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81.
A novel, simple and green procedure is presented for the determination of boron. The method is based on ultrasound-assisted conversion of boron to tetrafluoroborate anion and the formation of an ion pair between BF4− and Astra Phloxine reagent (R), followed by dispersive liquid-liquid microextraction of the ion pair formed and subsequent UV-vis spectrophotometric detection. The conversion of boron to tetrafluoroborate anion is performed in an acidic medium of 0.9 mol L−1 H2SO4 in the presence of 0.1 mol L−1 F- by means of 10 min of ultrasonication. The extraction of the ion pair formed between BF4− and R (1 × 10−4 mol L−1 R) is carried out by dispersive liquid-liquid microextraction using 0.5 mL of amyl acetate (as extraction solvent), tetrachloromethane (as auxiliary solvent) and acetonitrile (as dispersive solvent) in a ratio of 1:1:2. The absorbance of the coloured extracts obeys Beer's law in the range 0.22-18.7 mg L−1 of B(III) at 553 nm wavelength. The limit of detection calculated from a blank test (n = 10) based on 3 s is 0.015 mg L−1 of B(III). The method was applied to the determination of boron in mineral waters. 相似文献
82.
Jiménez MV Lahoz FJ Lukešová L Miranda JR Modrego FJ Nguyen DH Oro LA Pérez-Torrente JJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(29):8115-8128
The treatment of [{Rh(μ-SH){P(OPh)(3)}(2)}(2)] with [{M(μ-Cl)(diolef)}(2)] (diolef=diolefin) in the presence of NEt(3) affords the hydrido-sulfido clusters [Rh(3)(μ-H)(μ(3)-S)(2)(diolef){P(OPh)(3)}(4)] (diolef=1,5-cyclooctadiene (cod) for 1, 2,5-norbornadiene (nbd) for 2, and tetrafluorobenzo[5,6]bicyclo[2.2.2]octa-2,5,7-triene (tfb) for 3) and [Rh(2)Ir(μ-H)(μ(3)-S)(2)(cod){P(OPh)(3)}(4)] (4). Cluster 1 can be also obtained by treating [{Rh(μ-SH){P(OPh)(3)}(2)}(2)] with [{Rh(μ-OMe)(cod)}(2)], although the main product of the reaction with [{Ir(μ-OMe)(cod)}(2)] was [RhIr(2)(μ-H)(μ(3)-S)(2)(cod)(2){P(OPh)(3)}(2)] (5). The molecular structures of clusters 1 and 4 have been determined by X-ray diffraction methods. The deprotonation of a hydrosulfido ligand in [{Rh(μ-SH)(CO)(PPh(3))}(2)] by [M(acac)(diolef)] (acac=acetylacetonate) results in the formation of hydrido-sulfido clusters [Rh(3)(μ-H)(μ(3)-S)(2)(CO)(2) (diolef)(PPh(3))(2)] (diolef=cod for 6, nbd for 7) and [Rh(2)Ir(μ-H)(μ(3)-S)(2)(CO)(2)(cod)(PPh(3))(2)] (8). Clusters 1-3 and 5 exist in solution as two interconverting isomers with the bridging hydride ligand at different edges. Cluster 8 exists as three isomers that arise from the disposition of the PPh(3) ligands in the cluster (cis and trans) and the location of the hydride ligand. The dynamic behaviour of clusters with bulky triphenylphosphite ligands, which involves hydrogen migration from rhodium to sulfur with a switch from hydride to proton character, is significant to understand hydrogen diffusion on the surface of metal sulfide hydrotreating catalysts. 相似文献
83.
The following properties are in the present literature associated with the behavior of supercooled glass-forming liquids: faster than exponential growth of the relaxation time, dynamical heterogeneities, growing point-to-set correlation length, crossover from mean-field behavior to activated dynamics. In this paper we argue that these properties are also present in a much simpler situation, namely the melting of the bulk of an ordered phase beyond a first order phase transition point. This is a promising path toward a better theoretical, numerical and experimental understanding of the above phenomena and of the physics of supercooled liquids. We discuss in detail the analogies and the differences between the glass and the bulk melting transitions. 相似文献
84.
Lenka Hal?inová Radko Mesiar 《Nonlinear Analysis: Theory, Methods & Applications》2011,74(5):1545-1554
In this paper we continue the study of a submeasure notion introduced in Hutník and Mesiar (2009) [1] involving a class of operations which provides a generalization ofτT-submeasures. We construct pseudo-metrics and metrics generated by such probabilistic submeasures. Two possible generalizations of our submeasure notion are discussed. 相似文献
85.
The effect of new synthetic pyrazinecarboxamide derivatives as potential elicitors of flavonolignan and flavonoid production in Silybum marianum and Ononis arvensis cultures in vitro was investigated. Both tested elicitors increased the production of flavonolignans in S. marianum callus and suspension cultures and flavonoids in O. arvensis callus and suspension cultures. Compound I, 5-(2-hydroxybenzoyl)-pyrazine-2-carboxamide, has shown to be an effective elicitor of flavonolignans and taxifoline production in Silybum marianum culture in vitro. The maximum content of silydianin (0.11%) in S. marianum suspension culture was induced by 24 h elicitor application in concentration of 1.159 × 10?3 mol/L. The maximum content of silymarin complex (0.08%) in callus culture of S. marianum was induced by 168 h elicitor application of a concentration 1.159 × 10?? mol/L, which represents contents of silydianin (0.03%), silychristin (0.01%) and isosilybin A (0.04%) compared with control. All three tested concentrations of compound II, N-(2-bromo-3-methylphenyl)-5-tert-butylpyrazin-2-carboxamide increased the flavonoid production in callus culture of O. arvensis in a statistically significant way. The best elicitation effect of all elicitor concentrations had the weakest c? concentration (8.36 × 10?? mol/L) after 168 h time of duration. The maximum content of flavonoids (about 5,900%) in suspension culture of O. arvensis was induced by 48 h application of c? concentration (8.36 × 10?? mol/L). 相似文献
86.
V. N. Lazukov P. A. Alekseev E. S. Klement’ev E. V. Nefedova I. P. Sadikov J. -M. Mignot N. B. Kol’chugina O. D. Chistyakov 《Journal of Experimental and Theoretical Physics》1998,86(5):943-952
To examine the effect of hybridization of 4f electrons with conduction electrons on the crystal field potential using neutron spectroscopy, we studied the effects of
the crystal electric field (CEF) in intermetallic compounds of the type ReNi, in which chemical substitution is followed by
a transition of the cerium ions from an intermediate valence state to the Kondo state. Measurements were performed both on
cerium ions in the compounds Ce1−x
LaxNi (x=0.5, 0.8), where they have a whole-number population of the 4f shell, and on the paramagnetic impurity ion Nd in the series of compounds Re1−x
NdxNi (Re=Ce, La, Y), in which the cerium ions are found either in an intermediate valence state or in the Kondo state. From
the neutron inelastic magnetic scattering spectra on Nd ions, we have reconstructed the crystal field parameters in ReNi compounds
and calculated the CEF level diagram of Ce ions in these compounds as functions of the interion distances Re-Ni. The results
of our calculations are in good agreement with the experimentally determined splitting diagram of the ground-state multiplet
of the Ce ions. We have determined that as the degree of hybridization with the conduction electrons grows the CEF potential
varies considerably and the effective splitting of the 4f shell of the cerium ions increases. The estimated energy scale of the splitting of the ground-state multiplet of the Ce3+ ions in the ReNi CEF (ΔCEF∼15 meV) turns out to be commensurate with the Kondo temperature (T
K
;140 K for CeNi. Analysis indicates that the CEF potential has a substantial effect on the formation of the valence-unstable
ground state of the f shell in this compound.
Zh. éksp. Teor. Fiz. 113, 1731–1747 (May 1998) 相似文献
87.
88.
89.
The quark model and exchange degeneracy of leading Reggeon contributions to quark-quark scattering amplitudes are combined for deriving a number of relations on polarizations, the real parts of forward scattering amplitudes and total cross sections. The comparison of these relations with experimental data is discussed.The authors are grateful to Ya. I.Asimov, E. M.Levin and L. L.Frankfurt for their interest in this work. 相似文献
90.
The degree of diastereoselectivity in the wrapping of four new chiral Salan ligands to form chiral-at-metal titanium complexes ranged from mild to perfect as a function of the ligands' N substituents; the enantiomerically pure complexes catalyzed the addition of diethyl zinc to benzaldehyde in 73-76% enantiomeric excess. 相似文献