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51.
A system to determine the spectral responsivity of ultraviolet (UV) radiometers has been developed and is routinely operated at the Central Ultraviolet Calibration Facility, at the National Oceanic and Atmospheric Administration. The instrument and the measurement methodologies are described. Results of measurements from thermally controlled broadband UV radiometers of the Robertson-Berger (R-B)-type are described. Systematic differences in the spectral response curves for these instruments have been detected. The effect of these differences on the field operation of UV-B radiometers has been studied by calculating the instrumental response from modeled UV spectra. The differences of the weighted spectral UV irradiances, measured by two radiometers with different spectral response functions, caused by the daily variation in the position of the sun were estimated for fixed values of total ozone, altitude and albedo, and for cloud-free conditions. These differences increase with the solar zenith angle and are as large as 8%. Larger differences in the instrumental response may be produced by ozone variations. Thus, care must be taken when analyzing data from R-B radiometers and comparing results from different instruments. Routine cycling of UV-B radiometers in operative networks without a careful determination of the spectral responsivity, or small drifts of the spectral responsivity, may strongly affect the accuracy of UV radiation measurements and produce an erroneous trend. Because of the possible differences among radiometers, it would not be practical to derive the long-term behavior of UV radiation without routine and thorough characterization of the spectral responsivities of the instruments. 相似文献
52.
R.?Ben Smail H.?ChebbiEmail author B.?R.?Srinivasan M.?F.?Zid 《Journal of Structural Chemistry》2017,58(4):724-733
Crystals of bis(4-aminopyridinium) dichromate (C5H7N2)2[Cr2O7] (1) were isolated via slow solvent evaporation and characterized by energy dispersive spectroscopy (EDS), infrared (IR) and ultratviolet-visible (UV-Vis) spectroscopy, and single crystal X-ray diffraction. The room-temperature (RT; 298 K) phase of 1 crystallizes in the monoclinic space group P21/m. Its asymmetric unit consists of two crystallographically independent 4-aminopyridinium cations (A and B) and two halves of symmetry-independent dichromate anions (A and B). Cations and anions are linked with the aid of several moderate N–H?O hydrogen bonds and weak C–H?O interactions resulting in a three-dimensional supramolecular network. The crystal structure is further stabilized by extensive π–π stacking interactions between adjacent pyridine rings. A comparison of the structure of the RT phase of 1 and that of the low temperature (LT; 150 K) phase is described. 相似文献
53.
M. Said F. Ben Zid C.M. Bertoni Stefano Ossicini 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):191-199
The electronic properties of rare-earth arsenides have been calculated from first principles. In the calculations we have
treated the rare-earth f electrons both as core-like and as valence-like electrons. We consider the changes in the energy bands and in the density
of states near the Fermi level which are found to be relevant, except for the case of LuAs, and discuss this in relation with
the role played from the rare-earth 5d derived states. Moreover we show that the rare-earth 5d related bands are particularly sensitive to the variation of the lattice constant; change in the lattice constant of less
than 1% leads to a different behaviour with respect to the crossing of the rare-earth 5d derived bands and the As 4p derived bands along the Δ-direction. This point is discussed in connection with the possibility of having a semimetal-semiconductor
transition in the rare-earth arsenides.
Received 22 February 2001 相似文献
54.
Kenia Melchor-Rodríguez Chayan Carmenate-Rodríguez Anthuan Ferino-Prez Sarra Gaspard Ulises J. Juregui-Haza 《Molecules (Basel, Switzerland)》2021,26(22)
The influence of nitrogen-containing surface groups (SGs) onto activated carbon (AC) over the adsorption of chlordecone (CLD) and β-hexachlorocyclohexane (β-HCH) was characterized by a molecular modelling study, considering pH (single protonated SGs) and hydration effect (up to three water molecules). The interactions of both pollutants with amines and pyridine as basic SGs of AC were studied, applying the multiple minima hypersurface (MMH) methodology and using PM7 semiempirical Hamiltonian. Representative structures from MMH were reoptimized using the M06-2X density functional theory. The quantum theory of atoms in molecules (QTAIM) was used to characterize the interaction types in order understanding the adsorption process. A favorable association of both pesticides with the amines and pyridine SGs onto AC was observed at all pH ranges, both in the absence and presence of water molecules. However, a greater association of both pollutants with the primary amine was found under an acidic pH condition. QTAIM results show that the interactions of CLD and β-HCH with the SGs onto AC are governed by Cl···C interactions of chlorine atoms of both pesticides with the graphitic surface. Electrostatic interactions (H-bonds) were observed when water molecules were added to the systems. A physisorption mechanism is suggested for CLD and β-HCH adsorption on nitrogen-containing SGs of AC. 相似文献
55.
The KLOE- collaboration A. Anastasi D. Babusci G. Bencivenni M. Berlowski C. Bloise F. Bossi P. Branchini A. Budano L. Caldeira Balkest?hl B. Cao F. Ceradini P. Ciambrone F. Curciarello E. Czerwinski G. D’Agostini E. Danè V. De Leo E. De Lucia A. De Santis P. De Simone A. Di Cicco A. Di Domenico R. Di Salvo D. Domenici A. D’Uffizi A. Fantini G. Felici S. Fiore A. Gajos P. Gauzzi G. Giardina S. Giovannella E. Graziani F. Happacher L. Heijkenskj?ld W. Ikegami Andersson T. Johansson D. Kaminska W. Krzemien A. Kupsc S. Loffredo G. Mandaglio M. Martini M. Mascolo R. Messi S. Miscetti G. Morello D. Moricciani P. Moskal M. Papenbrock A. Passeri V. Patera E. Perez del Rio A. Ranieri P. Santangelo I. Sarra M. Schioppa M. Silarski F. Sirghi L. Tortora G. Venanzoni W. Wislicki M. Wolke 《Journal of High Energy Physics》2016,2016(5):19
56.
57.
Gam-Derouich S Lamouri A Redeuilh C Decorse P Maurel F Carbonnier B Beyazıt S Yilmaz G Yagci Y Chehimi MM 《Langmuir : the ACS journal of surfaces and colloids》2012,28(21):8035-8045
In this paper we describe a novel methodology for grafting polymers via radical photopolymerization initiated on gold surfaces by aryl layers from diazonium salt precursors. The parent 4-(dimethylamino)benzenediazonium salt was electroreduced on a gold surface to provide 4-(dimethylamino)phenyl (DMA) hydrogen donor layers; free benzophenone in solution was used as a photosensitizer to strip hydrogen from the grafted DMA. This system permitted efficient surface initiation of photopolymerization of 2-hydroxyethyl methacrylate. The resulting poly(2-hydroxyethyl methacrylate) (PHEMA) grafts were found to be very adherent to the surface as they resist total failure after being soaked in the well-known paint stripper methyl ethyl ketone. The PHEMA grafts were reacted with 1,1'-carbonyldiimidazole to yield carbamate groups that are able to react readily with amino groups from proteins. The final surface consisted of protein-functionalized PHEMA grafts where bovine serum albumin (BSA) protein is specifically linked to the grafts by covalent bonds. We used X-ray photoelectron spectroscopy to monitor the chemical changes at the gold surface all along the process from the neat gold to the end-protein-functionalized polymer grafts: the PHEMA graft thickness ranged from 7 to 27 nm, and the activation by 1,1'-carbonyldiimidazole reached 37% of the OH groups, which was sufficient for 90% surface coverage of the grafts by BSA. This work conclusively provides a new approach for bridging reactive and functional polymers to surfaces via aryl diazonium salts in a simple, fast, and efficient approach of importance in biomedical and other applications. 相似文献
58.
Rolfe A Samarakoon TB Klimberg SV Brzozowski M Neuenswander B Lushington GH Hanson PR 《Journal of combinatorial chemistry》2010,12(6):850-854
The construction of a library of benzothiaoxazepine-1,1'-dioxides utilizing a one-pot, S(N)Ar diversification-ODCT(50) scavenging protocol is reported. This protocol combines microwave irradiation to facilitate the reaction, in conjunction with a soluble ROMP-derived scavenger (ODCT) to afford the desired products in good overall purity. Utilizing this protocol, a 78-member library was successfully synthesized and submitted for biological evaluation. 相似文献
59.
Abderrahmen Guesmi Mohamed Faouzi Zid Ahmed Driss 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):511-512
In the title compound, disodium cobalt tetrakis(dihydrogenphosphate) tetrahydrate, the CoII ion lies on an inversion centre and is octahedrally surrounded by two water molecules and four H2PO4 groups to give a cobalt complex anion of the form [Co(H2PO4)4(OH2)]2?. The three‐dimensional framework results from hydrogen bonding between the anions. The relationship with the structures of Co(H2PO4)2·2H2O and K2CoP4O12·5H2O is discussed. 相似文献
60.