首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   692篇
  免费   16篇
  国内免费   2篇
化学   370篇
晶体学   23篇
力学   10篇
数学   66篇
物理学   241篇
  2022年   8篇
  2021年   10篇
  2020年   23篇
  2019年   19篇
  2018年   16篇
  2017年   21篇
  2016年   27篇
  2015年   12篇
  2014年   18篇
  2013年   39篇
  2012年   35篇
  2011年   50篇
  2010年   28篇
  2009年   25篇
  2008年   17篇
  2007年   17篇
  2006年   18篇
  2005年   29篇
  2004年   20篇
  2003年   11篇
  2002年   13篇
  2001年   11篇
  2000年   9篇
  1999年   4篇
  1997年   7篇
  1996年   20篇
  1995年   18篇
  1994年   15篇
  1993年   9篇
  1992年   13篇
  1991年   8篇
  1990年   5篇
  1989年   6篇
  1988年   7篇
  1987年   5篇
  1986年   12篇
  1984年   6篇
  1983年   5篇
  1982年   10篇
  1981年   5篇
  1980年   7篇
  1979年   5篇
  1978年   6篇
  1977年   5篇
  1976年   4篇
  1971年   4篇
  1970年   5篇
  1969年   4篇
  1968年   4篇
  1967年   7篇
排序方式: 共有710条查询结果,搜索用时 15 毫秒
541.
542.
The projected shell model (PSM) study of 100?C118Pd nuclei is carried out. The reliability of the ground-state wave functions is checked by reproducing yrast spectra and electromagnetic properties. The results of calculations indicate that the observed deformation systematics in 100?C118Pd isotopes depends on the increase of occupation probability of (1h 11/2 ?? ) orbit and the deformation producing tendency of n-p interaction operating between Spin Orbit Partner (SOP) orbits (d 5/2)???(d 3/2) ?? and (g 9/2)???(g 7/2) ?? . Beside this, the results on band diagrams show that the yrast spectra in Pd isotopes do not arise from a single intrinsic state only but also from multi-quasiparticle states.  相似文献   
543.
Volumetric, acoustic, refractometric, excess and deviation properties of glycylglycine–MnCl2 in aqueous ethanol mixtures have been reported at T = (288.15 to 318.15) K. Redlich–Kister equation was used to fit the derivate properties. The experimental data of the constituent binaries were analyzed to discuss the nature and strengths of intermolecular interactions. The interdependence of Lf and u has been evolved from Eyring and Kincaid model. The variations in specific acoustic impedance revealed that hydrogen bonding was predominant in the studied binary mixtures. Solvation number indicated structure-breaking tendency of the solute and weakening of local solvent structure.  相似文献   
544.
A combined experimental and theoretical approach establishes the long-lived nature of protein adsorption on surfaces coated with chemically grafted macromolecules. Specifically, we monitor the time dependence of adsorption of lysozyme on surfaces comprising polymer assemblies made of poly(2-hydroxyethyl methacrylate) brushes grafted onto flat silica surfaces such that they produce patterns featuring orthogonal and gradual variation of the chain length (N) and grafting density (σ). We show that in the kinetically controlled regime, the amount of adsorbed protein scales universally with the product σN, while at equilibrium the amount of adsorbed protein is governed solely by σ. Surprisingly, for moderate concentrations of protein in solution, adsorption takes more than 72 h to reach an equilibrium, or steady state. Our experimental findings are corroborated with predictions using molecular theory that provides further insight into the protein adsorption phenomenon. The theory predicts that the universal behavior observed experimentally should be applicable to polymers in poor and theta solvents and to a limited extent also to good solvent conditions. Our combined experimental and theoretical findings reveal that protein adsorption is a long-lived phenomenon, much longer than generally assumed. Our studies confirm the previously predicted important differences in behavior for the kinetic versus thermodynamic control of protein adsorption.  相似文献   
545.
Fourier transform infrared and Raman spectra of 2,3-pyrazinedicarboxylic acid were recorded and analyzed using density functional theory. The complete assignments of the anharmonic vibrational modes have been performed based on potential energy distribution. The anharmonic frequencies were computed using vibrational second-order perturbation theory as well as vibrational self-consistent field and correlation corrected vibrational self-consistent field methods. Mode–mode coupling strength is also estimated using two-mode representation of quartic force field approximation. The intra- and intermolecular interactions were also studied in the dimer and trimer forms of the title molecule. The ultraviolet–visible absorption spectra in ethanol, methanol, and acetonitrile solvents were recorded and analyzed using time-dependent density functional theory involving the polarization continuum model. The observed and calculated results are well comparable. Molecular electrostatic potential and the highest occupied and the lowest unoccupied molecular orbital analyses are also reported.  相似文献   
546.
The thermal decomposition of urania-ceria gel corresponding to the composition U(0.7)Ce(0.3)O(2+x) obtained through external and internal gelation routes were studied using infrared spectroscopy (IR). In the case of externally gelated compound, the gel decomposes with the release of H2O and NH3 below 500 degrees C. A part of the NH3 released is entrapped in the solid and above 500 degrees C self reduction occurs in which U(VI) in the gel is reduced to U3O8. The decomposition products were identified to be U3O8 and CeO2. In the case of internally gelated compound, decomposition similar to the one for externally gelated compound occurred below 500 degrees C. Above 500 degrees C the carbon present in the gel reduced U(VI) to UO2 which formed solid solution with CeO2 around 650 degrees C.  相似文献   
547.
We have investigated the microstructure and phase behavior of monoglyceride-based lyotropic liquid crystals in the presence of hydrophilic silica colloidal particles of size comparable to or slightly exceeding the repeat units of the different liquid crystalline phases. Using small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC), we compare the structural properties of the neat mesophases with those of the systems containing silica colloidal particles. It is found that the colloidal particles always macrophase separate in inverse bicontinuous cubic phases of gyroid (Ia3d) and double diamond (Pn3m) symmetries. SAXS data for the inverse columnar hexagonal phase (H(II)) and lamellar phase (L(α)) suggest that a low volume fraction of the nanoparticles can be accommodated within the mesophases, but that at concentrations above a given threshold, the particles do macrophase separate also in these systems. The behavior is interpreted in terms of the enthalpic and entropic interactions of the nanoparticles with the lamellar and hexagonal phases, and we propose that, in the low concentration limit, the nanoparticles are acting as point defects within the mesophases and, upon further increase in concentration, initiate nucleation of nanoparticles clusters, leading to a macroscopic phase separation.  相似文献   
548.
JPC – Journal of Planar Chromatography – Modern TLC - The fruits of Benincasa hispida (Thunb.) Cogniaux, a ‘rasayana’ in ‘Ayurveda’, are enriched with several...  相似文献   
549.
We report for the first time a cyclic voltammetric nitrate sensor with a low detection limit based on the immobilization of zinc oxide nanoparticles on the surface of the platinum working electrode using chitosan membrane. Cyclic voltammetric data demonstrated that zinc oxide nanoparticles can electrochemically reduce nitrate ions to ammonium ions with high conductivity. In order to estimate electroanalytical parameters for each of the nitrate concentrations, Gaussian and Lorentzian curve fitting algorithms were performed on cyclic voltammetric data. Among them, the best analytical performance results were obtained with Gaussian calibration linear model. The zinc oxide modified platinum electrode showed a linear response to nitrate ions over a concentration range from 0.1 to 2.0 mM with a low detection limit and high sensitivity of 10 nM and 39.91 μA/cm2 mM, respectively. The nitrate ion concentrations in drinking water samples were determined using Gaussian calibration linear model and the predicted, added nitrate ion concentration values showed good correlation.  相似文献   
550.
An expedient direct and regioselective thiocyanation of phenols, anilines and heterocycles is described. Transformation is realized via the direct CH functionalization under transition metal free conditions at ambient temperature in excellent yields. Method proved to be monoselective and variety of functional groups tolerated the reaction conditions. The practicality of the protocol is demonstrated in gram scale synthesis of a precursor of PPAR δ agonist in excellent yield.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号