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101.
102.
103.
The results of dielectric studies performed in a broad frequency range for two compounds, 4-cyanophenyl 4-n-heptylbenzoate (7BBCN) and 4-(4-cyanobutyloxy)phenyl 4- n-heptylbenzoate (7BB4CN), are compared. They have the same molecular core whereas the strongly polar CN group is attached to the benzene ring in 7BBCN or is separated from it by the butyloxy chain in 7BB4CN. 7BBCN has a nematic phase, whereas 7BB4CN exhibits a monotropic nematic and smectic A2 polymorphism. Large differences in the dielectric properties of the two substances were found. The analysis of the results led to the conclusion that the antiparallel dipole-dipole associations are considerably stronger in the substance with a decoupled CN group. 相似文献
104.
Boulatov R Collman JP Shiryaeva IM Sunderland CJ 《Journal of the American Chemical Society》2002,124(40):11923-11935
Catalytic reduction of O(2) and H(2)O(2) by new synthetic analogues of the heme/Cu site in cytochrome c and ubiquinol oxidases has been studied in aqueous buffers. Among the synthetic porphyrins yet reported, those employed in this study most faithfully mimic the immediate coordination environment of the Fe/Cu core. Under physiologically relevant conditions, these biomimetic catalysts reproduce key aspects of the O(2) and H(2)O(2) chemistry of the enzyme. When deposited on an electrode surface, they catalyze the selective reduction of O(2) to H(2)O at potentials comparable to the midpoint potential of cytochrome c. The pH dependence of the half-wave potentials and other data are consistent with O-O bond activation at these centers proceeding via a slow generation of a formally ferric-hydroperoxo intermediate, followed by its rapid reduction to the level of water. This kinetics is analogous to that proposed for the O-O reduction step at the heme/Cu site. It minimizes the steady-state concentration of the catalytic intermediate whose decomposition would release free H(2)O(2). The maximum catalytic rate constants of O(2) reduction by the ferrous catalyst and of H(2)O(2) reduction by both ferric and ferrous catalysts are comparable to those reported for cytochrome oxidase. The oxidized catalyst also displays catalase activity. Comparison of the catalytic properties of the biomimetic complexes in the FeCu and Cu-free forms indicates that, in the regime of rapid electron flux, Cu does not significantly affect the turnover frequency or the stability of the catalysts, but it suppresses superoxide-releasing autoxidation of an O(2)-catalyst adduct. The distal Cu also accelerates O(2) binding and minimizes O-O bond homolysis in the reduction of H(2)O(2). 相似文献
105.
Roman Luboradzki Janusz Lipowski Yurii A. Simonov Marina S. Fonari Edward V. Ganin Arkadii A. Yavolovskii 《Journal of inclusion phenomena and macrocyclic chemistry》2001,40(1-2):59-65
The X-ray crystal structures of two closely related molecular complexes of 15-crown-5 and benzo-15-crown-5 with 3,4-diamino-1,2,5-oxadiazole are reported (I and II). Both complexes are of 1:1 stoichiometry with the host–guest alternation in the infinitechains formed due to the unsymmetrical H-bonding patterns between the components. Crystals of I are monoclinic, P21/c, a = 7.856(3), b = 12.994(1), c = 16.033(1) , = 94.79(2)°, Z = 4, final R-factor is 0.0488. Crystals of II are orthorhombic, P212121, a = 8.260(4), b = 15.692(5),c = 13.955(7) , Z = 4, final R-factor is 0.0522. 相似文献
106.
Transition Metal Free Cycloamination of Prenyl Carbamates and Ureas Promoted by Aryldiazonium Salts 下载免费PDF全文
Roman Abrams Dr. Quentin Lefebvre Prof. Jonathan Clayden 《Angewandte Chemie (International ed. in English)》2018,57(41):13587-13591
Upon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox‐neutral azocycloamination. In general, N‐aryl O‐prenyl carbamates cyclize in a photocatalytic reaction with visible light and an organic dye. With electron‐deficient diazonium salts, electronic matching with an electron‐rich N‐aryl substituent results in a reaction proceeding in the ground state, without either light or photocatalyst. Cyclic voltammetry suggests that this radical reaction is initiated by hydrogen‐atom abstraction mediated by an aryl radical, followed by a radical addition cascade and proton‐coupled hole propagation. The reaction proceeds at room temperature in short reaction times, and a range of functional groups is tolerated. 相似文献
107.
108.
Rudolf Knorr Ernst Lattke Jakob Ruhdorfer Kathrin Ferchland Ulrich von Roman 《Tetrahedron》2018,74(14):1621-1631
Common wisdom might anticipate that two methyl groups placed on a molecular migration route should act as an impediment. However, the “conducted tour” migration of Li+(THF)4 across the aryl ring (“π-route”) during the cis/trans stereoinversion of α-arylvinyllithiums had been found to occur with practically equal velocities in the presence of either one or two ortho-alkyl substituents. We now report that the omission of both ortho-methyl groups retards the stereoinversion process. In order to arrive at an answer to the title question, we investigate the aggregation equilibria and microsolvation states of ortho, ortho′-unsubstituted α-lithiostyrenes by means of approved secondary NMR criteria. Beyond such necessary knowledge about the ground-state properties, we provide kinetic evidence showing that the retarded cis/trans stereoinversion of α-lithiostyrene proceeds by the pseudomonomolecular, ionic mechanism with Li+(THF)4 migration. 相似文献
109.
O. Habarova O. Bobiļeva E. Loža N. Romančikova 《Chemistry of Heterocyclic Compounds》2011,47(6):719-727
Inhibition of histone deacetylase activity appears as an original and effective approach for the treatment of cancer. A series of novel quinoline-containing derivatives has been synthesized and found that some of these compounds possess nanomolar histone deacetylase inhibitory activity. 相似文献
110.
Nesterov DS Kokozay VN Jezierska J Pavlyuk OV Boča R Pombeiro AJ 《Inorganic chemistry》2011,50(10):4401-4411
The three novel heterometallic complexes [CuCo(III)Co(II)(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.55)(H(2)O)(0.45)](H(2)O)(0.45) (1), [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.74)(H(2)O)(0.26)](H(2)O)(0.26) (2), and [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(DMF)] (3) have been prepared using a one-pot reaction of copper powder with cobalt chloride (1) and zinc nitrate (2, 3) in a methanol (1, 2) or dimethylformamide (3) solution of N-methyldiethanolamine. A search of the Cambridge Structural Database shows that the tetranuclear asymmetric cores M(4)(μ(3)-X)(μ-X)(5) of 1-3 represent an extremely rare case of M(4)X(6) arrays. The magnetic investigations of 1 disclose antiferromagnetic coupling in a Co(II)-Cu(II)-Co(II) exchange fragment with J(Co-Cu)/hc = -4.76 cm(-1), J(Co-Co)/hc = -2.76 cm(-1), and D(Co)/hc = +34.3 cm(-1). Compounds 1-3 act as precursors for the mild peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone with overall yields up to 23%. The synthetic and structural features as well as the thermogravimetric behavior and electrospray ionization mass spectrometry data are discussed. 相似文献