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11.
Arumugam Thangavel Marika Wieliczko Christopher Scarborough Birger Dittrich John Bacsa 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(11):936-943
In the crystal structure of the title homoleptic CrII complex, [Cr(CH3CN)6](C24H20B)2·CH3CN, the [Cr(CH3CN)6]2+ cation is a high‐spin d4 complex with strong static, rather than dynamic, Jahn–Teller distortion. The electron density of the cation was determined by single‐crystal X‐ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn–Teller distortion of the CrII cation away from idealized octahedral symmetry. The topological analysis of the aspherical d‐electron density about the CrII cation showed that there are significant valence charge concentrations along the axial Cr—N axes. Likewise, there were significant valence charge depletions about the CrII cation along the equatorial Cr—N bonds. These charge concentrations are in accordance with a Jahn–Teller‐distorted six‐coordinate complex. 相似文献
12.
A. Righi J.P. Salvestrini P. Bourson R.L. Moreira M.D. Fontana 《Applied physics. B, Lasers and optics》1998,67(5):559-562
1-x RbxSO4 for x varying between 0 and 0.50 were investigated by an ac modulation method based upon the Sénarmont arrangement. The electro-optic
coefficient rc, and for the first time the coefficients r41 and r51 were determined with good accuracy in pure LiKSO4 around room temperature at a wavelength of 633 nm. The frequency dependence of the electro-optic coefficient rc was measured in the frequency range from 1 kHz up to 1 MHz. The values of the factor of merit ne
3rc of the mixed crystals LiK1-xRbxSO4 were obtained for the first time, for the concentrations x=0.05, 0.10, 0.20, and 0.50. The electro-optic properties are shown
to be affected by the random presence of the rubidium ions in this disordered system.
Received: 16 March 1998/Revised version: 2 June 1998 相似文献
13.
Straightforward synthesis for two pentaerythrityltetramine precursors, 2,2-bis(azidomethyl)propane-1,3-diamine (1) and 2-[N-(allyloxycarbonyl)aminomethyl]-2-azidomethylpropane-1,3-diamine (2), has been described. Both propane-1,3-diamines have been attached by reductive amination to a solid-supported backbone amide linker derived from 4-(4-formyl-3,5-dimethoxyphenoxy)butyric acid. The presence of the two methoxy substituents on the linker is essential to avoid cross-linking between two linkers. The remaining free primary amino group of the propane-1,3-diamine moiety may then be selectively acylated with an appropriately protected amino acid using conventional N,N-dicyclohexylcarbodiimide/1-hydroxybenzotriazole (DCC/HOBt) activation without any interference by the secondary amino function. The latter group may be subsequently acylated by an anhydride method. Sequential reduction of the azido group and removal of the allyloxycarbonyl protection from 2 allow further coupling of two different amino acids, and hence, this handle may be utilized in construction of branched structures containing four different amino acids or peptides. Solid-supported 1 may, in turn, be used for the synthesis of similar constructs containing two identical branches. It is worth noting that no acid-labile protecting groups are required in this approach, and hence, this dimension may be saved for the cleavage of the linker. The applicability of the scaffolds to library synthesis has been demonstrated by preparation of 11 pentaerythrityl-branched tetra- and octapeptides. 相似文献
14.
(1,10-Phenanthroline)bis(piperidinecarbodithioato-S,S′)cadmium(II), [Cd(pipdtc)2(1,10-phen)] (1) and (2,2′-bipyridine)bis(piperidinecarbodithioato-S,S′)cadmium(II), [Cd(pipdtc)2(bipy)] (2) adducts were prepared and the crystal structures are reported. Cd–S and Cd–N distances and the angles subtended at cadmium are almost the same in both complexes but the Cd–S distances in the adducts are longer than those in Cd(pipdtc)2 (3) complexes due to the presence of an additional neutral ligand. Thioureide C–N distance in 1 and 2 are supported by νC–N bands observed at 1471 and 1470 cm−1, respectively. S2p binding energies for the adducts show a significant reduction in value compared to the parent dithiocarbamate indicating the weakening of the Cd–S bond on adduct formation. The observed reduction in binding energy is due to the increased electron density on the metal in the adducts. The cyclic voltammetric study on the complexes also show an increase of electron density on cadmium in the adducts compared to Cd(pipdtc)2. 相似文献
15.
A simple and rapid method for determining six ergot alkaloids and four of their respective epimers was developed for rye and wheat. The analytes were extracted from the sample matrix with ACN/ammonium carbonate solution. The extract was purified with a commercial push‐through SPE column (Mycosep® 150 Ergot). After concentration and filtration steps, the final separation of the analytes was achieved with ultra‐performance LC‐MS/MS. The chromatographic separation of the ergot alkaloids was achieved in 4.5 min. The method performance proved satisfactory in the preliminary validation. The calculated LOQs were low ranging from 0.01 to 1.0 μg/kg for wheat and from 0.01 to 10.0 μg/kg for rye. At the concentration levels of 10, 50 and 200 μg/kg, the recoveries were between 80 and 120% in most cases and the within‐day repeatability (expressed as RSD) ranged between 1.3 and 13.9%. Despite the cleanup of the samples, some matrix effect was observed in the MS, highlighting the necessity of using matrix‐assisted standards. This is the first article to describe the application of the push‐through columns and ultra‐performance LC in the analysis of ergot alkaloids. 相似文献
16.
Marika E. Nissil? Ya-Chieh Li Shu-Yi Wu Jaakko A. Puhakka 《Applied biochemistry and biotechnology》2012,168(8):2160-2169
Concentrated acid hydrolysis of cellulosic material results in high dissolution yields. In this study, the neutralization step of concentrated acid hydrolysate of conifer pulp was optimized. Dry conifer pulp hydrolysis with 55?% H2SO4 at 45?°C for 2?h resulted in total sugar yields of 22.3?C26.2?g/L. The neutralization step was optimized for solid Ca(OH)2, liquid Ca(OH)2 or solid CaO, mixing time, and water supplementation. The highest hydrogen yield of 1.75?mol?H2/mol glucose was obtained with liquid Ca(OH)2, while the use of solid Ca(OH)2 or CaO inhibited hydrogen fermentation. Liquid Ca(OH)2 removed sulfate to below 30?mg SO4 2?/L. Further optimization of the neutralization conditions resulted in the yield of 2.26?mol?H2/mol glucose. 相似文献
17.
18.
19.
The electrophilic iodocyclization reaction of (Z)- and (E)-5-n-alkylsubstituted 4-alken-1-ols followed by base-induced hydrodeiodination reaction stereoselectively gave, respectively, (Z)- and (E)-alkylidentetrahydrofurans in high yield. Completely different outcomes were observed with (Z)- and (E)-6,6-dimethylhept-4-en-1-ol: their iodocyclization furnished, respectively, threo- and erythro-2-(1-iodo-2,2-dimetylpropyl)tetrahydrofuran with high stereoselectivity. The threo isomer gave clean formation of 6-tert-butyl-3,4-dihydro-2H-pyran by base-induced ring expansion, while erythro isomer underwent a base-induced ring contraction to 1-cyclopropyl-3,3-dimethylbutan-1-one. Moreover, (Z)- and (E)-5-cyclopropylpent-4-en-1-ol underwent a 6-endo-iodocyclization to threo- and erythro-2-cyclopropyl-3-iodotetrahydro-2H-pyran, respectively, that under the same basic treatment, gave two isomeric 6-cyclopropyldihydro-2H-pyrans in a stereoselective fashion. 相似文献
20.
Morone M Beverina L Abbotto A Silvestri F Collini E Ferrante C Bozio R Pagani GA 《Organic letters》2006,8(13):2719-2722
The microwave-enhanced synthesis, comparative singlet oxygen sensitization efficiency, and nonlinear optical characterization of a new beta-functionalized porphyrin and its copper complex are described. We show that the introduction of a donor-acceptor push-pull conjugated fragment in the beta position strongly perturbs the porphyrin electronic structure leading to a remarkable one- and two-photon NIR absorption enhancement. 相似文献