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排序方式: 共有292条查询结果,搜索用时 15 毫秒
41.
Kim HM Jeong BH Hyon JY An MJ Seo MS Hong JH Lee KJ Kim CH Joo T Hong SC Cho BR 《Journal of the American Chemical Society》2008,130(13):4246-4247
We report a new two-photon fluorescence turn-on probe 6-[(E)-3-oxo-1-dodecenyl]-2-[N-methyl-N-(carboxymethyl)amino]naphthalene (CL2) that is designed specifically for visualizing lipid rafts in living cells and tissues. This probe emits much brighter two-photon excited fluorescence in lipid rafts than in non-raft domains and allows direct visualization of the lipid rafts in the live cells and pyramidal neuron layer of the CA1 region at a depth of 100-250 mum in live tissues using two-photon microscopy. 相似文献
42.
Jovana Šakota Rosić Jelena Munćan Ivana Mileusnić Boris Kosić Lidija Matija 《Soft Materials》2016,14(4):264-271
The aim of this study was to determine if it is possible to distinguish between the groups of spoiled and unspoiled soft contact lenses using near-infrared spectroscopy and new analytical approach – Aquaphotomics. Using the principal component analysis, it was established that the absorbance spectra of worn and new contact lenses are differed at water absorption band related to hydration of proteins. Detection of proteins thus was performed indirectly by using vibrations of water molecules. This exploratory study showed that near-infrared spectroscopy and Aquaphotomics have potential for non-invasive, chemical-free detection of protein deposits on hydrated soft contact lenses. 相似文献
43.
Direct Catalytic Asymmetric Mannich Reaction with Dithiomalonates as Excellent Mannich Donors: Organocatalytic Synthesis of (R)‐Sitagliptin
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Dr. Han Yong Bae Mun Jong Kim Jae Hun Sim Prof. Dr. Choong Eui Song 《Angewandte Chemie (International ed. in English)》2016,55(36):10825-10829
In this study, dithiomalonates (DTMs) were demonstrated to be exceptionally efficient Mannich donors in terms of reactivity and stereoselectivity in cinchona‐based‐squaramide‐catalyzed enantioselective Mannich reactions of diverse imines or α‐amidosulfones as imine surrogates. Owing to the superior reactivity of DTMs as compared to conventional malonates, the catalyst loading could be reduced to 0.1 mol % without the erosion of enantioselectivity (up to 99 % ee). Furthermore, by the use of a DTM, even some highly challenging primary alkyl α‐amidosulfones were smoothly converted into the desired adducts with excellent enantioselectivity (up to 97 % ee), whereas the use of a malonate or monothiomalonate resulted in no reaction under identical conditions. The synthetic utility of the chiral Mannich adducts obtained from primary alkyl substrates was highlighted by the organocatalytic, coupling‐reagent‐free synthesis of the antidiabetic drug (?)‐(R)‐sitagliptin. 相似文献
44.
Differences in the rate of electrocatalytic proton reduction by Fe2(mu-PPh2)2(CO)6, DP, and the linked phosphido-bridged analogue Fe2(mu,mu-PPh(CH2)3PPh)(CO)6, 3P, suggest that dihydrogen elimination proceeds through a bridging hydride. The reaction path was examined using electrochemical, spectroscopic, and in silico studies where reduction of 3P gives a moderately stable monoanion [Kdisp(3P-) = 13] and a distorted dianion. The monomeric formulation of 3P- is supported by the form of the IR and EPR spectra. EXAFS analysis of solutions of 3P, 3P-, and 3P2- indicates a large increase in the Fe-Fe separation following reduction (from 2.63 to ca. 3.1-3.55 A). DFT calculations of the 3P, 3P-, 3P2- redox series satisfactorily reproduce the IR spectra in the nu(CO) region and the crystallographic (3P) and EXAFS-derived Fe-Fe distances. Digital simulation of the electrocatalytic response for proton reduction indicates a low rate of dihydrogen evolution from the two-electron, two-proton product of 3P (H23P), with more rapid dihydrogen evolution following further reduction of H23P. Because dihydrogen evolution is not observed upon formation of H2DP, dihydrogen evolution at the two-electron-reduced level does not involve protonation of a hydridic Fe-H ligand. The rates of dihydrogen elimination from H2DP, H23P, and H2Fe2(mu,mu-S(CH2)3S)(CO)6 (H23S) are related to the DFT-calculated H-H distances [H23S (1.880 A) < H23P (2.064 A) < H2DP (3.100 A)], and this suggests a common reaction path for the thiolato- and phosphido-bridged diiron carbonyl compounds. 相似文献
45.
Kim HM Yang PR Seo MS Yi JS Hong JH Jeon SJ Ko YG Lee KJ Cho BR 《The Journal of organic chemistry》2007,72(6):2088-2096
A novel, two-photon probe for the detection of free Mg2+ ions in living cells and live tissues has been developed. The probe can be excited by 880 nm laser photons, emits strong two-photon excited fluorescence in response to Mg2+ ions, can be easily loaded into the cell and tissue, shows high photostability, and can measure the Mg2+ ion concentration without interference by Ca2+ ions in living cells. The intracellular dissociation constant (Kdi) for Mg2+ determined by the two-photon process is 2.5 mM, which is suitable for dynamic Mg2+ concentration measurement. In addition, the probe is capable of imaging endogenous stores of free Mg2+ at a few hundred micrometers depth in live tissues using two-photon microscopy (TPM). 相似文献
46.
J. Rams N.V. Sochinskii V. Munõz J.M. Cabrera 《Applied Physics A: Materials Science & Processing》2000,71(3):277-279
CdTe epilayers have been grown by vapor phase epitaxy (VPE) on glass, MgO, sapphire, LiNbO3 and mica substrates. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies show the good structural quality
of the epilayers. In these epilayers, a few optical modes were excited with a 1.33-μm laser. The measured propagation losses
were in the range between 5 dB/cm and less than 0.5 dB/cm. From dark-mode m-lines, the epilayer thickness was found to be
in the 1–3 μm range, in good accord with that obtained by SEM measurements. The refractive index obtained from the fitting
is also in good accord with that of bulk CdTe.
Received: 7 October 1999 / Accepted: 13 March 2000 / Published online: 5 July 2000 相似文献
47.
ABSTRACTThe electronic rearrangements involved in Noyori hydrogenation reactions with double bonds (ethene and formaldehyde) are analysed using the bonding evolution theory. The study and analysis of the changes on the electron localisation function topology along a given reaction path reveals fluxes of electron density, allowing to unambiguously identify the main chemical events happening along the chemical reactions. This analysis shows that the first hydrogen transfer (with hydride character) occurs before the transition state (TS), while the second hydrogen transfer (with proton character) takes places after having reached the TS. The lower energy barrier found for formaldehyde over ethene is explained by two reasons. First, the hydride transfer is favoured for the C?=?O bond over C?=?C due to the electrophilic character of the carbon atom. Second, a negatively charged CH3–X (X?=?CH2, O) hidden intermediate is formed in the proximities of the TS region. The oxygen atom is able to stabilise this negatively charged species more effectively than the CH2 group due to its higher electronegativity and the presence of V(O) lone pairs. The obtained analysis explains and rationalises catalyst chemoselectivity (C?=?O vs. C?=?C). Finally, a curly arrow representation diagram accounting for the electronic rearrangements is proposed on the basis of BET results. 相似文献
48.
Chang Liu Takeshi Kondo A.D. Palczewski G.D. Samolyuk Y. Lee M.E. Tillman Ni Ni E.D. Mun R. Gordon A.F. Santander-Syro S.L. Bud’ko J.L. McChesney E. Rotenberg A.V. Fedorov T. Valla O. Copie M.A. Tanatar C. Martin B.N. Harmon P.C. Canfield A. Kaminski 《Physica C: Superconductivity and its Applications》2009,469(9-12):491-497
We present an overview of the electronic properties of iron arsenic high temperature superconductors with emphasis on low energy band dispersion, Fermi surface and superconducting gap. ARPES data is compared with full-potential linearized plane wave (FLAPW) calculations. We focus on single layer NdFeAsO0.9F0.1 (R1111) and two layer Ba1?xKxFe2As2 (B122) compounds. We find general similarities between experimental data and calculations in terms of character of Fermi surface pockets, and overall band dispersion. We also find a number of differences in details of the shape and size of the Fermi surfaces as well as the exact energy location of the bands, which indicate that magnetic interaction and ordering significantly affects the electronic properties of these materials. The Fermi surface consists of several hole pockets centered at Γ and electron pockets located in zone corners. The size and shape of the Fermi surface changes significantly with doping. Emergence of a coherent peak below the critical temperature Tc and diminished spectral weight at the chemical potential above Tc closely resembles the spectral characteristics of the cuprates, however the nodeless superconducting gap clearly excludes the possibility of d-wave order parameter. Instead it points to s-wave or extended s-wave symmetry of the order parameter. 相似文献
49.
A. Braun A. Kubatova S. Wirick S.B. Mun 《Journal of Electron Spectroscopy and Related Phenomena》2009,170(1-3):42
Carbon NEXAFS and EELS spectra of soot, and NEXAFS spectra of soot extracts, are presented. The EELS spectra of solid soot particles from a TEM-EELS show fewer structures than the corresponding NEXAFS spectra obtained at two different synchrotron beamlines. We attribute radiation damage in the TEM-EELS to the failure at resolving structures of surface functional carbon groups in or on soot. NEXAFS spectra of soot extracts studied with a scanning transmission X-ray microscope show alterations during X-ray exposure, which can be explained by a simple chemical model where oxygen apparently reacts with the sample. When the same extract is studied in an ultrahigh-vacuum beamline, no such alterations are observed. 相似文献
50.
Jen-Yang Chung Michael E. Grass Phil Ross Jr. Bongjin Simon Mun 《Surface science》2009,603(5):L35-20325
CO and O2 co-adsorption and the catalytic oxidation of CO on a Pt(1 1 0) surface under various pressures of CO and O2 (up to 250 mTorr) are studied using ambient pressure X-ray photoelectron spectroscopy (APXPS) and mass spectrometry. There is no surface oxide formation on Pt under our reaction conditions. CO oxidation in this pressure (<500 mTorr), O2 to CO ratio (<10), and temperature (150 °C) regime is consistent with the Langmuir-Hinshelwood reaction mechanism. Our findings provide in-situ surface chemical composition data of the catalytic oxidation of CO on Pt(1 1 0) at total pressures below 1 Torr. 相似文献