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991.
992.
Dr. Yvonne Schmidt Dipl.‐Chem. Konrad Lehr Lucie Colas Prof. Dr. Bernhard Breit 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7071-7081
The determination of the relative configuration of 1,3‐dimethyl‐substituted alkyl chains is possible by interpretation of 1H NMR shift differences. Additionally, assignments are feasible in a variety of deuterated solvents, because the corresponding shift differences are not significantly influenced by the solvent. The trends for Δδ values depending on functional groups adjacent to the stereogenic centers are shown. Based on a thorough comparison with literature data, the relative configuration of natural products can be predicted. For this purpose, we derived an empirical rule for the ranges in which Δδ values usually occur. Furthermore, we were able to proof the validity of our method by the successful prediction of the relative configuration for the polyketide natural product xylarinic acid A, which was confirmed by the asymmetric total synthesis of its enantiomer. Based on the proposed simple analysis of published 1H NMR data and the determination of the relevant chemical‐shift differences, we predicted the relative configurations of several previously unassigned natural products. 相似文献
993.
João M. Batista Jr. Andrea N.L. BatistaMassuo J. Kato Vanderlan S. BolzaniSilvia N. López Laurence A. NafieMaysa Furlan 《Tetrahedron letters》2012,53(45):6051-6054
A reinvestigation of the monoterpene chromane ester enriched fraction from Peperomia obtusifolia using chiral chromatography led to the identification of a minor peak, which was elucidated by NMR and HRMS as fenchyl-3,4-dihydro-5-hydroxy-2,7-dimethyl-8-(3″-methyl-2″-butenyl)-2-(4′-methyl-1′,3′-pentadienyl)-2H-1-benzopyran-6-carboxylate, the same structure assigned to two other fenchyl esters described previously, pointing out a stereoisomeric relationship among them. Further NMR analysis revealed that it was actually a mixture of two compounds, whose absolute configurations were determined by VCD measurements. Although, almost no vibrational transitions could be assigned to the chiral chromane, the experimental VCD spectrum was largely opposite to that obtained for the average experimental VCD [(2S,1?R,2?R,4?S + 2R,1?R,2?R,4?S)/2] for fenchol derivatives. These results allowed us to assign the putative compounds as a racemic mixture of the chiral chromane esterified with the monoterpene (1S,2S,4R)-fenchol, which had not been identified in our early work. 相似文献
994.
A concise total synthesis of (+)-deoxocassine (1) and (−)-deoxoprosophylline (2) has been achieved for the first time from d-xylose. The key steps involved in these synthesis are alkyl Grignard reaction, SN2 substitution of mesylate by azide, Wittig reaction, and reductive amination. 相似文献
995.
《Analytical letters》2012,45(15):2733-2742
Abstract A simple flow-injection spectrophotometric method for the determination of thioridazine is described. The method is based on the oxidation of thioridazine with phosphotungstic acid in hydrochloric acidic media. Concentrations of thioridazine in the range 10 – 60 ppm are determined with a relative standard deviation of 1.1%. The method was applied to the determination of thioridazine in pharmaceutical formulations. 相似文献
996.
Stereo- and enantioselective syntheses of (+)-harveynone and (−)-asperpentyn are reported. 相似文献
997.
Kamila Malecka Iwona Grabowska Jerzy Radecki Anna Stachyra Anna Góra‐Sochacka Agnieszka Sirko Hanna Radecka 《Electroanalysis》2012,24(2):439-446
The working principle of a genosensor is based on the mechanism of ion‐channel mimetic sensors. The analytical signals generated upon hybridization processes were recorded by a redox active marker [Fe(CN)6]3?/4? present in the sample solution using voltammetric techniques. The developed genosensor was suitable for determination of 20‐mer complementary oligonucleotide sequence, and also of the PCR products containing the complementary 20‐mer sequence in various positions, with detection limits in the 10 pM range. The noncomplementary 20‐mer oligonucleotide sequence as well as the PCR product without complementary region generated very weak response. The good discrimination of the position of the complementary part in the PCR products was observed. 相似文献
998.
999.
《Analytical letters》2012,45(8):1433-1455
Abstract A method was developed for separation and analysis of corrosion products formed on the surface of Cu-Ni alloys immersed in sea water polluted by sulphide ions. This method is based on the selective dissolution of oxidation compounds by suitable solvents dissolving the metal matrix only to a negligeable extent. The following solvents were used: 1) methanol to dissolve Na+, Cu2+, Ni2+ chlorides and sulphates; 2) glycine to dissolve bivalent metal compounds - Cu2+, Ni2+ oxides, sulphides, oxysulphates, oxychlorides and oxycarbonates; 3) ammonia solution to dissolve Cu+ compounds (i.e. Cu2O and CuCl); 4) potassium cyanide to dissolve CU+ sulphides. Reasonable agreement between chemical and X-Ray analysis results was observed only for copper compounds, since nickel and iron compounds could not tie observed by X-Ray diffraction. The results of Auger and chemical analyses better agree with each other, yet no Fe compounds could be detected. This is to be attributed to the non-homogeneous corrosion layer which notably contains Fe compounds in the innermost region at a depth where Auger spectroscopy is unable to detect them, whereas their detection is possible by chemical analysis, since it is a bulk analysis. 相似文献
1000.
《Analytical letters》2012,45(17):3138-3146
Abstract A new, simple, and sensitive method for the determination of riboflavin based on the single-sweep polarographic reduction wave of the photolysis products of riboflavin has been developed. Under the irradiation of an iodine-tungsten lamp, the photolysis reaction of riboflavin in pH 9.3 NH3-NH4Cl buffer solution can be complete in about 20 min. The reaction products yield a single adsorptive reduction wave at ?0.63 V (vs. SCE) negative to the reduction wave of riboflavin by 0.18 V. The derivative wave height is linearly proportional to the concentration of riboflavin in the range of 0.01–17.5 µg/mL (correlation coefficient 0.996). The detection limit is 0.00 5µg/mL. The proposed method has been applied to the determination of multivitamin tablets with satisfactory results. In comparison with the methods directly using the reduction wave of riboflavin for the determination, this method eliminates the effect of the degradation of riboflavin on the determination accuracy and is much more sensitive. The new method could be useful in many fields. 相似文献