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21.
C. Peter Sebastian Constanze Fehse J. Paul Attfield Sudhindra Rayaprol Rainer Pöttgen 《Journal of solid state chemistry》2006,179(8):2376-2385
The rare earth-silver-stannides YAgSn, TmAgSn, and LuAgSn were synthesized from the elements by arc-melting and subsequent annealing. The three stannides were investigated by X-ray powder and single-crystal diffraction: NdPtSb type, P63mc, Z=2, a=468.3(1), pm, wR2=0.0343, 353 F2 values, 12 variables for YAgSn, and ZrNiAl type, P6¯2 m, a=726.4(2), , wR2=0.0399, 659 F2 values, 15 variables for TmAgSn, and a=723.8(2), , wR2=0.0674, 364 F2 values, 15 variables for LuAgSn. Besides conventional laboratory X-ray data with monochromatized Mo radiation, the structures were also refined on the basis of synchrotron data with , in order to clarify the silver-tin ordering more precisely. YAgSn has puckered, two-dimensional [AgSn] networks with Ag-Sn distances of 278 pm, while the [AgSn] networks of TmAgSn and LuAgSn are three-dimensional with Ag-Sn distances of 279 and 284 pm for LuAgSn. Susceptibility measurements indicate Pauli paramagnetism for YAgSn and LuAgSn. TmAgSn is a Curie-Weiss paramagnet with an experimental magnetic moment of 7.2 μB/Tm. No magnetic ordering is evident down to 2 K. The local environments of the tin sites in these compounds were characterized by 119Sn Mössbauer spectroscopy and solid-state NMR (in YAgSn and LuAgSn), confirming the tin site multiplicities proposed from the structure solutions and the absence of Sn/Ag site disordering. Mössbauer quadrupolar splittings were found in good agreement with calculated electric field gradients predicted quantum chemically by the WIEN2k code. Furthermore, an excellent correlation was found between experimental 119Sn nuclear magnetic shielding anisotropies (determined via MAS-NMR) and calculated electric field gradients. Electronic structure calculations predict metallic properties with strong Ag-Sn bonds and also significant Ag-Ag bonding in LuAgSn. 相似文献
22.
In the course of screening new streptomycete strains, the strain Streptomyces sp. Cl 58-27 caught our attention due to its interesting secondary metabolite production profile. Here, we report the isolation and characterization of an ansamycin natural product that belongs structurally to the already known kendomycins. The structure of the new kendomycin E was elucidated using NMR spectroscopy, and the corresponding biosynthetic gene cluster was identified by sequencing the genome of Streptomyces sp. Cl 58-27 and conducting a detailed analysis of secondary metabolism gene clusters using bioinformatic tools. 相似文献
23.
Peptide natural products displaying a wide range of biological activities have become important drug candidates over the years. Microorganisms have been a powerful source of such bioactive peptides, and Streptomyces have yielded many novel natural products thus far. In an effort to uncover such new, meaningful compounds, the metabolome of Streptomyces acidiscabies was analyzed thoroughly. Three new compounds, scabimycins A–C (1–3), were discovered, and their chemical structures were elucidated by NMR spectroscopy. The relative and absolute configurations were determined using ROESY NMR experiments and advanced Marfey’s method. 相似文献
24.
Dr. Xiao Shen Constanze N. Neumann Claudia Kleinlein Nathaniel W. Goldberg Prof. Dr. Tobias Ritter 《Angewandte Chemie (International ed. in English)》2015,54(19):5662-5665
An alkyl aryl ether bond formation reaction between phenols and primary and secondary alcohols with PhenoFluor has been developed. The reaction features a broad substrate scope and tolerates many functional groups, and substrates that are challenging for more conventional ether bond forming processes may be coupled. A preliminary mechanistic study indicates reactivity distinct from conventional ether bond formation. 相似文献
25.
Peter Thumbs Timm T. Ensfelder Markus Hillmeier Mirko Wagner Matthias Heiss Constanze Scheel Alexander Schn Markus Müller Stylianos Michalakis Stefanie Kellner Thomas Carell 《Angewandte Chemie (International ed. in English)》2020,59(30):12352-12356
Queuosine (Q) is a hypermodified RNA nucleoside that is found in tRNAHis, tRNAAsn, tRNATyr, and tRNAAsp. It is located at the wobble position of the tRNA anticodon loop, where it can interact with U as well as C bases located at the respective position of the corresponding mRNA codons. In tRNATyr and tRNAAsp of higher eukaryotes, including humans, the Q base is for yet unknown reasons further modified by the addition of a galactose and a mannose sugar, respectively. The reason for this additional modification, and how the sugar modification is orchestrated with Q formation and insertion, is unknown. Here, we report a total synthesis of the hypermodified nucleoside galactosyl‐queuosine (galQ). The availability of the compound enabled us to study the absolute levels of the Q‐family nucleosides in six different organs of newborn and adult mice, and also in human cytosolic tRNA. Our synthesis now paves the way to a more detailed analysis of the biological function of the Q‐nucleoside family. 相似文献
26.
Eugen Wuckert Sabine Laschat Angelika Baro Constanze H gele Frank Giesselmann Heinrich Luftmann 《Liquid crystals》2006,33(1):103-107
We report the synthesis and liquid crystalline properties of novel ester-substituted tetraphenylenes obtained from octamethoxytetraphenylene by demethylation and esterification. The target compounds display focal-conic textures typical for columnar mesophases, which are either rectangular or hexagonal columnar in nature, depending on the alkyl chain length. 相似文献
27.
28.
Alexandroff T
0
-spaces have been studied as topological models of the supports of digital images and as discrete models of continuous spaces
in theoretical physics. Recently, research has been focused on the dimension of such spaces. Here we study the small inductive
dimension of the digital space X(W) constructed in [15] as a minimal open quotient of a fenestration W of R
n
. There are fenestrations of R
n
giving rise to digital spaces of Alexandroff dimension different from n , but we prove that if W is a fenestration, each of whose elements is a bounded convex subset of R
n
, then the Alexandroff dimension of the digital space X(W) is equal to n .
Received December 6, 1999, and in revised form July 5, 2001, and August 31, 2001. Online publication January 7, 2002. 相似文献
29.
30.
Strojek W Fehse CM Eckert H Ewald B Kniep R 《Solid state nuclear magnetic resonance》2007,32(3):89-98
A comprehensive solid-state NMR investigation on crystalline Na(5)B(2)P(3)O(13) is presented. Triple-quantum magic angle spinning (TQMAS) and rotational echo double resonance (REDOR) studies are used for accurate determinations of the (11)B, (23)Na and (31)P interaction parameters. Based on these results and complementary quantum mechanical calculations, plausible site assignments can be derived. Generally, the results show that detailed, quantitative information about structures in borophosphate compounds can be obtained by investigating both the local site environments characterized by chemical shift and quadrupolar interaction parameters and the correlated dipolar interactions to atoms in the second coordination sphere. 相似文献