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391.
New aromatic polyketones were obtained by reaction of terephthalolyl chloride with phenanthrene, naphthalene, 2-methylnaphthalene or 2,3-dimethylnaphthalene in the presence of anhydrous AlCl3 in various solvents. The influence of the structure of the aromatic hydrocarbon on the thermal stability of the polymer was examined. 相似文献
392.
An ensemble of magnetic clusters is approximated by an ensemble of two-singlet systems: at each lattice site l there are two levels, ?l,1 and ?l,2. ?l,1 is associated with spin zero and ?l,2 with spin 1 (or vice versa). Δ = ?l,2??l,1 originates from some intra-cluster interaction and some effective magnetic field; for the both some distribution is assumed. An exchange interaction between different clusters is also taken into account. The excitation spectrum of this ensemble as function of Hext is calculated and applied to discuss the response of the system to some external magnetic field Hext in the low-temperature region. Typical instabilities of magnetization as function of Hext are obtained. Finally, possible applications of our results to spin-glass systems are discussed. 相似文献
393.
L.J. Maksymowicz D. Sendorek R. Żuberek 《Journal of magnetism and magnetic materials》1985,46(3):295-299
Surface excitations in thin amorphous (Gd1?xCox)1?yMoy films obtained by the rf sputtering technique were studied. A microwave spectrometer at X-band was used for magnetic resonance investigation with external magnetic field rotating from perpendicular to parallel resonance orientations. The critical angle and angular dependence of the position of the surface mode and the uniform mode were determined. The Surface Inhomogeneity (SI) model was applied with symmetrical boundary conditions. The surface anisotropy energy term was assumed as a superposition of the uniaxial anisotropy term and a biaxial anisotropy term. The origin of the latter term is not known yet. We also performed the resonance experiment for different temperatures ranging from 180 to 300 K. From the experiment, the uniaxial surface anisotropy constant K′s1 and the biaxial surface anisotropy constant K′s2 were found as functions of the temperature; the uniaxial anisotropy energy against temperature changes the sign for y=0.02 from easy axis to easy plane while the biaxial surface anisotropy does not change its character. 相似文献
394.
Nils A. Törnqvist Piotr Żenczykowski 《Zeitschrift fur Physik C Particles and Fields》1986,31(3):439-442
Isospin violating mass splittings of the ground state baryons are discussed within the frame-work of the unitarized quark model. It is shown that the long-distance, nonperturbative unitarity effects are important, and that a good agreement with the observed mass splittings can be retained. The importance of six mass sum rules which hold independently of dynamical assumptions is emphasized. 相似文献
395.
396.
Faraldos JA Antonczak AK González V Fullerton R Tippmann EM Allemann RK 《Journal of the American Chemical Society》2011,133(35):13906-13909
Stabilization of the reaction intermediate eudesmane cation (3) through interaction with Trp 334 during catalysis by aristolochene synthase from Penicillium roqueforti was investigated by site-directed incorporation of proteinogenic and non-canonical aromatic amino acids. The amount of germacrene A (2) generated by the mutant enzymes served as a measure of the stabilization of 3. 2 is a neutral intermediate, from which 3 is formed during PR-AS catalysis by protonation of the C6,C7 double bond. The replacement of Trp 334 with para-substituted phenylalanines of increasing electron-withdrawing properties led to a progressive accumulation of 2 that showed a good correlation with the interaction energies of simple cations such as Na(+) with substituted benzenes. These results provide compelling evidence for the stabilizing role played by Trp 334 in aristolochene synthase catalysis for the energetically demanding transformation of 2 to 3. 相似文献
397.
Dr. Michael Capron Dr. Sergio Díaz‐Tendero Sylvain Maclot Dr. Alicja Domaracka Elie Lattouf Dr. Arkadiusz Ławicki Dr. Rémi Maisonny Prof. Jean‐Yves Chesnel Dr. Alain Méry Dr. Jean‐Christophe Poully Dr. Jimmy Rangama Prof. Lamri Adoui Prof. Fernando Martín Prof. Manuel Alcamí Dr. Patrick Rousseau Prof. Bernd A. Huber 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(30):9321-9332
Fragmentation of the γ‐aminobutyric acid molecule (GABA, NH2(CH2)3COOH) following collisions with slow O6+ ions (v≈0.3 a.u.) was studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multicoincidence detection method was used to deduce the charge state of the GABA molecule before fragmentation. This is essential to unambiguously unravel the different fragmentation pathways. It was found that the molecular cations resulting from the collisions hardly survive the interaction and that the main dissociation channels correspond to formation of NH2CH2+, HCNH+, CH2CH2+, and COOH+ fragments. State‐of‐the‐art quantum chemistry calculations allow different fragmentation mechanisms to be proposed from analysis of the relevant minima and transition states on the computed potential‐energy surface. For example, the weak contribution at [M?18]+, where M is the mass of the parent ion, can be interpreted as resulting from H2O loss that follows molecular folding of the long carbon chain of the amino acid. 相似文献
398.
Dr. Alicja Franke Dr. Christoph Fertinger Prof. Dr. Rudi van Eldik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(22):6935-6949
The present study focuses on the formation and reactivity of hydroperoxo–iron(III) porphyrin complexes formed in the [FeIII(tpfpp)X]/H2O2/HOO? system (TPFPP=5,10,15,20‐tetrakis(pentafluorophenyl)‐21H,23H‐porphyrin; X=Cl? or CF3SO3?) in acetonitrile under basic conditions at ?15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high‐spin [FeIII(tpfpp)(OOH)] and low‐spin [FeIII(tpfpp)(OH)(OOH)] could be observed with the application of a low‐temperature rapid‐scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O? O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo‐ to heterolytic O? O bond cleavage is observed for high‐ [FeIII(tpfpp)(OOH)] and low‐spin [FeIII(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron‐rich porphyrin ligands, electron‐deficient [FeIII(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [FeIII(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)–oxo porphyrin π‐cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450. 相似文献
399.
Capron M Díaz-Tendero S Maclot S Domaracka A Lattouf E Ławicki A Maisonny R Chesnel JY Méry A Poully JC Rangama J Adoui L Martín F Alcamí M Rousseau P Huber BA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(30):9321-9332
Fragmentation of the γ-aminobutyric acid molecule (GABA, NH(2)(CH(2))(3)COOH) following collisions with slow O(6+) ions (v≈0.3?a.u.) was studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multicoincidence detection method was used to deduce the charge state of the GABA molecule before fragmentation. This is essential to unambiguously unravel the different fragmentation pathways. It was found that the molecular cations resulting from the collisions hardly survive the interaction and that the main dissociation channels correspond to formation of NH(2)CH(2)(+), HCNH(+), CH(2)CH(2)(+), and COOH(+) fragments. State-of-the-art quantum chemistry calculations allow different fragmentation mechanisms to be proposed from analysis of the relevant minima and transition states on the computed potential-energy surface. For example, the weak contribution at [M-18](+), where M is the mass of the parent ion, can be interpreted as resulting from H(2)O loss that follows molecular folding of the long carbon chain of the amino acid. 相似文献
400.
A new type of bonded stationary phase for liquid chromatography, with the properties of immobilized artificial membranes, has been synthesized. Alkyl-phosphate adsorbents were obtained by modification of aminopropyl silica gel. The structures of the synthesized materials were confirmed by use of instrumental techniques--elemental analysis, infrared spectroscopy (FTIR), and (13)C and (29)Si CP/MAS NMR. Analysis revealed that the adsorbents mimic the phospholipids present in natural cell membranes. The new synthesized alkyl-phosphate stationary phases may be used for liquid chromatographic separation of biologically active compounds of different polarity. 相似文献