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排序方式: 共有189条查询结果,搜索用时 15 毫秒
1.
Spataro A. Deval Y. Begueret J.-B. Fouillat P. Belot D. 《Solid-State Circuits, IEEE Journal of》2002,37(3):336-341
In this paper, we present a waveform converter implemented on a 0.25-μm CMOS technology using a dedicated design methodology (Delay Oriented Design). The circuit converts a square wave signal in both in-phase and quadrature-phase sinusoidal differential outputs. It also multiplies the frequency by seven. The output frequency range of this converter extends from 1.05 GHz up to 2.17 GHz. This converter is dedicated for the design of a third-generation mobile phone synthesizer using a double-loop architecture. For an output frequency of 2 GHz, the measured phase noise at 10-kHz offset from the carrier is -97 dBc/Hz. The circuit consumes 50 mW from a 2.5-V supply 相似文献
2.
A q × n array with entries from 0, 1,…,q − 1 is said to form a difference matrix if the vector difference (modulo q) of each pair of columns consists of a permutation of [0, 1,… q − 1]; this definition is inverted from the more standard one to be found, e.g., in Colbourn and de Launey (1996). The following idea generalizes this notion: Given an appropriate δ (-[−1, 1]t, a λq × n array will be said to form a (t, q, λ, Δ) sign-balanced matrix if for each choice C1, C2,…, Ct of t columns and for each choice = (1,…,t) Δ of signs, the linear combination ∑j=1t jCj contains (mod q) each entry of [0, 1,…, q − 1] exactly λ times. We consider the following extremal problem in this paper: How large does the number k = k(n, t, q, λ, δ) of rows have to be so that for each choice of t columns and for each choice (1, …, t) of signs in δ, the linear combination ∑j=1t jCj contains each entry of [0, 1,…, q t- 1] at least λ times? We use probabilistic methods, in particular the Lovász local lemma and the Stein-Chen method of Poisson approximation to obtain general (logarithmic) upper bounds on the numbers k(n, t, q, λ, δ), and to provide Poisson approximations for the probability distribution of the number W of deficient sets of t columns, given a random array. It is proved, in addition, that arithmetic modulo q yields the smallest array - in a sense to be described. 相似文献
3.
The influence of aryl substituents in dibenzylidene acetone (dba) ligands, for Pd(0) complexes, has been evaluated for Suzuki-Miyaura cross-coupling reactions. Electron-withdrawing substituents such as NO(2) or CF(3) deactivate the catalyst species whereas strongly donating substituents such as OMe increase catalytic activity over that of unsubstituted dba ligands. [reaction: see text] 相似文献
4.
A simple and rapid spectrophotometric method for the determination of six phenothiazines can be based on the formation of a coloured compound between molybdophosphoric acid and phenothiazines. The i.r. and e.s.r. spectra of the coloured compounds showed that molybdophosphoric acid oxidizes phenothiazines to a radical cation with which it then forms a coloured compound. The proposed method is employed for the determination of phenothiazines in pharmaceutical preparations. Calibration graphs are linear over ranges of about 100–2000 μg of the phenothiazine. 相似文献
5.
Madan Mohan Harish C. Khera Shri G. Mittal Anant K. Sirivastava 《Monatshefte für Chemie / Chemical Monthly》1978,109(2):357-368
The complexes of pyridine-2-aldoxime (HPOX) and 6-methylpyridine-2-aldoxime (HMPX) with iron (II) thiocyanate of the type [Fe(L)(NCS)2] (L=HPOX and HMPX) have been prepared and characterized. A study of X-ray, magnetic, vibrational spectra (conventional and far-infrared), electronic spectra andMössbauer spectra has indicated that these complexes have polymeric, pseudo octahedral, coordination geometry with linear bridging thiocyanate ligands. The electronic spectra of mono complexes show a larger, low symmetry, ligand field than that present in [Fe(L)2(NCS)2] complexes. UnperturbedMössbauer spectra show a large quadrupole splitting, E
Q, and smaller isomer shift values in these iron (II) thiocyanate complexes. The magnetically perturbedMössbauer spectra of these iron(II) thiocyanate complexes at room temperature show that the principal component of the electric field gradient tensor is positive and corresponds to ad
xy
(5B2) ground state.With 2 Figures 相似文献
6.
Taris Thierry Begueret Jean-Baptiste Lapuyade Hervé Deval Yann 《Microelectronics Journal》2006,37(11):1251-1260
After a theoretical and analytical study of the body effect in MOS transistors, this paper offers two useful models of this parasitic phenomenon. Thanks to these models, a design methodology, which takes advantage of the bulk terminal, allows to turn this well-known body-effect drawback into an analog advantage, giving thus an efficient alternative to overcome the design constraints of the CMOS VLSI wireless mass market. To illustrate the approach, four RF building blocks are presented. First, a 0.9 V 10 dB gain LNA, covering a frequency range 1.8-2.4 GHz, thanks to a body-effect common mode feedback, is detailed. Secondly, a body-effect linearity controlled pre-power amplifier is presented exhibiting a 5 dB m input compression point (ICP1) variation under 1.8 V power supply for half the current consumption. Lastly, two mixers based on body-effect mixing are presented, which achieve a 10 dB conversion gain under 1.4 V for a −52 dB LO-to-RF isolation. Well suited for low-power/low-voltage applications, these circuits implemented in a 0.18 μm CMOS VLSI technology are dedicated to multi-standard architectures and system-on-chip implementations. 相似文献
7.
Anant Hegde Jose C. Principe Deniz Erdogmus Umut Ozertem Yadunandana N. Rao Hemanth Peddaneni 《The Journal of VLSI Signal Processing》2006,45(1-2):85-95
Principal components analysis is an important and well-studied subject in statistics and signal processing. Several algorithms
for solving this problem exist, and could be mostly grouped into one of the following three approaches: adaptation based on
Hebbian updates and deflation, optimization of a second order statistical criterion (like reconstruction error or output variance),
and fixed point update rules with deflation. In this study, we propose an alternate approach that avoids deflation and gradient-search
techniques. The proposed method is an on-line procedure based on recursively updating the eigenvector and eigenvalue matrices
with every new sample such that the estimates approximately track their true values as would be calculated analytically from
the current sample estimate of the data covariance matrix. The perturbation technique is theoretically shown to be applicable
for recursive canonical correlation analysis, as well. The performance of this algorithm is compared with that of a structurally
similar matrix perturbation-based method and also with a few other traditional methods like Sanger’s rule and APEX.
相似文献
相似文献
8.
9.
Combining low-, high-level and empirical domain knowledge for automated segmentation of ultrasonic breast lesions 总被引:11,自引:0,他引:11
Breast cancer is the most frequently diagnosed malignancy and the second leading cause of mortality in women. In the last decade, ultrasound along with digital mammography has come to be regarded as the gold standard for breast cancer diagnosis. Automatically detecting tumors and extracting lesion boundaries in ultrasound images is difficult due to their specular nature and the variance in shape and appearance of sonographic lesions. Past work on automated ultrasonic breast lesion segmentation has not addressed important issues such as shadowing artifacts or dealing with similar tumor like structures in the sonogram. Algorithms that claim to automatically classify ultrasonic breast lesions, rely on manual delineation of the tumor boundaries. In this paper, we present a novel technique to automatically find lesion margins in ultrasound images, by combining intensity and texture with empirical domain specific knowledge along with directional gradient and a deformable shape-based model. The images are first filtered to remove speckle noise and then contrast enhanced to emphasize the tumor regions. For the first time, a mathematical formulation of the empirical rules used by radiologists in detecting ultrasonic breast lesions, popularly known as the "Stavros Criteria" is presented in this paper. We have applied this formulation to automatically determine a seed point within the image. Probabilistic classification of image pixels based on intensity and texture is followed by region growing using the automatically determined seed point to obtain an initial segmentation of the lesion. Boundary points are found on the directional gradient of the image. Outliers are removed by a process of recursive refinement. These boundary points are then supplied as an initial estimate to a deformable model. Incorporating empirical domain specific knowledge along with low and high-level knowledge makes it possible to avoid shadowing artifacts and lowers the chance of confusing similar tumor like structures for the lesion. The system was validated on a database of breast sonograms for 42 patients. The average mean boundary error between manual and automated segmentation was 6.6 pixels and the normalized true positive area overlap was 75.1%. The algorithm was found to be robust to 1) variations in system parameters, 2) number of training samples used, and 3) the position of the seed point within the tumor. Running time for segmenting a single sonogram was 18 s on a 1.8-GHz Pentium machine. 相似文献
10.
Manoj Kumar Anant Deshpande Chintan Gupta A. K. Biswas A. K. Nath 《Journal of Chemical Sciences》2002,114(6):659-673
Selective multi-photon dissociation (MPD) of Freon-22 (CF2HC1) molecules has been carried out using a TEA CO2 laser at various CO2 laser lines (9P(20)-9P(26)) in order to maximize the yield of C-13 isotope in the product (C2F4) at an enrichment factor of 100. The effects of laser pulse tail due to the presence of N2 in the laser mixture on the enrichment factor and yield of C-13 are investigated. It is found that the addition of a small
amount of N2 is possible in the laser mixture without a significant drop in the yield at desired enrichment factor. Addition of a small
amount of N2 improves the laser efficiency considerably. At a given pulse energy, a slight change in the near field intensity distribution
of a laser severely affects the selectivity of C-13 isotope. The computed far-field intensity distributions of the measured
near-field intensities show marked spatial variation in the focal spots that leads to a drop in selectivity. For macroscopic
production of C-13 isotope a simple and novel multi-pass cavity has been designed and tested to focus the energy repeatedly
keeping the optimum fluence constant at each focal spot. 相似文献