全文获取类型
收费全文 | 1021篇 |
免费 | 36篇 |
国内免费 | 6篇 |
专业分类
化学 | 782篇 |
晶体学 | 17篇 |
力学 | 18篇 |
数学 | 32篇 |
物理学 | 214篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 9篇 |
2017年 | 23篇 |
2016年 | 17篇 |
2015年 | 26篇 |
2014年 | 28篇 |
2013年 | 55篇 |
2012年 | 82篇 |
2011年 | 78篇 |
2010年 | 39篇 |
2009年 | 41篇 |
2008年 | 64篇 |
2007年 | 66篇 |
2006年 | 80篇 |
2005年 | 72篇 |
2004年 | 53篇 |
2003年 | 61篇 |
2002年 | 43篇 |
2001年 | 26篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有1063条查询结果,搜索用时 15 毫秒
921.
Masayoshi?OkuboEmail author Ryu?Takekoh Naohiko?Saito 《Colloid and polymer science》2003,281(10):945-950
Some factors contributing to the formation of an alternately multilayered structure of micron-sized, monodisperse poly(methyl methacrylate) (PMMA)/polystyrene (PS) (1/1, w/w) composite particles by reconstruction of the morphology with the solvent-absorbing/releasing method (SARM) were discussed. The original composite particles, which were produced by seeded dispersion polymerization (SDP) of styrene, had a core–shell structure. When PS/PMMA (1/1, w/w) composite particles produced by SDP of methyl methacrylate were treated by the SARM with toluene, the reconstructed morphology of the composite particles was not the multilayered structure but a hemisphere (or core–shell). The PS/PMMA composite particle contained less than 10 wt% PMMA- g-PS. On the other hand, the PMMA/PS composite particles contained about 40 wt% graft polymer. The graft polymer would exist at the interfaces of the alternate multilayers and decrease their interfacial energy. This was the main reason why the alternately multilayered structure was constructed by the SARM, though the total interfacial area between PMMA and PS layers in the multilayered particle is much larger than that of the hemisphere (or core–shell). 相似文献
922.
Magnesium isotopes effects were investigated by chemical ion exchange using synthesized 2-aminomethyl-18-crown-6 (AM18C6) bonded Merrifield peptide resin. It was found that separation factors larger those reported previously were obtained, and the hydration and isotope mass effects are more significant than that of the complexation. The capacity of the crown ion exchanger was 2.3 meq/g dry resin. The adsorption capacity of the resin for magnesium ion was 26.8 mg/g dry resin at pH 7. The heavier isotopes of magnesium were enriched in the solution phase, while the lighter isotopes were enriched in the resin phase. The separation factors of (24)Mg-(25)Mg, (24)Mg-(26)Mg, and (25)Mg-(26)Mg were 1.0085, 1.0162, and 1.0081, respectively. 相似文献
923.
Tae-Jeong Kim Hee-Yeol LeeEun-Sook Ryu Dong-Kyu ParkChan Sik Cho Sang Chul ShimJong Hwa Jeong 《Journal of organometallic chemistry》2002,649(2):258-267
A series of chiral C1- and C2-symmetric ferrocenyl Schiff bases (1a-c), ferrocenyl aminoalcohols (2a), ferrocenylphosphinamides (2b-c), 1,1′-ferrocenyl-diol (3), and 1,1′-ferrocenyl-disulfonamide (4) were prepared and employed as base catalysts or as ligand for titanium(IV) complexes in the asymmetric addition of diethylzinc to aromatic aldehydes. High enantioselectivity up to almost 100% ee was achieved for the alkylation of benzaldehyde and p-methoxybenzaldehyde with 1 or 3. In contrast, however, the β-aminoalcohol (2a) and phosphinamides (2b and c) that are ubiquitous classes of base catalysts for this reaction proved inefficient in our hands, regardless of the types of substrates or reaction conditions. Comparative studies show that there exist various reaction parameters governing not only chemical yields but also optical yields. These include steric and electronic environment of the substrate, the solvent, the reaction temperature, and the nature of the ferrocene moieties. 相似文献
924.
Byung-Seon Choi Geun-Il Park Jung-Won Lee Ho-Yeon Yang Seung-Kon Ryu 《Journal of Radioanalytical and Nuclear Chemistry》2003,256(1):19-26
The complexes of six organic carboxylic acids (containing {O,O} donor atoms) with Bu2Sn(IV)2+ and Ph3Sn(IV)+ with ligand to metal ratios of 1 : 1 and 1 : 2, were prepared by two different methods. The FtIR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the {O,O} atoms of the ligands. It was found that in most cases the -COO-group was chelated to the central metal ions, but monodentate coordination was also sometimes observed. Complex formation was accompanied by a rearrangement of the hydrogen-bonding network existing in the ligands. The complexes probably have polymeric structures. Comparison of the experimental Mössbauer D values with those calculated on the basis of the point charge model formalism revealed that the organotin(IV) moiety has a trigonal-bipyramidal (tbp) geometry, and in certain cases a tetrahedral (tetr) geometry too. Finally, the local structure of the maleic acid complex formed with Bu2Sn(IV)2+ was determined by an EXAFS method. 相似文献
925.
The magnesium isotope effects were investigated by chemical ion exchange with a hydrous manganese(IV) oxide. The capacity of manganese(IV) oxide was 0.5 meq g(-1). The distribution coefficient of magnesium ions on the MnO(2) was determined by a batch method. The heavier isotopes of magnesium were enriched in the solution phase, while the lighter isotopes were enriched in the hydrous MnO(2) phase. The separation factor was determined according to the method of Glueckauf from the elution curve and isotopic assays. The separation factors of (24)Mg(2+)-(25)Mg(2+), (24)Mg(2+)-(26)Mg(2+), and (25)Mg(2+)-(26)Mg(2+) isotope pair fractionations were 1.011, 1.021, and 1.011, respectively. 相似文献
926.
Yoon M Jeong S Nicol CJ Lee H Han M Kim JJ Seo YJ Ryu C Oh GT 《Experimental & molecular medicine》2002,34(6):481-488
To determine whether the PPARalpha agonist fenofibrate regulates obesity and lipid metabolism with sexual dimorphism, we examined the effects of fenofibrate on body weight, white adipose tissue (WAT) mass, circulating lipids, and the expression of PPARalpha target genes in both sexes of high fat diet-fed C57BL/6J mice. Both sexes of mice fed a high-fat diet for 14 weeks exhibited increases in body weight, visceral WAT mass, as well as serum triglycerides and cholesterol, although these effects were more pronounced among males. Feeding a high fat diet supplemented with fenofibrate (0.05% w/w) reduced all of these effects significantly in males except serum cholesterol level. Females on a fenofibrate-enriched high fat diet had reduced serum triglyceride levels, albeit to a smaller extent compared to males, but did not exhibit decreases in body weight, WAT mass, and serum cholesterol. Fenofibrate treatment resulted in hepatic induction of PPARalpha target genes encoding enzymes for fatty acid beta-oxidation, the magnitudes of which were much higher in males compared to females, as evidenced by results for acyl-CoA oxidase, a first enzyme of the beta-oxidation system. These results suggest that observed sexually dimorphic effects on body weight, WAT mass and serum lipids by fenofibrate may involve sexually related elements in the differential activation of PPARalpha. 相似文献
927.
928.
929.
930.
Ryu Sato Hidetoshi Ohta Tatsuya Yamamoto Shiduko Nakajo Satoshi Ogawa Ashraful Alam 《Tetrahedron letters》2007,48(29):4991-4994
Novel axially chiral benzopentathiepins were synthesized by sulfurization of dithiastannole. Naphthyl moiety was introduced near the pentathiepin ring by Suzuki-Miyaura cross-coupling reaction. Pentathiepins were found as diastereomeric mixture. Rotational energy barrier for C-C bond was estimated by theoretical calculation. Energy barrier for the inversion of pentathiepin ring was experimentally determined by variable temperature 1H NMR. 相似文献