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排序方式: 共有271条查询结果,搜索用时 15 毫秒
41.
Vanhaelewyn GC Pauwels E Callens FJ Waroquier M Sagstuen E Matthys PF 《The journal of physical chemistry. A》2006,110(6):2147-2156
Beta-D-fructose single crystals were in situ X-irradiated at 80 K and measured using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and ENDOR-induced EPR (EIE) techniques at Q-band (34 GHz) microwave frequencies. The measurements revealed the presence of at least four carbon-centered radicals stable at 80 K. By means of ENDOR angular variations in the three principal crystallographic planes, six proton hyperfine coupling tensors could be determined and were assigned to four different radicals by the aid of EIE. Two of the radicals exhibit only beta-proton hyperfine couplings and reveal almost identical EIE spectra. For the other two radicals, the major hyperfine splitting originates from a single alpha-proton hyperfine coupling and their EIE spectra were also quite similar. The similarity of the EIE spectra and hyperfine tensors led to the assumption that there are only two essentially different radical structures. The radical exhibiting only beta-proton hyperfine couplings was assigned to a C3 centered radical arising from H3 abstraction and the other radical suggested to be an open-ring species with a disrupted C2-C3 bond and a double C2-O2 bond. A possible formation mechanism for the latter open-ring radical is presented. By means of cluster density functional theory (DFT) calculations, the structures of the two radicals were determined and a fairly good agreement between the calculated and experimental hyperfine tensors was found. 相似文献
42.
43.
Surface‐enhanced Raman scattering and density functional theory studies of bis(4‐aminophenyl)sulfone
Guillermo Diaz‐Fleming Freddy Clis Carlos Fredes Marcelo Campos‐Vallette Alvaro E. Aliaga Rainer Koch 《Journal of Raman spectroscopy : JRS》2010,41(2):160-166
Raman and surface‐enhanced Raman scattering (SERS) spectra of dapsone by using colloidal silver nanoparticles have been recorded. Density functional theory was used for the optimization of ground state geometries and simulation of the vibrational spectrum of this molecule. The SERS spectrum with a large silver cluster as a model metallic surface was simulated for the first time. Taking into account the experimental and calculated Raman as well as the SERS normal modes and the corresponding assignments, along with the modeling of the free dapsone and the one in the presence of the colloidal silver nanoparticles, the importance of the sulfone group on the SERS effect in dapsone was inferred. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
44.
De Schutter DP Saison D Delvaux F Derdelinckx G Rock JM Neven H Delvaux FR 《Journal of chromatography. A》2008,1179(2):75-80
The aim of this study was to create a simple, solventless technique without derivatisation in order to analyze a broad range of volatiles in beer wort. A method was developed using headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry. The procedure was optimised by selection of the appropriate fibre and optimisation of extraction temperature, extraction time, and salting-out. The detection limits were well below the actual wort concentrations of the selected volatiles, ranging from 12 ng/l for linalool to 0.53 microg/l for furfural. Moreover, the procedure showed a good linearity and was applied to the analysis of wort samples taken from a wort boiling process in an industrial brewery. 相似文献
45.
Huang S Yee WA Tjiu WC Liu Y Kotaki M Boey YC Ma J Liu T Lu X 《Langmuir : the ACS journal of surfaces and colloids》2008,24(23):13621-13626
Polyvinylidene difluoride (PVDF) solutions containing a very low concentration of single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) of similar surface chemistry, respectively, were electrospun, and the nanofibers formed were collected using a modified rotating disk collector. The polymorphic behavior and crystal orientation of the nanofibers were studied using wide-angle X-ray diffraction and infrared spectroscopy, while the nanotube alignment and interfacial interactions in the nanofibers were probed by transmission electron microscopy and Raman spectroscopy. It is shown that the interfacial interaction between the SWCNTs and PVDF and the extensional force experienced by the nanofibers in the electrospinning and collection processes can work synergistically to induce highly oriented beta-form crystallites extensively. In contrast, the MWCNTs could not be well aligned along the nanofiber axis, which leads to a lower degree of crystal orientation. 相似文献
46.
Besides the known compounds ( ± ) 3,3-bis-demethylpinoresinol (2), americanol A (3), spergulagenic acid (4), epi-acetylaleuritolic acid (5), 6′-palmityl-α-spinateryl-d-glucoside (6a) and 6′-palmityl-δ7-stigmastenyl-d-glucoside (6b), a novel peltogynoid (1) named icosandrin was obtained from the dried fruits of Phytolacca icosandra. This new compound was characterised by 1D-/2D-NMR, UV, IR and HR-MS techniques as 11ξ-methoxy-6,7-methylenedioxy-[2]benzopyrano-[4,3-b][1]-benzopyran-4-one. Toxicity of 1 was assessed through the Brine Shrimp Lethality Assay. Lignan 2 is reported for the first time in Phytolaccaceae family. 相似文献
47.
Strzelczak G Sadło J Danilczuk M Stachowicz W Callens F Vanhaelewyn G Goovaerts E Michalik J 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(5):1206-1209
Irradiated samples of deproteinized powdered human bone (femur) have been examined by electron paramagnetic resonance (EPR) spectroscopy in X, Q and W bands. In the bone powder sample only one type of CO2- radical ion is stabilized in the hydroxyapatite structure in contrast to powdered human tooth enamel, a material also containing hydroxyapatite, widely used for EPR dosimetry and in which a few radicals are stable at room temperature. It is suggested that the use of deproteinized bone for EPR dosimetry could improve the accuracy of dose determination. 相似文献
48.
Freddy Tjosås 《Tetrahedron》2007,63(48):11893-11901
Alkylation of aromatic rings is a major challenge in organic syntheses since more complex carbon skeletons can be constructed. The alkylation of pyridine by nucleophilic aromatic substitution of the nitro group in methyl 3-nitro-4-pyridylcarboxylate (1) with malonic ester is reported. The versatility of the α-(3-pyridyl) malonic ester product (3) is demonstrated by the formation of a number of new 3-alkylated pyridines and new fused bis-heterocycles. cis 2-Halomethyl-4-(3-pyridyl)tetrahydrofuran products were selectively prepared. Exact 1H and 13C NMR assignments of practically all products were obtained by a series of NMR experiments. 相似文献
49.
Let G be an abelian group, ε an anti-bicharacter of G and L a G-graded ε Lie algebra (color Lie algebra) over a field of characteristic zero. We prove that for all G-graded, positively filtered A such that the associated graded algebra is isomorphic to the G-graded ε-symmetric algebra S(L), there is a G- graded ε-Lie algebra L and a G-graded scalar two cocycle , such that A is isomorphic to U
ω
(L) the generalized enveloping algebra of L associated with ω. We also prove there is an isomorphism of graded spaces between the Hochschild cohomology of the generalized universal enveloping
algebra U(L) and the generalized cohomology of the color Lie algebra L.
Supported by the EC project Liegrits MCRTN 505078. 相似文献
50.
A theoretical method for the estimation of mechanical characteristics of polymeric structures is proposed. This method uses the statistical polymer method for modeling branched/crosslinked structures. The proposed method is utilized for the estimation of mechanical resistance and stability of microporous polymeric materials. An engineering method for the evaluation of mechanical stability and resistance of polymeric materials is derived. 相似文献