全文获取类型
收费全文 | 4791篇 |
免费 | 712篇 |
国内免费 | 656篇 |
专业分类
化学 | 2470篇 |
晶体学 | 78篇 |
力学 | 252篇 |
综合类 | 54篇 |
数学 | 112篇 |
物理学 | 1508篇 |
无线电 | 1685篇 |
出版年
2024年 | 18篇 |
2023年 | 106篇 |
2022年 | 195篇 |
2021年 | 267篇 |
2020年 | 246篇 |
2019年 | 144篇 |
2018年 | 147篇 |
2017年 | 228篇 |
2016年 | 236篇 |
2015年 | 206篇 |
2014年 | 260篇 |
2013年 | 354篇 |
2012年 | 306篇 |
2011年 | 343篇 |
2010年 | 268篇 |
2009年 | 273篇 |
2008年 | 279篇 |
2007年 | 272篇 |
2006年 | 296篇 |
2005年 | 232篇 |
2004年 | 207篇 |
2003年 | 184篇 |
2002年 | 184篇 |
2001年 | 114篇 |
2000年 | 119篇 |
1999年 | 88篇 |
1998年 | 97篇 |
1997年 | 73篇 |
1996年 | 70篇 |
1995年 | 49篇 |
1994年 | 57篇 |
1993年 | 35篇 |
1992年 | 40篇 |
1991年 | 26篇 |
1990年 | 24篇 |
1989年 | 8篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有6159条查询结果,搜索用时 156 毫秒
1.
2.
In this study, parenchyma cellulose, which was extracted from maize stalk pith as an abundant source of agricultural residues, was applied for preparing cellulose nanoparticles (CNPs) via an ultrasound-assisted etherification and a subsequent sonication process. The ultrasonic-assisted treatment greatly improved the modification of the pith cellulose with glycidyltrimethylammonium chloride, leading to a partial increase in the dissolubility of the as-obtained product and thus disintegration of sheet-like cellulose into nanoparticles. While the formation of CNPs by ultrasonication was largely dependent on the cellulose consistency in the cationic-modified system. Under the condition of 25% cellulose consistency, the longer sono-treated duration yielded a more stable and dispersible suspension of CNP due to its higher zeta potential. Degree of substitution and FT-IR analyses indicated that quaternary ammonium salts were grafted onto hydroxyl groups of cellulose chain. SEM and TEM images exhibited the CNP to have spherical morphology with an average dimeter from 15 to 55 nm. XRD investigation revealed that CNPs consisted mainly of a crystalline cellulose Ι structure, and they had a lower crystallinity than the starting cellulose. Moreover, thermogravimetric results illustrated the thermal resistance of the CNPs was lower than the pith cellulose. The optimal CNP with highly cationic charges, good stability and acceptable thermostability might be considered as one of the alternatively renewable reinforcement additives for nanocomposite production. 相似文献
3.
随着经济的飞速发展,社会对能源的需求日益扩大,对工业废水的无害化处理也提出了更高的要求。光催化燃料电池 (photocatalytic fuel cell, PFC) 在燃料电池中引入半导体光催化材料作为电极,实现了有机污染物高效降解和同步对外产电的双重功能,在废水无害化与资源化利用方面具有潜在的应用价值。半导体光催化电极是PFC系统高效运行的核心组件,增强其可见光响应和光生载流子分离是提高PFC性能的关键策略。反应器结构设计和运行参数优化也有利于改善PFC性能。本文从PFC基本原理和应用入手,综述了PFC在环境污染物资源化处理中的研究进展,并详细阐述了提高PFC的污染控制性能和产电效率的优化手段,为进一步设计高效稳定的PFC系统并实现其在水污染控制和清洁能源生产中的应用提供理论指导。 相似文献
4.
Design and development of a two‐dimensional system based on hydrophilic and reversed‐phase liquid chromatography with on‐line sample treatment for the simultaneous separation of excreted xenobiotics and endogenous metabolites in urine
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Diego García‐Gómez Encarnación Rodríguez‐Gonzalo Rita Carabias‐Martínez 《Biomedical chromatography : BMC》2015,29(8):1190-1196
In the present work we describe a two‐dimensional liquid chromatographic system (2D‐LC) with detection by mass spectrometry (MS) for the simultaneous separation of endogenous metabolites of clinical interest and excreted xenobiotics deriving from exposure to toxic compounds. The 2D‐LC system involves two orthogonal chromatographic modes, hydrophilic interaction liquid chromatography (HILIC) to separate polar endogenous metabolites and reversed‐phase (RP) chromatography to separate excreted xenobiotics of low and intermediate polarity. Additionally, the present proposal has the novelty of incorporating an on‐line sample treatment based on the use of restricted access materials (RAMs), which permits the direct injection of urine samples into the system. The work is focused on the instrumental coupling, studying all possible options and attempting to circumvent the problems of solvent incompatibility between the RAM device and the two chromatographic columns, HILIC and RP. The instrumental configuration developed, RAM‐HILIC‐RPLC‐MS/MS, allows the simultaneous assessment of urinary metabolites of clinical interest and excreted compounds derived from exposure to toxic agents with minimal sample manipulation. Thus, it may be of interest in areas such as occupational and environmental toxicology in order to explore the possible relationship between the two types of compounds. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
5.
Elsye Agustina Jeungchoon Goak Suntae Lee Youngho Seo Jun-Young Park Naesung Lee 《ChemistryOpen》2015,4(5):613-619
Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red–orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs. 相似文献
6.
机械力化学作用对低介硅灰石瓷料的相变和相组成的影响 总被引:1,自引:0,他引:1
采用X射线衍射仪(XRD)、差热分析(DTA)手段详细研究了由氧化物粉末制备硅灰石陶瓷时,机械力化学作用及后续热处理对硅灰石陶瓷相组成和相变过程的影响,分析了机械力化学在球磨过程中的作用机理主要是细化晶粒、使晶格畸变、晶格缺陷增多、非晶化和诱导低温化学反应。结果表明:高能球磨中的机械力化学作用能够有效地降低硅灰石陶瓷的烧成温度(11160~11220℃)。探明了经高能球磨的样品在烧成过程中的晶相转变规律。瓷料最终的晶相为单一的-硅灰石(高温变体)。 相似文献
7.
8.
集成电路生产中废气的污染及治理 总被引:1,自引:1,他引:0
介绍集成电路生产中产生各种废气的种类,废气中有害物质浓度及其危害性,并依据工程实践,评述了各类有害废气的各种处理方法。 相似文献
9.
10.