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991.
Nilanjan Chakraborty Henrik Hesse Epaminondas Mastorakos 《Flow, Turbulence and Combustion》2010,84(1):125-166
The influences of fuel Lewis number Le F on localised forced ignition of inhomogeneous mixtures are analysed using three-dimensional compressible Direct Numerical Simulations (DNS) of turbulent mixing layers for Le F = 0.8, 1.0 and 1.2 and a range of different root-mean-square turbulent velocity fluctuation u′ values. For all Le F cases a tribrachial flame has been observed in case of successful ignition. However, the lean premixed branch tends to merge with the diffusion flame on the stoichiometric mixture fraction isosurface at later stages of the flame evolution. It has been observed that the maximum values of temperature and reaction rate increase with decreasing Le F during the period of external energy addition. Moreover, Le F is found to have a significant effect on the behaviours of mean temperature and fuel reaction rate magnitude conditional on mixture fraction values. It is also found that reaction rate and mixture fraction gradient magnitude \(\vert \nabla \xi \vert \) are negatively correlated at the most reactive region for all values of Le F explored. The probability of finding high values of \(\vert \nabla \xi \vert \) increases with increasing Le F . For a given value of u′, the extent of burning decreases with increasing Le F . A moderate increase in u′ gives rise to an increase in the extent of burning for Le F = 0.8 and 1.0, which starts to decrease with further increases in u′. For Le F = 1.2, the extent of burning decreases monotonically with increasing u′. The extent of edge flame propagation on the stoichiometric mixture fraction ξ = ξ st isosurface is characterised by the probability of finding burned gas on this isosurface, which decreases with increasing u′ and Le F . It has been found that it is easier to obtain self-sustained combustion following localised forced ignition in case of inhomogeneous mixtures than that in the case of homogeneous mixtures with the same energy input, energy deposition duration when the ignition centre is placed at the stoichiometric mixture. The difficultly to sustain combustion unaided by external energy addition in homogeneous mixture is particularly prevalent in the case of Le F = 1.2. 相似文献
992.
Michael Neumeier Uttam Chakraborty Dieter Schaarschmidt Victor de la Pena O'Shea Raul Perez‐Ruiz Axel Jacobi von Wangelin 《Angewandte Chemie (International ed. in English)》2020,59(32):13473-13478
Successful combinations of visible‐light photocatalysis with metal catalysis have recently enabled the development of hitherto unknown chemical reactions. Dual mechanisms from merging metal‐free photocatalysts and earth‐abundant metal catalysts are still in their infancy. We report a photo‐organo‐iron‐catalyzed cyclotrimerization of alkynes by photoredox activation of a ligand‐free Fe catalyst. The reaction operates under very mild conditions (visible light, 20 °C, 1 h) with 1–2 mol % loading of the three catalysts (dye, amine, FeCl2). 相似文献
993.
Habibul Arfin Jagjit Kaur Tariq Sheikh Sudip Chakraborty Angshuman Nag 《Angewandte Chemie (International ed. in English)》2020,59(28):11307-11311
Bi3+ and lanthanide ions have been codoped in metal oxides as optical sensitizers and emitters. But such codoping is not known in typical semiconductors such as Si, GaAs, and CdSe. Metal halide perovskite with coordination number 6 provides an opportunity to codope Bi3+ and lanthanide ions. Codoping of Bi3+ and Ln3+ (Ln=Er and Yb) in Cs2AgInCl6 double perovskite is presented. Bi3+‐Er3+ codoped Cs2AgInCl6 shows Er3+ f‐electron emission at 1540 nm (suitable for low‐loss optical communication). Bi3+ codoping decreases the excitation (absorption) energy, such that the samples can be excited with ca. 370 nm light. At that excitation, Bi3+‐Er3+ codoped Cs2AgInCl6 shows ca. 45 times higher emission intensity compared to the Er3+ doped Cs2AgInCl6. Similar results are also observed in Bi3+‐Yb3+ codoped sample emitting at 994 nm. A combination of temperature‐dependent (5.7 K to 423 K) photoluminescence and calculations is used to understand the optical sensitization and emission processes. 相似文献
994.
Voids in a medium are defined as the regions that are located outside an appropriately defined occupied space associated with molecules. Dynamical properties like diffusion can be related to the structure and distribution of voids present in the medium. This work deals with an analysis of voids and diffusion in liquid ammonia. The analysis of voids is done by the construction of Voronoi polyhedra and Delaunay tessellation. We have performed a series of molecular dynamics simulations of monovalent cations and anions of varying size in liquid ammonia at two different temperatures of 210 and 240 K to investigate the effects of ion size on the diffusion of ions and roles of voids in determining the observed diffusion behavior. It is found that with the increase of ion size, the diffusion coefficients first increase and then pass through a maximum similar to the behavior observed earlier for diffusion in water. The observed results are explained in terms of passage through voids and necks that are present in liquid ammonia. © 2012 Wiley Periodicals, Inc. 相似文献
995.
Jishnunil Chakraborty Partha Roy Heike Mayer-Figge William S. Sheldrick Pradyot Banerjee 《Polyhedron》2007
This work describes the synthesis and X-ray crystallographic characterization of three nickel(II) complexes [Ni(3,2,3-tet){Ag(CN)2}2] (1), [Ni(3,2,3-tet)(μ-tp)]n · 1.5nH2O (2) and {[Ni(3,2,3-tet)(μ1,5-dca)](ClO4)}n (3) where 3,2,3-tet = N,N′-bis(3-aminopropyl)-1,2-ethylenediamine, tp = terephthalate and dca = dicyanamide. Compound 1 is a heterotrinuclear discrete distorted octahedral molecule whereas compound 2 forms a 1D polymeric network and an extended 2D network is formed by intermolecular hydrogen bonding. Interestingly, two adjacent 1D chains execute a novel double-helical network constructed by Ni(II) and the bridging dca ligand in compound 3. The variable temperature magnetic susceptibility measurements for compounds 2 and 3 were also carried out. 相似文献
996.
We have carried out ab initio molecular dynamics simulations of a liquid-vapor interfacial system consisting of a mixture of water and ammonia molecules. We have made a detailed analysis of the structural and dynamical properties of the bulk and interfacial regions of the mixture. Among structural properties, we have looked at the inhomogeneous density profiles of water and ammonia molecules, hydrogen bond distributions, orientational profiles, and also vibrational frequency distributions of bulk and interfacial molecules. It is found that the interfacial molecules show preference for specific orientations so as to form water-ammonia hydrogen bonds at the interface with ammonia as the acceptor. The structure of the system is also investigated in terms of inter-atomic voids present in the system. Among the dynamical properties, we have calculated the diffusion, orientational relaxation, hydrogen bond dynamics, and vibrational spectral diffusion in bulk and interfacial regions. It is found that the diffusion and orientation relaxation of the interfacial molecules are faster than those of the bulk. However, the hydrogen bond lifetimes are longer at the interface which can be correlated with the time scales found from the decay of frequency time correlations. 相似文献
997.
998.
An atomistic molecular dynamics (MD) simulation has been carried out to investigate the structural and dynamical properties of a monolayer of the anionic surfactant sodium bis(2-ethyl-1-hexyl) sulfosuccinate (aerosol-OT or AOT) adsorbed at the air/water interface. The simulation is performed at room temperature and at a surface coverage corresponding to that at its critical micelle concentration (78 A(2)/molecule). The estimated thickness of the adsorbed layer is in good agreement with neutron reflection data. The study shows that the surfactants exhibit diffusive motion in the plane of the interface. It is observed that the surfactant monolayer has a strong influence in restricting both the translational and reorientational motions of the water molecules close to the interface. A drastic difference in the dipolar reorientational motion of water molecules in the aqueous layer is observed with a small variation of the distance from the surfactant headgroups. It has been observed that the water molecules in the first hydration layer (region 1) form strong hydrogen bonds with surfactant headgoups. This results in the slower structural relaxation of water-water hydrogen bonds in the first hydration layer compared to that in the pure bulk water. Most interestingly, we notice that the water molecules present in the layer immediately after the first hydration layer form weaker hydrogen bonds and thus relax faster than even pure bulk water. 相似文献
999.
2-C-Acetoxymethyl glycal derivatives react with aliphatic alcohols in the presence of InCl3 (30 mol %) to furnish the corresponding 2-C-methylene glycosides in excellent yields and with exclusive α-selectivity except for the methyl 2-C-methylene glycosides, which are formed in ∼2:1 anomeric ratio in favour of the α-anomer. The reaction of 2-C-acetoxyglycals with phenols, however, produces the corresponding chiral carbohydrate-derived pyranobenzopyran derivatives via initial Ferrier rearrangement followed by tandem cyclization in excellent yields and moderate to high stereoselectivities in favour of the corresponding 10a-R-pyrano[2,3-b][1]benzopyran derivatives. 相似文献
1000.
Syed Arshad Hussain S. Chakraborty D. Bhattacharjee R.A. Schoonheydt 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2010,75(2):664-670
In this communication we investigate two dyes N,N′-dioctadecyl thiacyanine perchlorate (NK) and octadecyl rhodamine B chloride (RhB) in Langmuir and Langmuir–Blodgett (LB) films with or with out a synthetic clay laponite. Observed changes in isotherms of RhB in absence and presence of nano-clay platelets indicate the incorporation of clay platelets onto RhB-clay hybrid films. AFM images confirm the incorporation of clay into hybrid films. FRET is observed in clay dispersion and LB films with and without clay. Efficiency of energy transfer is maximum in LB films with clay. 相似文献