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排序方式: 共有141条查询结果,搜索用时 15 毫秒
61.
62.
Pengcheng Gao Jihong Xu Tongliang Zhou Dr. Yanhong Liu Prof. Dr. Elwira Bisz Dr. Błażej Dziuk Prof. Dr. Roger Lalancette Prof. Dr. Roman Szostak Prof. Dr. Dongju Zhang Prof. Dr. Michal Szostak 《Angewandte Chemie (International ed. in English)》2023,62(12):e202218427
In the last decade, major advances have been made in homogeneous gold catalysis. However, AuI/AuIII catalytic cycle remains much less explored due to the reluctance of AuI to undergo oxidative addition and the stability of the AuIII intermediate. Herein, we report activation of aryl halides at gold(I) enabled by NHC (NHC=N-heterocyclic carbene) ligands through the development of a new class of L-shaped heterobidentate ImPy (ImPy=imidazo[1,5-a]pyridin-3-ylidene) N,C ligands that feature hemilabile character of the amino group in combination with strong σ-donation of the carbene center in a rigid conformation, imposed by the ligand architecture. Detailed characterization and control studies reveal key ligand features for AuI/AuIII redox cycle, wherein the hemilabile nitrogen is placed at the coordinating position of a rigid framework. Given the tremendous significance of homogeneous gold catalysis, we anticipate that this ligand platform will find widespread application. 相似文献
63.
Anna Migdał-Mikuli Elżbieta Szostak K. Drużbicki Diana Dołȩga 《Journal of Thermal Analysis and Calorimetry》2008,93(3):853-856
Tetrakis(dimethyl sulphoxide)nickel(II) bis(iodide) was studied by thermogravimetry (TG) and simultaneous differential thermal
analysis (SDTA) and differential scanning calorimetry (DSC). The gaseous products of the decomposition were on-line identified
by a quadrupole mass spectrometer (QMS). Thermal decomposition of the title compound proceeds in three main stages. In the
first stage, which starts just above ca. 419 K, the compound loses two dimethyl sulphoxide (DMSO) molecules per one formula
unit and small amount of iodide ion. In the second stage (464–552 K) the next DMSO ligands and the iodide ion simultaneously
are released. In the last stage (552–900 K) NiSO4 is created which next decomposes to NiO and SO3. 相似文献
64.
N-methyl amino acids (N-Me AAs) are a common component of nonribosomal peptides (NRPs), a class of natural products from which many clinically important therapeutics are obtained. N-Me AAs confer peptides with increased conformational rigidity, membrane permeability, and protease resistance. Hence, these analogues are highly desirable building blocks in the ribosomal synthesis of unnatural peptide libraries, from which functional, NRP-like molecules may be identified. By supplementing a reconstituted Escherichia coli translation system with specifically aminoacylated total tRNA that has been chemically methylated, we have identified three N-Me AAs (N-Me Leu, N-Me Thr, and N-Me Val) that are efficiently incorporated into peptides by the ribosome. Moreover, we have demonstrated the synthesis of peptides containing up to three N-Me AAs, a number comparable to that found in many NRP drugs. With improved incorporation efficiency and translational fidelity, it may be possible to synthesize combinatorial libraries of peptides that contain multiple N-Me AAs. Such libraries could be subjected to in vitro selection methods to identify drug-like, high-affinity ligands for protein targets of interest. 相似文献
65.
Wójcik Kamil Czaja Tomasz Szostak Roman Grzeszczuk Maria 《Journal of Solid State Electrochemistry》2018,22(12):3933-3945
Journal of Solid State Electrochemistry - Silver(I) halide particles embodied in polypyrrole matrices are synthesized and further processed electrochemically to get nanoparticles of silver with... 相似文献
66.
67.
B J van der Veken W A Herrebout R Szostak D N Shchepkin Z Havlas P Hobza 《Journal of the American Chemical Society》2001,123(49):12290-12293
In the infrared spectra of solutions in liquid argon of dimethyl ether ((CH(3))(2)O) and fluoroform (HCF(3)), bands due to a 1:1 complex between these monomers have been observed. The C-H stretch of the HCF(3) moiety in the complex appears 17.7 cm(-1) above that in the monomer, and its intensity decreases by a factor of 11(2). These characteristics situate the interaction between the monomers in the realm of improper, blue-shifting hydrogen bonding. The complexation shifts the C-F stretches downward by some 9 cm(-1), while the C-H stretches in (CH(3))(2)O are shifted upward by 9-15 cm(-1), and the C-O stretches are shifted downward by 5 cm(-1). These shifts are in very good agreement with those calculated by means of correlated ab initio methods, and this validates a two-step mechanism for improper, blue-shifting hydrogen bonding. In the first step, the electron density is transferred from the oxygen lone electron pairs of the proton acceptor ((CH(3))(2)O) to fluorine lone electron pairs of the proton donor (CHF(3)) which yields elongation of all CF bonds. Elongation of CF bonds is followed (in the second step) by structural reorganization of the CHF(3) moiety, which leads to the contraction of the CH bond. It is thus clearly demonstrated that not only the spectral manifestation of H-bonding and improper H-bonding but also their nature differ. 相似文献
68.
Yang Zhang Prof. Dr. Michal Szostak 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(22):e202104278
Total synthesis is considered by many as the finest combination of art and science. During the last decades, several concepts were proposed for achieving the perfect vision of total synthesis, such as atom economy, step economy, or redox economy. In this context, C−H functionalization represents the most powerful platform that has emerged in the last years, empowering rapid synthesis of complex natural products and enabling diversification of bioactive scaffolds based on natural product architectures. In this review, we present an overview of the recent strategies towards the total synthesis of heterocyclic natural products enabled by C−H functionalization. Heterocycles represent the most common motifs in drug discovery and marketed drugs. The implementation of C−H functionalization of heterocycles enables novel tactics in the construction of core architectures, but also changes the logic design of retrosynthetic strategies and permits access to natural product scaffolds with novel and enhanced biological activities. 相似文献
69.
Anna Migdał-Mikuli Elżbieta Szostak Paweł Bernard 《Journal of Thermal Analysis and Calorimetry》2014,115(1):443-449
Thermal analysis (TG/DTG/QMS), performed for [Sr(OS(CH3)2)6](ClO4)2 in a flow of argon and in temperature range of 295–585 K, indicated that the compound is completely stable up to ca. 363 K, and next starts to decompose slowly, and in the temperature at ca. 492 K looses four (CH3)2SO molecules per one formula unit. During further heating [Sr(DMSO)2](ClO4)2 melts and simultaneously decomposes with explosion. Differential scanning calorimetry (DSC) measurements performed in the temperature range of 93–370 K for [Sr(DMSO)6](ClO4)2 revealed existence of the following phase transitions: glass ? crystal phase Cr5 at T g ≈ 164 K (235 K), phase Cr5 → phase Cr4 at $ T_{\text{c6}}^{\text{h}} $ ≈ 241 K, phase Cr4 → phase Cr3 at $ T_{\text{c5}}^{\text{h}} $ ≈ 255 K, phase Cr3 → phase Cr2 at $ T_{\text{c4}}^{\text{h}} $ ≈ 277 K, phase Cr2 ? phase Cr1 at $ T_{\text{c3}}^{\text{h}} $ ≈ 322 K and $ T_{\text{c3}}^{\text{c}} $ ≈ 314 K, phase Cr1 ? phase Rot2 at $ T_{\text{c2}}^{\text{h}} $ ≈ 327 K and $ T_{\text{c2}}^{\text{c}} $ ≈ 321 K and phase Rot2 ? phase Rot1 at $ T_{\text{c1}}^{\text{h}} $ ≈ 358 K and $ T_{\text{c1}}^{\text{c}} $ ≈ 347 K. Entropy changes values of the phase transitions at $ T_{\text{c1}}^{\text{h}} $ and $ T_{\text{c2}}^{\text{h}} $ (?S ≈ 79 and 24 J mol?1 K?1, respectively) indicated that phases Rot1 and Rot2 are substantially orientationally disordered. The solid phases (Cr1–Cr5) are more or less ordered phases (?S ≈ 7, 10, 4 and 3 J mol?1 K?1, respectively). Phase transitions in [Sr(DMSO)6](ClO4)2 were also examined by Fourier transform middle infrared spectroscopy (FT-MIR). The characteristic changes in the FT-MIR absorption spectra of the low- and high-temperature phases observed at the phase transition temperatures discovered by DSC allowed us to relate these phase transitions to the changes of the reorientational motions of DMSO ligands and/or to the crystal structure changes. 相似文献
70.
On the Role of Pre‐ and Post‐Electron‐Transfer Steps in the SmI2/Amine/H2O‐Mediated Reduction of Esters: New Mechanistic Insights and Kinetic Studies 下载免费PDF全文
Dr. Michal Szostak Malcolm Spain Prof. Dr. David J. Procter 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4222-4226
The mechanism of the SmI2‐mediated reduction of unactivated esters has been studied using a combination of kinetic, radical clocks and reactivity experiments. The kinetic data indicate that all reaction components (SmI2, amine, H2O) are involved in the rate equation and that electron transfer is facilitated by Brønsted base assisted deprotonation of water in the transition state. The use of validated cyclopropyl‐containing radical clocks demonstrates that the reaction occurs via fast, reversible first electron transfer, and that the electron transfer from simple Sm(II) complexes to aliphatic esters is rapid. Notably, the mechanistic details presented herein indicate that complexation between SmI2, H2O and amines affords a new class of structurally diverse, thermodynamically powerful reductants for efficient electron transfer to carboxylic acid derivatives as an attractive alternative to the classical hydride‐mediated reductions and as a source of acyl‐radical equivalents for C?C bond forming processes. 相似文献