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排序方式: 共有257条查询结果,搜索用时 437 毫秒
111.
Paulo R. R. Costa ClÁUdio C. Lopes Rosacaronngela S. C. Lopes Maria F. G. Marinho Rosane N. Castro 《合成通讯》2013,43(14):1723-1730
Phthalides have bcen employed as useful intcriucdiates in tic sqrnthcsis of my condcnscld aromatic carbocyclic and heterocyclic compounds, including several natural products In this paper we report two alternative synthetic pathways for the preparation of phthalides as shown for the synthesis of the isomeric pairs of compounds 5a-d and 7a-d. 相似文献
112.
Vanda R. Marinho 《合成通讯》2013,43(24):4423-4428
One relatively unexploited commercial ligand, Walphos 1, was tested in the Pd(0)-catalyzed asymmetric allylic alkylation using rac-1,3-diphenyl propenyl acetate and rac-1-acetoxycyclohexene as substrates, methyl malonate as nucleophile, and a variety of Pd precatalysts under standard conditions. The conversions and enantioselectivities were generally good, with the greatest substrate conversion of 99% and a greatest ee of 70%. With the latter cyclic substrate, an enantioselectivity of 98% was obtained, but the conversions were all poor (15–33%). 相似文献
113.
Daniela Pott Marinho Ballottin Leonardo Lataro Paim Nelson Ramos Stradiotto 《Electroanalysis》2013,25(7):1751-1755
A glassy carbon electrode chemically modified with nickel oxyhydroxide from a nickel hexacyanoferrate (NiHCF) film was used to determine glycerol in biodiesel by cyclic voltammetry. The modified electrode exhibited a linear response to glycerol concentration in the range from 0.05 to 0.35 mmol L?1, and a detection limit of 0.030 mmol L?1. The glycerol concentration found in the biodiesel sample was 0.156 mmol L?1. The method developed in this study showed a recovery of (100.3±5.0)%. 相似文献
114.
Anna C. Closs Elina Fuks Maximilian Bechtel Prof. Dr. Oliver Trapp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(47):10702-10706
Organocatalysis is a powerful approach to extend and (enantio-) selectively modify molecular structures. Adapting this concept to the Early Earth scenario offers a promising solution to explain their evolution into a complex homochiral world. Herein, we present a class of imidazolidine-4-thione organocatalysts, easily accessible from simple molecules available on an Early Earth under highly plausible prebiotic reaction conditions. These imidazolidine-4-thiones are readily formed from mixtures of aldehydes or ketones in presence of ammonia, cyanides and hydrogen sulfide in high selectivity and distinct preference for individual compounds of the resulting catalyst library. These organocatalysts enable the enantioselective α-alkylation of aldehydes under prebiotic conditions and show activities that correlate with the selectivity of their formation. Furthermore, the crystallization of single catalysts as conglomerates opens the pathway for symmetry breaking. 相似文献
115.
We have computed vibrational high-frequency overtone spectra of the water-ammonia complex, H(2)O-NH(3), and its isotopomers. The complex has been modeled as two independently vibrating monomer units. The internal coordinate Hamiltonians for each monomer unit have been constructed using exact gas phase kinetic energy operators. The potential energy and dipole moment surfaces have been calculated with the explicitly correlated coupled cluster method CCSD(T)-F12A and the valence triple-ζ VTZ-F12 basis around the equilibrium geometry of the complex. The vibrational eigenvalues have been calculated variationally and the eigenfunctions obtained have been used to compute the intensities of the absorption transitions. In H(2)O-NH(3), the water molecule acts as the proton donor and its symmetry is broken. The hydrogen-bonded OH bond oscillator undergoes a large redshift and intensity enhancement compared to the free hydrogen bond. Broken degeneracy of the asymmetric vibrations, quenched inversion splittings, and blueshift of the symmetric bending mode are the most visible changes in the ammonia unit. 相似文献
116.
Delatorre P Rocha BA Simões RC Pereira-Júnior FN Silva HC Bezerra EH Bezerra MJ Marinho ES Gadelha CA Santi-Gadelha T Farias DL Assreuy AM Marques-Domingos GF Nagano CS Cavada BS 《Applied biochemistry and biotechnology》2011,164(6):741-754
The lectin from seeds of Dioclea virgata (DvirL) was purified in a single step affinity chromatography, sequenced by tandem mass spectrometry and submitted to crystallization and biological experiments. DvirL has a molecular mass of 25,412?±?2 Da and the chains β and γ has 12,817 Da?±?2 and 12,612 Da?±?2, respectively. Primary sequence determination was assigned by tandem mass spectrometry and revealed a protein with 237 amino acids and 87% of identify with ConA. The protein crystals were obtained native and complexed with X-Man using vapor-diffusion method at a constant temperature of 293 K. A complete X-ray dataset was collected at 1.8 ? resolution. DvirL crystals were found to be orthorhombic, belonging to the space group I222, with a unit cell parameters a?=?647.5 ?, b?=?86.6 ?, c?=?90.2 ?. Molecular replacement search found a solution with a correlation coefficient of 77.1% and an R(factor) of 44.6%. The present study also demonstrated that D. virgata lectin presents edematogenic and antinociceptive activities in rodents electing this protein as a candidate to structure/function analysis. 相似文献
117.
Elina Manova Daniela Paneva Nikolay Velinov Krassimir Tenchev 《Journal of solid state chemistry》2011,184(5):1153-1158
Nanodimensional powders of cubic copper ferrite are synthesized by two-steps procedure of co-precipitation of copper and iron hydroxide carbonates, followed by mechanochemical treatment. X-ray powder diffraction, Mössbauer spectroscopy and temperature-programmed reduction are used for the characterization of the obtained materials. Their catalytic behavior is tested in methanol decomposition to hydrogen and CO and total oxidation of toluene. Formation of nanosized ferrite material is registered even after one hour of milling time. It is established that the prolonging of treatment procedure decreases the dispersion of the obtained product with the appearance of Fe2O3. It is demonstrated that the catalytic behavior of the samples depends not only on their initial phase composition, but on the concomitant ferrite phase transformations by the influence of the reaction medium. 相似文献
118.
Emanuele Pace J. Adnei Marinho Giovanni Salm�� Tobias Frederico 《Few-Body Systems》2011,50(1-4):431-434
The deuteron electromagnetic properties are investigated within the Light-Front Hamiltonian dynamics using one-body and two-body currents. The dynamical nature of the latter is generated within a Yukawa model from an analysis of the Light-Front current that acts on the three-dimensional valence component and fulfills the Ward?CTakahashi identity. Preliminary results for the magnetic moment and the probability of the nonvalence component are shown. 相似文献
119.
Abstract: Steroids are an important class of organic compounds containing a vast array of biologically and physiologically essential molecules. Due to their availability, relatively straightforward derivatizability, and endogeneity, they are widely used in pharmacological applications. The investigation of molecular and physicochemical properties of active pharmaceutical ingredients (APIs) in the solid state is important, because these properties are directly related to their pharmacological activity. Several methods are available for this purpose. Solid-state NMR spectroscopy offers a nondestructive and flexible technique, providing both structural and dynamic information. It can be applied to every solid physical state (both crystalline and amorphous) as well as to materials with different compositions. The current article aims at gathering together some of the recent and most important studies in the area of high-resolution solid-state NMR spectroscopy of steroids and their derivatives completed with related theoretical reports not forgetting to outline the future remarks. 相似文献
120.
Antti J. Koivisto Maija M?kinen Elina M. Rossi Hanna K. Lindberg Mirella Miettinen Ghita C.- M. Falck Hannu Norppa Harri Alenius Anne Korpi Joakim Riikonen Esa Vanhala Minnamari Vippola Pertti Pasanen Vesa-Pekka Lehto Kai Savolainen Jorma Jokiniemi Kaarle H?meri 《Journal of nanoparticle research》2011,13(7):2949-2961
This study presents a novel exposure protocol for synthesized nanoparticles (NPs). NPs were synthesized in gas phase by thermal decomposition of metal alkoxide vapors in a laminar flow reactor. The exposure protocol was used to estimate the deposition fraction of titanium dioxide (TiO2) NPs to mice lung. The experiments were conducted at aerosol mass concentrations of 0.8, 7.2, 10.0, and 28.5 mg m?3. The means of aerosol geometric mobility diameter and aerodynamic diameter were 80 and 124 nm, and the geometric standard deviations were 1.8 and 1.7, respectively. The effective density of the particles was approximately from 1.5 to 1.7 g cm?3. Particle concentration varied from 4 × 105 cm?3 at mass concentrations of 0.8 mg m?3 to 12 × 106 cm?3 at 28.5 mg m?3. Particle phase structures were 74% of anatase and 26% of brookite with respective crystallite sized of 41 and 6 nm. The brookite crystallites were approximately 100 times the size of the anatase crystallites. The TiO2 particles were porous and highly agglomerated, with a mean primary particle size of 21 nm. The specific surface area of TiO2 powder was 61 m2 g?1. We defined mice respiratory minute volume (RMV) value during exposure to TiO2 aerosol. Both TiO2 particulate matter and gaseous by-products affected respiratory parameters. The RMV values were used to quantify the deposition fraction of TiO2 matter by using two different methods. According to individual samples, the deposition fraction was 8% on an average, and when defined from aerosol mass concentration series, it was 7%. These results show that the exposure protocol can be used to study toxicological effects of synthesized NPs. 相似文献