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51.
New Hg2+ and Cu2+ selective chromo- and fluoroionophore based on a bichromophoric azine 总被引:1,自引:0,他引:1
[graph: see text] A new probe, 1,4-bis(1-pyrenyl)-2,3-diaza-1,3-butadiene, selectively senses Hg2+ and Cu2+ through two different channels: the yellow-deep-pink color change and the enhancement of the fluorescence with the red shift of the excimer emission, which can visually be discernible by a green fluorescence in the presence of Hg2+ and an orange fluorescence in the presence of Cu2+. 相似文献
52.
Alcaide B Almendros P Alonso JM Aly MF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(14):3415-3426
Imines derived from 4-oxoazetidine-2-carbaldehydes have been found to be versatile Diels-Alder reagents in that they exhibit two reactivity patterns. 2-Azetidinone-tethered imines undergo diastereoselective reaction with Danishefsky's diene in the presence of different Lewis acids. The effect of the amount of catalyst on the conversion rate as well as on the product ratio has been studied. Under standard reaction conditions, indium(III) chloride and zinc(II) iodide provided the best yields, and indium(III) triflate the highest diastereoselectivity in the Lewis acid promoted aza-Diels-Alder cycloaddition. Treatment of the aforementioned imines with cyclopentadiene, 2,3-dimethyl-1,3-butadiene or 3,4-dihydro-2 H-pyran led to cycloadducts arising from inverse electron-demand condensation involving the beta-lactam-tethered aryl imine as the heterodiene component. In addition, the first methodology for preparing indolizidines from beta-lactams has been developed. This process involves amide bond cleavage of the beta-lactam ring in the aza-Diels-Alder cycloadducts with concomitant cyclization. Full chirality transfer occurs when the reaction is performed with an enantiomerically pure substrate. 相似文献
53.
Alibés R Bayón P de March P Figueredo M Font J García-García E González-Gálvez D 《Organic letters》2005,7(22):5107-5109
[reaction: see text] A highly versatile approach to the enantioselective synthesis of securinega alkaloids is presented. Crucial steps are a palladium-catalyzed enantioselective imide alkylation, a vinylogous Mannich reaction, and a ring-closing metathesis process. Through this strategy, the synthesis of (-)-norsecurinine has been accomplished in nine steps and 11% overall yield. 相似文献
54.
Borba A Gómez-Zavaglia A Simões PN Fausto R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(7):1461-1470
The preferred conformations of dimethyl sulfate and their vibrational spectra were studied by matrix-isolation FT-IR spectroscopy and theoretical methods (DFT and MP2, with basis sets of different sizes, including the quadruple-zeta, aug-cc-pVQZ basis). Conformer GG (of C2 symmetry and exhibiting OSOC dihedral angles of 74.3 degrees ) was found to be the most stable conformer in both the gaseous phase and isolated in argon. Upon annealing of the matrix, the less stable observed conformer (GT; with C1 symmetry) quickly converts to the GG conformer, with the resulting species being embedded in a matrix-cage which corresponds to the most stable matrix-site for GG form. The highest energy TT conformer, which was assumed to be the most stable conformer in previous studies, is predicted by the calculations to have a relative energy of ca. 10 kJ mol-1 and was not observed in the spectra of the matrix-isolated compound. 相似文献
55.
TG and DTA have been carried out on new anhydrous rare-earth selenites R2SeaO3+2a (a=3.5,4) in order to establish their stability. Decomposition occurs in three steps attributed to successive losses of SeO2. The first process gives rise to other new group of selenites of composition R2Se3O9, which crystallize in two different forms depending on the rare-earth element. The second process leads to isomorphous compounds R2SeO5. The final product of thermal degradation is R2O3. All products were characterized by chemical analysis and X-ray powder diffraction methods. 相似文献
56.
Pedro A. Fernandes Elsa S. Henriques Vineet Pande Maria. J. Ramos Ana R. R. Maia André A. S. Almeida Bruno F. B. Silva Carla M. S. Ribeiro César F. B. Ribeiro David S. M. Ribeiro Diana A. P. Fonseca Eva M. S. Cunha Filipe R. N. C. Maia Joana A. A. Pereira João P. G. Pacheco Joaquim A. A. D. Ferreira Liliana R. C. Matos Manuel A. B. P. Pinto Maria C. S. Borges Paulo J. C. R. Magalhães Pedro F. R. D. Teixeira Pedro N. B. C. Veloso Ricarte J. F. Ferreira Sandro S. Gomes Tiago F. Barros Tiago S. J. T. Selão Virgínia M. M. C. Fernandes 《Theoretical chemistry accounts》2005,113(4):197-204
We present a series of new inhibitors of the association between nuclear factor kappa B (NF-B) and the corresponding B site in DNA. They were designed using the lead compound 15-deoxy-12,14 -prostaglandin J2 (PGJ2), which is a natural product with demonstrated inhibitory efficiency for this system. First, the binding mode of PGJ2 to NF-B was unraveled by GOLD docking calculation. Subsequently, substitutions were made to PGJ2 to optimize its association with NF-B. Care was taken not to strongly increase the reactivity of the new compounds, and to keep the overall shape, size and hydrophilicity of the lead compound, which should render them a similar bioavailability. Molecular mechanics calculations were performed to decide on the suitability of the substitutions, and to evaluate the energies of association with NF-B. Density functional theory calculations were performed also to study the overall reactivity of the substituted drugs towards NF-B. Important general conclusions were obtained, concerning the improvement of these natural inhibitors; namely, a set of rational methodologies were deduced to improve the association between the PGJ2 derivatives and NF-B, and their efficiency demonstrated by generating a set of substituted complexes, some of them with a very much increased affinity for NF-B, opening new doors to enlarge the therapeutic capabilities of this class of drugs. 相似文献
57.
The nucleophilic addition of lithiated allylphenylsulfone to nitrones at −80 °C proceeds exclusively α to the phenylsulfonyl group affording anti adducts in high yield. At 0 °C isoxazolidines are obtained with complete all-trans selectivity. The formation of these compounds involves isomerization of the allylsulphonyl moiety to give a transient vinylsulfone that then undergoes a subsequent intramolecular Michael addition. The addition to several nitrones has been studied and theoretical calculations have been refined to accurately explain the selectivity of the allylation reaction. 相似文献
58.
A multisite molecular mechanism for Baeyer-Villiger oxidations on solid catalysts using environmentally friendly H2O2 as oxidant 总被引:1,自引:0,他引:1
Boronat M Corma A Renz M Sastre G Viruela PM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(23):6905-6915
The molecular mechanism of the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide catalyzed by the Sn-beta zeolite has been investigated by combining molecular mechanics, quantum-chemical calculations, spectroscopic, and kinetic techniques. A theoretical study of the location of Sn in zeolite beta was performed by using atomistic force-field techniques to simulate the local environment of the active site. An interatomic potential for Sn/Si zeolites, which allows the simulation of zeolites containing Sn in a tetrahedral environment, has been developed by fitting it to the experimental properties of quartz and SnO2(rutile). The tin active site has been modeled by means of a Sn(OSiH3)3OH cluster, which includes a defect in the framework that provides the flexibility necessary for the interaction between the adsorbates and the Lewis acid center. Two possible reaction pathways have been considered in the computational study, one of them involving the activation of the cyclohexanone carbonyl group by Sn (1) and the other one involving hydrogen peroxide being activated through the formation of a tin-hydroperoxo intermediate (2). Both the quantum-chemical results and the kinetic study indicate that the reaction follows mechanism 1, and that the catalyst active site consists of two centers: the Lewis acid Sn atom to which cyclohexanone has to coordinate, and the oxygen atom of the Sn-OH group that interacts with H2O2 forming a hydrogen bond. 相似文献
59.
Irma L. Botto Enrique J. Baran José C. Pedregosa Pedro J. Aymonino 《Monatshefte für Chemie / Chemical Monthly》1979,110(4):895-898
The infrared and laser-Raman spectra of crystalline Ba2V2O7 are reported and discussed by means of a Site Symmetry analysis.
28. Mitt. der Reihe Orthovanadate und verwandte Verbindungen. 27. Mitt.:E. J. Baran undM. E. Escobar, J. Phys. Chem. Solids, im Druck; 26. Mitt.:E. J. Baran, I. L. Botto, J. F. Ramos undP. J. Aymonino, Mh. Chem.109, 1139 (1978); 25. Mitt.:E. J. Baran, J. Mol. Struct.48, 441 (1978); 24. Mitt.:E. J. Baran undI. L. Botto, J. inorg. nucl. Chem.40, 1603, (1978); 23. Mitt.:M. E. Escobar undE. J. Baran, Z. Anorg. allg. Chem.,441, 273 (1978). 相似文献
60.
We investigate the role that local motions and slow cooperative fluctuations have on the relaxation of the intrapair dipolar order in the nematic 5CB. With this purpose we present a theoretical and experimental systematic study which allow us to quantify the contribution from each type of molecular fluctuation to the intrapair dipolar order relaxation time, T(1D). The experimental work includes measurements of Zeeman and intrapair dipolar order relaxation times (T(1Z) and T(1D)) as a function of temperature at conventional NMR frequencies, in three complementary samples: normal and chain deuterated 4-n-pentyl-4(')-cyanobiphenyl (5CB and 5CB(d11)) and a mixture of normal 5CB and fully deuterated 4-n-pentyl-4'-cyanobiphenyl (5CB(d19)), 50% in weight. Additionally we perform T(1Z) field-cycling Larmor frequency-dependent measurements to obtain the spectral density of the cooperative fluctuations. The obtained results are as follows. (a) The cooperative molecular fluctuations have a strong relative weight in the relaxation of the intrapair dipolar order state, even at Larmor frequencies in the range of conventional NMR. (b) Alkyl chain rotations are an important relaxation mechanism of the intrapair dipolar order at megahertz frequencies. (c) Intermolecular fluctuations mediated by translational self-diffusion of the molecules is not an efficient mechanism of relaxation of the intrapair dipolar order. 相似文献