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101.
Recent optical kerr effect (OKE) studies have revealed that orientational relaxation of rodlike nematogens near the isotropic-nematic
(I-N) phase boundary and also in the nematic phase exhibit temporal power law decay at intermediate times. Such behaviour
has drawn an intriguing analogy with supercooled liquids. Here, we have investigated the single-particle and collective orientational
dynamics of a family of model system of thermotropic liquid crystals using extensive computer simulations. Several remarkable
features of glassy dynamics are on display including non-exponential relaxation, dynamical heterogeneity, and non-Arrhenius
temperature dependence of the orientational relaxation time. Over a temperature range near the I-N phase boundary, the system
behaves like a fragile glass-forming liquid. Using proper scaling, we construct the usual relaxation time versus inverse temperature
plot and explicitly demonstrate that one can successfully define a density dependent fragility of liquid crystals. The fragility
of liquid crystals shows a temperature and density dependence which is remarkably similar to the fragility of glass forming
supercooled liquids. Energy landscape analysis of inherent structures shows that the breakdown of the Arrhenius temperature
dependence of relaxation rate occurs at a temperature that marks the onset of the growth of the depth of the potential energy
minima explored by the system. 相似文献
102.
A new expression is derived for the differential reflectance from an arbitrary metal surface, with chemisorbed impurities, using -polarized radiation. The use of the result, which depends entirely on the dielectric response tensor of the system, to study experimental Surface Reflectance data is discussed. 相似文献
103.
Kim S Chung JK Kwak K Bowman SE Bren KL Bagchi B Fayer MD 《The journal of physical chemistry. B》2008,112(32):10054-10063
Unfolded vs native CO-coordinated horse heart cytochrome c (h-cyt c) and a heme axial methionine mutant cyt c552 from Hydrogenobacter thermophilus ( Ht-M61A) are studied by IR absorption spectroscopy and ultrafast 2D-IR vibrational echo spectroscopy of the CO stretching mode. The unfolding is induced by guanidinium hydrochloride (GuHCl). The CO IR absorption spectra for both h-cyt c and Ht-M61A shift to the red as the GuHCl concentration is increased through the concentration region over which unfolding occurs. The spectra for the unfolded state are substantially broader than the spectra for the native proteins. A plot of the CO peak position vs GuHCl concentration produces a sigmoidal curve that overlays the concentration-dependent circular dichroism (CD) data of the CO-coordinated forms of both Ht-M61A and h-cyt c within experimental error. The coincidence of the CO peak shift curve with the CD curves demonstrates that the CO vibrational frequency is sensitive to the structural changes induced by the denaturant. 2D-IR vibrational echo experiments are performed on native Ht-M61A and on the protein in low- and high-concentration GuHCl solutions. The 2D-IR vibrational echo is sensitive to the global protein structural dynamics on time scales from subpicosecond to greater than 100 ps through the change in the shape of the 2D spectrum with time (spectral diffusion). At the high GuHCl concentration (5.1 M), at which Ht-M61A is essentially fully denatured as judged by CD, a very large reduction in dynamics is observed compared to the native protein within the approximately 100 ps time window of the experiment. The results suggest the denatured protein may be in a glassy-like state involving hydrophobic collapse around the heme. 相似文献
104.
Two series of thiol-bridged dimeric desoxo molybdenum(IV) and tungsten(IV) bis(dithiolene) complexes, [Et(4)N](2)[M(IV)(2)(SR)(2)(mnt)(4)] [M = Mo, R = (1) -Ph, (2) -CH(2)Ph, (3) -CH(2)CH(3), (4) -CH(2)CH(2)OH; M = W, R = (1a) -Ph, (2a) -CH(2)Ph, (3a) -CH(2)CH(3), (4a) -CH(2)CH(2)OH] and one monomeric desoxo complex, [Et(4)N](2)[WIV(SPh)(2)(mnt)(2)] (5a) are reported. These complexes are diamagnetic, and crystal structures of each of the complex (except 5a) exhibits a dimeric {M(IV)(2)(SR)(2)} core without any metal-metal bond where each metal atom possesses hexa coordination. The M-SR distance ranges from 2.437 to 2.484 Angstrom in molybdenum complexes and from 2.418 to 2.469 Angstrom in tungsten complexes. These complexes display Mo-S(R)-Mo angles ranging from 92.84 degrees to 96.20 degrees in the case of 1-4 and W-S(R)-W angles ranging from 91.20 degrees to 96.25 degrees in the case of 1a-4a. Interestingly, both the series of Mo(IV) and W(IV) dimeric complexes respond to an unprecedented interconversion between the dimer and the corresponding hexacoordinated monomer upon change of pH. This pH-dependent interconversion establishes the fact that even the pentacoordinated Mo(IV) and W(IV) bis(dithiolene) moieties are forced to dimerize; these can easily be reverted back to the corresponding monomeric complex, reflecting the utility of dithiolene ligand in stabilizing the Mo(IV)/W(IV) moiety in synthesized complexes similar to the active sites present in native proteins. 相似文献
105.
Golden opportunity: [4+3] Cycloaddition reactions of arenynamides and epoxides are enabled under gold catalysis and have a broad substrate scope (see scheme; Ms=methanesulfonyl). An S(N) 2-type front-side attack of phenyl at the oxiranyl ring is expected to cause the retention of stereochemistry. 相似文献
106.
107.
Nanocrystalline Cr2O3 and NiO are prepared using high-energy ball milling. Average sizes of the particles obtained from Scanning Electron Microscopy and crystallite sizes obtained from X-ray diffraction are larger for Cr2O3 than NiO particles. At low temperature, large high-field magnetization and small coercivity lead to a weak exchange bias for Cr2O3, whereas small high-field magnetization and large coercivity lead to a considerable exchange bias for NiO. The training effect is observed for NiO at 4 K which could be described with a recursive formula constructed in the framework of the spin configurational relaxation model. The results suggest that the pinning mechanism at the interface between the antiferromagnetic and the weak ferromagnetic component ascribed to uncompensated spins leads to the exchange bias effect. 相似文献
108.
The kinetics of phase separation subsequent to a finite temperature quench is assumed to be driven by diffusion on the altered free energy surface and is generally assumed to be slow. The situation can be different in phase separating liquid binary mixtures, especially for systems characterized by the large difference in mutual interactions between solute and solvent molecules. In such cases, the phase separation kinetics could be fast and may get completed within a short time (ns) scale. As a result, in these systems, one may observe diverse dynamical features arising out of local heterogeneity leading to the onset of phase separation through pattern formation, spinodal decomposition, nucleation, and growth. By using a coarse-grained analysis, we examine phase separation kinetics in each spatial grid and indeed observe important effects of initial heterogeneity on the subsequent evolution. Interestingly, we observe slower separation kinetics for those regions that correspond to the composition at the minimum of the high-temperature surface. The heterogeneous dynamics has been captured here through the non-linear susceptibility function, which shows a pattern similar to what is observed in the supercooled liquid. Each grid shows somewhat different dynamics in the three-stage (exponential, power-law, and logarithmic regime) phase separation dynamics. The late stage of phase separation kinetics is usually attributed to the coarsening of the phase-separated domains. However, in a liquid binary mixture, the late-stage power-law decay undergoes a further change. A new dynamical regime arises characterized by a logarithmic time dependence, which is due to the “smoothening” of the rough interface of already well-separated phases. This can also be described as opposite to the roughening transition described by Chui and Weeks [Phys. Rev. Lett. 40, 733 (1978)]. This reverse roughening transition can explain the logarithmic time dependence observed in the simulation. 相似文献
109.
A Triphenyl Amine‐Based Solvatofluorochromic Dye for the Selective and Ratiometric Sensing of OCl− in Human Blood Cells 下载免费PDF全文
Prof. Shyamaprosad Goswami Krishnendu Aich Sangita Das Bholanath Pakhira Kakali Ghoshal Dr. Ching Kheng Quah Dr. Maitree Bhattacharyya Prof. Hoong‐Kun Fun Prof. Sabyasachi Sarkar 《化学:亚洲杂志》2015,10(3):694-700
A new visible‐light‐excitable fluorescence ratiometric probe for OCl? has been developed based on a triphenylamine‐diamiomaleonitrile (TAM) moiety. The structure of the dye was confirmed by single‐crystal X‐ray analysis. It behaves as a highly selective and sensitive probe for OCl? over other analytes with a fast response time (~100 s). OCl? reacts with the probe leading to the formation of the corresponding aldehyde in a mixed‐aqueous system. The detection limit of the probe is in the 10?8 M range. The probe (TAM) also exhibits solvatofluorochromism. Changing the solvent from non‐polar to polar, the emission band of TAM largely red‐shifted. Moreover, the probe shows an excellent performance in real‐life application in detecting OCl? in human blood cells. The experimentally observed changes in the structure and electronic properties of the probe after reaction with OCl? were studied by DFT and TDDFT computational calculations. 相似文献
110.