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121.
Andreas Heilmann Jamie Hicks Petra Vasko Jose M. Goicoechea Simon Aldridge 《Angewandte Chemie (International ed. in English)》2020,59(12):4897-4901
Anionic molecular imide complexes of aluminium are accessible via a rational synthetic approach involving the reactions of organo azides with a potassium aluminyl reagent. In the case of K2[( NON )Al(NDipp)]2 ( NON =4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethyl‐xanthene; Dipp=2,6‐diisopropylphenyl) structural characterization by X‐ray crystallography reveals a short Al?N distance, which is thought primarily to be due to the low coordinate nature of the nitrogen centre. The Al?N unit is highly polar, and capable of the activation of relatively inert chemical bonds, such as those found in dihydrogen and carbon monoxide. In the case of CO, uptake of two molecules of the substrate leads to C?C coupling and C≡O bond cleavage. Thermodynamically, this is driven, at least in part, by Al?O bond formation. Mechanistically, a combination of quantum chemical and experimental observations suggests that the reaction proceeds via exchange of the NR and O substituents through intermediates featuring an aluminium‐bound isocyanate fragment. 相似文献
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This study investigated vocal vibrato in trained singers through the use of electroglottography (EGG). Ten adult trained singers (7 women, 3 men) were each required to produce four singing tasks. The tasks involved the production of /a/ during an ascending interval of a third in both chest and falsetto registers, once with and once without vibrato. Audio and EGG output during these tasks were directly digitized for subsequent analysis. Results pertaining to changes in the EGG waveform as a function of the singer's gender, the vocal register and the vibrato condition are discussed. A major finding was the apparent absence of consistent, distinctive differentiation in the EGG waveforms when comparing the vibrato and vibrato-inhibited conditions for the majority of subjects. Possible explanations for the majority findings, as well as comment on the feasibility of the EGG for investigating vocal vibrato, are discussed. 相似文献
126.
Gonzalez E Barankin MD Guschl PC Hicks RF 《Langmuir : the ACS journal of surfaces and colloids》2008,24(21):12636-12643
The surfaces of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) were treated with an atmospheric-pressure oxygen and helium plasma. Changes in the energy, adhesion, and chemical composition of the surfaces were determined by contact angle measurements, mechanical pull tests, and X-ray photoelectron spectroscopy (XPS). Surface-energy calculations revealed that after plasma treatment the polarity of PET and PEN increased 6 and 10 times, respectively. In addition, adhesive bond strengths were enhanced by up to 7 times. For PET and PEN, XPS revealed an 18-29% decrease in the area of the C 1s peak at 285 eV, which is attributable to the aromatic carbon atoms. The C 1s peak area due to ester carbon atoms increased by 11 and 24% for PET and PEN, respectively, while the C 1s peak area resulting from C-O species increased by about 5% for both polymers. These results indicate that oxygen atoms generated in the plasma rapidly oxidize the aromatic rings on the polymer chains. The Langmuir adsorption rate constants for oxidizing the polymer surfaces were 15.6 and 4.6 s(-1) for PET and PEN, respectively. 相似文献
127.
The synthesis and characterization of six transition metal complexes of 3-cyano- and 3-nitroformazans are described. Three different formazans were reacted with nickel(II) to produce complexes with bidentate formazan ligands. Mononuclear NiL2 (L = deprotonated formazan) or binuclear hydroxo-bridged (LNi)2(mu-OH) 2 species were produced depending on the steric bulk on the formazan N-aromatic substituents. 1,5-Bis(2-methoxyphenyl)-3-cyanoformazan acts as a tetradentate monoanionic ligand in a copper(II) complex, whereas the analogous 1,5-bis(2-hydroxyphenyl)-3-cyanoformazan binds as a trianion in a tetradentate manner to Fe(III) and Co(III). Crystal structures-the first examples of metal complexes of cyano- or nitroformazans-as well as the electronic spectra of the complexes are discussed in relation to each other as well as that of the uncoordinated formazans. 相似文献
128.
Lewis GT Nowling GR Hicks RF Cohen Y 《Langmuir : the ACS journal of surfaces and colloids》2007,23(21):10756-10764
Surface graft polymerization of 1-vinyl-2-pyrrolidone onto a silicon surface was accomplished by atmospheric pressure (AP) hydrogen plasma surface activation followed by graft polymerization in both N-methyl-2-pyrrolidone (NMP) and in an NMP/water solvent mixture. The formation of initiation sites was controlled by the plasma exposure period, radio frequency (rf) power, and adsorbed surface water. The surface number density of active sites was critically dependent on the presence of adsorbed surface water with a maximum observed at approximately a monolayer surface water coverage. The surface topology and morphology of the grafted polymer layer depended on the solvent mixture composition, initial monomer concentration, reaction temperature, and reaction time. Grafted polymer surfaces prepared in pure NMP resulted in a polymer feature spacing of as low as 5-10 nm (average feature diameter of about 17 nm), an rms surface roughness range of 0.18-0.72 nm, and a maximum grafted polymer layer thickness of 5.5 nm. Graft polymerization in an NMP/water solvent mixture, however, resulted in polymer feature sizes that increased up to a maximum average feature diameter of about 90 nm at [NMP] = 60% (v/v) with polymer feature spacing in the range of 10-50 nm. The surface topology of the polymer-modified silicon surfaces grafted in an NMP/water solvent mixture exhibited a bimodal feature height distribution. In constrast, graft polymerization in pure NMP resulted in a narrow feature height distribution of smaller-diameter surface features with smaller surface spacing. The results demonstrated that, with the present approach, the topology of the grafted polymer surface was tunable by adjusting the NMP/water ratio. The present surface graft polymerization method, which is carried out under AP conditions, is particularly advantageous for polymer surface structuring via radical polymerization and can, in principle, be scaled to large surfaces. 相似文献
129.
Das U Raghavachari K Woo RL Hicks RF 《Langmuir : the ACS journal of surfaces and colloids》2007,23(20):10109-10115
Adsorption of phosphine on indium phosphide compound semiconductor surfaces is a key process during the chemical vapor deposition of this material. Recent experimental infrared studies of the In-rich InP surfaces exposed to phosphine show a complex vibrational pattern in the P-H stretch region, presumably due to overlapping contributions from several structural species. We have performed density functional calculations using finite-sized cluster models to investigate the dissociative adsorption of PH3 on the In-rich InP surface. We find that initially PH3 forms a dative bond with one of the surface In atoms with a binding energy of approximately 11 kcal mol-1 at 298 K. The In-PH3 bond length is 2.9 A, 0.3 A greater than the In-P covalent bond length computed for In-PH2 species produced by hydrogen migration to a neighboring atom. However, the dissociation process, though exothermic, involves a significant activation barrier of approximately 23 kcal mol-1, suggesting the possibility of metastable trapping of the dative bonded PH3 molecules. Indeed, a careful vibrational analysis of different P-H stretching modes of the surface-bound PH3 and PH2 units gives excellent agreement with the observed infrared frequencies and their relative intensities. Moreover, at higher temperatures the frequency modes associated with PH3 disappear either due to desorption or dissociation of this molecule, an observation also well supported from the computed thermochemical parameters at different temperatures. The computed energy parameters and infrared analysis provide direct evidence that PH3 is present as a dative bonded complex on the InP surface at room temperature. 相似文献
130.