全文获取类型
收费全文 | 268篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 224篇 |
晶体学 | 2篇 |
数学 | 11篇 |
物理学 | 39篇 |
出版年
2023年 | 2篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 17篇 |
2012年 | 16篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 9篇 |
2008年 | 18篇 |
2007年 | 12篇 |
2006年 | 15篇 |
2005年 | 15篇 |
2004年 | 8篇 |
2003年 | 18篇 |
2002年 | 7篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有276条查询结果,搜索用时 15 毫秒
11.
Nakanishi I Miyazaki K Shimada T Iizuka Y Inami K Mochizuki M Urano S Okuda H Ozawa T Fukuzumi S Ikota N Fukuhara K 《Organic & biomolecular chemistry》2003,1(22):4085-4088
Electron-transfer reduction of molecular oxygen (O2) by the phenolate anion (1-) of a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H), occurred to produce superoxide anion, which could be directly detected by a low-temperature EPR measurement. The rate of electron transfer from 1- to O2 was relatively slow, since this process is energetically unfavourable. The one-electron oxidation potential of 1- determined by cyclic voltammetric measurements is sufficiently negative to reduce 2,2-bis(4-tert-octylphenyl)-1-picrylhydrazyl radical (DOPPH*) to the corresponding one-electron reduced anion, DOPPH-, suggesting that 1- can also act as an efficient radical scavenger. 相似文献
12.
Muranaka A Matsumoto Y Uchiyama M Jiang J Bian Y Ceulemans A Kobayashi N 《Inorganic chemistry》2005,44(11):3818-3826
A series of heteroleptic rare-earth sandwich complexes [M(Nc)(OEP)] (M = La, Nd, Eu, Dy, and Lu; Nc = 2,3-naphthalocyaninate; OEP = octaethylporphyrinate) have been investigated by electronic absorption and magnetic circular dichroism (MCD) spectroscopy. The electronic absorption spectra of the neutral forms showed two characteristic transitions (bands I and II) in the near-IR region, both of which were systematically shifted depending on the size of their central metal. In the MCD spectra, a relatively intense Faraday A term and a significantly weak Faraday B term have been observed corresponding to bands II and I, respectively. The spectral features were successfully interpreted using a simple MO model by considering the relevant interactions of Gouterman's four orbitals of the constituent chromophores. The model succeeded in assigning the MCD spectra of the related compounds, the oxidized and reduced forms of the dimer ([M(Nc)(OEP)]+ and [M(Nc)(OEP)]-), and neutral forms of the triple-decker compounds (M2(Nc)(OEP)2, M = Nd, Eu). DFT calculations of the dimers supported the validity of this model. 相似文献
13.
S. Kittaka N. Uchida M. Katayama A. Doi M. Fukuhara 《Colloid and polymer science》1991,269(8):835-842
The colloidal stability of V2O5
nH2O was studied on the basis of the measurements of critical flocculation concentration (CFC) by metal ions, amount of ions exchanged (or intercalated), and -potential. In total, the CFC values obeyed the Schulze Hardy law and strong Hofmeister's series was found in the systems including alkaline ions. The sequence of colloidal stability of V2O5
nH2O in the electrolyte solutions was related to the intercalation of metal ions in the interlayer spaces of the solid. The largest CFC value for Li+ (87 mmol dm–3) was explained by smaller affinity of Li+ to be intercalated in V2O5
nH2O as well as smaller Hamaker constant of the intercalated solid compared to the other systems.Effect of intercalation of metal ions on the crystalline properties of the materials was measured by use of XRD and electron microscope. Under highly dehydrated condition the ions whose radii are smaller than 0.1 nm are captured in the structure of V2O5
nH2O without changing interlayer distances, while those larger than 0.1 nm increase the interlayer distance. In a saturated H2O vapor interlayer distances increased with increasing charge of intercalated ions. However, when intercalated with ions carrying the same valency the interlayer distances of the sample decreased with decrease in the hydration property of ions. Hydrolyzable Cr3+ gave exceptionally larger interlayer distances, both in a vacuum and in H2O vapor. 相似文献
14.
Ebisawa K Nagashima N Fukuhara K Kumon S Kishimoto S Suzuki E Yoneda S Umeyama H 《Chemical & pharmaceutical bulletin》2000,48(5):708-715
Aspartame (L-alpha-aspartyl-L-phenylalanine methyl ester) is a dipeptide sweetener about 200 times as sweet as sugar. It exists in crystal forms such as IA, IB, IIA, and IIB, which differ in crystal structure and in the degree of hydration. Among these, IIA is the most stable crystal form, and its crystal structure has been well determined (Hatada et al., J. Am. Chem. Soc., 107, 4279-4282 (1985)). To elucidate the structural factors of thermal stability in the IIA form of aspartame and to examine the physical process in the crystal transformation between the IIA and IIB forms, we performed a thermal analysis and solid-state NMR measurements. We found that a quasi-stable intermediate state exists in the transformation, and it has the same crystal lattice as the usual IIA form, despite the dehydration from 1/2 mol to 1/3 mol per 1 mol of aspartame. The results of the energy component analysis and the molecular dynamics simulation suggest that the entropic effect promotes the generation of the intermediate state, which is presumably caused by the evaporation of the water of crystallization and the increase of molecular motion in aspartame. Thus, the thermal stability of the IIA form is attributable to a structural property, i.e., the crystal lattice itself is retained during the above dehydration. Moreover, the molecular dynamics simulations suggest that the aspartame molecules have two kinds of conformational flexibility in the intermediate state. 相似文献
15.
trans- and cis-1-(4-Dimethylaminophenyl)-6-(4-nitrophenyl)hex-3-ene-1,5-diynes (trans- and cis-DANE) were synthesized and their photochemical properties were studied. The absorption spectra of trans-DANE red-shifted compared with the parent compound bisphenylethynylethene (BEE) due to intramolecular charge transfer. The fluorescence spectra, Stokes shift, fluorescence lifetime, fluorescence quantum yield, and quantum yield of trans-to-cis photoisomerization of trans-DANE showed strong dependence upon the solvent polarity in the less-polar region. No fluorescence emission from trans-DANE was observed in medium-polar and polar solvents. The quantum yield of cis-to-trans isomerization was almost solvent independent. The donor-acceptor substituents shifted the equilibrium between the trans perpendicular triplet state and the trans planar triplet state to the trans triplet state, and resulted in an increase in the triplet lifetime. Comparison of the photochemical properties of trans-DANE with trans-4-dimethylamino-4'-nitrostilbene (DANS) suggests that trans-DANE is a possible fluorescent probe in the non-polar region. 相似文献
16.
17.
Dr. Yusaku Nomura Dr. Frédéric Thuaud Dr. Daisuke Sekine Prof. Dr. Akihiro Ito Satoko Maeda Dr. Hiroyuki Koshino Dr. Daisuke Hashizume Dr. Atsuya Muranaka Dr. Thomas Cruchter Prof. Dr. Masanobu Uchiyama Prof. Dr. Satoshi Ichikawa Prof. Dr. Akira Matsuda Prof. Dr. Minoru Yoshida Prof. Dr. Go Hirai Prof. Dr. Mikiko Sodeoka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(35):8387-8392
A synthetic methodology to access all possible stereoisomers of spectomycin A1 (SMA1) and A2 (SMA2) has been established through late-stage diversification. The key reaction for the construction of all four diastereomers is an intramolecular cyclization based on the umpolung of π-allyl palladium species with bis(pinacolato)diborane (B2(pin)2). Silyl group assisted direct benzylic oxidation of each isomer enabled construction of the fragile β-hydroxytetralone skeleton to provide the SMAs. The relative and absolute stereochemistry of SMA2 was also determined, and the absolute stereochemistry of SMA1 was extrapolated based on the optical rotation of SMA2. The axial chirality of SMAs is discussed based on circular dichroism spectra and DFT calculations, and it is concluded that the M isomer is predominant in solution. Biochemical assessment of all isomers in vitro revealed that the C9 hydroxyl group and dimeric structure were both important for protein SUMOylation-inhibitory activity. 相似文献
18.
19.
Naoyuki Toriumi Atsuya Muranaka Daisuke Hashizume Masanobu Uchiyama 《Tetrahedron letters》2017,58(23):2267-2271
Methylene-bridged benziphthalocyanine dimer 2 was unexpectedly generated by the reaction of dihydroxybenziphthalocyanine 1 and formaldehyde in the presence of a catalytic amount of a base at room temperature. Single-crystal X-ray diffraction analysis of 2 revealed a V-shaped structure. Dimer 2 exhibited longer-wavelength absorption and fluorescence bands than monomer 1 in the near-IR region. 相似文献
20.
Harry Adams Neil A. Bailey David E. Fenton Choki Fukuhara Masatoshi Kanesato 《Supramolecular chemistry》2013,25(4):325-330
Abstract The synthesis and crystal structure of the diprotonated cryptand derived from the reaction of tren and 2,6-diacetyl pyridine is reported. The imino nitrogens of the Schiff base linkages are directed so that the dicarbimine functions are in trans, trans geometry relative to the pyridine C-N bond. This configuration has not previously been reported in related pyridine-derived Schiff base macrocycles. 相似文献