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171.
This work reports spectroscopic studies of uranium containing plasma generated in air and argon environments. The 532 nm Q-switched Nd:YAG laser generates the optical breakdown plasma, which was recorded by a spectrometer and an intensified charge coupled device having a resolution of 25 pm. Neutral and ionized uranium lines in the wavelength range of 385.8–391.9 nm indicate significant width and shift variations during the first few microseconds. Electron temperature and density of the plasma are determined using the Boltzmann plot and the Saha–Boltzmann equation at various time delay. The study reveals the power law decay pattern of electron temperature and density, which changes to exponential decay pattern if large gate- width is used to acquire the signal, due to an averaging effect. 相似文献
172.
Laser-induced breakdown spectroscopy (LIBS) has become a widely used atomic spectroscopic technique for rapid coal analysis. However, the vast amount of spectral information in LIBS contains signal uncertainty, which can affect its quantification performance. In this work, we propose a hybrid variable selection method to improve the performance of LIBS quantification. Important variables are first identified using Pearson’s correlation coefficient, mutual information, least absolute shrinkage and selection operator (LASSO) and random forest, and then filtered and combined with empirical variables related to fingerprint elements of coal ash content. Subsequently, these variables are fed into a partial least squares regression (PLSR). Additionally, in some models, certain variables unrelated to ash content are removed manually to study the impact of variable deselection on model performance. The proposed hybrid strategy was tested on three LIBS datasets for quantitative analysis of coal ash content and compared with the corresponding data-driven baseline method. It is significantly better than the variable selection only method based on empirical knowledge and in most cases outperforms the baseline method. The results showed that on all three datasets the hybrid strategy for variable selection combining empirical knowledge and data-driven algorithms achieved the lowest root mean square error of prediction (RMSEP) values of 1.605, 3.478 and 1.647, respectively, which were significantly lower than those obtained from multiple linear regression using only 12 empirical variables, which are 1.959, 3.718 and 2.181, respectively. The LASSO-PLSR model with empirical support and 20 selected variables exhibited a significantly improved performance after variable deselection, with RMSEP values dropping from 1.635, 3.962 and 1.647 to 1.483, 3.086 and 1.567, respectively. Such results demonstrate that using empirical knowledge as a support for data-driven variable selection can be a viable approach to improve the accuracy and reliability of LIBS quantification. 相似文献
173.
Laser-induced breakdown spectroscopy (LIBS) is a capable technique for elementary analysis, while LIBS quantitation is still under development. In quantitation, precise laser focusing plays an important role because it ensures the distance between the laser and samples. In the present work, we employed spectral intensity as a direct way to assist laser focusing in LIBS quantitation for copper alloys. It is found that both the air emission and the copper line could be used to determine the position of the sample surface by referencing the intensity maximum. Nevertheless, the fine quantitation was only realized at the position where the air emission (e.g. O (I) 777.4 nm) reached intensity maximum, and also in this way, a repeatable quantitation was successfully achieved even after 120 days. The results suggested that the LIBS quantitation was highly dependent on the focusing position of the laser, and spectra-assisted focusing could be a simple way to find the identical condition for different samples' detection. In the future, this method might be applicable in field measurements for LIBS analysis of solids. 相似文献
174.
AbstractAn instrument combining laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy was developed for the in situ atomic and molecular composition analysis of minerals. The apparatus consists of an optical system, a sample chamber, a spectrometer for Raman and another for LIBS, as well as a control system equipped with laboratory-written software. Gypsum, calcite, prehnite, pearl, lazurite, and several mixtures of NaBr and CaCO3 were selected as samples for evaluation of the performance of the instrument. Sulfate, carbonate, silicate, and crystalline water were identified and different structures of CaCO3 were clearly distinguished by the use of a Gaussian fit. The limit of detection for CaCO3 in a NaBr mixture was 5.7?mg/g by Raman. LIBS was employed to determine calcium, magnesium, iron, sodium, aluminum, and carbon with the newly developed system. The limits of detection obtained for Ca, Na, and C were 90.2?μg/g, 84.6?μg/g, and 2.5?mg/g, respectively. The experimental results from commercial Raman spectroscopy instruments were used to verify and support the measurements from this novel instrument. 相似文献
175.
G.P. Gupta B.M. SuriA. Verma M. SundararamanV.K. Unnikrishnan K. AltiV.B. Kartha C. Santhosh 《Journal of Alloys and Compounds》2011,509(9):3740-3745
This work reports on the quantitative elemental analysis of nickel alloys using laser-induced breakdown spectroscopy (LIBS) in air at atmospheric pressure. The LIBS plasma is generated using a Q-switched ultraviolet Nd:YAG laser, which evolves with time. The LIBS spectra of three samples with known composition are recorded at five detector gate delays. Employing the internal standardization method, the calibration curves for Cr present in the samples are produced. The Cr concentration in the samples is determined using the generated linear calibration curves having varying slopes and regression coefficients at different delays. The effect of slopes and regression coefficients of the linear calibration curves on the analytical predictive capability of the LIBS system is studied through the correlation of the LIBS determined concentration of Cr with its known value. The analytical predictive capability of the LIBS system is noted to be the best when the calibration-based analysis is performed at an appropriate delay (2000 ns in the present experiment) where the linear calibration curve has both the regression coefficient and the slope close to the ideal value. 相似文献
176.
G. Papastergiou C. Georgiou L. Mamatas V. Tsaoussidis 《International Journal of Communication Systems》2011,24(8):1065-1086
In this paper, we depart from our previously proposed Non‐Congestive Queuing (NCQ) mechanism and propose a new scheduling discipline that allows for efficient interoperation of dedicated systems (such as sensor and voice networks) with the Internet. More precisely, our approach provides delay guarantees to applications that do not contribute noticeably to congestion because of their tiny packet sizes and low transmission rates. In addition, our approach uses a second level of prioritization that conditionally favors, in terms of delay, applications with slightly longer packets as well. Based on the NCQ concept, Non‐Congestive Queuing Plus (NCQ+) promotes applications that require comparatively small service times, as long as their total service times cause insignificant delays to other packets in the queue. Therefore, we prioritize packets, and in turn corresponding flows, according to their impact on total delay. We evaluate NCQ+ using ns‐2‐based experiments. Results show that whenever prioritization buffer resources are sufficient, NCQ+ can provide non‐detectable delays to sensor applications and conditionally improve the performance of VoIP applications, while maintaining the impact on the performance of the other flows insignificant. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
177.
Laser-induced breakdown spectroscopy has been recognized as a significant tool for element diagnostics in plasma–wall interaction. In this work, a one-dimensional numerical model is developed to simulate the laser ablation processes of a molybdenum(Mo) target in vacuum conditions. The thermal process of the interaction between the ns-pulse laser with wavelength of 1064 nm and the Mo target is described by the heat conduction equation. The plasma plume generation and expansion are described by Euler equations, in which the conservation of mass density, momentum and energy are included. Saha equations are used to describe the local thermal equilibrium of electrons, Mo atoms,Mo~+ and Mo~(2+) Plasma shielding and emission are all considered in this model. The mainly numerical results are divided into three parts, as listed below.Firstly, the rule of the plasma shielding effect varying with laser intensity is demonstrated quantitatively and fitted with the Nelder function. Secondly, the key parameters of plasma plume,such as the number density of species, the propagation velocity and the temperature, are all calculated in this model. The results indicate that the propagation velocity of the plume center increased with time in a general trend, however, one valley value appeared at about 20 ns due to the pressure gradient near the target surface leading to negative plasma velocity. Thirdly, the persistent lines of a Mo atom in the wavelength range from 300 nm to 600 nm are selected and the spectrum is calculated. Moreover, the temporal evolutions of Mo's spectral lines at wavelength of 550.6494 nm,553.3031 nm and 557.0444 nm are given and the results are compared with experimental data in this work. 相似文献
178.
179.
传统的土壤重金属元素检测方法流程复杂,时间长.我们采用波长1 064 nm的调Q脉冲Nd:YAG激光器和多通道小型光纤光栅光谱仪,建立了一套可移动的激光诱导击穿光谱系统.详细研究了重金属元素Ba,Mn的特征谱线强度、标准偏差与数据采样方式以及采样平均次数的关系,在优化工作参数的基础上,采用一种新的光谱采样和数据处理方法,对土壤中金属Ba、Mn的含量进行检测,并获得了检测土壤中金属Ba、Mn含量的定标曲线,对元素Ba、Mn的监测的相对标准偏差分别为9.0%和10.24%,检测灵敏度分别为19.4 mg/kg和115.4 mg/kg,优于目前文献报道的结果. 相似文献
180.
《深圳大学学报(理工版)》2019,36(05):538-543
We develop a laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy (RS) combined detection system for remote detection of substance composition. It can scan a 2-dimensional region with scanning accuracy of 2 mm and detect element contents and elementary surface distribution in samples at the maximum distance of 30 m away from the detector. Using our 2-dimensional scanning system, we analyze Fe element distribution on the surface of wollastonite at a distance of 30 m. According to the time difference between LIBS signal and Raman signal, both LIBS and Raman spectrum signals are collected by a gated intensified CCD (ICCD) camera. The experimental result shows that the system can be applied to identify the type of aluminum alloys and also be used in alloy sorting process to save resources and energy. The system can also be applied in remote mineral identification. Molecular information such as C—O, S—O and Si—O stretching patterns can be obtained from Raman spectroscopy analysis of minerals and rocks, thus distinguishing minerals and rocks, i. e. carbonates, sulphates and silicates. 相似文献