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101.
Vânia P. Campos Adriana S. Oliveira Lícia P.S. Cruz Jomar Borges Tania M. Tavares 《Microchemical Journal》2010,96(2):283-289
Reduced sulfur compounds, RSCs (H2S, COS, CH3SH, CH3SCH3, CS2 and CH3S2CH3) play a role in global cycle and acid rain formation. At trace levels RSCs in air are difficult to collect, store and analyze because of their highly adsorptive and reactive properties. This work optimizes parameters of sampling and instrumental determination of RSCs for urban measurements. The method used is based on cryogenic sampling and gas chromatography provided with a cryofocusing trap and flame photometric detection.Greater sampling efficiency was obtained with liquid argon as freezing fluid and air flow rate of 150 mL min? 1 for two hours. Best results have been obtained with preconcentration for 3 min and injection volume of 3 ml. For H2S, CH3SH and CH3S2CH3 the method showed a precision of 89%, limit of detection of 0.10 µg m? 3 and limit of quantification 0.3 µg m? 3. For CH3SCH3 and CS2 the corresponding values were 89%, 0.15 µg m? 3 and 0.5 µg m? 3 and for COS were 75%, 0.18 µg m? 3 and 0.8 µg m? 3 respectively. Sampling efficiency varied between 70–80% for all the RSCs. Accuracy of H2S from field measurements obtained with parallel measurements using a continuous monitor varied between 88 and 98%. The optimized methodology proved to be suitable for field measurements in urban tropical atmospheres with different characteristics. 相似文献
102.
103.
Determination of the minimal erythema dose and colorimetric measurements as indicators of skin sensitivity to UV-B radiation 总被引:2,自引:0,他引:2
There is a strong relation between chronic UV-B-induced sunburns and the development of skin cancer. Therefore, it is important to obtain a method that can be reproduced easily to detect individuals with similar skin color but different sensitiveness to sun exposure. The study evaluated 193 healthy volunteers (68% women; the average age was 38 years). They were divided into six groups of at least 30 subjects, according to skin type. The minimal erythema dose (MED) was assessed in two non-sun-exposed areas (thorax-infra-axillary area and on the buttocks), using a UV-B source (0.5 mW/cm2), with openings of 1 cm2, in increasing doses. The same areas were evaluated with a Minolta CR 300 Chromameter (L*a*b* system). The MED values ranged from 13 to 156 mJ/cm2; the coordinate L* (brightness) ranged from 75.96 to 30.15. The correlation between the MED and the brightness was negative in both areas (Pearson's correlation r = -0.91, P < 0.05). Color measurements, especially brightness, can be used to quickly assess skin sensibility. Considering the MED, there is a substantial overlapping of adjacent phototypes, but they could be separated into two groups: more sensitive individuals (Types I, II, III and IV) and less sensitive ones (Types V and VI). 相似文献
104.
Tungsten complex with a coordinated 2-azidoethyl isocyanide ligand reacts with PMe3 at the azido function to give a complex with a coordinated iminophosphorane which upon hydrolysis of the P=N bond yields a complex with an NH,NH-stabilized N-heterocyclic carbene ligand, 7; alkylation of the carbene ring nitrogen atoms gives a complex with an N,N'-dialkylated imidazolidin-2-ylidene ligand, 8 . 相似文献
105.
Marniev Luiggi Rosa M. Dominguez Alexandra Rotinov Armando Herize Mary Cordova Gabriel Chuchani 《国际化学动力学杂志》2002,34(1):67-71
The elimination kinetics of ethyl N‐benzyl‐N‐cyclopropylcarbamate and ethyl diphenylcarbamate were investigated over the temperature range of 349.9–440.0°C and the pressure range of 31–106 Torr. These reactions have been found to be homogeneous, unimolecular, and obey a first‐order rate law. The products are ethylene, carbon monoxide, and the corresponding secondary amine. The rate coefficient is expressed by the following Arrhenius equations: For ethyl N‐benzyl‐N‐cyclopropylcarbamate log k1 (s?1) = (12.94 ± 0.09) ? (198.5 ± 0.9) kJ mol?1 (2.303RT)?1 For ethyl diphenylcarbamate log k1 (s?1) = (12.91 ± 0.18) ? (208.2 ± 2.4) kJ mol?1 (2.303RT)?1 The presence of phenyl and bulky groups at the nitrogen atom of the ethylcarbamate showed a decrease in the rate of elimination. Steric factor may be operating during the process of decomposition of these substrates. These reactions appear to undergo a semipolar six‐membered cyclic transition type of mechanism.© 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 67–71, 2002 相似文献
106.
Tania Crucitti 《Accreditation and quality assurance》2001,6(8):379-381
Quality assurance is an important aspect of laboratory management. One of the activities involved is the participation in
external quality assessment (EQA) schemes by the clinical laboratory. These EQA schemes should be organised according to well-defined
guidelines, such as the ESO/IEC Guide 43. The present work provides an inventory of the EQA schemes organised in Europe. The
schemes are related to the fields of bacteriology, parasitology and virology. For each field various surveys have been organised.
Data such as the number of participants, frequency of survey and number of samples in a survey are presented. The nature and
way of manufacturing the control material is specified. 相似文献
107.
Tania B. Mahajan Fiona L. Plows J. Seb Gillette Richard N. Zare Graham A. Logan 《Journal of the American Society for Mass Spectrometry》2001,12(9):989-1001
Microprobe two-step laser desorption/laser ionization mass spectrometry (μL2MS) and gas chromatography/mass spectrometry (GC/MS) were used to analyze polycyclic aromatic hydrocarbons (PAHs) in ancient terrestrial rocks. μL2MS provides an in situ analysis of very small samples, records the PAHs with no isomer information, and gives quantitative data on the degree of alkylation of a given PAH series over the complete mass range. GC/MS provides isomer separation and quantitation of PAHs in bitumen but not kerogen, and is limited by sample size. Combination of these techniques allows analysis of very small samples by μL2MS with GC/MS confirmation of isomer distributions of the solvent extractable components (bitumen). It was found that the concentration of bitumen within the rock samples affects the PAH alkylation signal for μL2MS. At low bitumen concentrations μL2MS can produce pyrolysis products from kerogen that is present; however, as bitumen concentrations increase, the PAH distribution from bitumen dominates the signal. 相似文献
108.
Giorgio Della Sala Alessandra Lattanzi Tania Severino Arrigo Scettri 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):219-224
Investigations were carried out on the oxidation of sulfides to sulfoxides catalyzed by the commercial Cp2Ti(X)2 (X=Cl, OTf)/t-butyl hydroperoxide (TBHP). The asymmetric version of prochiral sulfides oxidation was achieved using Cp2TiCl2, as transition metal catalyst, in the presence of (+)-(R)-BINOL, as chiral ligand and activated 4 Å molecular sieves (m.s.). 相似文献
109.
Erika C. Pavarina Lara D. Sette Tania A. Anazawa Lucia R. Durrant 《Applied biochemistry and biotechnology》1999,82(2):153-163
Four fungal strains able to grow under low oxygenation conditions were selected and used in studies to determine the production
of enzymes (endoglucanases, exoglucases, β-glucosidase, and peroxidases) that promote the degradation of lignocellulosic materials.
The capacity of the fungi to ferment lignocellulosic materials was also investigated. Avicel, xylan, Whatman no. 1 filter
paper, or agroindustrial residues were used as carbon sources in a medium containing mineral salts, vitamins, and cysteine
as a reducing agent, under either microaerophilic or combined conditions (aerobic followed by microaerophilic conditions).
The results obtained with strains Q10, H2, and LH5 suggest that they prefer a low oxygen concentration for growth and enzyme
production. However, strain F20 seems to need higher levels of oxygenation. Lignocellulolytic activities were detected in
all strains but varied with the carbon source used for growth. In general, the highest levels of these activities were produced
by strain H2 under microaerophilic conditions. Ethanol and other nongaseous fermentation products were detected following
high-performance liquid chromatography analysis using a Supelcogel C-610H column, demonstrating the fermentative capability
of these strains. 相似文献
110.
Jose R. Rojas Marcos Loroño Jose R. Mora Rosa M. Dominguez Tania Cordova Gabriel Chuchani 《国际化学动力学杂志》2009,41(3):168-175
The gas‐phase elimination of several ω‐bromonitriles (ZCH2CH2Br, Z = NC, NCCH2, NCCH2CH2) has been examined at the MP2/6‐31G(d,p), MP2/6‐31G(2d,2p), B3PW91/6‐31G(2d,2p), and MPW91PW91/6‐31(2p,2d) levels of theory. The bromonitriles yield the corresponding cyano‐olefin and HBr gas in a rate‐determining step. The MPW91PW91/6‐31G(2p,2d) results suggest a concerted mechanism, with a polar, four‐membered transition state. The calculated kinetic and thermodynamic parameters were found to be within reasonable agreement with the experimental determinations. Substituent effects are discussed in terms of electronic structure. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 168–175, 2009 相似文献