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71.
Fourier-Transform infrared (FTIR) spectroscopy and surface energy analysis (contact angle measurements) have been performed as a means of identification and quantification of the functionalization of polystyrene surfaces upon vacuum ultraviolet- (VUV-) photochemically initiated oxidation. Photochemical oxidation was performed in the presence of water vapor and molecular oxygen using a pulsed Xe2-excimer radiation source (lambda(exc): 172 nm). Surface oxidation was studied as a function of two parameters: irradiation time and distance between sample and radiation source. During the first 1-2 min of irradiation, an increase of the concentrations of hydroxyl (OH) and carbonyl (C=O) groups on the surface was observed, both reaching limiting values. As expected, the rate of oxidation diminished exponentially with increasing distance between the radiation source and the surface of the polystyrene film. Changes in the surface energy due to the introduction of these polar (i.e. OH and C=O) groups were also determined. The densities of the functional groups decreased upon washing with acetonitrile, and analysis of the washing solution by means of gas chromatography-mass spectrometry (GC-MS) revealed the presence of a large number of products. The application of pulsed Xe2-excimer radiation sources as a valuable alternative to conventional means (i.e. laser and plasma) for the photochemical oxidation and surface modification of polystyrene is discussed. 相似文献
72.
Andreas Pfrang Boris Reznik Thomas Schimmel Dagmar Gerthsen 《Microscopy and microanalysis》2005,11(1):46-55
The microstructure of carbon-carbon composites obtained by chemical vapor infiltration of a carbon fiber felt was comparatively studied by reflection light microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and laser scanning confocal microscopy (LSCM). Ar+ ion etching was used to reveal and distinguish structural units of the pyrolytic carbon matrix. Mechanically polished samples, polished and subsequently ion etched samples, and fractured samples were compared. The values of surface roughness and surface height after polishing or after polishing and subsequent etching determined by AFM and LSCM correlate well with the degree of texture of the matrix layers obtained by polarized light microscopy and selected area electron diffraction. The carbon matrix is composed of structural units or "cells," which contain a carbon fiber and a sequence of several differently textured layers around each fiber. Within high-textured layers columnar grains are well recognizable using polarized reflection light microscopy and confocal microscopy. The size of depressions within high-textured carbon layers found by AFM after ion etching correlates well with the size of differently tilted domains detected by both TEM and SEM. 相似文献
73.
T. Wiedmann H. Schimmel K. Ballschmiter 《Fresenius' Journal of Analytical Chemistry》1998,360(1):117-119
It has been shown that the concept of molar response, which is applicable to single ion monitoring of M+, can also be employed for ion trap MS/MS measurements, simplifying the determination of PCDD/PCDF by an extended IDA approach.
Received: 22 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997 相似文献
74.
The influence of the molecular weight distribution of network chains on the mechanical properties of polymer networks 总被引:1,自引:0,他引:1
End-linked poly(dimethylsiloxane) (PDMS) networks with different molecular weight distributions (MWD) of the primary chains were prepared and investigated by isothermal stress-strain measurements. We found a lowering of the elastic modulus with increasing broadness of the MWD. The observed range of the moduli seems not to be restricted to the region limited by the classical models of rubber elasticity. This result is based on our own experimental investigations and on a reanalysis of data taken from the literature. In the case of nearly monodisperse distributions (M
n
/M
w
1) the effect of configurational restrictions of the network strands probably dominates. In the opposite case (M
n
/M
w
1), we discuss that spatial clustering of the crosslinks may reduce the effective number of elastically active network junctions. 相似文献
75.
76.
Schimmel u. Co. 《Fresenius' Journal of Analytical Chemistry》1923,62(10):411
Ohne Zusammenfassung 相似文献
77.
78.
Sturgeon RE Wahlen R Brandsch T Fairman B Wolf-Briche C Alonso JI González PR Encinar JR Sanz-Medel A Inagaki K Takatsu A Lalere B Monperrus M Zuloaga O Krupp E Amouroux D Donard OF Schimmel H Sejerøe-Olsen B Konieczka P Schultze P Taylor P Hearn R Mackay L Myors R Win T Liebich A Philipp R Yang L Willie S 《Analytical and bioanalytical chemistry》2003,376(6):780-787
The capabilities of National Metrology Institutes (NMIs—those which are members of the Comité Consultatif pour la Quantité de Matière (CCQM)of the CIPM) and selected outside "expert" laboratories to quantitate (C4H9)3Sn+ (TBT) in a prepared marine sediment were assessed. This exercise was sanctioned by the 7th CCQM meeting, April 4–6, 2001, as an activity of the Inorganic Analysis Working Group and was jointly piloted by the Institute for National Measurement Standards of the National Research Council of Canada (NRC) and the Laboratory of the Government Chemist (LGC), UK. A total of 11 laboratories submitted results (7 NMIs, and 4 external labs). Two external laboratories utilized a standard calibration approach based on a natural abundance TBT standard, whereas all NMIs relied upon isotope dilution mass spectrometry for quantitation. For this purpose, a species specific 117Sn-enriched TBT standard was supplied by the LGC. No sample preparation methodology was prescribed by the piloting laboratories and, by consequence, a variety of approaches was adopted by the participants, including mechanical shaking, sonication, accelerated solvent extraction, microwave assisted extraction and heating in combination with Grignard derivatization, ethylation and direct sampling. Detection techniques included ICP–MS (with GC and HPLC sample introduction), GC–MS, GC–AED and GC–FPD. Recovery of TBT from a control standard (NRCC CRM PACS-2 marine sediment) averaged 93.5±2.4% (n=14). Results for the pilot material averaged 0.680±0.015 µmol kg–1 (n=14; 80.7±1.8 µg kg–1) with a median value of 0.676 µmol kg–1. Overall, performance was substantially better than state-of-the-art expectations and the satisfactory agreement amongst participants permitted scheduling of a follow-up Key comparison for TBT (K-28), a Pilot intercomparison for DBT (P-43), and certification of the test sediment for TBT content and its release as a new Certified Reference Material (HIPA-1) with a TBT content of 0.679±0.089 µmol kg–1 (expanded uncertainty, k=2, as Sn) (80.5±10.6 µg kg–1).Electronic Supplementary Material Supplementary material is available in the online version of this article at . 相似文献
79.
G N Kramer J Pauwels L Le Guern H Schimmel S Trapmann 《Fresenius' Journal of Analytical Chemistry》2001,370(2-3):142-146
In the execution of its mission to promote a common European measurement system in support of EU policies, IRMM's Reference Materials Unit is currently involved in preparation of proficiency-testing samples and candidate reference materials. Recent work related to bovine spongiform encephalopathy in cows, genetically modified organisms, and a variety of environmental materials is described. 相似文献
80.
P. E. R. Durigon D. F. S. Petri H. Drings Th. Schimmel M. Bruns 《Colloid and polymer science》2001,279(10):1013-1019
Films of immiscible blends of (PS) and poly(methyl methacrylate) (PMMA) were characterized by contact-angle measurements
with sessile drop and atomic force microscopy (AFM). These blends showed a linear dependence of the contact angles on the
composition, as predicted by Cassie's equation for ideal surfaces. The surface structure investigated by AFM showed low roughness
and phase-separation features. The ratio between the drop radius and the roughness amounted to the order of 104–105. This magnitude seemed to be sufficient to put the PS/PMMA films close to ideality. Upon sulfonation, the wettability and
the microscopic surface roughness of the PS/PMMA blends increased. The treatment with sulfuric acid yielded sulfonated PS
domains on the surface, causing an increase in the surface wettability. The SO3
− groups were evidenced by X-ray photoelectron spectroscopy. The sulfonation of the PS/PMMA blends enables the formation of
multiphase surfaces with hydrophobic, charged and polar domains.
Received: 11 December 2000 Accepted: 6 April 2001 相似文献