全文获取类型
收费全文 | 90篇 |
免费 | 3篇 |
专业分类
化学 | 17篇 |
数学 | 15篇 |
物理学 | 61篇 |
出版年
2022年 | 1篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 8篇 |
2011年 | 2篇 |
2010年 | 4篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2002年 | 1篇 |
2000年 | 14篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有93条查询结果,搜索用时 31 毫秒
41.
42.
43.
Design and development of microfabricated capillary electrophoresis devices with electrochemical detection 总被引:1,自引:0,他引:1
R.S. Keynton T.J. Roussel Jr. D.J. Jackson J.F. Naber R.P. Baldwin 《Analytica chimica acta》2004,507(1):95-105
Our efforts have been focused on developing a self-contained and transportable microfabricated electrophoresis (CE) system with integrated electrochemical detection (ED). The current prototype includes all necessary electrodes “on-chip” and utilizes miniaturized CE and ED supporting electronics custom designed for this purpose. State-of-the-art design/modeling tools and novel microfabrication procedures were used to create recessed platinum electrodes with complex geometries and the CE/ED device from two patterned ultra-flat glass substrates. The electrodes in the bottom substrate were formed by a self-aligned etch and deposition technique followed by a photolithographic lift-off process. The microchannels (20 μm deep×65 μm wide (average)) were chemically etched into the top substrate followed by thermal bonding to complete the microchip device. CE/ED experiments were performed using 0.02 M phosphate buffer (pH 6), an analyte/buffer solution (2.2 mM dopamine, 2.3 mM catechol) and varying separation voltages (0-500 V) with a custom electronics unit interfaced to a laptop computer for data acquisition. Detection limits (S/N=3) were found to be at the micromolar level and a linear detection response was observed up to millimolar concentrations for dopamine and catechol. The microchip CE/ED system injected 50 pl volumes of sample, which corresponded to mass detection limits on the order of 200 amol. For the first time, an integrated “on-chip” multi-electrode array CE/ED device was successfully designed, fabricated and tested. The majority of the electrodes (six out of eight) in the array were capable of detecting dopamine with the amplitude of the signal (i.e., peak heights) decreasing as the electrode distance from the channel exit increased. 相似文献
44.
In this note, we prove an ?‐regularity theorem for the Ricci flow. Let (Mn,g(t)) with t ? [?T,0] be a Ricci flow, and let Hx0(y,s) be the conjugate heat kernel centered at some point (x0,0) in the final time slice. By substituting Hx0(?,s) into Perelman's W‐functional, we obtain a monotone quantity Wx0(s) that we refer to as the pointed entropy. This satisfies Wx0(s) ≤ 0, and Wx0(s) = 0 if and only if (Mn,g(t)) is isometric to the trivial flow on Rn. Then our main theorem asserts the following: There exists ? > 0, depending only on T and on lower scalar curvature and μ‐entropy bounds for the initial slice (Mn,g(?T)) such that Wx0(s) ≥ ?? implies |Rm| ≤ r?2 on P? r(x0,0), where r2 ≡ |s| and Pρ(x,t) ≡ Bρ(x,t) × (t?ρ2,t] is our notation for parabolic balls. The main technical challenge of the theorem is to prove an effective Lipschitz bound in x for the s‐average of Wx(s). To accomplish this, we require a new log‐Sobolev inequality. Perelman's work implies that the metric measure spaces (Mn,g(t),dvolg(t)) satisfy a log‐Sobolev; we show that this is also true for the heat kernel weighted spaces (Mn,g(t),Hx0(?,t)dvolg(t)). Our log‐Sobolev constants for these weighted spaces are in fact universal and sharp. The weighted log‐Sobolev has other consequences as well, including certain average Gaussian upper bounds on the conjugate heat kernel. © 2014 Wiley Periodicals, Inc. 相似文献
45.
E. Bauer M. Liendl L. Naber D. Werner H. Michor G. Hilscher A. Dönni P. Fischer F. Fauth M. Zolliker 《Zeitschrift für Physik B Condensed Matter》1997,102(3):291-298
We present various investigations on the transport, magnetic and thermodynamic properties of the new ternary compounds REPd2Ga3 with RE = Pr, Nd, Sm. While PrPd2Ga3 does not show long-range magnetic order down to about 0.3 K, both NdPd2Ga3 and SmPd2Ga3 order magnetically. The latter exhibits a ferromagnetic ground state with weak ordered moments below T c = 16.9 K and the former orders antiferromagnetically below T N = 6.5 K with ordered Nd moments of 1.99(4) μB at saturation in the basal plane oriented perpendicular to the propagation vector k = [1/2, 0, 0]. The possibility of a Kondo type interaction in PrPd2Ga3 is discussed. 相似文献
46.
A Balz-Schiemann reaction was developed to convert 2-cyano-5-aminopyridine to 2-cyano-5-fluoropyridine. The use of an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, BMIMBF4) as a solvent was found to be critical in achieving high assay yields and high selectivity for the fluorination vs. protonation. A process was developed to recycle and reuse the ionic liquid enabling its cost-effective use as a solvent. Finally, the optimal conditions were demonstrated under as a continuous process to address process safety risks associated with diazonium intermediates and the product was used to access a key intermediate in the synthesis of β-amyloid cleaving enzyme 1 inhibitor, verubecestat. 相似文献
47.
Toyoda H Trischuk W de Troconiz JF Truitt S Tseng J Turini N Ukegawa F Valls J Vejcik S Velev G Vidal R Vilar R Vologouev I Vucinic D Wagner RG Wagner RL Wahl J Wallace NB Walsh AM Wang C Wang CH Wang MJ Watanabe T Waters D Watts T Webb R 《Physical review letters》2000,84(10):2094-2099
We have reconstructed the radiative decays chi(b)(1P)-->Upsilon(1S)gamma and chi(b)(2P)-->Upsilon(1S)gamma in p&pmacr; collisions at sqrt[s] = 1.8 TeV, and measured the fraction of Upsilon(1S) mesons that originate from these decays. For Upsilon(1S) mesons with p(Upsilon)(T)>8.0 GeV/c, the fractions that come from chi(b)(1P) and chi(b)(2P) decays are [27.1+/-6.9(stat)+/-4. 4(syst)]% and [10.5+/-4.4(stat)+/-1.4(syst)]%, respectively. We have derived the fraction of directly produced Upsilon(1S) mesons to be [50.9+/-8.2(stat)+/-9.0(syst)]%. 相似文献
48.
Poolman HR Boersma DJ Harvey M Higinbotham DW Passchier I Six E Alarcon R van Amersfoort PW Bauer TS Boer Rookhuizen H van Den Brand JF van Buuren LD Bulten HJ Ent R Ferro-Luzzi M Geurts DG Heimberg P de Jager CW Klimin P Koop I Kroes F van Der Laan J Luijckx G Lysenko A Militsyn B Nesterenko I 《Physical review letters》2000,84(17):3855-3858
We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space. 相似文献
49.
In this paper we study solutions to elliptic linear equations either on or a Riemannian manifold, under the assumption that the coefficient functions aij are Lipschitz bounded. We focus our attention on the critical set and the singular set , and more importantly on effective versions of these. Currently, with just the Lipschitz regularity of the coefficients, the strongest results in the literature say that the singular set is (n –2)–dimensional; however, at this point it has not even been shown that unless the coefficients are smooth. Fundamentally, this is due to the need of an ?‐regularity theorem that requires higher smoothness of the coefficients as the frequency increases. We introduce new techniques for estimating the critical and singular set, which avoids the need of any such ?‐regularity. Consequently, we prove that if the frequency of u is bounded by Λ, then we have the estimates and , depending on whether the equation is critical or not. More importantly, we prove corresponding estimates for the effective critical and singular sets. Even under the assumption of real analytic coefficients these results are much sharper than those currently in the literature. We also give applications of the technique to give estimates on the volume of the nodal set of solutions and estimates for the corresponding eigenvalue problem.© 2017 Wiley Periodicals, Inc. 相似文献
50.
M. Plaschke J. Rothe M. K. Armbruster M. A. Denecke A. Naber H. Geckeis 《Journal of synchrotron radiation》2010,17(2):158-165
Humic acids (HA) have a high binding capacity towards traces of toxic metal cations, thus affecting their transport in aquatic systems. Eu(III)–HA aggregates are studied by synchrotron‐based scanning transmission X‐ray microscopy (STXM) at the carbon K‐edge and laser scanning luminescence microscopy (LSLM) at the 5D0→7F1,2 fluorescence emission lines. Both methods provide the necessary spatial resolution in the sub‐micrometre range to resolve characteristic aggregate morphologies: optically dense zones embedded in a matrix of less dense material in STXM images correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. In the C 1s‐NEXAFS of metal‐loaded polyacrylic acid (PAA), used as a HA model compound, a distinct complexation effect is identified. This effect is similar to trends observed in the dense fraction of HA/metal cation aggregates. The strongest complexation effect is observed for the Zr(IV)–HA/PAA system. This effect is confirmed by quantum chemical calculations performed at the ab initio level for model complexes with different metal centres and complex geometries. Without the high spatial resolution of STXM and LSLM and without the combination of molecular modelling with experimental results, the different zones indicating a `pseudo'‐phase separation into strong complexing domains and weaker complexing domains of HA would never have been identified. This type of strategy can be used to study metal interaction with other organic material. 相似文献