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451.
Chemoselective hydrogenation of nitroarenes with carbon nanofiber-supported platinum and palladium nanoparticles 总被引:1,自引:0,他引:1
Platinum and palladium nanoparticles supported on three types of carbon nanofibers (CNFs) are synthesized and used as catalysts in the hydrogenation of nitroarenes. Nanosized platinum particles dispersed on platelet-type CNF efficiently catalyze the reduction of functionalized nitroarenes to the corresponding substituted anilines in high turnover numbers with other functional groups remaining intact. 相似文献
452.
Ionic liquids based on dicyanamide anion: influence of structural variations in cationic structures on ionic conductivity 总被引:1,自引:0,他引:1
A series of dicyanamide [N(CN)2]-based ionic liquids were prepared using 1-alkyl-3-methylimidazolium cations with different alkyl chain lengths and ethyl-containing heterocyclic cations with different ring structures, and the influence of such structural variations on their thermal property, density, electrochemical window, viscosity, ionic conductivity, and solvatochromic effects was investigated. We found that the 1,3-dimethylimidazolium salt shows the highest ionic conductivity among ionic liquids free from halogenated anions (3.6 x 10(-2) S cm(-1) at 25 degrees C), and the elongation of the alkyl chain causes the pronounced depression of fluidity and ionic conductivity. Also, such an elongation gives rise to the increase in the degree of ion association in the liquids, mainly caused by the van der Waals interactions between alkyl chains. N(CN)2 salts with 1-ethyl-2-methylpyrazolium (EMP) and N-ethyl-N-methylpyrrolidinium (PY(12)) cations as well as 1-ethyl-3-methylimidazolium (EMI) cation are liquids at room temperature (RT), while the N-ethylthiazolium salt shows a melting event at higher temperature (57 degrees C). Among the three RT ionic liquids with ethyl-containing cations, RT ionic conductivity follows the order EMI > PY(12) > EMP, which does not coincide with the order of fluidity at RT (EMI > EMP > PY(12)). Such a discrepancy is originated from a high degree of ion dissociation in the PY(12) salt, which was manifested in the Walden rule deviation and solvatochromic effects. A series of N(CN)2/C(CN)3 binary mixtures of the EMI salts were also prepared. RT ionic conductivity decreases linearly with increasing the molar fraction of C(CN)3 anion. 相似文献
453.
Katsumoto Y Tanaka T Ihara K Koyama M Ozaki Y 《The journal of physical chemistry. B》2007,111(44):12730-12737
Changes in the local environment around amide groups of poly(N-isopropylacrylamide) (PNiPA) during a solvent-induced reentrant phase separation have been investigated by infrared spectroscopy combined with quantum chemical calculations. The addition of methanol or tetrahydrofuran as a cosolvent to an aqueous solution of PNiPA causes spectral changes in the amide I regions. By preparing a dimer model compound for PNiPA, we can establish the assignment of the amide I bands for the polymer in solutions. Hydrogen-deuterium exchange experiments of the amide protons of PNiPA and its dimer models have revealed that the amide groups of PNiPA form an intramolecular C=O...H-N hydrogen bond even in a good solvent. The result has suggested that the change in the amide I envelope of PNiPA observed during the solvent-induced phase transition reflects the modification of the intramolecular C=O...H-N hydrogen bond of PNiPA as well as the variation in solvation state of the amide groups. On the basis of the assignment, we have discussed contributions of the intramolecular C=O...H-N hydrogen bond to the phase behavior of PNiPA. 相似文献
454.
Temperature-dependent polarized infrared spectra were measured over the temperature range 105-30°C for a ferroelectric liquid crystal with a naphthalene ring (FLC-1) in the isotropic, smectic A (SmA), and chiral smectic C (SmC*) phases to investigate its molecular conformation, interactions, and alignment in each phase. It has been found, from the temperaturedependent spectral changes in the 1610-1600 cm-1 region, that the degree of twist between the naphthalene and benzene rings of FLC-1 changes with temperature. The peak intensity of the band at 1606 cm-1 containing contributions from both the benzene and naphthalene ring stretching modes begins to decrease, not suddenly but gradually, upon going from the SmA phase to the SmC* phase, suggesting that the molecular orientation of the two rings changes gradually between the two phases. The frequencies of two CH2 stretching bands suggest that the disorder of the alkyl chain of FLC-1 is similar for the liquid crystal phase and the isotropic liquid phase. The splitting of the core C=O stretching band indicates that the resonance system consisting of the benzene ring and the C=O group in the core part of FLC-1 is involved in two kinds of intermolecular interaction between adjacent molecules in the liquid crystal phase. 相似文献
455.
456.
Langmuir-Blodgett films and cast films of a ferroelectric liquid crystal of sec-butyl-6-(4-(nonyloxy)benzoyloxy)-2-naphthoate have been fabricated. Their thermal behavior was investigated using infrared spectroscopy at elevated temperature combined with principal component analysis. The result shows a new phase transition from smectic A to nematic phase, compared to the phase sequence obtained by polarizing optical microscopy. Another solid transition of different isomeric crystals was also found, which was confirmed by calorimetric measurement. 相似文献
457.
Miriam Unger Harumi Sato Yukihiro Ozaki Heinz W. Siesler 《Macromolecular Symposia》2011,305(1):90-100
Variable-temperature FT-IR spectra of poly(3-hydroxybutyrate) (PHB), poly(ε-caprolactone) (PCL) and a PHB/PCL (50:50 wt.%) blend were analyzed by two-dimensional correlation spectroscopy (2DCOS). For this purpose the ν(CO) region was employed to characterize in some detail the crystallization behavior of the investigated polymer systems during cooling from the melt. The asynchronous 2D correlation spectra clearly captured the existence of three components in the crystallinity-sensitive region of the CO stretching mode for PHB and PCL, respectively: a well-ordered, an inter-mediate and a less ordered crystalline state. Furthermore, by 2DCOS application a sequential order of the observed structural changes could be proposed for the whole temperature range during the crystallization of both polymers. In the case of the PHB/PCL (50:50 wt.%) polymer blend, we have split up the spectral data set in the sub-sets between 200–120 °C and 70–30 °C for a more detailed 2DCOS analysis. In this way we could separate the crystallization process of PHB and PCL in the polymer blend. 相似文献
458.
Mohammad Kamal Hossain Yasutaka Kitahama Genin Gary Huang Xiaoxia Han Yukihiro Ozaki 《Analytical and bioanalytical chemistry》2009,394(7):1747-1760
Surface-enhanced Raman scattering (SERS) enhancement and the reproducibility of the SERS signal strongly reflect the quality
and nature of the SERS substrates because of diverse localized surface plasmon resonance (LSPR) excitations excited at interstitials
or sharp edges. LSPR excitations are the most important ingredients for achieving huge enhancements in the SERS process. In
this report, we introduce several gold and silver nanoparticle-based SERS-active substrates developed solely by us and use
these substrates to investigate the influence of LSPR excitations on SERS. SERS-active gold substrates were fabricated by
immobilizing colloidal gold nanoparticles on glass slides without using any surfactants or electrolytes, whereas most of the
SERS-active substrates that use colloidal gold/silver nanoparticles are not free of surfactant. Isolated aggregates, chain-like
elongated aggregates and two-dimensional (2D) nanostructures were found to consist mostly of monolayers rather than agglomerations.
With reference to correlated LSPR and SERS, combined experiments were carried out on a single platform at the same spatial
position. The isolated aggregates mostly show a broadened and shifted SPR peak, whereas a weak blue-shifted peak is observed
near 430 nm in addition to broadened peaks centered at 635 and 720 nm in the red spectral region in the chain-like elongated
aggregates. In the case of 2D nanostructures, several SPR peaks are observed in diverse frequency regions. The characteristics
of LSPR and SERS for the same gold nanoaggregates lead to a good correlation between SPR and SERS images. The elongated gold
nanostructures show a higher enhancement of the Raman signal than the the isolated and 2D samples. In the case of SERS-active
silver substrates for protein detection, a new approach has been adopted, in contrast to the conventional fabrication method.
Colloidal silver nanoparticles are immobilized on the protein functionalized glass slides, and further SERS measurements are
carried out based on LSPR excitations. A new strategy for the detection of biomolecules, particularly glutathione, under aqueous
conditions is proposed. Finally, supramolecular J-aggregates of ionic dyes incorporated with silver colloidal aggregates are
characterized by SERS measurements and correlated to finite-difference time-domain analysis with reference to LSPR excitations.
Figure SPR and SERS images for isolated, elongated and two-dimensional gold nanostructures 相似文献
459.
Demizu Y Wakana D Kamakura H Kurihara M Okuda H Goda Y 《Chemical & pharmaceutical bulletin》2011,59(10):1314-1316
We isolated a new illegal sildenafil analogue named mutaprodenafil from a dietary supplement for erectile dysfunction (ED) and proposed that it is an aildenafil derivative containing an imidazole moiety. We subsequently synthesized mutaprodenafil from a thioaildenafil and authenticated its structure. 相似文献
460.
The electrochemical reduction of 9,10-anthraquinone (AQ) was investigated in CH(3)CN in both the absence and presence of the hydrogen-bond and proton donating additives, CH(3)OH, CH(CF(3))(2)OH, phenol, 4-methoxyphenol, 4-cyanophenol, 2,4,6-trichlorophenol, and benzoic acid (BA). Three clearly different types of electrochemical behavior were observed with increasing concentrations of the additives, and were simulated to analyze the reaction mechanisms. Type I was observed for weakly interacting additives, such as CH(3)OH, characterized by positive shifts of the two well-separated reduction waves, corresponding to the formation of AQ(?-) and AQ(2-), with no loss of reversibility. The second wave shifted more strongly, and finally merged with the first. These behaviors are explained by the association of AQ(2-) with the additives via strong hydrogen-bonding. Type II is attributed to a reduction mechanism involving quantitative formation of strong hydrogen-bonded complexes of AQ(2-) with additives, such as CH(CF(3))(2)OH, phenol and 4-methoxyphenol, showing a reversible or quasireversible two-electron reduction wave with increasing concentrations of the additives. The behavior of Type III, observed in the presence of strongly interacting additives, such as 2,4,6-trichlorophenol and BA, is characterized by a voltammogram composed of the 2-electorn cathodic and the broad anodic waves without keeping reversibility, facilitated by proton transfer in the hydrogen-bonded complexes, AQ(?-)-BA and AQ(2-)-BA. The effects of hydrogen-bonding and protonation on the electrochemistry of AQ have been systematically demonstrated in terms of the potentials and reaction pathways of the various species, which appear in quinone-hydroquinone systems. 相似文献