子能技术 | 1819篇 |
自动化技术 | 24109篇 |
出版年
2024年 | 450篇 |
2023年 | 1906篇 |
2022年 | 3664篇 |
2021年 | 5618篇 |
2020年 | 5330篇 |
2019年 | 6265篇 |
2018年 | 6646篇 |
2017年 | 7602篇 |
2016年 | 7711篇 |
2015年 | 9337篇 |
2014年 | 11135篇 |
2013年 | 13347篇 |
2012年 | 13008篇 |
2011年 | 13287篇 |
2010年 | 12692篇 |
2009年 | 12127篇 |
2008年 | 11531篇 |
2007年 | 11025篇 |
2006年 | 10383篇 |
2005年 | 8729篇 |
2004年 | 6814篇 |
2003年 | 6441篇 |
2002年 | 6589篇 |
2001年 | 5885篇 |
2000年 | 4570篇 |
1999年 | 3515篇 |
1998年 | 2067篇 |
1997年 | 1828篇 |
1996年 | 1571篇 |
1995年 | 1330篇 |
1994年 | 1049篇 |
1993年 | 766篇 |
1992年 | 575篇 |
1991年 | 457篇 |
1990年 | 412篇 |
1989年 | 307篇 |
1988年 | 220篇 |
1987年 | 148篇 |
1986年 | 134篇 |
1985年 | 74篇 |
1984年 | 52篇 |
1983年 | 35篇 |
1982年 | 50篇 |
1981年 | 36篇 |
1980年 | 27篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1959年 | 9篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
71.
72.
73.
Jincy Joy Jessica Pereira Rachida Aid‐Launais Graciela Pavon‐Djavid Alok R Ray Didier Letourneur Anne Meddahi‐Pell Bhuvanesh Gupta 《Polymer International》2019,68(7):1367-1377
The work reported involved the fabrication of an electrospun tubular conduit of a gelatin and polycaprolactone (PCL) blend as an adventitia‐equivalent construct. Gelatin was included as the matrix for increased biocompatibility with the addition of PCL for durability. This is contrary to most of the literature available for biomaterials based on blends of gelatin and PCL where PCL is the major matrix. The work includes the assiduous selection of key electrospinning parameters to obtain smooth bead‐free fibres with a narrow distribution of pore size and fibre diameter. Few reports elucidate the optimization of all electrospinning parameters to fabricate tubular conduits with a focus on obtaining homogeneous pores and fibres. This stepwise investigation would be unique for the fabrication of gelatin–PCL electrospun tubular constructs. The fabricated microfibrous gelatin–PCL constructs had pores of size ca 50–100 μm reportedly conducive for cell infiltration. The measured value of surface roughness of 57.99 ± 17.4 nm is reported to be favourable for protein adhesion and cell adhesion. The elastic modulus was observed to be similar to that of the tunica adventitia of the native artery. Preliminary in vitro and in vivo biocompatibility tests suggest safe applicability as a biomaterial. Minimal cytotoxicity was observed using MTT assay. Subcutaneous implantation of the scaffold demonstrated acute inflammation which decreased by day 15. The findings of this study could enable the fabrication of smooth bead‐free microfibrous gelatin–PCL tubular construct as viable biomaterial which can be included in a bilayer or a trilayer scaffold for vascular tissue engineering. © 2019 Society of Chemical Industry 相似文献
74.
75.
Joon‐Young Jun Sosuke Nakajima Koji Yamazaki Yuji Kawai Hajime Yasui Yasuyuki Konishi 《International Journal of Food Science & Technology》2015,50(4):871-877
Cystoseira hakodatensis is an unutilised brown algae belonging to family Sargassaceae. A crude methanol extract from the algae showed inhibitory effects on the growths of Bacillus cereus and Bacillus licheniformis. To isolate the major antimicrobial agent, a sequential active‐guided isolation procedure was applied: liquid–liquid extraction, column chromatography and bio‐autography. A marked antimicrobial agent (active α) was isolated in hydrophobic fraction and was determined to phenolics without carbohydrates and proteins by phytochemical test. Regarding the antimicrobial potential, the isolated active α showed better inhibitory effects against B. cereus and B. licheniformis at 2 and 4 times of lower concentrations (62.5 and 31.3 μg mL?1) in comparison with epigallocatechin gallate. These results showed that C. hakodatensis is a potential source of antimicrobial agent capable of preventing the growth of the two bacteria. 相似文献
76.
77.
78.
In this study, 30 subjects were exposed to different combinations of air temperature (Ta: 24, 27, and 30°C) and CO2 level (8000, 10 000, and 12 000 ppm) in a high-humidity (RH: 85%) underground climate chamber. Subjective assessments, physiological responses, and cognitive performance were investigated. The results showed that as compared with exposure to Ta = 24°C, exposure to 30°C at all CO2 levels caused subjects to feel uncomfortably warm and experience stronger odor intensity, while increased mental effort and greater intensity of acute health symptoms were reported. However, no significant effects of Ta on task performance or physiological responses were found. This indicated that subjects had to exert more effort to maintain their performance in an uncomfortably warm environment. Increasing CO2 from 8000 to 12 000 ppm at all Ta caused subjects to report higher rates of headache, fatigue, agitation, and feeling depressed, although the results were statistically significant only at 24 and 27°C. The text typing performance and systolic blood pressure (SBP) decreased significantly at this exposure, whereas diastolic blood pressure (DBP) and thermal discomfort increased significantly. These effects suggest higher arousal/stress. No significant interaction effect of Ta and CO2 concentration on human responses was identified. 相似文献
79.
The effect of Li2O on the crystallization properties of CaO-Al2O3-SiO2-Li2O-Ce2O3 slags was investigated. With increasing the Li2O content, LiAlO2 and CaCeAlO4 were the main crystalline phases. LiAlO2 formed for the charge compensating of Li+ ions to [AlO45?]-tetrahedrons, and CaCeAlO4 formed as a result of the charge balance of Ce3+ ions, Ca2+ ions, and [AlO69?]-octahedrons. Increasing the content of Li2O to 10%, the crystallization temperature was the highest, and the incubation time was the shortest. The crystallization ability was strong due to the three factors of strengthening the interaction between ions and ion groups, decreasing the polymerization degree, and increasing the melting temperature. Further increasing the content of Li2O, the crystallization performance was obviously suppressed, because the melting temperature and the force between the cations and the anion groups decreased. 相似文献
80.
高光谱激光雷达谱位合一的角度效应分析 总被引:1,自引:0,他引:1
高光谱激光雷达以其谱位合一的技术优势为实现超三维精准遥感观测提供了可行途径,因此成为当前激光雷达与高光谱遥感领域共同大力推进的前沿发展方向。目前已有多型原型系统研发出来并得到了原理性验证,然而针对其数据处理核心环节问题的基础技术仍较为欠缺。典型问题之一是不同波段回波信号受激光入射角度的影响,该角度效应限制了高光谱激光雷达实现高性能遥感。以芬兰空间信息研究所高光谱激光雷达原型系统扫描桦树树干为例探讨了该角度效应,发现了不同激光波段对不同入射角度的回波强度响应模式,推导出了角度效应的基本规律及其精细尺度的统计规律,为后续该方向的系统研发、数据处理及信息提取等提供了可借鉴的底层机理与技术基础。 相似文献