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161.
In the presence of a phosphine oxide cocatalyst, a bimetallic aluminium(salen) complex was found to catalyse the asymmetric addition of trimethylsilyl cyanide to aldehydes. Under optimised conditions, enantioselectivities of 53-96% were obtained using 2 mol % of the catalyst. An analysis of the reaction kinetics showed that the reactions exhibited first-order kinetics, with the rate of reaction being independent of the aldehyde concentration. 相似文献
162.
Mehmet F. Yilmaz Alla S. SafronovaVictor L. Kantsyrev Andrey A. EsaulovKenneth M. Williamson Ishor K. ShresthaMichael E. Weller Glenn C. OsborneVeronica V. Shlyaptseva 《High Energy Density Physics》2012,8(1):30-37
Radiative emission from alloyed Al single, double and compact cylindrical wire arrays have been studied using the 1 MA Zebra UNR generator. Single planar wire arrays using ten wires and double planar wire arrays and compact cylindrical wire arrays (CCWA) that both had sixteen wires were utilized. The wire composition is Al-5056 (95% of Al and 5% of Mg). We have observed that implosion of these alloyed Al wire loads generated optically thick Al plasmas that can be diagnosed using K-shell Mg lines. In particular, among the considered loads, the K-shell lines of Al from implosions of the double planar wire arrays have the highest optical depth for He-like Al resonance transitions, which occurred near the stagnation phase. X-ray time-gated and time-integrated spectra and pinhole images as well as photoconductive detectors signals were analyzed to provide information on the plasma parameters; electron temperatures and densities, implosion dynamics features and power and yields of the X-ray radiation. Previously developed non-LTE models were applied to model axially-resolved time-integrated, as well as time-gated spatially-integrated, K-shell spectra from Al and Mg. The derived time-dependent electron temperature, density and axial opacity were studied and compared. In addition, the wire ablation dynamics model (WADM) was used to calculate the kinetic energy of the plasma, which with the aid of a Local Thermal Equilibrium (LTE) magneto-hydrodynamics (MHD) simulation, allowed to estimate the precursor and stagnated z-pinch plasma electron temperatures from implosions of wire array loads. 相似文献
163.
Josep Saurí Yizhou Liu R. Thomas Williamson Gary E. Martin 《Magnetic resonance in chemistry : MRC》2016,54(4):341-345
Despite the tremendous usage of HMBC to establish long‐range 1H–13C and 1H–15N heteronuclear correlations, an inherent drawback of the experiment is the indeterminate nature of the nJXH correlations afforded by the experiment. A priori there is no reliable way of determining whether a given nJCH correlation is, for example, via two‐, three‐, or sometimes even four‐bonds. This limitation of the HMBC experiment spurred the development of the ADEQUATE family of NMR experiments that rely on, in the case of 1,1‐ADEQUATE, an out‐and‐back transfer of magnetization via the 1JCC homonuclear coupling constant, which is significantly larger than nJCC (where n = 2–4) couplings in most cases. Hence, the 1,1‐ADEQUATE experiment has generally been assumed to unequivocally provide the equivalent of 2JCH correlations. The recent development of the 1,1‐ and 1,n‐HD‐ADEQUATE experiments that can provide homodecoupling for certain 1JCC and nJCC correlations has increased the sensitivity of the ADEQUATE experiments significantly and can allow acquisition of these data in a fraction of the time required for the original iterations of this pulse sequence. With these gains in sensitivity, however, there occasionally come unanticipated consequences. We have observed that the collapse of proton multiplets, in addition to providing better s/n for the desired 1JCC correlations can facilitate the observation of typically weaker 2JCC correlations across intervening carbonyl resonances in 1,1‐HD‐ADEQUATE spectra. Several examples are shown, with the results supported by the measurement of the 2JCC coupling constants in question using J‐modulated‐HD‐ADEQUATE and DFT calculations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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165.
E. Rosenberg Kenneth L. Williamson John D. Roberts 《Magnetic resonance in chemistry : MRC》1976,8(3):117-119
15N chemical shifts of twenty-four substituted indoles have been determined in natural abundance (in organic solvents) using Fourier transform NMR. The overall chemical shift range is 27 ppm, with groups in the 2-, 3- and 5-ring positions showing the largest substituent effects. Substituents capable of resonance interaction with the indole nitrogen give shifts in the expected directions but they cannot be correlated with known substituent parameters. Compounds measured in DMSO give 0·2 to 10·2 ppm downfield shifts with respect to the same compound measured in CDCl3. 13C NMR data for previously unreported compounds are also reported. 相似文献
166.
Metallic multilayers of Fe and Zr, prepared by electron-beam evaporation and sputter deposition, have been characterized by conversion electron Mössbauer spectroscopy and x-ray diffraction. Amorphous phase formation occurs at the interfaces during deposition for all samples and there is a critical layer thickness near 10 monolayers of each constituent where complete amorphization occurs. The amorphous phase formed upon annealing the 50 monolayer electron-beam sample consumes only about one-third of the Fe before the process saturates. 相似文献
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168.
Probability Theory and Related Fields - 相似文献
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