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981.
Ivanova SM Nolan BG Kobayashi Y Miller SM Anderson OP Strauss SH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(2):503-510
The relative Lewis basicities of six Al(ORF)4- ions, Al[OC(CH3)(CF3)2]4-, Al(OC(CF3)3]4-, Al(OCPh(CF3)2]4-, Al[OC[4-C6H4(tBu)](CF3)2]4-, Al(OC(Cy)(CF3)2]4-, and Al(OCPh2(CF3)]4-, have been determined by measuring their relative coordinating abilities towards Li+ in dichloromethane. The relative Li- Lewis basicities of the Al(ORF)4- ions are linearly related to the aqueous pKa values of the corresponding parent HORF fluoroalcohols. The Lewis basicity of Al[OCH(CF3)2]4- could not be measured because two of these anions can coordinate to one Li+ cation. The structures of LiAl[OCH(CF3)2]4 and [1-Et-3-Me-1,3-C3H3N2][Li[Al[OCH(CF3)2)4]2] were determined. 相似文献
982.
The review analyzes the reactions of alicyclic epoxy compounds with oxygen-containing nucleophiles (alcohols, water, and organic acids), describes biologically active products of these reactions, and discusses their mechanisms and results of their simulation by quantum-chemical methods. The regio-and stereoselectivity of nucleophilic reactions of epoxy compounds and the activation of epoxy ring by achiral and chiral catalysts are also considered. 相似文献
983.
Potassium Iodide as a Chemical Actinometer for 254 nm Radiation: Use of lodate as an Electron Scavenger 总被引:2,自引:0,他引:2
Ronald O. Rahn 《Photochemistry and photobiology》1997,66(4):450-455
Abstract— A solution of 0.6 M iodide and 0.1 M iodate in 0.01 M borate buffer (pH 9.25) can be used as a chemical actinometer to measure the incident fluence from a low-pressure mercury lamp that puts out more than 85% of its energy at 254 nm. The actinometric solution is optically opaque to light below 290 nm and is optically transparent to wavelengths greater than 330 nm. Hence, the solution absorbs all of the germicidal wavelengths but little if any of the ambient light normally present in the laboratory. Iodate acts as an electron scavenger and prevents the back reaction of the free electron with the iodine atom following UV excitation of KI. Irradiation results in the linear formation of triiodide, which is quantitated by measuring its absorbance at 352 nm. The quantum yield for this system is approximately 0.75 0.03 at 20.7Ao C or approximately three times greater than that obtained previously using nitrous oxide as an electron scavenger. A model is proposed to account for this difference. A precise expression to account for the concentration and temperature dependence of the quantum yield is given by pH = 0.75(1 + 0.23[C - 0.577])(1 + 0.02[T - 20.7]) where C is the concentration of iodide and T is the temperature. The concentration of iodide can be obtained from the absorbance at 300 nm prior to irradiation using 1.061 MJ cm−1 as the molar extinction coefficient. This actinometric system meets the quality criteria established by the International Union of Pure and Applied Chemistry with the caveat that it is designed to measure only germicidal radiation (i.e. wavelengths less than 290 nm). 相似文献
984.
G. A. Gavrilova M. G. Voronkov N. N. Chipanina L. I. Gubanova O. M. Trofimova Yu. L. Frolov 《Russian Chemical Bulletin》1995,44(4):667-669
The IR spectra of solutions of (=OSi)-(benzoyloxymethyl)trifluorosilane (1),-(benzoyloxymethyl)methyldifluorosilane (2), and butyl benzoate (3) are examined in the region of thev(C=O) stretching vibrations in 24 solvents. The ability of compounds1—3 to undergo specific intermolecular interactions is evaluated from the dependence ofv(C=O) on the Kamlet-Taft (*,, ) parameters, which was obtained for the carbonyl groups involved in the intramolecular coordinate (=OSi) bond and for free carbonyl groups. The corresponding values of the coefficients in the Kamlet-Taft equations are indicative of a weak ability of pentacoordinate silicon compounds1 and2 to undergo acid-base interactions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 689–692, April, 1995. 相似文献
985.
The conditions of formation of Y, La and lanthanide (from Ce(III) to Lu) enanthates were worked out, their composition and their solubilities in water at 291 K were determined, and the conditions of their thermal decomposition were studied. They were prepared as crystalline solids with general formula Ln(C7H13O2)3·nH2O, wheren=2–10. On heating, they decompose in two or three steps. They first lose some water molecules and then decompose to the oxides directly (salts of Y and heavy lanthanides) or via the intermediate formation of Ln2O2CO3 (salts of La, Pr, Nd, Sm and Eu). Only yttrium enanthate dihydrate loses 2 water molecules on heating to form an anhydrous complex, which decomposes directly to Y2O3. The temperatures of dehydration are similar for all complexes (323–343 K), while the temperatures of oxide formation vary irregularly from 823 K for CeO2 to 1078 K for La2O3. 相似文献
986.
M. V. Alfimov S. P. Gromov O. B. Stanislavskii E. N. Ushakov O. A. Fedorova 《Russian Chemical Bulletin》1993,42(8):1385-1389
Styryl dyes containing a crown ether group and a heteroaromatic moiety with a sulfoalkylN-substituent (1a,b) undergo photocyclodimerization in acetonitrile in the presence of Mg(ClO4)2 to give only the typeA isomer of cyclobutane derivative (2a,b). The photochemical regio- and stereoselectivity of the cycloaddition is explained by self-organization of thetrans-isomers of the styryl dyes upon complexation with the Mg2+ cations into dimers with a fixed mutual arrangement of multiple bonds.For part 7, see ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1449–1452, August, 1993. 相似文献
987.
Compared to Pt or Pd electrodes, Au is a poor catalyst for the direct anodic oxidation of HCOOH, but the formation of Au surface oxides in acidic solutions is accompanied by a fast oxidation of HCOOH. This fast reaction is not simply a secondary reaction of Au surface oxides since those oxides are kinetically stable in HCOOH solutions. They do oxidize HCOOH only via a slow and purely electrochemical process which occurs on free Au sites and is “driven” by oxide reduction. The fast HCOOH oxidation is due to a highly reactive intermediate which is able either to form stable Au oxides AunOm or to react with HCOOH. Our results are consistent with the model that by the charge transfer step a reactive non-equilibrium {Au…O> species is formed which converts to stable equilibrium oxides AunOm after migration and rearrangement steps. Pre-equilibrium <Au…O> oxidizes HCOOH and this oxidation is of lower order with respect to <Au…O> compared with the formation of AunOm. 相似文献
988.
É. A. Zvezdina O. M. Golyanskaya I. M. Andreeva A. N. Popova E. A. Medyantseva G. N. Dorofeenko 《Chemistry of Heterocyclic Compounds》1982,18(4):340-343
2-Substituted 3,5,7-triaryl-1,2-oxazepinium perchlorates were obtained by the reaction of 2,4,6-triarylpyrylium salts in dimethylformamide with nitrones and N-arylhydroxylamines. The products are the first representatives of seven-membered cations with eight electrons.See [1] for Communication 9.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 457–460, April, 1982. 相似文献
989.
E. O. Ashevaskaya L. L. Scherbakova V. A. Scherbakov 《Journal of Radioanalytical and Nuclear Chemistry》1990,143(2):307-316
Uranyl hydration and solvation numbers of uranyl benzenesulfonate (BSU) aqueous-organic solutions have been determined by means of dynamic NMR spectroscopy technique. Three aqua-complexes have been found to exist in aqueous-acetone solution: [UO2 (U6H5SO3)2·4H2O] and [UO2(C6H5SO3)2·(H2O)n] where n=1 or 2 and anions are bridging bidentate. Transition from [UO2 (C6H5SO3)2·4H2O] to the higher aqua complexes begins at P>40. There is a disolvate in the non-aqueous solution of BSU in tri-n-butyl phosphate (TBP). Composition of aqueous and organic phase of the BSU-water-TBP ternary system has been determined at room temperature, allowing to produce the phase diagram of the system. The binodale position is related to the anion amphiphilicity. The solvation number determined for BSU in the organic phases corresponds exactly to the low temperature data and allows to observe BSU dehydration and desolvation in the region of mutual dissolution of water and the organic phase, as well as TBP and the aqueous phase. 相似文献
990.
A. S. Knyazev A. I. Boronin O. V. Vodyankina S. V. Koshcheev L. N. Kurina 《Kinetics and Catalysis》2005,46(1):144-150
The chemical composition, structure, and properties of an H3PO4-promoted polycrystalline silver foil are studied by XPS. The surface of the doped sample contains oxygen in two states with binding energies of 531.1 and 533.0 eV. Heat treatment results in silver clusters distributed in the polyphosphate matrix. It follows from TDS data that the surface of the promoted catalyst contains a strongly bound oxygen species that desorbs at ~900 K. It is believed that the silver clusters stabilized by the phosphate matrix are active sites on the surface of the phosphorus-promoted catalyst.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 153–160. Original Russian Text Copyright © 2005 by Knyazev, Boronin, Vodyankina, Koshcheev, Kurina. 相似文献