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491.
We have studied the hard-square lattice gas, using corner transfer matrices. In particular, we have obtained the first 24 terms of the high-density series for the order parameter
2–
1. From these we estimate the critical activity to be 3.7962±0.0001. This is in excellent agreement with the earlier work of Gaunt and Fisher. It conflicts with the value 4.0 given by Müller-Hartmann and Zittartz's formula for the critical point of the antiferromagnetic Ising model in a field, so we conclude that this formula, while a good approximation, is not exact. 相似文献
492.
Hei-wun Leung Chun Wai Tsang Alex. G. Harrison 《Journal of mass spectrometry : JMS》1976,11(6):664-668
The mass spectrum of 13C centrally labeled neopentane has been re-examined at a mass resolution sufficient to resolve 13C-CH mass doublets. Contrary to earlier low resolution results, the [C3H5]+ fragment ion is formed with 75% retention of the central carbon under all experimental conditions, indicating complete carbon scrambling in the fragmentation reaction [C4H9]+→[C3H5]+ + CH4. The higher retention of the central carbon in [C3H5]+ in the mass spectra of (CH3)3CCl and (CH3)3CBr is shown to be due to the occurrence of the reaction sequence 相似文献
493.
The effect of changes in the internal energy distribution of the fragmenting ion on the ratio of metastable ion intensities for two competing fragmentation reactions has been investigated both theoretically and experimentally. Model calculations have shown that if the competing reactions have significantly different activation energies the metastable intensity ratio does depend on the internal energy distribution although large changes are necessary before the ratio changes by more than a factor of two. Experimentally the metastable characteristics of [C3H7O]+ ions of nominal structures [CH3CH2O+?CH2] (I), [(CH3)2C?O+H] (II), [CH3CH2CH?O+H] (III) and [CH3O+?CHCH3] (IV) have been examined. For each structure the metastable characteristics are found to be distinctive and independent of changes in the internal energy distribution of the fragmenting ion where these changes result from altering the precursor of the [C3H7O]+ ions. It is suggested that these internal energy changes can be estimated from the fraction of [C3H7O]+ ions which fragment in the ion-source. It is concluded that structures I to IV represent stable and distinct ionic structures. 相似文献
494.
Ming Ng K Ling Ma N Wai Tsang C 《Rapid communications in mass spectrometry : RCM》2003,17(18):2082-2088
Abundant Ag(I)-cationized complexes of 13 polyaromatic hydrocarbons (PAHs), [Ag+PAH](+) and [Ag+2(PAH)](+), were readily generated by electrospray ionization (ESI). In-source collision-induced dissociation (CID) of the [Ag+2(PAH)](+) complex yielded the monomer complex [Ag+PAH](+), which fragmented further to yield the radical molecular ion [PAH](+.). Based on significant differences in relative intensities of [Ag+2(PAH)](+), [Ag+PAH](+) and [PAH](+.), isomeric PAHs can be differentiated. The [PAH](+.)/[Ag+PAH](+) ion intensity ratio was found to increase with decreasing ionization potentials (IPs) of PAHs. The ratio was significantly different for the isomeric PAHs studied over a wide range of PAH concentrations (1.6-100 nmol/mL), and showed good measurement reproducibility; the coefficient of variation of inter-day measurements was in the range 3-12% for four representative PAHs (n = 5). Detection limits for phenanthrene, pyrene, chrysene and benzo[a]pyrene, in the form of the monomer complexes [(107)Ag+PAH](+) and measured in the selected-ion monitoring (SIM) mode, were 0.31, 0.63, 0.16 and 1.25 pmol/5 microl injection, respectively (S/N ratio approximately 2-3). 相似文献
495.
Handzy DO Bauer W Daffin FC Gaff SJ Gelbke CK Glasmacher T Gualtieri E Hannuschke S Huang MJ Kunde GJ Lacey R Li T Lisa MA Llope WJ Lynch WG Martin L Montoya CP Pak R Peaslee GF Pratt S Schwarz C Stone N Tsang MB Vander Molen AM Westfall GD Yee J Yennello SJ 《Physical review letters》1995,75(16):2916-2919
496.
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498.
Various azines and substituted phenylene diamines are oxidized by the nitrite ion to give stable radicals in an autocatalytic reaction. This finding has now been developed into highly sensitive methods for nitrite determination by EPR spectrometry. Thus, when the reagent is phenothiazine, the detection limit for nitrite is 0.012 ppm, the relative standard deviation at 0.05 ppm is 1.9%, and the analytical range is 0-1.5 ppm. With N,N,N',N'-tetramethyl-p-phenylenediamine as the reagent, the corresponding values are 0.025 ppm, 2.6%, and 0-1.3 ppm. Nitrate can be determined after prior reduction to nitrite. A mixture of nitrite and nitrate ions can also be quantitatively analysed. The EPR methods were applied to the determination of the nitrite and nitrate contents of prepacked cooked ham and of soft-spreading cheese. The results agreed well with those obtained by ISO and AOAC standard methods for these samples. ca*|Author for correspondence. 相似文献
499.
500.