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991.
The position of proton inside manganese dioxide, γ-MnO2, was studied by the total neutron-scattering technique using H/D isotopic substitution. The first-order difference was obtained by subtracting the results for the two different isotopic compositions and obtaining the weighted sum of partial structure factors and radial distribution functions related to the structure around hydrogens. The deuterium-substituted γ-MnO2 was prepared by de-intercalation of the proton via an oxidative treatment prior to re-intercalation with deuterium. The proton occupied two different positions with the H-O length of 1.0 and 1.9 Å, which corresponds to the ‘Ruetschi’ and ‘Coleman’ protons, respectively. The former protons situated in the Mn4+ vacant site and the latter in the tunnel centered in an oxygen octahedron. The isotopic substitution technique and the structure around protons are discussed in details. 相似文献
992.
993.
Krasovsky A. L. Pissarev S. A. Nenajdenko V. G. Balenkova E. S. 《Russian Chemical Bulletin》2003,52(8):1791-1796
A procedure was developed for the synthesis of previously unknown CF3-containing -azolyl-substituted enones by the reactions of 1,1,1-trifluoro-4-sulfonyl-3-butene-2,2-diols with various azoles. Quaternization of the azolyl group with methyl triflate afforded -azolium-substituted enones in quantitative yields. 相似文献
994.
995.
996.
A kinetic and product study of the dichloroacetic acid catalyzed chlorination of 1-methylpyrrole with 3- and 4-substituted N-chlorobenzamides was carried out. Protonated N-chlorobenzamides served as carriers of CI+. A Hammett correlation was obtained with ρ=−0.68 (r=0.98, n=8). General acid catalysis was observed with α=0.48 (r=0.99 and n=7). The yields of 2-chlorination (84±0.7%) and 3-chlorination (2.6±0.4%) were essentially constant (constant intramolecular selectivity) as the substituent on the N-chlorobenzamide was varied. Observation of constant intramolecular selectivity indicated that two intermediates were formed during the acid catalyzed chlorination of 1-methylpyrrole with N-chlorobenzamides. The carrier method is applicable to all types of aromatic systems and limited only by the availability of suitable carrier molecules. 相似文献
997.
Tomachinskaya L. A. Kolotilova Yu. Yu. Chernii V. Ya. Volkov S. V. 《Theoretical and Experimental Chemistry》2003,39(2):104-108
We have used cyclic voltammetry to study the electrochemical properties of novel bis(-diketonate)phthalocyanine complexes of Zr(IV) and Hf(IV) in dichloromethane. We found three waves for the studied complexes that can be attributed to one-electron processes MPc(L)0/1–
2, MPc(L)1+/0
2 and MPc(L)2+/1+
2. We have shown that the electrochemical behavior of the complexes depends on the nature of the substituents in axial ligands and does not depend on the nature of the metals. We have analyzed the stability of the one-electron oxidation products of the complexes relative to disproportionation. 相似文献
998.
Estela M. Alvarez Patricia H. Risso Carlos A. Gatti Mariano Burgos Virginia Suarez Sala 《Colloid and polymer science》2007,285(5):507-514
The formation of colloidal particles by Ca2+ precipitation of whole caseinates in the presence of phosphate (Pi), citrate (Cit), or both of the anions in concentrations
found to be effective in previous works was followed comparing the colloidal particle size and the ionic and proteic composition
of the precipitates obtained. Ca2+ was incorporated to the precipitate and colloidal particles in a different way than Pi, differences which were related to
the presence of Pi and/or Cit in the media. A sequential salting-out process due to progressive Ca2+ binding to at least two kinds of sites was observed. The precipitation curves were fitted, and the affinity constants and
binding site numbers were calculated with a modification of the Farrell’s equation based on the concept of Wyman’s linked
functions. Precipitates obtained at low total Ca2+ concentrations in different conditions varied their casein composition. Colloidal particles appeared at the beginning of
the second salting-out step, in different amount, and in average size according to the presence or absence of Pi and/or Cit
in the media. Consideration of these differences showed that Cit favored the formation of bigger colloidal particles, acting
especially in the first steps of the casein aggregation and conditioning the mechanism of this process. 相似文献
999.
A. V. Shastin T. I. Godovikova B. L. Korsunskii 《Chemistry of Heterocyclic Compounds》2003,39(5):624-631
The reaction of 2,4,6-tris[di(tert-butoxycarbonyl)nitromethyl]-1,3,5-triazine with ammonia, amines, and hydrazine has been studied. It was possible to substitute one of the di(tert-butoxycarbonyl)nitromethyl groups in this compound in the presence of ammonia, primary aliphatic amines, dimethylamine, and morpholine. The reaction with hydrazine leads to both mono- and disubstituted products. A double dealkoxylation occurs in the presence of diethylamine to give the bis(dimethylammonium) salt of 2,4-bis(tert-butoxycarbonylnitromethyl)-6-[di(tert-butoxycarbonyl)nitromethyl]-1,3,5-triazine. 相似文献
1000.
Anna V Gulevskaya Olga V SerdukeAlexander F Pozharskii Denis V Besedin 《Tetrahedron》2003,59(39):7669-7679
N(2)-Oxide and 3-amino derivatives of 6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-dione have been shown to react with primary alkylamines in the presence of an oxidant to produce condensed imidazolines or imidazoles. Both conversions based on SNH-strategy represent a new approach to imidazoline-(imidazole-)ring annulation. Heterocyclic analogues of the still unknown dibenzo[a,o]pycene were obtained as a by-products of the above transformations upon using of cyclohexylamine. 相似文献