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51.
A first simultaneous EPR- and VIS-spectrophotometric study is reported on the interaction of the stable free radical 1,1-diphenyl-2-picryl-hydrazyl
(DPPH) dissolved in ethanol with thioglycolic acid (HSCH2CO2H, TGA). The results of the kinetic studies at room temperature permit to assume 1:1 stoichiometry of the reaction between
DPPH and TGA giving 1,1-diphenyl-2-picryl-hydrazine (DPPH2) and thioglycolic disulphide. The linear plots of EPR- and UV/Vis responses vs. the quantity of added TGA are used to find
the DPPH molar absorptivity at 520 nm to be 12350 ± 3% l · mol–1· cm–1 which may be used as a criterion for the purity of the material itself. It was also found that the paramagnetic and optical
properties of a 30 year old sample give results suggesting that in the solid state DPPH is a fairly stable material.
Received: 12 October 1996 / Revised: 6 December 1996 / Accepted: 12 December 1996 相似文献
52.
Aging of aqueous solutions of poly (vinyl alcohol) obtained by melting of gels, formed in the aging process from solutions prepared by the dissolution of the polymer in hot water, was investigated using non-Newtonian viscometry and normal stress measurement. It was shown that, if the gels undergo melting at the same temperature at which the original solutions were prepared, aging of such solutions proceeds in the same way as in the case of the original solutions. If melting occurred due to heating at lower temperature, the resulting solutions aged more quickly. 相似文献
53.
ABSTRACTThis work presents new rod-like compounds being fluorene derivatives linked with other parts of the core at 2 and 7 positions – its synthesis and properties. The fluorene moiety is located in the central position of the four rings molecular core. The chain system in most cases was symmetrical and limited to pentyl or hexyl chains. To study the influence of the lateral substituents on mesomorphic properties two types of substituents have been incorporated, centrally located various short alkyl groups at fluorene’s 9,9 positions and outer core fluorosubstitutions located at side phenyl rings. All synthesised compounds exhibit liquid crystalline properties, where for laterally non-substituted and fluorosubstituted derivatives the dominant phases are smectics, while the nematics phases (nematic and chiral nematic – observed mostly on cooling cycle) occurs for compounds having alkyl substituents at 9,9 positions of fluorene. The synthetic methodology and mesomorphic properties of title compounds will be presented in detail as well as photophysical properties such as UV-visible absorption spectra and fluorescence spectra. 相似文献
54.
The influence of the temperature and time of heating during dissolution on the aging of concentrated aqueous solutions of poly(vinyl alcohol) and aging at different temperatures are described. Changes occuring during aging are interpreted on the basis of non-Newtonian viscosity and normal stress measurements. 相似文献
55.
Trimethylsilyl fluorosulfonyldifluoroacetate (TFDA): a new, highly efficient difluorocarbene reagent
William R Dolbier Jr. Feng Tian An-Rong Li Olivia Bautista J Marshall Baker Pauline Anselme Aneta Modzelewska Merle A Battiste 《Journal of fluorine chemistry》2004,125(3):459-469
TFDA is readily prepared from the reaction of fluorosulfonyldifluoroacetic acid with trimethylsilyl chloride, and it is a very effective and efficient source of difluorocarbene for use in addition reactions to alkenes of a broad scope of reactivities. Acid-sensitive substrates may require an additional purification step involving treatment of the distilled TFDA with sufficient Et3N to remove the acid impurity. Other trialkylsilyl fluorosulfonyldifluoroacetates can also be prepared, and they have been found to have reactivities similar to TFDA. The triethyl derivative, TEFDA is more convenient to prepare in a pure state and has similar reactivity to TFDA. Thus, it may prove to be a superior reagent. 相似文献
56.
Naumov P Jovanovski G Todorovska A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(9):1903-1910
Adducts of bis(o-sulfobenzimidato)zinc(II) and mercury(II) with imidazole are synthesized for the first time and their mid-infrared vibrational spectra at ambient conditions and at 77 K are coupled with the earlier spectra-structural inferences to predict aspects of the respective solid-state structures. The spectrum of the H2O-matrix isolated OD fundamentals in the hydrated zinc compound is also investigated. The structure of the latter adduct contrasts the octahedral isostructural tetrad of mixed imidazole-saccharinates [M(H2O)2(C3H4N2)4](C7H4NO3S)2 [M = Mn(II), Fe(II), Co(II) and Ni(II)] in that it bears only a single crystallographic type of hydrogen bonded C2v water molecules and at least two structurally different o-sulfobenzimidate ligands, some of them likely utilized in a bridging fashion. The rotation and the partial ionic character of a pair of N-monodentate o-sulfobenzimidato ligands placed about 212-214 pm from the metal accommodates another pair of imidazole molecules in the tetrahedral arrangement around the metal in the neutral unhydrous mercury complex. 相似文献
57.
Hałka-Grysińska Aneta Płocharz Paweł W. Skwarek Ewa Janusz Władysław Dzido Tadeusz H. 《平面色谱法杂志一现代薄层色谱法》2015,28(2):133-138
JPC – Journal of Planar Chromatography – Modern TLC - In the paper, the influence of the addition of different ion-pair reagents — sodium-1-heptane sulfonate (HS),... 相似文献
58.
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60.
Jarosław J. Panek Riccardo Mazzarello Marjana Novič Aneta Jezierska-Mazzarello 《Molecular diversity》2011,15(1):215-226
Mercury(II) has a strong affinity for the thiol groups in proteins often resulting in the disruption of their biological functions.
In this study we present classical and first-principles, DFT-based molecular dynamics (MD) simulations of a complex of Hg(II)
and proteinase K, a well-known serine protease with a very broad and diverse enzymatic activity. It contains a catalytic triad
formed by Asp39, His69, and Ser224, which is responsible for its biological activity. It was found previously by X-ray diffraction
experiments that the presence of Hg(II) inhibits the enzymatic action of proteinase K by affecting the stereochemistry of
the triad. Our simulations predict that (i) the overall structure as well as the protein backbone dynamics are only slightly
affected by the mercury cation, (ii) depending on the occupied mercury site, the hydrogen bonds of the catalytic triad are
either severely disrupted (both bonds for mercury at site 1, and the His69–Ser224 contact for mercury at site 2) or slightly
strengthened (the Asp39–His69 bond when mercury is at site 2), (iii) the network of hydrogen bonds of the catalytic triad
is not static but undergoes constant fluctuations, which are significantly modified by the presence of the Hg(II) cation,
influencing in turn the triad’s ability to carry out the enzymatic function—these facts explain the experimental findings
on the inhibition of proteinase K by Hg(II). 相似文献