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191.
The significance of terms "metal bioavailability" and "bioavailable metal fraction" is evolved in the time, passing from a very simple concept to a complex concept bound to abiotic and biotic aspects. At the beginning metal toxicity was related to metal fraction present in water phase, than only free metal ion activity was considered and the free ion activity model (FIAM) was proposed. Successively, due to the exceptions observed and to the consciousness that metal bioavailability could be considered as dynamic characteristic the concept of metal bioavailability became very complex, depending on physical, chemical and biological factors. 相似文献
192.
Edda Wehner Raffaella Seno Nicoletta Sterpi Berthold-Georg Englert Herbert Walther 《Optics Communications》1994,110(5-6):655-669
Although in standard micromaser experiments the collective events, in which two or more atoms are inside the resonator at one time, are very rare, they may cause dramatic effects nevertheless. We find in particular that the so-called “trapped vacuum state” (in which single atoms would undergo a complete Rabi cycle while traversing the cavity and emerge without having emitted a photon) is destroyed even when more than 99% of the atoms participate in one-atom events. 相似文献
193.
A short review concerning the role of organic matter on metal toxicity and bio-availability in aqueous systems is carried out. The complexity of the issue derives both from the high number of natural and anthropogenic organic compounds and from the variability of their structures. In fact, the binding capacity and affinity is dependent on the number and type of ligands, on their position in the structures, on the ligand/metal ratio. It is also necessary to develop analytical protocol in order to carry out speciation studies of organic carbon and of metals bound to organic compounds, and at the same time to characterise the nature of the complexes. 相似文献
194.
The freshness of virgin olive oils (VOO) from typical cultivars of Garda regions was evaluated by attenuated total reflectance (ATR) and Fourier transform infrared (FTIR) spectroscopy, in combination with multivariate analysis. The olive oil freshness decreased during storage mainly because of oxidation processes. In this research, 91 virgin olive oils were packaged in glass bottles and stored either in the light or in the dark at room temperature for different periods. The oils were analysed, before and after storage, using both chemical methods and spectroscopic technique.Classification strategies investigated were partial least square discriminant analysis (PLS-DA), linear discriminant analysis (LDA), and soft independent modelling of class analogy (SIMCA).The results show that ATR-MIR spectroscopy is an interesting technique compared with traditional chemical index in classifying olive oil samples stored in different conditions. In fact, the FTIR PCA results allowed a better discrimination among fresh and oxidized oils, than samples separation obtained by PCA applied to chemical data. Moreover, the results obtained by the different classification techniques (PLS-DA, LDA, SIMCA) evidenced the ability of FTIR spectra to evaluate the olive oil freshness. FTIR spectroscopy results are in agreement with classical methods. The spectroscopic technique could be applied for the prediction of VOOs freshness giving information related to chemical modifications. The great advantages of this technique, compared to chemical analysis, are related to rapidity, non-destructive characteristics and low cost per sample. In conclusion, ATR-MIR represents a reliable, cheap and fast classification tool able to assess the freshness of virgin olive oils. 相似文献
195.
Aim of this work was to investigate which are the effects on barley crops grown on two different soils: a soil lacking in Cu, an essential micronutrient (A) and a naturally polluted soil rich in lead, zinc, copper (B). In particular we investigated the relationship between some ecophysiological parameters such as biomass, chlorophyll concentration and guaiacolo peroxidase activity and the chemical-physical properties of the soils like pH, organic matter and heavy metal content. Because metals uptake by plants is strongly correlated with the bioavailable fraction rather then their total amount in a soil, we have measured also metal exchangeable forms, using a single extraction method (MgCl2 as extractant). Plants grown on soil B showed a metal content higher than background limits, whereas plants grown on soil A were characterised by a background Fe and Zn concentrations and by a tolerant Pb concentration. Conversely, Cu content in tissues of plants grown in soil A is found to be under the background limits. Copper-deficiency plants present chlorotic leaves followed by a reduced clorophyll content, while plants grown on metals contaminated soil showed an increase of peroxidase activity. 相似文献
196.
E.O. Kahya 《Physics letters. [Part B]》2011,701(3):291-295
We present an extension of a previously suggested test of all modified theories of gravity that would reproduce MOND at low accelerations. In a class of models, called “dark matter emulators”, gravitational waves and other particles couple to different metrics. This leads to a detectable time lag between their detection at Earth from the same source. We calculate this time lag numerically for any event that occurs in our galaxy up to 400 kpc, and present a graph of this possible time lag. This suggests that, gravitational wave observers might have to consider the possibility of extending their analysis to non-coincident gravitational and electromagnetic signals, and the graph that we present might be a useful guideline for this effort. 相似文献
197.
MALDI-MS and multivariate analysis for the detection and quantification of different milk species 总被引:1,自引:0,他引:1
The extensive consumption of milk and dairy products makes these foodstuffs targets for potential adulteration with financial
gains for unscrupulous producers. Such practices must be detected as these can impact negatively on product quality, labelling
and even health. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF-MS) is a potentially
useful technique, with proven abilities in protein identification and more recently through the use of internal standards
for quantification purposes of specific proteins or peptides. In the current work, we therefore aim to explore the accuracy
and attributes of MALDI-ToF-MS with chemometrics for the detection and quantification of milk adulteration. Three binary mixtures
containing cows' and goats', cows' and sheep's, and goats' and sheep's milk and a fourth tertiary mixture containing all types
of milk were prepared and analysed directly using MALDI-ToF-MS. In these mixtures, the milk concentrations of each milk varied
from 0% to 100% in 5% steps. Multivariate statistical methods including partial least squares (PLS) regression and non-linear
Kernel PLS regression were employed for multivariate calibration and final interpretation of the results. The results for
PLS and KPLS were encouraging with between 2% and 13% root mean squared error of prediction on independent data; KPLS slightly
outperformed PLS. We believe that these results show that MALDI-ToF-MS has excellent potential for future use in the dairy
industry as a rapid method of detection and enumeration in milk adulteration. 相似文献
198.
Jessica Lanzo Fiore P. Nicoletta Giovanni De Filpo Giuseppe Chidichimo 《Liquid crystals》2013,40(8):1029-1033
We have investigated the electro-optical performance of switchable nematic emulsions as a function of temperature. The electro-optical properties of nematic emulsions are highly dependent on temperature because several parameters such as droplet size, number density, viscosity, surface free energy, elastic constant, refractive indices, dielectric anisotropy, and liquid crystal/monomer solubility are affected by temperature. In particular, both ON state transmittances and decay times show a decreasing behaviour with increasing temperature. On the contrary, the OFF state transmittances increase, and the rise times do not change in an appreciable way. 相似文献
199.
Daniela Cupelli Fiore P. Nicoletta Giovanni De Filpo Patrizia Formoso Giuseppe Chidichimo 《Journal of Polymer Science.Polymer Physics》2011,49(4):257-262
The development of electrically activated chromogenic materials is important for their potential applications in smart windows. Several previous works have reported on reverse mode operation polymer dispersed liquid crystals (PDLCs) based on negative dielectric anisotropy liquid crystals. They have a transparent OFF state, which turns opaque after the application of a suitable external electric field. Nevertheless, these devices have some limitations such as the use of large amount of expensive liquid crystals with peculiar physical‐chemical properties. In addition, a good matching between the refractive index of liquid crystal and the polymer matrix one is required. The main result of this work is the achievement of reverse mode operation devices prepared with a positive dielectric anisotropy liquid crystal and characterized by a high OFF state transmittance obtained by the onset of high intensity built‐in DC electric fields in a direct mode operation PDLC, which allows the OFF state homeotropic alignment of liquid crystal directors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献