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81.
We consider atomic Bose-Fermi mixtures in optical lattices and study the superfluidity of fermionic atoms due to s-wave pairing induced by boson-fermion interactions. We prove that the induced fermion-fermion coupling is always attractive if the boson-boson on-site interaction is repulsive, and predict the existence of an enhanced BEC-BCS crossover as the strength of the lattice potential is varied. We show that for direct on-site fermion-fermion repulsion, the induced attraction can give rise to superfluidity via s-wave pairing at striking variance with the case of pure systems of fermionic atoms with direct repulsive interactions. 相似文献
82.
We classify the entanglement of two-mode Gaussian states according to their degree of total and partial mixedness. We derive exact bounds that determine maximally and minimally entangled states for fixed global and marginal purities. This characterization allows for an experimentally reliable estimate of continuous variable entanglement based on measurements of purity. 相似文献
83.
We study, through the variational Monte Carlo technique, an extended Hubbard model away from half filled band density which contains two competing nearest-neighbor interactions: a superexchange J favoring d-wave superconductivity and a repulsion V opposing it. We find that the on-site repulsion U effectively enhances the strength of J while suppressing that of V, thus favoring superconductivity. This result shows that attractions which do not involve charge fluctuations are very well equipped against strong electron-electron repulsion so much to get advantage from it. 相似文献
84.
Gutsul EI Belkova NV Sverdlov MS Epstein LM Shubina ES Bakhmutov VI Gribanova TN Minyaev RM Bianchini C Peruzzini M Zanobini F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(10):2219-2228
The reactions of the octahedral dihydrido complexes [MH(2)(PP(3))] [M=Fe, Ru, Os; PP(3)=P(CH(2)CH(2)PPh(2))(3)] with a variety of weak ROH acids have been studied by IR and NMR methods in either CH(2)Cl(2) or THF in the temperature range from 190 to 290 K. This study has allowed the determination of the spectral and thermodynamic properties associated with the formation of dihydrogen bonds (DHB) between the terminal hydrides and the OH group. Both the DHB enthalpy values and the hydride basicity factors (E(j)) have been found to increase in the order Fe < Ru < Os. The proton transfer process, leading to the DHB complexes, and eventually to eta(2)-H(2) products, has been found to depend on the acidic strength of the alcohol as well as the nature of the solvent. Low temperature IR and NMR techniques have been used to trace the complete energy profile of the proton transfer process involving the osmium complex [OsH(2)(PP(3))] with trifluoroethanol. 相似文献
85.
Fresh (larch and fir, in its white and red varieties) and ancient wood samples (dating respectively to the 13th, 15th and 17th centuries) were subjected to thermogravimetric analysis (TG and DTG). The resulting thermogravimetric data were then used to construct archeometric curves for the wood varieties tested. In a preliminary approach, it was attempted to correlate the onset temperature of the thermogravimetric step corresponding to cellulose decomposition with the age (expressed in centuries) of the samples, although the results obtained were anything but brilliant. More encouraging results were obtained by examining the relationship between wood sample age and the value of the (percent cellulose/percent lignin) ratio computed from the thermogravimetric data. Lastly, a procedure for processing data obtained from the TG curves was applied to a kinetic analysis of the processes that take place when wood samples are subjected to a temperature regime with a constant heating rate, obtaining values for the activation energy of the TG step corresponding to the decomposition of cellulose. Also using these data it was attempted to construct archeometric curves, obtaining results that varied quite significantly according to the wood species tested. 相似文献
86.
We shall give, in an optimal form, a sufficient numerical condition for the finiteness of the fundamental group of the smooth
locus of a normal K3 surface. We shall moreover prove that, if the normal K3 surface is elliptic and the above fundamental
group is not finite, then there is a finite covering which is a complex torus.
Received: 13 April 2001 / Published online: 16 October 2002
RID="⋆"
ID="⋆" Supported by Korea Research Foundation Grant(KRF-2001-041-D00025)
Mathematics Subject Classification (2000): 14J28 相似文献
87.
Ylenia Pecci Fabrizio Rivardo Maria Giovanna Martinotti Gianna Allegrone 《Journal of mass spectrometry : JMS》2010,45(7):772-778
Lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain showed an interesting anti‐adhesion activity against biofilm formation of human pathogenic bacterial strains. The chemical characterisation of the crude extract of V9T14 strain was first developed through electrospray ionisation mass spectrometry (ESI‐MS) and ESI‐MS/MS direct infusions: two sets of molecular ion species belonging to the fengycin and surfactin families were revealed and their structures defined, interpreting their product ion spectra. The LC/ESI‐MS analysis of the crude extract allowed to separate in different chromatogram ranges the homologues and the isoforms of the two lipopeptide families. The extract was then fractionated by silica gel chromatography in two main fractions, I and II. The purified biosurfactants were analysed through a new, rapid and suitable LC/ESI‐MS/MS method, which allowed characterising the composition and the structures of the produced lipopeptides. LC/ESI‐MS/MS analysis of fraction I showed the presence of C13, C14 and C15 surfactin homologues, whose structures were confirmed by the product ion spectra of the sodiated molecules [M + Na]+ at m/z 1030, 1044 and 1058. LC/ESI‐MS/MS analysis of fraction II confirmed the presence of two main fengycin isoforms, with the protonated molecules [M + H]+ at m/z 1478 and 1506 corresponding to C17 fengycin A and C17 fengycin B, respectively. Other homologues (C14 to C16) were revealed and confirmed as belonging to fengycin A or B according to the retention times and the product ions generated, although with the same nominal mass. Finally, a relative percentage content of each homologue for both lipopeptides families in the whole extract was proposed. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
88.
89.
90.
Stefano Gialanella Fabrizio Girardi Gloria Ischia Ivan Lonardelli Maurizio Mattarelli Maurizio Montagna 《Journal of Thermal Analysis and Calorimetry》2010,102(3):867-873
This study deals with some microstructural and crystallographic aspects of the thermally induced transformation of goethite
(α-FeOOH) into hematite (α-Fe2O3), occurring at about 300 °C. Powder specimens of goethite have been annealed in air at different temperatures, ranging from
200 °C up to 1,000 °C. The resulting products have been analyzed for a complete characterization of the changes brought about
by the thermal treatments, using a multianalytical approach, based on: thermogravimetry, differential thermal analysis, transmission
electron microscopy, Raman spectroscopy, and X-ray diffraction. At lower temperatures, the transition to hematite produces
no important changes in size and shape of the original goethite grains. Recrystallization, and partial sintering, occurs only
at temperatures in excess of 800 °C. The relevant evolution of pores present in both phases has been also considered, as it
may provide important indications on the actual formation mechanism of hematite. 相似文献