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排序方式: 共有197条查询结果,搜索用时 15 毫秒
81.
Akira Imamura Kazuyoshi Tanaka Tokio Yamabe Kenichi Fukui 《Theoretical chemistry accounts》1979,54(1):1-14
A non-empirical tight-binding LCAO SCF MO treatment of one-dimensional molecular crystals based on the SCF perturbation theory
is presented. The simpler version of this method at the level of the CNDO/2 approximation is also given. 相似文献
82.
Yoshimasa Orita Akio Ando Hiroshi Abe Shin-ichi Yamabe Hélène Berthod Alberte Pullman 《Theoretical chemistry accounts》1979,54(1):73-82
SCFab initio computations have been performed on the structure, molecular potential and hydration scheme of thiourea in view of a comparison
with urea and more generally as a model of the conjugated S=CNH-group as compared to O=CNH-. In contrast to the carbonyl oxygen,
both σ and π acceptor, the sulfur atom of the thiocarbonyl is a σ donor but a π acceptor and this results in an enhancement
of the double-bond character of thiourea. The CN bond is less attractive for a proton than urea. The hydration scheme indicates
a maximum number of four water molecules directly bound to thiourea. 相似文献
83.
The charge distributions in octahedral PF?6, AsF?6, and SbF?6 anions are studied by means of the ab initio molecular orbital method. We find that the central P, As, and Sb atoms are all positively charged in these anions, while F atoms negatively charged, the order of the positive charge being Sb > P > As. 相似文献
84.
A fundamental reduction reaction, nitrobenzene to aniline in SnCl2 and hydrochloric acid, was investigated by density functional theory (DFT) calculations. First, the change of SnCl2 → SnCl42? → Cl4SnH? was discussed, and the reaction path of SnCl42? + H3O+ → Cl4SnH? + H2O was obtained. Starting from nitrobenzene, six elementary processes were found so as to arrive at the protonated aniline. The hydride ion from Cl4SnH? is connected always to the cationic nitrogen, and the proton is always to oxygens. An intermediate Ph?N+H2OH was obtained, which is isomerized to the para O?H adduct protonated imine via the Bamberger rearrangement. This species may undergo the H? acceptance at the sp2 N+H2 center. In the nitrobenzene reduction, the proton enhances the electrophilicity of the nitrogen center, which makes the hydride shift ready. N?H bonds are formed, and N?O bonds are cleaved both by the proton attach and subsequent H2O elimination and by the formal [1,5] OH shift. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
85.
Nitrogen incorporation in saturated aliphatic C6–C8 hydrocarbons and ethanol in low‐pressure nitrogen plasma generated by a hollow cathode discharge ion source
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Dilshadbek T. Usmanov Lee Chuin Chen Kenzo Hiraoka Hiroshi Wada Hiroshi Nonami Shinichi Yamabe 《Journal of mass spectrometry : JMS》2016,51(6):446-452
Ion/molecule reactions of saturated hydrocarbons (n‐hexane, cyclohexane, n‐heptane, n‐octane and isooctane) in 28‐Torr N2 plasma generated by a hollow cathode discharge ion source were investigated using an Orbitrap mass spectrometer. It was found that the ions with [M+14]+ were observed as the major ions (M: sample molecule). The exact mass analysis revealed that the ions are nitrogenated molecules, [M+N]+ formed by the reactions of N3+ with M. The reaction, N3+ + M → [M+N]+ + N2, were examined by the density functional theory calculations. It was found that N3+ abstracts the H atom from hydrocarbon molecules leading to the formation of protonated imines in the forms of R′R″C?NH2+ (i.e. C–H bond nitrogenation). This result is in accord with the fact that elimination of NH3 is the major channel for MS/MS of [M+N]+. That is, nitrogen is incorporated in the C–H bonds of saturated hydrocarbons. No nitrogenation was observed for benzene and acetone, which was ascribed to the formation of stable charge‐transfer complexes benzene????N3+ and acetone????N3+ revealed by density functional theory calculations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
86.
Shinichi Yamabe Shoko Yamazaki Shigeyoshi Sakaki 《International journal of quantum chemistry》2015,115(21):1533-1542
Hydride‐transfer reactions between benzylic substrates and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) were investigated by DFT (density functional theory) calculations. The lowest unoccupied molecular orbital of DDQ has the largest extension on two carbonyl oxygens, which comes from two‐step mixing of antisymmetric orbitals of fragment π MOs. Transition‐state (TS) geometries and activation energies of reactions of four benzylic substrates R2? CH2‐para‐C6H4? R1 (R1, R2 = H and/or OCH3) with DDQ were calculated. M06‐2X/6‐311(+*)G* was found to be a practical computational method, giving energies and geometries similar to those of M06‐2X/6‐311++G(3df,2pd) and wB97xD/6‐311++G(3df,2pd). For toluene (R1 = R2 = H), an initiation‐propagation model was suggested, and the calculated kinetic isotope effect k(H)/k(D) = 5.0 with the tunnel correction at the propagating step is in good agreement with the experimental value 5.2. A reaction of para‐MeO? C6H4? CH2(OMe) + DDQ + (H2O)14 → para‐MeO? C6H4? C(?O)H + HOMe + DDQH2 + (H2O)13 was investigated by M06‐2X/6‐311(+*)G*. Four elementary processes were found and the hydride transfer (TS1) is the rate‐determining step. The hydride transfer was promoted by association with the water cluster. The size of the water cluster, (H2O)n, at TS1 was examined. Three models of n = 14, 20, and 26 were found to give similar activation energies. Metal‐free neutral hydride transfers from activated benzylic substrates to DDQ were proposed to be ready processes both kinetically and thermodynamically. © 2015 Wiley Periodicals, Inc. 相似文献
87.
Atmospheric pressure chemical ionization of explosives using alternating current corona discharge ion source
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Dilshadbek Tursunbaevich Usmanov Lee Chuin Chen Zhan Yu Shinichi Yamabe Shigeyoshi Sakaki Kenzo Hiraoka 《Journal of mass spectrometry : JMS》2015,50(4):ii-ii
The high‐sensitive detection of explosives is of great importance for social security and safety. In this work, the ion source for atmospheric pressure chemical ionization/mass spectrometry using alternating current corona discharge was newly designed for the analysis of explosives. An electromolded fine capillary with 115 µm inner diameter and 12 mm long was used for the inlet of the mass spectrometer. The flow rate of air through this capillary was 41 ml/min. Stable corona discharge could be maintained with the position of the discharge needle tip as close as 1 mm to the inlet capillary without causing the arc discharge. Explosives dissolved in 0.5 µl methanol were injected to the ion source. The limits of detection for five explosives with 50 pg or lower were achieved. In the ion/molecule reactions of trinitrotoluene (TNT), the discharge products of NOx? (x = 2,3), O3 and HNO3 originating from plasma‐excited air were suggested to contribute to the formation of [TNT ? H]? (m/z 226), [TNT ? NO]? (m/z 197) and [TNT ? NO + HNO3]? (m/z 260), respectively. Formation processes of these ions were traced by density functional theory calculations. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
88.
Kusama H Karibe Y Imai R Onizawa Y Yamabe H Iwasawa N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(17):4839-4848
Tungsten(0)- and rhenium(I)-catalyzed reactions of acetylenic dienol silyl ethers based on the concept of geminal carbo-functionalization of alkynes are reported. Treatment of 3-siloxy-1,3-diene-7-ynes with catalytic amounts of [W(CO)(6)] or [ReCl(CO)(5)] under photoirradiation conditions gives synthetically useful bicyclo[3.3.0]octane derivatives in good yields. Extremely high catalytic activity is noted for the rhenium(I) complex. The reaction has been extended to substrates containing a nitrogen atom in their tethers. In this case, two kinds of synthetically useful heterocyclic compounds-the 2-azabicyclo[3.3.0]octane derivatives 9 and the monocyclic dihydropyrroles 10, with allenyl substituents-are obtained, and selective preparation of either product can be achieved through the use of an appropriate combination of the nitrogen substituent and the type of the rhenium(I) catalyst. The 2-azabicyclo[3.3.0]octane derivatives 9 are obtained selectively by carrying out treatment of N-Ns derivatives in the presence of [ReCl(CO)(4)(PPh(3))], whereas the dihydropyrrole derivatives 10 are obtained by treatment of N-Mbs derivatives with [ReCl(CO)(5)]/AgSbF(6) . Finally, we have applied this geminal carbo-functionalization to one-carbon-elongated substrates containing N-Ts moieties in their tethers. Selective 5-exo cyclization is achieved in the presence of gold(I) or rhenium(I) catalysts, whereas 6-endo cyclization is observed on use of [W(CO)(6)]. 相似文献
89.
N. Yoshikawa S. Yamabe N. Kanehisa T. Inoue H. Takashima K. Tsukahara 《Journal of Physical Organic Chemistry》2011,24(11):1110-1118
Electronic structures of binuclear ruthenium complexes [Ru2(terpy)2(tppz)]4+ ( 1A ) and [Ru2Cl2(L)2(tppz)]2+ {L = bpy ( 2A ), phen ( 3A ), and dpphen ( 4A )} were studied by density functional theory calculations. Abbreviations of the ligands (Ls) are bpy = 2,2′‐bipyridine, phen = 1,10‐phenanthroline, dpphen = 4,7‐diphenyl‐1,10‐phenanthroline, terpy = 2,2′:6′,2″‐terpyridine, and tppz = tetrakis(2‐pyridyl)pyrazine. Their mononuclear reference complexes [Ru(terpy)2]2+ ( 1B ) and [RuClL(terpy)]+ {L = bpy ( 2B ), phen ( 3B ), and dpphen ( 4B )} were also examined. Geometries of these mononuclear and binuclear Ru(II) complexes were fully optimized. Their geometric parameters are in good agreement with the experimental data. The binuclear complexes were characterized by electrospray ionization mass spectrometry, UV–Vis spectroscopy, and cyclic voltammograms. Hexafluorophosphate salts of binuclear ruthenium complexes of 3A and 4A were newly prepared. The crystal structure of binuclear complex 1A (PF6)4 was also determined. Orbital interactions were analyzed to characterize the metal‐to‐ligand charge‐transfer (MLCT) states in these complexes. The Cl? ligand works to raise the orbital energy of the metal lone pair, which leads to the low MLCT state. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
90.
For the parent reacting system, HCOOOH + CH(2)=CH(2) --> HCOOH + ethylene oxide, the overall potential energy surface has been determined using ab initio methods. The oxygen-addition transition state is found to be remarkably similar to that deduced experimentally. The O-H bond is retained in the transition state. Reasonable kinetic isotopic effects are obtained theoretically. The transition state leads to an unprecedented transient intermediate. That intermediate is converted to a hydrogen-bonded system between ethylene oxide and formic acid. Substituent effects on transition-state geometries are small, but the effects on activation energies are large. 相似文献