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101.
The metalloporphyrins, Me-TSPP [Me=Cr(III), Mn(III), Mn(II), Fe(III), and TSPP=meso-(tetra-p-sulfonatophenyl)porphyrin], which possess electron spins S=3/2, 2, 5/2, and 5/2, respectively, comprise an important series of model systems for mechanistic studies of NMR paramagnetic relaxation enhancement (NMR-PRE). For these S>1/2 spin systems, the NMR-PRE depends critically on the detailed form of the zero-field splitting (zfs) tensor. We report the results of experimental and theoretical studies of the NMR relaxation mechanism associated with Fe(III)-TSPP, a spin 5/2 complex for which the overall zfs is relatively large (D approximately = 10 cm(-1)). A comparison of experimental data with spin dynamics simulations shows that the primary determinant of the shape of the magnetic relaxation dispersion profile of the water proton R1 is the tetragonal fourth-order component of the zfs tensor. The relaxation mechanism, which has not previously been described, is a consequence of zfs-induced mixing of the spin eigenfunctions of adjacent Kramers doublets. We have also investigated the magnetic-field dependence of electron-spin relaxation for S=5/2 in the presence of a large zfs, such as occurs in Fe(III)-TSPP. Calculations show that field dependence of this kind is suppressed in the vicinity of the zfs limit, in agreement with observation. 相似文献
102.
Molecular dynamics (MD) simulations combined with water-water H-bond angle analysis and calculation of solvent accessible surface area and approximate free energy of solvation were used to determine the influence of hydroxyl orientation on solute hydration and surrounding water structure for a group of chemically identical solutes-the aldohexopyranose sugars. Intramolecular hydrogen bond cooperativity was closely associated with changes in water structure surrounding the aldohexopyranose stereoisomers. The OH-4 group played a pivotal role in hydration as it was able to participate in a number of hydrogen bond networks utilizing the OH-6 group. Networks that terminated within the molecule (OH-4 --> OH-6 --> O-5) had relatively more nonpolar-like hydration than those that ended in a free hydroxyl group (OH-6 --> OH-4 --> OH-3). The OH-2 group modulated the strength of OH-4 networks through syndiaxial OH-2/4 intramolecular hydrogen bonding, which stabilized and induced directionality in the network. Other syndiaxial interactions, such as the one between OH-1 and OH-3, only indirectly affected water structure. Water structure surrounding hydrogen bond networks is discussed in terms of water-water hydrogen bond populations. The impact of syndiaxial versus vicinal hydrogen bonds is also reviewed. The results suggest that biological events such as protein-carbohydrate recognition and cryoprotection by carbohydrates may be driven by intramolecular hydrogen bond cooperativity. 相似文献
103.
104.
3H-1,2-Diazepines () give dinuclear complexes () on reaction with diiron nonacarbonyl. Complexation much reduces the rate of the [1,5] sigmatropic hydrogen shift across the diazepine ring and also reduces the activation energy for ring inversion. 相似文献
105.
106.
Kennedy JH Bowers JL Dodge JA Lugar CW Shepherd TA Sharp VS 《Journal of chromatography. A》2000,872(1-2):75-84
Chromatographic separations of new growth hormone secretagogue compounds were developed to support structure-activity relationship (SAR) studies in conjunction with lead optimization. These new compounds differed from Merck's MK-677 by having two chiral centers and thus diastereomeric mixtures were generated. Separation of initial compounds in the SAR was achieved on a Kromasil C18 column using an ammonium acetate buffer and acetonitrile. However, additional candidates were not separable on C18 columns and a chiral Kromasil CHI-DMB column was used to resolve the diastereomeric compounds. The Kromasil CHI-DMB packing was also used in a preparative chromatographic system to resolve multigram quantities of secretagogue candidates for testing. Chiral separations of different intermediates were also developed in support of evolution of an asymmetric synthetic route. This report summarizes development of the preparative chromatographic system used to purify diastereomeric mixtures and chiral separations of intermediates in the synthesis. 相似文献
107.
Kendra V. Sharp David Hill Daniel Troolin Geoffrey Walters Wing Lai 《Experiments in fluids》2010,48(1):167-183
Volumetric three-component velocimetry measurements have been taken of the flow field near a Rushton turbine in a stirred
tank reactor. This particular flow field is highly unsteady and three-dimensional, and is characterized by a strong radial
jet, large tank-scale ring vortices, and small-scale blade tip vortices. The experimental technique uses a single camera head
with three apertures to obtain approximately 15,000 three-dimensional vectors in a cubic volume. These velocity data offer
the most comprehensive view to date of this flow field, especially since they are acquired at three Reynolds numbers (15,000,
107,000, and 137,000). Mean velocity fields and turbulent kinetic energy quantities are calculated. The volumetric nature
of the data enables tip vortex identification, vortex trajectory analysis, and calculation of vortex strength. Three identification
methods for the vortices are compared based on: the calculation of circumferential vorticity; the calculation of local pressure
minima via an eigenvalue approach; and the calculation of swirling strength again via an eigenvalue approach. The use of two-dimensional
data and three-dimensional data is compared for vortex identification; a ‘swirl strength’ criterion is less sensitive to completeness
of the velocity gradient tensor and overall provides clearer identification of the tip vortices. The principal components
of the strain rate tensor are also calculated for one Reynolds number case as these measures of stretching and compression
have recently been associated with tip vortex characterization. Vortex trajectories and strength compare favorably with those
in the literature. No clear dependence of trajectory on Reynolds number is deduced. The visualization of tip vortices up to
140° past blade passage in the highest Reynolds number case is notable and has not previously been shown. 相似文献
108.
Stephen C. Johns Laurie L.E. Crouch Stephen Grieve Holly L. Maloney Gary R. Peczkowski Allison E. Jones Duncan Sharp Robert B. Smith 《Tetrahedron letters》2014
Microwave irradiation was applied to a sequence of condensation reactions from readily available 9-chloroacridines to provide a range of novel acridine–isoalloxazine conjugates. The combination of these two moieties, both of biological interest, was achieved by a chromatography-free route. 相似文献
109.
Dr. James E. H. Day Dr. Swee Y. Sharp Dr. Martin G. Rowlands Dr. Wynne Aherne Dr. William Lewis Dr. S. Mark Roe Dr. Chrisostomos Prodromou Prof. Dr. Laurence H. Pearl Prof. Dr. Paul Workman Prof. Dr. Christopher J. Moody 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(34):10366-10372
A series of resorcylic acid macrolactones, analogues of the natural product radicicol has been prepared by chemical synthesis, and evaluated as inhibitors of heat shock protein 90 (Hsp90), an emerging attractive target for novel cancer therapeutic agents. The synthesis involves acylation of an ortho‐toluic acid dianion, esterification, followed by a ring‐closing metathesis to form the macrocycle. Subsequent manipulation of the protected hydroxymethyl side chain allows access to a range of new analogues following deprotection of the two phenolic groups. Co‐crystallization of one of the new macrolactones with the N‐terminal domain of yeast Hsp90 confirms that it binds in a similar way to the natural product radicicol and to our previous synthetic analogues, but that the introduction of the additional hydroxymethyl substituent appears to result in an unexpected change in conformation of the macrocyclic ring. As a result of this conformational change, the compounds bound less favorably to Hsp90. 相似文献
110.
N. G. Semaltianos W. Perrie J. Cheng P. French M. Sharp G. Dearden K. G. Watkins 《Applied Physics A: Materials Science & Processing》2010,98(2):345-355
Picosecond laser (10.4 ps, 1064 nm) ablation of the nickel-based superalloy C263 is investigated at different pulse repetition
rates (5, 10, 20, and 50 kHz). The two ablation regimes corresponding to ablation dominated by the optical penetration depth
at low fluences and of the electron thermal diffusion length at high fluences are clearly identified from the change of the
surface morphology of single pulse ablated craters (dimples) with fluence. The two corresponding thresholds were measured
as F
th(D1)1=0.68±0.02 J/cm2 and F
th(D2)1=2.64±0.27 J/cm2 from data of the crater diameters D
1,2 versus peak fluence. The surface morphology of macroscopic areas processed with a scanning laser beam at different fluences
is characterised by ripples at low fluences. As the fluence increases, randomly distributed areas among the ripples are formed
which appear featureless due to melting and joining of the ripples while at high fluences the whole irradiated surface becomes
grainy due to melting, splashing of the melt and subsequent resolidification. The throughput of ablation becomes maximal when
machining at high pulse repetition rates and with a relatively low fluence, while at the same time the surface roughness is
kept low. 相似文献