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31.
An interpretative strategy (factorial design experimentation+total resolution analysis+chromatogram simulation) was employed to optimize the separation of 16 polycyclic aromatic hydrocarbons (PAHs) (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo(a)anthracene, benzo(k)fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, indeno(1,2,3-c,d)pyrene, dibenzo(a,h)anthracene, benzo(g,h,i)perylene) in temperature-programmed gas chromatography (GC). Also, the retention behavior of PAHs in the same GC system was studied by a feed-forward artificial neural network (ANN). GC separation was investigated as a function of one (linear temperature ramp) or two (linear temperature ramp+the final hold temperature) variables. The applied interpretative approach resulted in rather good agreement between the measured and the predicted retention times for PAHs in both one and two variable modeling. The ANN model, strongly affected by the number of input experiments, was shown to be less effective for one variable used, but quite successful when two input variables were used. All PAHs, including difficult to separate peak pairs (benzo(k)fluoranthene/benzo(b)fluoranthene and indeno(1,2,3-c,d)pyrene/dibenzo(a,h)anthracene), were separated in a standard (5% phenyl-95% dimethylpolysiloxane) capillary column at an optimum temperature ramp of 8.0 degrees C/min and final hold temperature in the range of 260-320 degrees C. 相似文献
32.
33.
Ma?a?Raji?? Linari? Zora?Popovi?Email author ?eljka?Soldin 《Journal of Thermal Analysis and Calorimetry》2007,88(2):489-493
This work presents preparation and thermal characterization of three
novel organomercurials: Hg2(CF3COCHCOCF3)2-μ2-(CF3COCCOCF3)μ2(CF3C(OH)2CH2C(OH)2CF3)
(I), Hg2(CF3COCHCOCF3)2-μ2-(CF3COCCOCF3)
(II) and Hg2(CH3COCHCOCF3)2-μ2-(CH3COCCOCF3)
(III) which means that they contain at least
one direct mercury-to-carbon bond among the carbonyl groups of β-diketone
molecules which are capable for chelating of metal ions. IR-spectra support
the conclusion that mercury is most probably bound to the γ-carbon of
fluorinated derivatives of acetylacetone and is not chelated through oxygen
in any of the isolated compounds.
The thermal decomposition of
mercurated hexafluoro- and trifluoroacetylacetone in nitrogen occurs in a
few steps. Each step was identified and studied by simultaneous DTA/TG analyzer.
On the basis of dynamic heating experiments by TG applying Flynn-Wall method
the activation energy for each of them was determined. 相似文献
34.
X. G. Feng Dragana Popovi S. Washburn V. Dobrosavljevi 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
We report the discovery of a new and unexpected kind of metal in two dimensions (2D), which exists in the presence of scattering by local magnetic moments. The experiment was carried out on a 2D electron system in silicon, where the local magnetic moments have been induced by disorder and their number was varied using substrate bias (Vsub). In the new metal, the conductivity decreases as σ(ns,T)=σ(ns,T=0)+A(ns)T2 (ns – carrier density) to a non-zero value as temperature T→0. In three dimensions, this T2 dependence is well known, and results from Kondo scattering by local magnetic moments. In 2D, however, the existence of a metal with dσ/dT>0 is very surprising. As the number of local moments is reduced, the range of temperatures [T<Tm(Vsub)] where they dominate transport becomes smaller. For T>Tm, we observe the usual 2D metallic behavior with dσ/dT<0. 相似文献
35.
Iva ikuten Petra tambuk Jasminka Karoglan Konti Edi Maleti Ivana Tomaz Darko Preiner 《Molecules (Basel, Switzerland)》2021,26(23)
(1) Background: Solid phase microextraction (SPME)-Arrow is a new extraction technology recently employed in the analysis of volatiles in food materials. Grape volatile organic compounds (VOC) have a crucial role in the winemaking industry due to their sensory characteristics of wine.; (2) Methods: Box–Behnken experimental design and response surface methodology were used to optimise SPME-Arrow conditions (extraction temperature, incubation time, exposure time, desorption time). Analyzed VOCs were free VOCs directly from grape skins and bound VOCs released from grape skins by acid hydrolysis.; (3) Results: The most significant factors were extraction temperature and exposure time for both free and bound VOCs. For both factors, an increase in their values positively affected the extraction efficiency for almost all classes of VOCs. For free VOCs, the optimum extraction conditions are: extraction temperature 60 °C, incubation time 20 min, exposure time 49 min, and desorption time 7 min, while for the bound VOCs are: extraction temperature 60 °C, incubation time 20 min, exposure time 60 min, desorption time 7 min.; (4) Conclusions: Application of the optimized method provides a powerful tool in the analysis of major classes of volatile organic compounds from grape skins, which can be applied to a large number of samples. 相似文献
36.
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38.
Marijana??akovi?Email author Maja?Do?en Zora?Popovi?Email author 《Journal of chemical crystallography》2011,41(2):180-185
Abstract
The synthesis, thermal and spectral characterization, and crystal structure of isomorphous thiocyanate cobalt(II) and nickel(II) complexes with 3-hydroxypicolinamide (3-OHpia), [M(C6H6N2O2)2(NCS)2]·2H2O, are reported. The metal(II) ions are chelated by two cis-oriented 3-OHpia and two thiocyanate ligands in distorted octahedral geometry. The distortion within the coordination sphere is mainly imposed by formation of the chelate rings. The compounds crystallize in monoclinic space group P2/c with two symmetrically independent molecules and a = 14.4945(2) ?, b = 8.5906(1) ?, c = 16.3865(3) ?, β = 105.987(2)°, Z = 4 (1) and a = 14.4927(5) ?, b = 8.5912(3) ?, c = 16.2712(6) ?, β = 105.740(4)°, Z = 4 (2). Commonly observed supramolecular amide synthons are not robust enough to accommodate thiocyanate ions and H2O molecules. But instead, neutral complexes are linked through hydrogen bonds leading to two different hydrogen bonding ribbon motifs involving amide moieties and H2O molecules [C(8)R 22(12) along c axis] and amide moieties and thiocyanate ions [C(8)R 22(16) along b axis] for symmetrically related molecules labelled as 1 [Co1 (1) and Ni1 (2)] and 2 [Co2 (1) and Ni2 (2)], respectively. 相似文献39.
Branka Dra?i? Sanja Grguri?-?ipka Ivanka Ivanovi? ?ivoslav Lj. Te?i? Gordana Popovi? 《Journal of the Iranian Chemical Society》2012,9(1):7-12
Acid?Cbase equilibria of the aqua adducts of Ru(II) arene complexes, general formulae [(??6-p-cymene)Ru (L1?3)Cl2] where L1?=?3-acetylpyridine (1), L2?=?4-acetylpyridine (2) and L3?=?2-amino-5-chloropyridine (3), then [(??6-p-cymene)Ru(HL4)Cl2] with HL4?=?isonicotinic acid (4); [(??6-p-cymene)Ru(HL5?8)Cl] where H2L5?=?2,3-pyridine dicarboxylic acid (5), H2L6?=?2,4-pyridine dicarboxylic acid (6), H2L7?=?2,5-pyridine dicarboxylic acid (7) and H2L8?=?2,6-pyridine dicarboxylic acid (8) have been studied. pK a values were determined by potentiometry at 25?°C and constant ionic strength of 0.1?M NaNO3. The assumed equilibria were confirmed by UV and 1H-NMR spectroscopy. 相似文献
40.
Andersson CS Öhrström M Popović-Bijelić A Gräslund A Stenmark P Högbom M 《Journal of the American Chemical Society》2012,134(1):123-125
The essential catalytic radical of Class-I ribonucleotide reductase is generated and delivered by protein R2, carrying a dinuclear metal cofactor. A new R2 subclass, R2c, prototyped by the Chlamydia trachomatis protein was recently discovered. This protein carries an oxygen-activating heterodinuclear Mn(II)/Fe(II) metal cofactor and generates a radical-equivalent Mn(IV)/Fe(III) oxidation state of the metal site, as opposed to the tyrosyl radical generated by other R2 subclasses. The metal arrangement of the heterodinuclear cofactor remains unknown. Is the metal positioning specific, and if so, where is which ion located? Here we use X-ray crystallography with anomalous scattering to show that the metal arrangement of this cofactor is specific with the manganese ion occupying metal position 1. This is the position proximal to the tyrosyl radical site in other R2 proteins and consistent with the assumption that the high-valent Mn(IV) species functions as a direct substitute for the tyrosyl radical. 相似文献