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21.
Soft X-ray photoemission experiments have led to the unambiguous observation of a metal surface core level () shift, due to an adsorbate (CO), to a binding energy larger than the bulk binding energy. The clean (110) surface component, with a binding energy 0.35 ± 0.02 eV lower than the bulk, is shifted by 1.06 ± 0.04 eV towards higher binding energy upon CO chemisorption. The lack of significant changes in the bulk component indicates the localized nature of the CO-Pt surface bonding. 相似文献
22.
Dr. Zhengqing Guo Dr. Shek‐Man Yiu Dr. Michael C. W. Chan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8937-8947
The development of molecular frameworks derived from binuclear platinum(II) aromatic Schiff base (salphen) complexes and their supramolecular chemistry have been undertaken. A series of axially rotating (Pt‐salphen)2 luminophores, tethered in a cofacial manner by a rigid linker (xanthene, 1 ; dibenzofuran, 2 ; biphenylene, 3 ), was synthesized in which the O(salphen) groups are potentially amenable for guest‐binding. The molecular structures of 1 and 3 have been determined by X‐ray crystallography, revealing intra‐ and intermolecular π‐stacking interactions, as well as contrasting syn ( 1 ) and anti ( 3 ) configurations, for the (Pt‐salphen)2 moiety. All complexes are luminescent in solution at room temperature. Their photophysical and solvatochromic properties have been examined, and the emissions are assigned to mixed triplet O(p)/Pt(d)→π*(diimine) excited states. The red‐shifted fluid emissions and lower quantum yields of 1 and 3 , relative to 2 , are ascribed to enhanced intramolecular π‐stacking interactions. Photophysical changes and selective responses to metal ions (particularly Pb2+) have been investigated by using various spectroscopic methods and DFT calculations, and through comparative studies with control complexes. A plausible binding mechanism is proposed based on occupation of the O(salphen)‐binding cavity, which induces perturbation of intramolecular π–π interactions, and hence the self‐quenching and emission properties, of the (Pt‐salphen)2 unit. 相似文献
23.
Zhengzheng Zhou Henry H. Y. Tong Liang Li Fanny L. Y. Shek Yang Lv Ying Zheng 《Crystal Research and Technology》2015,50(7):538-548
This study performed a solid‐state characterization of ursolic acid (UA) crystalline forms, a poorly water‐soluble triterpene with anticancer activity. Two new polymorphs (form I, II), two new solvates (propanol and isopropanol solvates), and a known ethanol solvate were determined and elucidated using a combination of multi‐techniques, including X‐ray single crystal and powder diffraction, Fourier transform infrared spectroscopy (FT‐IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A colorless single crystal of UA was grown from a propanol solution, and its crystalline structure was determined through X‐ray single crystal diffraction. It was determined that the propanol solvate was crystallized in the orthorhombic space group P212121 with unit‐cell parameters a = 7.17200 (8) Å, b = 12.24100 (16) Å, c = 33.8950 (4) Å and Z = 4. The ethanol solvate and propanol solvate were isomorphous crystals. The results of the thermal analysis demonstrate that form I is a meta‐stable form, while form II is a stable form that is monotropically related. 相似文献
24.
Dr. Wai‐Lun Man Jianhui Xie Po‐Kam Lo Dr. William W. Y. Lam Dr. Shek‐Man Yiu Dr. Kai‐Chung Lau Prof. Tai‐Chu Lau 《Angewandte Chemie (International ed. in English)》2014,53(32):8463-8466
Exploring new reactivity of metal nitrides is of great interest because it can give insights to N2 fixation chemistry and provide new methods for nitrogenation of organic substrates. In this work, reaction of a (salen)ruthenium(VI) nitrido complex with various alkynes results in the formation of novel (salen)ruthenium(III) imine complexes. Kinetic and computational studies suggest that the reactions go through an initial ruthenium(IV) aziro intermediate, followed by addition of nucleophiles to give the (salen)ruthenium(III) imine complexes. These unprecedented reactions provide a new pathway for nitrogenation of alkynes based on a metal nitride. 相似文献
25.
Y.F. Shek C.C. Ling C.D. Beling S. Fung 《Applied Physics A: Materials Science & Processing》2002,74(2):233-237
Positrons from a radioactive source are implanted into a reverse-biased metal–semiconductor contact and are drifted back towards
the contact by the internal electric field where they trap into voids and annihilate. The electric field dependent interface
annihilation fraction is monitored by way of the intensity of the long (∼400–500 ps) void lifetime component using positron-lifetime
spectroscopy. Unlike previous analyses of such systems a numerical model involving positron drift, annihilation and trapping
into the interfacial state has been constructed to describe the positron dynamics in the presence of the non-uniform junction
electric field. The use of the positron-lifetime technique in probing the internal electric field at buried contacts is thus
demonstrated. Results obtained using the numerical method for the Au, Al and Ni/Semi-Insulating (SI)-GaAs contact systems
are found to be consistent with the findings of previous studies on the Au/SI-GaAs system.
Received: 29 November 2000 / Accepted: 26 February 2001 / Published online: 25 July 2001 相似文献
26.
Hong Sun Yingwu Tang Fushi Zhang Guoshi Wu Shek‐Kiu Chan 《Journal of Polymer Science.Polymer Physics》2002,40(19):2164-2169
Fuzzy set theory was used to study the relationship between the glass‐transition temperature (Tg) and structure of homopolymers. The method can map the relationship and give the Tg for 235 polymers with a standard deviation of 8 K (the confidence bound was 90%). The entropy of the fuzziness was used to quantitatively describe the interactions among groups. The method was used to predict the Tg of 10 polymers not included in the 235 polymers, with a standard deviation of 9 K (the confidence bound was 90%). The study demonstrates again that fuzzy set theory can be effectively used to investigate the quantitative structure–property relationship of polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2164–2169, 2002 相似文献
27.
A Soibel SS Banerjee Y Myasoedov ML Rapparort E Zeldov S Ooi T Tamegai 《Pramana》2002,58(5-6):893-898
Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals
of Bi2Sr2CaCu2O8 (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface
with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across
the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local
melting temperature/field, we have constructed maps of the melting landscape T
m(H, r), viz., the melting temperature (T
m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather
dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale
and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite
effects on the local melting transition. 相似文献
28.
C Binns C Norris I Lindau M.L Shek B Pate P.M Stefan W.E Spicer 《Solid State Communications》1982,43(11):853-855
A LEED, Auger photoemission study of ultra-thin overlayers of iron on palladium (111) is reported. At room temperature and below, the overlayer grows epitaxially in a simultaneous multi-layer mode. On annealing a sub-monolayer coverage to create flat two-dimensional platelets it was found that the density of the Fe 3d states at the Fermi level was reduced and the local iron magnetic moment could not be detected. 相似文献
29.
A Gurtu P K Malhotra I S Mittra P M Sood SC Gupta VK Gupta GL Kaul LK Mangotra Y Prakash NK Rao ML Sharma 《Pramana》1974,3(5):311-322
This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR em = 〈n s〉/〈n ch〉, where 〈n ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R em = 1·71 implies an effectiveA-dependence ofR A =A 0.18,i.e., a very weak dependence. Predictions ofR em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production. 相似文献
30.
Yingying Liu Dr. Siu‐Mui Ng Dr. William W. Y. Lam Dr. Shek‐Man Yiu Prof. Tai‐Chu Lau 《Angewandte Chemie (International ed. in English)》2016,55(1):288-291
Seven‐coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven‐coordinate group 8 metal‐oxo species, [OsV(O)(qpy)(pic)Cl]2+ (qpy=2,2′:6′,2′′:6′′,2′′′‐quaterpyridine, pic=4‐picoline). The X‐ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os?O distance of 1.7375 Å. This oxo species undergoes facile O‐atom and H‐atom‐transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C? H bond dissociation energy as high as 90 kcal mol?1. This work suggests that highly active oxidants may be designed based on group 8 seven‐coordinate metal oxo species. 相似文献