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81.
Dartnell LR Page K Jorge-Villar SE Wright G Munshi T Scowen IJ Ward JM Edwards HG 《Analytical and bioanalytical chemistry》2012,403(1):131-144
Raman spectroscopy has proven to be a very effective approach for the detection of microorganisms colonising hostile environments
on Earth. The ExoMars rover, due for launch in 2018, will carry a Raman laser spectrometer to analyse samples of the martian
subsurface collected by the probe’s 2-m drill in a search for similar biosignatures. The martian surface is unprotected from
the flux of cosmic rays, an ionising radiation field that will degrade organic molecules and so diminish and distort the detectable
Raman signature of potential martian microbial life. This study employs Raman spectroscopy to analyse samples of two model
organisms, the cyanobacterium Synechocystis sp. PCC 6803 and the extremely radiation resistant polyextremophile Deinococcus radiodurans, that have been exposed to increasing doses of ionising radiation. The three most prominent peaks in the Raman spectra are
from cellular carotenoids: deinoxanthin in D. radiodurans and β-carotene in Synechocystis. The degradative effect of ionising radiation is clearly seen, with significant diminishment of carotenoid spectral peak
heights after 15 kGy and complete erasure of Raman biosignatures by 150 kGy of ionising radiation. The Raman signal of carotenoid
in D. radiodurans diminishes more rapidly than that of Synechocystis, believed to be due to deinoxanthin acting as a superior scavenger of radiolytically produced reactive oxygen species, and
so being destroyed more quickly than the less efficient antioxidant β-carotene. This study highlights the necessity for further
experimental work on the manner and rate of degradation of Raman biosignatures by ionising radiation, as this is of prime
importance for the successful detection of microbial life in the martian near subsurface. 相似文献
82.
A toroidal grating monochromator (TGM) based beamline was designed earlier and it is being setup on the 450 MeV Indus-1 synchrotron radiation source. This beamline operates in 40–1000 Å wavelength range and gives a moderate resolution (~500) at high throughput. Now-a-days, spherical gratings are giving very high resolution in some complex monochromators. We have evaluated the use of spherical gratings in the simple rotation mount of a TGM. The motivation has been to evaluate if the existing TGM beamline, without any hardware changes, can be used with the much cheaper spherical gratings. The two monochromators, employing toroidal and spherical gratings respectively, have been compared by performing detailed ray tracing calculations. Our study shows that, with the same mechanical hardware, a real spherical grating monochromator gives better performance compared to the conventional TGM with respect to the spectral resolution and the flux. Furthermore, for moderate resolution this improvement is realized even when the exit slit is not moved to keep the spherical grating in-focus. 相似文献
83.
84.
Polyacrylamide nanoparticles of different size (<100 nm) were prepared in reverse micelles under various dynamic conditions of micellar systems. The nanoparticles were always larger than the aqueous core in which they were formed; however, the size of the nanoparticles could be controlled if the interdroplet interaction and coalescence rate in reverse micelles were regulated. Factors such as interfacial rigidity of the droplets, size of the aqueous core, temperature, and concentrations of acrylamide (monomer) andN,N′-methylenebisacrylamide (crosslinking agent) have a profound effect on the size of nanoparticles. By adjustment of these parameters in reverse micelles, nanoparticles ranging from about 10 to more than 100 nm have been prepared. 相似文献
85.
Zirconium forms two complexes each with Gallion, 1:1 in 0.1 M HCl (λmax 600 nm) and 2:1 (Zr:Gallion) at pH 2.0 (λmax 540 nm) and with, PAR, 1:2 (Zr:PAR) in 0.1 M HCl (λmax 410 nm) and 1:1 at pH 2.0 (λmax 420 nm). In all cases the exact nature of the equilibrium involved with the hydroxy species of zirconium participating in complexation reaction is evaluated. Kinetic study, and the number of protons liberated during complexation reaction have been studied and the position of the chelate rings have been suggested. The values of equilibrium constants for these complexes have also been evaluated. 相似文献
86.
Amit Aran Soumika Munshi Vinod K. Beri Arun K. Gupta 《Optics and Lasers in Engineering》2008,46(9):656-665
Filters synthesized with images of a specific spectral band in general fail to recognize targets in a different spectral band. In this paper, we therefore demonstrate the use of the wavelet-modified maximum average correlation height (WaveMACH) filter for automatic target recognition applications in both the visible and infrared (IR) spectral bands. As any input target appears different when imaged through two different sensors, i.e., a CCD or an IR camera, a WaveMACH filter synthesized using a CCD image shows no correlation with the image of the same target from an IR camera and vice-versa. Hence, separate filters are required to match the input targets from the two sensors. To avoid the synthesis and storage of separate filters, the images from CCD and IR camera are fused using Daubechies wavelet and then the rotation-invariant WaveMACH filter generated with the fused image. In all, 18 WaveMACH filters (each of 20° range) are required for in-plane rotation invariance in both the spectral bands for the full range of 0–360°. Computer simulation and experimental results implemented in hybrid digital–optical correlator architecture are shown for the proposed idea. The same filters have also been used to identify multiple targets in a scene. Performance measures like peak-to-sidelobe ratio (PSR), peak correlation energy (PCE) and correlation peak intensity (CPI) have been calculated as metrics of goodness. 相似文献
87.
Michael D. Hargreaves Neil A. Macleod Victoria L. Brewster Tasnim Munshi Howell G. M. Edwards Pavel Matousek 《Journal of Raman spectroscopy : JRS》2009,40(12):1875-1880
In this paper, we demonstrate the ability of portable Raman spectroscopy and benchtop spatially offset Raman spectroscopy (SORS) techniques to rapidly identify real and fake ivory samples. Both techniques were able to identify exposed genuine from fake ivory samples. In contrast to conventional Raman spectroscopy, SORS was, in addition, able to identify ivory concealed by plastics, paints, varnishes and cloth. Application of the SORS technique allows the interrogation of biomaterial samples through materials in which conventional Raman spectroscopic instrumentation cannot penetrate. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
88.
Monochura Saha Sheelbhadra Chatterjee Munshi Sahid Hossain Arijeet Ghude Subhajit Bandyopadhyay 《化学:亚洲杂志》2019,14(24):4659-4664
Metal ions often influence the photoswitching efficiency of a photochromic system. This article reports a one‐dimensional polymer having cyclic azobenzenes coordinated to silver ions that are bridged by nitrates. The coordination polymer (CP‐ 2 ) displays a photoresponsive behavior. The switching ability in the polymer form was faster compared to the parent azobenzene ligand without the metal ions. Azobenzenes are reported to be poorly conducting. Here, although the azobenzene ligand does not show significant electronic mobility, the coordination polymer (CP‐ 2 ) displays a modest conductivity. The conductance in the cis form of the polymer is significantly higher compared to the trans form. Upon exposure to visible light, the cis form undergoes photoisomerization to the trans form with a drastic drop in the electronic mobility. The trans form can be reverted to the cis form thermally or by using UV light. Thus, this system offers a reversible control of the conductivity using light. 相似文献
89.
Hydrogenation of carbon dioxide catalyzed by ruthenium trimethylphosphine complexes: the accelerating effect of certain alcohols and amines 总被引:1,自引:0,他引:1
Munshi P Main AD Linehan JC Tai CC Jessop PG 《Journal of the American Chemical Society》2002,124(27):7963-7971
A trace amount of alcohol cocatalyst and a stoichiometric amount of base are required during the hydrogenation of CO(2) to formic acid catalyzed by ruthenium trimethylphosphine complexes. Variation of the choice of alcohol and base causes wide variation in the rate of reaction. Acidic, nonbulky alcohols and triflic acid increase the rate of hydrogenation an order of magnitude above that which can be obtained with traditionally used methanol or water. Similarly, use of DBU rather than NEt(3) increases the rate of reaction by an order of magnitude. Turnover frequencies up to 95,000 h(-1) have now been obtained, and even higher rates should be possible using the cocatalyst and amine combinations identified herein. Preliminary in situ NMR spectroscopic observations are described, and the possible roles of the alcohol and base are discussed. 相似文献
90.