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51.
Marlito Gomes Jr. R. Hernández-Valdés Carlos E. S. J. Marques Marcelo L. Bastos Donato A. G. Aranda O. A.C. Antunes 《Reaction Kinetics and Catalysis Letters》2005,87(1):19-24
Summary In the present paper the heterogeneous catalytic preparation of alpha-amino acids by hydrogenation of the dehydroamino acids
catalyzed by palladium is described. Enantiomeric excess of up to 26% was achieved when the hydrogenation was carried out
in ethanol at 0.5 MPa, 298 K with substrate concentration kept at 80 mmol L-1, 50 mol% cinchonidine as modified and triethylamine as addictive.</o:p> 相似文献
52.
53.
Dr. Maria A. Antunes Joana T. Coutinho Dr. Isabel C. Santos Dr. Joaquim Marçalo Prof. Manuel Almeida José J. Baldoví Dr. Laura C. J. Pereira Dr. Alejandro Gaita‐Ariño Prof. Eugenio Coronado 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17817-17826
A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2NPh)3‐tacn}UIV(η2‐N2Ph2.)] ( 2 ), was obtained by one‐electron reduction of azobenzene by the trivalent uranium compound [UIII{(SiMe2NPh)3‐tacn}] ( 1 ). Compound 2 was characterized by single‐crystal X‐ray diffraction and 1H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single‐molecule magnet behaviour for the first time in a mononuclear UIV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single‐ion Hamiltonian. 相似文献
54.
In order to validate the theoretical approach described in Part 1, an extensive experimental study has been performed at Instituto Tecnológico e Nuclear (I.T.N.), using a test rig presenting some improvements over previous experiments by the authors. In agreement with the theoretical model, concentric configurations always display flutter instability of the forward mode only, at velocities much higher than the critical unbalance-excited rotor velocity. Also predicted by theory, an instability of the backward mode may occur at much lower spinning velocities, for some eccentric configurations—which is a conclusion of practical significance. Therefore, rotor-annulus eccentricity is a very important parameter, when stability of the system is addressed. The quantitative agreement of both modal frequencies and damping values, with respect to the rotor spinning velocity, is quite satisfactory at lower velocities. However, it deteriorates somewhat at higher velocities, even for concentric configurations. Discrepancies are discussed, in connection with experimental difficulties (some unavoidable three-dimensional flow effects in the test rig) or other possibly pertinent phenomena (dynamic flow nonlinearities)—which were not accounted for in the theoretical model. However, these problems should not be overstressed, as theoretical instability boundaries are usually fairly close to the experimental results. 相似文献
55.
56.
Costa M Areias F Castro M Brea J Loza MI Proença F 《Organic & biomolecular chemistry》2011,9(11):4242-4249
A one-pot procedure was developed for the synthesis of novel 3-[amino(methoxy)methylene]-2-oxo-3,4-dihydro-2H-chromen-4-yl)-3-cyanoacetamides and chromeno[3,4-c]pyridine-1-carbonitriles from the reaction of 2-oxo-2H-chromene-3-carbonitriles and cyanoacetamides. These chromene derivatives were identified as new scaffolds for adenosine receptors and the hits 3a, 3c, 5a, and 5b were found. 相似文献
57.
Morphology development and phase inversion were investigated during dynamic vulcanisation of ethylene–propylene–diene terpolymer (EPDM)/polypropylene (PP) blends. The effects of viscosity ratio and cross-linking reactions were also addressed. EPDM/PP blends were dynamically vulcanised in a Haake batch mixer using resole and SnCl2 as cross-linking agents. The morphology development and cross-linking degree with reaction time were followed by morphology analysis (SEM and TEM) and measurement of EPDM gel content, respectively. For the same reaction time, it was found that the EPDM gel content decreased when the low-molecular-weight EPDM was used. As a result, the morphological development was delayed and the phase-inversion point was shifted to higher reaction times, allowing us to monitor morphological development during a thermoplastic vulcanisate (TPV) preparation. Using the low-molecular-weight EPDM and increasing the PP viscosity accelerated the morphological development, shifting phase-inversion to lower reaction times. While blend composition influenced final TPV morphology, it had a minor effect on the mechanism of morphological development. A correlation between cross-linking degree and morphology development was established. The results obtained allowed to propose a mechanism of morphology development during dynamic vulcanisation of the EPDM/PP blends, including phase inversion. 相似文献
58.
59.
Daniela de Luna Martins Lúcia C.S. Aguiar Octavio A.C. Antunes 《Journal of organometallic chemistry》2011,696(15-16):2845-2849
Suzuki cross-coupling reactions between arylboronic acids and aroyl chlorides with phosphine-free palladium catalysis under microwave irradiation were performed to obtainment of aromatic ketones in good yields within short times. Heterogeneous and homogeneous catalysts were studied as well as their influence in the reaction selectivity relative to homocoupling of the boronic acids. 相似文献
60.
Ferreira da Silva F Almeida D Antunes R Martins G Nunes Y Eden S Garcia G Limão-Vieira P 《Physical chemistry chemical physics : PCCP》2011,13(48):21621-21629
Electron transfer to uracil (U), 5-chlorouracil (5-ClU) and 5-fluorouracil (5-FU) yielding anion formation has been investigated in 30-100 eV potassium-molecule collisions. The rich fragmentation patterns of all three molecules suggest that electron transfer in collisions with electronegative neutrals may cause efficient damage to RNA. The main ring fragment anion in all the mass spectra was NCO(-) while the production of X(-) (X = F, Cl) was a strong decomposition of the halouracil temporary negative ions. Cl(-) was the most intense fragment anion in the 5-chlorouracil measurements, whereas NCO(-) production dominated in the U and 5-FU data. Arguments based on energetics and vibrational dynamics have been proposed to explain these differences. Electronic coupling between dipole- and valence-bound states may play a particularly important role in the fragmentation pathways of the 5-ClU parent anion. The stabilizing influence of the potassium cation following electron transfer (ionic scattering) on the observed fragmentation patterns is discussed, notably in the context of comparisons with free electron attachment processes. 相似文献