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891.
Dorota Prukala Igor Khmelinskii Jacek Koput Mateusz Gierszewski Tomasz Pędziński Marek Sikorski 《Photochemistry and photobiology》2014,90(5):972-988
The photophysical properties of 5‐deazaalloxazine and 1,3‐dimethyl‐5‐deazaalloxazine were studied in different solvents. These compounds have higher values of fluorescence quantum yields and longer fluorescence lifetimes, compared to those obtained for their alloxazine analogs. Electronic structure and S0–Si transitions were investigated using the ab initio methods [MP2, CIS(D), EOM‐CCSD] with the correlation‐consistent basis sets. Also the time‐dependent density functional theory (TD‐DFT) has been employed. The lowest singlet excited states of 5‐deazaalloxazine and 1,3‐dimethyl‐5‐deazaalloxazine are predicted to have the π, π* character, whereas similar alloxazines have two close‐lying π, π* and n, π* transitions. Experimental steady‐state and time‐resolved spectral studies indicate formation of an isoalloxazinic excited state via excited‐state double‐proton transfer (ESDPT) catalyzed by an acetic acid molecule that forms a hydrogen bond complex with the 5‐deazaalloxazine molecule. Solvatochromism of both 5‐deazaalloxazine and its 1,3‐dimethyl substituted derivative was analyzed using the Kamlet–Taft scale and four‐parameter Catalán solvent scale. The most significant result of our studies is that the both scales show a strong influence of solvent acidity (hydrogen bond donating ability) on the emission properties of these compounds, indicating the importance of intermolecular solute–solvent hydrogen‐bonding interactions in their excited state. 相似文献
892.
Tomasz Bauer S?awomir SmolińskiPrzemys?aw Gawe? Janusz Jurczak 《Tetrahedron letters》2011,52(38):4882-4884
We present the synthesis of β-hydroxy sulfonamides derived from d-glucosamine and their application as ligands in titanium tetraisopropoxide promoted enantioselective addition of phenylacetylene to benzaldehyde and selected aromatic and aliphatic aldehydes. The N-3,5-bis(trifluoromethyl)benzenesulfonamido-d-glucosamine derivative was chosen as the most efficient ligand for this addition. The reaction is highly enantioselective for several aromatic aldehydes and enantiomeric excesses up to 92% were obtained. 相似文献
893.
1,3-Dipolar cycloaddition of alkyl glyoxylate-derived nitrones to E-crotonaldehyde can be catalyzed by hybrid diamines, obtained from (S)-BINAM and l-α-amino acids. The hybrid of (S)-BINAM and l-Phe was found to be the best organocatalyst. Products were obtained in good yield and diastereoselectivity as well as high enantioselectivity (82-91% ee). Subsequent transformations into functionalized pyrrolidinones have been demonstrated. 相似文献
894.
Grzegorz M. Salamończyk 《Tetrahedron letters》2011,52(1):155-158
The efficient synthesis of new dendrimeric polyesters up to generation 3 that consist of 1,3,5-benzenetricarboxylic acid building blocks with potential applications in drug delivery is described. The dendrimers possess hydroxy or allyl functional groups on the surface and were prepared through a divergent approach using readily available 2-(hydroxymethyl)-2-ethylpropan-1,3-diol and 1,3,5-benzenetrimethanol as central cores, with 3,5-bis[(allyloxy)methyl]benzoic acid being an essential unit of the dendrimer. The latter compound was synthesized, in high yield, from 1,3,5-benzenetricarboxylic acid, applying selective hydrolysis of the corresponding triester as the key step. 相似文献
895.
Katarzyna HeliosRafa? Wysokiński Adam PietraszkoDanuta Michalska 《Vibrational Spectroscopy》2011,55(2):207-215
The crystal and molecular structure of a polymeric Cu(II)-orotate complex, [Cu(μ-HOr)(H2O)2]n, has been reinvestigated by single crystal X-ray diffraction. It is shown that several synergistic interactions: two axial Cu-O interactions; intramolecular and intermolecular hydrogen bonds; and π-π stacking between the uracil rings contribute to the stability of the crystal structure. The Raman and FT-IR spectra of the title complex are reported for the first time. Comprehensive theoretical studies have been performed by using three unrestricted DFT methods: B3LYP; and the recently developed M06, and M05-2X density functionals. Clear-cut assignments of all the bands in the vibrational spectra have been made on the basis of the calculated potential energy distribution, PED. The very strong Raman band at 1219 cm−1 is diagnostic for the N1-deprotonation of the uracil ring and formation of the copper-nitrogen bond, in this complex. The Cu-O (carboxylate) stretching vibration is observed at 287 cm−1 in the IR spectrum, while the Cu-N (U ring) stretching vibration is assigned to the strong Raman band at 263 cm−1. The molecular structure and vibrational spectra (frequencies and intensities) calculated by the M06 functional method are very similar to the results obtained by the B3LYP method, but M06 performs better than B3LYP in calculations of the geometrical parameters and vibrational frequencies of the interligand O-H?O hydrogen bonding. Unfortunately, the M05-2X method seriously overestimates the strength of interligand hydrogen bond. 相似文献
896.
Marzec E Olszewski J Grześkowiak E Kamińska A Bienert A Iwanik K 《Colloids and surfaces. B, Biointerfaces》2011,84(1):131-134
This paper reports on the effect of paracetamol on the dielectric behavior of the rabbit lens. Measurements were performed over the frequency range of 100 Hz-100 kHz in air and at the temperature of 35°C. The frequency dependencies of the relative permittivity and dielectric loss for the control and paracetamol-control lenses are described in terms of a power-low, Debye and Cole-Cole relations. The effect of paracetamol on the dielectric properties of the lens is visible in the lower values of the relative permittivity than those for the control sample at the same frequency. In addition, the relaxations around 18 and 46 kHz for the paracetamol-control lens are shifted to lower frequencies compared with the control lens. The results of this work indicate that the present method is useful in detection of the lens toxicity elicited by overdoses of paracetamol in animal. 相似文献
897.
Ilia E. SerdiukMicha? Wera Alexander D. RoshalPawe? Sowiński Beata ZadykowiczJerzy B?a?ejowski 《Tetrahedron letters》2011,52(21):2737-2740
According to computational predictions 1,1′,1″-(2,4,6-trihydroxybenzene-1,3,5-triyl)triethanone (triacetylphloroglucinol) (TTT, form a) can exist in five tautomeric forms, among which 2,4,6-tris(1-hydroxyethylidene)-1,3,5-cyclohexanetrione (form e) exhibits thermodynamic stability comparable to that of form a. X-ray investigations reveal that the compound exists in form a in the crystalline solid phase. Analysis of the arrangement of atoms involved in the three intramolecular H-bonds, responsible for the stabilization of tautomer a by 55.4 kcal/mol, suggests that there could be fast H atom (proton) transfer within the hydrogen bonds, bringing about the transformation of a into e and vice versa. Such an effect could explain the unique behaviour and spectral properties of TTT in solutions. 相似文献
898.
899.
B. Machura A. ?witlicka D. Tabak J. Polański 《Journal of organometallic chemistry》2011,696(3):731-738
The molecular structure of 7-acetamido-2-methyl-quinoline-5,8-dione has been determined and the reactivity of 7-acetamido-2-methyl-quinoline-5,8-dione (1) and 6-acetamido-2-methyl-quinoline-5,8-dione (2) towards Re(CO)5Cl has been examined. Two novel tricarbonyl rhenium complexes, fac-[Re(CO)3(7-acetamido-2-methyl-quinoline-5,8-dione)Cl]·CHCl3 (3·CHCl3) and fac-[Re(CO)3(6-acetamido-2-methyl-quinoline-5,8-dione)Cl]2·CHCl3 (4·CHCl3), have been synthesized and characterized spectroscopically and structurally. The electronic spectrum of 3 was investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ. 相似文献
900.
Barbara Le?niewska Monika Kosi��ska Beata Godlewska-?y?kiewicz El?bieta Zambrzycka Agnieszka Z. Wilczewska 《Mikrochimica acta》2011,175(3-4):273-282
An ion-imprinted polymer (IIP) was obtained by copolymerization of methacrylic acid (as a functional monomer) and ethylene glycol dimethacrylate (as a crosslinking agent) in the presence of various chelators for Pt(II) ion and using 2,2??-azo-bis-isobutyronitrile as the initiator. Specifically, acetaldehyde thiosemicarbazone (AcTSn) and benzaldehyde thiosemicarbazone (BnTSn) were used as chelators. The IIPs were applied as sorbents for solid-phase extraction of Pt(II) and Pt(IV) ions from aqueous solutions. The effects of acidity and flow rate of the sample, of elution conditions and of potentially interfering ions were investigated. The imprinting effect of analyte is clearly demonstrated by the fact that only the IIP is capable of quantitative retention of Pt(II) and Pt(IV) ions. The method works best in the pH range from 0.5 to 1 and from 3.5 to 9.5. The ions can be recovered with an acidic solution of thiourea. The Pt-AcTSn polymer displays better sorption properties for the separation of analytes. The selectivity coefficients of the Pt-AcTSn and control polymers for Pt(IV) in the presence Pd(II), Rh(III), Ru(III), Al(III) and Cu(II) were calculated, and the sorbent capacity for Pt(IV) was found to be 4.56???g?g?-1. The method was successfully applied to the determination of Pt(IV) by electrothermal atomic absorption spectrometry in tap water, tunnel dust and anode slime samples. Figure
The new ion imprinted polymers based on Pt(II)-thiosemicarbazone derivative chelates were prepared and used as solid phase extraction sorbent for selective separation of platinum. The method was successfully applied to the determination of analyte in environmental samples by electrothermal atomic absorption spectrometry 相似文献