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781.
We have quantum chemically studied the structure and nature of 1-substituted 3-trimethylsilyl cyclobutenes and 2,2-disubstituted-7-trimethylsilyl bycyclo[4.2.0]octa-1(6),3-dienes comparing their reactivity to archetypal 3-substituted cyclobutene systems using density functional theory at M06-2X(PCM)/TZ2P level. We wish to understand how the ring opening reaction is affected by a substituent not directly connected to the σ Carbon-Carbon breaking bond. To this end, we have analyzed the reaction profiles considering second order perturbation energies and natural steric analysis within NBO framework. 相似文献
782.
783.
784.
In this article we present recent developments in (3+2) cycloadditions with special emphasis on 1,3-dipolar reactions involving azomethine ylides and alkenes possessing electron withdrawing groups. It is found that there is not a general mechanism for these reactions since both concerted aromatic [(π)4(s)+(π)2(s)] mechanisms and stepwise processes involving zwitterionic intermediates can be found. These computational models can be extended to analyse the role of chiral catalysts in these reactions in order to understand the nature of the catalytic cycle and the origins of chiral induction. 相似文献
785.
Nanosecond laser flash photolysis employing transient detection of emission and absorption in combination with pulse radiolysis and quantum theory has been employed to shed light into the kinetics, quantum yields, and mechanisms of the deactivation of the first excited singlet state of 1- and 2-thionaphthols (NpSH(S(1))). In contrast to thiophenols (ArSH(S(1))), the results revealed that the decay of the first excited singlet state of 1- and 2-thionaphthols (NpSH(S(1))) is governed by radiationless internal conversion (Φ(IC) = 0.29-0.46; 0.016-0.190) and intersystem crossing (Φ(ISC) = 0.14-0.15; 0.4-0.6), respectively, with pronounced S-H photodissociation (Φ(D) = 0.40-0.55; 0.35-0.40). Fluorescence as a deactivation channel plays a minor role (Φ(F) = 0.001-0.010; 0.010-0.034). Quantum chemical calculations helped in understanding the formation of naphthylthiyl radicals and rationalizing the differences in the efficiency of intersystem crossing of the 1- and 2-thionaphthol systems. 相似文献
786.
Petr Vinš Martina Vermachová Pavel Drašar Melisa del Barrio Carmen Jarne Vicente L. Cebolla Abel de Cózar Ronen Zangi Fernando P. Cossío 《Tetrahedron》2013
Different generations of dendrimers incorporating one fluorescent core of apigenin and three Fréchet benzylic dendrons have been prepared. The chief geometric features of these dendrimers have been obtained by Molecular Dynamics simulations. These computational data suggest that the asphericities of dendrimers belonging to the third and fourth generations are considerably larger than those associated with lower radii of gyration. Fluorescence spectra of high generation dendrimers evolve along time and quantum yields show an appreciable lowering for the fourth generation dendrimer. All these data suggest aggregation phenomena and lower quantum yields for nonspheric dendrimers in solution. 相似文献
787.
M. Dolores Santana Gabriel García Gregorio López Abel Lozano Consuelo Vicente Luís García José Pérez 《Polyhedron》2007
Substituted-benzoate complexes of nickel(II) of the types bidentate [Ni(mcN3)(Bz)](PF6) and monodentate [Ni(mcN3)(Bz)(H2O)](PF6) have been prepared by acid-base reaction between the hydroxo complexes [Ni(mcN3)(μ-OH)]2(PF6)2 (mcN3 = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene (Me3-mcN3) or its 9-methyl derivative (Me4-mcN3)) and the corresponding benzoic acid. The paramagnetic nickel(II) complexes have been characterized in solution by NMR spectroscopy. The influence of the substituents on the hyperfine shift patterns for substituted-benzoate complexes of nickel(II) has been studied. The substituent effects upon the coordination mode of substituted benzoates have been established by X-ray diffraction. 相似文献
788.
R. Julian R. Abel Diana Combe Adrian M. Nelson William D. Palmer 《Designs, Codes and Cryptography》2013,69(2):189-201
We show that the established necessary conditions for a GBRD ${(v,3,\lambda; \mathbb {G})}$ are sufficient (i) when ${\mathbb {G}}$ is supersolvable and (ii) when ${\mathbb {G}}$ is solvable with ${\vert \mathbb {G} \vert }$ prime to 3. 相似文献
789.
Kheiria Hcini Abir Bahi Monia Bendhifi Zarroug Mouna Ben Farhat Antonio Abel Lozano-Prez Jos Luis Cenis María Quílez Sondes Stambouli-Essassi Maria Jos Jordn 《Molecules (Basel, Switzerland)》2022,27(24)
During the last decade there has been growing interest in the formulation of new cosmetic, food and pharmaceutical products containing natural compounds with antioxidant activity and other beneficial properties. Aromatic and medicinal plants have always been the major source of bioactive compounds, especially, wild thyme (Thymbra capitata L.), which has been used since ancient times for its valuable health benefits that could be attributed to the richness of polyphenolic compounds. This study was undertaken with the following aims: to estimate the total polyphenolic content (TPC); to evaluate the antioxidant activity; to identify and quantify the phenolic compounds of post-distilled residues of Tunisian thyme, and their contribution to the antioxidant activity. The TPC, as determined by the Folin–Ciocalteu method, was found to reach the values of 126.7 and 107.84 mg gallic acid equivalent/g plant dry weight (mg GAE/g PDW). The antioxidant activity, which is assessed by DPPH and FRAP assays, reached the values of 42.97–45.64 μg/mL and 42.22–50.21 mMFe2+/mg PDW, respectively. HPLC analysis revealed the presence of fourteen polyphenolic compounds, of which diosmin and rosmarinic acid were found to be the most abundant (24.26 to 33.80 and 22.0.1 to 26.29 mg/g PDW, respectively). An important correlation was found between the antioxidant activity and several identified phenolic compounds (p < 0.05). The findings revealed that thyme post-distilled residues have an effective natural antioxidant potential due to their high concentration of bioactive molecules, and they appear to be useful in the pharmaceutical, cosmetic, and food industries, with beneficial effects on human health. Therefore, supplementing a balanced diet with herbs may have beneficial health effects. 相似文献
790.
Ulrich Abel Ovidiu Furdui Ioan Gavrea Mircea Ivan 《Czechoslovak Mathematical Journal》2010,60(4):1049-1053
In this note we give an answer to a problem of Gheorghiţă Zbăganu that arose from the study of the properties of the moments of the iterates of the integrated tail operator. 相似文献