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   226篇
  免费   4篇
  国内免费   1篇
化学   135篇
晶体学   6篇
力学   6篇
数学   38篇
物理学   46篇
  2016年   2篇
  2015年   3篇
  2014年   4篇
  2013年   3篇
  2012年   5篇
  2011年   7篇
  2010年   9篇
  2009年   7篇
  2008年   7篇
  2007年   11篇
  2006年   4篇
  2005年   7篇
  2004年   6篇
  2003年   2篇
  2002年   3篇
  2000年   4篇
  1999年   5篇
  1997年   2篇
  1996年   2篇
  1995年   3篇
  1994年   5篇
  1993年   5篇
  1992年   6篇
  1991年   7篇
  1989年   2篇
  1988年   3篇
  1987年   2篇
  1986年   7篇
  1985年   6篇
  1984年   4篇
  1983年   2篇
  1982年   4篇
  1981年   8篇
  1980年   6篇
  1979年   3篇
  1978年   5篇
  1977年   6篇
  1976年   6篇
  1975年   1篇
  1974年   5篇
  1973年   4篇
  1972年   2篇
  1971年   4篇
  1970年   8篇
  1969年   1篇
  1968年   8篇
  1967年   5篇
  1954年   1篇
  1932年   1篇
  1928年   1篇
排序方式: 共有231条查询结果,搜索用时 15 毫秒
221.
Zinc oxide thin films were deposited by radio frequency magnetron sputtering at room temperature using a metallic zinc target in a gas mixture of argon and oxygen. Plasma power, oxygen /argon gas ratio, gas pressure, and substrate temperature were varied, and an experimental design method was used to optimize these deposition parameters by considering their interdependence. Crystalline structures and film stresses were examined. Post-deposition rapid thermal annealing was also carried out to observe its effects on the film properties. Statistical analysis was then used to find the optimal sputtering conditions. Results indicated that plasma power and gas pressure have the largest effects on film crystallization and stress and that postdeposition annealing can be used to improve the quality of the film properties.  相似文献   
222.
223.
224.
Ion-induced electron emission from solid surfaces is studied using a beam of caesium ions. Features of the spectra obtained during depth profiling of layered structures suggest a novel technique for investigating ion-induced Auger processes. Depth profiles are presented in terms of measured secondary ion signals, electron-induced Auger emission, and the intensities of features in the ion-induced electron spectra. It is shown that changes in features of the ion-induced electron spectra can be related to changes of chemical composition and sputtering probability. These help in the interpretation of variations in secondary-ion yields with matrix composition during depth profiling.  相似文献   
225.
Two methods of computing re-order levels are compared under an assumed state of nature. The results indicate that the difference, measured in terms of the expected lost sales is significant.  相似文献   
226.
A new family of non-acrylate UV cured three-dimensional polymeric networks for coatings and adhesives based on the photoinitiated cyclopolymerization of diallylamine salts and diallylamides using a low power (75 W) UVA domestic sunlamp is described.  相似文献   
227.
We give a direct formulation of the invariant polynomials μGq(n)(, Δi,;, xi,i + 1,) characterizing U(n) tensor operators p, q, …, q, 0, …, 0 in terms of the symmetric functions Sλ known as Schur functions. To this end, we show after the change of variables Δi = γi − δi and xi, i + 1 = δi − δi + 1 thatμGq(n)(,Δi;, xi, i + 1,) becomes an integral linear combination of products of Schur functions Sα(, γi,) · Sβ(, δi,) in the variables {γ1,…, γn} and {δ1,…, δn}, respectively. That is, we give a direct proof that μGq(n)(,Δi,;, xi, i + 1,) is a bisymmetric polynomial with integer coefficients in the variables {γ1,…, γn} and {δ1,…, δn}. By making further use of basic properties of Schur functions such as the Littlewood-Richardson rule, we prove several remarkable new symmetries for the yet more general bisymmetric polynomials μmGq(n)1,…, γn; δ1,…, δm). These new symmetries enable us to give an explicit formula for both μmG1(n)(γ; δ) and 1G2(n)(γ; δ). In addition, we describe both algebraic and numerical integration methods for deriving general polynomial formulas for μmGq(n)(γ; δ).  相似文献   
228.
We prove that Holman's hypergeometric series well-poised in SU(n) satisfy a general difference equation. We make use of the “path sum” function developed by Biedenharn and this equation to show that a special class of these series, multiplied by simple products, may be regarded as a U(n) generalization of Biedenharn and Louck's G(Δ; X) functions for U(3). The fact that these generalized G-functions are polynomials follows from a detailed study of their symmetries and zeros. As a further application of our general difference equations, we give an elementary proof of Holman's U(n) generalization of the 5F4(1) summation theorem.  相似文献   
229.
A link between a substructure searching system and a 13C NMR data base has been established and permits the retrieval and examination of the chemical shifts associated with specific substructures. The means by which these searches are accomplished is described and the results from the searches are presented and discussed. The system is interactive, and can be used to locate in the data base the chemical shifts of carbon atoms in precisely defined environments. Alternatively, it may be used to learn the range of the chemical shifts possessed by particular types of carbon atoms, such as N-methyl or O-methyl carbons.  相似文献   
230.
Mercury in plants or animal tissue is supposed to occur in the form of complexes formed with biologically relevant thiols (biothiols), rather than as free cation. We describe a technique for the separation and molecular identification of mercury and methylmercury complexes derived from their reactions with cysteine (Cys) and glutathione (GS): Hg(Cys)2, Hg(GS)2, MeHgCys, MeHgGS. Complexes were characterised by electrospray mass spectrometry (MS) equipped with an ion trap and the fragmentation pattern of MeHgCys was explained by using MP2 and B3LYP calculations, showing the importance of mercury–amine interactions in the gas phase. Chromatographic baseline separation was performed within 10 min with formic acid as the mobile phase on a reversed-phase column. Detection was done by online simultaneous coupling of ES-MS and inductively coupled plasma MS. When the mercury complexes were spiked in real samples (plant extracts), no perturbation of the separation and detection conditions was observed, suggesting that this method is capable of detecting mercury biothiol complexes in plants. Figure Separation and structural identification of Hg and MeHg biothiols A part of this work was presented as a poster at the European Winter Conference on Plasma Spectrochemistry, 2007, held in Taormina, Italy.  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