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541.
Two decades have passed since the metathesis polymerisation of α,ω-dienes was successfully demonstrated by the group of Wagener and the term acyclic diene metathesis (ADMET) polymerisation was coined. Since then, the advances of metathesis chemistry have allowed to expand the scope of this versatile polymerisation reaction that nowadays finds applications in different fields, such as polymer, material, or medicinal chemistry. This critical review provides an insight into the historical aspects of ADMET and a detailed overview of the work done to date applying this versatile polymerisation reaction (221 references). 相似文献
542.
Three chromium(III) complexes of general formula [Cr(ox)2(Aa)]2− (Aa is an α-amino acid, namely alanine, valine or cysteine) were obtained and characterized in solution. In acidic solutions,
[Cr(ox)2(Aa)]2− undergo acid-catalysed aquation to cis-[Cr(ox)2(H2O)2]− and the appropriate amino acid. The process goes through a metastable intermediate with monodentate amino acid coordinated
via the carboxylate oxygen atom. The kinetics of the chelate ring opening were studied under isolation conditions. The determined
pseudo-first-order rate constants were linearly dependent on [H+]. A mechanism is proposed, in which the reactive form of substrate is in the form of the conjugate acid. 相似文献
543.
Arim Woo Young Hoon Lee Shinya Hayami Leonard F. Lindoy Pierre Thu??ry Yang Kim 《Journal of inclusion phenomena and macrocyclic chemistry》2011,71(3-4):409-417
The interaction of the enantiopure (R)- and (S)-1-phenyl-N,N-bis(pyridine-3- ylmethyl)ethanamine ligands, R-L 1 and S-L 1 , with copper(II) chloride followed by addition of hexafluorophosphate resulted in the isolation of the corresponding enantiomeric complexes [Cu(R-L 1 )Cl](PF6) (1), [Cu(S-L 1 )Cl](PF6) (2) and [Cu(S-L 1 )Cl](PF6)??0.5Et2O (3), in which dimerization occurs through two long Cu??????Cl interactions, the ??-chloro bridges being thus strongly asymmetric. The organic ligand is bound to the metal centre via its N3-donor dipyridylmethylamine fragment in a planar fashion, such that each copper centre is in a square planar environment (or distorted square pyramidal with a long axial bond length if the additional interaction is considered). When R,S-L 1 was employed in a parallel synthesis, the similar racemic complex [Cu(R,S-L 1 )Cl](PF6)??0.5MeOH (4) was obtained, in which the L 1 ligands in each dimeric unit have opposite hands. In contrast to the complexes of L 1 , the reaction of Cu(II) chloride with the related ligand, (R)-1-cyclohexyl-N,N-bis(pyridine-3-ylmethyl)ethanamine (R-L 2 ), yielded the mononuclear complex [Cu(R,S-L 2 )Cl2] (5), displaying a distorted square pyramidal coordination geometry. The structure of this product along with its corresponding circular dichroism spectrum revealed that racemisation of the starting R-L 2 ligand has occurred under the relatively mild (basic) conditions employed for the synthesis. A temperature-dependent magnetic studies of the complexes 1, 2 and 5 indicate that a week ferromagnetic interaction is operative in each dicopper core in 1 and 2 with 2J?=?1.2?cm?1. On the other hand, a week antiferromagnetic intermolecular interaction is operative for 5. 相似文献
544.
Lidija?Fras?Zemlji?Email author Du?ko??akara Nico?Michaelis Thomas?Heinze Karin?Stana Kleinschek 《Cellulose (London, England)》2011,18(1):33-43
The protonation behavior of 6-deoxy-6-(2-aminoethyl)amino cellulose as a novel soluble aminated derivate of cellulose was
studied by means of the potentiometric titration technique. The resulting proton binding isotherms exhibit two equivalent
steps, which can be described by the standard macroscopic two-pK model, in which the degree of protonation is averaged over
all the amine groups. In addition, a microscopic proton binding model was applied, in which the protonation sites are distinguished
and the protonation free energy is expanded into an intrinsic term and an electrostatic repulsion between the primary and
secondary amine groups. The protonation behavior of 6-deoxy-6-(2-aminoethyl)amino cellulose was compared with a model compound
(N-methylethylenediamine). 相似文献
545.
Magnetic properties, arising from surface exchange and interparticle interactions of the Fe3O4 (magnetite) nanoparticles, were investigated in the temperature range of 5–300 and 120–300 K using vibrating sample magnetometer
technique and electron spin resonance spectroscopy, respectively. The research was based on to figure out the origin of intraparticle
interactions and the change of interparticle interactions in wide size range Fe3O4 nanoparticles. The analyses were done for samples having almost same particle size distributions. The average particle sizes
were changed in between 30 ± 2 and 34 ± 2 nm. The observed magnetization values were demonstrated the mixture of single-domain
size particles, exhibiting both single-domain (SD) and superparamagnetic (SPM) states. The symmetry of resonance curves changed
according to the ratio of SD and SPM-stated particles in mixture under located temperature. The changes of anisotropy up to
domain state were understood by freezing magnetic moment in glycerol matrix from room temperature to 120 K under 5-kG field.
The shift of H
R values to higher magnetic fields and the more symmetric resonance spectrum proved the effect of anisotropy and interparticle
interactions fields on magnetic behave. In addition, the origin of intra-interaction was exposed from Fe3+ centers and exchange coupling in between Fe2+, Fe3+, and O−, and Fe3+ centers found from g factor (g). 相似文献
546.
K.A. Stasiewicz R. Krajewski L.R. Jaroszewicz M. Kujawińska R. ?wi??o 《Opto-Electronics Review》2010,18(1):102-109
Investigations of internal structure changes along an optical fiber during the manufacture of biconical taper have been described. Basing on the constant volume theory, classification of biconical structures manufactured on a special set-up is presented and discussed. The interferometric tomography method has been used for determination of 3D geometry and refractive index distribution in manufactured optical fiber tapers. The experiments provide detailed information on external (diameter of cladding) as well as internal (core diameter and refractive index profile) changes along the taper region. The results have been discussed in relation to the parameters of the manufacturing process. 相似文献
547.
U?ur?Tamer Yusuf?Gündo?du ?smail?Hakk??Boyac? Kadir?Pekmez 《Journal of nanoparticle research》2010,12(4):1187-1196
The production of monodispersed magnetic nanoparticles with appropriate surface modification has attracted increasing attention
in biomedical applications including drug delivery, separation, and purification of biomolecules from the matrices. In the
present study, we report rapid and room temperature reaction synthesis of gold-coated iron nanoparticles in aqueous solution
using the borohydride reduction of HAuCl4 under sonication for the first time. The resulting nanoparticles were characterized with transmission electron microscopy
(TEM), electron spectroscopy for chemical analysis (ESCA), ultraviolet visible spectroscopy (UV–Vis), and X-ray diffraction
(XRD). Surface charges and magnetic properties of the nanoparticles were also examined. The pattern of Fe3O4 nanoparticles is face centered cubic with an average diameter of 9.5 nm and the initial reduction of gold on the surface
of Fe3O4 particles exhibits uniform Fe3O4–Au nanoparticles with an average diameter of 12.5 nm. The saturation magnetization values for the uncoated and gold-coated
Fe3O4 nanoparticles were found to be 30 and 4.5 emu/g, respectively, at 300 K. The progression of binding events between boronic
acid terminated ligand shell and fructose based on the covalent bonding interaction was measured by absorbance spectral changes.
Immunomagnetic separation was also performed at different E. coli concentration to evaluate capturing efficiency of resulting nanoparticles. Immunomagnetic separation percentages were varied
in a range of 52.1 and 21.9% depend on the initial bacteria counts. 相似文献
548.
Sait?Y?lmaz Haluk??afak Recep??ahingoz Mustafa?Erol 《Central European Journal of Physics》2010,8(3):438-444
In this study, we calculate the photoionization cross section and refractive-index change of an on-center hydrogenic impurity
in a CdS-SiO2 spherical quantum dot. In numerical calculations, both the finite- and infinite-confinement cases are considered and a variational
scheme is adopted to determine the energy eigenvalues for the impurity. The variations of the photoionization cross section
with the dot radius, the refractive-index change, and the normalized photon energy are investigated, and the effect of the
potential-barrier height on the cross section is discussed. The results obtained show that the photoionization cross section
and the refractive-index change in CdS-SiO2 spherical quantum dots are sensitively dependent on the incident optical intensity and on the dot sizes. 相似文献