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71.
The desire to mitigate climate change due to greenhouse gas emissions has led to the exploration of plant fibers as alternative materials for various industrial applications, sound absorption inclusive. In this investigation, sound absorption properties of Antiaris toxicaria barkcloth, and the thermal insulation properties of the barkcloth epoxy laminar composites were characterized. Theoretical sound absorption models were utilized to validate the experimental data and the empirical models were in agreement with experimental data. The lowest thermal conductivity was achieved by the Antiaris toxicaria epoxy composites. 相似文献
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Štefko M Slavětínská L Klepetářová B Hocek M 《The Journal of organic chemistry》2011,76(16):6619-6635
A general modular and practical methodology for preparation of diverse 5-substituted pyridin-2-yl and 6-substituted pyridin-3-yl C-ribonucleosides was developed. Regioselective lithiation of 2,5-dibromopyridine proceeded at position 5 or 2 depending on the solvent, and the resulting bromopyridyl lithium species underwent additions to TBS-protected ribonolactone and follow-up transformations to corresponding acetylated hemiketal intermediates 7 and 10 that were diastereoselectively reduced to give either 5-bromopyridin-2-yl or 6-bromopyridin-3-yl silyl-protected C-ribonucleosides 8 or 11 in 68% and 77% overall yields as pure β-anomers. These bromopyridyl C-nucleoside intermediates were then subjected to a series of palladium-catalyzed cross-coupling reactions, aminations, aminocarbonylations, and hydroxylations to give a series of protected 1β-(5-alkyl-, 5-aryl-, 5-amino-, 5-carbamoyl-, and 5-hydroxypyridin-2-yl)-C-ribonucleosides 13a-i and β-(6-alkyl-, 6-aryl-, 6-amino-, 6-carbamoyl-, and 6-hydroxypyridin-3-yl)-C-ribonucleosides 15a-i. Deprotection of silylated nucleosides by Et(3)N·3HF, TBAF, or TFA gave a series of free C-nucleosides 14a-i and 16a-i. 相似文献
74.
Smejkal P Sisková K Vlcková B Pfleger J Sloufová I Slouf M Mojzes P 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(10):2321-2329
A four step Ag foil laser ablation-Ag nanoparticle fragmentation procedure in ultrapure water was carried out both under argon and in air. Pulses of a high power Nd/YAG laser were used for laser ablation (1064 nm) and for the three step Ag hydrosol treatment in the absence of Ag foil in the sequence 1064-532-1064 nm. Transmission electron microscopy (TEM) and surface plasmon (SP) extinction spectra provide evidence of Ag nanoparticle fragmentation in the second and third step of the procedure carried out under argon. While polydispersity of Ag hydrosol increases in the second step, both the polydispersity and the mean size of the nanoparticles are reduced in the third step. Qualitative and quantitative surface-enhanced Raman scattering (SERS)/surface-enhanced resonance Raman scattering (SERRS) spectral probing of systems with Ag hydrosols and the selected adsorbates at 514.5 nm excitation shows that Ag hydrosols obtained in the second step of the preparation procedure carried out in air are the most suitable substrates for SERS/SERRS experiments performed at this excitation wavelength. 相似文献
75.
Ohne ZusammenfassungHerrn Prof. Dr.E. Ziegler zum 60. Geburtstag gewidmet. 相似文献
76.
Blanka Wladislaw Liliana Marzorati Francisco C. Biaggio Marian Mikolajczyk 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Some α-methylsulfanyl phosphorylsulfoxides were obtained by sulfenylation reaction in homogeneous phase. 相似文献
77.
[Structure: see text] Direct C-H arylation of purines to position 8 by diverse aryl iodides was achieved with Pd catalysis in the presence of CuI and Cs2CO3. The methodology is general and efficient and was applied in the consecutive regioselective synthesis of 2,6,8-trisubstituted purines bearing three different C-substituents in combination with two cross-coupling reactions. 相似文献
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Spiwok V Lipovová P Skálová T Vondrácková E Dohnálek J Hasek J Králová B 《Journal of computer-aided molecular design》2005,19(12):887-901
Summary Aromatic amino acid residues are often present in carbohydrate-binding sites of proteins. These binding sites are characterized
by a placement of a carbohydrate moiety in a stacking orientation to an aromatic ring. This arrangement is an example of CH/π
interactions. Ab initio interaction energies for 20 carbohydrate–aromatic complexes taken from 6 selected ultra-high resolution X-ray structures
of glycosidases and carbohydrate-binding proteins were calculated. All interaction energies of a pyranose moiety with a side
chain of an aromatic residue were calculated as attractive with interaction energy ranging from −2.8 to −12.3 kcal/mol as
calculated at the MP2/6-311+G(d) level. Strong attractive interactions were observed for a wide range of orientations of carbohydrate
and aromatic ring as present in selected X-ray structures. The most attractive interaction was associated with apparent combination
of CH/π interactions and classical H-bonds. The failure of Hartree–Fock method (interaction energies from +1.0 to −6.9 kcal/mol)
can be explained by a dispersion nature of a majority of the studied complexes. We also present a comparison of interaction
energies calculated at the MP2 level with those calculated using molecular mechanics force fields (OPLS, GROMOS, CSFF/CHARMM,
CHEAT/CHARMM, Glycam/AMBER, MM2 and MM3). For a majority of force fields there was a strong correlation with MP2 values. RMSD
between MP2 and force field values were 1.0 for CSFF/CHARMM, 1.2 for Glycam/AMBER, 1.2 for GROMOS, 1.3 for MM3, 1.4 for MM2,
1.5 for OPLS and to 2.3 for CHEAT/CHARMM (in kcal/mol). These results show that molecular mechanics approximates interaction
energies very well and support an application of molecular mechanics methods in the area of glycochemistry and glycobiology. 相似文献