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排序方式: 共有140条查询结果,搜索用时 15 毫秒
1.
Abstract 1,1′-Dihydroxyethyl-2,2′-biimidazole has been used as a copolymerizing monomer with the diglycidyl ether of bisphenol A in the preparation of biimidazole-containing epoxy polymers. Polymerization reactions were studied in bulk, with and without catalyst, and in N,N-dimethylforma-mide and anisole solvents, with and without catalyst. FT-IR and NMR spectra, molecular weight, thermal and solubility characteristics were obtained. Polymers isolated as amorphous light brown solids were found to be only sparingly soluble in THF or in highly polar nitrogen-containing solvents (DMF, NMP, pyridine). These materials exhibited molecular weights up to 37 000 for SnC14-catalyzed polymerization carried out in DMF. A glass-transition temperature of 391°C was observed for polymers obtained under uncatalyzed solventless conditions. The glass transition temperature was 373°C for product obtained under SnC14-catalyzed, solventless conditions. Thermogravimetric analysis in air of polymers obtained under varying solvent and catalyst conditions showed less than 25% weight loss below 330°C and greater than 75% weight loss above 400°C. 相似文献
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3.
Saeed KA Ayorinde FO Eribo BE Gordon M Collier L 《Journal of AOAC International》2001,84(4):1109-1115
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used for the characterization of a partially transesterified poly(beta-hydroxyalkanoate) (PHA), a polymer produced by the bacterial strain Alcaligenes eutrophus with saponified vegetable oils as the sole carbon sources. The transesterification was carried out separately under acidic and basic conditions to obtain PHA oligomers weighing <10 kDa. The intact oligomers were detected in their cationized forms, [M + Na]+ and [M + K]+, by MALDI-TOFMS. A composition analysis, using the MALDI-TOF spectra, indicated that the oligomers obtained via acid catalysis contained a methyl 3-hydroxybutyrate end group, and those obtained by base catalysis had a methyl crotonate (olefinic) end group. In addition to hydroxybutyrate (HB), the oligomers were found to contain a small percentage of hydroxyvalerate, which was independently confirmed by gas chromatography/mass spectrometry. In comparison, analysis of a commercial PHA polymer, transesterified under identical conditions, showed only the presence of HB, i.e., a pure poly(HB) homopolymer. 相似文献
4.
Amber L. H. Gray Aleksandra Antevska Benjamin A. Link Bryan Bogin Susan J. Burke Samuel D. Dupuy J. Jason Collier Zachary A. Levine Michael D. Karlstad Thanh D. Do 《Chemical science》2021,12(16):5853
Despite being relatively benign and not an indicative signature of toxicity, fibril formation and fibrillar structures continue to be key factors in assessing the structure–function relationship in protein aggregation diseases. The inability to capture molecular cross-talk among key players at the tissue level before fibril formation greatly accounts for the missing link toward the development of an efficacious therapeutic intervention for Type II diabetes mellitus (T2DM). We show that human α-calcitonin gene-related peptide (α-CGRP) remodeled amylin fibrillization. Furthermore, while CGRP and/or amylin monomers reduce the secretion of both mouse Ins1 and Ins2 proteins, CGRP oligomers have a reverse effect on Ins1. Genetically reduced Ins2, the orthologous version of human insulin, has been shown to enhance insulin sensitivity and extend the life-span in old female mice. Beyond the mechanistic insights, our data suggest that CGRP regulates insulin secretion and lowers the risk of T2DM. Our result rationalizes how migraine might be protective against T2DM. We envision the new paradigm of CGRP : amylin interactions as a pivotal aspect for T2DM diagnostics and therapeutics. Maintaining a low level of amylin while increasing the level of CGRP could become a viable approach toward T2DM prevention and treatment.CGRP concentration is elevated in migraine conditions. The protective effect of migraine against type 2 diabetes is attributed to the ability of CGRP to remodel human amylin aggregation and to suppress the secretion of mouse insulin 2 (the orthologue of human insulin). 相似文献
5.
Substituted 1,1′-diester, diketone and dinitrile derivatives are prepared from 2,2′-biimidazole. The reactions involved include: Michael addition with halogenated olefins; nucleophilic substitution with ketones, nitriles, and esters; and condensation with amines. 相似文献
6.
Maysa Faisal Suyagh Godwill Iheagwaram Prashant Laxman Kole Jeff Millership Paul Collier Henry Halliday James C. McElnay 《Analytical and bioanalytical chemistry》2010,397(2):687-693
A selective and sensitive high-performance liquid chromatography method with UV detection for the determination of metronidazole in dried blood spots (DBS) has been developed and validated. DBS samples [spiked or patient samples] were prepared by applying blood (30 µL) to Guthrie cards. Discs (6 mm diameter) were punched from the cards and extracted using water containing the internal standard, tinidazole. The extracted sample was chromatographed without further treatment using a reversed phase system involving a Symmetry® C18 (5 µm, 3.9?×?150 mm) preceded by a Symmetry® guard column of matching chemistry and a detection wavelength of 317 nm. The mobile phase comprised acetonitrile/0.01?M phosphate solution (KH2PO4), pH 4.7, 15:85, v/v, with a flow rate of 1 mL/min. The calibration was linear over the range 2.5–50 mg/mL. The limits of detection and quantification were 0.6 and 1.8 µg/mL, respectively. The method has been applied to the determination of 203 DBS samples from neonatal patients for a phamacokinetic/pharmacodynamic study. 相似文献
7.
Investigating microfluidic flow profiles is of interest in the microfluidics field for the determination of various characteristics of a lab-on-a-chip system. Microparticle tracking velocimetry uses computational methods upon recording video footage of microfluidic flow to ultimately visualize motion within a microfluidic system across all frames of a video. Current methods are computationally expensive or require extensive instrumentation. A computational method suited to microparticle tracking applications is the robust Kanade–Lucas–Tomasi (KLT) feature-tracking algorithm. This work explores a microparticle tracking velocimetry program using the KLT feature-tracking algorithm. The developed program is demonstrated using pressure-driven and EOF and compared with the respective mathematical fluid flow models. An electrostatics analysis of EOF conditions is performed in the development of the mathematical using a Poisson's Equation solver. This analysis is used to quantify the zeta potential of the electroosmotic system. Overall, the KLT feature-tracking algorithm presented in this work proved to be highly reliable and computationally efficient for investigations of pressure-driven and EOF in a microfluidic system. 相似文献
8.
T.D. Klots P. Devlin W.B. Collier 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2445-2456
Infrared and Raman measurements for benzimidazole are presented and discussed, including its argon-matrix infrared spectrum. To assist in the assignment, benzimidazole's harmonic force fields for the 321G* and 631G* levels were scaled by scaled factors derived by fitting the respective computed force fields of other indene derivatives to previously reported experimental vibrational frequencies. Comparison to the best set of experimental wavenumbers, usually taken from the matrix, shows mean 321G* and 631G* deviations of 7.0 and 5.8 cm−1 for the planar modes, and 14.0 and 6.8 cm−1 for the nonplanar modes, respectively, with much of the error residing in imino-hydrogen group modes. Standard entropies are derived with the matrix wavenumbers and the methods of statistical mechanics. An attempt to determine standard entropies by calorimetric methods was unsuccessful. The triple-point temperature Ttp and enthalpy of fusion Δ1crHm only are reported. 相似文献
9.
Walton B Najmudin Z Wei MS Marle C Kingham RJ Krushelnick K Dangor AE Clarke RJ Poulter MJ Hernandez-Gomez C Hawkes S Neely D Collier JL Danson CN Fritzler S Malka V 《Optics letters》2002,27(24):2203-2205
A short-pulse laser beat wave scheme for advanced particle accelerator applications is examined. A short, intense (3-ps, >10(18)-W cm(-2)) two-frequency laser pulse is produced by use of a modified chirped-pulse amplification scheme and is shown to produce relativistic plasma waves during interactions with low-density plasmas. The generation of plasma waves was observed by measurement of forward Raman scattering. Resonance was found to occur at an electron density many times that expected, owing to ponderomotive displacement of plasma within the focal region. 相似文献
10.
In this paper a new, computer approach to the study of the interactions of particles with differing masses is applied to the study of planetary type evolution. The formulation contains an inherent self-reorganization property in which particles self-stratify in accordance with their masses. Computer examples are described and discussed. 相似文献