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651.
652.
Rannes JB Ioannou A Willies SC Grogan G Behrens C Flitsch SL Turner NJ 《Journal of the American Chemical Society》2011,133(22):8436-8439
A directed evolution approach has been used for the generation of variants of galactose oxidase (GOase) that can selectively oxidize glycans on glycoproteins. The aldehyde function introduced on the glycans D-mannose (Man) and D-N-acetyl glucosamine (GlcNAc) by the enzyme variants could then be used to label the glycoproteins and also whole cells that display mannosides on their surface. 相似文献
653.
Xu X Lu H Ruppel JV Cui X Lopez de Mesa S Wojtas L Zhang XP 《Journal of the American Chemical Society》2011,133(39):15292-15295
3,5-Di(t)Bu-QingPhyrin, a new D(2)-symmetric chiral porphyrin derived from a chiral cyclopropanecarboxamide containing two contiguous stereocenters, has been developed using an iterative approach based on Co(II)-catalyzed asymmetric cyclopropanation of alkenes. The Co(II) complex of 3,5-Di(t)Bu-QingPhyrin, [Co(P2)], has proved to be a general and effective catalyst for asymmetric intramolecular cyclopropanation of various allylic diazoacetates (especially including those with α-acceptor substituents) in high yields with excellent stereoselectivities. The [Co(P2)]-based intramolecular metalloradical cyclopropanation provides convenient access to densely functionalized 3-oxabicyclo[3.1.0]hexan-2-one derivatives bearing three contiguous quaternary and tertiary chiral centers with high enantiomeric purity. 相似文献
654.
Hydrous silicate glasses with compositions along the join diopside-anorthite (An, CaAl(2)Si(2)O(8))-(Di, CaMgSi(2)O(6)) containing up to 3 wt. % H(2)O were synthesized at temperatures 1523-1723 K and pressures of 200 MPa in an internally heated gas pressure vessel. The water content of the glasses was analyzed by Karl-Fischer titration. Infrared microspectroscopy was used to test the homogeneity of the water distribution and to measure the concentrations of OH groups and H(2)O molecules before and after conductivity measurements. The electrical conductivity was measured by impedance spectroscopy at temperature up to 685 K. A positive correlation between water content and conductivity was observed for An(100) from 0 to 1.8 wt.% H(2)O, for An(50)Di(50) (in mol.%) from 1.5 to 2.8 wt.% H(2)O, and for Di(100) from 0 to 1.2 wt.% H(2)O. At same water content of ~1.2 wt.%, the conductivity was three orders of magnitude higher in Di(100) than in the other two glasses, emphasizing the importance of non-bridging oxygens on the transport of hydrous charge carriers. Consistent with findings in literature, we conclude that protons are the predominant mobile charge carriers in alkali-free hydrous silicate glasses. Conductivity data were evaluated in terms of proton diffusivity by the Nernst-Einstein equation. The obtained diffusion coefficients range from 10(-17) m(2)/s for An(50)Di(50) with 1.50 wt.% of H(2)O at 596 K to 10(-12) m(2)/s for An(50)Di(50) with 2.77 wt.% of H(2)O at 685 K. 相似文献
655.
Biosynthesis of the molybdenum cofactor in bacteria is described with a detailed analysis of each individual reaction leading to the formation of stable intermediates during the synthesis of molybdopterin from GTP. As a starting point, the discovery of molybdopterin and the elucidation of its structure through the study of stable degradation products are described. Subsequent to molybdopterin synthesis, the molybdenum atom is added to the molybdopterin dithiolene group to form the molybdenum cofactor. This cofactor is either inserted directly into specific molybdoenzymes or is further modified by the addition of nucleotides to the molybdopterin phosphate group or the replacement of ligands at the molybdenum center. 相似文献
656.
We have developed a method for quantification of a specific monoclonal IgM directed toward embryonic stem cells based on a peptide affinity monolith. A peptide affinity ligand with the sequence C-C-H-Q-R-L-S-Q-R-K was obtained by epitope mapping using peptide SPOT synthesis. The peptide ligand was covalently immobilized by coupling the N-terminal cysteine to a monolithic disk that was previously modified with iodated spacer molecules. The monolithic disc was used for quantification of purified IgM and for IgM present in mammalian cell culture supernatant. We observed 17% unspecific binding of IgM to the monolithic disk and additionally a product loss in the flow through of 20%. Nevertheless, calibration curves had high correlation coefficients and inter/intra-assay variability experiments proved sufficient precision of the method. A limit of quantification of 51.69 μg/mL for purified IgM and 48.40 μg/mL for IgM in cell culture supernatant could be calculated. The binding capacity was consistent within the period of the study which included more than 200 cycles. The analysis time of less than 2 min is an advantage over existing chromatographic methods that rely on pore diffusion. 相似文献
657.
An artificial operon was synthesized, consisting of the genes for chorismate pyruvate-lyase of E. coli and for 4-hydroxybenzoate 3-hydroxylase of Corynebacterium cyclohexanicum. This operon, directing the biosynthesis of 3,4-dihdroxybenzoate, was expressed in the heterologous expression host Streptomyces coelicolor M512, together with a modified biosynthetic gene cluster for the aminocoumarin antibiotic clorobiocin. The resulting strain produced a clorobiocin derivative containing a 3,4-dihdroxybenzoyl moiety. Its structure was confirmed by MS and NMR analysis, and it was found to be a potent inhibitor of the gyrases from Escherichia coli and Staphylococcus aureus. Bioassays against different E. coli mutants suggested that this compound is actively imported by catechol siderophore transporters in the cell envelope. This study provides an example of the structure of a natural product that can be rationally modified by synthetic biology. 相似文献
658.
Klokishner S Behrens M Reu O Tzolova-Müller G Girgsdies F Trunschke A Schlögl R 《The journal of physical chemistry. A》2011,115(35):9954-9968
In the present paper we report combined experimental and theoretical studies of the UV-vis-NIR spectra of the mineral compounds malachite, rosasite, and aurichalcite and of the precursor compounds for Cu/ZnO catalysts. For the copper species in the minerals the crystal field splitting and the vibronic coupling constants are estimated using the exchange charge model of the crystal field accounting for the exchange and covalence effects. On this basis the transitions responsible for the formation of the optical bands arising from the copper centers in minerals are determined and the profiles of the absorption bands corresponding to these centers are calculated. The profiles of the absorption bands calculated as a sum of bands of their respective Cu species are in quite good agreement with the experimental data. In agreement with crystal chemical considerations, the Zn ions were found to be preferentially located on the more regular, i.e., less distorted, octahedral sites in zincian malachite and rosasite, suggesting a high degree of metal ordering in these phases. This concept also applies for the mineral aurichalcite, but not for synthetic aurichalcite, which seems to exhibit a lower degree of metal ordering. The catalyst precursor was found to be a mixture of zincian malachite and a minor amount of aurichalcite. The best fit of the optical spectrum is obtained assuming a mixture of contributions from malachite (0% Zn) and rosasite (38% Zn of [Zn + Cu]), which is probably due to the intermediate Zn content of the precursor (30%). 相似文献
659.
Behrens CR Hooker JM Obermeyer AC Romanini DW Katz EM Francis MB 《Journal of the American Chemical Society》2011,133(41):16398-16401
A highly efficient protein bioconjugation method is described involving addition of anilines to o-aminophenols in the presence of sodium periodate. The reaction takes place in aqueous buffer at pH 6.5 and can reach high conversion in 2-5 min. The major product was characterized using X-ray crystallography, which revealed that an unprecedented oxidative ring contraction occurs after the coupling step. The compatibility of the reaction with protein substrates has been demonstrated through attachment of small molecules, polymer chains, and peptides to p-aminophenylalanine residues introduced into viral capsids through amber stop codon suppression. Coupling of anilines to o-aminophenol groups derived from tyrosine residues is also described. The compatibility of this method with thiol modification chemistry is shown through attachment of a near-IR fluorescent chromophore to cysteine residues inside the viral capsid shells, followed by attachment of integrin-targeting RGD peptides to anilines on the exterior surface. 相似文献
660.
Max Herberhold Silke Gerstmann Und Bernd Wrackmeyer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):273-283
Abstract Reactions of the salts K2SN2 and K[(NSN)R] (R = ′Bu, SiMe3 and P′Bu2) with organoelement chlorides R′R′ěl have been used to prepare four series of model sulfur diimides: R′R″E(NSN)ER″R′, ′Bu(NSN)ER″R′, Me3Si(NSN)E″R′ and tBu2P(NSN)ER″R′, respectively (E = C, Si, Ge, Sn; R′ and R″ = alkyl or aryl group). All compounds have been characterized by ′H and 13C NMR and—if possible—by 31P, 29Si and 119Sn NMR spectroscopy. The configuration (Z or E) of the substituents R and E″R′ has been assigned in several cases using tBu(NSN)tBu (1) as a reference. The E,Z assignment of 1H, 13C and 15N nuclei in 1 is based on selectively 1H-decoupled refocused INEPT 15N NMR and two-dimensional (2D) 13C/1H heteronuclear shift correlations. The sulfur diimides under study are in general fluxional in solution. 相似文献