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151.
Rinaldo Cervellati Nicoletta Crespi‐Perellino StanleyD. Furrow Anacleto Minghetti 《Helvetica chimica acta》2000,83(12):3179-3190
Inhibitory effects by addition of aqueous extracts of soy flour to an active Briggs‐Rauscher mixture are reported. The effect consists of an immediate cessation of oscillations, but, after some time, the oscillatory behavior is regenerated with amplitude and frequency different from those observed in a reference mixture. The inhibition time depends linearly on the concentration of substances contained in the extract in a wide range of concentration. The inhibitory effects are due to the high free‐radical scavenging activity of substances contained in the soy flour. Two preponderant products contained in the soy flour extract were identified and characterized as malonyldaidzin and malonylgenistin. The antioxidant activity of these isoflavones contained in the extracts was determined on the basis of the inhibition time. A qualitative mechanistic explanation of the inhibitory effects is given. Our findings are decisive indirect evidence of involvement and important role played by HOO. radicals in establishing oscillations in the Briggs‐Rauscher (BR) system. The linear relationship between the inhibition time and the whole‐mass concentration of antioxidant contained in soy extracts added to a BR mixture is an indication of the possibility to develop and implement an analytical procedure for monitoring the activity of antioxidant scavengers of free radicals based on the oscillating Briggs‐Rauscher reaction. 相似文献
152.
Rinaldo Cubeddu Paola Taroni Dan-Ning Hu Naomi Sakai Koji Nakanishi Joan E. Roberts 《Photochemistry and photobiology》1999,70(2):172-175
With age, human retinal pigment epithelial cells accumulate lipofuscin that can absorb photons in the visible range leading to light-induced damage and impaired vision. A putative precursor of lipofuscin, 2-[2,6-dimethyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E, 5E,7E- octatetraenyl]-1-(2-hydroxyethyl)-4-[4-methyl-6-(2,6,6-trimethyl-1 - cyclohexen-1-yl)-1E,3E,5E-hexatrienyl]-pyridinium (A2-E), has recently been isolated and characterized from aged human retinal pigment epithelial cells. We have found that A2-E inhibits the growth of human retinal pigment epithelial cells at concentrations greater than 1 microM. Time-resolved fluorescence measurements of 1 microM A2-E in solution, performed under 413 nm excitation, showed that fluorescence wave forms integrated across the spectrum (450-600 nm) were best-fitted with three decay times in the nanosecond and subnanosecond time scale: 6.6, 1.9 and 0.33 ns. Untreated retinal pigment epithelial cells were characterized by three fluorescence lifetimes: 6.3, 1.7 and 0.35 ns. In retinal pigment epithelial cells treated with 1 microM A2-E, the fluorescence decay was significantly faster, with the marked presence (approximately equal to 30%) of a fourth short lifetime (0.12 ns). These fluorescence decay times for A2-E bound to human retinal pigment epithelial cells are similar to those of lipofuscin granules isolated from aged human retinal pigment epithelial cells. This similarity supports the hypothesis that A2-E is a precursor of lipofuscin and suggests that A2-E may play a role in the overall light damage associated with age-related retinal diseases. 相似文献
153.
Rinaldo Gregorio Marcelo Marino Botta 《Journal of Polymer Science.Polymer Physics》1998,36(3):403-414
A systematic study was carried out on the effect of the crystallization temperature (Tcr), on the phase transitions presented by P(VDF/TrFE) copolymers cast from dimethylformamide (DMF) solution with molar ratios 60/40, 70/30, and 80/20. The results obtained by differential scanning calorimetry (DSC) showed that two-phase transitions are observed only when the copolymer crystallizes above a certain temperature To, and that the temperatures at which these transitions occur are reduced slightly with Tcr increase. It also was observed that when Tcr increases, the intensity of the endotherm corresponding to the lowest temperature transition is increased, whereas the one corresponding to the highest temperature transition is reduced. In order to explain these phenomena, the existence of two ferroelectric and two paraelectric phases is suggested. The conformational differences between like phases occur due to the distinct origin of each one: the best organized phase crystallizes directly from solution, whereas the least organized is the result of a solid phase transition. Wide angle x-ray diffusion (WAXD) diffractograms corroborate this hypothesis. Phase diagrams for samples crystallized below and above To have been proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 403–414, 1998 相似文献
154.
Francesca Leonelli Stefano Borocci LuisaM. Migneco Rinaldo MariniBettolo Doriano Lamba 《Helvetica chimica acta》2002,85(9):2817-2826
The preparation of podocarp‐9(11)‐en‐12‐one ( 1a ) from O‐methylpodocarpane ( 2 ) was investigated with the aim of clarifying whether 8‐epipodocarp‐9(11)‐en‐12‐one ( 1b ) is formed to any extent during the early stages of the process. This study, supported by molecular‐mechanics calculations, resulted in the preparation, along with 1a , of the previously undescribed 1b , which could be fully characterized by means of 2D‐NMR experiments. Significant differences recorded in the NMR and NOESY spectra of 1a and 1b were of diagnostic value in establishing the relative configuration at C(8) and possibly might be helpful to solve similar problems on podocarp‐9(11)‐en‐12‐one derivatives. 相似文献
155.
Remor Marcelo Bevilacqua Vilas Boas Marcio Antnio Sampaio Silvio Csar Damatto Sandra Regina Stevaux Jos Cndido dos Reis Ralpho Rinaldo 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(2):1019-1027
Journal of Radioanalytical and Nuclear Chemistry - The objective was to rebuild the history of sedimentation and accumulation of nutrients rate in the Upper Paraná River floodplain. Two corers... 相似文献
156.
Meenu Murali Dimitri Berne Dr. Christine Joly-Duhamel Dr. Sylvain Caillol Dr. Eric Leclerc Dr. Eric Manoury Dr. Vincent Ladmiral Prof. Rinaldo Poli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(61):e202202058
Vitrimers are 3D “covalent adaptable networks” (CANs) with flow properties thanks to thermally activated associative exchange reactions. This contribution introduces coordination adaptable networks, or CooANs, that are topologically related to metal–organic frameworks with octahedral Zr6 clusters as secondary building units in a carboxylic acid-functionalized acrylate-methacrylate copolymer matrix. A series of Zr-CooAN-x materials (x=percent of Zr6 loading relative to maximum capacity) was synthesized with x=5, 10, 15, 20, 25, 50 and 100. The mechanical and rheological investigations demonstrate vitrimer-like properties for x up to 50, the crosslink migration being ensured by carboxylate ligand exchange, with relaxation becoming slower as the Zr6 content is increased. The flow activation energy of Zr-CooAN-10 is 92.9±3.6 kJ mol−1. Rapid (30 min) hot-press reshaping occurs at temperatures in the 50–100 °C range under a 3-ton pressure and does not significantly alter the material properties. 相似文献
157.
Antoine Debuigne Dr. Rinaldo Poli Prof. Julien De Winter Pascal Laurent Dr. Pascal Gerbaux Prof. Philippe Dubois Prof. Jean‐Paul Wathelet Prof. Christine Jérôme Prof. Christophe Detrembleur Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(6):1799-1811
Cobalt‐mediated radical coupling (CMRC) is a straightforward approach to the synthesis of symmetrical macromolecules that relies on the addition of 1,3‐diene compounds onto polymer precursors preformed by cobalt‐mediated radical polymerization (CMRP). Mechanistic features that make this process so efficient for radical polymer coupling are reported here. The mechanism was established on the basis of NMR spectroscopy and MALDI‐MS analyses of the coupling product and corroborated by DFT calculations. A key feature of CMRC is the preferential insertion of two diene units in the middle of the chain of the coupling product mainly according to a trans‐1,4‐addition pathway. The large tolerance of CMRC towards the diene structure is demonstrated and the impact of this new coupling method on macromolecular engineering is discussed, especially for midchain functionalization of polymers. It is worth noting that the interest in CMRC goes beyond the field of polymer chemistry, since it constitutes a novel carbon–carbon bond formation method that could be applied to small organic molecules. 相似文献
158.
Pavel A. Dub Natalia V. Belkova Dr. Oleg A. Filippov Dr. Jean‐Claude Daran Dr. Lina M. Epstein Prof. Agustí Lledós Prof. Elena S. Shubina Prof. Rinaldo Poli Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(1):189-201
Low‐temperature (200 K) protonation of [Mo(CO)(Cp*)H(PMe3)2] ( 1 ) by Et2O ? HBF4 gives a different result depending on a subtle solvent change: The dihydrogen complex [Mo(CO)(Cp*)(η2‐H2)(PMe3)2]+ ( 2 ) is obtained in THF, whereas the tautomeric classical dihydride [Mo(CO)(Cp*)(H)2(PMe3)2]+ ( 3 ) is the only observable product in dichloromethane. Both products were fully characterised (νCO IR; 1H, 31P, 13C NMR spectroscopies) at low temperature; they lose H2 upon warming to 230 K at approximately the same rate (ca. 10?3 s?1), with no detection of the non‐classical form in CD2Cl2, to generate [Mo(CO)(Cp*)(FBF3)(PMe3)2] ( 4 ). The latter also slowly decomposes at ambient temperature. One of the decomposition products was crystallised and identified by X‐ray crystallography as [Mo(CO)(Cp*)(FH???FBF3)(PMe3)2] ( 5 ), which features a neutral HF ligand coordinated to the transition metal through the F atom and to the BF4? anion through a hydrogen bond. The reason for the switch in relative stability between 2 and 3 was probed by DFT calculations based on the B3LYP and M05‐2X functionals, with inclusion of anion and solvent effects by the conductor‐like polarisable continuum model and by explicit consideration of the solvent molecules. Calculations at the MP4(SDQ) and CCSD(T) levels were also carried out for calibration. The calculations reveal the key role of non‐covalent anion–solvent interactions, which modulate the anion–cation interaction ultimately altering the energetic balance between the two isomeric forms. 相似文献
159.
Aleix Comas‐Vives Dr. Agustí Lledós Prof. Rinaldo Poli Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(7):2147-2158
A DFT analysis of the epoxidation of C2H4 by H2O2 and MeOOH (as models of tert‐butylhydroperoxide, TBHP) catalyzed by [Cp*MoO2Cl] ( 1 ) in CHCl3 and by [Cp*MoO2(H2O)]+ in water is presented (Cp*=pentamethylcyclopentadienyl). The calculations were performed both in the gas phase and in solution with the use of the conductor‐like polarizable continuum model (CPCM). A low‐energy pathway has been identified, which starts with the activation of ROOH (R=H or Me) to form a hydro/alkylperoxido derivative, [Cp*MoO(OH)(OOR)Cl] or [Cp*MoO(OH)(OOR)]+ with barriers of 24.9 (26.5) and 28.7 (29.2) kcal mol?1 for H2O2 (MeOOH), respectively, in solution. The latter barrier, however, is reduced to only 1.0 (1.6) kcal mol?1 when one additional water molecule is explicitly included in the calculations. The hydro/alkylperoxido ligand in these intermediates is η2‐coordinated, with a significant interaction between the Mo center and the Oβ atom. The subsequent step is a nucleophilic attack of the ethylene molecule on the activated Oα atom, requiring 13.9 (17.8) and 16.1 (17.7) kcal mol?1 in solution, respectively. The corresponding transformation, catalyzed by the peroxido complex [Cp*MoO(O2)Cl] in CHCl3, requires higher barriers for both steps (ROOH activation: 34.3 (35.2) kcal mol?1; O atom transfer: 28.5 (30.3) kcal mol?1), which is attributed to both greater steric crowding and to the greater electron density on the metal atom. 相似文献
160.
Juliana Mo?o Corrêa Luciana Graciano Josielle Abrah?o Eduardo Alexandre Loth Rinaldo Ferreira Gandra Marina Kimiko Kadowaki Caroline Henn Rita de Cássia Garcia Sim?o 《Applied biochemistry and biotechnology》2012,168(8):2218-2229
In the present work, the gene xynB2, encoding a ??-xylosidase II of the Glycoside Hydrolase 39 (GH39) family, of Caulobacter crescentus was cloned and successfully overexpressed in Escherichia coli DH10B. The recombinant protein (CcXynB2) was purified using nickel-Sepharose affinity chromatography, with a recovery yield of 75.5?%. CcXynB2 appeared as a single band of 60?kDa on a sodium dodecyl sulfate polyacrylamide gel and was recognized by a specific polyclonal antiserum. The predicted CcXynB2 protein showed a high homology with GH39 ??-xylosidases of the genus Xanthomonas. CcXynB2 exhibited an optimal activity at 55?°C and a pH of 6. CcXynB2 displayed stability at pH values of 4.5?C7.5 for 24?h and thermotolerance up to 50?°C. The K M and V Max values were 9.3?±?0.45?mM and 402?±?19???mol?min?1 for ??-nitrophenyl-??-d-xylopyranoside, respectively. The purified recombinant enzyme efficiently produced reducing sugars from birchwood xylan and sugarcane bagasse fibers pre-treated with a purified xylanase. As few bacterial GH39 family ??-xylosidases have been characterized, this work provides a good contribution to this group of enzymes. 相似文献