全文获取类型
收费全文 | 82465篇 |
免费 | 9427篇 |
国内免费 | 6150篇 |
专业分类
电工技术 | 7593篇 |
技术理论 | 4篇 |
综合类 | 7370篇 |
化学工业 | 10453篇 |
金属工艺 | 5206篇 |
机械仪表 | 6224篇 |
建筑科学 | 6430篇 |
矿业工程 | 2900篇 |
能源动力 | 2420篇 |
轻工业 | 6839篇 |
水利工程 | 2675篇 |
石油天然气 | 3676篇 |
武器工业 | 1097篇 |
无线电 | 10123篇 |
一般工业技术 | 7326篇 |
冶金工业 | 3037篇 |
原子能技术 | 1257篇 |
自动化技术 | 13412篇 |
出版年
2024年 | 246篇 |
2023年 | 1256篇 |
2022年 | 2749篇 |
2021年 | 3870篇 |
2020年 | 2831篇 |
2019年 | 2116篇 |
2018年 | 2448篇 |
2017年 | 2707篇 |
2016年 | 2476篇 |
2015年 | 3834篇 |
2014年 | 4751篇 |
2013年 | 5558篇 |
2012年 | 6717篇 |
2011年 | 7365篇 |
2010年 | 6715篇 |
2009年 | 6414篇 |
2008年 | 6600篇 |
2007年 | 6358篇 |
2006年 | 5416篇 |
2005年 | 4379篇 |
2004年 | 3045篇 |
2003年 | 2088篇 |
2002年 | 2041篇 |
2001年 | 1687篇 |
2000年 | 1390篇 |
1999年 | 826篇 |
1998年 | 452篇 |
1997年 | 361篇 |
1996年 | 296篇 |
1995年 | 260篇 |
1994年 | 199篇 |
1993年 | 140篇 |
1992年 | 114篇 |
1991年 | 73篇 |
1990年 | 51篇 |
1989年 | 42篇 |
1988年 | 33篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 12篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 13篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1959年 | 14篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
11.
Keran Su Kim Huey Ee Jingcan Sun Shao Quan Liu Benjamin Lassabliere Ulrich Feiter Yunle Huang Rui Min Vivian Goh Aileen Pua Bin Yu 《International Journal of Food Science & Technology》2022,57(3):1666-1678
The structural diversity of polyphenols and the inherent limitations of current extraction techniques pose a challenge to extract polyphenols using a simple and green method. Hence, in this study, a method was developed to simultaneously fractionate multiple classes of polyphenols by only varying ethanol-water solutions. Honeybush tea, which is rich in polyphenols, was selected as a model for this study. Solvent extraction followed by solid-phase extraction (SPE) was developed to obtain a polyphenol-rich fraction from six honeybush samples. Based on a gradient elution programme (10%, 30%, 50%, 70% and 90% (v/v) ethanol-water solution) of SPE, the Strata X cartridge showed a better recovery of most targeted polyphenols under 0.9 mL of the drying volume and 1 mL min−1 of the dispensing speed. The elution programme for fractionating most polyphenols was as follows: single elution with 50% ethanol, followed by twice elution with 70% ethanol. The antioxidant capacity was used to analyse the differences among the polyphenol-rich fractions from six honeybush samples. Principal component analysis (PCA) revealed that unfermented C. genistoides (GG) has the greatest antioxidant capacity among the honeybush species studied. Additionally, mangiferin, isomangiferin and vicenin-2 were the main contributors to the antioxidant capacity in six honeybush fractions according to the correlation study. 相似文献
12.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB2and(1-100)NbB2surface can be substituted by Al to form(Al,Nb)B2intermedia layers.In addition,a layer of NbAl3-like compound(NbAl3')can cover the surface of NbB2with the orientation relation of(1-100)[11-20]NbB2//(110)[110]NbAl3'.Both of the(Al,Nb)B2and NbAl3'intermedia layers contribute to enhancing the nucleation potency of NbB2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys. 相似文献
13.
Bin Feng Xin Jiang Guisheng Zou Wengan Wang Tianming Sun Heng Yang Guanlei Zhao Mingye Dong Yu Xiao Hongwei Zhu Lei Liu 《Advanced functional materials》2021,31(29):2102359
The realization of liquid metal-based wearable systems will be a milestone toward high-performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal-based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre-inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as “bricks” and strain-sensitive Ag film as “mortar” is developed, which breaks the long-standing sensitivity bottleneck of liquid metal-based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal-based strain sensors rival the state-of-art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut-through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid-metal paths and create crack-free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal-based electronic skins, and reveals a pathway for sensor development via crack engineering. 相似文献
14.
目的:鉴定中国白酒发酵过程中的微生物种类,研究关键酶的特征与作用机制有利于提高白酒的优质品率。方法:本研究用形态学和生理学、16S rRNA、gyr B基因和antiSMASH分析的方法对酒曲中的一株微生物进行了验证;对该菌株的特性进行了研究,采用分子建模的方法获得了羧酸酯酶的3D模型,用分子对接的方法探讨了该菌株的羧酸酯酶的机理。结果:该菌株为产羧酸酯酶的革兰氏阴性菌Pb1(MW580690);该菌株呈现典型的S型生长曲线,产物曲线为S型,羧酸酯酶活化最优pH范围为5.0~9.0。分子对接结果显示Phe21A为该酶具有催化活性的主要氨基酸,水解三丁酸甘油酯为丁酸和甘油。分子对接结果显示三丁酸甘油酯经过构象变化被转移到催化中心后,进一步被加工;酶的亲水性和疏水性的相互作用表面有利于配体向下转移,进而从疏水性通道释放产物到的酶表面。结论:产羧酸酯酶的菌株为贝莱斯芽胞杆菌,并为羧酸酯酶水解三丁酸甘油酯类物质的底物识别、转移和催化机理提供了新的见解。 相似文献
16.
17.
19.
介绍了合成革企业废水、废气治理现状,分析了生产过程中存在的问题,提出了相关环境监管对策,重点是监管塔顶水的去向,核心是做好二甲胺废水及废气的治理,日常做好废水站、雨水口及废气设施运行的监督管理,对环境违法行为实施"零容忍",倒逼企业加快DMF集中回收和采用水性树脂工艺,为合成革企业环保整治指明方向,取得了较好的效果。 相似文献
20.
Jayamani Elammaran Loong Ting Goa Bakri Muhammad Khusairy Bin 《Polymer Bulletin》2020,77(4):1605-1629
Polymer Bulletin - Kenaf and luffa fibres are hydrophilic due to the presence of water sensitive constituents, which tend to form a poor compatibility when binding with polymers. Thus, the surface... 相似文献