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41.
Daly SR Klaehn JR Boland KS Kozimor SA MacInnes MM Peterman DR Scott BL 《Dalton transactions (Cambridge, England : 2003)》2012,41(7):2163-2175
Synthetic routes to alkyl and aryl substituted dithiophosphinate salts that contain non-coordinating PPh(4)(+) counter cations are reported. In general, these compounds can be prepared via a multi-step procedure that starts with reacting secondary phosphines, i.e. HPR(2), with two equivalents of elemental S. The synthetic transformation proceeds by oxidation of the phosphine followed by insertion of S into the H-P bond. This approach was used to synthesize a series of dithiophosphinic acids that were fully characterized, namely HS(2)P(p-CF(3)C(6)H(4))(2), HS(2)P(m-CF(3)C(6)H(4))(2), HS(2)P(o-MeC(6)H(4))(2) and HS(2)P(o-MeOC(6)H(4))(2). Although the insertion step was found to be much slower than the oxidation reaction, the formation of (NH(4))S(2)PR(2) from HPSR(2) occurred rapidly upon addition of NH(4)OH. Subsequent cation exchange reactions proceeded readily with PPh(4)Cl in water, under air and at ambient conditions to provide analytically pure samples of [PPh(4)][S(2)PR(2)] (R = p-CF(3)C(6)H(4), m-CF(3)C(6)H(4), o-CF(3)C(6)H(4), o-MeC(6)H(4), o-MeOC(6)H(4), Ph, and Me, 1b-7b, respectively), which were characterized by elemental analysis, multinuclear NMR, and IR spectroscopy. In addition, S(2)PPh(2)(-) and dithiophosphinates with ortho-substituted aryl groups (3b-6b) were characterized by X-ray crystallography. As opposed to the acids, which have short P=S double bonds and long P-SH single bonds, the metric parameters for the S atoms in S(2)PR(2)(-) are equivalent. In addition, the presence of large non-coordinating PPh(4)(+) cations guard against intermolecular P-S···X interactions and ensure that the P-S bond is isolated. These S(2)PR(2)(-) anions, which can be prepared in large quantities and isolated in crystalline form, are attractive for spectroscopic and theoretical studies because the P-S interaction can be probed independently in the absence of intermolecular interactions. 相似文献
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43.
Molly H. Fisher David Royster 《International Journal of Mathematical Education in Science & Technology》2016,47(7):993-1008
As part of a larger study, four mathematics teachers from diverse backgrounds and teaching situations report their ideas on teacher stress, mathematics teacher retention, and their feelings about the needs of mathematics teachers, as well as other information crucial to retaining quality teachers. The responses from the participants were used to develop a hierarchy of teachers’ needs that resembles Maslow's hierarchy, which can be used to better support teachers in various stages of their careers. The interviews revealed both non content-specific and content-specific needs within the hierarchy. The responses show that teachers found different schools foster different stress levels and that as teachers they used a number of resources for reducing stress. Other mathematics-specific ideas are also discussed such as the amount of content and pedagogy courses required for certification. 相似文献
44.
Brooke A. Versaw Molly E. McFadden Corey C. Husic Maxwell J. Robb 《Chemical science》2020,11(17):4525
Mechanochromic molecular force probes conveniently report on stress and strain in polymeric materials through straightforward visual cues. We capitalize on the versatility of the naphthopyran framework to design a series of mechanochromic mechanophores that exhibit highly tunable color and fading kinetics after mechanochemical activation. Structurally diverse naphthopyran crosslinkers are synthesized and covalently incorporated into silicone elastomers, where the mechanochemical ring–opening reactions are achieved under tension to generate the merocyanine dyes. Strategic structural modifications to the naphthopyran mechanophore scaffold produce dramatic differences in the color and thermal electrocyclization behavior of the corresponding merocyanine dyes. The color of the merocyanines varies from orange-yellow to purple upon the introduction of an electron donating pyrrolidine substituent, while the rate of thermal electrocyclization is controlled through electronic and steric factors, enabling access to derivatives that display both fast-fading and persistent coloration after mechanical activation and subsequent stress relaxation. In addition to identifying key structure–property relationships for tuning the behavior of the naphthopyran mechanophore, the modularity of the naphthopyran platform is demonstrated by leveraging blends of structurally distinct mechanophores to create materials with desirable multicolor mechanochromic and complex stimuli-responsive behavior, expanding the scope and accessibility of force-responsive materials for applications such as multimodal sensing.Structure–activity relationships for strategic substitution of the naphthopyran mechanophore scaffold enable polymeric materials with tunable mechanochromic behavior. 相似文献
45.
Schaeffer N Tan B Dickinson C Rosseinsky MJ Laromaine A McComb DW Stevens MM Wang Y Petit L Barentin C Spiller DG Cooper AI Lévy R 《Chemical communications (Cambridge, England)》2008,(34):3986-3988
The synthesis of fluorescent water-soluble gold nanoparticles by the reduction of a gold salt in the presence of a designed polymer ligand is described, the size and fluorescence of the particles being controlled by the polymer to gold ratio; the most fluorescent nanomaterial has a 3% quantum yield, a 1.1 nm gold core and a 6.9 nm hydrodynamic radius. 相似文献
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48.
M. J. Kurian S. Jyothi S. K. Leju Molly Isaac Chandu Venugopal G. Renuka 《Pramana》2009,73(6):1111-1122
We have studied the stability of the electrostatic ion cyclotron wave in a plasma consisting of isotropic hydrogen ions (H+) and temperature-anisotropic positively (O+) and negatively (O−) charged oxygen ions, with the electrons drifting parallel to the magnetic field. Analytical expressions have been derived
for the frequency and growth/damping rate of ion cyclotron waves around the first harmonic of both hydrogen and oxygen ion
gyrofrequencies. We find that the frequencies and growth/damping rates are dependent on the densities and temperatures of
all species of ions. A detailed numerical study, for parameters relevant to comet Halley, shows that the growth rate is dependent
on the magnitude of the frequency. The ion cyclotron waves are driven by the electron drift parallel to the magnetic field;
the temperature anisotropy of the oxygen ions only slightly enhance the growth rates for small values of temperature anisotropies.
A simple explanation, in terms of wave exponentiation times, is offered for the absence of electrostatic ion cyclotron waves
in the multi-ion plasma of comet Halley. 相似文献
49.
Daniel V. Schiavone Diana M. Kapkayeva Qilan Li Molly E. Woodson Andreu Gazquez Casals Prof. Lynda A. Morrison Prof. John E. Tavis Prof. Ryan P. Murelli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(10):e202104112
Polyoxygenated tropolones possess a broad range of biological activity, and as a result are promising lead structures or fragments for drug development. However, structure–function studies and subsequent optimization have been challenging, in part due to the limited number of readily available tropolones and the obstacles to their synthesis. Oxidopyrylium [5+2] cycloaddition can effectively generate a diverse array of seven-membered ring carbocycles, and as a result can provide a highly general strategy for tropolone synthesis. Here, we describe the use of 3-hydroxy-4-pyrone-based oxidopyrylium cycloaddition chemistry in the synthesis of functionalized 3,7-dimethoxytropolones, 3,7-dihydroxytropolones, and isomeric 3-hydroxy-7-methoxytropolones through complementary benzyl alcohol-incorporating procedures. The antiviral activity of these molecules against herpes simplex virus-1 and hepatitis B virus is also described, highlighting the value of this approach and providing new structure–function insights relevant to their antiviral activity. 相似文献
50.
Valentina Iannace Dr. Ferran Sabaté Molly Bartlett Dr. Jessica Berrones Reyes Dr. Ariadna Lázaro Alessia Fantoni Prof. Ramon Vilar Prof. Laura Rodríguez Prof. Antonella Dalla Cort 《欧洲无机化学杂志》2023,26(28):e202300144
Three series of metal salophen complexes derived from Zn2+, Cu2+, Pt2+ and Ni2+ have been synthesized and their interaction with quadruplex DNA has been evaluated. The compounds differ on the number of ethyl piperidine substituents. They have been characterized by 1H NMR, IR and UV-visible spectroscopies and by HR-mass spectrometry. Their luminescent properties have been also evaluated and we can observe that, as expected, Zn2+ and Pt2+ complexes are those displaying more interesting luminescence with an emission band red-shifted with respect to the corresponding uncoordinated ligand. DNA interactions with G4 and duplex DNA were evaluated by FRET melting assays (for the Zn2+, Cu2+ and Ni2+ complexes) and by emission titrations (for one Pt2+ complex) which indicated that the disubstituted compounds 2-Ni and 2-Pt are the only ones that display good affinity for G4 DNA structures. 相似文献