全文获取类型
收费全文 | 191篇 |
免费 | 5篇 |
专业分类
化学 | 89篇 |
晶体学 | 11篇 |
力学 | 4篇 |
数学 | 2篇 |
物理学 | 90篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 10篇 |
2012年 | 15篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 4篇 |
2008年 | 17篇 |
2007年 | 11篇 |
2006年 | 18篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有196条查询结果,搜索用时 15 毫秒
61.
62.
M.?IzquierdoEmail author L.?Roca J.?Avila G.?Gu Z. Z.?Li H.?Raffy M. C.?Asensio 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,46(3):309-314
Angle resolved photoemission spectroscopy (ARPES) has been
used to investigate the shadow bands present at the Fermi surface of
bismuth based superconductors. Bi2Sr2CaCu2O8+δ
(Bi2212) single crystals with different doping levels and
Bi2Sr2CuO6+δ (Bi2201) thin films have been studied
by means of momentum distribution curves along the ΓY high
symmetry direction in two different Brillouin zones and for an
extensive photon energy range. The results show an enhancement of
the shadow band intensity in the second Brillouin zone for photon
energies around hν=30 eV. Furthermore, the ratio Shadow
Bands/Main Band is shown to be constant as a function of both the
doping level and the number of CuO2 planes. An interpretation of
this observation on the basis of the current theoretical models will
be provided. 相似文献
63.
van Eis MJ van Der Linde BS de Kanter FJ de Wolf WH Bickelhaupt F 《The Journal of organic chemistry》2000,65(14):4348-4354
In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway. 相似文献
64.
Claude Roca Raymond Kraemer Jean-Pierre Majoral Jacques Navech Jean Franois Brault Philippe Savignac 《Magnetic resonance in chemistry : MRC》1976,8(8):407-412
The 1H n.m.r. spectra of some new 1,3,2-oxazaphosphorinanes are analysed. The stereochemistry and the ring conformation is discussed. The free energy and the torsional angle of the C-4? C-5 and C-5? C-6 fragments are calculated for some of these 1,3,2-oxazaphosphorinanes. 相似文献
65.
Ruggiero GD Williams IH Roca M Moliner V Tuñón I 《Journal of the American Chemical Society》2004,126(28):8634-8635
Secondary alpha-D3 kinetic isotope effects calculated by the hybrid AM1/TIP3P/CHARMM method for the reaction of S-adenosylmethionine with catecholate anion in aqueous solution and catalyzed by rat liver catechol O-methyltransferase at 298 K are 0.94 and 0.85, respectively, in good accord with experiment. The large inverse effect for the enzymatic reaction is not due to compression but arises from significant increases in the stretching and bending force constants involving the isotopically substituted atoms of the transferring methyl group as between the reactant complex and the transition structure, larger than for the reaction in water. 相似文献
66.
Martí S Roca M Andrés J Moliner V Silla E Tuñón I Bertrán J 《Chemical Society reviews》2004,33(2):98-107
In this tutorial review we show how the methods and techniques of computational chemistry have been applied to the understanding of the physical basis of the rate enhancement of chemical reactions by enzymes. This is to answer the question: Why is the activation free energy in enzyme catalysed reactions smaller than the activation free energy observed in solution? Two important points of view are presented: Transition State (TS) theories and Michaelis Complex (MC) theories. After reviewing some of the most popular computational methods employed, we analyse two particular enzymatic reactions: the conversion of chorismate to prephenate catalysed by Bacillus subtilis chorismate mutase, and a methyl transfer from S-adenosylmethionine to catecholate catalysed by catechol O-methyltransferase. The results and conclusions obtained by different authors on these two systems, supporting either TS stabilisation or substrate preorganization, are presented and compared. Finally we try to give a unified view, where a preorganized enzyme active site, prepared to stabilise the TS, also favours those reactive conformations geometrically closer to the TS. 相似文献
67.
José Lamartine Soares-Sobrinho Monica Felts de La Roca Soares Pedro José Rolim-Neto Juan J. Torres-Labandeira 《Journal of Thermal Analysis and Calorimetry》2011,106(2):319-325
Although not being the ideal drug due to its low solubility and high toxicity, the benznidazole is the drug currently chosen
for Chagas disease treatment. The deep knowledge about the characteristics of the drug in addition to the knowledge of more
effective vectorization techniques of drugs in pharmaceutical forms allows a faster and cheaper development of a new therapeutic
alternative in comparison to the introduction of a new molecule in the treatment. The aim of this study is the characterization
of inclusion complexes Benznidazole and cyclodextrins in solid state. The interactions between Benznidazole (BNZ) and β-cyclodextrins
(β-CD) modified: randomly methylated β-CD (RMβCD) and sulfobutylether β-CD (SBβCD) were studied by differential scanning calorimetry
(DSC), fourier transform-infrared spectroscopy, RAMAN, and scanning electron microscopy. The preparation of solid-state binary
systems by different techniques, namely, kneading, evaporated, and freeze-drying. The results suggest the formation of inclusion
complexes of the drug with both CDs types in solid state by the techniques which were used, based on physicochemical data
of interaction compared to the drug or the CDs/drug physical mixture. Thus, the preparation technique played an important
role in the BNZ and modified CDs. 相似文献
68.
Andrew Fairbrother Xavier Fontané Dr. Victor Izquierdo‐Roca Moises Espindola‐Rodriguez Simon López‐Marino Dr. Marcel Placidi Dr. Juan López‐García Prof. Alejandro Pérez‐Rodríguez Dr. Edgardo Saucedo 《Chemphyschem》2013,14(9):1836-1843
Pentenary Cu2ZnSn(SySe1?y)4 (kesterite) photovoltaic absorbers are synthesized by a one‐step annealing process from copper‐poor and zinc‐rich precursor metallic stacks prepared by direct‐current magnetron sputtering deposition. Depending on the chalcogen source—mixtures of sulfur and selenium powders, or selenium disulfide—as well as the annealing temperature and pressure, this simple methodology permits the tuning of the absorber composition from sulfur‐rich to selenium‐rich in one single annealing process. The impact of the thermal treatment variables on chalcogenide incorporation is investigated. The effect of the S/(S+Se) compositional ratio on the structural and morphological properties of the as‐grown films, and the optoelectronic parameters of solar cells fabricated using these absorber films is studied. Using this single‐step sulfo‐selenization method, pentenary kesterite‐based devices with conversion efficiencies up to 4.4 % are obtained. 相似文献
69.
70.
A. Di Pietro G. Cardella A. Musumarra M. Papa G. Pappalardo F. Rizzo A. De Rosa A. D'Onofrio G. Inglima V. Roca M. Romano M. Romoli M. Sandoli F. Terrasi E. Fioretto 《Zeitschrift für Physik A Hadrons and Nuclei》1994,350(3):199-205
The28Si+64Ni reaction at 163.8 MeV incident energy is studied by measuring in coincidenceγ-rays and charged particles identified from Z=2 to Z=16. The transition from quasi-elastic to more damped reactions is observed when the difference between the detected charge and the projectile one is increased. The strong influence of the particle decay on the measuredγ-ray multiplicity is evidenced with the help of the statistical model computer code CASCADE. Dissipative events are well described in the rolling limit with excitation energy equally shared between the fragments. The overall agreement is lost for the fragments with the projectile charge which show a small value of theγ-multiplicity even for dissipative events. This is probably connected with the previously observed non statistical behavior of gamma rays emitted in coincidence with projectile-like fragments. In the alpha-spectrum measured in coincidence with gamma-rays, the deexcitation of fused systems is clearly separated from in flight emission of deep inelastic fragments. The low measured gamma-ray multiplicity for fusion events is qualitatively explained taking into account the effect of alpha-emission in the statistical decay. 相似文献