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21.
Sharma A Thampi SP Suggala SV Bhattacharya PK 《Langmuir : the ACS journal of surfaces and colloids》2004,20(11):4708-4714
Dense polymeric membranes with extremely small pores in the form of free volume are used widely in the pervaporative separation of liquid mixtures. The membrane permeation of a component followed by its vaporization on the opposite face is governed by the solubility and downstream pressure. We measured the evaporative flux of pure methanol and 2-propanol using dense membranes with different free volumes and different affinities (wettabilities and solubilities) for the permeant. Interestingly, the evaporative flux for different membranes vanished substantially (10-75%) below the equilibrium vapor pressure in the bulk. The discrepancy was larger for a smaller pore size and for more wettable membranes (higher positive spreading coefficients). This observation, which cannot be explained by the existing (mostly solution-diffusion type) models ofpervaporation, suggests an important role for the membrane-permeant interactions in nanopores that can lower the equilibrium vapor pressure. The pore sizes, as estimated from the positron annihilation, ranged from 0.2 to 0.6 nm for the dry membranes. Solubilities of methanol in different composite membranes were estimated from the Flory-Huggins theory. The interaction parameter was obtained from the surface properties measured by the contact angle goniometry in conjunction with the acid-base theory of polar surface interactions. For the membranes examined, the increase in the "wet" pore volume due to membrane swelling correlates almost linearly with the solubility of methanol in these membranes. Indeed, the observations are found to be consistent with the lowering of the equilibrium vapor pressure on the basis of the Kelvin equation. Thus, a higher solubility or selectivity of a membrane also implies stronger permeant-membrane interactions and a greater retention of the permeant by the membrane, thus decreasing its evaporative flux. This observation has important implications for the interpretation of existing experiments and in the separation of liquid mixtures by pervaporation. 相似文献
22.
J.S. Yadav Saibal Das J. Satyanarayana Reddy N. Thrimurtulu A.R. Prasad 《Tetrahedron letters》2010,51(31):4050-4052
The first total synthesis of (3R),(5R)-5-hydroxy-de-O-methyllasiodiplodin and its epimer is reported from malic acid. The adopted approach is highly convergent and stereoselective. The strategy utilizes syn selective reduction and ring-closing metathesis as key steps. 相似文献
23.
Among physical and nutritional parameters optimized by “one variable at a time” approach, four cultural variables (sucrose,
MgSO4
.7H2O, inoculum size, and incubation period) significantly affected glucoamylase production. These variables were, therefore,
selected for optimization using response surface methodology. The p-values of the coefficients for linear effect of sucrose and inoculum size were less than 0.0001, suggesting them to be the
key experimental variables in glucoamylase production. The enzyme production (34 U/ml) attained under optimized conditions
(sucrose, 2%; MgSO4
.7H2O, 0.13%; yeast extract, 0.1%; inoculum size, 5 × 106 spores per 50 ml production medium; incubation time, 48 h; temperature, 40°C; and pH 7.0) was comparable with the value predicted
by polynomial model (34.2 U/ml). An over all 3.1-fold higher enzyme titers were attained due to response surface optimization.
The experimental model was validated by carrying out glucoamylase production in shake flasks of increasing capacity (0.25–2.0 l)
and 22-l laboratory bioreactors (stirred tank and airlift), where the enzyme production was sustainable. Furthermore, the
fermentation time was reduced from 48 h in shake flasks to 32 h in bioreactors. 相似文献
24.
Venkata Swamy Tangeti Ramesh Varma K. G. V. Siva Prasad K. V. V. V. Satyanarayana 《合成通讯》2016,46(7):613-619
An efficient method was developed for the synthesis of dihydrofuran substituted coumarin from a one-pot, four-component reaction of 2-hydroxy aromatic aldehydes, 6-methyl, 4-hydroxy pyranone, aromatic aldehyde, and pyridinium ylide in the presence of tri-ethylamine under microwave irradiation. The reaction proceeds under solvent-free conditions to afford C3-dihydrofuran substituted coumarin in a diastereoselective manner in good yields (71–89%). 相似文献
25.
A formal total synthesis of the marine sesquiterpene (±)-9-isocyanoneopupukeanane starting from the readily available monoterpene carvone has been accomplished employing a combination of intermolecular Michael addition-intramolecular Michael addition reaction and an intramolecular rhodium carbenoid C-H insertion reaction as key steps, and identifying the isopropenyl group as a masked hydroxy group. 相似文献
26.
Satyanarayana A. V. S. Rao M. Jagannadha Mouli K. Chandra 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(3):1509-1513
Journal of Radioanalytical and Nuclear Chemistry - 相似文献
27.
P. V. Subba Rao G. Krishna Rao K. Ramakrishna G. Rambabu A. Satyanarayana 《国际化学动力学杂志》1997,29(3):171-179
Iron(III)-2,2′-bipyridyl complex obtained, in situ, by direct mixing of iron(III) and 2,2′-bipyridyl, oxidizes aniline, thiourea, and ascorbic acid. The reaction is markedly accelerated by sodium dodecyl sulphate. The rate-[surfactant] profile exhibits a maximum. The kinetic analysis of the micellar effect has been carried out using Berezin's approach. The binding constants of 2,2′-bipyridyl, aniline, thiourea, and ascorbic acid have been determined. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 171–179, 1997. 相似文献
28.
Anjaiah Aitha Satyanarayana Yennam Manoranjan Behera Jaya Shree Anireddy 《Tetrahedron letters》2017,58(6):578-581
The reaction of 1,3,4-oxathiazol-2-one derivative with 2-arylidene-1,3-indandione to furnish novel spiroindene-1,3-dione isothiazoline derivatives by Michael/1,3-dipolar [3+2]-cycloaddition reaction was investigated. The key 1,3-dipolar cycloaddition reaction step was examined in toluene solvent at reflux temperature to obtain mixture of two regioisomers (6a and 6b – 14a and 14b) and single isomers (15–20). The scope of this new reaction was demonstrated with many examples with high reactivity and yields. 相似文献
29.
Kinetics of the bis(2,2,6,2-terpyridine) iron(II)-cobalt(III) electron transfer reaction in sulfuric acid medium has been studied using stopped-flow spectrophotometry. The reaction is first order both in substrate and oxidant. Hydrogen ions accelerate the reaction, whereas bisulfate ions retard. A suitable mechanism is proposed considering Co3+, CoSO
4
+
and Co(SO4)
2
–
as the reactive oxidizing species.
(2,2,6,2-)(II)(III) . , , . , -. , Co3+, CoSO4 + Co(SO4)2 – .相似文献
30.
A study has been made on the oxidation of bis(2,2,6, 2-terpyridine)-iron(II), Fe(tpy)
2
2+
by manganese (IV) using stopped-flow spectrophotometry in H2SO4–H3PO4 mixtures. The reaction is first order in each the substrate and the oxidant. The rate of the reaction increases with hydrogen ion concentration. A plausible mechanism is proposed considering the protonated forms of manganese(IV) as reactive oxidizing species. The reaction obeys the rate law
相似文献 |