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131.
The coherent nonlinear response of the entire amide line shapes of N-methyl acetamide to three infrared pulses is simulated using an electrostatic density functional theory map. Positive and negative cross peaks contain signatures of correlations between the fundamentals and the combination state. The amide I-A and I-III cross-peak line shapes indicate positive correlation and anticorrelation of frequency fluctuations, respectively. These can be ascribed to correlated hydrogen bonding at C[double bond]O and N-H sites. The amide I frequency is negatively correlated with the hydrogen bond on carbonyl C[double bond]O, whereas the amide A and III are negatively and positively correlated, respectively, with the hydrogen bond on amide N-H. 相似文献
132.
Zhuang W Abramavicius D Hayashi T Mukamel S 《The journal of physical chemistry. B》2006,110(7):3362-3374
Two algorithms for simulating the response of peptides to sequences of IR pulses are developed and applied to N-methyl acetamide (NMA) and a 17 residue alpha-helical peptide (YKKKH17) in D(2)O. A fluctuating vibrational-exciton Hamiltonian for the amide I mode is constructed from molecular dynamics trajectories. Coupling with the environment is described using a density functional theory electrostatic map. The cumulant expansion of Gaussian fluctuation incorporates motional narrowing due to fast frequency fluctuations and is adequate for NMA and for isotopically labeled bands in large peptides. Real-space truncation of the scattering matrix of the nonlinear exciton equations significantly reduces the computational cost, making it particularly attractive for slow fluctuations in large globular proteins. 相似文献
133.
The stochastic Liouville equations are employed to investigate the combined signatures of chemical exchange (two-state jump) and spectral diffusion (coupling to an overdamped Brownian oscillator) in the coherent response of an anharmonic vibration to three femtosecond infrared pulses. Simulations reproduce the main features recently observed in the OD stretch of phenol in benzene. 相似文献
134.
Polarization tuning of the interference of chirality-induced tensor components is used to simulate the suppression of diagonal peaks and amplification of cross peaks in femtosecond two-dimensional photon echo signals of excitons in a chiral porphyrin dimer. Superpositions of various tensor components which generate the optimized signals are constructed using a genetic learning algorithm. Exciton couplings and bath correlations may be extracted from these highly resolved signals. 相似文献
135.
Catriona H. E. Rooney Dr. Ayelet Gamliel David Shaul Prof. Damian J. Tyler Dr. James T. Grist Prof. Rachel Katz-Brull 《Chemphyschem》2023,24(18):e202300144
Deuterated 13C sites in sugars (D-glucose and 2-deoxy-D-glucose) showed 6.3-to-17.5-fold higher solid-state dynamic nuclear polarization (DNP) levels than their respective protonated sites at 3.35T. This effect was found to be unrelated to the protonation of the bath. Deuterated 15N in sites bound to exchangeable protons ([15N2]urea) showed a 1.3-fold higher polarization than their respective protonated sites at the same magnetic field. This relatively smaller effect was attributed to incomplete deuteration of the 15N sites due to the solvent mixture. For a 15N site that is not bound to protons or deuterons ([15N]nitrate), deuteration of the bath did not affect the polarization level. These findings suggest a phenomenon related to DNP of X-nuclei directly bound to deuteron(s) as opposed to proton(s). It appears that direct binding to deuterons increases the solid-state DNP polarization level of X-nuclei which are otherwise bound to protons. 相似文献
136.
137.
EPR experiments carried out at various temperatures for partially hydroxylated nanocrystalline MgO exposed to atomic hydrogen reveal that the entrapped electrons arising from spontaneous dissociation of hydrogen atoms exhibit an antiferromagnetic ordering. The measured magnetic data is found to be compatible with a phenomenological model of interacting paramagnetic centres at high temperature, and with a Pauli like behaviour below a certain temperature. This is further corroborated with density functional calculations of the effective magnetic coupling parameter for Heisenberg model between entrapped electrons on suitable embedded cluster models of MgO nanocrystals. 相似文献
138.
The broadening of the NMR lines of a solute dissolved in a nematic solvent upon spinning of the sample is interpreted. This model is used to fit the broadening of the NMR lines of 1,2,3,4-tetrachlorobenzene dissolved in EBBA. 相似文献
139.
140.
Shaul P Green KD Rutenberg R Kramer M Berkov-Zrihen Y Breiner-Goldstein E Garneau-Tsodikova S Fridman M 《Organic & biomolecular chemistry》2011,9(11):4057-4063
Amongst the many synthetic aminoglycoside analogues that were developed to regain the efficacy of this class of antibiotics against resistant bacterial strains, the 1-N-acylated analogues are the most clinically used. In this study we demonstrate that 6'-N-acylation of the clinically used compound tobramycin and 6'-N-acylation of paromomycin result in derivatives resistant to deactivation by 6'-aminoglycoside acetyltransferase (AAC(6')) which is widely found in aminoglycoside resistant bacteria. When tested against AAC(6')- or AAC(3)-expressing bacteria as well as pathogenic bacterial strains, some of the analogues demonstrated improved antibacterial activity compared to their parent antibiotics. Improvement of the biological performance of the N-acylated analogues was found to be highly dependent on the specific aminoglycoside and acyl group. Our study indicates that as for 1-N-acylation, 6'- and 6'-N-acylation of aminoglycosides offer an additional promising direction in the search for aminoglycosides capable of overcoming infections by resistant bacteria. 相似文献