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431.
We generated models of the amorphous phase of Sb-rich GeSbTe phase change alloys by quenching from the melt within density functional molecular dynamics. We considered the two compositions Ge(1)Sb(1)Te(1) and Ge(2)Sb(4)Te(5). Comparison with previous results on the most studied Ge(2)Sb(2)Te(5) allowed us to draw some conclusions on the dependence of the structural properties of the amorphous phase on the alloy composition. Vibrational and electronic properties were also scrutinized. Phonons at high frequencies above 200?cm(-1) are localized in tetrahedra around Ge atoms in Sb-rich compounds as well as in Ge(2)Sb(2)Te(5). All compounds are semiconducting in the amorphous phase, with a band gap in the range 0.7-1.0?eV. 相似文献
432.
Hapiuk D Marques MA Melinon P Flores-Livas JA Botti S Masenelli B 《Physical review letters》2012,108(11):115903
The issue of p doping in nanostructured cagelike ZnO is investigated by state-of-the-art calculations. Our study is focused on one prototypical structure, namely, sodalite, for which we show that p-type doping is possible for elements of the V, VI, and VII columns of the periodic table. However, some dopants tend to form dimers, thus impairing the stability of this kind of doping. This difference of behavior is discussed, and two criteria are proposed to ensure stable p doping. 相似文献
433.
434.
Gas-phase acidities of CH3Y (Y: NO, C identical to CH, CH=NH, and CH=S), barriers to the identity proton-transfer CH3Y + CH2=Y- reversible CH2=Y- + CH3Y, as well as geometries and charge distributions of CH3Y, CH2=Y- and the transition states of the proton transfers were determined by ab initio methods at the MP2/6-311 + G(d,p)//MP2/6-311 + G(d,p), B3LYP/6-311 + G(d,p), and BPW-91/6-311 + G-(d,p) levels of theory. The acidities were also calculated at the CCSD(T)/6-311 + G(2df,2p) level. To make more meaningful comparisons, the same quantities for previously studied systems (Y: H, CH=CH2, CH=O, CN, NO2) were recalculated at the levels used in the present work. The geometric parameters as well as the group charges indicate that the transition states for all the reactions are imbalanced, although there is no correlation between the degree of imbalance and the pi-acceptor strength of the Y group. Based on multi-parameter correlations with the field (sigma F), resonance (sigma R), and polarizability effect (sigma alpha) substituent constants, the contributions of each of these effects to the acidities and barriers were evaluated. For the Y groups whose sigma F, sigma R, and sigma alpha are unknown (CH=NH, CH=S, C identical to CH), a method for estimating these substituent constants is proposed. The barriers for the CH3Y/CH2=Y- systems are all lower than for the CH4/CH3- system; this contrasts with the situation in solution where the Y groups lead to an increase in the barrier. The reasons for this reversal are analyzed. We also make an attempt to clarify the issue as to why the transition states of these reactions are imbalanced, a question which continues to draw attention in the literature. 相似文献
435.
Silvana Guilardi Ruggiero Maria Teresa do Prado Gambardella Marcelo Cardoso Branco Antonio Jacinto Demuner Luis Claudio A. Barbosa Dorila Pil‐Veloso 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(7):868-869
The crystal structure of 21α‐fluoro‐7‐norvouacapane‐17β,21α‐lactone, C20H25FO3, a new synthetic derivative of the diterpenoid 6α,7β‐dihydroxyvouacapan‐17β‐oic acid isolated from Pterodon polygalaeflorus Benth fruits, is described. 相似文献
436.
Rolf Brandl Silvana Franciosi Francesco De Giovanni 《Rendiconti del Circolo Matematico di Palermo》1999,48(1):13-22
IfH is a subgroup of a groupG, theautomizer ofH inG is the group of all automorphisms ofH induced by elements of its normalizerN
G
(H). the subgroupH is said to havesmall automizer ifAut
G
(H)=Inn(H), i.e. ifN
G
(H)=HC
G
(H). This article is devoted to the study of groups for which many subgroups have small automizer.
In Memoriam Valeria Fedri
R. Brandl wishes to express his sincerest thanks for the warm hospitality offered by the Department of Mathematics of the
University of Napoli “Federico II” for the time of writing this paper. 相似文献
437.
Domenico La Camera Vittorio Petraccone Silvana Artimagnella Odda Ruiz de Ballesteros 《Macromolecular Symposia》2001,166(1):157-164
The influence of the shape and size of guest molecules on the structural organization of the α and β class clathrates of syndiotactic poly(p‐methylstyrene) is described, through the analysis of the packing model proposed for the crystal structures of the clathrate forms containing o‐dichlorobenzene and tetrahydrofuran. Preliminary data of the crystal structure of the s‐PPMS clathrate containing benzene and a comparison with the crystal structure of the clathrate forms of syndiotactic polystyrene are also presented. 相似文献
438.
Arlen Ferrari Massimo Merlin Silvana Sostero Orazio Traverso Heinz Rüegger Luigi M. Venanzi 《Helvetica chimica acta》1998,81(11):2127-2139
Photolysis of [Ir(η2-coe)H2(TpMe2)] ( 1 ; TpMe2=hydrotris(3,5-dimethylpyrazolyl)borato, coe=(Z)-cyclooctene) in CH3OH gives a mixture of [IrH4(TpMe2)] ( 4 ) and [Ir(CO)H2(TpMe2)] ( 5 ) in a ca. 1 : 1 ratio. Mass-spectral analysis of the distillate of the reaction mixture at the end of the photolysis shows the presence of coe. When pure CD3OD is used as solvent, the deuteride complexes [IrD4(TpMe2)] ((D4)- 4 ) and [Ir(CO)D2(TpMe2)] ((D2)- 5 ) are obtained. Also the photolysis of [Ir(η4-cod)(TpMe2)] ( 3 ) (cod=cycloocta-1,5-diene) gives 4 and 5 . A key feature of this photoreaction is the intramolecular dehydrogenation of cod with formation of cycloocta-1,3,5-triene, detected by mass spectroscopy at the end of the photolysis. Labeling experiments using CD3OD show that the hydrides in 4 originate from MeOH. When 13CH3OH is used as solvent, [Ir(13CO)H2(TpMe2)] is formed demonstrating that CH3OH is the source of the CO ligand. The observation that the photolysis of both 1 and 3 give the same product mixture is attributed to the formation of a common intermediate, i.e., the coordinatively unsaturated 16e− species {IrH2(TpMe2)}. 相似文献
439.
Arlen Ferrari Massimo Merlin Silvana Sostero Heinz Rüegger LuigiM. Venanzi 《Helvetica chimica acta》1999,82(9):1454-1457
The photochemical rearrangement of [Rh(η4-1,5-cod)TpMe2](TpMe2=hydrotris(3,5-dimethylpyrazolyl)borato, 1,5-cod=cycloocta-1,5-diene) to the new compound [Rh(η4-1,3-cod)TpMe2] ( 2 ) is described. The characterization of 2 was carried out using 1H-, 13C-, and 103Rh-HMQC-NMR spectroscopy. Photolysis of 2 is a versatile entry point into the organometallic chemistry of the {RhTpMe2} fragment as it can be used to produce a) hydrido-carbonyl ([Rh(CO)H2TpMe2]), b) hydrido-phenyl-phosphite ([RhH(Ph)(P(OMe)3)TpMe2]), and c) ethoxide-hydrido-phosphite ([RhH(OEt)(P(OMe)3)TpMe2]) complexes. 相似文献
440.
Sofía Raffaelli Eduardo Abreo Nora Altier lvaro Vzquez Silvana Albors 《Molecules (Basel, Switzerland)》2022,27(6)
Antimicrobial resistance is a growing concern in public health and current research shows an important role for bacterial biofilms in recurrent or chronic infections. New strategies, therefore, are necessary to overcome antimicrobial resistance, through the development of new therapies that could alter or inhibit biofilm formation. In this sense, antibiofilm natural products are very promising. In this work, a bioprospection of antimicrobial and antibiofilm extracts from Uruguayan soil bacteria and insect gut bacteria was carried out. Extracts from extracellular broths were tested for their ability to inhibit planktonic cell growth and biofilm formation. Genomic analysis of Bacillus cereus ILBB55 was carried out. All extracts were able to inhibit the growth of, at least, one microorganism and several extracts showed MICs lower than 500 µg mL−1 against microorganisms of clinical relevance (Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacter cloacae). Among the extracts evaluated for biofilm inhibition only ILBB55, from B. cereus, was able to inhibit, S. aureus (99%) and P. aeruginosa (62%) biofilms. Genomic analysis of this strain showed gene clusters similar to other clusters that code for known antimicrobial compounds. Our study revealed that extracts from soil bacteria and insect gut bacteria, especially from B. cereus ILBB55, could be potential candidates for drug discovery to treat infectious diseases and inhibit S. aureus and P. aeruginosa biofilms. 相似文献