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11.
C.L. Chakrabarti S.B. Chang T.J. Huston P.C. Bertels J.T. Rogers R. Dick 《Analytica chimica acta》1985
The predictions of a theoretical model, embodied in a computer program, describing the heating characteristics of the furnace surface and the gas phase of an anisotropic pyrolytic graphite furnace heated by the capacitive discharge technique are compared with the experimental results obtained by optical pyrometry and by two-line atomic absorption spectrometry, respectively. The surface temperature gradient around the circumference of the type 1 furnace and along the optical axis of the type 3 furnace are calculated and compared with the measured temperatures. The weighted-average of the theoretically predicted gas temperature is in reasonable agreement with the effective vapour temperature measured by two-line atomic absorption method. The heating rate of the furnace does not have a significant effect on the temperature distribution of either the furnace surface or the gas phase. The effect of the difference in the temperature distribution of the type 1 and type 3 furnaces on the atomic absorption signals is also discussed. 相似文献
12.
Phenyl radicals have been generated by photodecomposition of nitrosobenzene isolated in solid argon at 12 K. In this medium the origin of the first UV absorption band of nitrosobenzene corresponding to theS
0 S
2 transition is found at 30260 cm–1. Excitation with an excess energy of 2200 cm–1 results in very efficient photodissociation. The fragments NO and phenyl are stable for many hours. Annealing of the sample above 35 K led to partial recombination and recovery of the absorption spectrum of nitrosobenzene. The UV spectrum of the phenyl radical was obtained in the wavenumber range 25000–45000 cm–1, apparently without contamination by other species. It shows sharp lines at 25220, 33880, and 34820 cm–1 and two broader maxima at 38360 and 41060 cm–1. Of these only the line at 34820 cm–1 had been assigned to the phenyl radical in earlier work. These data are compared to recent molecular orbital calculations.Dedicated to Prof. F. P. Schäfer on the occasion of his 65th birthday. 相似文献
13.
Two-photon excitation spectra of naphthalene and acenaphthene have been measured up to 50000 cm?1. In naphthalene. three two-photon allowed states are observed for which the symmetry assignment is confirmed by polarization. The corre- sponding transitions are also seen in acenaphthene. The experimental data are in excellent agreement with theoretical predictions. 相似文献
14.
The protonated form of 1,8-bis(dimethylamino)naphthalene (DMANH(+)) consists of a rigid, aromatic framework, substituted by two amino groups that are connected by a strong, symmetric (on the NMR time-scale) hydrogen bond bridge. The reorientational motion of the molecule in dimethylformamide-d7 solution was characterized by T(1) and NOE measurements for aromatic (13)C nuclei. Treating the reorientation of DMANH(+) as anisotropic rotational diffusion of a rigid body, the diffusion tensor was determined with good accuracy. Measurements and interpretation of (15)N T(1) and NOE indicate that the proton transfer between potential minima in the hydrogen bond bridge is faster than the molecular reorientation. 相似文献
15.
R. Sanduja G. E. Martin A. J. Weinheimer M. Alam M. B. Hossain Dick van der Helm 《Journal of heterocyclic chemistry》1984,21(3):845-848
The marine coelenterate Echinopora lamellosa (class Anthozoa, family Scleractinidae) was found to contain a number of unprecedented secondary metabolites which were isolated and identified as smilagenin (I), neodunol methyl ether (II), glycyrrhetic acid (III), 3β-acetoxyglycyrrhetic acid (IV), and 3β-acetoxy-11-deoxoglycyrrhetic acid (V). The structure of neodunol methyl ether was confirmed and its absolute configuration determined by the x-ray diffraction method. 相似文献
16.
Lawrence W Dick Jr. 《Analytica chimica acta》2004,511(2):197-205
The synthesis and the spectroscopic and potentiometric characterization of electropolymerized films obtained from neutral red (NR) on Pt surface are described. FT Raman and NMR spectroscopy were used for evaluation of the resulting poly(NR) layers. Then potentiometry was applied to study the characteristics of the complexation of carboxylates with the poly(NR) films. A potentiometric poly(NR) sensor showing high selectivity for citrate anion was employed for its determination in soft drinks. 相似文献
17.
Zhijia Wang Antonio Toffoletti Yuqi Hou Jianzhang Zhao Antonio Barbon Bernhard Dick 《Chemical science》2021,12(8):2829
The triplet state lifetimes of organic chromophores are crucial for fundamental photochemistry studies as well as applications as photosensitizers in photocatalysis, photovoltaics, photodynamic therapy and photon upconversion. It is noteworthy that the triplet state lifetime of a chromophore can vary significantly for its analogues, while the exact reason was rarely studied. Herein with a few exemplars of typical BODIPY derivatives, which show triplet lifetimes varying up to 110-fold (1.4–160 μs), we found that for these derivatives with short triplet state lifetimes (ca. 1–3 μs), the electron spin polarization (ESP) pattern of the time-resolved electron paramagnetic resonance (TREPR) spectra of the triplet state is inverted at a longer delay time after laser pulse excitation, as a consequence of a strong anisotropy in the decay rates of the zero-field state sublevel of the triplet state. For the derivatives showing longer triplet state lifetimes (>50 μs), no such ESP inversion was observed. The observed fast decay of one sublevel is responsible for the short triplet state lifetime; theoretical computations indicate that it is due to a strong coupling between the Tz sublevel and the ground state mediated by the spin–orbit interaction. Another finding is that the heavy atom effect on the shortening of the triplet state lifetime is more significant for the T1 states with lower energy. To the best of our knowledge, this is the first systematic study to rationalize the short triplet state lifetime of visible-light-harvesting organic chromophores. Our results are useful for fundamental photochemistry and the design of photosensitizers showing long-lived triplet states.The electron spin polarization inversion and anisotropic decay of triplet substates explain the short triplet state lifetime of BODIPY derivatives. 相似文献
18.
We propose a Cohen-type bond order analysis in terms of orthogonalized atomic basis functions which can be used to analyze NDO wave functions of large organic and metal–organic molecules. It is shown that for small molecules the results gained with this method are in excellent agreement with the same analysis based on ab initio STO -3G wavefunctions. For large planar aromatic systems these all-valence electron bond orders are found to be a consistent generalization of the π-bond order. A simple relation between these bond orders and the corresponding covalent bond energies is established. The method can be easily extended to study excited state multiconfiguration wave functions. We present calculations for C2H2, C2H4, C2H6, and Mn2(CO)10. The results indicate that the method can be used to discuss the photochemistry of organic and metal–organic compounds. 相似文献
19.
The traditional microphone configuration used to measure room impulse responses (IRs) according to ISO 3382:2009 is an omnidirectional and figure-8 microphone pair. IRs measurements were taken in a 2500-seat auditorium to determine how the results from a spherical microphone array (an mh acoustics Eigenmike-em32) compare to those from the traditional microphone setup (a Brüel & Kjær Type-4192 omnidirectional microphone and a Sennheiser MKH30 figure-8 microphone). Measurements were obtained at six receiver locations, with three repetitions each in order to first evaluate repeatability. The metrics considered in this study were: reverberation time (T30), early decay time (EDT), clarity index (C80), strength (G), lateral energy fraction (JLF) and late lateral energy level (LJ). Before calculating these quantities, the IRs were filtered to equalize the frequency response of the microphones and sound source. For the spherical array measurements, the omnidirectional (monopole) and figure-8 (dipole) patterns were extracted using beamforming. In terms of repeatability, the average standard deviation of the three measurements at each receiver location averaged across all metrics, receivers, and octave bands was found to be 0.01 just noticeable differences (JNDs). The analysis comparing the measurements from the two microphone configurations yielded differences which were less than 1 JND for the majority of metrics, with a few exceptions of EDT and C80 slightly above 1 JND. Based on this case study, these results indicate that spherical microphone arrays can be used to obtain valid room IR measurements, which will allow for the development of new metrics utilizing the higher spatial resolution made possible with spherical arrays. 相似文献
20.