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11.
J. Orbán Sz. Halasi G. Papp Szilvia Barkó Beáta Bugyi 《Journal of Thermal Analysis and Calorimetry》2005,82(1):287-290
Summary The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases
of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties
of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free
energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated
form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated
form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between
the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between
the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of
these proteins as well. 相似文献
12.
Summary A method was devised to assay four forms of vitamin C: L-ascorbic acid (AA), dehydroascorbic acid (DHA), ascorbate-2-mono-
and polyphosphate (AMP, APP), as well as ascorbate-2-monosulphate (AMS), in sample series of different fish tissues and feed.
Direct and indirect detection were combined. Sample extractions were carried out with 0.2 mol L−1 sodium acetate buffer (pH 4.8) and extracts were deproteinized after different chemical or enzymatic reactions, with perchloric
acid. The DHA was reduced to AA with dithioerythritol (DTE). Ascorbate oxidase enzyme was used for the detection of background
and an acidic phosphatase enzyme for the hydrolysis of different phosphate esters. Ascorbate-2-sulphate was detected directly
with help of coinjection of the compound. Chromatographic analysis was carried out with a single column isocratic reverse
phase method. The mobile phase was an aqueous buffer of 0.04 M sodium-acetate, 0.05 mM EDTA, 0.5 mM tetrabutylammonium dihydrogen
phosphate (TBA) adjusted to pH 3.76 with 85% H3PO4 and with 24 mL methanol added to 1000 mL. C-18 columns were used with 0.6 mL min−1 flow rate at 23°C. The vitamin C forms were detected by UV absorption at 250 nm. The determination limit was 1.0–5.0 μg g−1 in AA equivalent. The standard deviations were between 1–6% and depended on the concentrations of vitamin C forms and tissues.
Recoveries were between 90–96% in samples.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997 相似文献
13.
K. Papp É. Kocsárdy A. Kiss T. Lakatos 《Journal of Thermal Analysis and Calorimetry》1977,11(2):249-256
The effect of reduction of pressure on the shapes of the TG, DTG and DTA curves and the mass-spectra of hydroxide and carbonate phases was investigated in some typical Hungarian red muds. The pressure change caused different decomposition rates of the phases and resulted in better separation of the overlapping thermal curves; this led to advantages as regards phase analysis. For phase analysis the red muds were extracted with water, and the extracts and solid residues were identified by IR- and X-ray methods.
Paper presented at the Scientific Session on Thermal Analysis held at Balatonfüred, Hungary, on 14–16 October 1976. 相似文献
Zusammenfassung Die Wirkung der Druckänderung auf die Form der TG-, DTG- und DTA-Kurven, sowie der MS-Spektra der Hydroxid- und Carbonatphasen in einigen typischen ungarischen Rotschlamm-Sorten wurde geprüft. Die Druckänderung verursachte verschiedene Zersetzungsgeschwindigkeiten der Phasen, führte zur besseren Auftrennung der sich überlappenden thermischen Kurven, und war ausserdem auch hinsichtlich der Phasenanalyse vom Vorteil. Zur Phasenanalyse wurden die Rotschlämme mit Wasser extrahiert und die Extrakte und festen Rückstände mittels IR- und Röntgenmethoden identifiziert.
Résumé On a étudié dans quelques espèces typiques de boues rouges de Hongrie l'effet des variations de pression sur la forme des courbes TG, TGD et ATD ainsi que les spectres de masse des phases hydroxyde et carbonate. La variation de la pression entraîne des vitesses de décomposition différentes. Il en résulte une meilleure séparation des phénomènes dans le cas où ceux-ci se chevauchent ainsi que des avantages du point de vue de l'analyse des phases. L'analyse des phases présentes dans les boues rouges a été effectuée par extraction à l'eau. Les extraits et les résidus solides ont été identifiés par spectrométrie infrarouge et par diffraction des rayons X.
, - . , , . .
Paper presented at the Scientific Session on Thermal Analysis held at Balatonfüred, Hungary, on 14–16 October 1976. 相似文献
14.
Joseph C. P. Koo Janice S. W. Lam Gregory A. Chass Ladislaus L. Torday Andras Varro Julius Gy. Papp 《Journal of Molecular Structure》2003,620(2-3):231-255
The sidechain conformational potential energy hypersurfaces (PEHS) for the γL, βL, αL, and αD backbone conformations of N-acetyl-
-aspartate-N′-methylamide were generated. Of the 81 possible conformers initially expected for the aspartate residue, only seven were found after geometric optimizations at the B3LYP/6-31G(d) level of theory. No stable conformers could be located in the δL, L, γD, δD, and D backbone conformations. The ‘adiabatic’ deprotonation energies for the endo and exo forms of N-acetyl-
-aspartic acid-N′-methylamide were calculated by comparing their optimized relative energies against those found for the seven stable conformers of N-acetyl-
-aspartate-N′-methylamide. Sidechain conformational PEHSs were also generated for the estimation of ‘vertical’ deprotonation energies for both endo and exo forms of N-acetyl-
-aspartic acid-N′-methylamide. All backbone–sidechain (N–H−O–C) and backbone–backbone (N–HO=C) hydrogen bond interactions were analyzed. A total of two backbone–backbone and four backbone–sidechain interactions were found for N-acetyl-
-aspartate-N′-methylamide. The deprotonated sidechain of N-acetyl-
-aspartate-N′-methylamide may allow the aspartyl residue to form strong hydrogen bond interactions (since it is negatively charged) which may be significant in such processes as protein–ligand recognition and ligand binding. As a primary example, the molecular geometry of the aspartyl residue may be important in peptide folding, such as that in the RGD tripeptide. 相似文献
15.
Bimolecular nucleophilic substitution (SN2) reactions at carbon center are well known to proceed with the stereospecific Walden-inversion mechanism. Reaction dynamics simulations on a newly developed high-level ab initio analytical potential energy surface for the F− + NH2Cl nitrogen-centered SN2 and proton-transfer reactions reveal a hydrogen-bond-formation-induced multiple-inversion mechanism undermining the stereospecificity of the N-centered SN2 channel. Unlike the analogous F− + CH3Cl SN2 reaction, F− + NH2Cl → Cl− + NH2F is indirect, producing a significant amount of NH2F with retention, as well as inverted NH2Cl during the timescale within the unperturbed NH2Cl molecule gets inverted with only low probability, showing the important role of facilitated inversions via an FH…NHCl−-like transition state. Proton transfer leading to HF + NHCl− is more direct and becomes the dominant product channel at higher collision energies.Multiple-inversion, the analogue of the double-inversion pathway recently revealed for SN2@C, is the key mechanism in SN2 at N center undermining stereospecificity. 相似文献
16.
Datta S Kumar K 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(1-3):473-477
The isotropic component of Raman band for C=O stretching mode of acetophenone in solution was analyzed by estimating the correlation coefficient with reference to Lorentzian lineshape. In the intermediate region of solute/solvent concentration there is a sharp decrease in the correlation coefficient and there appears to be a transition from non-Lorentzian to Lorentzian lineshape. The vibrational relaxation rates have been estimated from the isotropic component of Raman band in different solvents. The rate is shown to be dependent on several macroscopic as well as microscopic properties of the solute-solvent system and intermolecular interactions. The hydrodynamic and dispersion forces appear to play a major role in determining the vibrational relaxation rate and the broadening of the bands. 相似文献
17.
Guan F Uboh CE Soma LR Luo Y Li R Birks EK Teleis D Rudy JA Tsang DS 《Rapid communications in mass spectrometry : RCM》2002,16(17):1642-1651
Clenbuterol (CBL) is a potent beta(2)-adrenoceptor agonist used for the management of respiratory disorders in the horse. The detection and quantification of CBL can pose a problem due to its potency, the relatively low dose administered to the horse, its slow clearance and low plasma concentrations. Thus, a sensitive method for the quantification and confirmation of CBL in racehorses is required to study its distribution and elimination. A sensitive and fast method was developed for quantification and confirmation of the presence of CBL in equine plasma, urine and tissue samples. The method involved liquid-liquid extraction (LLE), separation by liquid chromatography (LC) on a short cyano column, and pseudo multiple reaction monitoring (pseudo-MRM) by electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS). At very low concentrations (picograms of CBL/mL), LLE produced better extraction efficiency and calibration curves than solid-phase extraction (SPE). The operating parameters for electrospray QTOF and yield of the product ion in MRM were optimized to enhance sensitivity for the detection and quantification of CBL. The quantification range of the method was 0.013-10 ng of CBL/mL plasma, 0.05-20 ng/0.1 mL of urine, and 0.025-10 ng/g tissue. The detection limit of the method was 13 pg/mL of plasma, 50 pg/0.1 mL of urine, and 25 pg/g of tissue. The method was successfully applied to the analysis of CBL in plasma, urine and various tissue samples, and in pharmacokinetic (PK) studies of CBL in the horse. CBL was quantified for 96 h in plasma and 288 h in urine post-administration of CLB (1.6 micro g/kg, 2 x daily x 7 days). This method is useful for the detection and quantification of very low concentrations of CBL in urine, plasma and tissue samples. 相似文献
18.
Ashis Kumar Pondit Asim Kumar Das Soma Gangopadhyay Debabrata Banerjea 《Transition Metal Chemistry》1988,13(6):437-439
Summary Acid catalysed dissociation of the copper(II) and nickel(II) complexes (ML2+ of the quadridentate macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene (L) has been studied spectrophotometrically. Both complexes dissociate quite slowly with the observed pseudo-first order rate constants (kobs) showing acid dependence; for the nickel(II) complex (kobs)=kO+kH[H+], the ko path is however absent with the copper(II) complex. At 60°C (I=0.1M) the kH values areca 10–4 M–1 s–1 for both complexes; k
H
Cu
/k
H
Ni
=ca. 3.9, comparable to some other square-planar complexes of these metal ions. The rate difference is primarily due to H values [copper(II) complex, 29.4±0.5 kJ mol–1; nickel(II) complex, 35.6±1.5 kJ mol–1] with highly negative S values [for copper(II), –215.5 ±6.1 JK–1 mol–1 and for nickel(II), –208.1 ±5.6 JK–1 mol–1] which are much higher than the entropy of solvation of Ni2+ (ca. –160 JK–1 mol–1) and Cu2+ (ca. –99 JK–1 mol–1) ions; significant solvation of the released metal ions and the ligand is indicated. 相似文献
19.
Wind JJ Papp L Happel M Hahn K Andriole EJ Poutsma JC 《Journal of the American Society for Mass Spectrometry》2005,16(7):1151-1161
A new version of the single-reference-extended kinetic method is presented in which direct entropy correction is incorporated. Results of calibration experiments with the monodentate base pyridine and the bidentate base ethylenediamine are presented for which the method provides proton affinities in excellent agreement with published values and reasonable predictions for the protonation entropies. The method is then used to determine the proton affinity and protonation entropy of the non-protein amino acid beta-oxalylaminoalanine (BOAA). The PA of BOAA is found to be 933.1 +/- 7.8 kJ/mol and a prediction for the protonation entropy of -39 J mol(-1) K(-1) is also obtained, indicating a significant degree of intramolecular hydrogen bonding in the protonated form. These results are supported by hybrid density functional theory calculations at the B3LYP/6-311++G**//B3LYP/6-31+G* level. They indicate that the preferred site of protonation is the alpha-nitrogen atom (PA = 935.0 kJ/mol) and that protonated BOAA has a strong hydrogen bond between the hydrogen on the alpha-amino group and one of the carbonyl oxygen atoms on the side chain. 相似文献
20.
Summary Macromolecular organic compounds do not influence the selectivity of a precipitate-chloride membrane-electrode [2] and therefore, it is possible to determine the chloride content of biological liquids (urine, blood serum) without centrifuging the proteins. The electrode has been used in these determinations for direct measurement or as indicator in argentometric titration. Comparison of the results obtained with that of other methods showed good agreement. For the membrane-electrode method the urine and the serum were diluted 18 and 110, resp.
Bestimmung des Chloridgehalts in biologischem Material mit Hilfe einer chloridspezifischen Elektrode
Zusammenfassung Makromolekulare organische Lösungsbestandteile beeinflussen die Selektivität der früher beschriebenen [2] Chlorid-Membranelektrode nicht. Deshalb kann mit ihr der Chloridgehalt biologischer Flüssigkeiten (Urin, Blutserum) ohne vorherige Abtrennung der Proteine und anderer organischer Verbindungen bestimmt werden. Die Elektrode dient dabei teilweise zur direkten Messung, teilweise als Indicator bei argentometrischen Titrationen. Ein Vergleich der Ergebnisse mit solchen, die nach der klassischen Methode von Mohr erhalten wurden, beweist die gute Eignung der Elektrode. Es ist zweckmäßig, die Lösungen vor der Analyse im Verhältnis 18 bzw. 110 zu verdünnen.相似文献