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11.
Solvation of the thallous ion in dilute solutions of six binary solvent systems (formamide/water,N-methylformamide/water,N-ethylformamide/water, formamide/N-methylformamide, formamide/N-ethylformamide, andN-methylformamide/N-ethylformamide) was studied with205Tl NMR spectroscopy. An attempt was made to separate solvation effects related to the electrondonating ability (Lewis basicity) of the solvents from effects resulting from structural changes in the solvation sphere. Structural effects were found to be greatest in theN-methylformamide/water system and least in theN-methylformamide/formamide system. 相似文献
12.
J. Berakdar J. S. Briggs H. Klar 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,24(4):351-364
Single ionization of helium and atomic hydrogen by the impact of protons and antiprotons is considered. Using a multiple scattering model, first proposed by Garibotti and Miraglia [1], angular and energy distributions of the ejected electrons are calculated. Structures arising in the cross section, especially the Coulomb density of states effect (CDS), are analysed. The contributions of various scattering amplitudes to the cross section are studied. It is concluded that multiple scattering together with the CDS-effect play an important role in determining the transition amplitude. Differences between particle and antiparticle impact are examined. In addition to the different behaviour of the CDS-effect, the interference of two scattering amplitudes turns out to be decisive in ionization by particle and antiparticle impact. 相似文献
13.
D. L. Allara C. W. White R. L. Meek T. H. Briggs 《Journal of polymer science. Part A, Polymer chemistry》1976,14(1):93-104
Two surface analysis techniques (Rutherford backscattering and surface composition by analysis of neutral and ion impact radiation) have been applied to the study of interfacial copper transport in the oxidation of polyethylene films over copper surfaces. Analysis of films oxidized several thousand hours at 40, 57, and 87°C shows maximum concentrations of copper species in the polymer matrix of ~0.1M extending to depths of several thousand angstroms. These results, together with previous infrared spectroscopic studies, allow some significant conclusions and hypotheses to be drawn as regards the roles of heterogeneous and homogeneous catalytic processes which occur in the thermal-oxidative degradation of polyethylene–copper systems. 相似文献
14.
Tommaso R.I. Cataldi Ian G. Blackham G.Andrew D. Briggs John B. Pethica H.Alien O. Hill 《Journal of Electroanalytical Chemistry》1990,290(1-2)
The successful expansion which the scanning tunneling microscopy (STM) has had is dependent on its ability to examine surfaces on a sub-nanometric scale and on providing in situ (i.e. in the presence of bulk electrolyte) sample examination. In addition to the ability to study metals and semiconductors in vacuo, the application of the technique to surfaces in contact with an electrolytic solution has prompted increased interest amongst electrochemists. We discuss herein the technique, with particular reference to advances in electrochemical applications. A new scanning tunneling microscope for operation in electrolytic environments is described. Atomic force microscopy, scanning electrochemical microscopy and scanning ion-conducting microscopy are compared with the STM. 相似文献
15.
Orange crystals of Cs(4)Th(4)P(4)Se(26) were grown from the reaction of (232)Th and P in a Cs(2)Se(3)/Se molten salt flux at 750 degrees C. Cs(4)Th(4)P(4)Se(26) crystallizes in the orthorhombic space group Pbca with the unit cell parameters: a = 12.0130(6), b = 14.5747(7), c = 27.134(1) A; Z = 8. The compound exhibits a three-dimensional structure, consisting of dimeric [Th(2)Se(13)] polyhedral units. The two crystallographically independent, nine-coordinate, bicapped trigonal prismatic thorium atoms share a triangular face to form the dimer, and each dimer edge-shares two selenium atoms with two other dimers to form kinked chains along the [010] direction. While this structure shares features of the previously reported Rb(4)U(4)P(4)Se(26), including phosphorus in the 5+ oxidation state, careful inspection of the structure reveals that the selenophosphate anion that knits the structure together in three directions in both compounds is a unique (P(2)Se(9))(6-) anion. The formula may be described best as [Cs(2)Th(2)(P(2)Se(9))(Se(2))(2)](2). The (P(2)Se(9))(6-) anion features a nearly linear Se-Se-Se backbone with an angle of 171 degrees and Se-Se distances that are approximately 0.2-0.3 A longer than the typical single Se-Se bond. Magnetic studies confirm that this phase contains Th(IV). Raman data for this compound is reported, and structural comparisons will be drawn to its uranium analogue, Rb(4)U(4)P(4)Se(26). 相似文献
16.
We report a new structure-based strategy for the identification of novel inhibitors. This approach has been applied to Bacillus stearothermophilus alanine racemase (AlaR), an enzyme implicated in the biosynthesis of the bacterial cell wall. The enzyme catalyzes the racemization of l- and d-alanine using pyridoxal 5-phosphate (PLP) as a cofactor. The restriction of AlaR to bacteria and some fungi and the absolute requirement for d-alanine in peptidoglycan biosynthesis make alanine racemase a suitable target for drug design. Unfortunately, known inhibitors of alanine racemase are not specific and inhibit the activity of other PLP-dependent enzymes, leading to neurological and other side effects.This article describes the development of a receptor-based pharmacophore model for AlaR, taking into account receptor flexibility (i.e. a `dynamic' pharmacophore model). In order to accomplish this, molecular dynamics (MD) simulations were performed on the full AlaR dimer from Bacillus stearothermophilus (PDB entry, 1sft) with a d-alanine molecule in one active site and the non-covalent inhibitor, propionate, in the second active site of this homodimer. The basic strategy followed in this study was to utilize conformations of the protein obtained during MD simulations to generate a dynamic pharmacophore model using the property mapping capability of the LigBuilder program. Compounds from the Available Chemicals Directory that fit the pharmacophore model were identified and have been submitted for experimental testing.The approach described here can be used as a valuable tool for the design of novel inhibitors of other biomolecular targets. 相似文献
17.
Kanai M Porfyrakis K Briggs GA Dennis TJ 《Chemical communications (Cambridge, England)》2004,(2):210-211
We report the purification of the nitrogen-containing incar-fullerenes iNC(60) and iNC(70), and their characterisation by UV-Vis absorption spectroscopy. 相似文献
18.
19.
Methylene blue transfers electrons to a membrane-associated b-type cytochrome in particulate fractions from corn coleoptiles. The Km for methylene blue is less than 1 µM under optimal conditions. This reaction is destroyed by boiling, but not by 7 M urea. Kinetic analyses of the influence of light intensity on cytochrome reduction suggest that a first order photochemical reaction is limiting. Free EDTA may serve as an electron donor in this system at least at high methylene blue and protein concentrations. The photoactivity does not coincide either with mitochondrial or endoplasmic reticulum markers, and may be localized in plasma membrane. There is an estimated 5 times 10-10 mol photoreducible cytochrome per g coleoptile tissue. Studies on the effect of pH on the reaction in the presence of methylene blue or thionine indicate that dye photoreduction itself is not rate-limiting. Wavelength dependence studies suggest that it is methylene blue monomer and not dimer which mediates the reaction. Although oxygen is apparently required for the reaction, neither superoxide nor excited singlet oxygen appear to be involved. The reaction mechanism is still unknown. 相似文献