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排序方式: 共有150条查询结果,搜索用时 109 毫秒
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Confocal Raman micro-spectral imaging (CRMI) is a relatively novel technique for the construction of label-free images of biological entities, such as cells or tissue sections. This method utilizes thousands of spatially resolved Raman spectra, and sophisticated image analysis algorithms, to construct images which are based strictly on the inherent biochemical abundance contrast afforded by Raman microscopy. Here, we apply this methodology to monitor the very early communication processes that occur in a growing stem cell colony, yielding information on biochemical composition during development processes of the early stages of embryogenesis. 相似文献
64.
Diego Venegas-Yazigi Daniel Aravena Evgenia Spodine Eliseo Ruiz Santiago Alvarez 《Coordination chemistry reviews》2010,254(17-18):2086-2095
Computational methods based on density functional theory have been employed to analyze the magnetic properties of dinuclear bis(phenoxo)-bridged CuII complexes. While the largest part of complexes in that family show antiferromagnetic coupling, we focus our study on those cases with distorted geometries that present ferromagnetic behaviour. The calculations reproduce such a magnetic behaviour, and a structural analysis reveals the main role played by several structural parameters, such as the Cu–O–Cu bridging angle. The out-of-plane shift of the phenoxo ring and the hinge distortion of the Cu2O2 central framework that are also important for similar hydroxo and alkoxo complexes. In this case the conformation of the phenoxo groups and the rotation of the phenyl rings can also play an important role. The last part of this work is dedicated to analyze the influence of the substituents of the phenoxo ring on the magnetic properties, which is especially important for structures with large out-of-plane shifted phenoxo rings. The presence of π electron releasing groups favours a ferromagnetic coupling. 相似文献
65.
I. Yu. Vashurina N. E. Kochkina Yu. A. Kalinnikov 《Russian Journal of Applied Chemistry》2006,79(2):321-324
Influence of peat humus acid microadditions on the structure of starch gels for sizing cotton yarn is studied by rheology. 相似文献
66.
Ji Ma Yubin Fu Dr. Evgenia Dmitrieva Dr. Fupin Liu Dr. Hartmut Komber Dr. Felix Hennersdorf Dr. Alexey A. Popov Prof. Dr. Jan J. Weigand Dr. Junzhi Liu Prof. Dr. Xinliang Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(14):5686-5691
Three unprecedented helical nanographenes ( 1 , 2 , and 3 ) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X-ray crystallographic analysis. The embedded azulene unit in 2 possesses a record-high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis-spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps ( 2 : 1.88 eV; 3 : 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in-situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties. 相似文献
67.
The influence of the sample preparation parameters (the choice of the matrix, matrix:analyte ratio, salt:analyte ratio) was investigated and optimal conditions were established for the MALDI time-of-flight mass spectrometry analysis of the poly(styrene-co-pentafluorostyrene) copolymers. These were synthesized by atom transfer radical polymerization. Use of 2,5-dihydroxybenzoic acid as matrix resulted in spectra with consistently high ion yields for all matrix:analyte:salt ratios tested. The optimized MALDI procedure was successfully applied to the characterization of three copolymers obtained by varying the conditions of polymerization reaction. It was possible to establish the nature of the end groups, calculate molecular weight distributions, and determine the individual length distributions for styrene and pentafluorostyrene monomers, contained in the resulting copolymers. Based on the data obtained, it was concluded that individual styrene chain length distributions are more sensitive to the change in the composition of the catalyst (the addition of small amount of CuBr2) than is the pentafluorostyrene component distribution. 相似文献
68.
Sebastian N. Intorp Manuel Hodecker Matthias Müller Olena Tverskoy Marco Rosenkranz Evgenia Dmitrieva Alexey A. Popov Frank Rominger Jan Freudenberg Andreas Dreuw Uwe H. F. Bunz 《Angewandte Chemie (International ed. in English)》2020,59(30):12396-12401
Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low‐energy gap ΔEST′ of 0.58 to 1.0 kcal mol?1. The species are persistent in solution (half‐life≈14–21 h) and in the solid state they are stable for weeks. 相似文献
69.
Venegas-Yazigi D Brown KA Vega A Calvo R Aliaga C Santana RC Cardoso-Gil R Kniep R Schnelle W Spodine E 《Inorganic chemistry》2011,50(22):11461-11471
Structural, magnetic, and powder and single-crystal electron paramagnetic resonance (EPR) studies were performed on [{Cu(bipy)(en)}{Cu(bipy)(H(2)O)}{VO(3)}(4)](n) (bipy = 2,2'-bipyridine, en = ethylenediamine), which is a new copper-vanadium hybrid organic-inorganic compound containing Cu(II) and V(V) centers. The oxovanadium units provide an anionic scaffolding to the structure, where two types of Cu(II) coordination modes, octahedral (Cu1) and square pyramidal (Cu2), contribute to the magnetic properties. The crystal structure contains layers including Cu1 and Cu2 ions, separated by stacked arrangements of 2,2'-bipyridine molecules. Each type of Cu(II) ion in these layers forms parallel spin chains described by exchange coupling parameters J(1) and J(2) for Cu1 and Cu2, respectively (exchange couplings defined as H(ex)(i,j) = -J(ij)S(i)S(j)), which, for necessity, are assumed to be equal to J. These chains are coupled by much weaker Cu1-Cu2 exchange interactions J(3) connecting neighbor Cu1 and Cu2 ions within a layer, through paths acting as rungs of a ladder chain structure. The average coupling J, which is antiferromagnetic (J < 0), according to the susceptibility data, is estimated with similar results with a mean field approximation (J = -1.4 cm(-1)), and with a uniform chain model (J = -1.7 cm(-1)). The EPR spectra of powdered samples and oriented single crystals are shown to be independent of J(1) and J(2), but are dependent on the weak coupling J(3), and the data allow a lower limit to be established: |J(3)| > 0.04 cm(-1). The spectra are also strongly sensitive to extremely weak coupling interactions with average magnitude J(4) between copper atoms in neighboring layers, separated by ~10 ?, using the stacked 2,2'-bipyridine molecules, which produce a 2D-to-3D quantum phase transition. This is observed in single-crystal samples when the energy levels are changed with the orientation of the magnetic field. From the characteristics of these transitions, we estimate a value of |J(4)| = 0.0034 ± 0.0004 cm(-1) between Cu(II) ions in neighboring layers. This work emphasizes the important possibilities of EPR to evaluate extremely small exchange couplings between metal ions in a solid material, even in the presence of other much larger couplings. 相似文献
70.
Andrei S. Potapov Evgenia A. Nudnova Andrei I. Khlebnikov Vladimir D. Ogorodnikov Tatiana V. Petrenko 《Journal of heterocyclic chemistry》2011,48(3):645-651
Reaction of pyrazole and 1,1,2,2‐tetrabromoethane in a superbasic medium dimethylsulfoxide‐potassium hydroxide was investigated, and a number of pyrazolyl‐ and bromo‐substituted ethenes, which are the products of concurrent substitution and elimination reactions, were identified. Carrying out the reaction using different reagent mole ratios allowed to selectively isolate Z‐1,2‐bis(pyrazol‐1‐yl)ethene, 1,1,2‐tris(pyrazol‐1‐yl)ethane, and 1,1,2,2‐tetrakis(pyrazol‐1‐yl)ethane. Crystal structure of {Z‐1,2‐bis (pyrazol‐1‐yl)ethene}dichlorozinc was established using X‐ray diffraction method. J. Heterocyclic Chem., (2011). 相似文献