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   90篇
  免费   5篇
化学   54篇
力学   1篇
数学   8篇
物理学   32篇
  2018年   1篇
  2015年   4篇
  2014年   5篇
  2013年   1篇
  2012年   6篇
  2011年   2篇
  2010年   2篇
  2009年   4篇
  2008年   3篇
  2007年   3篇
  2006年   1篇
  2005年   4篇
  2004年   1篇
  2003年   5篇
  2002年   6篇
  2001年   4篇
  2000年   6篇
  1999年   7篇
  1998年   2篇
  1997年   3篇
  1996年   3篇
  1994年   1篇
  1993年   1篇
  1991年   2篇
  1990年   1篇
  1987年   1篇
  1983年   2篇
  1980年   1篇
  1976年   3篇
  1975年   2篇
  1974年   1篇
  1973年   1篇
  1915年   2篇
  1913年   1篇
  1899年   3篇
排序方式: 共有95条查询结果,搜索用时 31 毫秒
81.
82.
83.
"I" did it: An iodine(III)-mediated bromocarbocyclization was elaborated as an efficient tool for the synthesis of oxoindoles. This method is applicable to a variety of structurally different substrates, also with chemically sensitive groups, and gives access to the heterocycles in a regio- and stereoselective fashion. The indole-2-ones obtained can be converted easily into structurally complex target compounds, such as the alkaloid physostigmine.  相似文献   
84.
Let there be light: A heterogeneous photocatalytic system based on easily recyclable TiO(2) or ZnO allows cross dehydrogenative coupling reactions of tertiary amines. The newly developed protocols have successfully been applied to various C-C and C-P bond-forming reactions to provide nitro amines as well as amino ketones, nitriles and phosphonates.  相似文献   
85.
 Severing principles are reported concerning the certification of and quality assurance in a trace-analysis laboratory that handles a large number of real samples, about 60 000 analyses/year with 50 validated methods. ISO 9001 emphasizes monitoring rather than diagnostics. For monitoring purposes the trace-analysis methods must be highly selective and of high precision, with high throughput and uptime within a justifiable economic framework in the analytical range of interest. All trace-analysis methods must be cross-checked using independent analytical tools. The analytical laboratory must be fully integrated in the total quality management of the plant. The analyst must know not only the performance of the trace-analysis tools but also the materials and processes involved in manufacturing. Received: 19 October 1995 Accepted: 15 November 1995  相似文献   
86.
Summary We prove the existence of periodic solutions of a second order nonlinear ordinary differential equation whose nonlinearity is at resonance with two successive eigenvalues of the associated linear operator and satisfies some Landesman-Laser type conditions at both of them.  相似文献   
87.
Summary A capillary electrophoretic method for the ultra trace determination of anions on silicon wafer surfaces is presented. In several sets of experiments designed according to the methodology of Taguchi, electrokinetic sample introduction with transient isotachophoretic preconcentration was simultaneously optimized for peak height, peak area, peak asymmetry, efficiency, peak resolution, and reproducibility of migration time and peak area. The blank reading of the method showed no cross contamination. Thus, a detection limit of 10 nmol L−1 and a linear range from 50 to 500 nmol L−1 were obtained and verified by two independent instruments. Furthermore, the method was applied to the determination of anions on wafers from a regular production line wetting the whole wafer surface with ultrapure water. The capillary electrophoretic results agree with those obtained by ion chromatography. Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996.  相似文献   
88.
AFM imaging of the adsorption of self-assembled octadecylsiloxane (ODS) monolayers has been utilized for probing surface properties of silicon wafers. It has been found that both growth rate of the organic films and island size of sub-monolayer films are influenced by the doping level of the wafers as well as by the surface finishing step during wafer production. Generally, higher doping levels led to lower adsorption rates and smaller islands. Variation of the sample pretreatment used for surface finishing of similarly doped wafers led only to significant changes of the island size, but not of the surface coverage. The results presented open up a valuable perspective for characterizing the surface homogeneity of silicon wafers which is an important parameter for monitoring-wafers in semiconductor industry. Received: 26 June 2000 / Revised: 26 July 2000 / Accepted: 1 August 2000  相似文献   
89.
D. Elsner  B. Bantes  O. Bartholomy  D. E. Bayadilov  R. Beck  Y. A. Beloglazov  R. Castelijns  V. Crede  A. Ehmanns  K. Essig  R. Ewald  I. Fabry  F. Frommberger  K. Fornet-Ponse  M. Fuchs  C. Funke  A. B. Gridnev  E. Gutz  W. Hillert  S. H?ffgen  P. Hoffmeister  I. Horn  I. Jaegle  J. Junkersfeld  H. Kalinowsky  Frank Klein  Friedrich Klein  E. Klempt  M. Konrad  M. Kotulla  B. Krusche  H. L?hner  I. V. Lopatin  J. Lotz  S. Lugert  D. Menze  T. Mertens  J. G. Messchendorp  V. Metag  C. Morales  M. Nanova  D. V. Novinski  R. Novotny  M. Ostrick  L. M. Pant  H. van Pee  M. Pfeiffer  A. V. Sarantsev  C. Schmidt  H. Schmieden  B. Schoch  S. Shende  A. Süle  V. V. Sumachev  T. Szczepanek  U. Thoma  D. Trnka  D. Walther  C. Weinheimer  C. Wendel 《The European Physical Journal A - Hadrons and Nuclei》2009,39(3):373-381
At the electron accelerator ELSA a linearly polarised tagged photon beam is produced by coherent bremsstrahlung off a diamond crystal. Orientation and energy range of the linear polarisation can be deliberately chosen by accurate positioning of the crystal with a goniometer. The degree of polarisation is determined by the form of the scattered electron spectrum. Good agreement between experiment and expectations on the basis of the experimental conditions is obtained. Polarisation degrees of % are typically achieved at half of the primary electron energy. The determination of is confirmed by measuring the beam asymmetry, , in photoproduction and by a comparison of the results to independent measurements using laser backscattering.  相似文献   
90.
We performed measurements of gettering efficiencies for Cu in silicon wafers with competing gettering sites. Epitaxial wafers (p/p+) boron-doped with a polysilicon back side allowed us to compare p+ gettering with polysilicon gettering. We further measured metal distributions in p+/p- epitaxial test wafers, with the p- substrate wafers pretreated for oxygen precipitation to compare p+ gettering with oxygen precipitate gettering. Our test started with a reproducible spin-on contamination in the 1012 atoms/cm2 range, followed by thermal treatment in order to redistribute the metallic impurity. Wafers were then analyzed by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. This led to “stratigraphical” concentration profiles of the impurity, with typical detection limits of 5–10×1012 atoms/cm3. Twenty-five percent of the total Cu contamination in the p/p+/poly wafer was found in the p+ layer, whilst 75% was gettered by the polysilicon. Obviously, polysilicon exhibits a stronger gettering than p+ silicon, but due to the large distance from the front surface, polysilicon was less effective in reducing impurities from the front side of a wafer compared with p+ gettering. An epitaxial layer p+ on top of p- substrates with oxygen precipitates gettered 50% of the total Cu; while the other 50% of the Cu was measured in the p- substrate wafer with oxygen precipitates. Without oxygen precipitates, 100% of the spiked Cu contamination was detected inside the p+ layer. Gettering by oxygen precipitates thus occurs in the same temperature range as that where p+ silicon begins to getter Cu. Received: 3 September 2001 / Accepted: 17 October 2001 / Published online: 27 March 2002  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