全文获取类型
收费全文 | 286篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 267篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 7篇 |
物理学 | 23篇 |
出版年
2022年 | 7篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 12篇 |
2012年 | 14篇 |
2011年 | 20篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 12篇 |
2006年 | 18篇 |
2005年 | 18篇 |
2004年 | 18篇 |
2003年 | 22篇 |
2002年 | 14篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 4篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1961年 | 2篇 |
排序方式: 共有300条查询结果,搜索用时 15 毫秒
61.
Lifang Chen Yulv Yu Masako Kuwa Tao Cheng Yan Liu Hiroshi Murakami Harada Masafumi Yuan Wang 《物理化学学报》2020,36(1):1907008-0
碱-乙二醇法制备的"非保护型"金属及合金纳米簇由表面吸附的溶剂分子和简单离子实现稳定化,它们被广泛用于制备高性能复相催化剂和研究复相催化剂中的尺寸、组成、载体表面基团以及修饰剂对催化性能的影响。关于此类非保护金属纳米簇的形成过程及机理的认识尚有待进一步深化。本文采用原位快速扫描X射线吸收精细结构谱(QXAFS)、原位紫外-可见(UV-Vis)吸收光谱、透射电子显微镜和动态光散射技术研究了碱-乙二醇法合成中非保护型金属胶体纳米簇的形成过程与机理。结果表明,在碱-乙二醇法合成非保护型Pt金属纳米簇的过程中,室温下即有部分Pt(IV)被还原至Pt(II)。随着反应温度的升高,OH-逐渐取代与Pt离子配位的Cl-,在Pt―Pt键形成之前,反应体系的UV-Vis吸收光谱中可观察到明显的纳米粒子的散射信号,原位QXAFS分析表明Pt纳米簇是由Pt氧化物纳米粒子还原所形成的;在Ru金属纳米簇的形成过程中,OH-首先取代了Ru Cl_3中的Cl~-,形成羟基配合物Ru(OH) _6~(3-),后者进一步缩合形成氧化钌纳米粒子,最终Ru金属纳米簇由乙二醇还原氧化钌纳米粒子形成。由于先形成了氧化物纳米粒子,后续的还原反应被限制在氧化物纳米粒子内,使最终得到的非保护型金属纳米簇具有尺寸小、分布窄的特点。本工作所获得的知识对发展高性能能源转化催化剂、精细化学合成催化剂、传感器等功能体系具有重要意义。 相似文献
62.
Ken-ichi Iwamoto Masako Hamaya Naoki Hashimoto Hitomi Kimura Yumiko Suzuki Masayuki Sato 《Tetrahedron letters》2006,47(40):7175-7177
Benzoin reactions are catalyzed by N,N-dialkylbenzimidazole to yield α-hydroxy ketones; the reaction proceeds in water as an aqueous medium under mild conditions. The utility of these salts as pre-catalysts in these reactions has been demonstrated. 相似文献
63.
Hirotsugu Minami Masako Yada Tomomi Yoshida Qiangbin Zhang Sadanobu Inoue Ikuo Atsuya 《Analytical sciences》2004,20(3):455-459
A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%. 相似文献
64.
Yuge R Yudasaka M Miyawaki J Kubo Y Ichihashi T Imai H Nakamura E Isobe H Yorimitsu H Iijima S 《The journal of physical chemistry. B》2005,109(38):17861-17867
We succeeded in large-scale preparation of single-wall carbon nanohorns (SWNH) encapsulating C60 molecules in a liquid phase at room temperature using a "nano-precipitation" method, that is, complete evaporation of the toluene from a C60-SWNH-toluene mixture. The C60 molecules were found to occupy 6-36% of the hollow space inside the SWNH, depending on the initial quantity of C60. We showed that the C60 in C60@SWNHox was quickly released in toluene, and the release rate decreased by adding ethanol to toluene. Numerical analysis of the release profiles indicated that there were fast and slow release processes. We consider that the incorporation quantity and the release rate of C60 were controllable in/from SWNHs because SWNHs have large diameters, 2-5 nm. 相似文献
65.
66.
Issei Kasahara Masami Kanai Masako Taniguchi Ayako Kakeba Noriko Hata Shigeru Taguchi Katsumi Goto 《Analytica chimica acta》1989
The singly charged complex anion bis[2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulphopropylamino)phenolato]cobaltate(III) is intensely purple-violet and is stable over the pH range 1–13. Its absorption spectrum remains the same over this pH range. At pH2, it forms extractable ion pairs with long-chain quaternary ammonium ions and protonated alkylamines. Only the quaternary ammonium ions are extracted into chloroform at pH 11, hence separate extractions allow both types to be determined. The absorbance of the organic phase is measured at 594 nm. The apparent molar absorptivity is 7.0 × 104 l mol?1 cm?1. Calibration graphs for zephiramine, benzethonium and hexadecylpyridinium ions are linear over the range 0.1–2 × 10?6 M. The only interference found was from anionic surfactants. The method is applied to hair and fabric conditioners. 相似文献
67.
Abstract— We have found that clay acts as a novel model matrix for the amphiphilic protein-opsin to mimic the visible absorption spectrum of a protonated retinal Schiff base (RSB) in vivo. Without strong acids at ambient temperature, a visible broad absorption spectrum with a LDmax at 530 nm covering the range from 400 to 680 nm was achieved for the protonated RSB with cationic surfactant-modified montmorillonite clay. The interlayers of the dimethyloctadecylamine (DOA) modified clay were found to provide amphiphilic space allowing the amphiphilic RSB to be intercalated easily and sequentially and protonated by the DOA. It is proposed that the visible absorption spectrum at LD, 530 nm was attributable to electrostatic effects, permitting the appropriate distance between the nitrogen of the protonated RSB and the negatively charged clay interlayers and also to the anisotropic orientation of the RSB molecules in the interlayers. 相似文献
68.
Takahiro Hirotsu Shunsaku Katoh Kazuhiko Sugasaka Masako Sakuragi Kunihiro Ichimura Yoshio Suda Mitsugi Fujishima Yoshimoto Abe Takahisa Misonoo 《Journal of polymer science. Part A, Polymer chemistry》1986,24(8):1953-1966
Preparation of new chelating polymers bearing dihydroxamic acid groups and the adsorptive ability for uranium in sea water are described. Chloromethylated polystyrene crosslinked with divinylbenzene was treated with diethyl malonate in N, N-dimethylformamide to give the polymer having diethyl malonate groups. This polymer was then treated with hydroxylamine in methanol to afford the dihydroxamic acid polymer. The presence of hydroxamic acid groups was confirmed by the appearance of IR absorption band at 1680 cm?1. The dihydroxamic acid polymer contained carboxylic acid groups as well as hydroxamic acid ones, and the contents of carboxylic acid and hydroxamic acid groups were estimated from elemental analysis to be 2–3 and 2–4 mmol/g, respectively. The polymer showed the adsorptive ability of 40 μg-U/g in 8 days for uranium in sea water. In addition, the polymer showed the selective adsorptivity for iron, nickel, copper, and zinc as well as uranium. The macroreticular-type polymer showed much higher adsorption rate for uranium in sea water than the gel-type ones did, suggesting that the rate depends on the diffusion of the uranium in the polymer support. 相似文献
69.
Yanisa Mittraphab Yhiya Amen Maki Nagata Masako Matsumoto Dongmei Wang Kuniyoshi Shimizu 《Molecules (Basel, Switzerland)》2022,27(2)
The extract from Entada phaseoloides was employed as active ingredients of natural origin into cosmetic products, while the components analysis was barely reported. Using LC-DAD-MS/qTOF analysis, eleven compounds (1–11) were proposed or identified from acetone extract of E. phaseoloides leaves (AE). Among them, six phenolic compounds, protocatechuic acid (2), 4-hydroxybenzoic acid (3), luteolin-7-O-β-d-glucoside (5), cirsimaritin (6), dihydrokaempferol (9), and apigenin (10), were isolated by various chromatographic techniques. Protocatechuic acid (2), epicatechin (4), and kaempferol (11) at a concentration 100 μM increased the HaCaT cells viability of the UVB-irradiated cell without any cytotoxicity effect and reduced the expression of COX-2 and iNOS inflammation gene. Moreover, compounds 2 and 4 could have potent effects on cell migration during wound closure. These results suggest that compounds 2, 4, and 11 from AE have anti-photoaging properties and could be employed in pharmaceutical and cosmeceutical products. 相似文献