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排序方式: 共有162条查询结果,搜索用时 171 毫秒
71.
Bagley MC Chapaneri K Dale JW Xiong X Bower J 《The Journal of organic chemistry》2005,70(4):1389-1399
[reaction: see text] The synthesis of dimethyl sulfomycinamate, the acidic methanolysis product of the sulfomycin family of thiopeptide antibiotics, from methyl 2-oxo-4-(trimethylsilyl)but-3-ynoate is achieved in a 2,3,6-trisubstituted pyridine synthesis that proceeds with total regiocontrol in 13 steps by the Bohlmann-Rahtz heteroannulation of a 1-(oxazol-4-yl)enamine or in 12 steps and 9% yield by three-component cyclocondensation with N-[3-oxo-3-(oxazol-4-yl)propanoyl]serine and ammonia in ethanol. 相似文献
72.
Bower JF Svenda J Williams AJ Charmant JP Lawrence RM Szeto P Gallagher T 《Organic letters》2004,6(25):4727-4730
[reaction: see text] A structurally diverse series of mono- and disubstituted 1,2- and 1,3-cyclic sulfamidates react with stabilized enolates, including malonate and phosphonoacetate variants, to provide, after lactamization, substituted and alpha-functionalized pyrrolidinone and piperidinone derivatives. 相似文献
73.
E. C. Honea J. S. Kraus J. E. Bower M. F. Jarrold 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):141-143
Size selected silicon clusters have been isolated in rare gas matrices and studied by optical absorption spectroscopy. The clusters were produced in a pulsed laser vaporization source, size selected with a quadrupole mass spectrometer and deposited at low energies into a cocondensed krypton matrix held at T<20 K. A comparison of the optical spectra of ten atom wide bands (Si25-Si35, Si35-Si45 and Si45-Si55) shows the general size evolution of the optical properties. Single cluster sizes have also been isolated and show somewhat sharper spectra than the bands. The measured spectra show similarities to spectra calculated using Mie theory and bulk optical constants. Cluster-cluster agglomeration was studied by evaporating the inert gas matrix. The results suggest that the clusters agglomerate into larger particles even under the mildest "soft landing" conditions. 相似文献
74.
Under the conditions of ruthenium-catalyzed transfer hydrogenation, isoprene couples to benzylic and aliphatic alcohols 1a-g to deliver beta,gamma-unsaturated ketones 3a-g in good to excellent isolated yields. Under identical conditions, aldehydes 2a-g couple to isoprene to provide an identical set of beta,gamma-unsaturated ketones 3a-g in good to excellent isolated yields. As demonstrated by the coupling of butadiene, myrcene, and 1,2-dimethylbutadiene to representative alcohols 1b, 1c, and 1e, diverse acyclic dienes participate in transfer hydrogenative coupling to form beta,gamma-unsaturated ketones. In all cases, complete branch regioselectivity is observed, and, with the exception of adduct 3j, isomerization to the conjugated enone is not detected. Thus, formal intermolecular diene hydroacylation is achieved from the alcohol or aldehyde oxidation level. In earlier studies employing a related ruthenium catalyst, acyclic dienes were coupled to carbonyl partners from the alcohol or aldehyde oxidation level to furnish branched homoallylic alcohols. Thus, under transfer hydrogenative coupling conditions, all oxidation levels of substrate (alcohol or aldehyde) and product (homoallyl alcohol or beta,gamma-unsaturated ketone) are accessible. 相似文献
75.
Pyrrolidines and Piperidines by Ligand‐Enabled Aza‐Heck Cyclizations and Cascades of N‐(Pentafluorobenzoyloxy)carbamates
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Ian R. Hazelden Rafaela C. Carmona Dr. Thomas Langer Prof. Paul G. Pringle Prof. John F. Bower 《Angewandte Chemie (International ed. in English)》2018,57(18):5124-5128
Ligand‐enabled aza‐Heck cyclizations and cascades of N‐(pentafluorobenzoyloxy)carbamates are described. These studies encompass the first examples of efficient non‐biased 6‐exo aza‐Heck cyclizations. The methodology provides direct and flexible access to carbamate protected pyrrolidines and piperidines. 相似文献
76.
First measurement of the left-right cross section asymmetry in Z boson production by e+e- collisions
Abe K Abt I Acton PD Adolphsen CE Agnew G Alber C Alzofon DF Antilogus P Arroyo C Ash WW Ashford V Astbury A Aston D Au Y Axen DA Bacchetta N Baird KG Baker W Baltay C Band HR Baranko G Bardon O Barrera F Battiston R Bazarko AO Bean A Beer G Belcinski RJ Bell RA Ben-David R Benvenuti AC Berger R Berridge SC Bethke S Biasini M Bienz T Bilei GM Bird F Bisello D Blaylock G Blumberg R Bogart JR Bolton T Bougerolle S Bower GR Boyce RF Brau JE Breidenbach M Browder TE Bugg WM Burgess B Burke D 《Physical review letters》1993,70(17):2515-2520
77.
S. P. Ahlen S. Barwick J. J. Beatty C. R. Bower G. Gerbier R. M. Heinz D. Lowder S. McKee S. Mufson J. A. Musser P. B. Price M. H. Salamon G. Tarle A. Tomasch B. Zhou 《Hyperfine Interactions》1989,44(1-4):97-103
Kinematics predicts the severe suppression of low-energy (<1 GeV) secondary antiprotons in the Galactic cosmic rays. Thus
the observation several years ago of a finite flux of low-energy antiprotons could not be explained with existing models of
cosmic ray propagation, which led to a plethora of theoretical speculation. We have recently flown a balloon-borne instrument
to measure the energy spectrum of cosmic-ray
, and have found no antiprotons in the energy interval 200–640 MeV (corrected to the top of the atmosphere). This yields an
upper limit to the
ratio of 5.5×10−5 (90% confidence level), well below and hence contradicting the earlier result. 相似文献
78.
79.
80.
Timothy J. Donohoe John F. Bower Lisa P. Fishlock Cedric K.A. Callens 《Tetrahedron》2009,65(44):8969-1328
Ring-closing olefin metathesis (RCM) has been applied to the efficient synthesis of densely and diversely substituted pyridine and pyridazine frameworks. Routes to suitable metathesis precursors have been investigated and the scope of the metathesis step has been probed. The metathesis products function as precursors to the target heteroaromatic structures via elimination of a suitable leaving group, which also facilitates earlier steps by serving as a protecting group at nitrogen. Further functionalisation of the metathesis products is possible both prior to and after aromatisation. The net result is a powerful strategy for the de novo synthesis of highly substituted heteroaromatic scaffolds. 相似文献