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31.
On the basis of the calculated atomic polar tensors the generalized atomic polar tensor charges have been calculated for 4-isopropylphenol (4-IP) and related compounds: benzene, quinone, phenol and p-nitroaniline (p-NA). The second order Möller–Plesset perturbation method and Huzinaga–Dunning's double valence ζ basis set supplemented by d polarisation function on heavy atoms and p on hydrogen atoms (D95V**) have been used. Analysis of the atomic charges has been done. It is found that the phenyl rings of the 4-IP and p-NA molecules have an intermediate structure between the aromatic ring and the quinoid one. 相似文献
32.
Elżbieta Szostak Anna Migdał-Mikuli 《Journal of Thermal Analysis and Calorimetry》2010,101(2):601-606
Differential scanning calorimetry (DSC) measurements were performed over the temperature range 93–480 K and three enantiotropic
(at 323, 409, and 461 K) and one monotropic (at 271 K) phase transitions were detected. Thus, four solid phases (three of
them stable and one metastable) and one liquid phase were found. It was concluded, from the entropy change (ΔS) values of these phase transitions that two of them are stable rotational phases and two are crystalline phases (one stable
and one metastable). The thermal decomposition of [Mg((CH3)2SO)6](ClO4)2, which was studied using thermogravimetry (TG) with simultaneous differential thermal analysis (SDTA), takes place in two
main stages. The gaseous products of the decomposition were identified on-line by a quadruple mass spectrometer (QMS). In
the first stage, which starts just above ca. 432 K, the compound loses two dimethylsulphoxide (DMSO) molecules per one formula
unit. In the second stage (502–673 K) [Mg(DMSO)4](ClO4)2 decomposes explosively and Cl2, O2, H2, and MgSO4 are finally produced. 相似文献
33.
Antibodies have traditionally been used for isolating affinity reagents to new molecular targets, but alternative protein scaffolds are increasingly being used for the directed evolution of proteins with novel molecular recognition properties. We have designed a combinatorial library based on the DNA binding domain of the human retinoid-X-receptor (hRXRalpha). We chose this domain because of its small size, stable fold, and two closely juxtaposed recognition loops. We replaced the two loops with segments of random amino acids, and used mRNA display to isolate variants that specifically recognize adenosine triphosphate (ATP), demonstrating a significant alteration of the function of this protein domain from DNA binding to ATP recognition. Many novel independent sequences were recovered with moderate affinity and high specificity for ATP, validating this scaffold for the generation of functional molecules. 相似文献
34.
35.
V. I. Tsaryuk K. P. Zhuravlev V. F. Zolin V. A. Kudryashova J. Legendziewicz R. Szostak 《Journal of Applied Spectroscopy》2007,74(1):51-59
We discuss the possibility of optimizing the brightness of luminescence for phenylcarboxylates, naphthylcarboxylates, and
indolylcarboxylates of europium and terbium and their adducts with 1,10-phenanthroline and 2,2′-bipyridine by modifying the
ligands. We have studied the efficiency of luminescence and luminescence excitation. We consider the effect of blocking energy
transfer from the ligands to the Eu3+ and Tb3+ ions by methylene (-CH2-) bridges dividing the π-electron system of the ligands into two parts and by the electronacceptor nitro group (-NO2). We have analyzed the pathways for transfer and degradation of the excitation energy at 77 K and 300 K. From the phosphorescence
spectra of gadolinium salts, we have determined the energies of the lowest excited triplet states of the ligands. We consider
the effect of the relative positions of the triplet levels of the ligands and the excited levels of the Eu3+ and Tb3+ ions on the luminescence efficiency. We found channels for dissipation of the excitation energy via the ππ* and nπ* states
of the aromatic system of the carboxylate and the NO2 group.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 48–54, January–February, 2007. 相似文献
36.
The chemical synthesis of a fully protected ribonucleoside phosphoramidite, containing 2-aminopurine as the base component, and its incorporation into short oligoribonucleotides as substrates for an engineered ribozyme from Tetrahymena is described. 相似文献
37.
We have measured the surface photovoltage (SPV) of intrinsic (i.e., undoped) and phosphorus-doped amorphous Si : H between ?168 and 25°C in the spectral range from 0.5 to 2.5 eV. The a-Si : H was grown in a silane glow discharge. Vibrating Kelvin probe techniques were used for the SPV measurements; Auger spectroscopy was used for monitoring surface cleanliness and chemistry. At all temperatures and for both materials, (1) the SPV was invariably negative, (2) there was no correlation between the spectral, thermal and response-time properties of the SPV and the bulk photoconductivity, and (3) surface treatments such as sputtering and oxygen physisorption strongly affected the SPV but not the photoconductivity. These facts indicated that the SPV was due to the emptying of surface-states via surface transitions, and corresponded to the flattening of bands which, when unilluminated, were bent upwards. Intrinsic material showed a maximum SPV of about 0.2 V. The SPV was characterized at ?168°C by strong electronic isolation between surface-states and valence band (i.e., once light was removed, there was no surface-state refilling or decay of the SPV), slow rise times (~min), saturation at photon fluxes of about 1011/cm2 · s, and a SPV spectral threshold occurring at 0.7 eV. At 25°C, all SPV responses were much faster (<0.5 s) and the optical threshold was 0.9 eV. The thermal activation energies associated with the SPV were 0.11 eV for surface-state emptying and 0.22 eV for surface-state refilling. For P-doped material the maximum SPV at ?168°C was 0.3 V and its properties indicated less electronic isolation between surface-states and valence band. There was no SPV at room temperature. Our results are discussed in terms of an energy level scheme which contains a distribution of filled surface states isolated from both conduction and valence bands. The surface-state density is estimated to be about (1?2) × 1011/ cm2, a relatively low value which is consistent with the observed lack of Fermi level pinning. In both materials there is a very fast component of the SPV which suggests the presence of additional surface states below the valence band edge. 相似文献
38.
39.
Perschmann W. D. von Oppen G. Szostak D. 《Zeitschrift für Physik A Hadrons and Nuclei》1983,311(1-2):49-56
Zeitschrift für Physik A Hadrons and nuclei - Using level crossing techniques the fine-structure splittings and tensor polarizabilities of the 1snd 3 D levels of He I withn=3 to 7 have been... 相似文献
40.
Structural Characterization of N‐Alkylated Twisted Amides: Consequences for Amide Bond Resonance and N−C Cleavage
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Dr. Feng Hu Prof. Dr. Roger Lalancette Prof. Dr. Michal Szostak 《Angewandte Chemie (International ed. in English)》2016,55(16):5062-5066
Herein, we describe the first structural characterization of N‐alkylated twisted amides prepared directly by N‐alkylation of the corresponding non‐planar lactams. This study provides the first experimental evidence that N‐alkylation results in a dramatic increase of non‐planarity around the amide N?C(O) bond. Moreover, we report a rare example of a molecular wire supported by the same amide C=O‐Ag bonds. Reactivity studies demonstrate rapid nucleophilic addition to the N?C(O) moiety of N‐alkylated amides, indicating the lack of nN to π*C=O conjugation. Most crucially, we demonstrate that N‐alkylation activates the otherwise unreactive amide bond towards σ N?C cleavage by switchable coordination. 相似文献