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   308篇
  免费   8篇
  国内免费   1篇
化学   210篇
晶体学   3篇
力学   3篇
数学   39篇
物理学   62篇
  2023年   1篇
  2022年   4篇
  2021年   7篇
  2020年   8篇
  2019年   4篇
  2018年   7篇
  2017年   6篇
  2016年   6篇
  2015年   6篇
  2014年   15篇
  2013年   22篇
  2012年   12篇
  2011年   26篇
  2010年   20篇
  2009年   24篇
  2008年   28篇
  2007年   26篇
  2006年   16篇
  2005年   19篇
  2004年   16篇
  2003年   5篇
  2002年   4篇
  2001年   2篇
  2000年   3篇
  1999年   2篇
  1998年   2篇
  1996年   3篇
  1995年   1篇
  1994年   3篇
  1993年   5篇
  1992年   3篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1982年   1篇
  1980年   1篇
  1959年   1篇
  1958年   1篇
  1937年   2篇
  1931年   1篇
  1927年   1篇
排序方式: 共有317条查询结果,搜索用时 46 毫秒
101.
In this work, we introduce Z3-graded quantum group GL\({_q(2,{\mathbb C})}\) with the help of Z3-graded quantum plane and a Z3-graded bicovariant differential calculus on the Z3-graded quantum group GL q (2). The corresponding Z3-graded quantum Lie superalgebra is obtained.  相似文献   
102.
Metal-free (2) and Co(II), Zn(II), Ni(II), Cu(II) metallophthalocyanines (2ad) with four 4-phenyloxyacetic acid groups on the periphery were prepared by cyclotetramerization of new p-(3,4-dicyanophenoxy)phenylacetic acid (1) and the corresponding divalent metal salts. Further reactions of these products with thionylchloride and then benzylamine in tetrahydrofuran, and octanol in pyridine gave amide (3, 3ad) and ester (4, 4ad) derivatives, respectively. The new compounds have been characterized by elemental analyses, IR, UV–Vis, mass and 1H NMR spectroscopy. The redox properties of compounds 2 and 2ad were identified by cyclic voltammetry.  相似文献   
103.
This work focuses on the development of a CE method allowing, for the first time, the simultaneous separation of the underivatized first seven cellodextrin oligomers (glucose, cellobiose, cellotriose, cellotetraose, cellopentaose, cellohexaose, and celloheptaose), with a view to analyze the hydrolysates obtained after partial acid depolymerization of nitrocellulose, and eight carbohydrates (ribose, xylose, fructose, mannose, galactose, maltose, lactose, and sucrose), which might be potential interfering compounds in explosives samples. Separation was achieved with a highly alkaline BGE containing sodium chloride and direct mid‐UV‐absorbance detection was performed after photo‐oxidation in the detection window. EOF was reversed to speed up the analysis using a dynamic capillary coating by hexadimethrine bromide. A central composite design was carried out to determine the effects of BGE conductivity and sodium hydroxide concentration on resolutions between neighboring peaks, and analysis time. A desirability analysis on modeled responses was applied to maximize resolutions and to minimize analysis time. The simultaneous analysis in 20 min total runtime of the 15 carbohydrates plus internal reference (naphthalene sulfonate) was carried out at 25°C with a BGE composed of 77.4 mM NaOH and 183 mM NaCl to adjust the conductivity at the optimum value. Finally, the resolution robustness was checked. This new method should also be of interest to monitor food and nonfood crop products.  相似文献   
104.
This paper presents new definitions which are a natural combination of the definition for asymptotically equivalence and Δ m -lacunary strongly summable with respect to a modulus f. Using this definitions we have proved the (f, Δ m )-asymptotically equivalence and Δ m -lacunary statistical asymptotically equivalence analogues of theorems of Tripathy and Et (Stud Univ Babe?-Bolyai Math (1):119–130, 2005) and Çolak’s theorems (Filomat 17:9–14, 2003).  相似文献   
105.
Working within a plain texture (S,S), the authors construct a completion of a dicovering uniformity υ on (S,S) in terms of prime S-filters. In case υ is separated, a separated completion is then obtained using the T0-quotient, and it is shown that this construction produces a reflector. For a totally bounded di-uniformity it is verified that these constructions lead to dicompactifications of the uniform ditopology. A condition is given under which complementation is preserved on passing to these completions, and an example on the real texture (R,R,ρ) is presented.  相似文献   
106.
Cloud-point extraction (CPE) using the non-ionic surfactant Triton X-100 was used successfully to remove a highly toxic dye, rhodamine 6G (R6G), from water and wastewater. The effects of different analytical parameters such as pH, concentration of Triton X-100 (TX-100) and salts, equilibrium temperature, and incubation time on the efficiency of the extraction of R6G were studied in detail, and optimum conditions for dye extraction were obtained. Thermodynamic parameters including changes in Gibbs free energy, enthalpy, and entropy were also calculated, and these parameters indicated that the CPE of R6G was feasible, spontaneous, and endothermic in the temperature range of 75-95 degrees C. The equilibrium solubilization capacity of TX-100 was found to be 1.10 mmol/mol by using Langmuir isotherm models. No significant interference effects were observed in the presence of phenol and its derivatives, some acidic and basic dyes and most of the anions and cations. It was concluded that the CPE process described in this paper can be an alternative technique for removal of dyes and other pollutants from waters and wastewaters.  相似文献   
107.
The novel 6,7-[15-crown-5]-3-[p-(2,3-dicyanophenoxy)phenyl]coumarin (1) and its non-peripherally substituted zinc phthalocyanine complex (2) have been prepared and characterized by elemental analysis, 1H NMR (for compound 1), MALDI-TOF, FT-IR and UV-Vis spectral data. Fluorescence intensity changes of compound 1 have been determined by addition of Na+ or K+ ions at 25 °C in THF. The effects of the chromenone crown ether substituent of the phthalocyanine molecule on the photophysical (fluorescence quantum yield and lifetime) and photochemical (singlet oxygen generation and photodegradation) properties were also investigated. The fluorescence of the zinc phthalocyanine complex is effectively quenched by addition of 1,4-benzoquinone (BQ).  相似文献   
108.
Electrical discharges formed directly in liquid water include three general cases where (a) streamer-like plasma channels form in, but do not span, the electrode gap, (b) spark discharges produce transient plasma channels that span the electrode gap, and (c) arc discharges form plasma channels with relatively longer life times. Other factors including the input energy (from <1?J/pulse to >1?kJ/pulse) as well as solution properties and the rates of energy delivery affect the nature of the discharge channels. An understanding of the formation of chemical species, including the highly reactive hydroxyl radical and more stable molecular species such as hydrogen and hydrogen peroxide, in such plasma requires determination of temporal and spatial variations of temperature, pressure, plasma volume, and electrical characteristics including current, voltage (electric field), and plasma conductivity. In spark and arc discharges analysis of the physical processes has focused on hydrodynamic and thermal characterization, while only a limited amount of work has connected these physical processes to chemical reactions. On the other hand, the most successful model of the chemical reactions in streamer-like discharges relies on simple assumptions concerning the temperature and pressure in the plasma channels, while analysis of the physical processes is more limited. This paper reviews the literature on the mathematical modeling of electrical discharges in liquid water spanning the range from streamer-like to spark and arc discharges, and compares the properties and processes in these electrical discharges to those in electron beam radiolysis and ultrasound.  相似文献   
109.
The C(3 P)+OD(X 2Π) reaction has been studied by means of quantum mechanical real wave packet (RWP) and quasiclassical trajectory (QCT) methodologies on the ground potential energy surface of Zanchet et al. [J. Phys. Chem. A 110, 12017 (2006)]. Initial state selected total reaction probabilities at J?=?0 total angular momentum have been calculated for a wide range of collision energies. Product state-resolved integral cross-sections at selected collision energies and excitation functions have been determined from the RWP calculations using the J-shifting approximation and from QCT calculations. State-specific and thermal rate coefficients have been calculated using both methodologies up to 500 K. The effect of reagent rotational excitation on the dynamics for the C(3 P)+OH(X 2Π) and C(3 P)+OD(X 2Π) reactions has been investigated and interesting discrepancies between the QCT and RWP results have been found. The RWP results are found to be in an overall good agreement with the corresponding QCT results, although the QCT integral cross-section and rate coefficients are slightly smaller than those obtained from the RWP calculations.  相似文献   
110.
In this paper we establish a complete local theory for the energy-critical nonlinear wave equation (NLW) in high dimensions ? × ? d with d ≥ 6. We prove the stability of solutions under the weak condition that the perturbation of the linear flow is small in certain space-time norms. As a by-product of our stability analysis, we also prove local well-posedness of solutions for which we only assume the smallness of the linear evolution. These results provide essential technical tools that can be applied towards obtaining the extension to high dimensions of the analysis of Kenig and Merle [17 Kenig , C.E. , Merle , F. ( 2008 ). Global well-posedness, scattering and blow-up for the energy critical focusing non-linear wave equation . Acta Math. 201 : 147212 .[Crossref], [Web of Science ®] [Google Scholar]] of the dynamics of the focusing (NLW) below the energy threshold. By employing refined paraproduct estimates we also prove unconditional uniqueness of solutions for d ≥ 6 in the natural energy class. This extends an earlier result by Planchon [26 Planchon , F. ( 2003 ). On uniqueness for semilinear wave equations . Math. Z. 244 : 587599 .[Web of Science ®] [Google Scholar]].  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