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91.
Brad M. Rosen Gerard Lligadas Christian Hahn Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2009,47(15):3931-3939
The development of a novel nucleophilic thio‐bromo “Click” reaction, specifically base‐mediated thioetherification of thioglycerol with α‐bromoesters, is reported. Combination of this thio‐bromo click reaction with subsequent acylation with 2‐bromopropionyl bromide provides an iterative two‐step divergent growth approach to the synthesis of a new class of poly(thioglycerol‐2‐propionate) (PTP) dendrimers. This approach is demonstrated in the rapid preparation of four generation (G1–G4) of PTP dendrimers with high‐structural fidelity. The isolated G1–G4 bromide‐terminated dendrimers can be used directly as dendritic macroinitiators for the synthesis of star‐polymers via SET‐LRP. Additionally, the intermediate hydroxy‐terminated dendrimers are analogs of other water‐soluble polyester and polyether dendrimers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3931–3939, 2009 相似文献
92.
Brad M. Rosen Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2008,46(16):5663-5697
The heterolytic dissociation process associated with the activation of Single Electron‐Transfer Living Radical Polymerization is examined through the use of energy profile modeling. Monomer and initiator structure is correlated with the approximate activation barriers, energies of electrostatic ion‐radical pair formation, and stability of ion‐radical pair generated from the counteranion halide leaving group and the radical atom with partial positive charge density induced by its electron‐withdrawing substituent. Energy profiles permit access not just to one, but to all local minima, in the dissociation pathway and the identification of a global minimum. The location and energy of this global minimum allows for the placement of various initiators and dormant propagating macroradicals on the spectrum between stepwise and concerted dissociative electron‐transfer. The barrier for the activation step for alkyl‐halides derived from acrylates, vinyl halides, and styrenes, as well as from initiators bearing electron‐withdrawing groups is decreased in comparison to relatively more electron‐rich alkyl halides. This rate enhancement is explained through the sticky dissociative model wherein electron‐transfer is accelerated by the formation of strong ion‐radical pairs between radicals with partial positive charge density and their counteranion leaving group. Greater electron‐withdrawing capacity of the alkyl halide substituent increases the stability of the ion‐radical pair, reduces its equilibrium bond length, and accelerates electron‐transfer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5663–5697, 2008 相似文献
93.
Virgil Percec Shigeru Okita 《Journal of polymer science. Part A, Polymer chemistry》1992,30(6):1037-1049
This article describes the synthesis of a novel series of soluble polyarylenes containing alternating binapthylene and biphenylene structural units. They were obtained by the cation-radical polymerization of bis(1-naphthyl) biphenyls. The following monomers were synthesized and polymerized : 4,4′-bis(1-naphthyl) biphenyl ( 9 ), 3,3′-bis(1-naphthyl) biphenyl ( 10 ), 2,2′-bis(1-naphthyl)biphenyl ( 11 ), and 2,5-bis(1-naphthyl)biphenyl ( 14 ). All polymerizations were performed in nitrobenzene using FeCl3 as oxidant. Polymers with number average molecular weights of up to 4000 g/mol were obtained. 相似文献
94.
95.
Virgil Percec Anatoliy V. Popov 《Journal of polymer science. Part A, Polymer chemistry》2005,43(6):1255-1260
The chloroiodomethyl chain ends of poly(vinyl chloride) (PVC) obtained by the single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization of vinyl chloride initiated with iodoform were quantitatively functionalized by the reaction with 2‐allyloxyethanol (CH2?CHCH2OCH2CH2OH). This reaction was performed in dimethyl sulfoxide at 70 °C and was catalyzed by sodium dithionite/sodium bicarbonate. The resulting product is the first example of telechelic PVC [α,ω‐di(hydroxy)PVC]. A possible mechanism for this reaction was suggested. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1255–1260, 2005 相似文献
96.
97.
Virgil Percec Ernesto Ramirez‐Castillo Anatoliy V. Popov Luis A. Hinojosa‐Falcon Tamaz Guliashvili 《Journal of polymer science. Part A, Polymer chemistry》2005,43(10):2178-2184
Sodium dithionite in the presence of NaHCO3 in water acts as a single‐electron‐transfer agent and facilitates the single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization (SET–DTLRP) of acrylates initiated with iodoform at room temperature. The resulting α,ω‐di(iodo)polyacrylates can be used as macroinitiators for the SET–DTLRP of other acrylates. Ultrahigh‐molar‐mass poly(tert‐butyl acrylate) can be synthesized via the SET–DTLRP of tert‐butyl acrylate and has a very low weight‐average molecular weight/number‐average molecular weight ratio of 1.15. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2178–2184, 2005 相似文献
98.
C13 Nmr chemical shits of primaquine and chloroquine are reported. The signals are assigned on the basis of substituent effects on benzene shifts, intensities, multiplicities in SFORI) and the comparison with structurally related compounds. 相似文献
99.
Virgil E. Barnes 《Physics letters. [Part B]》1976,65(2):174-176
The nonobservation of photon-induced e+e? pairs pointing in the neutrino beam direction in large bubble chambers would allow one to set an upper limit on the product mνμλCM for muon-type neutrinos, where mνμ is the mass and λCM is the intrinsic partial decay width in sec?1 for νμ→γ+X. In the theory of Eliezer and Ross where , this implies an upper limit on mνμ considerably smaller than the present upper limit, and a large lower limit on the lifetime τνμ. 相似文献
100.
Shiva P. Singh Surendra S. Parmar Sylvia A. Farnum Virgil I. Stenberg 《Journal of heterocyclic chemistry》1978,15(7):1083-1087
The natural abundance carbon-13 nuclear magnetic resonance spectra of diazepam, clonazepam, flurazepam and chlordiazepoxide were recorded in suitable solvent using the Fourier transform technique on a JEOL FX-60 spectrometer. The relaxation time (T1) of these compounds were also measured. The chemical shift of the various carbon resonances have been assigned on the basis of chemical shift theory, multiplicity generated in single-frequency off-resonance decoupled spectra, relaxation time and the chemical shifts of the model compounds. 相似文献