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81.
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Vladimir O. Aseyev Stanislav I. Klenin Heikki Tenhu 《Journal of Polymer Science.Polymer Physics》1998,36(7):1107-1114
Samples of a polyelectrolyte poly(methacryloylethyl trimethylammonium methylsulfate), PMETMMS, with molar masses Mw = 22−25 × 106 were examined with viscosity, static light scattering, and conductivity measurements in a water–acetone solvent. Because acetone is a nonsolvent for this polymer the measurements were performed to determine the influence of the solvent composition, the polymer concentration, and the presence of added ions on the conformation of the polyelectrolyte in mixed solvents. The possible influence of a hydrodynamic field on the polymer conformation was also studied. The viscosity of the polymer solutions as a function of polymer concentration, as well as of the solvent composition, was studied using a broad range of shear rates. When the mass fraction of acetone in the solvent, γ, is below 0.5, the solutions show a usual polyelectrolyte behavior. When γ ≥ 0.80, the polymer adopts a compact conformation. This is observed as a decrease of the radius of gyration, Rg, second virial coefficient, A2, the viscosity, and also as a change in the conductivity of the solution. The change in the polymer conformation may be induced also by dilution. When 0.60 ≤ γ < 0.80, a gradual decrease in the polymer concentration leads to a sudden decrease of the reduced viscosity, which indicates a decrease in the particle size. The values of Mw measured by static light scattering were constant in all experiments. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1107–1114, 1998 相似文献
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使用疏水作用色谱研究蛋白质的构象变化 总被引:2,自引:0,他引:2
研究了高效疏水作用液相色谱中(HIC)色谱条件改变对蛋白质构象的影响。发现固定相配体的疏水性、温度及流动相中盐的阴离子、阳离子和pH值都影响蛋白质的构象。 相似文献
87.
The apparent molar volumes of equimolar concentrations of 18-crown-6-ether (CE) or dibenzo-18-crown-6-ether (B2CE) and MCl (M=Na, K, or Cs) or MI in dilute solutions of anhydrous methanol, acetonitrile and dimethylsulfoxide have been calculated from density data measured at 25°C. After extrapolation to infinite dilution these results together with the apparent molar volumes of the crown ethers and the alkali metal halides were used to calculate the limiting partial molar volume change for the formation of the complexes. By noting that the charge of the complexed cation has been shown to be completely shielded from the solvent, the volume of complexation can be assumed to be a good estimation of the volume change due to electrostriction of the solvent by the cationic charge. The results are compared to the predictions of the Hepler equation.Presented at the Symposium on Electrochemistry and Spectroscopy of Solutions, Honoring Johannes Coetzee, University of Pittsburgh, November 30, 1989.On leave from Rhodes University, Grahamstown, South Africa. 相似文献
88.
Yoshihiko Saito 《中国化学会会志》1991,38(5):405-424
A historical overview will be given on the structural studies on transition metal compounds and their interaction with other fields of coordination chemistry. About three decades have passed away since the structure and absolute configuration of tris(ethylenediamine)cobalt(III) complex ion were determined. At present accumulation of the structural data for isomers has enabled us to understand structural principles of chelate complexes in considerable detail. The energy minimization calculations can predict the detailed geometries of the complexes. Differences in thermodynamic properties between different conformers are well reproduced. Aspherical distribution of 3d electrons in transition metal complexes was detected for the first time in crystals of [Co(NH3)6][Co(CN)6] in 1973. Such an accurate electron density study provides important information on the d electrons placed in a ligand field. The high-spin and low-spin states can be distinguished unequivocally. In spite of a very small valence/total electron ratio, the asphericity of 4d and 5d electrons in a ligand field can be detected. The crystal structures of a series of dimeric copper(II) carboxylate adducts of the general formula [Cu(RCOO)2L]2 have been determined or redetermined as accurately as possible. The temperature dependent magnetic susceptibility of these crystals indicated that the isolated pairs of Cu(II) ions interact strongly through exchange forces. Molecular orbital calculations revealed that the electron population in the carbon atom of the bridging OCO group plays an important role in determining the strength of the spin superexchange interaction. In the crystals of some cobaloxime complexes, racemization of chiral groups bonded to Co proceeds on X-ray exposure without degradation of crystallinity. Several intermediate stages could be determined by X-ray analysis. Various reaction pathways were recognized and the reaction rate could be correlated with the atomic arrangement in the crystal. 相似文献
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微量元素与糖尿病 总被引:22,自引:6,他引:22
秦俊法 《广东微量元素科学》2000,7(2):1-15
糖尿病是一种常见病。成人糖尿病患病率约为3%,亦即现有糖尿病人达1亿左右。估计到2010年,全球糖尿病人将超过2亿。糖尿病的发展涉及多种病理过程,已有令人信服的证据表明,微量元素在胰岛素的生成和作用以及糖尿病人的能量底物代谢中起着极为重要的作用。本文从糖尿病行病学、微量元素在胰岛素代谢中的作用、糖尿病人的微量元素含量变化和糖尿病的微量元素治疗等四个方面综述了微量元素与糖尿病的关系。参考文献70,表 相似文献