首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   49篇
  免费   9篇
  国内免费   3篇
化学   39篇
数学   3篇
物理学   19篇
  2024年   1篇
  2022年   6篇
  2021年   1篇
  2020年   2篇
  2019年   2篇
  2018年   2篇
  2017年   2篇
  2016年   5篇
  2015年   3篇
  2014年   2篇
  2013年   3篇
  2012年   4篇
  2011年   4篇
  2010年   2篇
  2008年   2篇
  2007年   3篇
  2006年   1篇
  2003年   1篇
  2002年   2篇
  2000年   1篇
  1999年   3篇
  1998年   2篇
  1994年   1篇
  1993年   1篇
  1992年   3篇
  1985年   1篇
  1982年   1篇
排序方式: 共有61条查询结果,搜索用时 15 毫秒
1.
2.
3.
We propose a new scheme for the coherent control of birefringent light pulses propagation in a four-level atomic medium. We modify the splitting of a light pulse by controlling the electric and magnetic responses. The Doppler broadening effect is also noted on the propagation of the birefringent pulses. The dispersions of the birefringence beams are oppositely manipulated for delay and advancement of time at a Doppler width of 10γ. A time gap is created between the birefringence beams, which protects from hacking of information. The time gap is then closed to restore the pulse into the original form by a reverse manipulation of the dispersion of the birefringence beams, i.e., introducing another medium whose transfer function is the complex conjugate of that of the original medium. The results are useful for secure communication technology.  相似文献   
4.
This study was conducted to characterize the residual level and perform a risk assessment on buprofezin formulated as an emulsifiable concentrate, wettable powder, and suspension concentrate over various treatment schedules in plum (Prunus domestica). The samples were extracted with an AOAC quick, easy, cheap, effective, rugged, and safe, ‘QuEChERS’, method after major modifications. As intrinsic interferences were observed in blank plum samples following dispersive‐solid phase extraction (consisting of primary secondary amine and C18 sorbents), amino cartridges were used for solid‐phase extraction. Analysis was carried out using liquid chromatography with diode array detection and confirmed by liquid chromatography–tandem mass spectrometry. The method showed excellent linearity with determination coefficient (R2 = 1) and satisfactory recoveries (at two spiking levels, 0.5 and 2.5 mg/kg) between 90.98 and 94.74% with relative standard deviation (RSD) ≤8%. The limit of quantification (0.05 mg/kg) was considerably lower than the maximum residue limit (2 mg/kg) set by the Codex Alimentarius. Absolute residue levels for emulsifiable concentrates were highest, perhaps owing to the dilution rate and adjuvant. Notably, all formulation residues were lower than the maximum residue limit, and safety data proved that the fruits are safe for consumers. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
5.
There is always need for secure transmission of information and simultaneously compact-size photonic circuits. This can be achieved if surface plasmon-polaritons(SPPs) are used as source of information, and the reduced hacking as the transmission phenomenon. In this article, an SPP-based reduced hacking scheme is presented at interface between atomic medium and metallic conductor. The SPP propagation is manipulated with conductivity of the metal. The delay or advance of the SPP is found to create nanosecond time gap which can be used for storing and sending the information safely. The reduced hacking is further modified with conductivity of the metal and the control parameters of the atomic medium.  相似文献   
6.
The present study was carried out to develop an analytical method for simultaneously detecting and quantifying sulfoxaflor and its metabolites (X11721061, X11719474) in brown rice and rice straw using liquid chromatography–tandem mass spectrometry. The parent compound and its metabolites were extracted and purified using original ‘QuEChERS’ method with modification. The matrix-matched calibration curve of sulfoxaflor and its metabolites in both matrices achieved good linearity with determination coefficients (R2) ≥0.9944. The overall recoveries of sulfoxaflor at two fortification levels (rice: 0.2 and 1.0 mg/kg; rice straw: 0.4 and 2.0 mg/kg) ranged from 97.37% to 107.71% with relative standard deviations (RSDs) <5%. On the other hand, the recoveries of both metabolites (X11721061 and X11719474) at 0.1 and 0.5 mg/kg (rice) and 0.2 and 1.0 mg/kg (rice straw) were satisfactory with values ranging from 83.70 % to 112.60% with RSDs <8%. During storage at ?20°C, the analyte and its metabolites were stable for up to 87 days. The limits of quantification of 0.02 mg/kg were lower than the maximum residue limit (0.2 mg/kg) set by the Korean Ministry of Food and Drug Safety for brown rice. The method was successfully applied to paddy field treated with different programme schedules and a preharvest interval of 7 days was proposed based upon the current study. In sum, the developed method is accurate and reproducible for ensuring the reliable determination of sulfoxaflor (and its metabolites) in harvested rice grain and straw samples from the field. The residual level of parent compound does not seem to pose any hazardous effect and treated rice could be safely used for consumption.  相似文献   
7.
<正>Two new eudesmane derivatives were isolated from the leaves and flowers of Verbesina virginica,along with the known 6-O-β-E -p-coumaroyl-4α-hydroxyeudesmane(1).Their structures were determined as 6-O-β-Z-p-coumaroyl-4α-hydroxyeudesmane(2) and 6-O-α-E-p-coumaroyl-1β-4α-dihydroxyeudesmane(3) by spectroscopic methods.  相似文献   
8.
The E(4) 1Πu←X 1Σ+g band system of the K2 molecule is investigated by the technique of Doppler-free optical–optical double resonance polarization spectroscopy. The observed vibrational levels v=0 to 9 of the E state are subject to numerous rotational perturbations by the neighboring 4 3Πu, 4 1Σ+u, and 5 3Σ+u electronic states. By using deperturbation methods, the potential curves of the 4 1Πu and 4 3Πu states are determined as well as some properties of the 4 1Σ+u and 5 3Σ+u state potentials. The results are compared with predictions of ab initio calculations.  相似文献   
9.
This study deals with an investigation on the preparation and physicochemical interactions of ZnO nanoparticles with acid functionalized porphyrin [5‐mono‐(4‐carboxyphenyl)‐10,15,20‐triphenylporphyrin (CPTPP)] for photovoltaic applications in a detailed manner. Zinc acetate and sodium hydroxide were used as the starting materials for the synthesis of ZnO nanoparticles at 60 °C in an alcoholic medium. The freshly prepared fine particles were then functionalized with CPTPP. Both the virgin and pregnant ZnO particles were characterized by using UV‐Visible spectrophotometry (UV), fluorescence emission (PL), Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The band gap energy obtained for ZnO particles, having a value of 3.47 eV, shows significant quantum confinement effect and enhanced photophysical activity. FTIR analysis of the doped ZnO nanostructures showed the presences of some chemical species. SEM analysis revealed a clear change in the surface morphologies of undoped ZnO. The average crystallite size of nanoparticles, calculated from XRD peaks, was found in the nano regime. The lattice parameters calculated for ZnO nanocrystals were also found in good agreement with those given in the literature. From the enhancement in the red shift of the UV‐Vis spectra, it is concluded that hybridization of acid functionalized porphyrin can cause a significant expansion in the total absorption region of ZnO semiconductor for photovoltaic applications.  相似文献   
10.
Antimony(III) complexes of thioamides [thioamides=thiourea (Tu), N,N′‐dimethylthiourea (Dmtu), tetramethylthiourea (Tmtu), imidazolidine‐2‐thione (Imt) and diazinane‐2‐thione (Diaz)] with the general formulae, Sb(thione)nCl3 (n=1, 2, 2.5, 3) were prepared and characterized by elemental analysis, IR and NMR (1H, 13C) spectroscopic methods. The spectral data of the complexes are consistent with the coordination of the thiones to antimony(III). The crystal structure of one of them, {[Sb(Imt)2Cl2]2(μ2‐Imt)}Cl2 ( 1 ), was determined by X‐ray crystallography, which shows that the complex is dinuclear consisting of two [Sb(Imt)2Cl2] units bridged by an Imt molecule. In 1 , the antimony atom is bonded to two chlorine atoms, two sulfur atoms of coordinated Imt molecules and one sulfur atom of a bridging Imt molecule. The antimony environment can be considered to be distorted octahedral with one Cl? ion weakly bound to antimony.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号