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121.
Jaroslav Barto Ignc Capek Pavol Hrdlovi
《Journal of polymer science. Part A, Polymer chemistry》1975,13(12):2671-2690
The kinetics of acrylonitrile polymerization photoinitiated by aromatic hydrocarbons have been studied. For the acrylonitrile polymerization photoinitiated by naphthalene the rate of polymerization depends on the square root of incident light intensity, on the square root of naphthalene concentration, and on the 1.5 power of acrylonitrile concentration. In the system acrylonitrile-1-methoxynaphthalene the rate of acrylonitrile polymerization depends on the first power of acrylonitrile concentration. The monoradical character of this polymerization process has been established. For the interpretation of experimental results a reaction mechanism involving the formation of the exciplex between the first singlet or triplet of aromatic hydrocarbon and acrylonitrile in the ground state as a precursor of polymerization reactions is suggested. The photoinitiating efficiency of various aromatic hydrocarbons in acrylonitrile polymerization increases in the order: fluoranthene (zero efficiency) ? pyrene < phenanthrene, fluorene ≈ 2-methoxynaphthalene ≈ biphenyl < anthracene < 2-methylnaphthalene < 1-methoxynaphthalene < 2,3,6-trimethylnaphthalene < 2,3-dimethylnaphthalene ≈ naphthalene < 1-methylnaphthalene < 2,6-dimethylnaphthalene < p-terphenyl < acenaphthene, provided that the systems absorb the same amount of the incident light. The explanation of this result ensues from the study of the effect of concentration on the rate of polymerization and from the quenching of hydrocarbon fluorescence by acrylonitrile. The photoinitiating efficiency of a given aromatic hydrocarbon is mainly determined by the value of the rate constant kq for the formation of exciplex as well as the self-quenching efficiency of aromatic hydrocarbon. By using the literature data for the lifetime of fluorescence τ the values of kq were calculated from the Stern-Volmer equation expressing the quenching of hydrocarbon fluorescence by acrylonitrile. The order of aromatic hydrocarbons according to increasing values of kq is as follows: pyrene < phenanthrene < anthracene ≈ naphthalene < 2-methylnaphthalene ≈ 1-methylnaphthalene ≈ 2,3-dimethylnaphthalene < 2,6-dimethylnaphthalene < acenaphthene < p-terphenyl < 1-methoxynaphthalene. The study of the concentration effect reflecting the self-quenching of aromatic hydrocarbons during polymerization has given the following sequence for decreasing self-quenching efficiency of aromatic hydrocarbons: 2-methoxynaphthalene ≈ pyrene > anthracene > 1-methoxynaphthalene > fluorene > 2,6-dimethylnaphthalene, phenanthrene, acenaphthene > 2,3,6-trimethylnaphthalene > 2,3-dimethylnaphthalene > 1-methylnaphthalene > naphthalene. It has been shown that the photoinitiating efficiency of a given aromatic hydrocarbon in the polymerization of acrylonitrile can be roughly predicted from the position of that aromatic hydrocarbon in the above-mentioned sequences. 相似文献
122.
Ivan Luk
Christopher H. Evans J. C. Scaiano Pavol Hrdlovi
《Journal of polymer science. Part A, Polymer chemistry》1990,28(3):595-608
2-(4-Benzoylphenyl)-2-phenyl propane ( 4 ) was prepared by benzoylation of 2,2-diphenylpropane ( 2 ). Acylation of ( 4 ) with 3-chloropropanoic chloride gave 2-(4-benzoylphenyl)-2-(4-propenoylphenyl)propane ( 5 ). A monomer 2-(4-benzoylphenyl)-2-(4-propenoylphenyl)propane ( 6 ) was prepared through dehydrochlorination of ( 5 ). The homopolymer of 6 (P6) and the copolymer with styrene ( P6 / S) were prepared by radical polymerization. Laser flash photolysis was employed to determine the absorption and emission spectra of transients, their lifetimes (τ) and the rate constant (kq) of triplet quenching in benzene at laboratory temperature for 4 , P6 , and P6 / S. P6 exhibits a transient absorption maximum in a different spectral region than do the model 4 and copolymer P6/S . The products of kq and τ determined by laser flash photolysis for these transients are higher than th Stern–Volmer constants based on inhibition of degradation. Degradation leading to formation of quenchers is the likely cause of this difference although crosslinking may also contribute. Irradiation of polymers ( P6 and P6/S ) at 366 nm leads to main chain scission with aquantum yield of 0.13 under N2 for P6 and 0.03 for P6/S . In this bichromophoric structural unit, the benzophenone residue absorbs about 80–90% of the incident energy. Its triplet energy is about 5 kJ mol?1 lower than that of the 1-(4-alkylphenyl)-2-propene-1-one chromophore. Different possible pathways of degradation are discussed namely the Norrish Type II reaction of the alkyl aryl ketone and direct reaction of triplet benzophenone with the main chain. In the mechanism favored the benzophenone triplet is proposed to be in equilibrium with the upper acetophenone-like chromophore from which the Norrish Type II reaction leading to chain fragmentation takes place. 相似文献
123.
The density and surface tension of melts of the systems CaO-FeO-Fe2O3 MgO at the temperature 1623 K, CaO-FeO-Fe2O3-ZnO at 1573 K, and CaO-Fe2O3-Cu2O at 1573 K were determined using the maximum bubble pressure method. The molar volume, the excess molar volume, and the excess
surface tension were calculated on the basis of the obtained data. From these properties information on the interactions of
components and possible chemical reactions between them was obtained. Due to the absence of silica and the low concentration
of other network-forming oxides, only isolated FeO
4
5−
tetrahedra and the CaO·FeO ionic pairs are formed in these basic melts, the donor of the oxygen atoms being either CaO, FeO,
or both CaO+FeO oxides. Even the observed ternary interactions may be attributed to the formation of the anions FeO
4
5−
only. 相似文献
124.
125.
Kovácik V Bekesová S Tvaroska I Kovác P 《Journal of the American Society for Mass Spectrometry》2006,17(6):749-756
Oligosaccharides (mono- to hexamers) that mimic the terminal epitopes of O-antigens of Vibrio cholerae O:1, serotypes Ogawa and Inaba, have been studied by electrospray ion trap (ESI IT) mass spectrometry. Sodium or potassium-cationized adducts are characteristic ions under the conditions of ESI-MS analysis. The tentative pathways of fragmentation have been proven by multistage ion trap MS (MS(n), n = 1-3). The predominant pathway of fragmentation of the oligomers is the neutral loss of monosaccharide residue shortening the length of the oligosaccharide. In this way, conversion of the Ogawa to Inaba fragments takes place under the conditions of measurement. ESI MS/MS provided sufficient information about molecular mass, the number of saccharide residues, and the structure of saccharides, about the C (4)-amide of 3-deoxy-L-glycero-tetronic acid (DGT) of the compounds investigated, and allows to distinguish between Ogawa and Inaba serotypes. 相似文献
126.
A homomorphism of a digraph to another digraph is an edgepreserving vertex mapping. A local tournament is a digraph in which the inset as well as the outset of each vertex induces a tournament. Thus acyclic local tournaments generalize both directed paths and transitive tournaments. In both these cases there is a simple characterization of homomorphic preimages. Namely, if H is a directed path, or a transitive tournament, then G admits a homomorphism to H if and only if each oriented path which admits a homomorphism to G also admits a homomorphism to H. We prove that this result holds for all acyclic local tournaments. © 1995 John Wiley & Sons, Inc. 相似文献
127.
Ján Vajda Martin Weis Drahoslav Baranĉok Július Cirák Pavol Tomćík 《Central European Journal of Physics》2005,3(1):139-146
Maxwell's displacement current flowing through a metal electrode/air gap/Langmuir monolayer was detected. MDC experimental
results obtained during a step compression mode are presented and contrasted with the Debye-Brown rotational model. As an
alternative approach a theoretical model based on an analogy with a nonideal gas of polar molecules is derived from Lagrange's
equation of motion. 相似文献
128.
P.?Farka?ovskyEmail author H.??en?ariková 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,47(4):517-526
A combination of small-cluster exact-diagonalization calculations
and a well-controlled approximative method is used to study
the ground-state phase diagram of the spin-one-half
Falicov-Kimball model extended by the spin-dependent on-site interaction
between localized (f) and itinerant (d) electrons. Both the magnetic
and charge ordering are analysed as functions of the spin-dependent
on-site interaction (J) and the total number of itinerant (Nd) and
localized (Nf) electrons at selected U (the spin-independent
interaction between the f and d electrons).
It is shown that the spin-dependent interaction (for Nf=L,
where L is the number of lattice sites) stabilizes the fully polarized
(FP) and partially polarized (PP) state, while the stability
region of the non polarized (NP) phase is gradually reduced. The precisely
opposite effect on the stability of FP, PP and NP phases has a reduction
of Nf. Moreover, the strong coupling between the f and d-electron
subsystems is found for both Nf=L as well as Nf < L. 相似文献
129.
130.
The GeS8 chalcogenide glass was irradiated by four various doses of fast neutrons. An absorption band has appeared at 450 nm and developed with the neutron doses. It has been concluded that neutral defects are present in the material. From the measurements of the temperature dependence of the d.c. conductivity follows that the activation energy does not depend on the neutron dose within the measured range while the magnitude does with the peak value at neutron dose of 1017 ncm?2. 相似文献