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11.
Thermal reactions of polyethylene with coal were studied. Coal used exhibited an endothermal effect in the temperature range
of 425-495°C with a flat maximum (about 460°C). In contrast, polyethylene alone was decomposed in the temperature range of
420-540°C (mainly of 485-540°C) with the significant DSC maximum at 510°C. In the presence of coal this maximum shifted to
lower temperature (483°C), therefore, coal promoted the decomposition of polyethylene. As decomposition of polyethylene yields
alkenes and alkadienes, the thermal reaction of polyethylene with coal under low temperature conditions can be described as
two-stage process in which the first stage includes the decomposition of polyethylene giving unsaturated hydrocarbons and
the second stage adsorption and hydrogenation of these products (mainly by coal hydrogen) on the inner surfaces of semicoke
and coal. 相似文献
12.
Magnetic indication of the stress-induced martensitic transformation in ferromagnetic Ni–Mn–Ga alloy
A quantitative study of the stress-induced martensitic transformation in Ni49.7Mn29.1Ga21.2 magnetic shape memory alloy has been carried out in two different ways: the first way is based on the measurements of saturation magnetization under variable mechanical stress and the second one is founded on the quantitative theoretical treatment of experimental stress–strain loops. A functional dependence between the volume fraction of transformed martensite and applied stress has been determined from both magnetization and strain values. A quantitative agreement between the functions determined in two different ways has been observed, and hence, the effectiveness of the magnetic indication of the stress-induced martensitic transformations has been proved. This method can be used to monitor stress-induced transformations in martensitic films, needles and small specimens. 相似文献
13.
Michal?Straka Michael?Patzschke Pekka?Pyykk?Email author 《Theoretical chemistry accounts》2003,109(6):332-340
Relativistic small-core pseudopotential B3LYP and CCSD(T) calculations and frozen-core PW91–PW91 studies are reported for the series UF 4X 2 ( X=H, F, Cl, CN, NC, NCO, OCN, NCS and SCN). The bonding in UF 6 is analyzed and found to have some multiple-bond character, approaching at a theoretical limit a bond order of 1.5. In addition to these s and p orbital interactions, the electrostatic attraction is important. Evidence for p bonding in the other systems studied was also found. The triatomic pseudohalides as well as fluorine and chlorine are in this sense better ligands than cyanide. The –CN group is a s donor and p acceptor, as uranium itself, and hence is unfit to bond to U(VI). The s-bonded UH 6 is octahedral. 相似文献
14.
15.
A study of the electrochemistry of uranium in LiF–BeF2 system important for molten salt reactor concept was conducted at W and Ni electrodes. Cyclic voltammetry and chronopotentiometry
methods were used. Two-step reduction mechanism for U4+ ions involving one electron exchange in soluble/soluble U4+/U3+ system and three electron exchange in the second step were found on W electrode. Both processes were identified as reversible
and diffusion-controlled. Based on voltammetric and chronopotentiometric measurements, the diffusion coefficient of U4+ ions at 813 K was calculated: D(U4+) = 1.26 × 10−6 cm2 s−1 and D(U4+) = 1.28 × 10−6 cm2 s−1, respectively. Formation of U–Ni alloys was observed on Ni electrode. 相似文献
16.
J. Leitner M. Hampl K. Ri
ka M. Straka D. Sedmidubský P. Svoboda 《Thermochimica Acta》2008,475(1-2):33-38
The heat capacity and the enthalpy increments of strontium niobate Sr2Nb2O7 and calcium niobate Ca2Nb2O7 were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (720–1370 K). Temperature dependencies of the molar heat capacity in the form Cpm = 248.0 + 0.04350T − 3.948 × 106/T2 J K−1 mol−1 for Sr2Nb2O7 and Cpm = 257.2 + 0.03621T − 4.434 × 106/T2 J K−1 mol−1 for Ca2Nb2O7 were derived by the least-square method from the experimental data. The molar entropies at 298.15 K, Sm°(298.15 K) = 238.5 ± 1.3 J K−1 mol−1 for Sr2Nb2O7 and Sm°(298.15 K) = 212.4 ± 1.2 J K−1 mol−1 for Ca2Nb2O7, were evaluated from the low-temperature heat capacity measurements. 相似文献
17.
Brewer CT Brewer G Butcher RJ Carpenter EE Schmiedekamp AM Schmiedekamp C Straka A Viragh C Yuzefpolskiy Y Zavalij P 《Dalton transactions (Cambridge, England : 2003)》2011,40(1):181-194
Reaction of H(3)L(1), the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3-carboxaldehyde, with manganese(II)perchlorate or iron(II)tetrafluoroborate results in the isolation of [MH(3)L(1)]X(2) (M = Mn and X = ClO(4) and M = Fe and X = BF(4)). These complexes are high spin d(5) and d(6), respectively, as inferred from the long M-N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and M?ssbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH(3)L(1)](2+) with three equivalents of potassium hydroxide produced [CoL(1)]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH(3)L(1)](BF(4))(2) with 1.5 equivalents of potassium hydroxide to give {[FeH(1.5)L(1)](BF(4))}(2) or by the metathesis reaction of [FeH(2)L(1)][FeHL(1)](ClO(4))(2) with sodium hexafluorophosphate to give [FeH(3)L(1)][FeL(1)](PF(6))(2). The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal x-ray diffraction and M?ssbauer spectroscopy. The iron(III) atom is low spin while the iron(II) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1:1 reaction of [FeH(3)L(1)](BF(4))(2) or [MnH(3)L(1)](ClO(4))(2) with [CoL(1)]. [MH(3)L(1)][CoL(1)](X)(2) (M = Fe and X = BF(4) or M = Mn and X = ClO(4)), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and M?ssbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(II) and manganese(II), respectively. DFT calculations demonstrate that the spin state of the iron(II) atom in {[FeH(3)L(1)][FeL(1)]}(2+) changes from high spin to low spin as the iron(II)-iron(III) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(II)-N(pyrazole) bond distances. 相似文献
18.
The combination of IR, Raman and NMR spectroscopy was used in the study of the blends of semicrystalline and amorphous polymers with considerably different strength of intermolecular interactions: poly(ϵ-caprolactam)/polystyrene (PCL/PS), poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) and poly(N-methyllaurolactam)/poly(4-vinylphenol) (PNMLL/PVPh). In the vibrational and NMR spectra of the blends composed of non-interacting polymers (PCL/PS) and weakly interacting polymers (PEO/PMMA), no band changes were observed which would indicate changes of the conformational structures. 1H NMR relaxation of the PCL and PS components in the blends is the same as in the respective homopolymers similarly treated. In the blends of weakly interacting polymers (PEO/PMMA), the crystallinity of PEO is influenced by the presence of PMMA and is negligible in the blends with less than 30 wt.-% of PEO. The rotating-frame spin-lattice relaxation time for protons TH1p of PMMA indicates close contact of the PMMA and PEO chains. In the blends PNMLL/PVPh with strong hydrogen-bonding interactions, both components are intimately mixed on a scale of 3–4 nm and significant shifts of some bands both in vibrational and in NMR spectra reveal changes of structure. 相似文献
19.
Fully relativistic, four-component Dirac–Fock calculations and quasirelativistic pseudopotential calculations at different
ab initio levels are used to study the bonding trends among the naked, triatomic [OAnO]
q+
groups or the oxyfluorides [AnO
n
F
m
]
q
with f
0 configurations. The triatomic f
0 series is suggested to range from the bent ThO2 via the linear OPaO+ to at least NpO2
3+, a possible new gas-phase species. The neutral oxyfluoride molecules include the experimentally unknown NpO2F3 and PuO2F4. The latter is a candidate for the so far unknown oxidation state Pu(VIII), which is found to lie considerably above Pu(VI),
but to be locally stable. Their all-oxygen isoelectronic analogues are NpO5
3−, known in the solid state, and the unknown PuO6
4−. Further possible candidates for Pu(VIII) are PuO4(D
4h
) and the cube-shaped PuF8(O
h
). Isoelectronic UF8
2− is calculated to be D
4d
, in agreement with experiment.
Received: 18 May 2001 / Accepted: 21 June 2001 / Published online: 11 October 2001 相似文献
20.