全文获取类型
收费全文 | 1097篇 |
免费 | 34篇 |
国内免费 | 3篇 |
专业分类
化学 | 935篇 |
晶体学 | 9篇 |
力学 | 8篇 |
数学 | 32篇 |
物理学 | 150篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 16篇 |
2018年 | 5篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 28篇 |
2013年 | 55篇 |
2012年 | 84篇 |
2011年 | 68篇 |
2010年 | 33篇 |
2009年 | 29篇 |
2008年 | 66篇 |
2007年 | 71篇 |
2006年 | 74篇 |
2005年 | 81篇 |
2004年 | 61篇 |
2003年 | 67篇 |
2002年 | 72篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 6篇 |
排序方式: 共有1134条查询结果,搜索用时 378 毫秒
161.
Sato S Nakamura T Nitobe S Kiba T Hosokawa K Kasajima T Otsuka I Akimoto S Kakuchi T 《The journal of physical chemistry. B》2006,110(43):21444-21449
Dimethylanthracene (DMA), which exhibits almost no self-association in bulk organic solvents, forms a dimer and emits excimer-like fluorescence in a gamma-cyclodextrin nanocavity in a dilute aqueous solution. The 1Bb and 1La electronic transitions of the DMA dimer split by 2230 and 344 cm(-1), respectively, in a fluorescence excitation spectrum obtained with the excimer-like emission. From these energy splits, the structure of dimer in relation to a dielectric constant inside gamma-CD was discussed on the basis of atom-atom Lennard-Jones potential calculations including Coulombic interactions. Excitation relaxations of DMA in the presence of alpha-, beta-, and gamma-CDs in aqueous solutions were investigated by time-resolved fluorescence. The results suggest that both the hydrated and anhydrated species exist in the alpha- and gamma-CD complexes, while only the anhydrated species exists in the beta-CD complex. 相似文献
162.
[reaction: see text] The carboxylic acid catalyzed three-component aza-Friedel-Crafts reactions of aldehydes, primary amines, and indoles in water have been developed. The aza-Friedel-Crafts products could be easily transformed to various 3-substituted indoles including biologically active compounds. This system offers a novel efficient method for the synthesis of 3-substituted indoles. 相似文献
163.
Masashi Hashimoto Seiji Ujiie Akira Mori 《Molecular Crystals and Liquid Crystals》2013,570(1):809-814
Abstract New 5-cyanotroponoid liquid crystals with a 3,4-dialkoxybenzoyloxy and a 3,4-dialkoxybenzoylamino substituent at the C-2 position were prepared. These derivatives exhibited interdigitated bilayer smectic A phases while the corresponding benzenoids were non-mesogenic. Thermal stabilities of these troponoids were lower than those of 2-(4-alkoxybenzoyloxy)-5-cyanotropones and 2-(4-alkoxybenzoylamino)-5-cyanotropones. 相似文献
164.
Effects of pressure and temperature on the solubility of monosodium L-glutamate monohydrate in water
Yoshihisa Suzuki Hiroshi Matsuo Yoshikata Koga Katsuya Mukae Tetsuya Kawakita Seiji Sawamura 《高压研究》2013,33(2):93-104
Abstract The solubility of monosodium L-glutamate monohydrate (MSG.H2O) in water was measured at pressures in the range of 0.10-300MPa and 298.15K. The density of MSG solution at high concentrations and heat of solution at saturated concentration were also measured at atmospheric pressure. The solubility, ms, increased with increasing pressure and the pressure coefficient, Θp, [?(? In ms,? p)T] at 0.10 MPa was (2.0 ± 0.1) × 10-10Pa-1. It agrees well with (2.1 ±0.2)× 10-10 Pa-1 thermodynamically estimated using the partial molar volume, the activity coefficient of the solute in solution, and the molar volume of the crystal. The excellent agreement at 0.10MPa gives us confidence in the solubility data at higher pressures. The heat of solution data and other pertinent values were used to calculate the temperature coefficient of solubility, ΘT [? (? In ms/?(1/T))p], by a thermodynamic equality. The resulting ΘT compares well with the data directly measured by Ogawa. 相似文献
165.
Variations in the fluorescence in the intensities of anthracene derivatives under a magnetic field were investigated in the presence of a dilute magnetic fluid. When excitation was carried out with light that was polarized parallel to the magnetic field, the intensity of the fluorescence that was polarized paralell to the magnetic field decreased by about 10%. Although the fluorescence intensities of most of the anthracene derivatives showed a similar decrease in magnitude, that of 9,10-dimethylanthracene showed a large decrease. On the other hand, fluorescence increased when excitation and fluorescence were perpendicular to the magnetic field. The obtained phenomena can be explaned by the formation of anisotropic assembly of magnetic fluid particles in the solution. 相似文献
166.
Photoluminescence as well as photoinduced diamagnetic to paramagnetic phase transition in a strongly correlated electron system, an organic radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) crystal, was investigated under two-photon excitation with different photon densities. Below the threshold photon density to drive the photoinduced phase transition (PIPT), the diamagnetic phase shows a broad luminescence band with a large Stokes shift, whose intensity obeys almost second power law of the excitation photon density. Above the threshold photon density, on the other hand, the diamagnetic to paramagnetic phase transition effectively takes place with a large conversion yield and a steep response instead of an occurrence of the photoluminescence, indicating that the phase transition is optically induced by two-photon absorption. As far as we know, this is the first observation of the PIPT phenomena mediated by two-photon absorption. 相似文献
167.
168.
Yoshihiro Kikkawa Kazuhiro Taguchi Seiji Tsuzuki Hideo Tokuhisa 《Applied Surface Science》2008,254(23):7576-7580
Two-dimensional structures of pyrimido[5,4-d]pyrimidine derivatives (PD) were studied by scanning tunneling microscopy (STM) at solid/liquid interface. In order to tune the intervals of functional unit (hydrogen bonding site) in the molecule, the PD with different numbers and length of alkyl chain were designed and synthesized. STM observation at highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface revealed that the PD with four alkyl chains formed a columnar structure, and the alkyl chains were not interdigitated. By contrast, the PD with two alkyl chains formed similar columnar structure, whereas the alkyl chains were interdigitated. These structural features of the PD indicates that the intervals of the functional unit, i.e., hydrogen bonding sites in the PD can be controlled by changing not only the length but also the number of alkyl chains. 相似文献
169.
Spherical aggregates of SiC nanocrystallites can be grown in addition to SiC nanowires via metal organic chemical vapor deposition using methylvinyldichlorosilane as a source gas and Ni catalyst by controlling the growth temperature and the pressure of the source gas. Electron microscopy observations show that the aggregates are typically 300 nm in diameter, which consist of SiC nanocrystallites of about 5 nm in diameter. Electron diffraction reveals that the nanocrystallites have the 3C structure. 相似文献
170.
Dr. Hiromi Oshita Takashi Suzuki Kyohei Kawashima Prof. Dr. Hitoshi Abe Prof. Dr. Fumito Tani Prof. Dr. Seiji Mori Prof. Dr. Tatsuo Yajima Prof. Dr. Yuichi Shimazaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(32):7649-7658
In order to gain new insights into the effect of the π–π stacking interaction of the indole ring with the CuII–phenoxyl radical as seen in the active form of galactose oxidase, we have prepared a CuII complex of a methoxy-substituted salen-type ligand, containing a pendent indole ring on the dinitrogen chelate backbone, and characterized its one-electron-oxidized forms. The X-ray crystal structures of the oxidized CuII complex exhibited the π–π stacking interaction of the indole ring mainly with one of the two phenolate moieties. The phenolate moiety in close contact with the indole moiety showed the characteristic phenoxyl radical structural features, indicating that the indole ring favors the π–π stacking interaction with the phenoxyl radical. The UV/Vis/NIR spectra of the oxidized CuII complex with the pendent indole ring was significantly different from those of the complex without the side-chain indole ring, and the absorption and CD spectra exhibited a solvent dependence, which is in line with the phenoxyl radical–indole stacking interaction in solution. The other physicochemical results and theoretical calculations strongly support that the indole ring, as an electron donor, stabilizes the phenoxyl radical by the π–π stacking interaction. 相似文献