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251.
I. C. McNeill M. Zulfiqar 《Journal of polymer science. Part A, Polymer chemistry》1978,16(12):3201-3212
The polymers of lithium, sodium, potassium, and caesium salts of methacrylic acid have been prepared by free radical polymerization of the respective monomers in methanol solution. The degradation behavior of the polymers has been investigated by thermal volatilization analysis, thermogravimetry, and product analysis. These materials are stable to about 350°C under programmed heating at 10°C/min in vacuo. The principal degradation products are monomer, the corresponding isobutyrate, carbonate, oxide, carbon dioxide, and a fraction of liquid volatiles that is complex and contains a variety of aldehydes and ketones. The mechanism of degradation is discussed in detail. 相似文献
252.
Saatchi K Thompson KH Patrick BO Pink M Yuen VG McNeill JH Orvig C 《Inorganic chemistry》2005,44(8):2689-2697
Syntheses of vanadium complexes using the naturally occurring ligands isomaltol (Hima) and allomaltol (Hama), as well as a newly synthesized, potentially tetradentate diaminodipyrone [H(2)(en(ama)(2)], are reported. Complete characterization of the resulting compounds [trans-VO(ima)(2)(H(2)O), VO(ama)(2), V(ima)(3), V(ama)(3) and VO(en(ama)(2))], including X-ray crystallography analyses for trans-VO(ima)(2)(H(2)O) and V(ima)(3), are presented herein. Potentiometric titrations (25 degrees C, I = 0.16 M NaCl) were used to measure stability constants in the V(IV)-Hima system; these data were compared to previous data collected on the V(IV)-L (L = Hma, Hama) systems. The in vivo efficacy of these compounds to lower the blood glucose levels of STZ-diabetic rats was tested; all but VO(en(ama)(2)) produced significant decreases in plasma glucose levels. The results were compared to those of the benchmark compound BMOV [VO(ma)(2), bis(maltolato)oxovanadium(IV)], a known insulin-enhancing agent. 相似文献
253.
Three series of copolymers, each spanning the composition range from alkali metal methacrylate homopolymer to methyl methacrylate homopolymer, have been prepared; their degradations have been studied under programmed heating conditions, by means of simultaneous thermogravimetry and thermal volatilization analysis (TVA) in a vacuum system and by differential thermal analysis in dynamic nitrogen. Total volatile products have been characterised by infrared spectroscopy, subambient TVA and GLC. The thermal analysis data suggest that the two types of monomer unit tend to participate in degradation processes in different temperature ranges. However, in addition to those products characteristic of the degradation of each homopolymer, the copolymers give substantial amounts of methanol; this product must arise from a reaction specific to the copolymer structure. 相似文献
254.
Monga V Thompson KH Yuen VG Sharma V Patrick BO McNeill JH Orvig C 《Inorganic chemistry》2005,44(8):2678-2688
Four mixed O,S binding bidentate ligand precursors derived from maltol (3-hydroxy-2-methyl-4-pyrone) have been chelated to vanadium to yield new bis(ligand)oxovanadium(IV) and tris(ligand)vanadium(III) complexes. The four ligand precursors include two pyranthiones, 3-hydroxy-2-methyl-4-pyranthione, commonly known as thiomaltol (Htma), and 2-ethyl-3-hydroxy-4-pyranthione, commonly known as ethylthiomaltol (Hetma), as well as two pyridinethiones, 3-hydroxy-2-methyl-4(H)-pyridinethione (Hmppt) and 3-hydroxy-1,2-dimethyl-4-pyridinethione (Hdppt). Vanadium complex formation was confirmed by elemental analysis, mass spectrometry, and IR and EPR (where possible) spectroscopies. The X-ray structure of oxobis(thiomaltolato)vanadium(IV),VO(tma)(2), was also determined; both cis and trans isomers were isolated in the same asymmetric unit. In both isomers, the two thiomaltolato ligands are arranged around the base of the square pyramid with the V=O linkage perpendicular; the vanadium atom is slightly displaced from the basal plane [V(1) = 0.656(3) A, V(2) = 0.664(2) A]. All of the new complexes were screened for insulin-enhancing effectiveness in streptozotocin-induced diabetes in rats, and VO(tma)(2) was profiled metabolically for urinary vanadium and ligand clearance by GFAAS and ESIMS, respectively. The new vanadium complexes did not lower blood glucose levels acutely, possibly because of rapid dissociation and excretion. 相似文献
255.
Curve fitting using a genetic algorithm for the X-ray fluorescence measurement of lead in bone 总被引:2,自引:0,他引:2
L. Luo D. R. Chettle H. Nie F. E. McNeill M. Popovic 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):325-329
Summary We investigated the potential application of the genetic algorithm in the analysis of X-ray fluorescence spectra from measurement
of lead in bone. Candidate solutions are first designed based on the field knowledge and the whole operation, evaluation,
selection, crossover and mutation, is then repeated until a given convergence criterion is met. An average-parameters based
genetic algorithm is suggested to improve the fitting precision and accuracy. Relative standard deviation (RSD%) of fitting
amplitude, peak position and width is 1.3-7.1, 0.009-0.14 and 1.4-3.3, separately. The genetic algorithm was shown to make
a good resolution and fitting of K lines of Pb and g elastic peaks. 相似文献
256.
A. Jamieson I. C. McNeill 《Journal of polymer science. Part A, Polymer chemistry》1978,16(9):2225-2235
The degradation behavior of silver acetate—PMMA blends at salt/polymer ratios of 1:1, 1:5, and 1:10 has been studied by using thermal volatilization analysis (TVA) as the principal technique. Degradation of the salt has also been examined; it gives a variety of products best explained by a series of reactions resulting from an initial cleavage of CH3COO. radicals and silver atoms. Silver acetate, when present with PMMA during degradation, results in a severe destabilization of the polymer, which breaks down to monomer at a high rate at temperatures as low as 200°C. This effect is explained by diffusion of radicals from silver acetate decomposition into the polymer phase, in which they initiate chain scission and depolymerization. 相似文献
257.
Dean P. Phillips Bao Nguyen Thomas L. Lau Matthew H. McNeill Jackline E. Dalgard Jyun-Hung Chen Richard J. Penuliar Todd A. Miller Lin Zhi 《Tetrahedron letters》2006,47(40):7137-7138
The coupling of aryl bromides or iodides with oxindoles using a copper iodide-N,N′-dimethylethylene diamine system is presented. The reaction proceeds efficiently and tolerates a variety of substitution patterns. 相似文献
258.
S. H. Byun A. Pejović-Milić W. V. Prestwich D. R. Chettle F. E. McNeill 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(3):615-618
Summary Manganese contents in hand phantoms were analyzed by in vivo neutron activation analysis using a 4p NaI(Tl) detector array.
Solution-type phantoms with varying amount of Mn and fixed amounts of physiological normal elements (Na, Cl, Ca) were prepared
in a cylindrical shape to simulate fisted hands and were irradiated with the 7Li(p,n) neutron beam. The proton energy and polyethlyene cavity were set at optimized conditions established before. The g-ray
spectra were accumulated under the anticoincidence mode. The calibration was done both for the 847 keV full-energy peak area
and for the total area of 56Mn, which is defined as the total number of counts anywhere in the g-ray spectrum from 56Mn. From the analysis of the 847 keV peak, the Mn detection limit has been improved by a factor of 1.6 compared to the previous
feasibility test thanks to a significant gain in the g-ray detection efficiency. Further improvement by a factor of 1.2 was
identified when the total area of 56Mn was used for the calibration. The final sensitivity and detection limit for a 20 mSv hand dose reached 12,050 counts/mg
Mn, and 86 mg, respectively. The overall improvement achieved in this study will be a considerable contribution toward realization
of the clinical application. 相似文献
259.
Polyisobutene was chlorinated in carbon tetrachloride solution at 60°C. with radiochlorine, and the degree of chlorination was determined radiochemically. The extent of chlorination was varied by using a wide range of chlorine/polyisobutene ratios in the reaction mixture. The products were examined by PMR spectroscopy, which showed that both methyl and methylene groups were chlorinated but that the methylene hydrogens were more readily substituted and some disubstitution of the methylene groups occurred. The effect of chlorination on the thermal stability compared to the original polymer was studied by the new technique of thermal volatilization analysis. All the chlorinated derivatives were found to degrade at lower temperatures than polyisobutene. The stability dropped progressively as the chlorine content was increased to one chlorine atom per isobutene unit and then showed less change with further increase in chlorine content. 相似文献
260.
David L. VanderHart Vivek M. Prabhu Kristopher A. Lavery Cindi L. Dennis Ashwin B. Rao Eric K. Lin 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,201(1):100-110
Solid-state proton nuclear magnetic resonance (NMR) measurements are performed successfully on polymer blend thin films through the use of synthetic mica as a substrate. When used as a substrate, synthetic fluorophlogopite mica with its proton-free, diamagnetic character, allows for adequate measurement sensitivity while minimally perturbing the proton thin-film spectra, especially relative to more commonly available natural micas. Specifically, we use multiple-pulse techniques in the presence of magic-angle spinning to measure the degree of mixing in two different polymer blend thin films, polystyrene/poly(xylylene ether) and poly(1-methyladamantyl methacrylate) (PMAdMA)/triphenylsulfonium perfluorobutanesulfonate (TPS-PFBS), spin-coated onto mica substrates. Our earlier studies had focused on bulk systems where NMR signals are stronger, but may not be representative of thin films of the same systems that are relevant to many applications such as photoresist formulations in the electronics industry. The superiority of synthetic over natural paramagnetic mica is demonstrated by the maintenance of resolution and spinning sideband intensities (relative to bulk samples) for the synthetic mica samples. In contrast, degraded resolution and large spinning sidebands are shown to typify spectra of the natural mica samples. This approach can be applied to many other proton measurements of solid thin films, thereby greatly extending the types of systems to be investigated. Magnetic susceptibility measurements are also reported for all micas used. 相似文献