全文获取类型
收费全文 | 567篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 437篇 |
晶体学 | 6篇 |
力学 | 5篇 |
数学 | 12篇 |
物理学 | 131篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 16篇 |
2014年 | 23篇 |
2013年 | 30篇 |
2012年 | 21篇 |
2011年 | 32篇 |
2010年 | 20篇 |
2009年 | 21篇 |
2008年 | 32篇 |
2007年 | 17篇 |
2006年 | 35篇 |
2005年 | 30篇 |
2004年 | 38篇 |
2003年 | 37篇 |
2002年 | 30篇 |
2001年 | 19篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1966年 | 1篇 |
1960年 | 1篇 |
1929年 | 2篇 |
排序方式: 共有591条查询结果,搜索用时 31 毫秒
501.
Tatsuaki Nakanishi Yasuhiro Shirai Takeshi Yasuda Liyuan Han 《Journal of polymer science. Part A, Polymer chemistry》2012,50(23):4829-4839
We study the degree of π?π interactions in two copolymers composed of 2‐octylbenzotriazole and dialkyldithienosiloles with linear hexyl (P1) and branched 2‐ethylhexyl groups (P2). Although the branched ethyl group can be positioned above the π‐plane of dithienosilole to bring disadvantage to stack among the polymers, the solid‐state absorption spectra of the polymers reveal that P2 possesses stronger interchain interactions than P1. We also evaluate the photovoltaic properties of each polymer with [6,6]‐phenyl‐C71‐butyric acid methyl ester. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
502.
Norihito Hiyoshi Chandrashekhar V. Rode Osamu Sato Masayuki Shirai 《Research on Chemical Intermediates》2008,34(8-9):767-770
The hydrogenation behavior of tetralin in the presence and absence of benzothiophene was studied over a charcoal-supported rhodium catalyst in supercritical carbon dioxide solvent. The catalyst activity, as well ascis-decalin selectivity, decreased in the presence of benzothiophene. 相似文献
503.
In order to evaluate more precise kinetics parameters: rate constant k and Ea values for poly(l-lactic acid) hydrolysis, the reaction was carried out under high-pressure steam in a temperature range of 100-130 °C. Molecular weights of hydrolyzates were calculated by the universal calibration method without being influenced by any weight loss. The changes in molecular weight could be successfully explained according to the auto-catalytic hydrolysis mechanism, clearly indicating the critical point. Resulting k and Ea values were estimated as 8.4 × 10−5-7.2 × 10−4 s−1 and 87.2 kJ mol−1 with high R2 values, respectively. Moreover, to determine the deviation of the parameter values, influences of four factors on the measurements and calculation: (1) use of number-average molecular weight value alone, (2) use of relative molecular weight based on polystyrene standards, (3) weight loss during the hydrolysis, and (4) selection of reaction mechanism were evaluated quantitatively. 相似文献
504.
Palladium-catalyzed 1,2-addition of potassium aryl- and alkenyltrifluoroborates to aldehydes using thioether-imidazolinium carbene ligands proceeded readily under aqueous conditions. This process tolerated a diverse range of potassium trifluoroborate salts and aldehydes, giving a variety of carbinol derivatives with good to excellent yields. 相似文献
505.
Kamikubo H Koyama T Hayashi M Shirai K Yamazaki Y Imamoto Y Kataoka M 《Photochemistry and photobiology》2008,84(4):895-902
To study the role of the C-terminal domains in the photocycle of a light sensor histidine kinase (Ppr) having a photoactive yellow protein (PYP) domain as the photosensor domain, we analyzed the photocycles of the PYP domain of Ppr (Ppr-PYP) and full-length Ppr. The gene fragment for Ppr-PYP was expressed in Escherichia coli, and it was chemically reconstituted with p-coumaric acid; the full-length gene of Ppr was coexpressed with tyrosine ammonia-lyase and p-coumaric acid ligase for biosynthesis in cells. The light/dark difference spectra of Ppr-PYP were pH sensitive. They were represented as a linear combination of two independent difference spectra analogous to the PYP(L)/dark and PYP(M)/dark difference spectra of PYP from Halorhodospira halophila, suggesting that the pH dependence of the difference spectra is explained by the equilibrium shift between the PYP(L)- and PYP(M)-like intermediates. The light/dark difference spectrum of Ppr showed the equilibrium shift toward PYP(L) compared with that of Ppr-PYP. Kinetic measurements of the photocycles of Ppr and Ppr-PYP revealed that the C-terminal domains accelerate the recovery of the dark state. These observations suggest an interaction between the C-terminal domains and the PYP domain during the photocycle, by which light signals captured by the PYP domain are transferred to the C-terminal domains. 相似文献
506.
Man-Li Zhang Xiao-Ning Li Fançoise Sauriol Qing-Wen Shi Hiromasa Kiyota Bin Cong 《Tetrahedron letters》2008,49(21):3405-3408
A taxane with an amino-side chain on C-5 was identified for the first time from rooted cuttings of the Canadian yew, Taxus canadensis. The structure was characterized as 7β,9α,10β,13α-tetraacetoxy-5α-[3′-(N-formyl-N-methylamino)-3′-phenylpropanoyl]oxytaxa-4(20),12-diene (1) on the basis of 1D-, 2D-NMR data, and HR-FABMS analyses. The spectra revealed that in CDCl3 solution 1 was composed of two rotamers (1a and 1b) in a ratio of approximately 2:1. 相似文献
507.
Yamakawa N Sumimoto M Matsumoto T Yuto K Yoshikawa Y Goto M Yamaguchi Y Kurosaki H 《Chemical & pharmaceutical bulletin》2008,56(1):64-69
(1)H-NMR spectra of square-planar complexes with the formula [Pt(L(1))(L(2))]X(2) where L(1) is 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) and L(2) is N-(1-naphthyl)methyl-1,2-ethanediamine (Npen) or N-(9-anthryl)methyl-1,2-ethanediamine (Aten) indicate that the N-naphthylmethyl and N-anthrylmethyl groups are forced to adopt a pseudo axial disposition due to intramolecular repulsion of hydrogen atoms of the aromatic diimines. The aromatic-aromatic interactions in the N-arylmethyl-1,2-ethanediamine complexes and aromatic diimines caused them to undergo intramolecular stacking. (1)H-NMR spectra of these complexes showed a significant concentration and temperature dependence. The monomer-dimer equilibrium was estimated, based on the concentration dependency. Restricted single bond rotation was estimated from temperature dependency data. The rotation of the anthracene ring of the [Pt(bpy)(Aten)](2+) complex showed an activation energy of ca. 38 kJ mol(-1), which is in good agreement with a mechanism involving successive rotations about single bonds with restriction by intramolecular aromatic-aromatic ring interactions. 相似文献
508.
Kohichi Kashiwagi Ryoji Sugise Toshihiro Shimakawa Tunao Matuura Masashi Shirai 《Journal of molecular catalysis. A, Chemical》2008,286(1-2):120-123
A study of inhibitors in the dimerization of acrylonitrile using the novel catalytic system of [RuCl2(DMSO)4/CH3CH2COONa/DMSO/o-benzoylbenzoic acid] was carried out by examining the effect of reaction products on the catalytic activity. 1,4-Dicyanobuta-1,3-diene (3), one of the linear dimer products of acrylonitrile, inhibited the Ru-catalyzed reaction. Methylthiomethyl o-benzoylbenzoate (8), a by-product which was produced from carboxylic acid and DMSO under the reaction conditions, also acted as an inhibitor. 相似文献
509.
Uncoupler-mediated cation transport has been investigated by cyclic voltammetry for the ion transfer from one aqueous phase (W1) to another (W2) across a bilayer lipid membrane (BLM) in the presence of typical uncouplers, 3,5-di(tert-butyl)-4-hydroxybenzylidenemalononitril (SF6847) and 2,4-dinitrophenol (DNP). The voltammograms for the ion transfer were in a steady state and exhibited a rotated sigmoidal shape that was almost symmetrical about the origin (0 V, 0 A). The plot of the ion transfer current against pH was a bell-type curve centered on pH approximately = pK(a) + 1, K(a) being the dissociation constant of the uncouplers in the aqueous phase. Taking into account the ion transfer reactions at the W1|BLM and the BLM|W2 interfaces, these properties were well explained by our proposed model which considers that the ion transfer current is attributable to the facilitated transfers of H(+) and Na(+). The buffer action in the aqueous phase was found to play an important role in the facilitated H(+)-transfer across the BLM. The nature of the pH-dependence of the ion transfer current was reasonably explained from an electrochemical viewpoint based on the distribution coefficient of the anionic and neutral forms of SF6847, as estimated from its absorption spectra in liposomal membrane. The proposed model is also valuable for understanding the pH-dependence of uncoupling activity in mitochondria in the literature. 相似文献
510.
A wavelength-agile mid-infrared (IR) ZnGeP2 (ZGP) optical parametric oscillator (OPO) using a galvano-controlled double-crystal KTiOPO4 (KTP) OPO was demonstrated. The mid-IR wavelength was tuned by varying the KTP OPO pump wavelength while the ZGP crystal angle remained fixed. Rapid tuning of the KTP OPO was achieved by changing the crystal angle by using the galvano scanner. Our mid-IR source can jump to a different wavelength without scanning through the intermediate wavelengths while also permitting continuous-wavelength scanning. The mid-IR source can be tuned from approximately 5to10 microm at a phase-matching angle of 51 degrees , while the pump wavelength is controlled in the 1.95-2.2 microm range. 相似文献