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排序方式: 共有103条查询结果,搜索用时 15 毫秒
1.
Vladimir Katkovnik Jaakko Astola Karen Egiazarian 《IEEE transactions on image processing》2008,17(6):833-846
The local polynomial approximation (LPA) is a nonparametric regression technique with pointwise estimation in a sliding window. We apply the LPA of the argument of cos and sin in order to estimate the absolute phase from noisy wrapped phase data. Using the intersection of confidence interval (HCI) algorithm, the window size is selected as adaptive pointwise varying. This adaptation gives the phase estimate with the accuracy close to optimal in the mean squared sense. For calculations, we use a Gauss-Newton recursive procedure initiated by the phase estimates obtained for the neighboring points. It enables tracking properties of the algorithm and its ability to go beyond the principal interval [-pi, pi] and to reconstruct the absolute phase from wrapped phase observations even when the magnitude of the phase difference takes quite large values. The algorithm demonstrates a very good accuracy of the phase reconstruction which on many occasion overcomes the accuracy of the state-of-the-art algorithms developed for noisy phase unwrap. The theoretical analysis produced for the accuracy of the pointwise estimates is used for justification of the HCI adaptation algorithm. 相似文献
2.
Simple two-parameter Hückel and Pitzer equations were used for the calculation of the activity coefficients of aqueous hydrochloric acid at 25°C up to a molality of 2.0 mol-kg–1. The data obtained by Harned and Ehlers(12,13) from galvanic cells without liquid junction were used in the analysis and the parameters obtained were compared to those obtained from all reliable data presented in the literature for HCl at this temperature. A good agreement between the parameters was always observed. The activity coefficients obtained by the new equations were compared to those suggested by Robinson and Stokes,(8) Hamer and Wu,(1) and Pitzer and Mayorga,(9) and good agreement was also found. The data from the most important literature data sets for HCl were also predicted using the new activity coefficient equations, and the magnitude of the resulting errors was close to the precision of the measurements, the errors forming an almost random pattern for all data sets. 相似文献
3.
Published thermodynamic data measured in aqueous mixtures of sodium or potassium dihydrogen phosphate with hydrogen phosphate
and chloride at 25°C were used to test recently developed methods for calculation of the pH of phosphate buffer solutions.
Equations for ionic activity coefficients are used in these methods. It is shown that all data used in the tests up to an
ionic strength of about 0.5 mol-kg-1 can be accurately predicted by the two methods recommended. In one of these methods, equations of the Hückel type are used
for ionic activity coefficients and in the other equations of the Pitzer type. Several sets of phosphate buffer solutions
are recommended,e.g., for calibrations of glass electrode cells. In the recommended sets, the pH of the buffer solutions can be calculated either
by the Hückel or Pitzer method, and the pH predictions of these methods agree in most cases within 0.005 at least up to ionic
strengths of about 0.2 mol-kg-1. The pH values of the two primary pH standards endorsed by IUPAC based on aqueous mixtures of KH2PO4 and Na2HPO4,i.e., pH values of 6.865 and 7.413, can also be accurately predicted by the equations recommended in this study. 相似文献
4.
Khoroshko LO Takhistov VV Petrova VN Viktorovskii IV Lahtiperä M Paasivirta J 《European journal of mass spectrometry (Chichester, England)》2004,10(5):731-736
Structures of six cyclic polysulfides, previously unknown as organic environmental pollutants, were analyzed from a sediment sample from the Eastern Gulf of Finland. The determinations were done by gas chromatography connected to mass spectrometry. High resolution (HRMS) measurements of the isotopic composition of four compounds could be done to confirm their molecular formulae. Total low resolution (LRMS) spectra were used to elucidate structures of all six compounds by thermochemical approach, application of fragmentation rules and by ICLU simulation of the spectra. The compounds were deduced to be (in the order of GC- retention) 1,2,4-trithiacycloheptane, tetrathiacyclopentane, 1,2,4,5-tetrathia-cyclohexane, 1,2,3,4- tetrathiacycloheptane, 1,2,3,4-tetrathiacyclohexane and 1,2,4,6-tetrathiacyclooctane. 相似文献
5.
Simple two-parameter Hückel and Pitzer equations were used for the calculation of the activity coefficients of aqueous hydrochloric acid at temperatures 0–60°C up to a molality of 2.0 mol-kg–1. The data obtained by Harned and Ehlers(2,3) on galvanic cells without a liquid junction were used in the parameter estimations of these equations. These data consist of sets of measurements at the temperature intervals of 5°C. It was observed that all estimated parameters follow very simple equations with respect to temperature. They are either constant or depend linearly on the temperature. The values for the activity coefficient parameters calculated by these simple equations are recommended here. The recommended parameter values were tested by predicting the data of Gupta, Hills, and Ives,(5) consisting of cell measurements from 5 to 45°C and molalities up to 1.0 mol-kg–1, and the data of Bates and Bower,(4) which extend to 95°C but measurements were only made on molalities less than about 0.1 mol-kg–1. The activity coefficients obtained by the new equations were also compared to those calculated by the Pitzer equations with the parameter values determined by Saluja, Pitzer, and Phutela(6) from calorimetric data. The agreement observed was excellent up to a molality of 1.5 mol-kg–1 at temperatures from 0 to 60°C. 相似文献
6.
Saukkoriipi J Sillanpää A Laasonen K 《Physical chemistry chemical physics : PCCP》2005,7(22):3785-3792
Cationic aluminium(chloro) hydroxide complexes with two to four aluminium atoms were studied using quantum chemical methods. Complexes were studied in both gas and liquid phase. The liquid environment was modeled by using a conductor-like screening model (COSMO). COSMO calculations were carried out as a single point calculation at the optimized gas phase structures. Water (epsilon = 78.54) was used as the solvent. The minimum energy structures obtained from the gas phase studies were mostly compact cyclic structures. Aluminium preferred to be five-coordinated in oxygen rich clusters. Core oxygen preferred three-fold coordination but in the largest clusters the four-coordinated oxygen was observed. Water reacted dissociatively with hydrogen poor clusters. The COSMO calculations showed that the optimal structures of cationic aluminium(chloro) hydroxides tend to be more open in the liquid than in the gas phase. 相似文献
7.
Jaakko Marttila Markus All��n Mikko Valkama 《Circuits, Systems, and Signal Processing》2011,30(4):775-797
This article discusses the applicability of quadrature ΣΔ modulator (QΣΔM) based analog-to-digital (A/D) conversion in cognitive
radio (CR) receivers. First, unavoidable in-phase/quadrature (I/Q) mismatch effects, limiting the dynamic range, are analyzed
in closed-form in the case of a first-order modulator. In addition, using the derived analytical converter model, it is shown
that notching the signal transfer function (STF) of the modulator at the mirror frequencies of the desired signals will effectively
cancel the I/Q imbalance induced mirror-frequency interference in case of the modulator feedback mismatch. In practice, such
STF design is easy to implement within the existing converter circuitry, as will be demonstrated in this article. The latter
part of the article proposes a novel complex multiband QΣΔM scheme, particularly aimed for the CR receivers. This multiband
scheme allows parallel reception of scattered frequency chunks in the CR context and is stemming from the additional degrees
of freedom in noise transfer function (NTF) design, provided by the QΣΔM principle. Here multiple noise shaping notches on
distinct frequencies are effectively realized through proper design of complex NTF. The modulator structure also allows flexible
reconfigurability of the notches with straightforward parameterization of the modulator transfer functions. When combined
with the above mirror-frequency rejecting STF design, the concept is demonstrated and proved effective and robust against
I/Q imbalances using practical radio signal simulations in realistic received signal conditions. 相似文献
8.
Marika E. Nissil? Ya-Chieh Li Shu-Yi Wu Jaakko A. Puhakka 《Applied biochemistry and biotechnology》2012,168(8):2160-2169
Concentrated acid hydrolysis of cellulosic material results in high dissolution yields. In this study, the neutralization step of concentrated acid hydrolysate of conifer pulp was optimized. Dry conifer pulp hydrolysis with 55?% H2SO4 at 45?°C for 2?h resulted in total sugar yields of 22.3?C26.2?g/L. The neutralization step was optimized for solid Ca(OH)2, liquid Ca(OH)2 or solid CaO, mixing time, and water supplementation. The highest hydrogen yield of 1.75?mol?H2/mol glucose was obtained with liquid Ca(OH)2, while the use of solid Ca(OH)2 or CaO inhibited hydrogen fermentation. Liquid Ca(OH)2 removed sulfate to below 30?mg SO4 2?/L. Further optimization of the neutralization conditions resulted in the yield of 2.26?mol?H2/mol glucose. 相似文献
9.
10.
Jaakko Latvala 《今日电子》2006,(8):40-41
最近几年中,便携应用中的照明设备发生了很大的变化。对于消费者来说,这种变化意味着更大的显示器,更多的指示灯或照相用的闪光灯。 相似文献