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581.
Veronique Gibon Kristina Szafraniak Guy Evrard Francois Durant 《Journal of chemical crystallography》1987,17(6):751-760
The crystal structure of oxacillin sulfone has been determined by single-crystal X-ray diffraction techniques and refined by full-matrix least squares. The penicillin molecule cocrystallizes with H2O in an orthorhombic space groupP212121 witha=10.303(7) Å,b=26.735(17) Å, andc=7.384(4) Å. The calculated density is 1.526 g cm–3, with aZ value of 4. FinalR-factor is 0.035. The oxidation of the sulfur atom is discussed in terms ofS1 conformation of the penam moiety and in terms of hydrogen-bond formation between one oxygen of the sulfur atom and the amidic hydrogen of the C6 side-chain. A comparison with oxacillin and cloxacillin sulfoxide is also made. 相似文献
582.
Robert F. CampbellKevin Fitzpatrick Tord InghardtOlle Karlsson Kristina NilssonJohn E. Reilly Larry Yet 《Tetrahedron letters》2003,44(29):5477-5481
A series of substituted mandelic acids were prepared and subjected to enzymatic resolution utilizing Lipase PS ‘Amano’. 相似文献
583.
584.
Christopher J. Shaffer Ales Marek Robert Pepin Kristina Slovakova Frantisek Turecek 《Journal of mass spectrometry : JMS》2015,50(3):470-475
The combination of near‐UV photodissociation with electron transfer and collisional activation provides a new tool for structure investigation of isolated peptide ions and reactive intermediates. Two new types of pulse experiments are reported. In the first one called UV/Vis photodissociation–electron transfer dissociation (UVPD‐ETD), diazirine‐labeled peptide ions are shown to undergo photodissociation in the gas phase to form new covalent bonds, guided by the ion conformation, and the products are analyzed by electron transfer dissociation. In the second experiment, called ETD‐UVPD wherein synthetic labels are not necessary, electron transfer forms new cation–peptide radical chromophores that absorb at 355 nm and undergo specific backbone photodissociation reactions. The new method is applied to distinguish isomeric ions produced by ETD of arginine containing peptides. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
585.
Dr. Cher Hon Lau Dr. Kristina Konstas Dr. Aaron W. Thornton Dr. Amelia C. Y. Liu Dr. Stephen Mudie Dr. Danielle F. Kennedy Dr. Shaun C. Howard Dr. Anita J. Hill Dr. Matthew R. Hill 《Angewandte Chemie (International ed. in English)》2015,54(9):2669-2673
Porosity loss, also known as physical aging, in glassy polymers hampers their long term use in gas separations. Unprecedented interactions of porous aromatic frameworks (PAFs) with these polymers offer the potential to control and exploit physical aging for drastically enhanced separation efficiency. PAF‐1 is used in the archetypal polymer of intrinsic microporosity (PIM), PIM‐1, to achieve three significant outcomes. 1) hydrogen permeability is drastically enhanced by 375 % to 5500 Barrer. 2) Physical aging is controlled causing the selectivity for H2 over N2 to increase from 4.5 to 13 over 400 days of aging. 3) The improvement with age of the membrane is exploited to recover up to 98 % of H2 from gas mixtures with N2. This process is critical for the use of ammonia as a H2 storage medium. The tethering of polymer side chains within PAF‐1 pores is responsible for maintaining H2 transport pathways, whilst the larger N2 pathways gradually collapse. 相似文献
586.
Recently a new formulation of quantum mechanics has been suggested which is based on the concept of signed particles, that is, classical objects provided with a position, a momentum and a sign simultaneously. In this article, we comment on the plausibility of simulating atomic systems beyond the Born–Oppenheimer approximation by means of the signed particle formulation of quantum mechanics. First, to show the new perspective offered by this new formalism, we provide an example studying quantum tunnelling through a simple Gaussian barrier in terms of the signed particle formulation. Then, we perform a direct simulation of the hydrogen atom as a full quantum two‐body system, showing that the formalism can be a very promising tool for first‐principle‐only quantum chemistry. 相似文献
587.
Vanessa Kristina Seiler Wilhelm Maximilian Hützler Michael Bolte 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(5):379-388
In order to examine the preferred hydrogen‐bonding pattern of various uracil derivatives, namely 5‐(hydroxymethyl)uracil, 5‐carboxyuracil and 5‐carboxy‐2‐thiouracil, and for a conformational study, crystallization experiments yielded eight different structures: 5‐(hydroxymethyl)uracil, C5H6N2O3, (I), 5‐carboxyuracil–N,N‐dimethylformamide (1/1), C5H4N2O4·C3H7NO, (II), 5‐carboxyuracil–dimethyl sulfoxide (1/1), C5H4N2O4·C2H6OS, (III), 5‐carboxyuracil–N,N‐dimethylacetamide (1/1), C5H4N2O4·C4H9NO, (IV), 5‐carboxy‐2‐thiouracil–N,N‐dimethylformamide (1/1), C5H4N2O3S·C3H7NO, (V), 5‐carboxy‐2‐thiouracil–dimethyl sulfoxide (1/1), C5H4N2O3S·C2H6OS, (VI), 5‐carboxy‐2‐thiouracil–1,4‐dioxane (2/3), 2C5H4N2O3S·3C6H12O3, (VII), and 5‐carboxy‐2‐thiouracil, C10H8N4O6S2, (VIII). While the six solvated structures, i.e. (II)–(VII), contain intramolecular S(6) O—H…O hydrogen‐bond motifs between the carboxy and carbonyl groups, the usually favoured R22(8) pattern between two carboxy groups is formed in the solvent‐free structure, i.e. (VIII). Further R22(8) hydrogen‐bond motifs involving either two N—H…O or two N—H…S hydrogen bonds were observed in three crystal structures, namely (I), (IV) and (VIII). In all eight structures, the residue at the ring 5‐position shows a coplanar arrangement with respect to the pyrimidine ring which is in agreement with a search of the Cambridge Structural Database for six‐membered cyclic compounds containing a carboxy group. The search confirmed that coplanarity between the carboxy group and the cyclic residue is strongly favoured. 相似文献
588.
Angela Metz Alexander Hoffmann Kristina Hock Sonja Herres‐Pawlis 《Chemie in Unserer Zeit》2016,50(5):316-325
Bioplastics represent an important possibility to reduce environmental pollution by non‐degradable plastics and open up new resources for plastics production. To promote wide application of bioplastics, new catalysts are urgently needed. This article summarises recent developments of robust lactide polymerisation catalysts as well as the embedding of the produced PLA into the life cycle of bioplastics. 相似文献
589.
Kristina Bašnec Metka Hajzeri Marta Klanjšek Gunde 《Journal of Thermal Analysis and Calorimetry》2017,127(1):55-61
Leuco dye–developer–solvent composites with thermochromic properties were studied. The applied 1-dodecanol solvent shows β crystalline, α solid (rotator) and liquid phases. The inclusion of the crystal violet lactone dye increases transition temperatures of all phases and strengthens the α phase. The benzyl 4-hydroxybenzoate developer causes opposite effects and prevents the appearance of the α phase. These consequences combine in ternary composites, where lower transition temperatures were obtained as in the solvent, but the α phase is formed more likely as expected due to the presence of the developer. The hydration of the composite strengthens its crystalline network, but makes α phase more unstable. The thermal properties were related to the temperature-dependent colour. Composites with well-resolved α and β phases at cooling show a typical colour hysteresis. If only weak α phase or none at all was found in DSC curves, the colour hysteresis has an unusual shape with heating and cooling curves crossing each other. The hydration of the composite changes the colorimetric properties in accordance with the relation found for anhydrous composite. More conclusions and interrelations between the two properties require application of other analytical methods. 相似文献
590.
Shutov Dmitriy A. Smirnova Kristina V. Ivanov Alexander N. Rybkin Vladimir V. 《Plasma Chemistry and Plasma Processing》2022,42(1):179-190
Plasma Chemistry and Plasma Processing - The formation of precipitation under the action of a direct current atmospheric pressure discharge in air on a copper (II) nitrate solution was... 相似文献