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471.
The Influence of the Capping Agent on the Oxidation of Silver Nanoparticles: Nano‐impacts versus Stripping Voltammetry
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Her Shuang Toh Dr. Kerstin Jurkschat Prof. Richard G. Compton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):2998-3004
The influence of capping agents on the oxidation of silver nanoparticles was studied by using the electrochemical techniques of anodic stripping voltammetry and anodic particle coulometry (“nano‐impacts”). Five spherical silver nanoparticles each with a different capping agent (branched polyethylenimine (BPEI), citrate, lipoic acid, polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP)) were used to perform comparative experiments. In all cases, regardless of the capping agent, complete oxidation of the single nanoparticles was seen in anodic particle coulometry. The successful quantitative detection of the silver nanoparticle size displays the potential application of anodic particle coulometry for nanoparticle characterisation. In contrast, for anodic stripping voltammetry using nanoparticles drop casting, it was observed that the capping agent has a very significant effect on the extent of silver oxidation. All five samples gave a low oxidative charge corresponding to partial oxidation. It is concluded that the use of anodic stripping voltammetry to quantify nanoparticles is unreliable, and this is attributed to nanoparticle aggregation. 相似文献
472.
473.
On the Nature of Bridging Metal Atoms in Intermetalloid Clusters: Synthesis and Structure of the Metal‐Atom‐Bridged Zintl Clusters [Sn(Ge9)2]4− and [Zn(Ge9)2)]6−
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Manuel M. Bentlohner Laura‐Alice Jantke Thomas Henneberger Christina Fischer Kerstin Mayer Dr. Wilhelm Klein Prof. Dr. Thomas F. Fässler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):13946-13952
The addition of Sn and Zn ions to [Ge9] clusters by reaction of [Ge9]4? with SnPh2Cl2, ZnCp*2 (Cp*=pentamethylcyclopentadienyl), or Zn2[HC(Ph2P=NPh)2]2 is reported. The resulting Sn‐ and Zn‐bridged clusters [(Ge9)M(Ge9)]q? (M=Sn, q=4; M=Zn, q=6) display various coordination modes. The M atoms that coordinate to the open square of a C4v‐symmetric [Ge9] cluster form strong covalent multicenter M?Ge bonds, in contrast to the M atoms coordinating to triangular cluster faces. Molecular orbital analyses show that the M atoms of the Ge9M fragments coordinate to a second [Ge9] cluster with similar orbitals but in different ways. The [Ge9Sn]2?unit donates two electrons to the triangular face of a second [Ge9]2? cluster with D3h symmetry, whereas [Ge9Zn]2?acts as an electron acceptor when interacting with the triangular face of a D3h‐symmetric [Ge9]4? unit. 相似文献
474.
On the Reactivity of Silylated Ge9 Clusters: Synthesis and Characterization of [ZnCp*(Ge9{Si(SiMe3)3}3)], [CuPiPr3(Ge9{Si(SiMe3)3}3)], and [(CuPiPr3)4{Ge9(SiPh3)2}2]
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Kerstin Mayer Lorenz J. Schiegerl Prof. Dr. Thomas F. Fässler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18794-18800
We report on the synthesis of new derivatives of silylated clusters of the type [Ge9(SiR3)3]? (R = SiMe3, Me = CH3; R = Ph, Ph = C6H5) as well as on their reactivity towards copper and zinc compounds. The silylated cluster compounds were synthesized by heterogeneous reactions starting from the Zintl phase K4Ge9. Reaction of K[Ge9{Si(SiMe3)3}3] with ZnCl2 leads to the already known dimeric compound [Zn(Ge9{Si(SiMe3)3}3)2] ( 1 ), whereas upon the reaction with [ZnCp*2] the coordination of [ZnCp*]+ to the cluster takes place (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) under the formation of [ZnCp*(Ge9{Si(SiMe3)3}3)] ( 2 ). A similar reaction leads to [CuPiPr3(Ge9{Si(SiMe3)3}3)] ( 3 ) from [CuPiPr3Cl] (iPr=isopropyl). Further we investigated the novel silylated cluster units [Ge9(SiPh3)3]? ( 4 ) and [Ge9(SiPh3)2]? ( 5 ), which could be identified by mass spectroscopy. Bis‐ and tris‐silylated species can be synthesized by the respective stoichiometric reactions, and the products were characterized by ESI‐MS and NMR experiments. These clusters show rather different reactivity. The reaction of the tris‐silylated anion 4 with [CuPiPr3Cl] leads to [(CuPiPr3)3Ge9(SiPh3)2]+ as shown from NMR experiments and to [(CuPiPr3)4{Ge9(SiPh3)2}2] ( 6 ), which was characterized by single‐crystal X‐ray diffraction. Compound 6 shows a new type of coordination of the Cu atoms to the silylated Zintl clusters. 相似文献
475.
Coulomb Explosion Imaged Cryptochiral (R,R)‐2,3‐Dideuterooxirane: Unambiguous Access to the Absolute Configuration of (+)‐Glyceraldehyde
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Dipl.‐Chem. Kerstin Zawatzky Dipl.‐Phys. Philipp Herwig Manfred Grieser Dr. Oded Heber Dr. Brandon Jordon‐Thaden Dr. Claude Krantz Dr. Oldřich Novotný Dr. Roland Repnow Prof. Dr. Volker Schurig Prof. Dr. Dirk Schwalm Prof. Dr. Zeev Vager Prof. Dr. Andreas Wolf Dr. Holger Kreckel Prof. Dr. Oliver Trapp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5555-5558
The absolute configuration of (R,R)‐2,3‐dideuterooxirane, which has been independently determined using Coulomb explosion imaging, has been unambiguously chemically correlated with the stereochemical key reference (+)‐glyceraldehyde. This puts the absolute configuration of D (+)‐glyceraldehyde on firm experimental grounds. 相似文献
476.
Nika Erjavec Giulietta Pinato Kerstin Ramser 《Journal of Raman spectroscopy : JRS》2016,47(8):933-939
Raman spectroscopy allows the molecular chemical analysis of whole living cells by comparing them to known Raman signatures of specific vibrational bonds. In this work we used Raman spectroscopy to differentiate between wild type yeast cells and mutants characterized by increased or reduced mitochondrial fragmentation. To associate mitochondrial fragmentation with biochemical markers, we performed Linear Discriminant Analysis (LDA) of whole cell Raman spectra (~50–100 cells/spectrum). We show that the long‐lived, less fragmented mutants fall into a significantly distant cluster from the wild type and short‐lived, more fragmented mutants. Clustering depends on respiratory growth and coincides with that of membrane phospholipids and some respiratory chain components. Spectral clustering is supported by enzymatic activity measurements of OXPHOS Complexes. In addition, we find that NAD(P)H autofluorescence also correlates with mitochondrial fragmentation, representing another likely aging biomarker, besides phospholipids and OXPHOS components. In summary, we demonstrate that Raman spectroscopy has the potential to become a powerful tool for differentiating healthy from unhealthy aged tissues, as well as for the prognostic evaluation of mitochondrial function and fitness. © 2016 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons Ltd 相似文献
477.
From an Isolable Acyclic Phosphinosilylene Adduct to Donor‐Stabilized SiE Compounds (E=O,S, Se)
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Kerstin Hansen Dr. Tibor Szilvási Dr. Burgert Blom Dr. Elisabeth Irran Prof. Dr. Matthias Driess 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(52):18930-18933
Reaction of the arylchlorosilylene‐NHC adduct ArSi(NHC)Cl [Ar=2,6‐Trip2C6H3; NHC=(MeC)2(NMe)2C:] 1 with one molar equiv of lithium diphenylphosphanide affords the first stable NHC‐stabilized acyclic phosphinosilylene adduct 2 (ArSi(NHC)PPh2), which could be structurally characterized. Compound 2 , when reacted with one molar equiv selenium and sulfur, affords the silanechalcogenones 4 a and 4 b (ArSi(NHC)(?E)PPh2, 4 a : E=Se, 4 b : E=S), respectively. Conversion of 2 with an excess of Se and S, through additional insertion of one chalcogen atom into the Si?P bond, leads to 3 a and 3 b (ArSi(NHC)(?E)‐E‐P(?E)Ph2, 3 a : E=Se, 3 b : E=S), respectively. Additionally, the exposure of 2 to N2O or CO2 yielded the isolable NHC‐stabilized silanone 4 c , Ar(NHC)(Ph2P)Si?O. 相似文献
478.
479.
Dr. Monique J. Jacobs Dr. Guenter Schneider Dr. Kerstin G. Blank 《Angewandte Chemie (International ed. in English)》2016,55(8):2899-2902
Mechanophores, that is, molecules that show a defined response to force, are crucial building blocks of mechanoresponsive materials. The possibility of mechanically induced cycloreversion for a series of triazoles formed via strain‐promoted azide–alkyne cycloaddition reactions was investigated by density functional theory calculations, and these triazoles were compared to the 1,4‐ and 1,5‐regioisomers formed in the reaction of an azide with a terminal alkyne. We show that cycloreversion is in principal possible and that the pulling geometry is the most important parameter that determines the probability of cycloreversion. We further compared triazole stability to the mechanical stability of polymers that are frequently used as force transducers in mechanochemical experiments and identified DIBAC (azadibenzylcyclooctyne) as a promising mechanophore for future applications. 相似文献
480.
Thiele B Füllner K Stein N Oldiges M Kuhn AJ Hofmann D 《Analytical and bioanalytical chemistry》2008,391(7):2663-2672
A method has been developed for quantification of 20 amino acids as well as 13 (15)N-labeled amino acids in barley plants. The amino acids were extracted from plant tissues using aqueous HCl-ethanol and directly analyzed without further purification. Analysis of the underivatized amino acids was performed by liquid chromatography (LC)-electrospray ionization (ESI) tandem mass spectrometry (MS-MS) in the positive ESI mode. Separation was achieved on a strong cation exchange column (Luna 5micro SCX 100A) with 30 mM ammonium acetate in water (solvent A) and 5% acetic acid in water (solvent B). Quantification was accomplished using d (2)-Phe as an internal standard. Calibration curves were linear over the range 0.5-50 microM, and limits of detection were estimated to be 0.1-3.0 microM. The mass-spectrometric technique was employed to study the regulation of amino acid levels in barley plants grown at 15 degrees C uniform root temperature (RT) and 20-10 degrees C vertical RT gradient (RTG). The LC-MS-MS results demonstrated enhanced concentration of free amino acids in shoots at 20-10 degrees C RTG, while total free amino acid concentration in roots was similarly low for both RT treatments. (15)NO(3) (-) labeling experiments showed lower (15)N/(14)N ratios for Glu, Ser, Ala and Val in plants grown at 20-10 degrees C RTG compared with those grown at 15 degrees C RT. 相似文献