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排序方式: 共有201条查询结果,搜索用时 640 毫秒
41.
Jian Huang Xingguo Chen Zhide Hu Zhengfeng Zhao Martin Hooper 《Fresenius' Journal of Analytical Chemistry》1999,363(1):117-118
A flow injection method was developed for the determination of palladium, based on the reaction of palladium with DBOK-chlorophosphonazo
with a detection limit of 0.07 μg/mL and a linear calibration range from 0.1 to 3.2 μg/mL of palladium. The reaction product
has a maximum absorption at 630 nm. The method was applied to determine Pd2+ in catalysts and in anode mud samples. The relative error is less than 3% and the recovery of palladium is in the range 95%
to 105%
Received: 27 April 1998 / Revised: 24 August 1998 / Accepted: 26 August 1998 相似文献
42.
J. Sivaguru Catherine Hooper Marissa R. Solomon Waldemar Adam Yoshihisa Inoue Nicholas J. Turro 《Tetrahedron》2006,62(46):10647-10659
The stereoselectivity in the reactions of the E/Z enecarbamates 1, equipped with the oxazolidinone chiral auxiliary, has been examined for singlet oxygen (1O2), ozone (O3), and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) in a variety of solvents as a function of temperature. The oxidative cleavage of the alkenyl functionality by 1O2 and O3 releases the enantiomerically enriched methyldesoxybenzoin (MDB) product. The extent (% ee) as well as the sense (R vs S) of the stereoselectivity in the MDB formation depends on the electronic nature of the oxidant. A high stereoselectivity, substantially dependent on solvent and temperature, is displayed for the reactions with 1O2, whereas the ground-state reactants O3 and PTAD are rather unaffected by solvent and temperature variations. The present comparative analysis clearly substantiates our hypothesis of stereoselective vibrational quenching of the attacking 1O2, whereas O3 and PTAD are only subject to steric impositions. The electronically excited 1O2 is sensitive to all three stereochemically relevant structural characteristics embodied in the chiral enecarbamates, namely the R/S configuration at the C4 position of the oxazolidinone chiral auxiliary, the Z/E geometry of the ‘alkene’ functionality, and R/S configuration at the C3′ position of the enecarbamate side chain. 相似文献
43.
Williams KS Hooper JP Horn JM Lightstone JM Wang H Ko YJ Bowen KH 《The Journal of chemical physics》2012,136(13):134315
Negative-ion photoelectron spectroscopy and ab initio simulations are used to study the variation in magnetic structure in Mn(x)O(y) (x = 3, 4[semicolon] y = 1, 2) clusters. The ferrimagnetic and antiferromagnetic ground-state structures of Mn(x)O(y) are 0.16-1.20 eV lower in energy than their ferromagnetic isomers. The presence of oxygen thus stabilizes low-spin isomers relative to the preferred high-spin ordering of bare Mn(3) and Mn(4). Each cluster has a preferred overall magnetic moment, and no evidence is seen of competing states with different spin multiplicities. However, non-degenerate isomags, which possess the same spin multiplicity but different arrangements of local moments, do contribute additional features and peak broadening in the photoelectron spectra. Proper accounting for all possible isomags is shown to be critical for accurate computational prediction of the spectra. 相似文献
44.
45.
The redox stability domain of a polyethylene oxide-lithium trifluoromethanesulphonate polymer electrolyte has been investigated using low-sweep-rate voltammetry, in the range 100–170°C. Below 140°C, its voltage stability window is in excess of 3.3 volts, making it a candidate for use with practical electrochemical couples. The electrolyte is not, however, a pure cation conductor, and problems associated with the observed significant anion mobility must be overcome in order to improve the polymer's suitability as a solid-state electrolyte for battery applications. 相似文献
46.
J. M. Hammond J. F. Hooper W. G. P. Robertson 《Journal of polymer science. Part A, Polymer chemistry》1971,9(2):281-294
The cyclic oligomers formed as by-products in the polymerization of propylene oxide. 1,2-butylene oxide, and n-propyl glycidyl ether, and in the copolymerization of these monomers with tetrahydrofuran have been studied by gel-permeation chromatography and otherwise and their structures have been determined. Some of the physical properties of the cyclic oligomers are described. 相似文献
47.
Kesson T Albrow MG Almehed S Benary O Boggild H Botner O Breuker H Brody H Burkert V Callen B Carter AA Carter JR Cecil P Choi Y Cleland WE Dam P Dagan S Dahl-Jensen E Dahl-Jensen I Damgaard G Evans WM Fabjan CW Frandsen P Frankel S Frati W Gordon H Goerlach U Hansen KH Hedberg V Hooper JE Jarlskog G Kessler G Killian T Kroeger R Kulka K v d Lans J Lissauer D Lörstad B Ludlam T McCubbin NA Möller R Molzon W Nielsen BS Olsen LH Oren Y Rosso E Rudge A Specht H Stumer I Thompson JA Thorstensen G 《Physical review letters》1985,55(23):2535-2538
48.
Magdalene R. Schenkel Justin B. Hooper Mark J. Moran Lily A. Robertson 《Liquid crystals》2013,40(11):1668-1685
Recently, new thermotropic ionic liquid crystals (LCs) with a hexyl-linked tris(imidazolium bromide) core and two terminal alkyl chains were synthesised and characterised. To explore the effect of different counter-ions on the LC behaviour of this system, derivatives with BF4? and Tf2N? counter-ions were prepared and analysed. Five of the BF4? derivatives were found to exhibit thermotropic LC behaviour. The 12-, 14- and 16-carbon tail BF4? compounds form SmA phases. The 18- and 20-carbon tail homologues form what appears to be a smectic phase but are weakly mesogenic and harder to characterise. Only two of the Tf2N? derivatives exhibited mesogenic behaviour. The 18-carbon tail Tf2N? compound forms an as-yet unidentified, highly periodic smectic phase with positional order while the 20-carbon tail homologue forms a periodic SmA phase. The Tf2N? mesogens have much lower clearing points even though their LC phases have more order than the Br? and BF4? mesogens. X-ray diffraction showed that these mesogens have different amounts of tail interdigitation between the smectic layers depending on the counter-ion present. Atomistic molecular dynamics simulations indicated that counter-ion size plays an important role in defining the density of the ionic region, which in turn affects the amount of interdigitation in the smectic phases. 相似文献
49.
50.
Grating coupling of light to surface plasmon-polaritons (SPPs) supported by a thin metal film depends on the detailed geometry of the grating used to couple the incident light to the SPP modes. Here we show experimental and theoretical evidence that, in the case of square gratings having the same pitch and depth, the maximum coupling of light to the SPPs is achieved when the ratio between the groove width and the pitch of the grating is equal to 1/2. A straightforward explanation involving a Fourier analysis of the different grating profiles is given and compared with the experimental results. 相似文献