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291.
292.
Carmen A. Roba Cristina Jimenez Călin Baciu Simion Beldean-Galea Erika Levei Emil Cordoš 《Central European Journal of Chemistry》2011,9(4):598-604
In the present study, a simple procedure for the isolation by solid-phase extraction (SPE) and quantification by UV-Vis spectrometry
(400 nm) of the humic acids (HAs) in the natural waters was developed. Seven different sorbents: Porapak P (polystyrene-divinylbenzene
copolymer), Florisil (chemical composition: 84.0% SiO2, 15.5% MgO and 0.5% Na2SO4), Silica gel C18 (octadecyl silane), Strata X (surface modified polystyrene-divinylbenzene), Strata NH2 (silica-based trifunctional amino ligand), Strata SAX (silica-based trifunctional quaternary amine) and Strata C18-E (silica-based
trifunctional C18 with hydrophobic end-capping of silanols) were tested. The HAs, adsorbed on SPE cartridges, were eluted
using: NaOH (0.1 M), sodium dodecyl sulphate (SDS) (20 g L−1), and a 1:1 v/v mixture of SDS (20 g L−1) and NaOH (0.1 M). The extraction efficiency was evaluated by comparing the HAs recovery levels. The repeatability of results
was estimated by the relative standard deviation (RSD). The data confirmed that Porapak P, Silica gel C18, Florisil, Strata
NH2 and Strata X could be good alternatives for the traditional isolation of the aquatic HAs with XAD resin. The proposed method
was applied for the determination of HAs in some waters sampled from the Western Romanian Plain. The content of HAs was correlated
with the arsenic concentration and total organic carbon (TOC) level.
相似文献
293.
The synthesis and liquid crystalline properties of novel achiral amides (Ia–g, IIa–g and IVa,b), achiral Schiff's bases (IIIa–g and Va–g), chiral amides (VI, VII) and chiral Schiff's bases (VIII–XI) incorporating a 1,3,4-oxadiazole ring are reported. All amides of the series I and II display an enantiotropic smectic A phase. The amide IVa,b did not show mesomorphic properties. Amides of the series Ia–g and IIa–g contain a flexible n-tetradecylthio chain, the other terminal substituent is an n-alkoxy chain and n-alkyl chain, respectively (n?=?4–10) and the 1,3,4-oxadiazole is in the terminal rigid core. Amides Ia–g have broader mesomorphic range and higher thermal stability than the corresponding amides IIa–g. Amides IVa,d contain the 1,3,4-oxadiazole ring in the centre of the rigid core and two flexible alkoxy chains as flexible terminal substituents. Thus, the mesomorphic properties are favoured if 1,3,4-oxadiazole is shifted to a terminal position of the rigid core. Schiff's bases IIIa–g display an enantiotropic dimorphism smectic C–smectic A. Schiff's bases IIIa–g have a broader mesomorphic range than the analogous amides Ia–g. Schiff's bases Va–g exhibit a dimorphism smectic A–nematic, and in contrast to this the analogous amide IVa,b did not show mesomorphism. The chiral amides VI and VII and chiral Schiff's bases X and XI did not show mesomorphic properties and only the chiral Schiff's bases VIII and IX display a chiral smectic C phase in a short mesomorphic range. A density functional theory theoretical study at the B3LYP/6–311++G(d,p) level was performed in order to analyse the structural features that must be related with the mesomorphic behaviour of the reported compounds. 相似文献
294.
E. Rodriguez G. Kellermann A.F. Craievich E. Jimenez C.L. Csar L.C. Barbosa 《Superlattices and Microstructures》2008,43(5-6):626
Multilayers of PbTe quantum dots embedded in SiO2 were fabricated by alternate use of Pulsed Laser Deposition (PLD) and Plasma Enhanced Chemical Vapor Deposition (PECVD) techniques. The morphological properties of the nanostructured material were studied by means of High Resolution Transmission Electron Microscopy (HRTEM), Grazing-Incidence Small-Angle X-ray scattering (GISAXS) and X-ray Reflectometry (XRR) techniques. A preliminary analysis of the GISAXS spectra provided information about the multilayer periodicity and its relationship to the size of the deposited PbTe nanoparticles. Finally multilayers were fabricated inside a Fabry–Perot cavity. The device was characterized by means of Scanning Electron Microscopy (SEM). Transmittance measurements show the device functionality in the infrared region. 相似文献
295.
GabinoA. Carriedo J. Jimenez P. Gmez‐Elipe F.J. García Alonso 《Macromolecular rapid communications》2001,22(6):444-447
The reaction of [NPCl2]n with substoichiometric amounts of the thiophenols HS—C6H4—R (R = H, Br) and Cs2CO3 in THF at room temperature, gave solutions of {[NPCl2]1‐x[NP(S—C6H4—R)2]x}n [R = H ( 1a ), Br ( 1b )]. The reaction of the derivative with R = Br and x = 0.3 with HO—C6H4—Br gave the random copolymer {[NP(O—C6H4—Br)2]0.7 [NP(S—C6H4—Br)2]0.3}n ( 2 ); similarly, the reaction of 1 with the biphenol HO—C6H4—C6H4—OH gave the random copolymers {[NP(O2C12‐H8)]0.75[NP(S—C6H4—R)2]0.25}n [R = H, ( 3a ); R = Br, ( 3b )] as soluble and stable white solids. 相似文献
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297.