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101.
In this paper, an extension of the useful bandwidth in the low frequency band is applied to compensate the inherent poor bass response of Multiactuator Panels. These are a special type of flat panel loudspeakers that are commonly used to reproduce spatial audio under the Wave Field Synthesis system. The proposed algorithm combines two strategies: first, a dynamic electrical equalization, applied to additional exciters, which are carefully positioned to excite the lower frequency modes of the panel; second, a psycho-acoustical approach, taking profit of the behavior of human hearing based on the missing fundamental principle. For comparison purposes, the shelving and peak equalizations are also applied to the MAP prototypes developed in this paper. Objective and subjective results show that the combined approach results in an effective extension in the low frequency end of MAP with very low levels of distortion, outperforming conventional equalization methods, with better low frequency behavior, and hence better audio quality perception. 相似文献
102.
Carlos A.M Fraga Lis Helena P Teixeira Carla Maria de S Menezes Maria da Conceição K.V Ramos Eliezer J Barreiro 《Tetrahedron》2004,60(12):2745-2755
Reduction of 2-allyl-2-carboalkoxycyclohexanones (3d-f), 2-propyl-2-carboethoxycyclohexanone (3g) and 2-benzyl-2-carboethoxycyclohexanone (3h) with boron hydrides in the presence and absence of several chelating agents were studied. Molecular modeling studies using semiempirical PM3 method were performed in order to find a suitable explanation of the diastereoselection of ketone carbonyl faces during the reductive process, which yielded trans-2-allyl-2-carboethoxycyclohexanol (6e) and cis-2-allyl-2-carboethoxycyclohexanol (7e) in good diastereomeric excess by using inexpensive sodium and tetrabutylammonium borohydrides. 相似文献
103.
Ana P. X. Mariano Ana L. C. C. Ramos Afonso H. de Oliveira Júnior Yesenia M. García Ana C. C. F. F. de Paula Mauro R. Silva Rodinei Augusti Raquel L. B. de Araújo Júlio O. F. Melo 《Molecules (Basel, Switzerland)》2022,27(3)
Eugenia klotzschiana O. Berg is a native species to the Cerrado biome with significant nutritional value. However, its volatile organic compounds (VOCs) chemical profile is not reported in the scientific literature. VOCs are low molecular weight chemical compounds capable of conferring aroma to fruit, constituting quality markers, and participating in the maintenance and preservation of fruit species. This work studied and determined the best conditions for extraction and analysis of VOCs from the pulp of Eugenia klotzschiana O. Berg fruit and identified and characterized its aroma. Headspace solid-phase microextraction (HS-SPME) was employed using different fiber sorbents: DVB/CAR/PDMS, PDMS/DVB, and PA. Gas chromatography and mass spectrometry (GC-MS) were employed to separate, detect, and identify VOCs. Variables of time and temperature of extraction and sample weight distinctly influenced the extraction of volatiles for each fiber. PDMS/DVB was the most efficient, followed by PA and CAR/PDMS/DVB. Thirty-eight compounds that comprise the aroma were identified among sesquiterpenes (56.4%) and monoterpenes (30.8%), such as α-fenchene, guaiol, globulol, α-muurolene, γ-himachalene, α-pinene, γ-elemene, and patchoulene. 相似文献
104.
Moura Ramos JJ Correia NT Diogo HP Descamps M 《The journal of physical chemistry. B》2006,110(16):8268-8273
Molecular mobility in crystalline anhydrous caffeine was studied by the dielectric technique of thermally stimulated depolarization currents (TSDC). Two relaxational processes were found, one appearing at approximately -10 degrees C that is ascribed to a reorientational glass transition, and a higher temperature one that probably arises from local molecular motions that are precursors of diffusion and sublimation. The experimental results suggest that both crystalline phases II and I of caffeine, that have distinct crystal structures, are solid rotator phases. Furthermore, this dynamic reorientational disorder shows a reorientational glass transition at the same temperature in phase II and in metastable phase I. 相似文献
105.
106.
H. Morais C. Ramos E. Forgasc T. Cserháti N. Matos V. Almeida J. Oliveira 《Chromatographia》2002,56(1):S173-S175
Summary The extractability and stability of anthocyanins from the skins ofVitis vinifera were determined at different pH values. Anthocyanins were extracted using acetone, partitioned with chloroform and pre-purified
by solid-phase extraction (SPE). They were analysed by RP-HPLC, and the kinetic parameters of decomposition were calculated.
The total monomeric anthocyanin content was determined by spectrophotometry. Anthocianins were well separated by RP-HPLC.
The efficiency of extraction depended strongly on the pH of the extracting agent and on the character of the pigment to be
extracted. The amount of anthocyanins decreased with increasing duration of storage, more so at elevated temperatures.
Presented at Balaton Symposium '01 on High-Performance Separation Methods Siófok, Hungary, September 2–4, 2001. 相似文献
107.
Maria de Fátima V. Marques Danielle Ramos Juliana D. Rego 《European Polymer Journal》2004,40(11):2583-2589
Ethylene and different amounts of 1,7-octadiene were copolymerized using the metallocene catalyst system ethylidene-bis(fluorenyl) zirconium dichloride and methylaluminoxane (MAO) at both 50 and 90 °C. The catalyst activity has slightly increased with the addition of low amounts of the diene in relation to the homopolymerization of ethylene. The obtained polymers were characterized according to their melting temperature (Tm) and crystallinity degree (xc) by differential scanning calorimetry (DSC). Weight-average molecular weight (Mw) and polydispersity were determined by gel permeation chromatography (GPC). Diene contents in the copolymer were obtained through the FTIR spectroscopy. The results indicated that at polymerization temperature of 90 °C, crosslinking bonds in the obtained copolymers were low, differently from what was observed at 50 °C. The diene content in the copolymer achieved more than 3 mol% and the comonomer conversion was around 15%. Moreover, the obtained copolymers have Mw around 100,000 and large polydispersity. 相似文献
108.
Braulio Insuasty M
Nica Ramos Jairo Quiroga Adolfo Sanchez Manuel Nogueras Norbert Hanold Herbert Meier 《Journal of heterocyclic chemistry》1994,31(1):61-64
The reaction of 4,5-diamino-1,6-dihydropyrimidin-6-ones 1 with one equivalent of the chalcones 2 leads in an acidic medium to the formation of the 2,4-diaryl-2,3,6,7-tetrahydro-1H-pyrimido[4,5-b][1,4]diazepin-6-ones 3a-m . The structure elucidation of the products is based on detailed nmr investigations including selective 13C[1H] decoupling experiments. 相似文献
109.
2'-azido-2'-deoxyribonucleoside 5'-diphosphates are mechanism-based inhibitors of Ribonucleotide Reductase. Considerable effort has been made to elucidate their mechanism of inhibition, which is still controversial and not fully understood. Previous studies have detected the formation of a radical intermediate when the inhibitors interact with the enzyme, and several authors have proposed possible structures for this radical. We have conducted a theoretical study of the possible reactions involved, which allowed us to identify the structure of the new radical among the several proposals. A new reactional path is also proposed that is the most kinetically favored to yield this radical and ultimately inactivate the enzyme. The energetic involved in this mechanism, both for radical formation and radical decay, as well as the calculated Hyperfine Coupling Constants for the radical intermediate, are in agreement with the correspondent experimental values. This mechanistic alternative is fully coherent with remaining experimental data. 相似文献
110.
Ramos CI Santana-Marques MG Ferrer-Correia AJ Barata JF Tomé AC Neves MG Cavaleiro JA Abreu PE Pereira MM Pais AA 《Journal of mass spectrometry : JMS》2012,47(4):516-522
Two new isomeric aminomethyl corrole derivatives of [5,10,15-tris(pentafluorophenyl)corrolato]gallium(III) were synthesized with pyridine (py) molecules as axial ligands. When investigated by electrospray ionization mass spectrometry, in the positive and the negative ion modes, these compounds showed an unusual gas-phase behavior that could be used for their differentiation. In the positive ion mode, the differentiation was achieved through the formation of diagnostic fragment ions formed from [M-py?+?H](+) precursors, by (CH(3) )(2) NH and HF losses. An unusual addition of water to the main fragment ions provides an alternative route for isomer identification. Semi-empirical calculations were performed to elucidate the structures and stabilities of the main ionic species formed in the positive ion mode. In the negative ion mode isomer discrimination is accomplished via the fragmentation of the methoxide adduct ions [M-py?+?CH(3) O](-) through (CH(3) )(2) N(.) and HF losses. 相似文献