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161.
Crisan Manuela Vlase Gabriela Plesu Nicoleta Petric Mihaela Croitor Lilia Kravtsov Victor Chumakov Yurii Bourosh Paulina Vlase Titus 《Journal of Thermal Analysis and Calorimetry》2018,132(1):343-351
Journal of Thermal Analysis and Calorimetry - In the present studies, the thermal behaviour of NaUO2BO3 has been investigated. This compound is a potential product of interaction between the... 相似文献
162.
Gabriela Martins de Araújo Fábio Ruiz Simões 《Journal of Solid State Electrochemistry》2018,22(5):1439-1448
In this work, polypyrrole (PPy) and its respective composite with functionalized multi-walled carbon nanotubes (MWCNT) were obtained by chemical polymerization of the monomer pyrrole in aqueous solution. The obtained PPy as well as its composite (PPy-MWCNT) were characterized by Fourier transform infrared spectroscopy (FTIR) and were used to produce nanostructured self-assembled (SA) films deposited onto glass substrates covered with indium tin oxide (ITO). The SA films were produced with alternated layers of polystyrene sulphonated (PSS) and were characterized by UV-visible, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) analyses. The applicability of the SA films was evaluated by square wave voltammetry (SWV) with standard additions of aliquots of Diuron pesticide in Britton-Robinson buffer solutions (pH = 2.0). The results showed an oxidation peak at 0.23 V which increases in function of the Diuron concentration for both the SA films. It was also observed that the SA film based on the composite (PPy-MWCNT/PSS) showed a peak current intensity about ten times higher in comparison with its unmodified counterpart (PPy/PSS) for a Diuron concentration of 4.29 × 10?5 mol L?1, indicating a synergic effect between PPy and MWCNT in the composite. The limits of quantification (LOQ) and limits of detection (LOD) were respectively 8.6 × 10?7 mol L?1 and 2.6 × 10?7 mol L?1. 相似文献
163.
Acetylcholinesterase-based biosensors for quantification of carbofuran, carbaryl, methylparaoxon, and dichlorvos in 5% acetonitrile 总被引:1,自引:0,他引:1
Valdés-Ramírez G Cortina M Ramírez-Silva MT Marty JL 《Analytical and bioanalytical chemistry》2008,392(4):699-707
Amperometric acetylcholinesterase biosensors have been developed for quantification of the pesticides carbofuran, carbaryl,
methylparaoxon, and dichlorvos in phosphate buffer containing 5% acetonitrile. Three different biosensors were built using
three different acetylcholinesterase (AChE) enzymes—AChE from electric eel, and genetically engineered (B394) and wild-type
(B1) AChE from Drosophila melanogaster. Enzymes were immobilized on cobalt(II) phthalocyanine-modified electrodes by entrapment in a photocrosslinkable polymer
(PVA-AWP). Each biosensor was tested against the four pesticides. Good operational stability, immobilisation reproducibility,
and storage stability were obtained for each biosensor. The best detection limits were obtained with the B394 enzyme for dichlorvos
and methylparaoxon (9.6 × 10−11 and 2.7 × 10−9 mol L−1, respectively), the B1 enzyme for carbofuran (4.5 × 10−9 mol L−1), and both the B1 enzyme and the AChE from electric eel for carbaryl (1.6 × 10−7 mol L−1). Finally, the biosensors were used for the direct detection of the pesticides in spiked apple samples. 相似文献
164.
Compensation effect as a consequence of vibrational energy transfer in homogeneous and isotropic heat field 总被引:1,自引:1,他引:0
Nicolina Pop Gabriela Vlase T. Vlase N. Doca A. Mogoş A. Ioiţescu 《Journal of Thermal Analysis and Calorimetry》2008,92(1):313-317
By kinetics of decomposition of solids in both isothermal and non-isothermal conditions, the compensation effect (CE) is rather
a rule.
The topic of this work is to suggest an activation mechanism which leads to the dependences similar with CE.
The solid is assimilated to a system of the harmonic oscillator with a Bose-Einstein energy distribution.
Considering an activation process due to a vibrational energy transfer from a homogeneous and isotropic field of thermic oscillators
to the solid-state oscillator, the thermodynamic functions are in the relationship
where ΔH* and ΔS* are the activation functions and T
is is the isokinetic temperature.
Taking into account the definitions of H and S by means of the partition function, the isokinetic temperature is assimilated with the characteristic temperature
An important consequence, a correlation between the isokinetic temperature and the spectroscopic wavenumber of the activated
bond, is illustrated by a number of decomposition reactions under non-isothermal conditions. 相似文献
165.
Balderas-Hernández P Ramírez-Silva MT Romero-Romo M Palomar-Pardavé M Roa-Morales G Barrera-Diaz C Rojas-Hernández A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,69(4):1235-1245
This work presents the results obtained from a spectrophotometry study performed on some indicators of the sulfonphtaleins like phenol red (PR), thymol blue (TB), bromothymol blue (BTB), xylenol orange (XO) and methylthymol blue (MTB). During the first stage the acidity constants of some of the indicators were determined using the data from spectrophotometry, potentiometry and with the use of the software SQUAD. These were as follows: for the equilibrium 2H+BTB<-->H(2)BTB, log beta(2)=15.069+/-0.046 and for H+BTB<-->HBTB, log beta(1)=8.311+/-0.044. For the XO and the MTB five values were calculated for each, namely, for MTB: log beta(5)=42.035, log beta(4)=38.567+/-0.058, log beta(3)=32.257+/-0.057, log beta(2)=23.785+/-0.057, and log beta(1)=12.974+/-0.045 while for XO: log beta(5)=40.120+/-0.102, log beta(4)=35.158+/-0.062, log beta(3)=29.102+/-0.053, log beta(2)=21.237+/-0.044, and log beta(1)=11.682+/-0.044. During the second stage, a study was conducted on the effect of the substituents present in the indicators to determine the effect of different functional groups on the pK(a) value corresponding to the last indicator's dissociation. 相似文献
166.
Chenyi Yi Shi-Xia Liu Gabriela Frei Helen Stoeckli-Evans Silvio Decurtins 《Tetrahedron》2008,64(40):9437-9441
An efficient one-pot synthesis simultaneously results in three types of densely substituted mono-, di- and tetracyclic π-systems, which can easily be isolated. Each chromophore presents a strong fluorescence emission, either in the red, green or blue part of the spectrum. 相似文献
167.
Gabriela A. Grasa Antonio Zanotti-Gerosa Christopher A. Teleha Bruce E. Maryanoff 《Tetrahedron letters》2008,49(36):5328-5331
Enantioselective preparation of a key αvβ3 integrin antagonist intermediate was accomplished via catalytic asymmetric hydrogenation of the corresponding β,β-disubstituted α,β-unsaturated carboxylic acid bearing a 3-quinolinyl moiety. The successful application of a Ru-(R)-XylPhanePhos catalyst to this type of substrate is unprecedented. In situ NMR experiments of pre-catalyst formation/activation by CH3CO2H, and reaction parameter modification, revealed that [Ru(COD)(CF3CO2)2]2/(R)-XylPhanePhos is a highly active and efficient catalytic system. 相似文献
168.
Arráez-Román D Zurek G Bässmann C Segura-Carretero A Fernández-Gutiérrez A 《Electrophoresis》2008,29(10):2112-2116
This short communication describes the characterization of seven tropane alkaloid compounds in Atropa belladonna L. Thus a rapid and easy CE-electrospray interface (ESI)-TOF-MS procedure is developed to analyze these compounds in a pharmaceutical preparations of A. belladonna L. leaf extract. Optimum electrophoretic separation is obtained using an alkaline solution of 60 mM ammonium acetate at pH 8.5 containing 5% isopropanol. Under the optimum CE-ESI-TOF-MS conditions several important compounds such as tropine, belladonnine, norhyoscyamine, apoatropine, hyoscyamine, 6beta-hydroxyhyoscyamine, and scopolamine have been simultaneously identified from A. belladonna L. CE-ESI-IT-MS has been used to discriminate the putative presence of littorine. The sensitivity, together with mass accuracy and true isotopic pattern of the TOF-MS, allowed the identification of a broad series of tropane alkaloid compounds present in pharmaceutical preparations of A. belladonna L. leaf extract. 相似文献
169.
Recoverable (S(a))-binam-L-prolinamide in combination with benzoic acid is used as catalysts in the direct aldol reaction between cycloalkyl, alkyl, and alpha-functionalized ketones and aldehydes under solvent-free reaction conditions. Three different methods are assayed: simple conventional magnetic stirring, magnetic stirring after previous dissolution in THF and evaporation, and ball mill technique. These procedures allow one to reduce not only the amount of required ketone to 2 equiv but also the reaction time to give the aldol products with regio-, diastereo-, and enantioselectivities comparable to those in organic or aqueous solvents. Generally anti-isomers are mainly obtained with enantioselectivities up to 97%. The reaction can be carried out under these conditions also using aldehydes as nucleophiles, yielding after in situ reduction of the aldol products the corresponding chiral 1,3-diols with moderate to high enantioselectivities mainly as anti-isomers. The aldol reaction has been studied by the use of positive ESI-MS technique, providing the evidence of the formation of the corresponding enamine-iminium intermediates. 相似文献
170.
Theoretical and experimental investigation on the oxidation of gallic acid by sulfate radical anions
Caregnato P Gara PM Bosio GN Gonzalez MC Russo N Michelini Mdel C Martire DO 《The journal of physical chemistry. A》2008,112(6):1188-1194
By monitoring the decay of SO4*- after flash photolysis of aqueous solutions of S2O82- at different pH values, the kinetics of the reaction of SO4*- radicals with gallic acid and the gallate ion was investigated. The bimolecular rate constants for the reactions of the sulfate radicals with gallic acid and the gallate ion were found to be (6.3 +/- 0.7) x 10(8) and (2.9 +/- 0.2) x 10(9) M(-1) s(-1), respectively. On the basis of the oxygen-independent second-order decay kinetics and on their absorption spectra, the organic radicals formed as intermediates of these reactions were assigned to the corresponding phenoxyl radicals. DFT calculations in the gas phase and aqueous solution support formation of the phenoxyl radicals by H abstraction from the phenols to the sulfate radical anion. The observed recombination of the phenoxyl radicals of gallic acid to yield substituted biphenyls and quinones is also supported by the calculations. HPLC/MS product analysis showed formation of one of the predicted quinones. 相似文献