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521.
Upon reaction of the 3',4'-unsaturated adenosine derivative 2 with N-iodosuccinimide (NIS) and thiophenol, an unexpected electrophilic hydrophenylsulfanylation proceeded to provide 4'-phenylsulfanylcordycepin 7 in 79% yield with the ratio 7a/7b = 6.6/1. A study of the reaction mechanism revealed that hydrogen iodide (HI) generated from NIS and PhSH acted as an active species. On the basis of a deuterium experiment using PhSD, initial protonation occurred at the β face of the double bond to furnish the β-π complex III, which underwent anti addition of PhSH as a major pathway. Nucleophilic substitution of N(6)-pivaloylated 9 with various alcohols in the presence of N-bromosuccinimide (NBS) gave the respective 4'-α-alkoxycordycepins 15a-21a as the major stereoisomers. Use of DAST in place of an alcohol gave the 4'-α-fluoro analogue 23a stereoselectively. Radical-mediated carbon-carbon bond construction was also applicable to 7, giving 4'-α-allylcordycepin (24a) and 4'-α-cyanoethylcordycepin (25) derivatives. 相似文献
522.
Haraguchi K Horii C Yoshimura Y Ariga F Tadokoro A Tanaka H 《The Journal of organic chemistry》2011,76(21):8658-8669
We have developed a novel method for the synthesis of the β-anomer of 4'-thio-C-ribonucleosides from 3,5-O-(di-tert-butylsilylene)-4-thiofuranoid glycal. Palladium-catalyzed coupling of 1-tributylstannyl-4-thiofuranoid glycal with iodobenzene or a heteroaryl halide gave 1-C-phenyl- or 1-C-heteroaryl-glycals. Hydroboration of these glycals proceeded at the α-face, and subsequent alkaline hydrogen peroxide treatment of the resulting 2'-α-borane furnished the respective β-anomer of 4'-thio-C-ribonucleosides. These results demonstrate that this synthetic method has a wider scope in terms of heterocyclic base structure. During this study, unexpected Markovnikov-oriented hydroboration has been observed to lead to the respective 1'-α-boranes. These 1'-boranes were converted into either the ring-opened structure or the 2'-deoxy derivatives depending upon their stability. 相似文献
523.
Takamasa Seta Hiromichi Hoshina Iwao Hosako Stefan Loßow Mattias Ekström Donal Murtagh 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(1):144-150
The air induced broadening coefficients of the pure rotational transitions of H2O at 556.936 GHz (110←101), and 752.033 GHz (211←202) were measured by terahertz time-domain spectroscopy. The air broadening coefficient was determined to be for the 556.936 GHz line and for the 752.033 GHz line, respectively. The present broadening coefficients for the 556.936 GHz water line are significantly smaller than those of Markov and Krupnov [Measurements of the pressure shift of the 1(10)-1(01) water line at 556.936 GHz produced by mixtures of gases. J Mol Spect 1995:172;211-4] but relatively close to the values of the HITRAN database. The measured data may improve the accuracy of the abundance of water vapor retrieved from spectra obtained by the Odin/SMR satellite instrument. The effect on the satellite retrieval processing is discussed. 相似文献
524.
525.
Ishida Y Eguchi R Matsunami M Horiba K Taguchi M Chainani A Senba Y Ohashi H Ohta H Shin S 《Physical review letters》2008,100(5):056401
Resonant photoemission at the Ti 2p and O 1s edges on a Nb-doped SrTiO(3) thin film revealed that the coherent state (CS) at the Fermi level (E(F)) had a mainly Ti 3d character whereas the incoherent in-gap state (IGS) positioned approximately 1.5 eV below E(F) had a mixed character of Ti 3d and O 2p states. This indicates that the IGS is formed by a spectral-weight transfer from the CS and subsequent spectral-weight redistribution through d-p hybridization. We discuss the evolution of the excitation spectrum with 3d band filling and rationalize the IGS through a mechanism similar to that proposed by Haldane and Anderson. 相似文献
526.
The kinetics of CO molecules with excited electronic levels for a nonequilibrium flow in nozzles is studied. Three electronic energy levels are taken into account; the VV exchanges of the vibrational energy within each electronic energy level, VT transitions from the vibrational energy to the translational energy, and VE exchanges between the vibrational energy and the electronic terms occur in the system. The system of equations of vibrational level kinetics and gasdynamics, which is written in the zeroth approximation of the Chapman–Enskog method, is solved numerically. Special attention is paid to estimating the effect of the VE exchanges of the vibrational energy on the formation of nonequilibrium populations of the vibrational levels. It is shown that resonant VE transitions considerably affect the relaxation process and noticeably change the population of the upper vibrational levels even in the absence of recombination and dissociation processes; VE exchanges also affect the time dependence of the vibrational temperature. 相似文献
527.
R.W. Kempf P.T. Wilson J.D. Canterbury E.D. Mishina O.A. Aktsipetrov M.C. Downer 《Applied physics. B, Lasers and optics》1999,68(3):325-332
2 and Si(110)-SiO2 interfaces and DC-electric-field induced TH and FH generation is then observed in Si(111)-SiO2-Cr and Si(110)-SiO2-Cr MOS structures for the first time. A systematic phenomenological analysis of azimuthal anisotropy of TH and FH generation
intensity is performed for (111) and (110) surfaces of Oh symmetric single crystals. A phenomenological model of electro-induced effects in TH and FH generation is then developed
and the surface specificity and sensitivity of TH and FH generation are discussed. Optical interference of surface electro-induced
and bulk bias-independent contributions to the effective third-order nonlinear polarization is proposed as the mechanism underlying
surface sensitivity of electro-modulated TH probe.
Received: 16 October 1998 相似文献
528.
Masayori Fujioka Hideyuki Okada Yukihiko Kusaka Satoko Nishiyama Hiromichi Noguchi Shigeru Ishii Yasuhiko Yoshida 《Macromolecular rapid communications》2004,25(20):1776-1780
Summary: The title polymers, in which both the stem and the graft are biodegradable, have been synthesized for the first time in a one‐pot, lipase‐catalyzed, graft‐polymerization reaction (in bulk, at 70 °C) of β‐butyrolactone (β‐BL) and ε‐caprolactone (ε‐CL) onto chitin and chitosan. The reactivity order of the lactones was found to be ε‐CL > β‐BL ≫ γ‐BL (no reaction). All the graft polymers prepared are insoluble in common organic solvents.
529.
Yoshitaka Yamaguchi Noriyuki Suzuki Arno Fries Takaya Mise Hiroyuki Koshino Yuji Ikegami Hiromichi Ohmori Akira Matsumoto 《Journal of polymer science. Part A, Polymer chemistry》1999,37(3):283-292
Stereospecific polymerization of 1‐hexene under high pressures (up to 1,000 MPa = ca. 10,000 atm) using metallocene/methylaluminoxane (MAO) catalysts was investigated. Several C2‐symmetric ansa‐metallocenes, their meso‐isomers, and two Cs‐symmetric ansa‐metallocenes were employed as catalyst precursors. In the course of this study, novel C2‐symmetric germylene‐bridged ansa‐metallocenes, (rac‐[Me2Ge(η5‐C5H‐2,3,5‐Me3)2MCl2] (M = Zr, rac‐4a; M = Hf, rac‐4b), have been prepared. High pressures induced enhancement of the catalytic activity and the molecular weight of the polymers in most of the catalysts. The maximum of both the catalytic activity and the molecular weight of the polymers was mostly observed at 100–500 MPa in each catalyst, although the enhanced ratio was smaller than that observed for nonbridged metallocenes. Isospecificity of the C2‐symmetric ansa‐metallocene catalysts was essentially maintained even under high pressure. Highly isotactic polyhexene ([mmmm] = 91.6%) with very high molecular weight (Mw = 2,360,000) was achieved by rac‐4b under 250 MPa. High pressures slightly decreased syndiotacticity when the Cs‐symmetric ansa‐metallocene, isopropylidene(1‐η5‐cyclopentadienyl)(9‐η5‐fluorenyl)zirconium dichloride 5, was employed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 283–292, 1999 相似文献
530.