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941.
Chenmou Zheng Xinmin Zhang Shan He Qun Fu Deming Lei 《Journal of solid state chemistry》2003,170(2):221-226
V2O3 nanopowder with spherical particles was prepared by reducing pyrolysis of the precursor, (NH4)5[(VO)6(CO3)4(OH)9]·10H2O, in H2 atmosphere. The thermolysis process of the precursor in a H2 flow was investigated by thermogravimetric analysis and differential thermal analysis. The results indicate that pure V2O3 forms at 620°C and crystallizes at 730°C. The effects of various reductive pyrolysis conditions on compositions of V2O3 products were studied. Scanning electron micrographs show that the particles of the V2O3 powder obtained at 650°C for 1 h are spherical about 30 nm in size with more homogeneous distribution. Experiments show that nanopowder has larger adsorption capacity to gases and is more easily reoxidized by air at room temperature than micropowder. Differential scanning calorimetry experiment indicates that the temperature of phase transition of nano-V2O3 powder is −119.5°C on cooling or −99.2°C on heating. The transition heats are −12.55 J g−1 on cooling and 11.42 J g−1 on heating, respectively. 相似文献
942.
943.
Rahul Mukerjee 《The Journal of the Operational Research Society》1982,33(10):957-959
The problem of minimising E(X) subject to the constraints X ? 0, P(X ? b) ? a(0 < a < 1) has been considered, where b is a non-negative random variable with continuous probability distribution. A necessary and sufficient condition for randomised decisions to be superior to the non-randomised one has been derived. 相似文献
944.
A pseudo-first-order catalytic mechanism in which both reactant and product of a redox reaction are strongly immobilized
on an electrode surface is theoretically analysed under conditions of square-wave (SWV) and staircase cyclic voltammetry (SCV).
A mathematical procedure is developed under diffusionless conditions. The relationships between the properties of the voltammetric
response and both the kinetic parameters of the redox reaction and the parameters of the excitation signal are studied. The
phenomenon of the quasi-reversible maximum is discussed. A comparative study between SWV and SCV is presented and the limitations
and advantages of both techniques, from analytical and kinetic points of view, are discussed. The theoretical predictions
are experimentally confirmed by the redox reaction of azobenzene in the presence of hydrogen peroxide as an oxidizing agent.
Electronic Publication 相似文献
945.
A new ligand, 2-carboxybenzaldehyde-(4’-hydroxy)benzoylhydrazone(H2L) and its ZnII and NiII complexes have been synthesized and characterized on the basis of elemental analyses, molar conductivities, 1H-NMR, IR spectra and thermal analyses. In addition, DNA-binding properties of these two metal complexes were investigated
using spectrometric titrations, ethidium bromide displacement experiments, and viscosity measurements. The results show that
the two complexes, especially the NiII complex, strongly bind with calf-thymus DNA, presumably via an intercalation mechanism. The intrinsic binding constants of the ZnII and NiII complexes with DNA are 2.46 × 105 and 7.94 × 105
M
−1, respectively. 相似文献
946.
Jorge Pavez Maritza Páez Armelle Ringuedé Fethi Bedioui José H. Zagal 《Journal of Solid State Electrochemistry》2005,9(1):21-29
We studied the electrocatalytic activity of cobalt tetra-aminophthalocyanine (CoTAPc) for the reduction of molecular oxygen (O2) on adsorbed monomeric and on electropolymerized films of different thicknesses on glassy carbon (GC) electrode. The polymeric films, denoted poly-CoTAPc, were first characterized by electrochemical impedance spectroscopy and it appears that the types of phenomena revealed to be occurring depend less on the film thickness in basic than in acid media. For O2 reduction, the results showed that poly-CoTAPc is more active than the monomeric CoTAPc adsorbed on GC. Indeed, rotating ring-disk electrode data showed that polymeric CoTAPc promotes the four-electron reduction of O2 to water in parallel to a two-electron reduction to give peroxide. On monomeric and thin films of poly-CoTAPc, a two-electron reduction mechanism predominates. In basic media the activity increases very slightly with thickness, whereas in acid media this increase is more pronounced. This parallels the observed behavior revealed by electrochemical impedance spectroscopy. 相似文献
947.
Sorption of uranium by non-living water hyacinth roots 总被引:1,自引:0,他引:1
S. Shawky M. Abdel Geleel Ashraf Aly 《Journal of Radioanalytical and Nuclear Chemistry》2005,265(1):81-84
Summary Many studies have shown that water hyacinth (Eichhornia crassipes) roots can be used to accumulate high concentrations of organic as well as inorganic pollutants. They are currently used to remediate aquatic environments and aqueous solutions. In the present study, sorption of uranium from aqueous solutions by using dried roots of water hyacinth has been investigated. The sorption of uranium was examined as a function of initial concentration, pH, weight of roots and contact time. Five different concentrations 20, 40, 60, 80, and 100 μg . ml-1 were used. Sorption proves to be very rapid and depend on pH, weight of roots and concentration of uranium. Maximum sorption capacity of water hyacinth roots was 64,000 U6+ μg/g. The sorption of uranium by water hyacinth roots follows a Langmuir isotherm. 相似文献
948.
A dicyano-containing [Fe(bpb)(CN)2]- building block has been employed for the synthesis of cyano-bridged heterometallic Ni(II)-Fe(III) complexes. The presence of steric bpb(2-) ligand around the iron ion results in the formation of low-dimensional species: five are neutral NiFe2 trimers and three are one-dimensional (1D). The structure of the 1D complexes consists of alternating [NiL]2+ and [Fe(bpb)(CN)2]- generating a cyano-bridged cationic polymeric chain and the perchlorate as the counteranion. In all complexes, the coordination geometry of the nickel ions is approximately octahedral with the cyano nitrogen atoms at the trans positions. Magnetic studies of seven complexes show the presence of ferromagnetic interaction between the metal ions through the cyano bridges. Variable temperature magnetic susceptibility investigations of the trimeric complexes yield the following J(NiFe) values (based on the spin exchange Hamiltonian H = -2J(NiFe) S(Ni) (S(Fe(1)) + S(Fe(2))): J(NiFe) = 6.40(5), 7.8(1), 8.9(2), and 6.03(4) cm(-1), respectively. The study of the magneto-structural correlation reveals that the cyanide-bridging bond angle is related to the strength of magnetic exchange coupling: the larger the Ni-N[triple bond]C bond angle, the stronger the Ni- - -Fe magnetic interaction. One 1D complex exhibits long-range antiferromagnetic ordering with T(N) = 3.5 K. Below T(N) (1.82 K), a metamagnetic behavior was observed with the critical field of approximately 6 kOe. The present research shows that the [Fe(bpb)(CN)2]- building block is a good candidate for the construction of low-dimensional magnetic materials. 相似文献
949.
Levon A. Tavadyan Gegham Z. Sedrakyan Seyran H. Minasyan Frederick T. Greenaway John R.J. Sorenson 《Transition Metal Chemistry》2004,29(6):684-696
Bioactive copper(II), iron(III), and manganese(II) 3,5-di-i-propylsalicylate (3,5-DIPS) chelates were investigated in order to determine their ability to inhibit the free radical initiated chain reactions leading to the peroxidation of isopropylbenzene (i-PrPh) and ethylbenzene (EtPh). Quantitative kinetic studies of these chelates established the following order of anti-oxidant reactivities: manganese(II)-(3,5-DIPS)2>iron(III)(3,5-DIPS)3>copper(II)2(3,5-DIPS)4> > 3,5-DIPS acid. The mechanism of anti-oxidant reactivity of these three chelates is established as being due, in part, to their chain-breaking capacity resulting from the chemical reduction of the generated peroxyl radical to yield alkybenzenelhydroperoxides via reaction of the 3,5-DIPS ligand with the peroxyl radical. In the case of manganese(II)3,5-di-i-propylsalicylate, the central metalloelement also interacts with the peroxyl radical. The manganese(II)-(3,5-DIPS)2 and copper(II)2(3,5-DIPS)4 chelates were also found to exhibit alkylhydroperoxide pro-oxidative reactivity leading to the formation of the alkylbenzeneperoxyl radical. In addition, the manganese(II) atom underwent oxidation to manganese(III) with the formation of the alkylbenzenehydroperoxide or superoxide with air oxygen oxidation. Amyl acetate and dipropylamine (n-Pr2NH) were added to the reaction mixture to model the biochemical presence of ester or amine cellular components. Addition of amyl acetate to the reaction mixture increased the anti-oxidant reactivity of manganese(II)-(3,5-DIPS)2 while decreasing its pro-oxidant reactivity. The weaker anti-oxidant reactivites of iron(III)(3,5-DIPS)3 and copper(II)2(3,5-DIPS)4 were less affected by the addition of amyl acetate and the pro-oxidant reactivity of copper(II)2(3,5-DIPS)4 was not changed by the addition of amyl acetate, while the pro-oxidant property of iron(III)(3,5-DIPS)3 was eliminated. In contrast to 2,6-di-t-butyl-4-methylphenol, butylated hydroxy toluene (BHT), anti-oxidant reactivities of copper(II), iron(III), and manganese(II) 3,5-DIPS chelates were dramatically enhanced by the addition of n-Pr2NH to the reaction mixture. It is concluded that all three metalloelement chelates react with and remove alkylbenzeneperoxyl radicals and the hydroperoxyl radical. The manganese(II)-(3,5-DIPS)2 and copper(II)2(3,5-DIPS)4 chelates may also be useful in removing hydroperoxides in vivo. These reactivities, in addition to their established superoxide dismutase (SOD)-mimetic and catalase-mimetic reactivities, are suggested to possibly permit anti-oxidant and pro-oxidant reactivities in aqueous and organic cellular compartments. 相似文献
950.
M. B. Alamin A. A. Mhapes A. M. Bejey A. Sadek R. H. Atweer K. Dubali Daw M. Saad 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(1):247-250
Since there is no database in Libya defining the intake of the individuals from different essential (minor and trace) and
toxic elements provided through food, drinking water and aerosol, a project has been proposed with the cooperation of IAEA
to determine the concentration of a number of elements such as Cs, Fe, Cr, Rb, Sc, Se, Co, Zn in the three mentioned sources.
Emphasis was placed on the use of nuclear and nuclear-related techniques. In this paper, the primary results are presented
for the concentration of minor and trace elements in some vegetables, spices and other foods which are widely used in the
Libyan meals. Instrumental neutron activation analysis utilizing a 10 MW water pool reactor and a γ-ray spectroscopy facility
was employed. For quality control, certified reference materials were analyzed simultaneosly with the samples which show good
agreements compared with the certified data. Emphasis was given to both elements iron and zinc for their importance. 相似文献