全文获取类型
收费全文 | 67篇 |
免费 | 0篇 |
国内免费 | 5篇 |
专业分类
化学 | 53篇 |
力学 | 3篇 |
物理学 | 16篇 |
出版年
2020年 | 2篇 |
2017年 | 1篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2008年 | 4篇 |
2007年 | 2篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1993年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1984年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1964年 | 1篇 |
1930年 | 2篇 |
排序方式: 共有72条查询结果,搜索用时 15 毫秒
61.
Shoichiro Tanigawa 《Hyperfine Interactions》1993,79(1-4):575-589
The origin of the effect of defects on positron annihilation in semiconductors has been studied. The electron-positron momentum densities in elemental semiconductors (Si and Ge), III-V compound semiconductors (GaAs, InP and GaSb), diamond and the proton irradiated Si were investigated by a full-scale use of the two-dimensional angular correlation of positron annihilation radiations (2D-ACAR). The obtained results showed, as a whole, good agreement with the electron momentum distribution of the fully occupied Jones zone with a small exception for the fact that the low density channels are running along the three principal axes. This anisotropy was strong in elemental semiconductors, while it was weakened in compound semiconductors. This anisotropy and its dependence on the material were found to be generally understood by the incorporation of crystal symmetry. The anisotropy will be discussed by group theory in conjunction to the effect of defects on positron annihilation. 相似文献
62.
In order to get good antitumor agents especially better than 5-fluorouracil,tegafur and l-hexylcarbamoyl-5-fluorouracil (HCFU),fourty nine 1-carbamoyl-5-fluorouracil having aromatic ring were synthesized from 5-fluorouracil and isocyanates or amines.Antitumor activity was tested in the L-1210 tumor system,and 5 compounds gave better value of therapeutic ratio than 5-fluorouracil,tegafur,HCFU.l-(4-Methoxybenzylcarbamoyl)-5-fluorouracil gave the best result. 相似文献
63.
Total synthesis of dl-asparenomycins was accomplished with direct conversion of carbonates 13a, 13b and 14a, 14b to asparenomycin esters 15 and 16 and carboxy deprotection by the AlCl3-anisole method. 相似文献
64.
Polyoxytetramethyleneglycol (PTMG) can be directly prepared from tetrahydrofuran (THF) and water in the presence of heteropolyacids (HPA), without the hydrolysis step. The reaction is carried out by mixing two liquid phases: the THF phase and a heteropolyacid catalyst phase. In this reaction the molar ratio of water to a heteropolyacid (H2O/HPA) in the catalyst phase plays an important role in the THF polymerization activity and the molecular weight of PTMG. IR spectrometric studies revealed that THF is coordinated to a heteropolyanion through either a water molecule or a proton in the catalyst phase. The latter type of coordination bings about the activation of THF capable of initiating the ring-opening polymerization even in the presence of water at a lower acid strength. The PTMG prepared by this method has a narrow molecular weight distribution (M?w/M?n = 1.5 or less) and a number average molecular weight of 500–2000 which are requisite for the production of polyurethane elastomers. A new polymerization mechanism named “Phase Transfer Polymerization” is proposed for elucidating a narrow molecular weight distribution. 相似文献
65.
Mitsuru Yoshioka Teruji Tsuji Shoichiro Uyeo Sadao Yamamoto Tsutomu Aoki Yasuhiro Nishitani Sachio Mori Hisao Satoh Yoshinori Hamada Hiroyuki Ishitobi Wataru Nagata 《Tetrahedron letters》1980,21(4):351-354
Stereocontrolled and industrially feasible synthesis of a new antibiotic and related derivatives, which is characterized by using all the carbon atoms of the penicillin skeleton, is described. 相似文献
66.
测量气体样品的红外光谱时,红外光谱仪器内的水汽和气体样品中所含的水汽会严重干扰气体的红外光谱。为消除水汽的干扰,通常作法是测量前必须将水分子(气态)彻底排除掉,也就是使光谱仪器和气体样品保持干燥状态。该研究提供一个新测量方法,不需任何干燥预处理过程,直接获得含水汽的丙酮气体的红外光谱。经过几十次光谱扫描累加后,观察并根据水汽谱的吸收峰性质(吸光率>0或吸光率<0),向光谱仪样品室引入少量干燥氮气或少量潮湿空气,在接下来的光谱扫描累加过程中,水汽吸收峰将逐渐变小直至消失。实验结果表明该方法去除水汽干扰峰简单高效。新方法在0.5 cm-1光谱分辨率时效果非常好,为气体的高分辨分析提供了有力工具。 相似文献
67.
A simple model is proposed for the spin-dependent infrared absorption band observed in antiferromagnetic NiO crystals. The transition is attributed to the coupled action of the radiation field with the lattice vibrations. The variation of the exchange parameter due to the electric field and the displacement of the ions is taken as the perturbation giving rise to the electric dipole transition between different spin states accompanying the change in the vibrational states. The molecular field approximation is adopted to describe the spin states. The general features of the spectral pattern and its temperature dependence thus obtained are in good agreement with the experiments byNewman andChrenko. 相似文献
68.
Hisayoshi Itoh Akira Uedono Takeshi Ohshima Yasushi Aoki Masahito Yoshikawa Isamu Nashiyama Shoichiro Tanigawa Hajime Okumura Sadafumi Yoshida 《Applied Physics A: Materials Science & Processing》1997,65(3):315-323
2
+ and Al+ at temperatures from room temperature (RT) to 1200 °C at doses of 1013 and 1015/cm2. It is found from Doppler broadening spectra of annihilation gamma-rays obtained by varying the incident positron energy
that hot-implantation gives rise to clustering of vacancies, whereas it suppresses amorphization and diminishes the thickness
of damaged layers. The average size of such clusters increases with increasing implantation dose and temperature. Vacancy
clustering by hot-implantation can be interpreted by the combination of vacancies during implantation. Vacancy type defects
in the low-dose (1013/cm2) implanted samples are found to be removed by annealing at 1400 °C, whereas large vacancy clusters still remain after 1400 °C
annealing in the high-dose (1
015/cm2) implanted samples. It is also derived from the depth profile of positron diffusion length that positron scattering centers
are produced after annealing at 1400 °C in all implanted samples.
Received: 7 March 1997/Accepted: 6 May 1997 相似文献
69.
Shoichiro Ikeda Yasuhisa Saito Makoto Yoshida Hidetomo Noda Masunobu Maeda Kaname Ito 《Journal of Electroanalytical Chemistry》1989,260(2)
Photoelectrochemical reduction of CO2 was carried out using metal-coated p-GaP photocathodes in non-aqueous electrolytes prepared from tetraalkylammonium salts and propylene carbonate as an aprotic solvent. In non-aqueous electrolytes, the coating of Au, In and Pb increased the cathodic photocurrents and the stability of the electrodes, while Zn coating did not show such significant effects. Photoelectrochemical reduction products at a bare p-GaP in non-aqueous electrolytes were (COOH)2, HCOOH, CO and H2, and the faradaic efficiency for CO formation became 50%, in contrast to that in the aqueous electrolytes where it was only a few %. The Photoelectrochemical reduction products at metal-coated p-GaP photocathodes depended greatly on the catalytic properties of the coated metal, i.e. the catalytic effect on the electrochemical reduction of CO2. By Pb coating, the faradaic efficiency for (COOH)2 formation became ca. 50%, and by Au, In or Zn coating, that for CO became almost 100%. The water content in non-aqueous electrolytes affected the faradaic efficiency of each product significantly. 相似文献
70.
Takahiro Hirai Daiki Kato Dr. Binh Khanh Mai Shoichiro Katayama Shoko Akiyama Dr. Haruki Nagae Prof. Dr. Fahmi Himo Prof. Dr. Kazushi Mashima 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(47):10735-10742
A catalyst system of mononuclear manganese precursor 3 combined with potassium alkoxide served as a superior catalyst compared with our previously reported manganese homodinuclear catalyst 2 a for esterification of not only tertiary aryl amides, but also tertiary aliphatic amides. On the basis of stoichiometric reactions of 3 and potassium alkoxide salt, kinetic studies, and density functional theory (DFT) calculations, we clarified a plausible reaction mechanism in which in situ generated manganese–potassium heterodinuclear species cooperatively activates the carbonyl moiety of the amide and the OH moiety of the alcohols. We also revealed details of the reaction mechanism of our previous manganese homodinuclear system 2 a , and we found that the activation free energy (ΔG≠) for the manganese–potassium heterodinuclear complex catalyzed esterification of amides is lower than that for the manganese homodinuclear system, which was consistent with the experimental results. We further applied our catalyst system to deprotect the acetyl moiety of primary and secondary amines. 相似文献