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101.
Dyes and pigments are extensively used in polymer materials to confer colour-changing properties. However, these additives can significantly affect polymer stability against degradation. While the mechanism of stabilization of polymers by some pigments, such as carbon black, has been studied and is well known, the action of chromatic colorants, mainly in the sensitization of the degradation process, remains unclear. Cu-phthalocyanine dye can stabilize polymers against degradation as well as accelerate degradation in other situations. Cu-phthalocyanine incorporated into polycarbonate resulted in an acceleration of the degradation when the material was submitted to photochemical aging. The possible mechanism to explain the photodegradative behavior of PC containing Cu-phthalocyanine is based on the hypothesis that specific interactions among excited states of PC and Cu-phthalocyanine take place and enhance the formation of reactive species in polycarbonate. Excited states of Cu-phthalocyanine may abstract hydrogen atoms from methyl groups in polycarbonate, increasing the formation of free radicals P, which are the starting points for the sequential photo-oxidation reactions that lead to the degradation of the polycarbonate. Electron transfer sensitization is also a possible mechanism: the excited state of Cu-Ph abstracts an electron from PC to form the Cu-Ph radical anion and the PC radical cation. These reactive species in the presence of oxygen can cause oxidation of the aromatic ring. 相似文献
102.
Danieli B Giardini A Lesma G Passarella D Peretto B Sacchetti A Silvani A Pratesi G Zunino F 《The Journal of organic chemistry》2006,71(7):2848-2853
A dynamic combinatorial library of thiocolchicine-podophyllotoxin derivatives based on the disulfide bond exchange reaction is described. The influence of a biological target on the composition of the reaction mixture has been demonstrated. Use of high-resolution ESI mass spectrometry to evaluate the composition of the mixture shows promise for the design of new large libraries. The biological evaluation demonstrates that formation of a divalent compound affords a new chemical entity whose biological activity is not merely the sum of the single ligands activities, thus reflecting a different interaction with the biological target. 相似文献
103.
The ability to separate nitroaromatic and nitramine explosives in seawater sample matrices is demonstrated using both MEKC and CEC. While several capillary-based separations exist for explosives, none address direct sampling from seawater, a sample matrix of particular interest in the detection of undersea mines. Direct comparisons are made between MEKC and CEC in terms of sensitivity and separation efficiency for the analysis of 14 explosives and explosive degradation products in seawater and diluted seawater. The use of high-salt stacking with MEKC results, on average, in a three-fold increase in the number of theoretical plates, and nearly double resolution for samples prepared in 25% seawater. By taking advantage of long injection times in conjunction with stacking, detection limits down to sub mg/L levels are attainable; however, resolution is sacrificed. CEC of explosive mixtures using sol-gels prepared from methyltrimethoxysilane does not perform as well as MEKC in terms of resolving power, but does permit extended injection times for concentrating analyte onto the head of the separation column with little or no subsequent loss in resolution. Electrokinetic injections of 8 min at high voltage allow for detection limits of explosives below 100 microg/L. 相似文献
104.
G. Asher Newsome F. Lucus Steinkamp Braden C. Giordano 《Journal of the American Society for Mass Spectrometry》2016,27(11):1789-1795
As a reagent gas for positive- and negative-mode chemical ionization mass spectrometry (CI-MS), isobutane (i-C4H10) produces superior analyte signal abundance to methane. Isobutane has never been widely adopted for CI-MS because it fouls the ion source more rapidly and produces positive CI spectra that are more strongly dependent on reagent gas pressure compared with methane. Isobutane was diluted to various concentrations in argon for use as a reagent gas with an unmodified commercial gas chromatograph-mass spectrometer. Analyte spectra were directly compared using methane, isobutane, and isobutane/argon mixtures. A mixture of 10% i-C4H10 in argon produced twice the positive-mode analyte signal of methane, equal to pure isobutane, and reduced spectral dependence on reagent gas pressure. Electron capture negative chemical ionization using 1% i-C4H10 in argon tripled analyte signal compared with methane and was reproducible, unlike pure isobutane. The operative lifetime of the ion source using isobutane/argon mixtures was extended exponentially compared with pure isobutane, producing stable and reproducible CI signal throughout. By diluting the reagent gas in an inert buffer gas, isobutane CI-MS experiments were made as practical to use as methane CI-MS experiments but with superior analytical performance. 相似文献
105.
X Yi K Bernot F Pointillart G Poneti G Calvez C Daiguebonne O Guillou R Sessoli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(36):11379-11387
The reaction of [Ln(hfac)(3) ]?2?H(2) O and pyridine-N-oxide (PyNO) leads to isostructural dimers of the formula [Ln(hfac)(3) (PyNO)](2) (Ln=Eu, Gd, Tb, Dy). The Dy derivative shows a remarkable single-molecule magnet behavior with complex hysteresis at 1.4?K. The dynamics of the magnetization features are two relaxation regimes: a thermally activated one at high temperature (τ(0) =(5.62±0.4)×10(-11) s and Δ=(167±1)?K) and a quantum tunneling regime at low temperature with a tunneling frequency of 0.42?Hz. The analysis of the Gd derivative evidences intradimer antiferromagnetic interactions (J=(-0.034±0.001)?cm(-1) ). Moreover, the Eu, Tb, and Dy derivatives are luminescent with quantum yield of 51, 53, and 0.1?%, respectively. The thermal investigation of [Dy(hfac)(3) (PyNO)](2) shows that the dimers can be sublimated intact, suggesting their possible exploit as active materials for surface-confined nanostructures to be investigated by fluorimetry methods. 相似文献
106.
107.
Gonçalves Luciana R. B. Suzuki Glória S. Giordano Roberto C. Giordano Raquel L. C. 《Applied biochemistry and biotechnology》2001,91(1-9):691-702
Applied Biochemistry and Biotechnology - Kinetic and mass transport parameters were estimated for maltotriose hydrolysis using glucoamylase immobilized on macroporous silica and wrapped in pectin... 相似文献
108.
Giordano Raquel L. C. Hirano Paulo C. Gonçalves Luciana R. B. Netto Willibaldo Schmidell 《Applied biochemistry and biotechnology》2000,84(1-9):643-654
This article presents a detailed study on the conditions for achieving a stable biocatalyst to be used in the production of
ethanol from starch. Different pellets were used depending on which characteristic of the biocatalyst was being studied: (a)
Saccharomyces cerevisiae entrapped in pectin or calcium alginate gel particles; (b) silica containing immobilized glucoamylase entrapped in pectin
gel particles; or (c) pectin gel particles, with the silicaenzyme derivative and yeast coimmobilized. The influence of several
variables on the mechanical resistance of the particle, on the viability of the microorganism, and on the rate of substrate
hydrolysis was studied with biocatalyst. The best conditions found were 6% pectin gel, 2-mm particle diameter, and curein
0.2 M CaCl2·2H2O/60 mM acetate buffer, pH 4.2, for gel preparation; and 6.0 g/L of CaCl2·2H2O in the fermentation medium. Biocatalyst (c) was successfully tested for the production of ethanol from liquefield manioc
flour syrup. 相似文献
109.
Stefano Curcio Domenico Gabriele Vincenzo Giordano Vincenza Calabrò Bruno de Cindio Gabriele Iorio 《Rheologica Acta》2001,40(2):154-161
The aim of the present work is to analyze the complex phenomena involved in the concentrated milk clotting process in order
to define general criteria applicable to the design of a continuous coagulator. A full characterization of the rheological
properties of completely hydrolyzed milk as a function of two different parameters, i.e., the coagulator temperature and the
concentration degree of the milk, is presented. The dynamic evolution of loss, G′′, and storage, G′, moduli has been obtained
at different frequency values and for different concentration degrees during the clotting process. Time cure tests have been
performed on completely hydrolyzed milk samples showing that the rate of curing is very high and that the time for rheological
experiments is much too short for testing Winter's theory of gelation. To overcome this problem, the intersect of loss and
storage moduli was used for estimating the coagulation. Coagulation is faster when higher temperatures are used and the consistency
of the final curd is greater if a more concentrated milk is used. A tentative physical explanation based on the network theories
is presented. If an observation time far enough from the crossover point is chosen it can be seen that the curd strength estimated
at 40 °C is about 50 times higher than that one evaluated at 25 °C. Among the considered temperatures, a good processing value
was evaluated at 40 °C.
Received: 6 February 2000 Accepted: 24 October 2000 相似文献
110.
Dr. Vincent Maurice Dr. Guylhaine Clavel Prof. Markus Antonietti Dr. Cristina Giordano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11624-11630
Porous TiNxOy‐based particles were synthesized by an aerosol spray process. At first, the starting sol solution containing the metal precursor and the nitrogen source is sprayed to form an aerosol that is subsequently pyrolysed at different temperatures. The obtained dried particles are an amorphous coordination “polymer” rich in carbon and nitrogen. These “glassy” particles are finally thermally treated at 800 °C, promoting the crystallization of the particles and the release of a major part of the carbon. As the particles keep their original shape, carbon loss and density increase during the crystallization step and lead to the development of an accessible pore structure. The process was analyzed and extended to the synthesis of other metal nitrides, such as VN and W2N, thereby showing its general validity for the production of functional nanocrystalline nitride ceramics with high porosity still occupying a relatively small volume, and otherwise not easily accessible. 相似文献