全文获取类型
收费全文 | 198篇 |
免费 | 0篇 |
专业分类
化学 | 160篇 |
力学 | 2篇 |
数学 | 7篇 |
物理学 | 29篇 |
出版年
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 16篇 |
2011年 | 12篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有198条查询结果,搜索用时 15 毫秒
21.
Surface-charge-governed ion transport in nanofluidic channels 总被引:1,自引:0,他引:1
A study of ion transport in aqueous-filled silica channels as thin as 70 nm reveals a remarkable degree of conduction at low salt concentrations that departs strongly from bulk behavior: In the dilute limit, the electrical conductances of channels saturate at a value that is independent of both the salt concentration and the channel height. Our data are well described by an electrokinetic model parametrized only by the surface-charge density. Using chemical surface modifications, we further demonstrate that at low salt concentrations, ion transport in nanochannels is governed by the surface charge. 相似文献
22.
Low-level interferences in peroxyoxalate chemiluminescence 总被引:1,自引:0,他引:1
The role of interferences at concentrations lower than 10(-3) M in peroxyoxalate chemiluminescence is examined based on experimental results available in the literature. Implications for fluorophore and for hydrogen peroxide determinations are discussed. An interpretation in terms of the reaction mechanism is proposed. 相似文献
23.
Cees M Clorennec D Royer D Prada C 《The Journal of the Acoustical Society of America》2011,130(2):689-694
The local resonances of a free isotropic elastic plate are investigated using laser ultrasonic techniques. Experimental results are interpreted in terms of zero group velocity Lamb modes and edge mode. At a distance from the edge larger than the plate thickness a sharp resonance is observed at the frequency where the group velocity of the first symmetrical Lamb mode vanishes. Close to the edge of the plate, the resonance due to the edge mode dominates. Both zero group velocity and edge resonances appear at the theoretically predicted frequencies. These frequencies do not vary with the distance from the edge of the plate and the transition between the two modes of vibration, at about the plate thickness, is abrupt. Using a laser excitation on the edge, the amplitude profile of the normal displacement at the edge resonance frequency was determined. 相似文献
24.
The feasibility of laser-based excitation for quenched phosphorescence detection in capillary electrophoresis (CE) was explored for the first time by using a small-size, quadrupled Nd-YAG laser emitting 266 nm pulses (duration, 0.4 ns) at a repetition rate of 7.8 kHz. To provide a continuous phosphorescence background, the phosphorophore 1-bromo-4-naphthalene sulfonic acid (BrNS) was added to the separation buffer. Both experiments and theory show that in laser-induced phosphorescence (LIP) - in contrast with lamp-excited phosphorescence - one normally deals with such high triplet-state phosphorophore concentrations that triplet-triplet annihilation is the major deactivation pathway. This results in a lower quantum yield of the analyte-induced bimolecular quenching interaction and, thus, the observed quenching signal. The situation can be improved by using a cylindrical lens for excitation in order to reduce the irradiance. In this case limits of detection (LODs) similar to those obtained using lamp excitation (1x10(-8) M) were achieved, while the width of the detection window was reduced from about 4 mm to 1 mm. Even under exclusion of triplet-triplet annihilation, i.e., under conditions of low irradiance, for our setup the quenching yields in LIP were smaller than in lamp-based phosphorescence detection. This is due to the repetition rate of the laser (7.8 kHz), which is too high in view of the phosphorescence lifetime (ca. 300 micros at low irradiance). Theory shows that this disadvantageous effect will be fully eliminated if the repetition rate is decreased to 1 kHz. 相似文献
25.
Castro-Puyana M Lammers I Buijs J Gooijer C Ariese F 《Analytical and bioanalytical chemistry》2011,400(9):2913-2919
Quenched phosphorescence was used, for the first time, as detection mode in the chiral separation of methotrexate (MTX) enantiomers
by electrokinetic chromatography. The detection is based on dynamic quenching of the strong emission of the phosphorophore
1-bromo-4-naphthalene sulfonic acid (BrNS) by MTX under deoxygenated conditions. The use of a background electrolyte with
3 mg/mL 2-hydroxypropyl-β-cyclodextrin and 20% MeOH in 25 mM phosphate buffer (pH 7.0) and an applied voltage of 30 kV allowed
the separation of l-MTX and its enantiomeric impurity d-MTX with sufficient resolution. In the presence of 1 mM BrNS, a detection limit of 3.2 × 10−7 M was achieved, about an order of magnitude better than published techniques based on UV absorption. The potential of the
method was demonstrated with a degradation study and an enantiomeric purity assessment of l-MTX. Furthermore, l-MTX was determined in a cell culture extract as a proof-of-principle experiment to show the applicability of the method to
biological samples. 相似文献
26.
Graeme J. Gainsford Cees Lensink Andrew F. Falshaw 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(7):m331-m334
The title compound, [Rh(C8H12)(C34H38O6P2)]BF4·CHCl3, a novel asymmetric hydrogenation catalyst, crystallizes with two independent almost identical cations and anions. Cell‐packing interactions are provided by nonclassical hydrogen bonding between phenyl and chloroform H atoms and fluoro and chloro donors of the BF4− anion and the chloroform solvent molecule. 相似文献
27.
Gerard Van Koten Cees A. Schaap Johann T.B.H. Jastrzebski Jan G. Noltes 《Journal of organometallic chemistry》1980,186(3):427-445
The synthesis and structural characterization by 1H NMR and 197Au Mössbauer spectroscopy as well as by chiral labelling of the built-in ligands of three different types of arylgold(I) compounds is described.197Au Mössbauer data revealed that the benzyl- and arylgold(I) triphenylphosphine complexes which bear potential coordinating substituents at an ortho position still contain linearly coordinated AuI with 2c-2e gold(I)carbon bonds. The observation of isochronous NME resonances in (S)-2-Me2NCH(Me)C6H4AuPPh3 confirms that no additional intramolecular AuN coordination occurs in solution. Preliminary results of an X-ray diffraction study of 2,6-(MeO)2C6H3AuPPh3 are reported (R = 0.040, PAuC1 angle 172.6°. Unsymmetrical AuC1C2 and AuC1C6 angles of 126.4 and 117.4°, respectively).Pure, uncomplexed arylgold(I) compounds have been isolated from the reaction of diarylgoldlithium compounds (arylaurates) with trimethyltin bromide. (S)-2-Me2NCHMeC6H4Au has a dimeric structure which most likely consists of two monomeric units associated by intermolecular AuN coordination thus forming a ten-membered chelate ring. The structure of insoluble 2-Me2NCH2C6H4Au and 2-Me2NC6H4Au are less clear. The former compound probably has a structure similar to (S)-2-Me2NCHMeC6H4Au (IS/QS values for two-coordinate AuI centers). However, the strongly deviating IS and QS values of 2-Me2NC6H4Au indicate that a polynuclear structure for this compound similar to that proposed for 2-Me2NC6H4Cu cannot be excluded (a polymeric structure containing 2-Me2NC6H4 groups which span three Au atoms by 3c-2e Au2C bonds and AuN coordination).The mixed Au/Cu cluster (2-Me2NCH2C6H4)4Au2Cu2 is accessible via the reaction of (2-Me2NCH2C6H4)4Au2Li2 with CuI. Molecular weight and 1H NMR studies point to a tetranuclear structure in solution, while mass spectrometry shows fragment ions with m/e corresponding to (2-Me2NCH2C6H4)3Au2Cu2+, (2-Me2NCH2C6H4)3Cu2Au+, (2-Me2NCH2C6H4)2CuAu2+ and of (2-Me2NCH2C6H4)2Au+. 相似文献
28.
Adams N De Gans BJ Kozodaev D Sanchez C Bastiaansen CW Broer DJ Schubert US 《Journal of combinatorial chemistry》2006,8(2):184-191
A methodology for the rapid design, screening, and optimization of coating systems with surface relief structures, using a combination of statistical experimental design, high-throughput experimentation, data mining, and graphical and mathematical optimization routines was developed. The methodology was applied to photopolymers used in photoembossing applications. A library of 72 films was prepared by dispensing a given amount of sample onto a chemically patterned substrate consisting of hydrophilic areas separated by fluorinated hydrophobic barriers. Film composition and film processing conditions were determined using statistical experimental design. The surface topology of the films was characterized by automated AFM. Subsequently, models explaining the dependence of surface topologies on sample composition and processing parameters were developed and used for screening a virtual 4000-membered in silico library of photopolymer lacquers. Simple graphical optimization or Pareto algorithms were subsequently used to find an ensemble of formulations, which were optimal with respect to a predefined set of properties, such as aspect ratio and shape of the relief structures. 相似文献
29.
30.
Methods from nonlinear dynamics were applied to test the hypothesis that the dynamics of sustained atrial fibrillation (AF) is modified by the class Ic drug cibenzoline during pharmacological conversion. The experiments were performed in conscious goats in which sustained AF was induced by continuous maintenance of AF via programmed electrical stimulation. Data were collected from electrophysiological experiments in five goats to terminate sustained AF by continuous infusion of cibenzoline. Sets of five unipolar epicardial electrograms of one minute duration were recorded from the left and right atrial free wall during sustained AF (control), and at three episodes during infusion of cibenzoline, when the mean AF interval had been prolonged to 25%, 50% and 85% with respect to control. Ventricular far-field potentials were removed from atrial electrograms by a coherent averaging procedure. Using the Grassberger-Procaccia method, the dynamics of the local atrial electrograms was investigated by estimating the (coarse-grained) correlation dimension and correlation entropy from the correlation integral. The results were related to a recently proposed classification (types I-III) of AF based on the degree of complexity of atrial activation patterns. The coarse-grained correlation dimension D(cg) and entropy K(cg) indicated that sustained AF corresponded to type II. During drug administration the coarse-grained parameters were not significantly different from control. Scaling regions in the correlation integral were observed after infusion of cibenzoline (3 out of 5 goats) suggesting that the drug introduced low-dimensional features (type I) in the dynamics of AF (correlation dimension D ranging from 2.8 to 4.4 and correlation entropy K from 1.6 to 6.2 nats/s). Sinus rhythm recorded shortly after cardioversion was very regular (D<2 and K<3 nats/s). The hypothesis that the electrograms during AF and sinus rhythm were generated by a static transformation of a linear Gaussian random process was rejected using a test for time reversibility. The nonlinear analysis revealed that cibenzoline does not significantly alter the dynamics of sustained AF during pharmacological conversion other than a slowing down of the atrial activation and a somewhat increasing global organization of the atrial activation pattern. The sudden change in the dynamical behavior at cardioversion suggests a mechanism that is reminiscent of a bifurcation. (c) 1997 American Institute of Physics. 相似文献