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21.
Information
Congresses, Conferences, Symposia, Meetings, and Seminars in the Field of Chemical Sciences Held in 1995–1996 相似文献22.
Rapp A Schnell I Sebastiani D Brown SP Percec V Spiess HW 《Journal of the American Chemical Society》2003,125(43):13284-13297
Advanced solid-state NMR methods under fast magic-angle spinning (MAS) are used to study the structure and dynamics of large supramolecular systems, which consist of a polymer backbone with dendritic side groups and self-assemble into a columnar structure. The NMR experiments are performed on as-synthesized samples, i.e., no isotopic enrichment is required. The analysis of (1)H NMR chemical-shift effects as well as dipolar (1)H-(1)H or (1)H-(13)C couplings provide site-specific insight into the local structure and the segmental dynamics, in particular, of phenyl rings and -CH(2)O- linking units within the dendrons. Relative changes of (1)H chemical shifts (of up to -3 ppm) serve as distance constraints and allow protons to be positioned relative to aromatic rings. Together with dipolar spinning sideband patterns, pi-pi packing phenomena and local order parameters (showing variations between 30% and 100%) are selectively and precisely determined, enabling the identification of the dendron cores as the structure-directing moieties within the supramolecular architecture. The study is carried out over a representative selection of systems which reflect characteristic differences, such as different polymer backbones, sizes of dendritic side groups, or length and flexibility of linking units. While the polymer backbone is found to have virtually no effect on the overall structure and properties, the systems are sensitively affected by changing the generation or the linkage of the dendrons. The results help to understand the self-assembly process of dendritic moieties and aid the chemical design of self-organizing molecular structures. 相似文献
23.
24.
Adolf Emil Siegrist Hans Rudolf Meyer Peter Gassmann Serge Moss 《Helvetica chimica acta》1980,63(5):1311-1334
Preparation of Styryl and Distyryl Derivatives of Pyridine 2,4-, 2,5- and 2,6-Dimethylpyridines react with anils of aromatic aldehydes in the presence of dimethylformamide and potassium hydroxide to yield the corresponding distyrylpyridines (‘anil synthesis’). Under the same reaction conditions (4-methylstyryl)pyridines are converted to (stilbenylvinyl)pyridines. Similarly, the Schiff's base derived from pyridine-3-carbaldehyde and p-chloroaniline on treatment with methyl- and p-tolyl-substituted aromatic heterocycles gives the corresponding (heteroaryl-styryl)pyridines, whereas with the Schiff's bases derived from pyridine-2- and -4-carbaldehyde side reactions, such as dimerization followed by disproportionation predominate. 相似文献
25.
Information
Contests for gold medals and prizes named after outstanding scientists in the field of chemical sciences declared by the Russian Academy of Sciences in 1994 相似文献26.
Fast protein sequence determination with matrix-assisted laser desorption and ionization mass spectrometry 总被引:1,自引:0,他引:1
Measurement and identification of digested peptides by matrix-assisted laser desorption and ionization mass spectrometry (LDI-MS) is demonstrated. Synthetic human parathyroid hormone, pTH (1-34), with a molecular mass of 4117.8 Da was digested with carboxypeptidases Y and B and the sequence of 14 amino acids from the C-terminus of the peptide was determined by analyzing the molecular mass of the truncated peptides. Furthermore, a tryptic digestion of pTH (1-34) was carried out and a molecular mass map of pTH (1-34) was obtained. With the results of the proteolytic digestion a rapid confirmation of the amino-acid sequence of the protein was possible. It is shown that the results of the tryptic digestion can be used for the unambiguous identification of the amino acid residues Lys and Arg, which cannot be distinguished with a mass spectrometer because of their equal nominal masses. Several advantages of amino acid sequence determination by the combination of digestion and LDI-MS are obvious: high sensitivity in the low pmol range, fast digestion time due to high enzyme/substrate ratios, quantification is unnecessary because the amino acids are identified by their molecular mass differences, the low chemical expenditure for the digestions and the accuracy of the sequence determination. Measurements with LDI-MS are fast: sample preparation and the measurement take only a few min. The mass determination and amino acid sequence is completely unimpaired by amino acid contaminations or impurities in the sample. The sensitivity of the method is in the low pmol to fmol range and thus comparable to other analytical methods. 相似文献
27.
E. Mergel G. Schönwaβer H. Hübel D. Roβbach P. G. Thirolf M. Chromik D. Gassmann D. Habs P. Reiter 《Acta Physica Hungarica A》2001,13(1-3):199-202
Transitions between nuclear states with a large deformation difference may have large transition probabilities for E0 decay. Such an E0 decay has been found in the decay of the superdeformed 238U fission isomer back into the normal-deformed states [1]. However, a search for the E0 back-decay in 236U showed no result [2]. A setup has been developed to search for conversion electrons in this decay. 相似文献
28.
Percec V Glodde M Peterca M Rapp A Schnell I Spiess HW Bera TK Miura Y Balagurusamy VS Aqad E Heiney PA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(24):6298-6314
Semifluorinated first-generation self-assembling dendrons attached via a flexible spacer to electron-donor molecules induce pi-stacking of the donors in the center of a supramolecular helical pyramidal column. These helical pyramidal columns self-organize in various columnar liquid crystal phases that mediate self-processing of large single crystal liquid crystal domains of columns and self-repair their intracolumnar structural defects. In addition, all supramolecular columns exhibit a columnar phase at lower temperatures that maintains the helical pyramidal columnar supramolecular structure and displays higher intracolumnar order than that in the liquid crystals phases. The results described here demonstrate the universality of this concept, the power of the fluorous phase or the fluorophobic effect in self-assembly and the unexpected generality of pyramidal liquid crystals. 相似文献
29.
We propose an entanglement generation scheme that requires neither the coherent evolution of a quantum system nor the detection of single photons. Instead, the desired state is heralded by a macroscopic quantum jump. Macroscopic quantum jumps manifest themselves as a random telegraph signal with long intervals of intense fluorescence (light periods) interrupted by the complete absence of photons (dark periods). Here we show that a system of two atoms trapped inside an optical cavity can be designed such that a dark period prepares the atoms in a maximally entangled ground state. Achieving fidelities above 0.9 is possible even when the single-atom cooperativity parameter is as low as 10 and when using a photon detector with an efficiency as low as eta=0.2. 相似文献
30.
The first lanthanum fluoride borate La4B4O11F2 was obtained in a Walker-type multianvil apparatus at 6 GPa and 1300 °C. La4B4O11F2 crystallizes in the monoclinic space group P21/c with the lattice parameters a=778.1(2) pm, b=3573.3(7) pm, c=765.7(2) pm, β=113.92(3)° (Z=8), and represents a new structure type in the class of compounds with the composition RE4B4O11F2. The crystal structure contains BO4-tetrahedra interconnected with two BO3-groups via common vertices, B2O5-pyroborate units, and isolated BO3-groups. The structure shows a wave-like modulation along the b-axis. The crystal structure and properties of La4B4O11F2 are discussed and compared to Gd4B4O11F2. 相似文献