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991.
Milano F Gerencsér L Agostiano A Nagy L Trotta M Maróti P 《The journal of physical chemistry. B》2007,111(16):4261-4270
The kinetics and thermodynamics of cyclic electron transfer through the isolated reaction center protein of photosynthetic bacterium Rhodobacter sphaeroides were determined in detergent (Triton X-100) solution. The redox reactions between the reducing (ubiquinol-0 or ubiquinol-10) and oxidizing species (ferricenium, ferricytochrome, or ferricyanide) produced chemically or by light excitation of the protein were monitored by absorption changes of the reactants and by acidification of the solution accompanied with the disappearance of the quinol. The bimolecular rate constants of reactions of anionic ubiquinol-0 with different oxidizing agents showed large variation: 5 x 10(8) M(-1) s(-1) for ferricenium, 3.5 x 10(5) M(-1) s(-1) for ferricyanide, and 1.5 x 10(5) M(-1) s(-1) for ferricytochrome. Although the redox partners were created in pairs by the same protein promptly after light excitation, their bimolecular redox reaction was not observed even in the case of the fastest reacting partners of ferricenium and ubiquinol-0. Instead, they equilibrate with the corresponding (donor and acceptor) pools before the electron is transferred. The (logarithms of the) observed rate constants of quinol oxidation showed steep pH-dependence for water soluble ubiquinol-0 (slope +1) and mild pH-dependence for hydrophobic ubiquinol-10 (slope approximately 0.25). Combined with studies of the ionic strength dependence of the rate, it was concluded that the electron-transfer pathways of ubiquinol-0 and ubiquinol-10 oxidation started from their anionic and neutral forms, respectively. The mild pH-dependence of the rate of ubiquinol-10 oxidation came from the electrostatic interactions between ferricenium and the pH-dependent surface charges of the reaction center. The results help to understand, monitor, and design (cyclic) electron flow in bioenergetic proteins. 相似文献
992.
993.
Philipp A. Mueller Giuseppe Storti Massimo Morbidelli Charalampos A. Mantelis Thierry Meyer 《Macromolecular Symposia》2007,259(1):218-225
Summary: Experiments of methyl methacrylate dispersion polymerization are carried out in a reaction calorimeter using PDMS-mMA as surfactant. Different stabilizer concentrations from 0 to 10 wt% with respect to monomer have been considered in order to control particle morphology. The analysis by scanning electron microscopy reveals a definite decrease of the total particle surface area at decreasing stabilizer concentration. At the same time, the analysis of the polymer microstructure by gel permeation chromatography shows a trend of the average molecular weight towards smaller values. In particular, a second mode at low molecular weights has been observed leading to bimodal molecular weight distributions. The experimental results are compared with simulation results obtained through a detailed kinetic model developed in previous studies. 1 The key role of the radical exchange between continuous and dispersed phases is confirmed. 相似文献
994.
Dr. Nataliya Kalashnyk Dr. Praveen Ganesh Nagaswaran Dr. Simon Kervyn Massimo Riello Ben Moreton Prof. Dr. Tim S. Jones Prof. Dr. Alessandro De Vita Prof. Dr. Davide Bonifazi Prof. Dr. Giovanni Costantini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11856-11862
Two borazine derivatives have been synthesised to investigate their self‐assembly behaviour on Au(111) and Cu(111) surfaces by scanning tunnelling microscopy (STM) and theoretical simulations. Both borazines form extended 2D networks upon adsorption on both substrates at room temperature. Whereas the more compact triphenyl borazine 1 arranges into close‐packed ordered molecular islands with an extremely low density of defects on both substrates, the tris(phenyl‐4‐phenylethynyl) derivative 2 assembles into porous molecular networks due to its longer lateral substituents. For both species, the steric hindrance between the phenyl and mesityl substituents results in an effective decoupling of the central borazine core from the surface. For borazine 1 , this is enough to weaken the molecule–substrate interaction, so that the assemblies are only driven by attractive van der Waals intermolecular forces. For the longer and more flexible borazine 2 , a stronger molecule–substrate interaction becomes possible through its peripheral substituents on the more reactive copper surface. 相似文献
995.
M. Nikl K. Nitsch E. Mihkov K. Polk P. Fabeni G. P. Pazzi M. Gurioli S. Santucci R. Phani A. Scacco F. Somma 《Physica E: Low-dimensional Systems and Nanostructures》1999,4(4):323
Luminescence and decay kinetics of the Pb2+ aggregates in CsBr host crystals were measured in the 4–300 K temperature interval and in 10−10–10−3 time scale. Their emission properties are similar to those of CsPbBr3 bulk crystal showing a subnanosecond free exciton emission in the 520–540 nm spectral region and slower trapped exciton emission in the 530–580 nm spectral region. An efficient energy exchange between the free and trapped exciton states is shown by the temperature dependencies of emission spectra. The quantum size effect is demonstrated in the high energy shift and broadening of the absorption and emission spectra and an estimate of the size of the CsPbBr3-like aggregates is provided. Independent evidence of the presence of the CsPbBr3 and Cs4PbBr6 aggregated phases in the CsBr host was obtained by X-ray structural studies. 相似文献
996.
Pilar Lafuente Juan J. Novoa Michael J. Bearpark Paolo Celani Massimo Olivucci Michael A. Robb 《Theoretical chemistry accounts》1999,102(1-6):309-316
The model proposed by Dougherty for the design of high-spin organic systems has been studied from a quantitative point of
view using a Heisenberg Hamiltonian formalism. This analysis leads to a decomposition of the phenomenological coupling parameter,
J, into contributions from individual active orbital sites and a decomposition of the spin multiplicity into terms from the
ferromagnetic coupling unit and the spin-containing units. An analysis of the origin of quintet stability has been carried
out for four molecular systems with quintet ground states that have previously been synthesized by Dougherty and by Adam.
The results indicate that the ferromagnetic coupling unit plays the dominant role in determining high-spin stability as suggested
by Dougherty and gives some insights that may be useful in the rational design of high-spin systems.
Received: 31 July 1998 / Accepted: 21 September 1998 / Published online: 23 February 1999 相似文献
997.
Laura Andreozzi Massimo Faetti Giancarlo Galli Marco Giordano Diego Palazzuoli 《Macromolecular Symposia》2004,218(1):323-332
The possibility of achieving devices for rewritable optical storage is provided by liquid-crystalline polymers with azobenzene side groups, because they undergo photochemically induced trans-cis reversible isomerization. In this work we overview our investigations into a nematic azobenzene-polymethacrylate (PMA4) as a suitable material for optical nanowriting. Relaxation processes over different time-length scales are discussed with particular reference to understanding the interplay between homogeneity at the molecular level, bit stability and working temperature range. 相似文献
998.
999.
Adriana Trapani María ngeles Esteban Francesca Curci Daniela Erminia Manno Antonio Serra Giuseppe Fracchiolla Cristbal Espinosa-Ruiz Stefano Castellani Massimo Conese 《Molecules (Basel, Switzerland)》2022,27(2)
The supply of nutrients, such as antioxidant agents, to fish cells still represents a challenge in aquaculture. In this context, we investigated solid lipid nanoparticles (SLN) composed of a combination of Gelucire® 50/13 and Precirol® ATO5 to administer a grape seed extract (GSE) mixture containing several antioxidant compounds. The combination of the two lipids for the SLN formation resulted in colloids exhibiting mean particle sizes in the range 139–283 nm and zeta potential values in the range +25.6–43.4 mV. Raman spectra and X-ray diffraction evidenced structural differences between the free GSE and GSE-loaded SLN, leading to the conclusion that GSE alters the structure of the lipid nanocarriers. From a biological viewpoint, cell lines from gilthead seabream and European sea bass were exposed to different concentrations of GSE-SLN for 24 h. In general, at appropriate concentrations, GSE-SLN increased the viability of the fish cells. Furthermore, regarding the gene expression in those cells, the expression of antioxidant genes was upregulated, whereas the expression of hsp70 and other genes related to the cytoskeleton was downregulated. Hence, an SLN formulation containing Gelucire® 50/13/Precirol® ATO5 and GSE may represent a compelling platform for improving the viability and antioxidant properties of fish cells. 相似文献
1000.
Carlo Ciarrocchi Donatella Sacchi Massimo Boiocchi Maduka Lankani Weththimuni Alessio Orbelli Biroli Maurizio Licchelli 《Molecules (Basel, Switzerland)》2022,27(6)
Copper(II) azacyclam complexes (azacyclam = 1,3,5,8,12-pentaazacyclotetradecane) containing naphthyl or dansyl subunits can be prepared by template synthesis involving proper sulfonamide derivatives as locking fragments. The macrocyclic complexes are very poorly emissive due to the fluorescence-quenching behavior displayed by Cu2+ ions. However, the fluorescence can be recovered as a result of the decomposition of the complexes, which induces the release of free light-emitting subunits to the solution. This reaction takes place very slowly in neutral water but its rate is increased by the presence of sulfite. Therefore, [Cu(azacyclam)]2+ derivatives have been investigated as simple chemical probes for the fluorogenic detection of sulfite both on laboratory and real samples. Preliminary tests performed on samples of white wine provided sulfite concentration values that are in agreement with those obtained by a standard analytical method. 相似文献