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31.
As part of an investigation into new synthetic routes to poly(peri-naphthalene), the synthesis and cycloaromatization of tetraethynylbiphenyls is described. The temperature-dependent cyclization of biphenyls containing unsubstituted alkynes provides the desired perylene in good yield. 相似文献
32.
33.
Korth BD Keng P Shim I Bowles SE Tang C Kowalewski T Nebesny KW Pyun J 《Journal of the American Chemical Society》2006,128(20):6562-6563
A novel synthetic route to polymer-coated ferromagnetic colloids of metallic cobalt has been developed. Well-defined end-functional polystyrenes were synthesized using controlled radical polymerization and used as surfactants in the thermolysis of dicobaltoctacarbonyl to afford uniform ferromagnetic nanoparticles. The presence of the polymer shell enabled prolonged colloidal stability of dispersions in a wide range of organic solvents and formed glassy encapsulating coatings around ferromagnetic cores in the solid state. These polymer-coated colloids assembled into robust, micron-sized nanoparticle chains when cast onto supporting surfaces due to dipolar associations of magnetic cores. Hierarchical assemblies were also prepared by blending polystyrene-coated cobalt colloids with larger silica beads. 相似文献
34.
35.
Friesen DM Bowles OJ McDonald R Rosenberg L 《Dalton transactions (Cambridge, England : 2003)》2006,(22):2671-2682
The synthesis and structural characterization of a series of tripodal tris(phosphine) ligands, containing SiMe2 elbow groups, is described. The significant steric congestion in these ligands, due to the silylmethyl substituents, is manifest both in the solid-state structures and in the solution NMR spectra of the free ligands. Variable temperature 1H{31P} NMR studies of one of the ligands, CH3C(SiMe2PEt2)3 (4b) gave an estimated barrier to rotation around the Si-Capical bonds of approximately 10.4 kcal mol(-1). Octahedral kappa2- and kappa3-molybdenum complexes of these ligands also demonstrate the impact of the additional bulk imparted by the SiMe2 substituents, and the high Lewis basicity of these phosphines, with subtle changes at the apical and phosphine substituents changing the overall coordination chemistry observed. 相似文献
36.
We numerically approximate, on the real line, solutions to a large class of parabolic partial differential equations which are “gradient flows” of some energy functionals with respect to the L p -Wasserstein metrics for all p>1. Our method relies on variational principles involving the optimal transport problem with general strictly convex cost functions. 相似文献
37.
Castelnovo M Bowles RK Reiss H Gelbart WM 《The European physical journal. E, Soft matter》2003,10(2):191-197
We consider the problem of inserting a stiff chain into a colloidal suspension of particles that interact with it through
excluded volume forces. The free energy of insertion is associated with the work of creating a cavity devoid of colloid and
sufficiently large to accommodate the chain. The corresponding work per unit length is the force that resists the entry of
the chain into the colloidal suspension. In the case of a hard sphere fluid, this work can be calculated straightforwardly
within the scaled particle theory; for solutions of flexible polymers, on the other hand, we employ simple scaling arguments.
The forces computed in these ways are shown, for nanometer chain and colloid diameters, to be of the order of tens of pN for solution volume fractions of a few tenths. These magnitudes are argued to be important for biophysical processes such
as the ejection of DNA from viral capsids into the cell cytoplasm.
Received 18 December 2002 Published online: 16 April 2003
RID="a"
ID="a"e-mail: castel@chem.ucla.edu
RID="b"
ID="b"Present address: Courant Institute of Mathematical Sciences, NYU, New York, New York 10012, USA 相似文献
38.
Harold M. Bell Deborah B. Bowles Fred Senese 《Magnetic resonance in chemistry : MRC》1981,16(4):285-289
The use of additive parameters for the prediction of NMR chemical shifts is widely practised. However, no correlations are available for highly deshielded methine protons. In this work, methine chemical shifts have been studied using both multiple linear regression analysis and Simplex function minimization in an effort to determine under what limiting circumstances the additivity of shift parameters can be expected to apply. As expected, it was not possible to explain satisfactorily all methine shifts with a single set of substituent parameters. However, if only the deshielded cases were considered (H—CXYZ, where at least two of the three groups X, Y, and Z are electron-withdrawing), a much better set of parameters could be determined. Using a data set of 440 of these deshielded methine shifts, involving 31 different substituents, a standard error of estimate of 0.20 ppm is found for protons spread between 3.0 and 7.5 ppm. 相似文献
39.
The technique of ferromagnetic resonance at 23 GHz has been used to determine the first three anisotropy constants of pure Ni down to 4.2K. A temperature and orientation dependent linewidth has also been observed. 相似文献
40.
Ahmad QR Allen RC Andersen TC Anglin JD Barton JC Beier EW Bercovitch M Bigu J Biller SD Black RA Blevis I Boardman RJ Boger J Bonvin E Boulay MG Bowler MG Bowles TJ Brice SJ Browne MC Bullard TV Bühler G Cameron J Chan YD Chen HH Chen M Chen X Cleveland BT Clifford ET Cowan JH Cowen DF Cox GA Dai X Dalnoki-Veress F Davidson WF Doe PJ Doucas G Dragowsky MR Duba CA Duncan FA Dunford M Dunmore JA Earle ED Elliott SR Evans HC Ewan GT Farine J Fergani H Ferraris AP Ford RJ Formaggio JA Fowler MM 《Physical review letters》2002,89(1):011302
The Sudbury Neutrino Observatory (SNO) has measured day and night solar neutrino energy spectra and rates. For charged current events, assuming an undistorted 8B spectrum, the night minus day rate is 14.0%+/-6.3%(+1.5%)(-1.4%) of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the nu(e) asymmetry is found to be 7.0%+/-4.9%(+1.3%)(-1.2%). A global solar neutrino analysis in terms of matter-enhanced oscillations of two active flavors strongly favors the large mixing angle solution. 相似文献