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921.
Ali Morsali S. Ali Beyramabadi S. Hooman Vahidi Maryam Ghorbani 《Molecular physics》2013,111(8):483-490
The curves of experimental heat capacity against density show a minimum around and below the critical temperature (Tc), but at higher temperatures, this minimum is not observed. In this study, the role of attractive and repulsive forces on excess heat capacity of Lennard–Jones (LJ) dense fluids has been investigated using a molecular dynamics simulation technique. LJ potential is divided into attractive and repulsive parts. From the molecular dynamics calculations, potential energy and heat capacities have been obtained for Argon at temperatures of 100–500?K. The repulsive forces play the main role in causing the heat capacities at temperatures greater than critical point. Around and below the critical temperature, the role of repulsion is dominant at high densities, but attraction has the main role at low densities, consequently at middle densities, a minimum is formed. 相似文献
922.
We have applied density functional theory (DFT) calculations to study the structures, stabilities, electronic and magnetic properties of mono and multiply oxygenated Si60H60 fullerenes (Si60H60–2nOn, n = 1, 3, 6, 9, 10, 12, 18, 20, 21, 27 and 30). DFT results show that rearrangement between the closed [6,6] and [5,6] isomers of Si60H58O follows a two-step pathway involving an intermediate and two transition states. Preserving the C3 symmetry in the cage structure, extra epoxidation of Si60H60 has been accomplished. Based on our results, formation energies per oxygen atom for the multiple additions of oxygen atoms on Si60H60 cage are positive (endothermic character), and increase with the increasing of the number of oxygen atoms. In general, the oxygenation of Si60H60 cage leads to an increase in the electrophilicity of the Si60H60–2nOn oxides. The oxygenation of Si–Si bonds not only introduces a substantial broadening of the NMR pattern but also yield individual peaks, indicating different electrostatic environments of silicon nuclei in the Si60H60–2nOn oxides. 相似文献
923.
Maryam Jahangiri 《代数通讯》2013,41(12):5454-5463
924.
Let C be a semidualizing module for a commutative ring R. In this paper, we study the resulting modules of finite G C -projective dimension in Bass class, showing that they admit G C -projective precover. Over local ring, we prove that dim R (M) ≤ 𝒢? C ? id R (M) for any nonzero finitely generated R-module M, which generalizes a result due to Bass. 相似文献
925.
A new rarely reported ZnII mixed‐polypyridine coordination polymer with both rigid and flexible spacers, {[Zn(bpp)2(μ‐4,4′‐bipy)(H2O)2](ClO4)2 · H2O}n ( 1 ), has been synthesized and characterized by elemental analysis, IR‐, 1H NMR‐, 13C NMR spectroscopy and single‐crystal X‐ray diffraction. The thermal stability of compound 1 was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The single‐crystal X‐ray structure of 1 shows that the complex has been formed from a 1D polymer as a result of bridging by the 4,4′‐bipy ligands. Solution and solid‐state luminescent spectra of the compound 1 indicate intense fluorescent emissions at ca. 353.6 and 468.8 nm, respectively. Removal of the interstitial water guest molecules results in a loss of crystallinity, but exposure to water vapor reestablishes the original structure, thus constituting 1 as a third‐generation porous framework. 相似文献
926.
Maryam Shojaei Abdolreza Mirmohseni Yadollah Omidi Maryam Farbodi 《Applied biochemistry and biotechnology》2009,159(1):54-64
Homovanillic acid (HVA) and vanillylmandelic acid (VMA) were selectively determined by quartz crystal nanobalance sensor in
conjunction with net analyte signal (NAS)-based method called HLA/GO. An orthogonal design was applied for the formation of
calibration and prediction sets including HVA, VMA, and some common and structurally similar urine compounds. The selection
of the optimal time range involved the calculation of the NAS regression plot in any considered time window for each test
sample. The searching of a region with maximum linearity of NAS regression plot (minimum error indicator) and minimum of predicted
error sum of squares value was carried out by applying a moving window strategy. Based on the obtained results, the differences
on the adsorption profiles in the time range between 1 and 300 s were used to determine mixtures of compounds by HLA/GO method.
Several figures of merit like selectivity, sensitivity, analytical sensitivity, and limit of detection were calculated for
both compounds. The results showed that the method was successfully applied for the determination of VMA and HVA. 相似文献
927.
Maryam Bordbar Ali Yeganeh-Faal Jahanbakhsh Ghasemi Mohammad Mahdi Ahari-Mostafavi Nahid Sarlak Mohammad Taghi Baharifard 《Chemical Papers》2009,63(3):336-344
A simple, sensitive and selective spectrophotometric method for simultaneous determination of tretinoin and minoxidil using
partial least square (PLS) calibration and H-point standard addition method (HPSAM) is described. The results of the H-point
standard addition method show that minoxidil and tretinoin can be determined simultaneously with the concentration ratio of
tretinoin to minoxidil varying from 2: 1 to 1: 33 in mixed samples. A partial least squares multivariate calibration method
for the analysis of binary mixtures of tretinoin and minoxidil was also developed. The total relative standard error for applying
the PLS method to eleven synthetic samples in the concentration range of 0–10 μg mL−1 tretinoin and 0–32 μg mL−1 minoxidil was 2.59 %. Both proposed methods (PLS and HPSAM) were also successfully applied in the determination of tretinoin
and minoxidil in several synthetic pharmaceutical solutions. 相似文献
928.
1‐Butyl‐3‐methylimidazolium hydrogen sulfate [bmim]HSO4 as an acidic ionic liquid was prepared and used as a catalyst for the synthesis of 1,8‐dioxo‐octahydroxanthenes in excellent yields and short reaction times at 80 °C. The ionic liquid was easily separated from the reaction mixture by water extraction and was recycled four times without any loss in activity. 相似文献
929.
We have studied corrections to conductivity due to the coherent backscattering in low-disordered two-dimensional electron systems in silicon for a range of electron densities including the vicinity of the metal-insulator transition, where the dramatic increase of the spin susceptibility has been observed earlier. We show that the corrections, which exist deeper in the metallic phase, weaken upon approaching the transition and practically vanish at the critical density, thus suggesting that the localization is suppressed near and at the transition even in zero field. 相似文献
930.
Shashkin AA Rahimi M Anissimova S Kravchenko SV Dolgopolov VT Klapwijk TM 《Physical review letters》2003,91(4):046403
We accurately measure the effective mass in a dilute two-dimensional electron system in silicon by analyzing the temperature dependence of the Shubnikov-de Haas oscillations in the low-temperature limit. A sharp increase of the effective mass with decreasing electron density is observed. We find that the enhanced effective mass is independent of the degree of spin polarization, which points to a spin-independent origin of the mass enhancement and is in contradiction with existing theories. 相似文献