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1.
Oleinikova A Smolin N Brovchenko I Geiger A Winter R 《The journal of physical chemistry. B》2005,109(5):1988-1998
The formation of spanning hydrogen-bonded water networks on protein surfaces by a percolation transition is closely connected with the onset of their biological activity. To analyze the structure of the hydration water at this important threshold, we performed the first computer simulation study of the percolation transition of water in a model protein powder and on the surface of a single protein molecule. The formation of an infinite water network in the protein powder occurs as a 2D percolation transition at a critical hydration level, which is close to the values observed experimentally. The formation of a spanning 2D water network on a single rigid protein molecule can be described by adapting the cluster analysis of conventional percolation studies to the characterization of the connectivity of the hydration water on the surface of finite objects. Strong fluctuations of the surface water network are observed close to the percolation threshold. Our simulations also furnish a microscopic picture for understanding the specific values of the experimentally observed hydration levels, where different steps of increasing mobility in the hydrated powder are observed. 相似文献
2.
Experimental measurements of Tg for two series of lower homologues of polyethyleneoxide. differing in their end-groups, are discussed in terms of existing theories. Simple free-volume considerations predicting linear dependence of Tg on (molecular weight)?1 are inadequate in systems with end-groups capable of specific interactions (hydrogen bonding). Thermodynamic arguments show that the true Tg of infinitely long PEO chain is 220 ± 5°K. Suitable modification of parameters of the Gibbs-DiMarzio equations to account for the dependence of the free volume fraction on the concentration of end-groups results in good fit of the experimental data for hydroxyl-terminated samples and correctly predicts Tg(∞). Analysis of the data for chlorine-substituted oligomers suggests the existence of specific intermolecular interactions in the latter, involving chlorine atoms. 相似文献
3.
Piyarat Thanakoses Nagat Abd Alla Mostafa Mark T. Holtzapple 《Applied biochemistry and biotechnology》2003,107(1-3):523-546
Using the MixAlco process, biomass can be converted into carboxylic acids, which can be chemically converted into mixed alcohol
fuels. This study focused on the use of countercurrent fermentation to anaerobically convert sugarcane bagasse and chicken
manure to mixed carboxylic acids using a mixed culture of mesophilic microorganisms from terrestrial and marine sources. Bagasse
was pretreated with lime to increase digestibility. The continuum particle distribution model (CPDM) simulated continuous
fermentors based on data collected from batch experiments. This model saves considerable time in determining optimum operating
conditions. For an 80% bagasse/20% chicken manure fermentation with terrestrial inoculum at a volatile solids loading rate
(VSLR) of 7.36 g/(L of liquid·d) and a liquid residence time (LRT) of 8.88 d, total carboxylic acid productivity, total acid
selectivity, and yield were 2.49 g/(L of liquid·d), 0.581 g of total acid/g of VS digested, and 0.338 g of total acid/g of
VS fed, respectively, at a concentration of 18.7 g of total acid/L. At the same VSLR and LRT, fermentation with marine inoculum
gave higher total acid productivity, total acid selectivity, and yield than fermentation with terrestrial inoculum. For an
80% bagasse/20% chicken manure fermentation with marine inoculum at a VSLR of 3.83 g/(L of liquid·d) and an LRT of 12.1 d,
total carboxylic acid productivity, total acid selectivity, and yield were 1.38 g/(L of liquid·d), 0.667 g of total acid/g
of VS digested, and 0.359 g of total acid/g of VS fed, respectively, at a concentration of 16.2 g of total acid/L. 相似文献
4.
The reaction of cyclohexanone with arylidenebisureas (e.g. benzal-bisurea) in an acid medium has given 4, 4-diaryl-2, 2-dioxo-5, 5-trimethylene-6, 6-spirobishexahydropyrimidines (II). The acid hydrolysis of IIa (aryl-C6H5) in the presence of 2, 4-dinitrophenylhydrazine leads to the 2, 4-dinitrophenylhydrazone of 2-hydroxy-8-oxo-4-phenyl-5, 6, 7, 8-tetrahydroquinazoline (IV). Compound IV was also obtained by the ozonization of 2-acetoxy-8-benzal-4-phenyl-5, 6, 7, 8-tetrahydroquinazoline (IX) and subsequent decomposition of the ozonide with a solution of 2, 4-dinitrophenylhydrazine. The structure of the compounds obtained was confirmed by means of their IR, UV, and PMR spectra. Corresponding 6, 6-spirobishexahydropyrimidines have also been obtained from 2-methylcyclohexanone, acetone, and methyl ethyl ketone and benzalbisurea.For part XIV, see [1]. 相似文献
5.
B. I. Popov L. L. Sedova G. N. Kustova L. M. Plyasova Yu. V. Maksimov A. I. Matveev 《Reaction Kinetics and Catalysis Letters》1976,5(1):43-49
In the study of the Fe1–xCrxMo1·5O6 system by X-ray, IR and Mössbauer methods the formation of solid state substitution solutions has been detected, which possess similar catalytic properties in methanol oxidation.
, , Fe1–xMo1·5O6 , .相似文献
6.
T. V. Rybalova V. F. Sedova Yu. V. Gatilov O. P. Shkurko 《Chemistry of Heterocyclic Compounds》1998,34(10):1161-1165
The crystal structure of 2-nitropyridine has been determined by x-ray diffraction analysis. The influence of the nitro group
on the geometric parameters of the molecule was evaluated, as well as its influence on the molecular parameters of other nitropyridines,
depending on the position of this group in the pyridine ring.
Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090. E-mail:
gatilov@nioch.nsc.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1367–1371, October, 1998. 相似文献
7.
On the Constitution of Silicate Anions in Tetraethylammonium Silicates and their Aqueous Solutions Investigations by paperchromatography, 29Si-NMR spectroscopy and trimethylsilylation method show that concentrated solutions of tetraethylammonium (TEA) silicates with molar TEA:Si ratios from 2.8 to 1 contain mainly double three-ring silicate anions. Besides of these small amount of mono-, di-, tri-, tetra-, cyclotri-, cyclotetra-, double four-ring- and other polycyclic silicate anions are present. From these solutions a crystalline double three-ring silicate of the formula [N(C2H5)4]6[Si6O15] · 57 H2O could be obtained by crystallization at low temperature. Concentrated solutions with TEA:Si ratios of 0.8 to 0.6 contain mainly double three-, double four-, double five- an probably double six-ring silicate anions. From such solutions always the solid TEA-double four-ring silicate is obtained by crystallization. The reasons for the prefered formation of double ring silicate anions in TEA-silicate solutions and their crystallization are discussed. 相似文献
8.
Toxicity to algae is important characteristic of substances from ecologic point of view. The CORAL software (http://www.insilico.eu/coral) gives possibility to build up model of toxicity to algae using data on the molecular architecture and experimental toxicity, without additional data on physicochemical and/or biochemical parameters. Considerable improvement of the model is observed in the case of using the index of ideality of correlation (IIC) in the role of additional criterion of predictive potential. The IIC is calculated with using of the correlation coefficient between experimental and calculated values of endpoint for the calibration set, with taking into account the positive and negative dispersions between experimental and calculated values. The best model calculated with use the IIC is characterized (the validation set) by n?=?50, r2?=?0.947, RMSE?=?0.401 whereas, model calculated without use the IIC is characterized by n?=?50, r2?=?0.805, and RMSE?=?0.539. The suggested models are built up in accordance to five OECD principles. 相似文献
9.
Elka Kraleva Alla Spojakina Rumiana Edreva-Kardjieva Kveta Jiratova Lacezar Petrov 《Reaction Kinetics and Catalysis Letters》2007,92(1):111-119
HDS catalysts were prepared by loading H3PMo12O40 or H4PMo11V1O40 polyoxometallates on TiO2 (0.5 and 1.0 mmol (Mo+V)). Activity of the catalysts was tested in the HDS of thiophene. The activity of catalysts of low
concentration was 2–3 times higher than the activity of those of high concentration. Temperature programmed reduction (TPR)
and IR spectroscopy were used to determine the properties of the catalyst. TPR measurements proved that vanadium promotes
and stabilizes HDS activity due to an increase in the Mo5+/Mo4+ ratio. 相似文献
10.
Phenyl(methyl)-substituted 2- and 4-nitroso- and azoxypyrimidines were synthesized for the first time by the oxidation of phenyl(methyl)-substituted 2- and 4-hydroxy-aminopyrimidines by activated MnO2, Ag2CO3 on zeolite, or BaMnO4. Certain chemical properties of the synthesized nitrosopyrimidines were studied, such as reduction, nucleophilic substitution of the nitroso group, the condensation reaction with aniline and hydroxyaminopyrimidines.For Preliminary communication, see [1].DeceasedTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 962–968, July, 1989. 相似文献