全文获取类型
收费全文 | 194篇 |
免费 | 4篇 |
专业分类
化学 | 162篇 |
力学 | 1篇 |
数学 | 1篇 |
物理学 | 34篇 |
出版年
2023年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 6篇 |
2012年 | 12篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 9篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 9篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1965年 | 1篇 |
1962年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有198条查询结果,搜索用时 15 毫秒
1.
Hasegawa JY Takata K Miyahara T Neya S Frisch MJ Nakatsuji H 《The journal of physical chemistry. A》2005,109(14):3187-3200
Excited states of free-base porphyrin isomers, porphycene (Pc), corrphycene (Cor), and hemiporphycene (hPc), were studied by the Symmetry-Adapted Cluster (SAC)/SAC-Configuration Interaction (CI) method. The absorption peaks of the porphyrin isomers were assigned on the basis of the SAC-CI spectra. The X, Y, X', and Y' bands of the porphyrin isomers, which have weak intensities, are identified. The differences in the Q-band absorptions among the isomers were clearly explained by the four-orbital model. In Cor and hPc, the wave function of the B-band corresponds to the mixture of the four-orbital excitations and the optically forbidden excitation of free-base porphin (P), due to the molecular symmetry lowering in the isomers. The B-band character is described by the five-orbital model in Pc and the six-orbital model in Cor and hPc. Two tetrazaporphycenes and two ring-extended (dibenzo) porphycenes were designed, and the Q-band transition moment was successfully controlled. These examples show that the control of the four-orbital energy levels is the guiding principle for pigment design in porphyrin compounds. 相似文献
2.
Two steroidal compounds BR-1 (I) and ?2 (II) which had been obtained from the rhizomes of Baker, were isolated also from those of Roth. They were identified, respectively, by X-ray analysis and chemical correlation as 1β,2β,3β,4β,5β,7α-hydroxy-spirost-25(27)-en-6-one and its corresponding 6β-hydroxy compound. 相似文献
3.
Colloidal adsorption and spontaneous ordering of adsorbed particles on a substrate was simulated using a three-dimensional simulation model for colloidal dispersion system with an adsorptive surface under a specified bulk concentration, where the particle-particle and particle-substrate interactions were modeled on the DLVO theory. The key process for order formation is considered to be the adsorption of a particle that induces the transition from incomplete order to perfect order, and is found to involve a stochastic nature due to an energy barrier which must be overcome for the system to reach ordered state. Also, a model was developed to predict the energy barrier for order formation based on direct observation of the key process. Further, a model to describe the stochastic nature of the process was developed and its quantitative validity was demonstrated. Through the examination of the key process, it is concluded that the mechanism of the order formation is composed of two successive processes and the rate-determining step varies depending on the ionic strength. 相似文献
4.
5.
6.
The capillary immutability due to corrosion of glasses exposed to various solutions was studied. The analytical error of volume change caused by glass corrosion in a micro- and ultramicronitrometer was discussed. The present work has shown that the graduated tube of a decimicronitrometer made of borosilicate glass, which is used frequently in Dumas method, should be recalibrated after 1.5–2.3 months use. We therefore recommend the sealed tube method using an improved nitrometer for ultramicrodetermination of nitrogen in organic compounds. 相似文献
7.
Single nucleotide polymorphisms (SNPs) of cancer repression gene p53 were analyzed electrochemically with ferrocenyl naphthalene diimide (1) as a hybridization indicator. The SNPs studied were the transition to A from G in the codon for amino acid at positions 175, 248 or 273 and the transversion to C from G in the codon for the amino acid at position 72. Thus, 20-meric oligonucleotides carrying the SNP site were used both as a sample and a probe with the latter immobilized on an electrode. Even one base difference on the p53 gene resulted in a significant difference in the current response of 1 and the magnitude of the response correlated with the amount of the DNA hybrid on the electrode. Moreover, when PCR products of exon 4, on which the P72/R72 SNP resides, of the p53 gene were analyzed by this method, the heterozygote and homozygotes were discriminated with modest precision. 相似文献
8.
We have shown the Lennard-Jones (LJ) phase diagram for a slit-shaped nanopore by molecular simulations and thermodynamically
predicted the results with no adjustable parameter. With this success, LJ phase diagrams are predictable. In this study, the
freezing of an LJ CH4 capillary condensate under a tensile condition in a nonstructural carbon nanopore with a cylindrical geometry was examined
using molecular dynamics (MD) simulation. We employ a unit cell in contact with a bulk vapor phase, which is useful for the
determination of the bulk vapor pressure in equilibrium with the molecules in a pore. The MD simulation results show liquid-solid
(amorphous) phase transitions with a variation in the bulk vapor pressure. The frozen particles are arranged in concentric
circular regions along the wall similar to those reported by Maddox and Gubbins. The freezing points are determined from the
variations in density, enthalpy, arrangement, and structural functions. The obtained liquid-solid coexistence points are found
to exhibit a significant dependence of the freezing point on the equilibrium bulk vapor pressure, forming an extraordinarily
skewed curve on the p-T diagram, in contrast to the bulk phase coexistence that is represented by an almost vertical line.
The origin of the significant dependence is considered to be the Laplace effect on the capillary condensate similar to the
case with a slit-shaped pore. A simple model, which the authors earlier presented for slit-shaped nanopores, successfully
predicted the p-T relation of the freezing point for cylindrical nanopores as well. 相似文献
9.
Otohiko Tsuge Taizo Hatta Hisashi Kojima Nobutaka Miyahara Masafumi Sugaya 《Journal of heterocyclic chemistry》1994,31(5):1283-1287
2-Benzoyl- 5 and 2-acetylacenaphthenone 6 , prepared from the corresponding 1-acyl-2-(1-pyrrolidinyl)-acenaphthylenes 2 and 3 , reacted with arylhydrazines 8 under acidic conditions to give the corresponding 1-arylacenaphtho[1,2-d]pyrazoles 9 and 10 . Novel heteropentalene mesomeric betaines, 5,7-dehydro-5H,7H-benzo[b]acenaphtho[1,2-e]-1,3a,6a-triazapentalenes 13 and 14 were prepared by reductive cyclization of 1-(o-nitrophenyl)acenaphtho[1,2-d]pyrazoles 9d and 10d , respectively. 相似文献