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1.
Becky Lavi Abraham Marmur 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):409-414
An equation for the kinetics of partial drop spreading is proposed. This equation was empirically derived from experimental data for the spreading kinetics of partially wetting liquids in terms of the wet area versus time. The equation has the form of an exponential power law (EPL), and transforms into the well-known power law for complete wetting, when the equilibrium contact angle approaches zero. The EPL fits very well available experimental data. To lend additional support to the validity of this generalized equation, it will be demonstrated that when it is transformed to present the dynamic contact angle (DCA), it fits very well DCA experimental data for other wetting processes, such as capillary flow and tape coating. 相似文献
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Gribble GW Switzer FL Bushweller JH Jewett JG Brown JH Dion JL Bushweller CH Byrn MP Strouse CE 《The Journal of organic chemistry》1996,61(13):4319-4327
The (1)H NMR spectra of 10-benzyl-9,11-diphenyl-10-azatetracyclo[6.3.0.0.(4,11)0.(5,9)]undecane (BnPh(2)()) and 10-methyl-9,11-diphenyl-10-azatetracyclo[6.3.0.0.(4,11)0.(5,9)]undecane (MePh(2)()) decoalesce due to slowing inversion at nitrogen and to slowing isolated bridgehead phenyl rotation. The high nitrogen inversion barriers in MePh(2)() (DeltaG() = 12.2 +/- 0.1 kcal/mol at 250 K) and BnPh(2)() (DeltaG() = 10.6 +/- 0.1 kcal/mol at 215 K) are typical of tertiary amines in which at least one C-N-C bond angle is constrained to a small value. Compared to the minuscule rotation barriers about sp(2)-sp(3) carbon-carbon bonds in simple molecular systems, the bridgehead phenyl rotation barriers in MePh(2)() (DeltaG() = 9.8 +/- 0.1 kcal/mol at 210 K) and BnPh(2)() (DeltaG() = 9.8 +/- 0.1 kcal/mol at 210 K) are unusually high. Molecular mechanics calculations (MMX force field) suggest that the origin of the high phenyl rotation barriers lies in the close passage of an o-phenyl proton and a methyl (or benzylmethylene) proton in the transition state. BnPh(2)() crystallized from hexane as white needles in the monoclinic system Pn. Unit cell dimensions are as follows: a = 12.198(1) ?, b = 6.1399(6) ?, c = 14.938(2) ?, beta = 107.470(4) degrees, V = 1067.1(2) ?(3), Z = 2. In the crystal molecular structure, the imine bridge CNC bond angle in BnPh(2)() is constrained to a small value (96 degrees ). The benzylic phenyl group is oriented gauche to the nitrogen lone pair. 相似文献
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Burdzinski GT Gustafson TL Hackett JC Hadad CM Platz MS 《Journal of the American Chemical Society》2005,127(40):13764-13765
Ultrafast laser flash photolysis (266 nm) of para- and ortho-biphenyl azide in acetonitrile produces azide excited states that have broad absorption bands centered at 480 nm. The para-biphenyl azide excited singlet state has a lifetime of 100 fs. The excited-state lifetime of the ortho-azide isomer is 450 +/- 150 fs. Decay of the azide excited states is accompanied by the formation of the corresponding known singlet nitrenes (para, lambdamax = 350 nm, ortho, lambdamax = 400 nm). Singlet para-biphenylnitrene is born with excess energy and undergoes vibrational cooling with a time constant of 11 ps to form the long-lived (tau approximately 9 ns) relaxed singlet nitrene. Singlet ortho-biphenylnitrene decays with a lifetime of 16 ps in acetonitrile at ambient temperature. 相似文献
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A method is described for the accurate determination in plasma of the beta-hydroxyethylrutosides by measurement of the fluorescence of their borocitrate complexes by scanning densitometry following separation by thin-layer chromatography. A modification is also described for estimation of individual hydroxyethylrutosides and their glucuronide conjugates in samples of bile and urine. 相似文献
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Schroeder M Hogwood J Gray E Mulloy B Hackett AM Johansen KB 《Analytical and bioanalytical chemistry》2011,399(2):763-771
Protamine sulphate is an effective inhibitor of heparin and is used clinically to neutralise both low molecular weight heparins
(LMWH) and unfractionated heparin (UFH). However, protamine sulphate does not fully counter the anti-Xa effect of LMWH, even
in excess (>40 μg to 1 IU/ml). To investigate the molecular basis for this observation, the residual potencies in the presence
and absence of plasma as well as the molecular weight profiles of commercial LMWH neutralised with increasing amounts of protamine
were measured. Materials over 5000 Da are preferentially neutralised by protamine. To further investigate this molecular weight
dependence, monodisperse oligosaccharides were prepared from three commercial LMWHs. The specific anti-Xa activity for the
fractions increased with molecular weight, and was found to vary between the three preparations for oligosaccharides of the
same molecular weight. Our results indicate that protamine sulphate neutralisation is largely dependent on molecular weight,
leading to the implication that LMWHs containing a larger proportion of small oligosaccharides will not be as effectively
neutralised. Protamine sulphate neutralisation of any given LMWH is also affected by the specific anticoagulant activities
of its low molecular weight components, which varies between LMWH products, presumably with the method of manufacture. 相似文献