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141.
Coleen Pugh Jose M. Rodriguez-Parada Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》1986,24(4):747-758
N-(2-hydroxyethyl)carbazolyl methacrylate (HECM) and N-ethyl-3-hydroxymethyl carbazolyl methacrylate (HMCM-2) were polymerized by group transfer polymerization to varying molecular weights of somewhat narrow molecular weight distribution. The thermal behavior of the homopolymers and of their EDA complexes with poly(β-hydroxyethyl-3,5-dinitrobenzoyl methacrylate) (PDNBM-2) was studied as a function of molecular weight. The Tg′s of both polymers and their miscible complexes increase steadily as molecular weight increases and then become constant at about M n = 6000. Both the PHECM–PDNBM-2 and PHMCM-2—PDNBM-2 systems are thermally reversible miscible networks over all polymer molecular weights. Miscibility is thermodynamically controlled over the entire range of molecular weights in the first system and decomplexation does not occur below the decomposition temperature. However, miscibility is thermodynamically controlled in the second system when the molecular weight of PHMCM-2 is less than 5000, and kinetically controlled for higher molecular weights. The decomplexation temperature or LCST of the PHMCM-2–PDNBM-2 system occurs below the decomposition temperature and increases with decreasing PHMCM-2 molecular weight, in agreement with theoretical predictions on the dependence of LCST on polymer molecular weight. 相似文献
142.
Bojan B. Radak Ljubica T. Petkovska epan S. Miljani Raymond T. Bailey Francis R. Cruickshank David Pugh 《Journal of Chemical Sciences》1991,103(3):409-412
Spectra of coincidence of CH3C1 IR absorption with CO2-laser emission were recorded by a photoacoustic detection method in the whole range of CO2-laser emission. The samples were neat gas and mixtures with argon, at several pressures (10 to 600Torr) so that pressure
effects could be observed. The results show that argon affects absorption of CO2-laser emission quite differently from neat chloromethane, both regarding the most prominent coincidences and background absorption. 相似文献
143.
Virgil Percec Howard G. Schild Jos M. Rodriguez-Parada Coleen Pugh 《Journal of polymer science. Part A, Polymer chemistry》1988,26(3):935-951
The interpolymeric electron donor–acceptor (EDA) complex of donor poly[(N-ethylcarbazol-3-yl)methyl methacrylate] (PHMCM-2) with acceptor poly-(2-[(3,5-dinitrobenzoyl)oxy]ethyl methacrylate) (PDNBM-2) presents a single glass transition temperature and a decomplexation endotherm on differential scanning calorimetric (DSC) thermograms. This system is considered a “polymer blend model” which exhibits a lower critical solution temperature (LCST). Phase separation of this blend is kinetically controlled and positive deviations of the glass transition temperatures from weight average values suggest that it behaves as a thermally reversible crosslinked network. Calorimetric methods to determine the heats of mixing of small molecule complexes in solution were adapted for this solid state blend to estimate the equilibrium constant (Keq) and other thermodynamic parameters. Applying a computer iterative procedure and assuming 1 : 1 stoichiometry, a least-squares fit was found for several different donor molecular weights with three different high molecular weight acceptors. At moderate molecular weights, Keq rises to represent saturation fractions near unity as found in biological systems. Keq decreases for higher molecular weights, possibly due to trapped chain entanglements. These results are supported by a composition-independent, “horizontal line” phase diagram, thus resembling the completely complexed/denaturation process in DNA. 相似文献
144.
The method described by Gordon and Kim and modified by Rae has been further modified to restrict the self-exchange correction to an electron gas composed of the outer shell electrons. Revised results are presented for the interaction potentials between various pairs of inert gas atoms. 相似文献
145.
Reaction of the vanadium(V) imide [V(NAr)Cl(3)(THF)] (Ar = 2,6-C(6)H(3)(i)()Pr(2)) with the diamino-pyridine derivative MeC(2-C(5)H(4)N)(CH(2)NHSiMe(2)(t)()Bu)(2) (abbreviated as H(2)N'(2)N(py)) gave modest yields of the vanadium(IV) species [V(NAr)(H(3)N'N' 'N(py))Cl(2)] (1 where H(3)N'N' 'N(py) = MeC(2- C(5)H(4)N)(CH(2)NH(2))(CH(2)NHSiMe(2)(t)()Bu) in which the original H(2)N'(2)N(py) has effectively lost SiMe(2)(t)()Bu (as ClSiMe(2)(t)()Bu) and gained an H atom. Better behaved reactions were found between the heavier Group 5 metal complexes [M(NR)Cl(3)(py)(2)] (M = Nb or Ta, R = (t)()Bu or Ar) and the dilithium salt Li(2)[N(2)N(py)] (where H(2)N(2)N(py) = MeC(2-C(5)H(4)N)(CH(2)NHSiMe(3))(2)), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N(2)N(py))(py)] (M = Nb, R = (t)()Bu 2; M = Ta, R = (t)()Bu 3 or Ar 4). The compounds 2-4 are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N(2)N(py))]. Activation parameters are reported for the complexes 2 and 3. In the case of 2, high vacuum tube sublimation afforded modest quantities of [Nb(N(t)()Bu)Cl(N(2)N(py))] (5). The X-ray crystal structures of the four compounds 1, 2, 3, and 4 are reported. 相似文献
146.
147.
The role of particles in stabilising foams and emulsions 总被引:2,自引:0,他引:2
The use of particles as foam and emulsion stabilising species, with or without surfactants, has received great interest in recent years. The majority of work has studied the effects of particles as stabilisers in emulsion systems, but recent successes has widened consideration into foams, where industries such as flotation and food processing have encountered the effects of particle stabilisation for many years. This review seeks to clarify studies into emulsions, highlighting new research in this area, and relate similarities and differences to foam systems. Past research has focused on defining the interaction mechanisms of stability, such as principles of attachment energies, particle-particle forces at the interface and changes to the interfilm, with a view to ascertain conditions giving optimum stability. Studied conditions include effects of particle contact angle, aggregation formations, concentration, size and interactions of other species (i.e. surfactant). Mechanisms can be complex, but overall the principle of particles creating a steric barrier to coalescence, is a straitforward basis of interaction. Much research in emulsions can be applied to foam systems, however evidence would suggest foam systems are under a number of additional constraints, and the stability 'window' for particles is smaller, in terms of size and contact angle ranges. Also, because of increased density differences and interfilm perturbations in foam systems, retardation of drainage is often as important to stability as inhibiting coalescence. 相似文献
148.
A new method leading to Ni(NHC)2 (NHC = IMes, IPri, SIPr(i), SIBu(t)) complexes in moderate to good yields, involves the reaction of NHC (pre-formed or generated in situ) with Ni(CH3)2(tmed), tmed = N,N'-tetramethylethylenediamine; in one case, the intermediate Ni[I(Me2)Pr(i)]2(CH3)2, I(Me2)Pr(i) = N,N'-diisopropyl-4,5-dimethylimidazol-2-ylidene, has been isolated and structurally characterised. 相似文献
149.
Chaicharoen K Polce MJ Singh A Pugh C Wesdemiotis C 《Analytical and bioanalytical chemistry》2008,392(4):595-607
The unimolecular degradation of alkali-metal cationized polyacrylates with the repeat unit CH2CH(COOR) and a variety of ester pendants has been examined by tandem mass spectrometry. The fragmentation patterns resulting
from collisionally activated dissociation depend sensitively on the size of the ester alkyl substituent (R). With small alkyl
groups, as in poly(methyl acrylate), lithiated or sodiated oligomers (M) decompose via free-radical chemistry, initiated by
random homolytic C-C bond cleavages along the polymer chain. The radical ions formed this way dissociate further by backbiting
rearrangements and β scissions to yield a distribution of terminal fragments with one of the original end groups and internal
fragments with 2–3 repeat units. If the ester alkyl group bears three or more carbon atoms, cleavages within the ester moieties
become the predominant decomposition channel. This distinct reactivity is observed if R = t-butyl, n-butyl, or the mesogenic group (CH2)11-O-C6H4-C6H4-CN. The [M+alkali metal]+ ions of the latter polyacrylates dissociate largely by charge-remote 1,5-H rearrangements that convert COOR to COOH groups
by expulsion of 1-alkenes. The acid groups may displace an alcohol unit from a neighboring ester pendant to form a cyclic
anhydride, unless hindered by steric effects. Using atom transfer radical polymerization, hyperbranched polyacrylates were
prepared carrying ester groups both within and between the branches. Unique alkenes and alcohols are cleaved from ester groups
at the branching points, enabling determination of the branching architecture.
Figure MALDI-CAD tandem mass spectrum of the lithiated 4-mer from a hyperbranched polyacrylate. The fragments marked by green stars
diagnose the branched architecture shown on top of the spectrum. The fragments marked by violet stars diagnose a different
isomer. 相似文献
150.