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   245篇
  免费   2篇
化学   127篇
晶体学   3篇
力学   11篇
综合类   2篇
数学   24篇
物理学   80篇
  2018年   10篇
  2017年   3篇
  2016年   2篇
  2015年   5篇
  2014年   7篇
  2013年   17篇
  2012年   13篇
  2011年   9篇
  2010年   8篇
  2009年   5篇
  2008年   4篇
  2007年   8篇
  2006年   4篇
  2005年   5篇
  2004年   2篇
  2003年   2篇
  2002年   6篇
  2001年   2篇
  2000年   6篇
  1999年   6篇
  1997年   6篇
  1996年   3篇
  1995年   3篇
  1992年   2篇
  1990年   2篇
  1988年   2篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1982年   6篇
  1981年   6篇
  1980年   4篇
  1979年   2篇
  1978年   8篇
  1974年   3篇
  1973年   2篇
  1972年   2篇
  1971年   2篇
  1969年   3篇
  1968年   5篇
  1965年   2篇
  1961年   2篇
  1960年   5篇
  1959年   5篇
  1958年   3篇
  1953年   3篇
  1951年   3篇
  1939年   6篇
  1935年   2篇
排序方式: 共有247条查询结果,搜索用时 15 毫秒
1.
Zusammenfassung Durch Reduktion des 1,5-Dinitroanthrachinons mit Formaldehyd in warmer alkalischer Lösung und folgende Extraktion des 1,5-Diaminoanthrachinons mit Amylalkohol werden rötlich-orange gefärbte Lösungen mit einem Absorptionsmaximum bei 500 nm erhalten. Die Farbe bleibt Monate hindurch beständig. Die Reaktion ist auch zur Bestimmung von Anthracen und Anthrachinon verwendbar. Diese löst man in Mischsäure, neutralisiert und extrahiert mit Äther. Die isomeren Dinitroanthrachinone und andere sekundäre Produkte, welche entstehen könnten, beeinflussen die Linearität der Lichtabsorptionskurve als Funktion der vorhandenen Stoffmengen nicht merklich.Die Eichkurven für die Bestimmung von 1,5-Diaminoanthrachinon in amylalkoholischer Lösung bzw. die von 1,5-Dinitroanthrachinon, Anthrachinon und Anthracen, nach Umwandlung in 1,5-Diaminoanthrachinon, werden angegeben.
Summary By reduction of 1.5-dinitroanthraquinone with formaldehyde in warm alcaline solution, followed by the extraction of 1.5-diaminoanthraquinone with amyl alcohol, reddish-orange solutions are obtained, with an absorption maximum at 500 nm. Colour remains stable for several months. The reaction is applicable also to anthracene and anthraquinone, after dissolution in sulphuric-nitric acid, neutralisation and ether extraction. Isomeric diaminoanthraquinones as well as other secondary products induce no significant changes in the linearity of light absorption.Calibration curves for the determination of 1.5-dinitroanthraquinone, anthraquinone and anthracene, after conversion to diaminoanthraquinone, are presented.
  相似文献   
2.
A new polarimetric procedure has been developed for the rapid determination of zirconium in the presence of tartrazin as reagent This determination is possible in the presence of uranium.  相似文献   
3.
Zusammenfassung Durch Oxydation und Nitrierung mit Mischsäure werden Anthracen und Anthrachinon in Dinitroanthrachinone überführt, die mit Formaldehyd und Natriumhydroxid zu roten Diaminen reduziert werden. Diese werden mit Amylalkohol extrahiert. Die Empfindlichkeit beträgt 2g. Die Färbung wird von Benzol und Homologen, Naphthalin, Phenanthren, Acenaphthen, Fluoren, Chrysen, Acridin und Phenolen, sowie von den im Kokereipech vorhandenen Verbindungen, nicht gegeben.
Summary Anthracene and anthraquinone are converted by oxidation and nitrification with nitric-sulphuric acid to dinitro anthraquinones which are reduced to red diamines by formaldehyde and sodium hydroxide. These are extracted by amyl alcohol. Sensitivity is 2g. Benzene and its homologues, naphthalene, phenanthrene, acenaphtene, fluorene, chrysene, acridine, phenols and compounds contained in pitch do not interfere with the colour reaction.
  相似文献   
4.
5.
6.
The prototype of a thermal diffusion column for the use as basic unit in a N14N15 cascade is described. The hot wire separation column consists of a brass tube of effective length of 250 cm and inner diameter of 10 mm. Four columns are connected in series on a square cascade, the separation factors of which are compared with the values obtained by other investigators.  相似文献   
7.
We use the hydrodynamic formulation of Scale Relativity Theory to analyze the TDGL equation. As a result, London equations come naturally from the system, when equating to zero the real velocity, the imaginary one turns real, the superconducting fluid act as a subquantum medium energy accumulator, the vector potential, the real and the imaginary velocity are all written in terms of the elliptic function. When solving the resulted system by means of WKBJ method, we get tunneling and quantization. In other words, scale transformation laws produce, on the motion equation of particles governed by the TDGL equation, under some peculiar assumptions, effects which are analogous to those of a “macroscopic quantum mechanics”.  相似文献   
8.
9.
Electronic structure of an InAs spherical quantum dot placed at the center of a GaAs cylindrical nano-wire is investigated. The Schrodinger equation within the effective mass approximation is solved and the energy eigenvalues and transition energies are calculated as a function of quantum dot and nano-wire radii using the finite element method. The two types of heavy holes, hhI and hhII, with isotropic and anisotropic effective masses are considered, respectively. The effect of spherical and nano-wire confining potentials, the size of the dot and the nano-wire on ground and first excited state energies of the electron, heavy hole I and heavy hole II are investigated. The results show that the electron and heavy holes energies decrease as the dot and the nano-wire radii increase. The emitted wavelength of transitions between el-hhI and el-hhII are also calculated and compared. The results show that the anisotropy of the effective mass has great effect on the emitted wavelength.  相似文献   
10.
In this work, Mn0.7Zn0.3Fe2O4 and Ni0.7Zn0.3Fe2O4 nanoparticles with super-paramagnetic properties and size distribution from 10 to 52 nm were investigated. These particles were produced by a low-temperature solid-state reaction method without the ball-milling process. The size and morphology of the nanocrystallites were determined by X-ray diffraction, transmission electron microscopy and scanning tunneling microscopy methods. Magnetic measurements such as alternating gradient field magnetometers were used to justify the super-paramagnetic properties of these nanoparticles. Their microwave absorption in the range of 8-18 GHz was studied by a vector network analyzer. Responses of the device under tests were studied. Also, the percentage of the resin, the size and thickness of the mount were determined. The band width of 2.3 GHz was obtained with reflection-loss/written-loss of −16 dB around 10.4 GHz.  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