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131.
Francesco Alfani Maria Cantarella Nicoletta Spreti Raimondo Germani Gianfranco Savelli 《Applied biochemistry and biotechnology》2000,88(1-3):1-15
α-Chymotrypsin (α-CT) activity was tested with N-glutaryl-l-phenylalanine p-nitroanilide in buffered media with added cationic surfactants. The effect of the commercial cetyltrimethylammonium
bromide (CTABr) was compared with that of three other surfactants with ethyl (CTEABr), propyl (CTPABr), and butyl (CTBABr)
head groups. These were synthesized and purified in this laboratory. Surfactant head groups provided distinct environments
that largely modulated the catalytic performance. Larger alkyl head group hydrophobicity led to a marked enhancement of α-CT
activity. CTBABr-rich media induced the highest superactivity.
Kinetic measurements were performed in Tris-HCl buffer at a surfactant concentration either below or above CMC, and α-CT superactivity
occurred in both media. Positive interactions between the enzyme and surfactants happened independently of thesupramolecular
organization of the medium. The reaction followed the Michaelis-Menten kinetics. The substrate to micelle aggregates binding
constant was used to calculate the substrate concentration available for catalysis. The k
cat to k
m ratio was in CTBABr-rich media always higher than in pure buffer and depended on the surfactant concentration. α-CT superactivity
depended on the pH value of buffer solution. Enzyme inactivation followed a single-step mechanism in pure buffer and a series
mechanism in the presence of a surfactant. The rate of activity decay obeyed a first-order kinetics. 相似文献
132.
133.
Carlucci L Ciani G Proserpio DM Porta F 《Angewandte Chemie (International ed. in English)》2003,42(3):317-322
134.
Gianfranco Pacchioni Giuseppe Cogliandro Paul S. Bagus 《International journal of quantum chemistry》1992,42(5):1115-1139
The interaction of CO with the MgO(100) surface has been investigated by means of all electron cluster model calculations. The CO molecule is bound on the Mg2+ site of MgO with a chemisorption energy of about 0.2 eV. The binding mechanism is electrostatic in nature and arises almost entirely from the interaction of the weak electric field generated by the ionic surface and the CO charge distribution, with negligible contributions from chemical effects as the CO σ donation. When CO is bound through carbon, its vibrational frequency increases with respect to the gas-phase value. This shift, Δ, has been analyzed and decomposed into the sum of different contributions. It is found that the positive Δω does not arise entirely from the field–dipole interaction but is due, in part, to the increase in Pauli repulsion occurring when the C? O molecule vibrates in the presence of the surface “wall.” A stronger electrostatic interaction, bringing the CO adsorbate closer to the surface, increases this wall effect and results in a more pronounced positive ω shift. It is also found that the two CO orientations exhibit opposite shifts in ωe, thus, the two orientations can be distinguished, in principle, by IR spectroscopy. The analysis of our ab initio cluster wave functions gives a very different picture than the standard view of the metal–CO bond as arising from σ donation and π back donation. 相似文献
135.
Daniele Del Giudice Emanuele Spatola Matteo Valentini Cecilia Bombelli Gianfranco Ercolani Stefano Di Stefano 《Chemical science》2021,12(21):7460
In this report it is shown that nitroacetic acid 1 (O2NCH2CO2H) can be conveniently used to control the pH of a water solution over time. Time-programmable sequences of the kind pH1(high)–pH2(low)–pH3(high) can be achieved, where both the extent of the initial pH jump (pH1(high)–pH2(low)) and the time required for the subsequent pH rising (pH2(low)–pH3(high)) can be predictably controlled by a judicious choice of the absolute and relative concentrations of the reagents (acid 1 and NaOH). Successive pH1(high)–pH2(low)–pH3(high) sequences can be obtained by subsequent additions of acid 1. As a proof of concept, the method is applied to control over time the pH-dependent host–guest interaction between alpha-cyclodextrin and p-aminobenzoic acid.Predictable and time-programmable sequences of the kind pH1(high)–pH2(low)–pH3(high) in water solution are obtained by a judicious choice of the concentration of nitroacetic acid undergoing decarboxylation. 相似文献
136.
Elisabetta Borrione Maurizio Prato Gianfranco Scorrano Mariano Stivanello Vittorio Lucchini 《Journal of heterocyclic chemistry》1988,25(6):1831-1835
Lewis acid catalyzed cycloaddition reactions of ethyl glyoxylate imines to dihydrofuran and indene yield substituted hexahydrofuro[3,2-c]- and tetrahydro-7H-indeno[2,1-c]quinolines respectively. Oxidation of the adducts with 2,3-dichloro-5,6-dicyanobenzoquinone affords the corresponding aromatic compounds. 相似文献
137.
We studied decarboxylation of 6-nitrobenzisoxazole-3-carboxylate, 1, as a kinetic probe to investigate microinterface properties of aqueous micelles formed by cationic surfactants of increasing head group bulk, i.e., cetyltrialkylammonium bromide, with alkyl=Me (CTABr), Et (CTEABr), n-Pr (CTPABr), n-Bu (CTBABr) and p-octyloxybenzyltrialkylammonium bromide surfactants with alkyl=Me (pOOTABr), n-Pr (pOOTPABr), and n-Bu (pOOTBABr), and the longer p-dodecyloxybenzyltrimethylammonium bromide (pDoTABr) at concentrations higher than 0.05 M. The pseudophase kinetic treatment fails to fit the data that show anomalies with abrupt increases in k(obs) for CTPABr and CTBABr (but not for CTEABr) and with smooth and continuos increase of k(obs) for all p-alkyloxybenzyltrilakylammonium bromides. Abrupt and successive modifications of the micellar interface properties, undergoing only when the polar head or the alkyl chain have some covalent structure, account for the observed kinetic behavior. 相似文献
138.
Ottonelli M Izzo GM Rizzo F Musso G Dellepiane G Tubino R 《The journal of physical chemistry. B》2005,109(41):19249-19256
We use a simple quantum chemical semiempirical procedure to study the electronic properties of organic-lanthanide complexes, taking as a model system Er(8-hydroxyquinolinate)3. Among the problems inherent to such a study is the fact that the lanthanide ion has never been parametrized in any of the standard semiempirical Hamiltonians. To overcome this difficulty, the lanthanide ion is replaced by a different but somewhat similar parametrized ion, or merely by a point charge. Good agreement with experiment, where available, is obtained, particularly in the former case. In fact, the electronic properties of the complex (apart from the emission properties) are seen to be scarcely affected by the nature of the lanthanide ion itself, but the core interactions between the metal ion and the ligand units play a relevant role, also in the calculation of the excitation energies. In particular, the ordering and separation of both singlet and triplet excited states are affected. The main conclusion is that to describe in detail the mechanism of the energy-transfer process occurring in the complex it is essential to take into account the geometry relaxation effects in the excited states. 相似文献
139.
Innocenzi Plinio Brusatin Giovanna Guglielmi Massimo Signorini Raffaella Meneghetti Moreno Bozio Renato Maggini Michele Scorrano Gianfranco Prato Maurizio 《Journal of Sol-Gel Science and Technology》2000,19(1-3):263-266
A guest-host solid state device based on hybrid organic-inorganic materials and fullerene derivatives has been fabricated for optical limiting applications. Different 3-glycidoxypropyltrimethoxysilane derived hybrid matrices have been synthesized to increase the optical limiting performances. These matrices have shown high laser damage fluences, low light scattering, good transmittance in the visible range and allowed to deposit 10–100 m thick films per single layer. The C60 derivatives have been functionalized with Si tri-alkoxide terminal groups and have reached a final concentration in the solid matrix up to 2 × 10–2 M·l–1. A multilayer system with a bottleneck structure has been developed to optimize a laser protection device. 相似文献
140.
Dirk M. Guldi Michele Maggini Gianfranco Scorrano Maurizio Prato 《Research on Chemical Intermediates》1997,23(6):561-573
A systematic fluorescence and flash photolytic investigation of a series of covalently linked fullerene / ferrocene based donor-bridge-acceptor dyads is reported as a function of the nature of the bridge between the donor site and acceptor site. The fluorescence of the investigated dyads 2 (Φrel = 0.17 × 10?4, 3 (Φrel = 0.78 × 10?4), 4 (Φrel = 1.5 × 10?4), 5 (Φrel = 0.7 × 10?4), and 6 (Φrel = 2.9 × 10?4) were substantially quenched, relative to N-methyl fulleropyrrolidine (1) (Φrel = 6.0 × 10?4). Photolysis of N-methyl fulleropyrrolidine (1) in toluene revealed formation of the excited singlet state which was followed by a rapid intersystem crossing to the excited triplet state. On the other hand, the fate of the excited singlet state of 2, 3, 4, 5, and 6 was found to be governed by rapid intramolecular quenching, with rate constants of 28×109 s?1, 6.9×109 s?1, and 3.4×109 s?1, 14×109 s?1, 2.3×109 s?1 respectively. The electron transfer process and the charge separation were confirmed by monitoring the characteristic π-radical anion bands at λmax = 400 and 1055 nm in degassed benzonitrile with τ1/2 = 1.8 μs (3) and 2.5 μs (4). 相似文献