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141.
Ellis MJ Antonyuk SV Strange RW Sawers G Eady RR Hasnain SS 《Inorganic chemistry》2004,43(24):7591-7593
Copper nitrite reductases contain both an electron-transfer type 1 Cu site and a catalytic type 2 Cu site. We have mutated one of the type 2 copper ligating histidines to observe the effect on catalytic turnover. This mutation has created a unique site where Cu is ligated by 2 His Nepsilon2 atoms alone. 相似文献
142.
Leatherman MD Svejda SA Johnson LK Brookhart M 《Journal of the American Chemical Society》2003,125(10):3068-3081
The synthesis of a series of (alpha-diimine)NiR(2) (R = Et, (n)Pr) complexes via Grignard alkylation of the corresponding (alpha-diimine)NiBr(2) precursors is presented. Protonation of these species by the oxonium acid [H(OEt(2))(2)](+)[BAr'(4)](-) at low temperatures yields cationic Ni(II) beta-agostic alkyl complexes which model relevant intermediates present in nickel-catalyzed olefin polymerization reactions. The highly dynamic nature of these agostic alkyl cations is quantitatively addressed using NMR line broadening techniques. Trapping of these complexes with ethylene provides cationic Ni alkyl ethylene species, which are used to determine rates of ethylene insertion into primary and secondary carbon centers. The Ni agostic alkyl cations are also trapped by CH(3)CN and Me(2)S to yield Ni(R)(L)(+) (L = CH(3)CN, Me(2)S) complexes, and the dynamic behavior of these species in the presence of varied [L] is discussed. The kinetic data obtained from these experiments are used to present an overall picture of the ethylene polymerization mechanism for (alpha-diimine)Ni catalysts, including effects of reaction temperature and ethylene pressure on catalyst activity, polyethylene branching, and polymer architecture. Detailed comparisons of these systems to the previously presented analogous palladium catalysts are made. 相似文献
143.
The surfactants sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) displace human serum albumin (HSA) from loosely packed self-assembled monolayers (SAM) of hydrophobic alkyl chains by different means. Removal of HSA is of interest because previous work has suggested that the adsorption of HSA to such loosely packed SAMs may be sufficiently tenacious to offer opportunities for surface passivation. While HSA remains on the surface after exposure to SDS and rinsing, no protein remains after exposure to CTAB and rinsing. X-ray reflectivity and X-ray photoelectron spectroscopy measurements indicate that CTAB molecules remain interdigitated in the loosely packed SAM after rinsing, suggesting that CTAB is more effective in removing the HSA because it interacts more strongly with the SAM. 相似文献
144.
Derivatization of a variety of peptides by a method known to enhance anhydride formation is demonstrated by mass spectrometry to yield ions that have elemental composition and fragmentation properties identical to [b(n-1) + OH + H]+ ions formed by gas-phase rearrangement and fragmentation. The [b(n-1) + OH + H]+ ions formed by gas-phase rearrangement and fragmentation and the solution-phase [b(n-1) + OH + H]+ ion structural analogs formed by derivatization chemistry show two different forms of dissociation using multiple-collision CAD in a quadrupole ion trap and unimolecular decomposition in a TOF-TOF; one group yields identical product ions as a truncated form of the peptide with a free C-terminal carboxylic acid and fragments at the same activation energy; the other group fragments differently from the truncated peptide, being more resistant to fragmentation than the truncated peptide and yielding primarily the [b(n-2) + OH + H]+ product ion. Nonergodic electron capture dissociation MS/MS suggests that any structural differences between the specific-fragmenting [b(n-1) + OH + H]+ ions and the truncated peptide is at the C-terminus of the peptide. The specific-fragmentation can be readily observed by MS(n) experiments to occur in an iterative fashion, suggesting that the C-terminal structure of the original [b(n-1) + OH + H]+ ion is maintained after subsequent rearrangement and fragmentation events in peptides which fragment specifically. A mechanism for the formation of specific-fragmenting and nonspecific-fragmenting [b(n-1) + OH + H]+ ions is proposed. 相似文献
145.
Briggs CR Allen MJ O'Hagan D Tozer DJ Slawin AM Goeta AE Howard JA 《Organic & biomolecular chemistry》2004,2(5):732-740
The energies of the gauche and anti conformers of 2-fluoroethylamine, 2-fluoroethanol and their protonated analogues are calculated using density functional theory. Unlike the non protonated systems, the protonated systems show a strong gauche effect where the C-F and the C-(+)NH(3) or C-F and C-(+)OH(2) bonds are gauche rather than anti to each other. Single crystal X-ray diffraction studies of 2-fluoroethylammonium compounds identify the same conformational preference. 相似文献
146.
Polymers and plastics are receiving increased attention as materials for microfluidics and microTAS applications. Given the ubiquity of fluorescence detection techniques in micro-analytical systems, the fluorescence properties of polymers and plastics should not be overlooked. We survey some commonly available polymer thin-films for their fluorescence behaviour under standardized conditions to determine which materials are most suitable for high-sensitivity fluorescence detection lab chips. The initial fluorescence intensities of some of the materials surveyed were significantly higher than glass and fused silica controls, and decreased over the three hour period with complex kinetics. We then discuss how this has confounded fluorescence detection in our analytical context, and possible mechanisms for the decrease. 相似文献
147.
148.
Valahovic MT Gunnoe TB Sabat M Harman WD 《Journal of the American Chemical Society》2002,124(13):3309-3315
A series of complexes of the form TpRe(CO)(L)(eta(2)-naphthalene) (Tp = hydridotris(pyrazolyl)borate) undergoes tandem electrophile/nucleophile addition reactions with a high degree of regiocontrol depending on the auxiliary ligand, L. When L = PMe(3), the reaction of the eta(2)-naphthalene complex with triflic acid followed by a silyl ketene acetal favors the 1,4-addition product, whereas when L = pyridine, N,N-dimethylaminopyridine, N-methylimidazole, or NH(3) the 1,2-addition product is favored. These reactions proceed with excellent stereocontrol: both electrophile (H(+), D(+)) and nucleophile (silyl ketene acetal) add anti to the face of metal coordination, and a single coordination diastereomer can be isolated for each reaction. One-electron oxidation of the Re complex affords the corresponding free dihydronaphthalene in good yield. 相似文献
149.
Kenneth R. Seddon 《Journal of organometallic chemistry》1985,293(1):C21-C25
A close examination of the ESR spectrum of a paramagnetic complex formed from bis(ethoxythiocarbonyl)sulfide and dimanganese decacarbonyl has revealed, for the first in this type of radical adduct, 13C hyperfine coupling in natural abundance from the carbonyl ligands. 相似文献
150.
C.S. Dimbylow I.J. McColm C.M.P. Barton N.N. Greenwood G.E. Turner 《Journal of solid state chemistry》1974,10(2):128-136
Crystal chemistry and phase relations for the bronze-forming region of the EuWO system have been investigated. A bronze EuxWO3 is stable up to 1000°C when x ? 0.125 and in the region 0.085 ? x ? 0.125 the symmetry is cubic. A tetragonal bronze exists at x = 0.05, and an orthorhombic bronze with a structure closely related to the orthorhombic form of WO3 exists below x = 0.01. Mössbauer spectra at room temperature and at 80 K indicate that in all these phases the europium is highly ionized as Eu(III) with no electron localization to give (EuII) even at low values for x. The decomposition products of the bronzes have been established, and the Mössbauer parameters for the highly nonstoichiometric tungstates EuxWO4 were determined. Both Eu(II) and Eu(III) resonances were obtained, and a cation vacancy model for EuxWO4 was found to fit the data best. In conformity with the foregoing data, a sample of composition “Eu2W2O7” was found not be be a pyrochlore but to comprise a mixture of Eu6WO12, EuxWO4, and W. The phase relationships for the europium bronze system EuxWO3 are compared with those of other ionic bronzes NaxWO3, LixWO3, and AlxWO3. 相似文献