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951.
Maria Alice Bertolim Ketty Abaroa de Rezende Oziride Manzoli Neto Gioia M. Vago 《Geometriae Dedicata》2006,121(1):19-41
We present a constructive general procedure to build Morse flows on n-dimensional isolating blocks respecting given dynamical and homological boundary data recorded in abstract Lyapunov semi-graphs.
Moreover, we prove a decomposition theorem for handles which, together with a special class of gluings, insures that this
construction not only preserves the given ranks of the homology Conley indices, but it is also optimal in the sense that no
other Morse flow can preserve this index with fewer singularities.
相似文献
952.
953.
We prove that the crossing number of C4 × C4 is 8. © 1995 John Wiley & Sons, Inc. 相似文献
954.
955.
956.
Alice Mae Guckin 《School science and mathematics》1982,82(2):109-110
957.
Paula M. Secondo Russell G. Baughman Harvest L. Collier 《Journal of chemical crystallography》1997,27(6):371-375
The nucleophilic addition reactions between 1,1′-di(2-propanone)-2,2′-biimidazole or 2,6-diacetylpyridine and hydrazine hydrate afford 1,1′-di(2-propanone)-2,2′-biimidazole dihydrazone (1) and 2,6-diacetylpyridine dihydrazone (2), respectively. Compound1 crystallizes in the orthorhombic space groupP212121, witha=9.042(2),b=9.731(3),c=15.683(4)Å, V = 1379.9(6)Å? andZ=4. Compound2 crystallizes in the orthorhombic space groupPnma, witha=10.948(2),b=19.742(6),c=4.566(1)Å, V=986.9(4)Å? andZ=8. A pseudo center of inversion is present at the midpoint of the C?C bond joining the imidazole rings of1, whose substituents crystallize in atrans configuration. The imidazole rings are rotated 2.5(3)° about the C?C bond. In contrast to the essentially planar structure of2, the hydrazone substituent groups of1 are at angles of 89.9(1)° and 88.4(1)° with respect to the plane of the adjacent imidazole moiety. 相似文献
958.
Synthesis and crystal structure of 1,1′-di(ethylpropionato)-2,2′-biimidazole, a macromolecular precursor 总被引:1,自引:0,他引:1
W. Mark Barnett Russell G. Baughman Harvest L. Collier William G. Vizuete 《Journal of chemical crystallography》1999,29(7):765-768
1,1,-Di(ethylpropionato)-2,2-biimidazole, C16H22N4O4, crystallizes from ice-cold ethanol in the space group P
, with a = 4.6742(9), b = 9.1119(13), c = 10.175(2) Å, = 96.22(1), = 96.29(2), = 97.53(1)°, and Z = 1. The molecule crystallizes with coplanar rings and the substituents assume a trans conformation with a center of inversion between the bridging carbon atoms. 相似文献
959.
Joana Silva Alice Martins Celso Alves Susete Pinteus Helena Gaspar Amparo Alfonso Rui Pedrosa 《Molecules (Basel, Switzerland)》2020,25(22)
Parkinson’s disease (PD) is the second most common neurodegenerative disorder, and is characterized by a progressive degeneration of the dopaminergic neurons in the substantia nigra. Although not completely understood, several abnormal cellular events are known to be related with PD progression, such as oxidative stress, mitochondrial dysfunction and apoptosis. Accordingly, the aim of this study was to evaluate the neuroprotective effects of Codium tomentosum enriched fractions in a neurotoxicity model mediated by 6-hydroxydopamine (6-OHDA) on SH-SY5Y human cells, and the disclosure of their mechanisms of action. Additionally, a preliminary chemical screening of the most promising bioactive fractions of C. tomentosum was carried out by GC-MS analysis. Among the tested fractions, four samples exhibited the capacity to revert the neurotoxicity induced by 6-OHDA to values higher or similar to the vitamin E (90.11 ± 3.74% of viable cells). The neuroprotective effects were mediated by the mitigation of reactive oxygen species (ROS) generation, mitochondrial dysfunctions and DNA damage, together with the reduction of Caspase-3 activity. Compounds belonging to different chemical classes, such as terpenes, alcohols, carboxylic acids, aldehydes, esters, ketones, saturated and unsaturated hydrocarbons were tentatively identified by GC-MS. The results show that C. tomentosum is a relevant source of neuroprotective agents, with particular interest for preventive therapeutics. 相似文献
960.
Luke A. Johnson Alice Dunbabin Jennifer C. R. Benton Robert J. Mart Rudolf K. Allemann 《Angewandte Chemie (International ed. in English)》2020,59(22):8486-8490
Non‐natural terpenoids offer potential as pharmaceuticals and agrochemicals. However, their chemical syntheses are often long, complex, and not easily amenable to large‐scale production. Herein, we report a modular chemoenzymatic approach to synthesize terpene analogues from diphosphorylated precursors produced in quantitative yields. Through the addition of prenyl transferases, farnesyl diphosphates, (2E,6E)‐FDP and (2Z,6Z)‐FDP, were isolated in greater than 80 % yields. The synthesis of 14,15‐dimethyl‐FDP, 12‐methyl‐FDP, 12‐hydroxy‐FDP, homo‐FDP, and 15‐methyl‐FDP was also achieved. These modified diphosphates were used with terpene synthases to produce the unnatural sesquiterpenoid semiochemicals (S)‐14,15‐dimethylgermacrene D and (S)‐12‐methylgermacrene D as well as dihydroartemisinic aldehyde. This approach is applicable to the synthesis of many non‐natural terpenoids, offering a scalable route free from repeated chain extensions and capricious chemical phosphorylation reactions. 相似文献