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451.
452.
Sol-Gel Processed TiO2-Based Nano-Sized Powders for Use in Thick-Film Gas Sensors for Atmospheric Pollutant Monitoring 总被引:2,自引:0,他引:2
Enrico Traversa Maria Luisa Di Vona Silvia Licoccia Michele Sacerdoti Maria Cristina Carotta Luigi Crema Giuliano Martinelli 《Journal of Sol-Gel Science and Technology》2001,22(1-2):167-179
Sol-gel routes were used to prepare pure and 5 at% and 10 at% Ta- or Nb-dope TiO2 nano-sized powders. The thermal decomposition behaviour of the precursors was studied using simultaneous thermogravimetric and differential thermal analysis (TG/DTA). X-ray diffraction (XRD) analysis showed that the powders heated to 400°C were crystalline in the anatase TiO2 structure. The pure TiO2 powder heated to 850°C showed the rutile structure. The addition of Ta and Nb inhibited the anatase-to-rutile phase transformation up to 950–1050°C. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired for 1 h at different temperatures in the 650–1050°C range. Scanning electron microscopy (SEM) observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO2. The addition of Ta and Nb is effective to keep the TiO2 grain size at a nanometric level even at 950°C, though grain growth was observed with increasing temperature. The gas-sensitive electrical response of the thick films were tested in laboratory, in environments with CO in dry and wet air. Conductance measurements showed a good gas response only for the nanostructured titania-based films. For field tests, the prototype sensors were placed beside a conventional station for atmospheric pollutant monitoring. The electrical response of the thick films was compared with the results of the analytical instruments. The same trend was observed for both systems, demonstrating the use of gas sensors for this aim. 相似文献
453.
Giuliano Tomás Antelo Maximiliano Sánchez-Lamas Fernando Alberto Goldbaum Lisandro Horacio Otero Hernán Ruy Bonomi Jimena Rinaldi 《Photochemistry and photobiology》2020,96(6):1221-1232
Phytochromes are photosensitive proteins with a covalently bound open-chain chromophore that can switch between two principal states: red light absorbing Pr and far-red light absorbing Pfr. Our group has previously shown that the bacteriophytochrome from Xanthomonas campestris pv. campestris (XccBphP) is a bathy-like phytochrome that uses biliverdin IXα as a co-factor and is involved in bacterial virulence. To date, the XccBphP crystal structure could only be solved in the Pr state, while the structure of its Pfr state remains elusive. The aims of this work were to develop an efficient screening methodology for the rapid characterization and to identify XccBphP variants that favor the Pfr form. The screening approach developed here consists in analyzing the UV-Vis absorption behavior of clarified crude extracts containing recombinant phytochromes. This strategy has allowed us to quickly explore over a hundred XccBphP variants, characterize multiple variants and identify Pfr-favored candidates. The high-quality data obtained enabled not only a qualitative, but also a quantitative characterization of their photochemistry. This method could be easily adapted to other phytochromes or other photoreceptor families. 相似文献
454.
Botta B D'Acquarica I Monache GD Subissati D Uccello-Barretta G Mastrini M Nazzi S Speranza M 《The Journal of organic chemistry》2007,72(24):9283-9290
Four cone resorc[4]arene octamethyl ethers (10, 11, ent-10, and ent-11) tetrafunctionalized at the feet with valyl-leucine [LL- (6); DD- (ent-6)] and leucyl-valine [LL- (9); DD- (ent-9)] methyl esters have been synthesized. These compounds, obtained by conjugation of macrocycle tetracarboxylic acid chlorides with the appropriate terminal amino groups of the above dipeptides, are N-linked peptidoresorc[4]arenes. We found that these macrocycles (M) are capable of recognizing the homologue dipeptides as guests (G), both in solution and in the gas phase, by forming relatively stable host-guest complexes ([M.G]), resistant to chromatographic purification but not to heating. Complexation phenomena between M and G in solution were investigated by NMR methods, including NMR DOSY experiments, for the detection of translational diffusion. Heteroassociation constants of 2030 and 186 M(-1) were obtained by the Foster-Fyfe method for the complexes [10.6] and [10.ent-6], respectively, the latter being comparable to the self-association constant of dipeptide itself. Conversely, the structural features of the proton-bound complexes [M.H.Gn]+ (n = 1, 2), generated in the gas phase by electrospray ionization mass spectrometry (ESI-MS), were investigated by collision-induced dissociation (CID) experiments. In both cases, the four N-linked peptidoresorc[4]arenes were shown to act as synthetic receptors and to recognize the homologue dipeptide by means of hydrogen bonds. 相似文献
455.
Giuliano Gregori Behnaz RahmatiWilfried Sigle Peter A. van AkenJoachim Maier 《Solid State Ionics》2011,192(1):65-69
In the present study, the effect of the addition of boron on the electrical conduction properties of nanocrystalline cerium oxide (CeO2) was investigated. Pellets consisting of pure CeO2 and a mixture of CeO2 and 10 mol.% of boron oxide (B-CeO2 samples) were sintered at 800 °C as well as 1100 °C and their electrical conduction properties investigated by impedance spectroscopy at different temperatures and oxygen partial pressures. The nanocrystalline B-CeO2 samples exhibit a higher electronic grain boundary conductivity and higher activation energy compared to a pure CeO2 sample (1.41 eV for B-CeO2 vs. 1.21 eV for pure CeO2). According to electron energy-loss spectroscopy analysis, (i) boron can be detected only at the grain boundaries and (ii) cerium cations are lightly reduced at the grain boundaries. The results are consistent with both the formation of a space charge layer with a positive space charge potential but also with conduction along a glassy cerium-boron-oxide phase. 相似文献
456.
457.
Hong Ye Lincoln Noecker Walter J. Boyko Robert M. Giuliano Glenn P. A. Yap Arnold L. Rheingold 《Journal of carbohydrate chemistry》2013,32(3):373-383
Abstract The branched-chain nitro sugar methyl 2,3,6-trideoxy-3-C-methyl-3-nitro-α-D-ribo-hexopyranoside 4 was investigated as a precursor to D-rubranitrose, a nitro sugar found in the antibiotic rubradirin. X-ray cyrstallographic analysis of 4 shows that the pyranose ring adopts the 4 C 1 conformation with the methoxy group at C-1 and the nitro group at C-3 in a 1,3-diaxial relationship. There is an intermolecular hydrogen bond involving a nitro group oxygen of one monosaccharide residue and the C-4 hydroxyl group of the adjacent residue in the crystal lattice. This interaction results in a helical crystal packing. A series of nucleophilic displacement reactions was carried out on the triflate derivative of 4 in an attempt to introduce an axial carbon-oxygen bond at C-4 required for rubranitrose. Displacements with acetate and propionate gave as products the monosaccharide esters with the desired D-xylo configuration. 相似文献
458.
Rossin A Fairen-Jimenez D Düren T Giambastiani G Peruzzini M Vitillo JG 《Langmuir : the ACS journal of surfaces and colloids》2011,27(16):10124-10131
A detailed analysis of the solvothermal synthesis in DMF of the polymeric magnesium formate {H[Mg(HCOO)(3)]?NHMe(2)}(∞) (1) from Mg(ClO(4))(2)·6H(2)O revealed that the final crystalline product is formed after an acid-catalyzed DMF hydrolysis, producing formic acid and dimethylamine. The former bridges magnesium(II) centers, creating the 3D scaffold, while the latter is trapped inside the cubic cavities of the polymer, engaging in strong hydrogen bonding with the formate ions of the cage. After thermal activation and guest removal, the material was tested for hydrogen uptake at T = 77 K over the 0-80 bar pressure range, and the existence of preferred H(2) adsorption sites was assessed through grand canonical Monte Carlo (GCMC) simulations. No specific low-energy site was found, and the H(2) molecules positions within the framework cavities are mainly dependent on packing effects. Thus, at low H(2) loadings the most populated site is the center of the cubic cavities, even though, at higher pressures, two more "localized" positions have been found by the simulation because of the reduced freedom of movement. The maximum experimental H(2) uptake corresponds to 8.8 mg/g or 13.5 mg/cm(3). 相似文献
459.
Cohavi O Reichmann D Abramovich R Tesler AB Bellapadrona G Kokh DB Wade RC Vaskevich A Rubinstein I Schreiber G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(4):1327-1336
Interactions of peptides and proteins with inorganic surfaces are important to both natural and artificial systems; however, a detailed understanding of such interactions is lacking. In this study, we applied new approaches to quantitatively measure the binding of amino acids and proteins to gold surfaces. Real‐time surface plasmon resonance (SPR) measurements showed that TEM1‐β‐lactamase inhibitor protein (BLIP) interacts only weakly with Au nanoparticles (NPs). However, fusion of three histidine residues to BLIP (3H‐BLIP) resulted in a significant increase in the binding to the Au NPs, which further increased when the histidine tail was extended to six histidines (6H‐BLIP). Further increasing the number of His residues had no effect on the binding. A parallel study using continuous (111)‐textured Au surfaces and single‐crystalline, (111)‐oriented, Au islands by ellipsometry, FTIR, and localized surface plasmon resonance (LSPR) spectroscopy further confirmed the results, validating the broad applicability of Au NPs as model surfaces. Evaluating the binding of all other natural amino acid homotripeptides fused to BLIP (except Cys and Pro) showed that aromatic and positively‐charged residues bind preferentially to Au with respect to small aliphatic and negatively charged residues, and that the rate of association is related to the potency of binding. The binding of all fusions was irreversible. These findings were substantiated by SPR measurements of synthesized, free, soluble tripeptides using Au‐NP‐modified SPR chips. Here, however, the binding was reversible allowing for determination of binding affinities that correlate with the binding potencies of the related BLIP fusions. Competition assays performed between 3H‐BLIP and the histidine tripeptide (3 His) suggest that Au binding residues promote the adsorption of proteins on the surface, and by this facilitate the irreversible interaction of the polypeptide chain with Au. The binding of amino acids to Au was simulated by using a continuum solvent model, showing agreement with the experimental values. These results, together with the observed binding potencies and kinetics of the BLIP fusions and free peptides, suggest a binding mechanism that is markedly different from biological protein–protein interactions. 相似文献
460.
Maria Luisa Dalla Chiara Roberto Giuntini Roberto Leporini Giuliano Toraldo di Francia 《International Journal of Theoretical Physics》2008,47(1):44-60
In quantum computational logics meanings of formulas are identified with quantum information quantities: systems of qubits or, more generally, mixtures of systems of qubits. We consider two kinds of quantum computational semantics: (1) a compositional semantics, where the meaning of a compound formula is determined by the meanings of its parts; (2) a holistic semantics, which makes essential use of the characteristic “holistic” features of the quantum-theoretic formalism. The compositional
and the holistic semantics turn out to characterize the same logic. In this framework, one can introduce the notion of quantum-classical truth table, which corresponds to the most natural way for a quantum computer to calculate classical tautologies.
Quantum computational logics can be applied to investigate different kinds of semantic phenomena where holistic, contextual and gestaltic patterns play an essential role (from natural languages to musical compositions). 相似文献