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991.
992.
V. Yu. Buz’ko I. V. Sukhno V. T. Panyushkin D. N. Ramazanova 《Journal of Structural Chemistry》2005,46(4):596-602
The structure and relative stability of 1,4-dioxane-water, (Diox)n·(H2O )m (n = 1, 2, m = 1–6), molecular complexes have been calculated by semiempirical MNDO/PM3 method. A considerable variety of (Diox)n·(H2O )m isomeric structures was stated. The mean energy of ODiox…HW-OW hydrogen bond in (Diox)n·(H2O)m complexes formed by 1,4-dioxane molecules in the chair conformation amounts to ?2.293 ± 0.210 kcal/mol with the average bond length 2.797 0.015 Å. 相似文献
993.
Yu. N. Sazanov L. I. Kutsenko A. V. Novoselova 《Russian Journal of Applied Chemistry》2005,78(4):646-648
Thermochemical reactions of cyanoethyl ethers of cellulose with polyacrylonitrile in the temperature range of its cyclization were studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005, pp. 652–654.Original Russian Text Copyright © 2005 by Sazanov, Kutsenko, Novoselova. 相似文献
994.
Stavila V. Gulya A. Shova S. Gdanec M. Simonov Yu. A. 《Russian Journal of Coordination Chemistry》2002,28(8):565-572
Compounds of the [Co(DH)2A2](BiEdta) · 6H2O type (where DH is the monodeprotonated dimethylglyoxime –ON=C(CH3)–(CH3)C=NOH; A is the o-, m-, or p-toluidine; and Edta is the ethylenediaminetetraacetate(4–) ion) were synthesized and studied. The composition and structures of the complexes were determined from their UV and 1H NMR spectra and from X-ray diffraction data. The isomer [Co(DH)2(o-NH2C6H4CH3)2]2[Bi2(μ-Edta)2(H2O)2] · 10H2O was structurally characterized using X-ray diffraction analysis. The crystals are triclinic: a = 12.153(2) Å, b = 12.824(3) Å, c = 16.215(3) Å, α = 67.73(3)°, β = 86.18(3)°, γ = 66.96(3)°, space group P $\overline 1$ , ρ(calcd) = 1.719 g/cm3, Z = 4. The structure is composed of complex binuclear [Bi2(μ-Edta)2(H2O)2]2– anions, [Co(DH)2(o-NH2C6H4CH3)2]+ cations, and molecules of crystallization water. The Edta4– anion chelates with the Bi atom in a hexadentate manner (N2O4); the fifth O atom functions as a bridging ligand. The bismuth coordination polyhedron can be regarded as a strongly distorted antiprism. In the octahedral cation, the Co(III) atom coordinates four N atoms of two DH ligands (average Co–N 1.897 Å) and two N atoms of two o-toluidine molecules (Co–N 2.023 Å). Thermolysis of the complexes studied was found to proceed in several successive steps, namely, the deaquation, deamination, and pyrolysis of the ligands. 相似文献
995.
O. A. Sof''ina N. M. Igidov E. N. Koz''minykh N. N. Trapeznikova Yu. S. Kasatkina V. O. Koz''minykh 《Russian Journal of Organic Chemistry》2001,37(7):1017-1025
Acylpyruvic acids readily react with 2,3-diaminopyridine to form (Z)-3-acylmethylene-1H-3,4-di- hydropyrido[2,3-b]pyrazin-2-ones. 5-Aryl-2,3-dihydrofuran-2,3-diones which can be regarded as lactones derived from -enolized aroylpyruvic acids react with 2,3-diaminopyridine under mild conditions, yielding regioisomeric (Z)-2-aroylmethylene-4H-1,2-dihydropyrido[2,3-b]pyrazin-3-ones. The structure of the products and reaction chemoselectivity are discussed. 相似文献
996.
E. Yu. Savonina R. K. Chernova L. M. Kozlova P. S. Fedotov 《Journal of Analytical Chemistry》2005,60(9):874-879
A new approach was proposed to fractionating soil lead species differing in mobility and biological availability. Ground solid samples were retained as a stationary phase in a rotating coiled column while continuously pumping aqueous solutions of salts and complexing agents necessary for the sequential leaching of different element species. It was shown that field-flow fractionation in a rotating coiled column is suitable for separating three lead species in an automatic mode within 4 h, as compared to several days for conventional methods of sequential extraction. The study of lead elution curves at different fractionation steps provides additional information about its mobilization under changing environmental conditions. 相似文献
997.
Baikalova L. V. Zyryanova I. A. Tarasova O. A. Chipanina N. N. Shmidt E. Yu. Kashik T. V. Afonin A. V. Sinegovskaya L. M. Vashchenko A. V. Trofimov B. A. 《Russian Journal of General Chemistry》2003,73(10):1634-1640
1-Allenylpyrazole and 1-allenyl-1,2,4-triazole react with hydrogen chloride via proton addition at the pyridine-like nitrogen atom (N2 and N4, respectively). In the reaction with 1-allenylpyrazole, 1-[(E)-3-chloro-1-propenyl]pyrazole is also formed via regio- and stereoselective addition of hydrogen chloride to the propadienyl group. 1-Allenylpyrazole and 1-allenyl-1,2,4-triazole act as unidentate ligands with respect to Co, Ni, Cu, Zn, Cd, Pd, and Sn, the donor centers being N2 and N4, respectively. Apart from mononuclear coordination compounds, 1-allenylpyrazole gives rise to polymeric complexes which contain units and blocks formed by the free ligand. 相似文献
998.
It was found that the interaction of the modified paramagnetic defects SiO(CH2)
n
H2 (n = 0.1) with nitromethane on a thermochemically activated silica surface at 300 K results in the formation of the following nitroxyl radicals: SiO(CH2)
n
CH2ON(
)CH3 and SiO(CH2)
n
CH2N(
)CH3. It was suggested that these radicals are the products of two different reactions of the modified paramagnetic defects: the first results from a reaction with free nitromethane; the second, from a reaction with nitromethane bound as complexes with diamagnetic surface defects. 相似文献
999.
A theoretical study of prednisolone, 6-fluoroprednisolone, 9-fluoroprednisolone, and 6,9-difluoroprednisolone has been performed at the ab initio HF/6-31G, MP2/6-31G, and B3LYP/6-31G levels. Structural information and the electronic features of prednisolone and its derivatives and the synergistic effect of 6,9-difluoroprednisolone was examined. Contrary to the AM1 and MNDO results, we found 9-fluoroprednisolone is more stable than the 6-fluoroprednisolone. The increased corticosteroid activity of the 6,9-difluoroprednisolone is most likely due to electronic effects, mainly related to the receptor binding. 相似文献
1000.
V. O. Kudyshkin S. Sh. Rashidova A. V. Surdina M. Yu. Zaremski V. B. Golubev 《Polymer Science Series B》2007,49(11-12):297-300
The polymerization of N-vinylpyrrolidone has been studied in the presence of the stable radical 2,2,6,6-tetramethyl-1-piperidinyloxy. It has been shown that at 120°C the polymerization proceeds via the irreversible inhibition mechanism, while, at 60°C, secondary inhibition occurs in the system during the postinduction period. This effect may be used for regulation of the molecular-mass characteristics of polymers. 相似文献