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71.
Dr. Yunxi Yao Prof. Konstantinos P. Giapis 《Angewandte Chemie (International ed. in English)》2016,55(38):11595-11599
Most Eley–Rideal abstraction reactions involve an energetic gas‐phase atom reacting directly with a surface adsorbate to form a molecular product. Molecular projectiles are generally less reactive, may dissociate upon collision with the surface, and thus more difficult to prove that they can participate intact in abstraction reactions. Here we provide experimental evidence for direct reactions occurring between molecular N2+ and O2+ projectiles and surface‐adsorbed D atoms in two steps: first, the two atoms of the diatomic molecule undergo consecutive collisions with a metal surface atom without bond rupture; and second, the rebounding molecule abstracts a surface D atom to form N2D and O2D intermediates, respectively, detected as ions. The kinematics of the collisional interaction confirms product formation by an Eley–Rideal reaction mechanism and accounts for inelastic energy losses commensurate with surface re‐ionization. Such energetic hydrogenation of dinitrogen may provide facile activation of its triple bond as a first step towards bond cleavage. 相似文献
72.
Synthesis of (R)-dihydropyridones as key intermediates for an efficient access to piperidine alkaloids 总被引:2,自引:0,他引:2
Tzanetou EN Kasiotis KM Magiatis P Haroutounian SA 《Molecules (Basel, Switzerland)》2007,12(4):735-744
The efficient transformation of D-glucal to (2R)-hydroxymethyldihydropyridinone 5 in seven steps and 35 % overall yield is reported. Dihydropyridone 5 constitutes a versatile chiral building block for the synthesis of various piperidine alkaloids. In this regard, 5 was converted to piperidinol 13 and piperidinone 15, that may be further elaborated for the syntheses of (+)-desoxoprosophylline (1) and deoxymannojirimycin (3) or D-mannolactam (4), respectively. 相似文献
73.
Thalassinos K Jackson AT Williams JP Hilton GR Slade SE Scrivens JH 《Journal of the American Society for Mass Spectrometry》2007,18(7):1324-1331
Novel software has been developed to aid the interpretation of tandem mass spectrometry (MS/MS) data from synthetic polymers. The software is particularly focused toward aiding the end-group determination of these materials by significantly speeding up the interpretation process. This allows information on the initiator and/or chain transfer agents, used to generate the polymer, and the mechanism of termination to be inferred from the data much more rapidly. The software allows the validity of hypothesized structures to be rapidly tested by automatically annotating the data file using previously proposed fragmentation rules for synthetic polymers. Low-energy collision-induced dissociation (CID) data from methacrylate, styrene, and polyether oligomers are used as example data for the software. Exact-mass CID information was used to aid the understanding of the dissociation mechanism of the polymers. The software can use exact-mass data to provide more confidence in the results. The MS/MS results indicate that the fragmentation pathways are those previously proposed for these polymers. 相似文献
74.
Maria Tsoukka Konstantinos E. Litinas Demetrios N. Nicolaides Dimitra J. Hadjipavlou‐Litina 《Journal of heterocyclic chemistry》2007,44(3):529-534
Furocoumarins 3,5 and pyranocoumarin 7 were synthesized from the reaction of furonaphthalenediones 2,4 and pyranonaphthalenedione 6 respectively with carbethoxymethylene(triphenyl)phosphorane in refluxing DCM for 3‐6 hours or under microwave irradiation in toluene for a few minutes. Compounds 3,5,7 and their precursors were tested as anti‐inflammatory/antioxidant agents. They were found to compete significantly high DMSO for OH radicals, to scavenge O2? and to inhibit lipoxygenase to a high extent. 相似文献
75.
Georgios Patermarakis Konstantinos Moussoutzanis Nikolaos Nikolopoulos 《Journal of Solid State Electrochemistry》1999,3(4):193-204
A new method has been developed capable of describing the incorporation of electrolyte anions along the pore wall surface
and across both the barrier layer and the pore wall oxide after the establishment of the steady state of growth of porous
anodic Al2O3 where other methods cannot be applied to obtain reliable results. The knowledge of the nature/composition of anodic oxides
as regards the incorporation of species like electrolyte anions is of specific importance for both the understanding of the
electrochemical mechanism of oxide production and growth and the scientific and technological applications of porous anodic
Al2O3 films. The method consists of the selection and use of a suitable catalytic probe reaction on porous anodic oxides at thicknesses
varying from a value near zero up to the maximum limiting thickness and the treatment of the experimental reaction rate results
by a properly developed mathematical formalism. This method was employed in anodic Al2O3 films prepared in H2SO4 anodizing electrolyte at a constant bath temperature and different current densities using as a probe reaction the decomposition
of HCOOH on these oxides, which is almost exclusively a dehydration reaction, at relatively high reaction temperatures, 350 °C
and 390 °C, where the effect of other species except SO4
2− incorporated in the oxide on the reaction rate is eliminated. It has been shown that the fraction of the intercrystallite
surfaces occupied by SO4
2− follows a parabola-like distribution. It has a significant value at the pore base surface, depending on the current density,
then it passes through a maximum along the pore wall surface and across both the barrier layer and the pore walls near the
pore bases at positions depending on the current density and then becomes almost zero at the mouths of the pores of the oxide
with the maximum limiting thickness and at both the Al2O3/Al interface and cell boundaries. The maximum value of the surface coverage is almost independent of the current density
and is always near 1, showing an almost complete saturation of intercrystalline surfaces at these positions. The above distribution
of surface coverage predicts a qualitatively similar distribution of the SO4
2− bulk concentration across both the barrier layer and pore wall oxide around the pore bases. The method may be improved and
developed further either for a more detailed investigation of the above films or to investigate films prepared in other pore-forming
electrolytes.
Received: 30 July 1998 / Accepted: 30 September 1998 相似文献
76.
Konstantinos Chondroudis Debojit Chakrabarty Enos A. Axtell Mercouri G. Kanatzidis 《无机化学与普通化学杂志》1998,624(6):975-979
The reaction of one equivalent of In with a molten flux of (Ph4P)2Se5 and P2Se5 (1 : 2), at 250 °C gave the (Ph4P)[In(P2Se6)] ( I ). Stoichiometric elemental synthesis at 750 °C produced the Cs5In(P2Se6)2 ( II ). The thin, yellow crystals of ( I ), and the irregular, dark orange crystals of ( II ), appear to be air- and water-stable. Compound ( I ) crystallizes in the monoclinic space group C2/c (no. 15) and at 23 °C: a = 23.127(7) Å, b = 6.564(1) Å, c = 19.083(3) Å, β = 97.42(2)°, V = 2873(1) Å3, Z = 4, final R/Rw = 4.4/5.2%. Compound ( II ) crystallizes in the tetragonal space group P42/m (no. 84) and at 23 °C: a = b = 13.886(1) Å, c = 7.597(2) Å, V = 1464.9(3) Å3, Z = 2, final R/Rw = 3.9/5.1%. Compound ( I ) contains infinite [In(P2Se6)]nn– with a structure related to that of K2FeP2Se6. Compound ( II ) contains the discrete [In(P2Se6)2]5– which can be viewed as a fragment of the [In(P2Se6)]nn– chain. 相似文献
77.
Probing hemoglobin structure by means of traveling-wave ion mobility mass spectrometry 总被引:1,自引:0,他引:1
Charlotte A. Scarff Vibhuti J. Patel Konstantinos Thalassinos James H. Scrivens 《Journal of the American Society for Mass Spectrometry》2009,20(4):625-631
Hemoglobin (Hb) is a tetrameric noncovalent complex consisting of two α- and two β-globin chains each associated with a heme group. Its exact assembly pathway is a matter of debate. Disorders of hemoglobin
are the most common inherited disorders and subsequently the molecule has been extensively studied. This work attempts to
further elucidate the structural properties of the hemoglobin tetramer and its components. Gas-phase conformations of hemoglobin
tetramers and their constituents were investigated by means of traveling-wave ion mobility mass spectrometry. Sickle (HbS)
and normal (HbA) hemoglobin molecules were analyzed to determine whether conformational differences in their quaternary structure
could be observed. Rotationally averaged collision cross sections were estimated for tetramer, dimer, apo-, and holo-monomers
with reference to a protein standard with known cross sections. Estimates of cross section obtained for the tetramers were
compared to values calculated from X-ray crystallographic structures. HbS was consistently estimated to have a larger cross
section than that of HbA, comparable with values obtained from X-ray crystallographic structures. Nontetrameric species observed
included apo- and holo- forms of α- and β-monomers and heterodimers; α- and β-monomers in both apo- and holo- forms were found to have similar cross sections, suggesting they maintain a similar fold
in the gas phase in both the presence and the absence of heme. Heme-deficient dimer, observed in the spectrum when analyzing
commercially prepared Hb, was not observed when analyzing fresh blood. This implies that holo-α-apo-β is not an essential intermediate within the Hb assembly pathway, as previously proposed. 相似文献
78.
Aristidis E. Niotis Christos Mastichiadis Panagiota S. Petrou Ion Christofidis Athanasia Siafaka-Kapadai Konstantinos Misiakos Sotirios E. Kakabakos 《Analytical and bioanalytical chemistry》2009,393(3):1081-1086
An optical capillary waveguide fluoroimmunosensor based on glass capillaries internally coated with an ultrathin poly(dimethylsiloxane)
(PDMS) film is presented. The evaluation of the capillaries developed was done in comparison with aminosilanized [3-(aminopropyl)triethoxysilane,
APTES] glass and poly(methylpentene) (PMP) capillaries by immobilizing rabbit γ-globulins on the internal capillary wall.
Following reaction with (R)-phycoerythrin-labelled antibody, the capillary was scanned with a laser beam and the fluorescence waveguided through the
capillary wall was detected by a photomultiplier placed at one of its ends. The capillaries developed provided considerably
improved protein coating homogeneity (intracapillary coefficients of variation 2.9–6.6%) and repeatability (intercapillary
coefficients of variation 2.1–5.0%) compared with APTES-treated ones (7.9–13.4 and 8.5–15.2%, respectively). With use of these
capillaries in a sandwich-type immunosensor for the determination of rabbit γ-globulins, the assay detection limit was improved
eightfold (4.4 ng/mL) compared with that obtained using PMP capillaries (35.3 ng/mL), whereas the assay repeatability was
improved threefold (intra-assay coefficients of variation 5.9–13.1%) compared with APTES-treated capillaries (15.6–36%).
Optoelectronic set-up used to scan the capillaries (left) and representative fluorescence scannings of dual-band poly(methylpentene)
(PMP), PDMS-modified glass and APTES treated glass capillaries 相似文献
79.
We study PN and APN functions over the integers modulo n. We give some construction techniques based on Costas arrays, which allow us to construct APN permutations on where p is a prime. Although PN permutations do not exist, one set of our functions is very close to being a set of PN permutations. 相似文献
80.
Kararizou E Likomanos D Gkiatas K Markou I Triantafyllou N Kararizos G 《Magnetic resonance imaging》2006,24(2):205-207
Gliomatosis cerebri (GC) is characterized by a diffuse infiltration of neoplastic glial cells with preservation of neuronal architecture. It can be very difficult to diagnose during life because the clinical manifestations are protean and tests are often nondiagnostic. The diagnosis of GC needs to be based on radiological, clinical and pathological criteria. We present a patient with GC, which initially presented as acute stroke attack. We discuss the usefulness of noninvasive methods, such a MR spectroscopy, in the diagnosis, grading and management of GC. 相似文献