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991.
A theoretical comparative study of complexes of porphyrin (P), porphyrazine (Pz), phthalocyanine (Pc), porphycene (Pn), dibenzoporphycene (DBPn), and hemiporphyrazine (HPz) with iron (Fe) has been carried out using a density functional theory (DFT) method. The difference in the core size and shape of the macrocycle has a substantial effect on the electronic structure and properties of the overall system. The ground states of FeP and FePc were identified to be the 3A2g [(d(xy))2(d(z)2)2(d(pi))2] state, followed by 3E(g) [(d(xy))2(d(z)2)1(d(pi))3]. For FePz, however, the 3E(g)-3A2g energy gap of 0.02 eV may be too small to distinguish between the ground and excited states. When the symmetry of the macrocycle is reduced from D4h to D2h, the degeneracy of the d(pi) (d(xz), d(yz)) orbitals is removed, and the ground state becomes 3B2g [(d(xy))2(d(z)2)1(d(yz))2(d(xz))1] or 3B3g [...(d(yz))1(d(xz))2] for FePn, FeDBPn, and FeHPz. The calculations also show how the change of the macrocycle can influence the axial ligand coordination of pyridine (Py) and CO to the Fe(II) complexes. Finally, the electronic structures of the mono- and dipositive and -negative ions for all the unligated and ligated iron macrocycles were elucidated, which is important for understanding the redox properties of these compounds. The differences in the observed electrochemical (oxidation and reduction) properties between metal porphycenes (MPn) and metal porphyrins (MP) can be accounted for by the calculated results (orbital energy level diagrams, ionization potentials, and electron affinities). 相似文献
992.
V. Z. Sharf L. Kh. Freidlin A. S. Nekrasov A. A. Nazaryan S. A. Ponomareva 《Chemistry of Heterocyclic Compounds》1971,4(4):457-458
In the presence of tricalcium phosphate, 3-oxa-, 3-aza-, and 3-thia-1, 5-pentanediols undergo intramolecular dehydration with the formation of heterocycles and also of unstable readily-polymerizing vinyl compounds. The total degree of conversion of the diols rises in the sequence diethyleneglycol <1, 5-pentanediol 相似文献
993.
The vibrational relaxation of gaseous H2 in mixtures with He, Ne, Ar, and Kr was studied by the laser Schlieren technique in incidents shock waves at 1350–3000 K. From the results of 155 experiments the following standard relaxation times for self-relaxation of H2 and relaxation of H2 by He, Ne, Ar and Kr were obtained: pτ is in atm s, and the qouted uncertainties are standard deviations. The results for H2/H2 and H2/Ar are in very good agreement with previous results of Kiefer and Lutz, and the extrapolated for H2/H2, H2/He and H2/Ar agree very well with low temperature data Ducuing.The linear mixture rule for a additivity of relaxation rates was found to hold, to within experimental accuracy, for the mixtures studied in the present work. 相似文献
994.
P. Vaňura E. Makrlík Z. Valentová 《Journal of Radioanalytical and Nuclear Chemistry》2002,253(3):527-529
Extraction of microamounts of cesium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B−) in the presence of dibenzo-24-crown-8 (DB24C8,L) has been investigated. The equilibrium data have been explained assuming that the complexes HL+ and CsL+ are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined. 相似文献
995.
Xiaojuan Hao Luca Albertin L. John R. Foster Thomas P. Davis Christopher Barner‐Kowollik 《Macromolecular bioscience》2003,3(11):675-683
A novel synthetic method combining chemo and enzymatic synthesis strategies was employed to prepare a vinyl acetate type monomer, 6‐(4‐methoxybiphenyl‐4′‐oxy)hexyl vinyl hexanedioate (VA‐LC). Homo‐ and copolymers of VA‐LC with maleic anhydride (MAn) were prepared by conventional free radical polymerization using 2,2′‐azobisisobutyronitrile (AIBN) and 1,1′‐azobis (cyclohexane carbonitrile) (AHCN) as an initiator at 95 and 60 °C, respectively. The thermal properties of the generated polymeric material were investigated by differential scanning calorimetry (DSC), and the optical texture was inspected by polarizing optical microscopy (POM). While the monomer VA‐LC does not exhibit liquid‐crystalline properties, poly(VA‐LC), and the alternating copolymer of VA‐LC with maleic anhydride both displayed such properties.
996.
Z. G. Aliev L. O. Atovmyan E. A. Saratovskikh V. I. Krinichnii V. G. Kartsev 《Russian Chemical Bulletin》1988,37(11):2246-2252
1. | Treatment of chloropicolinic acids with aqueous solutions of various copper salts in alcohol media results in the formation of complexes of composition 21. |
2. | The structures of the newly synthesized complexes have been shown to be identical in the solid state and in solution. |
3. | Diverse modes of coordination of picolinic acid derivatives have been demonstrated; this may be one of the factors responsible for the ease of formation of metallocomplexes in biological systems, and thus may be responsible for the high biological activity (of picolinic acid derivatives). |
997.
Based on a computer-assisted analysis of the three-dimensional structure of the binary complex of E.coli dihydrofolate reductase (DHFR) with methotrexate, 5-(N-arylnortropan-3-yl)- and 5-(N-arylpiperidin-4-yl)-2,4-diaminopyrimidines 2 and 4 were designed as inhibitors of DHFR. Syntheses of the designed compounds have been carried out. The most potent compound 2a inhibited E. coli DHFR with Ki = 0.49.10?9M. The activities within the series of compounds synthesized could be rationalized by molecular-modelling experiments which served as the basis of this work. Several compounds within the presented series exhibit antimalarial activities in vitro and in vivo. 相似文献
998.
Z. G. Aliev O. P. Krasnykh A. N. Maslivets Yu. S. Andreichikov L. O. Atovmyan 《Russian Chemical Bulletin》1997,46(3):543-545
Thermal decarbonylation of 1-benzyl-4,5-dibenzoyl-2,3-dihydropyrrole-2,3-dione yields benzoyl[N-benzyl(phenylglyoxalimidoyl)]ketene. The latter undergoes intramolecular cyclization to 3-benzoyl-5-phenyl-2,3,4,5-tetrahydrofuro[3,2-c]isoquinolin-2-one. Which is oxidized to 3-benzoyl-5-phenyl-2H,4H-furo[3,2-c]isoquinolin-2-one under the reaction conditions. The crystal and molecular structure of the title compound was studied by
X-ray structural analysis.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 563–565, March, 1997. 相似文献
999.
The GC–MS characteristics of trifluoroacetate esters of phenolic compounds are discussed. Linear temperature programmed retention indices and total ion current MS response factors of over 120 phenolic esters are reported. The main GC advantages from analysis of trifluoroacetate esters as compared to plain phenols are enhanced volatility and improved resolution. For example, the elution temperature of a given phenol is typically 50 °C greater than that of the corresponding trifluoroacetate ester. Also, while retention of compounds with two trifluoroacetate groups is only moderately greater than mono esters, underivatized dihydroxy compounds are very difficult to elute from any GC column. Complete resolution of isomeric C0-, C1- and C2-alkylphenol esters is readily achieved on conventional fused silica GC columns; resolution of the corresponding underivatized compounds requires specialized GC columns with low temperature limits. In general, mass spectra of trifluoroacetate esters are more characteristic of a given structure than those of the corresponding phenols and may be more rigorously interpreted towards structural elucidation. A table in the report summarizes some of the more important spectral features used in compound identification. Example applications in analysis of coal-, shale- and petroleum-derived materials are presented. Selected ion monitoring is used to determine individual phenolic components in whole distillates; reconstructed ion chromatograms are used to illustrate distributions of selected species as a function of fuel storage and thermal stress. 相似文献
1000.
The first use of 4-(2-thiazolylazo)resorcinol (TAR) as a chelating reagent in the reversed-phase HPLC separation and determination of Os, Rh and Ru is reported. A precolumn derivatization method is used, followed by separation on an octadecyl-bonded silica stationary phase with a methanol-water mobile phase. The coloured complexes of Os, Rh, and Ru are completely separated within 8 min with a 60:40 v/v methanol-water mixture (pH 4.0, tetrabutylammonium as counter-ion). The detection limits for Rh, Ru and Os at 550 nm are 5, 6 and 17 ng/ml respectively. Recoveries of 94-102% have been obtained for these trace noble metals in analysis of anode slime. 相似文献