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71.
A study of the leptonic coupling types in K+→π+?+?? (? = e, μ) provides come model-independent distinction between the various underlying mechanism: lowest order weak cum electromagnetic vs higher order weak interactions vs genuine strangeness-changing semileptonic neutral currents. This distinction is necessary in order to know the existence of these neutral currents. Pion energy spectrum for ? = e and the ratio of the total rate for ? = e to that for ? = μ is useful for this purpose, and the pion energy spectrum for ? = μ is of further help. Available data (? = eonly) are inadequate to provide the above distinction. Estimates of various coupling strengths are made from the observed ? = e rate. 相似文献
72.
C Dass 《Rapid communications in mass spectrometry : RCM》1989,3(8):264-266
Positive- and negative-ion fast-atom bombardment (FAB) mass spectrometry and linked-field scan techniques at constant B/E are used to characterize phosphorylated serine, threonine, and tyrosine amino acids. Abundant molecular ions are formed for all three amino acids in both modes of ionization. The dominant fragmentation is cleavage of the phosphate ester bond with charge retention in positive-ion FAB by the amino acid backbone and in the negative-ion mode by the phosphate group. The unique feature of positive-ion FAB mass spectra of phosphoserine and -threonine is the loss, from the ion [M + H]+, of a molecule of phosphoric acid (98 Da), whereas the corresponding tyrosine expels a HPO4 (96 Da) moiety to yield a stable phenylalanine ion. 相似文献
73.
A new approach using fast atom bombardment combined with mass spectrometry to characterize polycyclic aromatic hydrocarbons (PAHs) in the range of 128–252 u molecular weight is described. Sulfolane was employed as a liquid matrix for these π-conjugated hydrocarbons. Bombardment of sulfolane solution of certain PAHs with an atom beam produces both radical cation (M+) and protonated molecule [(M + H)+], with no evidence of fragmentation. Collisional activation of the fast atom bombardment-desorbed M+ ions, however, results in several structure-specific fragment ions. Structural differences in a few isomeric hydrocarbons can be detected using the [(M + H)+]/[M+] abundance ratio and in the pyrene-fluoranthene pair by the B/E linked-field-collision-activated dissociation data. The [(M + H)+]/[M+] was found to be compound-specific and correlated well with certain properties (resonance energy, proton affinity, and ionizing energy) of PAHs. 相似文献
74.
Summary Morpholine complexes of copper(II) alkanoates and chloroacetates of formula Cu(O2CR)2(Morph)n (where R = H, Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, CH2Cl, CHCl2 and CCl3; Morph = Morpholine and n=1 and/or 2) have been isolated by the direct interaction of morpholine with the respective copper(II) carboxylates in a suitable organic medium and characterized by elemental analyses and various physicochemical techniques. Molecular weight determinations show that 11 complexes are dimeric whereas 21 complexes are monomeric in solution. Electronic spectra and magnetic moments suggest that 11 complexes are dinuclear carboxylate bridged species while 21 addition complexes have atrans-octahedral configuration. The i.r. spectra indicate that morpholine behaves as a monodentate ligand and coordinates through its nitrogen atom. 相似文献
75.
Methylmethacrylate (MMA) can be initiated by charge transfer complexes (i) formed by the interaction of aliphatic amines and MMA and (ii) formed by the interaction of aliphatic amines and carbon tetrachloride in a solvent like N-N dimethylformamide (DMF), dimethyl sulphoxide (DMSO) or chloroform. This paper reports the polymerization of MMA by isopropylamine (IPA) in the presence of CCl4 in DMSO at 30. The rate of polymerization, Rp increases rapidly with CCl4 up to a concentration of 0.25 mol l?1 but, for a higher concentration, it is practically independent of the CCl4 concentration. Rp is proportional to (IPA concentration)1 2 and to power of (MMA concentration)1.30 when [CCl4] ? [IPA]. The average rate constant, k, is 2.1 × 10?6 l mol· 1 sec? 1. 相似文献
76.
2-Vinyl pyridine (2-VP) can be initiated by a charge-transfer complex formed by the interaction of aliphatic amines such as n-butylamine (nBA) and carbon tetrachloride (CCl4) in a solvent like NN-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). This article describes the polymerization of 2-VP by n-butylamine (nBA) in the presence of carbon tetrachloride in DMSO at 60°C. The rate of polymerization Rp increases rapidly with carbon tetrachloride (CCl4) up to a concentration of 3.93 mol/L, but for a higher concentration it is almost independent of the carbon tetrachloride concentration; Rp is proportional to [nBA]0.5 and [2-VP]1.5 when [CCl4]>[nBA]. The average rate constant k is 1.03 × 10?5 L/mol s. When [CCl4] < [nBA] the rate constant in terms of [2-VP] was 1.06 × 10?5 s?1 at 60°C and the overall rate constant was 1.035 × 10?5 L/mol s at 60°C. 相似文献
77.
Dass A Guo R Tracy JB Balasubramanian R Douglas AD Murray RW 《Langmuir : the ACS journal of surfaces and colloids》2008,24(1):310-315
Two syntheses of gold nanoparticles with fluorinated alkyl and aryl thiolate ligands are reported. The fluorous Au nanoparticles are smaller than previous gold fluor-capped examples, and are in the 44-75 Au atom size range. Fluoroalkyl thiolate-protected (1H,1H,2H,2H-perfluorodecanethiolate) nanoparticles synthesized by a Brust reaction are a mixture of (mainly) approximately 8.5 kDa (ca. 44 core atoms) and approximately 14 kDa (ca. 75 core atoms) species, by MALDI-mass spectrometry. This composition is consistent with thermogravimetric analysis (TGA) results of the ligand shell composition. 19F NMR spectra display a progressive line broadening of resonances for fluorine sites closer to the Au core. A second synthetic route used a (ligand replacement) reaction of pentafluorobenzenethiol with Au55(PPh3)12Cl6. The exchange is (as previously observed for nonfluorinated thiols) accompanied by nanoparticle core size changes to produce a polydisperse mixture within which a Au75 core species could be electrochemically discerned by its characteristic 0.74 V electrochemical energy gap. Further characterization of the polydisperse nanoparticle product was done by HPLC, TEM, TGA, optical spectroscopy, and NMR data. Both varieties of fluorous nanoparticles exhibit solubilities typical of perfluorinated materials, as opposed to proteo versions. 相似文献
78.
Heaven MW Dass A White PS Holt KM Murray RW 《Journal of the American Chemical Society》2008,130(12):3754-3755
We report the crystal structure of the thiolate gold nanoparticle [TOA+][Au25(SCH2CH2Ph)18-], where TOA+ = N(C8H17)4+. The crystal structure reveals three types of gold atoms: (a) one central gold atom whose coordination number is 12 (12 bonds to gold atoms); (b) 12 gold atoms that form the vertices of an icosahedron around the central atom, whose coordination number is 6 (five bonds to gold atoms and one to a sulfur atom), and (c) 12 gold atoms that are stellated on 12 of the 20 faces of the Au13 icosahedron. The arrangement of the latter gold atoms may be influenced by aurophilic bonding. Together they form six orthogonal semirings, or staples, of -Au2(SCH2CH2Ph)3- in an octahedral arrangement around the Au13 core. 相似文献
79.
80.