全文获取类型
收费全文 | 112篇 |
免费 | 0篇 |
专业分类
化学 | 110篇 |
物理学 | 2篇 |
出版年
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2007年 | 1篇 |
2005年 | 1篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 8篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有112条查询结果,搜索用时 0 毫秒
11.
12.
Choji Kashima Yoshihiro Tsukamoto Yohei Miwa Kohei Higashide 《Journal of heterocyclic chemistry》2001,38(3):601-606
The enantioselective reduction of ketones was accomplished by borane in the presence of pyrazole derivatives, particularly 2‐methoxymethyl‐3‐phenyl‐1‐menthopyrazole (8). The catalysis of zinc chloride makes it possible to lower the reaction temperature below 0 °C, and to promote enantioselectivity. 相似文献
13.
Fukuji Higashi Shin-Ichi Ogata Yasuhiro Aoki 《Journal of polymer science. Part A, Polymer chemistry》1982,20(8):2081-2087
Poly(p-phenyleneterephthalamide) of high molecular weight was obtained when the polycondensation of terephthalic acid and p-phenylenediamine was carried out in N-methylpyrrolidone (NMP) that contained dissolved CaCl2 and LiCl in the presence of pyridine. The molecular weight of the polymer obtained varied with the amount of pyridine relative to the metal salts and with the molar ratios of CaCl2 to LiCl, the maximum ηinh value of 4.5 being obtained under the conditions Py/(CaCl2 + LiCl) ≈ 2.5 (mol/mol), CaCl2/LiCl ≈ 1.2 (mol/mol), and LiCl + CaCl2 ≈ 4 g. Among the solvents tested, NMP was significantly effective for the reaction. Polycondensations of several combinations of other dicarboxylic acids and diamines were carried out with limited success. 相似文献
14.
A fast and sensitive method for the simultaneous determination of Sudan dyes (I, II, III, and IV) in food samples was developed for the first time using partial filling micellar electrokinectic chromatography-mass spectrometry (MEKC-MS). The use of MEKC was essential to achieve the separation of these neutral analytes, while the partial filling technique was necessary to avoid the contamination of the ion source with non-volatile micelles. MEKC separation and MS detection conditions were optimized in order to achieve a fast, efficient, and sensitive separation of the four dyes. Filling 25% of the capillary with an MEKC solution containing 40 mM ammonium bicarbonate, 25 mM SDS, and 32.5% (v/v) acetonitrile, a baseline separation of the four azo-dyes was obtained in 10 min. Tandem MS was investigated in order to improve the sensitivity and selectivity of the analysis. Limits of detection (LOD) values 5, 8, 15, and 29 times better were obtained for Sudan III, I, II, and IV, respectively, using partial filling MEKC-MS/MS instead of partial filling MEKC-MS. Under optimized conditions, LOD from 0.05 to 0.2 μg/mL were obtained. The suitability of the developed method was demonstrated through the fast and sensitive determination of Sudan I, II, III, and IV in spiked chilli powder samples. This determination could not be achieved by MEKC-UV due to the existence of several interfering compounds from the matrix. 相似文献
15.
Fukuji Higashi Toshio Mashimo 《Journal of polymer science. Part A, Polymer chemistry》1986,24(7):1697-1701
The reaction promoted by thionyl chloride and pyridine could selectively activate carboxyl groups of hydroxybenzoic acids to give polyesters of high inherent viscosities up to 3.8. Favorable conditions were studied in terms of the temperatures for the initial reaction with the acids and subsequent aging at room temperature. Copolymers of several combinations of hydroxybenzoic acids with high molecular weights were obtained in quantitative yield by carrying out the polycondensation at 80°C for 3 h. The reaction could also produce high molecular polyesters in a simpler process without the initial activation of dicarboxylic acids by adding a mixture of these monomers to the condensing agent, and a tough film- and fiberforming polymer was obtained from 4,4′-dihydroxyphenylsulfone of low nucleophilicity whose polymer of high molecular weight is difficult to obtain. The process was also successfully applied to the direct copolycondensations of hydroxybenzoic acids, aromatic dicarboxylic acids, and bisphenols to produce polyesters of ηinh up to 5.6. 相似文献
16.
Fukuji Higashi Khoji Nakajima Wen Xion Zhang 《Journal of polymer science. Part A, Polymer chemistry》1994,32(4):747-752
It is proposed that depression of the transition temperatures, especially the melting point (Tm), can be achieved by the introduction of a different amide bond structure into the copolyamides of dicarboxylic acids and diamines by copolymerization of aminocarboxylic acids, such as p-aminobenzoic acid. The effect was examined by the amount and distribution of the structure in the copolylamindes. Copolycondensations of PEG3, p-aminobenzoic acid, and diamines with different chain lengths showed that the structural change of the amide bond in the copolymers, especially its distribution, was more important than its total amount in them. Several types of aminocarboxylic acids were briefly examined to study the effect. © 1994 John Wiley & Sons, Inc. 相似文献
17.
Fukuji Higashi Masato Koshio 《Journal of polymer science. Part A, Polymer chemistry》2003,41(4):616-623
A two‐stage copolycondensation of a mixture of equal parts of isophthalic acid and terephthalic acid first with a′,b′‐dihydroxyacetophenone (a′,b′‐DHAP) and then with isomeric c′,d′‐DHAP was examined at 60 and 80 °C. A structurally selective reaction was observed. At 80 °C, the preformed oligomers from symmetrically substituted 2′,6′‐DHAP reacted better with similarly substituted 2′,6′‐ or 3′,5′‐DHAP to give the copolymers of significantly higher inherent viscosity values than from the reaction with asymmetrically substituted 2′,4′‐DHAP, whereas at 60 °C they did almost equally well with any c′,d′‐DHAP. Similarly, the reaction of oligomers from 2′,4′‐DHAP with asymmetrically substituted 2′,4′‐DHAP or 2,4‐dihydroxybenzophenone yielded better results than those from the reaction with 2′,6′‐ or 3′,5′‐DHAP at both temperatures. The copolycondensations with comonomers of the structure independent of DHAPs were not affected by the preformed oligomers from DHAPs. The results are discussed in terms of the distributions of resulting oligomers determined by gel permeation chromatography. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 616–623, 2003 相似文献
18.
19.
Noboru Yamazaki Makoto Matsumoto Fukuji Higashi 《Journal of polymer science. Part A, Polymer chemistry》1975,13(6):1373-1380
Poly-p-benzamide of high molecular weight (ηinh = ~ in H2SO4) was obtained by the direct polycondensation reaction of p-aminobenzoic acid (p-ABA) by means of diphenyl and triaryl phosphites in N-methylpyrrolidone (NMP)-pyridine solution containing lithium and calcium chlorides. Molecular weight of polymer varied with the amount of these salts, showing maximum values at the concentration of about 4 wt-% of LiCl or about 8 wt-% of CaCl2 in the reaction mixture. The reaction temperature at around 80°C gave a polymer of the highest viscosity. The polycondensation reaction was also affected by monomer concentration, solvents, and tertiary amines like pyridine. Similarly, aromatic polyamides with high molecular weight (ηinh values up to 1.34 in H2SO4) were prepared from isophthalic acid and aromatic diamines, whereas terephthalic acid gave only low-viscosity polymers. 相似文献
20.