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61.
An effective algorithm for estimating the reliability of frame structures made of an elastic perfectly plastic material is presented. It is assumed that the structure is working in uniaxial state of stress, the material parameters and the limit values of the loads are described by random variables, all loads are acting in a static manner, the probability density functions of all random variables, which describe the structure and loads are known. As the structure reliability measure the probability of failure and corresponding reliability index are regarded. The dead (constant) load and the climatic loads are taken into account. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
62.
In this work the results of DC conductivity measurements of polycrystalline p-sexiphenyl thin films are presented. The investigations concerned the effect of temperature, film thickness and electric field on the DC conductivity mechanism. The thickness of the investigated material varied from 0.2 to 2.5 μm. The measurements were carried out for different electrode polarities of the 0 -100 V voltage and at temperatures ranging from 15 to 325 K. Thin films of p-sexiphenyl were obtained by controlled vacuum sublimation on BK-7 glass substrate with gold and aluminium electrodes. Analyzing the obtained results we conclude that injection of the charge carrier from electrodes into the investigated material proceeds by thermionic emission and field emission and it is dependent on temperature and external electric field. The charge carrier transport is controlled by localized states (traps) in the forbidden energy gap. The activation energy calculated from formula ln I = f(1/kT) varied from kT for low temperature up to 1.0 eV. 相似文献
63.
Julia Pretula Krzysztof Kaluzynski Jan Libiszowski Ryszard Szymanski Stanislaw Penczek 《Journal of polymer science. Part A, Polymer chemistry》1997,35(9):1733-1742
Copolymers of 7-oxabicyclo[2.2.1] heptane (B) (and of its 2-methyl derivatives) with 1,3-dioxane (D) were obtained by cationic copolymerization initiated with benzoylium hexafluoroantimonate. Structure of copolymers was determined by 1H- and 13C-NMR. The proportion of the acetal bonds in copolymers was additionally confirmed in studies of the products of hydrolysis (only the acetal bonds hydrolyze). D is unable to homopolymerize for the thermodynamic reasons and therefore mostly pseudoperiodic copolymers (-DBx-)y are formed. Nevertheless, the reshuffling reactions are responsible for the appearance of “wrong” units. These are: the separate oxymethylene and oxy-1,3-propylene units (P, subunits of D) located between two B units. Only the acetal bonds are cleaved in the acidic hydrolysis with dilute HCl. This gives the promesogenic telechelic oligomers of mostly HO-P-Bx-OH structure. This article is the first to describe successful cationic copolymerization of a cyclic acetal with a cyclic ether. Moreover, the inability of D to homopolymerize gives the thermodynamic basis of the pseudoperiodic copolymer formation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1733–1742, 1997 相似文献
64.
Stanislaw Slomkowski Mariusz Gadzinowski Stanislaw Sosnowski 《Macromolecular Symposia》1998,132(1):451-462
Pseudoanionic and anionic polymerizations of ε-caprolactone and lactides in 1,4-dioxane:heptane mixtures containing poly(dodecyl acrylate)-g-poly(ε-caprolactone) yield polyesters in form of microspheres. Monitoring partition of active centers between solution and microspheres revealed that particles are formed during initial period, when macromolecules reach their critical masses (ca. 1 000) and became insoluble. Then, propagation proceeds inside of microspheres into which monomer diffuses from solution. Monitoring of variation of the number of particles in a unit volume of reaction mixture with time indicated that after a primary nucleation the delayed nucleation and aggregation are absent. In effect, microspheres with narrow diameter distribution are obtained. Kinetic measurements revealed that in the dispersion pseudoanionic (initiator (CH3CH2)2AlOCH2CH3) and anionic (initiator (CH3)3SiONa) polymerizations of ε-caprolactone the overall rates of monomer conversion are from 10 to 30 times higher than for the corresponding polymerizations in solution (THF solvent). Analysis of kinetic equations indicated that the observed faster monomer conversions in polymerizations in dispersed systems are due to the high local concentrations of active centers and monomer in growing microspheres. 相似文献
65.
Jolanta Baran Andrzej Duda Adam Kowalski Ryszard Szymanski Stanislaw Penczek 《Macromolecular Symposia》1997,123(1):93-101
Chain transfer processes (ktr) taking place in the polymerization (anionic and pseudoanionic) of cyclic esters (lactones) are reviewed. These reactions are mostly responsible for the departure of these systems from the fully controlled (living) polymerizations. The ratios of kp/ktr have been determined for a number of initiating systems and the structures of the growing species are related to their selectivity, expressed by kp/ktr. It has been shown that the less reactive and more sterically crowded active species polymerize more selectively. 相似文献
66.
Melania Bednarek Tadeusz Biedron Jan Helinski Krzysztof Kaluzynski Przemysaw Kubisa Stanislaw Penczek 《Macromolecular rapid communications》1999,20(7):369-372
Cationic polymerization of 3-ethyl-3-hydroxymethyloxetane gives branched, soluble macromolecules with multiple glycolic end groups. There are approximately 3–4 “normal” units per one branched unit. 相似文献
67.
Emil Pop Stanislaw Rachwal Marcus E. Brewster 《International journal of quantum chemistry》1996,60(8):1829-1834
The allylic rearrangement of trans-pinocarveol esters ( I ) to myrtenol esters ( II ), a reaction of interest in the chemistry of terpenes and cannabinoids, has been theoretically investigated. The intramolecular, cyclization-induced rearrangement results in equilibrium mixtures of the starting compounds and the products with the ratio of I vs. II in the equilibrium mixture being determined by their thermodynamic stabilities. The relative thermodynamic stabilities as reflected by calculated AM1 heats of formations (ΔHf) were determined for various I-II ester pairs. The study, in agreement with available experimental evidence, indicates that generally I , which contain an endocyclic double bond, are more stable and thus predominantly form following rearrangements. In two cases (acetate and pivalate) the stability is reversed. Calculations performed for similar structures, esters of 2-methylene cyclohexane-1-ol ( IV ) and 1-cyclohexene-1-methanol ( V ) gave similar results. Structural and electronic factors which might influence the stability of these compounds were examined. Interestingly, a correlation between thermodynamic stability and dipole moments was observed. © 1996 John Wiley & Sons, Inc. 相似文献
68.
Summary: Synthesis, characteristics and medical diagnostic application of core-shell poly(styrene/α-tert-butoxy-ω-(vinylbenzyl)polyglycidol) (P(S/PGL)) microspheres are described. The particles were prepared by soap-free emulsion polymerization of styrene and α-tert-butoxy-ω-(vinylbenzyl)polyglycidol macromonomer (PGL) initiated with potassium persulfate. The polymerization in water yielded microspheres with diameters in the range from 220 to 650 nm, depending on concentration of the macromonomer. Polydispersity was usually below 1.06. The fraction of PGL in interfacial layer of microspheres ranged from 0 to 42 mol.% (estimated by XPS). Microspheres suspended in NaCl solutions manifested fully reversible swelling-deswelling properties of their interfacial layer with characteristic transition temperature (Tt) slightly dependent on NaCl concentration. The adsorption of human serum albumin on the surface of P(S/PGL) microspheres was highly reduced when the PGL surface fraction exceeded 40 mol.%. P(S/PGL) microspheres with immobilized antigens Helicobacter pylori were used for detection of antibodies against. The test was based on monitoring differences in electrophoretic mobility of P(S/PGL) microspheres covalently bound H. pylori antigens and antibodies against H. pylori in blood serum. 相似文献
69.
Krouse HR Parafiniuk J Nowak J Halas S 《Isotopes in environmental and health studies》2006,42(4):327-333
A slice of black shale rock cut by various metal sulphide veins of different generations from the Kupferschiefer deposits of Lubin, Poland was subjected to bombardment in a Laser Microprobe Combustion Reactor to produce SO2 for S-isotope analyses. The delta34S values ranged from-22 to-29 per thousand consistent with previous findings using conventional IRMS and attributable to primary generation of H2S by bacterial sulphate reduction. Systematic trends in delta34S values of a few per mil over distances of the order of mm attest to low temperatures of mineralization with accompanying change in the isotope composition of the fluids due to kinetic or equilibrium isotope fractionation. 相似文献
70.