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101.
We present a short review of the essential techniques of cooling free atoms by resonant laser radiation. The different contributions
to the light forces are explained and their application to the problem of damping the thermal motion of free atoms is described.
Due to quantum mechanical fluctuations of the light force there exists a limit temperature for a given atomic transition.
Deceleration of atomic beams by the radiation pressure demands techniques to maintain the resonance condition while the Doppler
shift of the decelerated atom is rapidly changing. Radiation forces may serve to compress and deflect slow atomic beams as
well as to trap cold atoms. The possible use of pulsed laser radiation is discussed. 相似文献
102.
103.
R. H. Wallis R. A. Davies S. K. Jones R. Beanland W. A. Phillips 《Journal of Crystal Growth》2001,230(3-4):569-572
This paper describes a comparison of material and device results obtained from AlGaN/GaN epitaxial HFET wafers from three commercial sources. Although all three sources supplied material to the same nominal specification, X-ray diffraction, Hall effect and C–V profiling revealed significant differences between them. Wafers from two of the suppliers showed poor inter-device isolation characteristics, indicative of a conducting buffer layer. Wafers from the third supplier showed excellent inter-device isolation, but C–V measurements showed that the AlGaN was about twice as thick as specified, resulting in devices with high pinch-off voltages (−16 V). For the wafers with poor buffer isolation, RF measurements on 1.2 μm gate length devices gave values of fT 5.0 GHz and values of fmax from 8.0 to 11.7 GHz (exact values depending on DC bias conditions), while for the wafer with over-thick AlGaN the corresponding values were 8.0 and 20.0 GHz. 相似文献
104.
Rolf Stomberg Knut Lundquist Adrian F. A. Wallis 《Journal of chemical crystallography》1993,23(4):317-331
The crystal structures ofthreo-2-[2,6-dimethoxy-4-(1-(Z)-propenyl)phenoxy]-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanol (7b),threo-2-(2,6-dimethoxy-4-propylphenoxy)-1-(3,4-5-trimethoxyphenyl)-1-propanol (7c), the diacetate oferythro-2-[2,6-dimethoxy-4-(1-(Z)-propenyl)phenoxy]-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanol (8d) and the acetate of 2,6-dimethoxy-4-(1-(E)-propenyl)phenol (9) have been determined by single-crystal X-ray diffraction methods;7b,7c, and8d are structurally closely related to a class of optically-active neolignans of 1-arylpropane-1,2-diol 2-aryl ether type occurring in plant extracts. The reflection intensities were recorded at room temperature for7b and8d, at -140°C for7c and at -120°C for9. Compound7b crystallized as needles in the orthorhombic space groupPna21 witha=27.055(3),b=11.850(8),c=6.717(4)Å andZ=4.R became 0.041 for 1792 observed [I>3(I)] reflections used in the refinement of the structure. Compound7c crystallized as prisms in the monoclinic space groupP21/a witha=12.565(4),b=13.96(1),c=12.846(7)Å,=93.86(3)° andZ=4. The refinement gaveR=0.051 for 2101 observed [I>3(I)], unique reflections. Compound8d crystallized as prisms in the monoclinic space groupP21/n witha=13.182(4),b=8.518(5),c=23.322(5)Å,=106.12(2)° andZ=4. The finalR-valuebecame 0.042 for 2131 observed [I>3(I)], unique reflections. Compound9 crystallized as prisms in the orthorhombic space groupPca21 witha=18.216(4),b=9.483(3),c=7.416(2)Å andZ=4. TheR-value became 0.038 for 1502 observed [I>3(I)], unique reflections. The crystals of7b are stabilized by moderately strong hydrogen bonds. All the 1-arylpropane-1,2-diol 2-aryl ethers examined adopted conformations in which the aromatic groups tend to be as remote as possible. Observed double bond lengths in the propenyl groups of the compounds examined (1.30 Å) deviate significantly from the expected value (1.34 Å). The cause of this discrepancy is discussed. 相似文献
105.
106.
107.
108.
Ipek Osken Onur Sahin Ali S. Gundogan Hakan Bildirir Asli Capan Erdal Ertas Mehmet S. Eroglu John D. Wallis Kevser Topal Turan Ozturk 《Tetrahedron》2012,68(4):1216-1222
Selective syntheses of 3,4-vinylenedithiathiophenes (VDTTs) and dithieno[2,3-b;2′,3′-d]thiophenes (DTTs), having Ph, 4-CH3OC6H4, 4-BrC6H4, 4-NO2C6H4 and 4-(CH3)2NC6H4 groups, were achieved through the reaction of 1,8-diketone with phosphorus decasulfide (P4S10). The reaction could be shifted between VDTT and DTT by adding base (sodium bicarbonate) or acid (para-toluenesulfonic acid), respectively, to the reaction mixture. While the VDTTs were obtained in moderate yields, an important achievement has been made with the syntheses of the DTTs, obtaining them in higher yields compared with the previous report. Polymers of the VDTTs, which are the analogues of ethylenedioxythiophene, EDOT, were prepared using FeCl3. Unfortunately, all attempts for their electropolymerization failed. Spin density calculations revealed that none of the VDTTs had a significant positive spin density at the ‘α’ carbon atoms of the thiophene ring. Considering their solubility and functional groups, which could be further derivatized, they are useful building blocks for the preparation of new organic materials. 相似文献
109.
Songjie Yang Lee Martin Melanie Pilkington Ross W. Harrington John D. Wallis 《Tetrahedron》2010,66(34):6977-6989
Six new enantiopure chiral organosulfur donors, with structures related to BEDT-TTF, have been synthesised for use in the preparation of organic metals, starting either by double nucleophilic substitutions on the bis-mesylate of 2R,4R-pentane-2,4-diol or by a cycloaddition with subsequent elimination of acetic acid on the enol acetate of (+)-nopinone. Crystal structures of some of their radical cation triiodides salts and TCNQ complexes are reported. 相似文献
110.