全文获取类型
收费全文 | 573篇 |
免费 | 39篇 |
国内免费 | 152篇 |
专业分类
化学 | 555篇 |
晶体学 | 10篇 |
力学 | 123篇 |
综合类 | 3篇 |
数学 | 7篇 |
物理学 | 66篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 24篇 |
2020年 | 14篇 |
2019年 | 23篇 |
2018年 | 21篇 |
2017年 | 29篇 |
2016年 | 25篇 |
2015年 | 26篇 |
2014年 | 34篇 |
2013年 | 37篇 |
2012年 | 34篇 |
2011年 | 52篇 |
2010年 | 27篇 |
2009年 | 34篇 |
2008年 | 38篇 |
2007年 | 38篇 |
2006年 | 40篇 |
2005年 | 35篇 |
2004年 | 26篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 19篇 |
2000年 | 17篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有764条查询结果,搜索用时 37 毫秒
101.
Single-phase LiCoPO4 nanoparticles were synthesized by solid-state reaction method and subsequent high-energy ball milling. The electrochemical
properties of LiCoPO4/Li batteries were analyzed by ac impedance experiments, cyclic voltammetry (CV), and charge/discharge tests. The structural
and morphological performance of LiCoPO4 nanoparticles was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron
microscope (TEM). The XRD result demonstrated that LiCoPO4 nanoparticles had an orthorhombic olivine-type structure with a space group of Pmnb. Different conductive additives including
acetylene black and carbon black (SP270) were used to fabricate electrodes. The morphologies of the electrodes and different
conductive additives were observed by field emission-scanning electron microscopy (FE-SEM). LiCoPO4/Li battery with acetylene black showed the best electrochemical properties, and exhibited a discharge plateau at around 4.7 V
with an initial discharge capacity of 110 mAh g−1 at a discharge current density of 0.05 mA cm−2 at 25 °C. 相似文献
102.
Guoyi Bai Hailong Wang Huisen Ning Fei He Guofeng Chen 《Reaction Kinetics and Catalysis Letters》2008,94(2):375-383
A continuous process for the dehydrogenation of cyclohexanol to cyclohexanone on copper-based catalysts was described. The
catalysts were characterized by XRD, XPS and TPR, and Cu0 was found to be the active site for the copper-based catalysts studied. The two carrier catalysts were proved to be more
active than the single carrier ones, and the Cr additive, which mainly existed as the CuCr2O4 phase on the catalyst’s surface, was found to have a significant effect on the activity and stability of the Cu-Cr-Mg-Al
catalyst. 相似文献
103.
Here we describe the story behind the link between molecular chirality and macroscopic phenomena, the latter being a probe for the direct assignment of absolute configuration of chiral molecules. First, a brief tour of the history of molecular stereochemistry, starting with the classic experiment reported by Pasteur in 1848 on the separation of enantiomorphous crystals of a salt of tartaric acid, and his conclusion that the molecules of life are chiral of single-handedness. With time, this study raised, inter alia, two fundamental questions: the absolute configuration of chiral molecules and how a molecule of given configuration shapes the enantiomorphous morphology of its crystal. As for the first question, following the beginning of crystal structure determination by X-ray diffraction in 1912, it took almost 40 years before Bijvoet assigned molecular chirality through the esoteric method involving anomalous X-ray scattering. We have been able to address and link both questions through ‘everyday concepts of left and right’ (in the words of Jack Dunitz) by the use of ‘tailor-made’ auxiliaries. By such means, it proved possible to reveal, through morphology, etch patterns, epitaxy and symmetry reduction of both chiral and, paradoxically, centrosymmetric crystals, the basic chiral symmetry of the molecules of life, the α-amino acids and sugars. 相似文献
104.
105.
An additive-free Watts type bath containing micron- and nano-SiC particles (1 μm and 20 nm respectively), as well as ultrafine-WC
particles (200 nm), was used for the production of pure Ni and nickel matrix composite electrocoatings under both direct and
pulse current conditions. Moreover, nickel nanocrystalline deposits were obtained from a Watts type bath containing small
amounts of 2-butyne-1,4-diol, in order to investigate the combined advantages of additives and pulse technique on the properties
of the deposits. The influence of the variable electrolysis parameters, the particle size and the organic additive concentration
on the surface morphology, the structure and properties of the deposits were discussed. It has been proved that the application
of pulse electrodeposition affects drastically the structural characteristics and properties of the deposits and under well-defined
conditions could lead to the preparation of nanostructured materials with improved mechanical properties.
Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 6, pp. 802–811.
The text was submitted by the authors in English. 相似文献
106.
镍氢电池的循环性能与活性物质微结构的研究 总被引:1,自引:0,他引:1
与循环试验大致同步, 用静态(初态和终态)或准动态(增加若干个中间态)的模式对MH/H电池循环性能、电极(包括负极和正极)材料的微结构进行了X射线衍射(XRD)研究, 发现循环性能衰减与正极材料β-Ni(OH)2的点阵参数、平均晶粒尺度、微应变和总的层错几率均随循环周期增加而减小以及负极材料中腐蚀产物A(OH)3和B相出现和增加有一定的对应关系, 发现MH/Ni 电池循环性能的衰减是正极材料和负极材料的结构和微结构随着循环次数的增加发生明显变化, 恶化了正负极材料的电化学性能, 同时消耗和恶化了电解液的综合结果. 为了提高电池的循环性能, 采用不同正极材料的添加剂. 结果表明, CaF2和Lu2O3有明显的效果, 其中CaF2效果最好, 并有广泛的实用性. 相似文献
107.
以合成的两种无灰型含磷/硫化合物为润滑添加剂, 以可生物降解的菜籽油作为基础油, 用四球机研究了体系的抗磨减摩性能, 以X射线光电子能谱(XPS)和X射线吸收精细结构光谱(XANES)对所形成的摩擦膜和热膜进行了表面分析, 并初步探讨了其润滑机理. 摩擦学研究结果表明, 两种含磷/硫化合物作为菜籽油的润滑添加剂时, 具有良好的抗磨减摩性能. XPS和XANES分析结果显示, 摩擦膜和热膜主要由吸附层和反应层组成; 在表面膜中, 磷主要以磷酸盐或焦磷酸盐等形式存在, 而硫主要以硫酸盐的形式存在. 研究结果还表明, 摩擦热在两种不同添加剂的摩擦膜形成过程中发挥着不同的作用. 相似文献
108.
Determination and purification of sesamin and sesamolin in sesame seed oil unsaponified matter using reversed‐phase liquid chromatography coupled with photodiode array and tandem mass spectrometry and high‐speed countercurrent chromatography 下载免费PDF全文
Miki Takahashi Yuzo Nishizaki Naoki Sugimoto Hiroaki Takeuchi Kazuya Nakagawa Hiroshi Akiyama Kyoko Sato Koichi Inoue 《Journal of separation science》2016,39(20):3898-3905
In Asian countries, sesame seed oil unsaponified matter is used as a natural food additive due to its associated antioxidant effects. We determined and purified the primary lignans sesamin and sesamolin in sesame seed oil unsaponified matter using reversed‐phase liquid chromatography coupled with photodiode array and tandem mass spectrometry and high‐speed countercurrent chromatography. Calibration curves showed good correlation coefficients (r2 > 0.999, range 0.08 and/or 0.15 to 5 μg/mL) with a limit of detection (at 290 nm) of 0.02 μg/mL for sesamin and 0.04 μg/mL for sesamolin. Sesame seed oil unsaponified matter contained 2.82% sesamin and 2.54% sesamolin, respectively. Direct qualitative analysis of sesamin and sesamolin was achieved using quadrupole mass spectrometry with positive‐mode electrospray ionization. Pure (>99%) sesamin and sesamolin standards were obtained using high‐speed countercurrent chromatographic purification (hexane/ethyl acetate/methanol/water; 7:3:7:3). An effective method for determining and purifying sesamin and sesamolin from sesame seed oil unsaponified matter was developed by combining these separation techniques for standardized food additives. 相似文献
109.
Jinlong Tan Lei Hua Jun Chen Jichun Liu Yongzhen Zhang 《Journal of Macromolecular Science: Physics》2019,58(1):88-98
Phenol-formaldehyde resin (PF) composites with a nano-porous graphite additive (NPGA) in various contents were fabricated and the wear behaviors under low and high sliding speeds were studied. The addition of NPGA significantly improved the wear resistance of the PF. The specific wear rates of PF composites under low sliding speed first decreased with increasing NPGA and then slightly increased when the NPGA content surpassed 15?wt%; the specific wear rate of the composite with 15?wt% NPGA was reduced by 77% compared with the neat PF. Under high sliding speed the specific wear rates of the composite material decreased continuously with increasing NPGA content and the maximum wear resistance of the composite with 20?wt% NPGA was more than 12 times that of the neat phenolic resin. The results are attributed to the combined effects of load-capacity and the lubrication role of the included NPGA. The surface morphology of the worn surface was characterized, and the wear mechanism for the composites is discussed. 相似文献
110.
采用MFT-R4000型往复摩擦磨损试验机测试四氟硼酸锂(Li BF4),双三氟甲烷基磺酰亚胺锂(Li NTf2)和六氟磷酸锂(Li PF6)这3种锂盐作为润滑油添加剂时对基础油的摩擦学性能的影响,利用OLS4000型三维形貌测量仪测量钢块的磨损体积,并利用扫描电子显微镜(SEM)观察钢块磨痕的表面形貌.采用DDSJ-308A型电导率测定仪测量不同锂盐含量下,润滑油的盐度和电导率的变化情况,阐述锂盐含量和润滑油电导率之间存在的关系.研究结果表明:锂盐能够降低润滑油的摩擦系数,增强其抗磨性,具有良好的摩擦学性能;同时锂盐的加入使基础油的导电性得到很大提高. 相似文献