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151.
Ricardo E. Rivas Ignacio López-GarcíaManuel Hernández-Córdoba 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009
A new procedure for the determination of inorganic arsenic (III,V) and antimony (III,V) in water samples by dispersive liquid–liquid micro extraction separation and electrothermal atomic absorption spectrometry (ETAAS) is presented. At pH 1, As(III) and Sb(III) are complexed with ammonium pyrrolidine dithiocarbamate and extracted into the fine droplets formed when mixing carbon tetrachloride (extraction solvent), methanol (disperser solvent) and the sample solution. After extraction, the phases are separated by centrifugation, and As(III) and Sb(III) are determined in the organic phase. As(V) and Sb(V) remain in the aqueous layer. Total inorganic As and Sb are determined after the reduction of the pentavalent forms with sodium thiosulphate. As(V) and Sb(V) are calculated by difference. The detection limits are 0.01 and 0.05 µg L− 1 for As(III) and Sb(III), respectively, with an enrichment factor of 115. The relative standard deviation is in the 2.9–4.5% range. The procedure has been applied to the speciation of inorganic As and Sb in bottled, tap and sea water samples with satisfactory results. 相似文献
152.
Ricardo R. Contreras Bernardo Fontal Marisela Reyes Trino Surez Fernndo Bellandi All Bahsas 《Journal of heterocyclic chemistry》2001,38(5):1223-1225
The new compound Methyl‐2,4‐bis(cyclohexane)dispiro‐1,2,3,4,4a,5,6,7‐octahydro‐(1H,3H)‐quinazo‐line‐8‐carbodithioate has been synthesized from cyclohexanone and carbon disulfide. It has been characterized by uv‐visible, FTTR , mass spectra and a complete structure proposed based on 1H and 13C NMR spectroscopy. 相似文献
153.
Maria A. Alvarez Edgardo J. Saavedra Mónica S. Olivella Fernando D. Suvire Miguel A. Zamora Ricardo D. Enriz 《Central European Journal of Chemistry》2012,10(1):248-255
The multidimensional Conformational Potential Energy Hypersurface (PEHS) of cyclotrisarcosyl was comprehensively investigated
at the DFT (B3LYP/6-31G(d), B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p)), levels of theory. The equilibrium structures, their
relative stability, and the Transition State (TS) structures involved in the conformational interconversion pathways were
analyzed. Aug-cc-pVTZ//B3LYP/6-311++G(d,p) and MP2/6-31G(d)//B3LYP/6-311++G(d,p) single point calculations predict a symmetric
cis-cis-cis crown conformation as the energetically preferred form for this compound, which is in agreement with the experimental data.
The conformational interconversion between the global minimum and the twist form requires 20.88 kcal mol-1 at the MP2/6-31G(d)//B3LYP/6-311++G(d,p)
level of theory. Our results allow us to form a concise idea about the internal intricacies of the PEHSs of this cyclic tripeptide,
describing the conformations as well as the conformational interconversion processes in this hypersurface. In addition, a
comparative analysis between the conformational behaviors of cyclotrisarcosyl with that previously reported for cyclotriglycine
was carried out 相似文献
154.
Antonio Galdámez Fernanda López-Vergara Patricia Barahona Victor Manríquez Ricardo E. ávila 《Journal of Solid State Electrochemistry》2012,16(2):697-702
The new solid solutions AgPbSb1 − x
Bi
x
S3 were prepared by solid state reactions. The phases were characterized by powder X-ray diffractions (XRD), scanning electron
microscopy, and thermal analysis. The XRD patterns of different members (x = 0.5, 0.7, 0.8, and 1.0) are consistent with pure phases crystallizing in the cubic PbS-type structure. The electrical characterization
was carried out using ac impedance spectroscopy and dc methods. The temperature dependence of the dc conductivity shows typical
semiconductor Arrhenius behavior. The impedance measurements were performed in the frequency range of 0.1 Hz to 10 MHz and
at the temperature range of 15 °C to 350 °C. The ac conductivity conforms to Jonscher’s universal power law. The frequency
dependence of the dielectric permittivity follows the normal dielectric material behavior, and the relaxation is thermally
activated. The frequency and temperature dependences of the electrical data are found to follow Summerfield scaling formalism. 相似文献
155.
The title reactions were studied with a solid superacid, which was prepared by exposing Zr(OH)4 to 1 N H2SO4, followed by calcination at 650°C in air. Pentane and isopentane were converted into isopentane and isobutane, respectively, the selectivities being 84% under short contact conditions at 80°C.
, - Zr(OH)4 1 N- H2SO4 650°C . , , 84% 80°C.相似文献
156.
A reversed‐phase compatible thin‐layer chromatography autography for the detection of acetylcholinesterase inhibitors 下载免费PDF全文
I. Ayelen Ramallo Paula García Ricardo L. E. Furlan 《Journal of separation science》2015,38(21):3788-3794
A dual readout autographic assay to detect acetylcholinesterase inhibitors present in complex matrices adsorbed on reversed‐phase or normal‐phase thin‐layer chromatography plates is described. Enzyme gel entrapment with an amphiphilic copolymer was used for assay development. The effects of substrate and enzyme concentrations, pH, incubation time, and incubation temperature on the sensitivity and the detection limit of the assay were evaluated. Experimental design and response surface methodology were used to optimize conditions with a minimum number of experiments. The assay allowed the detection of 0.01% w/w of physostigmine in both a spiked Sonchus oleraceus L. extract chromatographed on normal phase and a spiked Pimenta racemosa (Mill.) J.W. Moore leaf essential oil chromatographed on reversed phase. Finally, the reversed‐phase thin‐layer chromatography assay was applied to reveal the presence of an inhibitor in the Cymbopogon citratus (DC.) Stapf essential oil. The developed assay is able to detect acetylcholinesterase inhibitors present in complex matrixes that were chromatographed in normal phase or reversed‐phase thin‐layer chromatography. The detection limit for physostigmine on both normal and reversed phase was of 1×10?4 μg. The results can be read by a change in color and/or a change in fluorescence. 相似文献
157.
Ricardo M. Castro‐Acosta Alma L. Revilla Octavio T. Ramírez Laura A. Palomares 《Electrophoresis》2010,31(8):1376-1381
Virus‐like particles have been successfully used as safe vaccines, as their structure is identical to their native counterparts but devoid of the viral genetic material. However, production of these complex structures is not easy, as recombinant proteins must assemble into virus‐like particles. Techniques to differentiate assembled and soluble proteins, as well as assembly intermediaries often present in a sample, are required. An example of complex virus‐like particles mixture occurs when rotavirus proteins are recombinantly expressed. Rotavirus‐like particles (RLP) can be single (sl), double (dl), or triple layered (tl). The use of RLP preparations as vaccines requires their complete characterization, including separation and quantification of each RLP in a sample. In this work, CZE was evaluated for the separation and quantification of dl and triple‐layered rotavirus‐like particles (tlRLP). A fused‐silica capillary with a deoxycholate running buffer efficiently separated dl and tlRLP in RLP preparations, as they migrated in two discrete peaks with electrophoretic mobilities of 1.24±0.04 and 2.95±0.03 Ti, respectively. Standard curves for dl and tlRLP were generated, and the response was linearly proportional to analyte concentration. The methodology developed was quantitative, specific, accurate, precise, and reproducible. CZE allowed the quantitative characterization of RLP preparations, which is required for evaluation of immunogens, for process development, and for quality control protocols. 相似文献
158.
Francisco Núñez‐Zarur Eduardo Arguello Ricardo Vivas‐Reyes 《International journal of quantum chemistry》2010,110(9):1622-1636
The electronic structure and reactivity trends of a set of tris‐(n‐methyl‐8‐quinolinolato) metal (III) (n = 0, 3, 4, 5; metal = Al+3, Ga+3) used as electron‐transport layer in organic light‐emitting diodes were studied and compared. All geometries were optimized at B3LYP/6‐31G(d,p) level of theory. The geometries of the ground state (S0) of unsubstituted molecules AlQ3 and GaQ3 were found to be slightly affected by the methyl group, which is in agreement with previous works. Methyl‐derivatives conserve largely the electronic structures of AlQ3 and GaQ3. The energies of the frontier orbitals highest occupied and lowest unoccupied molecular orbital are raised by the electron‐releasing effect of methyl group. Molecular orbital contribution analysis reveals that the orbital population is essentially the same for both MQ3 and their derivatives. Analyses of the ionization potential and electron affinity showed that MQ3 tend to be better hole‐blockers than methylated analogues and 5Me‐MQ3 have higher hole‐injection capability than the other methyl‐substituted derivatives. The global reactivity analysis showed that the electrophilicity index can be an indicator of electron‐injection capability in these complexes. Local reactivity analysis showed that atomic sites that are prone to nucleophilic/electrophilic attack are atoms C‐4 in L3/C‐5 in L1. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
159.
Diego R. Pérez Susana H. Tarulli Oscar V. Quinzani Dr. Jorge Dristas Ricardo Faccio Leopoldo Suescun Alvaro W. Mombrú 《无机化学与普通化学杂志》2007,633(7):1066-1073
Four new lead(II) thiosaccharinate complexes: [Pb(tsac)2H2O] (1) (tsac: thiosaccharinate anion), [Pb2(tsac)4(py)4] (2) (py: pyridine), [Pb(tsac)(o‐phen)2](tsac)·CH3CN (3) (o‐phen: 1,10‐phenantroline), and [Pb(tsac)2(bipy)] (4) (bipy: 2,2′‐bipyridine) were prepared. The infrared and electronic spectra as well as the thermal analysis of all the compounds were recorded and discussed. The thiosaccharinate anion acts in three different coordination forms, one of then reported for the first time. The crystal structures of complexes 2 and 3 have been determined by single crystal X‐ray diffractometry. In complex 2 , two monomeric moieties are joined together forming a symmetric bis‐μ‐sulphur bridged dimer by interaction of two lead(II) atoms through the exocyclic sulphur atoms of two thiosaccharinate ligands. The seven‐fold coordination sphere of each lead atom is completed by two pyridine nitrogen atoms and by another sulfur and two nitrogen atoms of the thiosaccharinate anions. In complex 3 , the lead(II) atom is coordinated by four nitrogen atoms of two 1,10‐phenantroline molecules and by the sulfur and nitrogen atoms of one thiosaccharinate ion. The second anion has an electrostatic interaction with the nucleus. 相似文献
160.
Godoi AF Vilegas W Godoi RH Van Vaeck L Van Grieken R 《Journal of chromatography. A》2004,1027(1-2):127-130
Turnera diffusa Willd. var. afrodisiaca (Ward) Urb. (syn. T. aphrodisiaca) belongs to the family of Turneraceae and is an aromatic plant growing wild in the subtropical regions of America and Africa. It is widely used in the traditional medicine as e.g. anti-cough, diuretic, and aphrodisiac agent. This work presents a 3 min chromatographic analysis using low-pressure (LP) gas chromatography (GC)-ion-trap (IT) mass spectrometry (MS). The combination of a deactivated 0.6 m x 0.10 mm i.d., restrictor with a wide-bore CP-Wax 52 capillary column (10 m x 0.53 mm i.d., 1 microm) reduces the analysis time by a factor of 3-7 in comparison to the use of a conventional narrow bore column. Chromatographic conditions have been optimized to achieve the fastest separation with the highest signal/noise ratio in MS detection. These results allow fast and reliable quality control of the essential oil to be achieved. 相似文献