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   758篇
  免费   8篇
  国内免费   8篇
化学   344篇
晶体学   12篇
力学   11篇
数学   203篇
物理学   204篇
  2023年   3篇
  2022年   7篇
  2021年   18篇
  2020年   12篇
  2019年   10篇
  2018年   11篇
  2017年   12篇
  2016年   10篇
  2015年   13篇
  2014年   30篇
  2013年   71篇
  2012年   36篇
  2011年   38篇
  2010年   32篇
  2009年   43篇
  2008年   43篇
  2007年   42篇
  2006年   32篇
  2005年   31篇
  2004年   22篇
  2003年   21篇
  2002年   18篇
  2001年   23篇
  2000年   17篇
  1999年   16篇
  1998年   9篇
  1997年   12篇
  1996年   13篇
  1995年   6篇
  1994年   4篇
  1993年   5篇
  1992年   4篇
  1991年   6篇
  1990年   3篇
  1989年   3篇
  1988年   4篇
  1987年   6篇
  1986年   4篇
  1985年   5篇
  1984年   9篇
  1983年   5篇
  1982年   4篇
  1981年   4篇
  1978年   3篇
  1977年   5篇
  1976年   10篇
  1975年   4篇
  1974年   3篇
  1973年   3篇
  1972年   7篇
排序方式: 共有774条查询结果,搜索用时 31 毫秒
1.
2.
In this paper we continue to study the spectral norms and their completions ([4]) in the case of the algebraic closure $ \overline {\mathbb Q} $ of ? in ?. Let $ \widetilde{\overline{\mathbb{Q}}} $ be the completion of $ \overline {\mathbb Q} $ relative to the spectral norm. We prove that $ \widetilde{\overline{\mathbb{Q}}} $ can be identified with the R‐subalgebra of all symmetric functions of C(G), where C(G) denotes the ?‐Banach algebra of all continuous functions defined on the absolute Galois group G = Gal$ {\overline {\mathbb Q}} / {\mathbb Q} $. We prove that any compact, closed to conjugation subset of ? is the pseudo‐orbit of a suitable element of $ \widetilde{\overline{\mathbb{Q}}} $. We also prove that the topological closure of any algebraic number field in $ \widetilde{\overline{\mathbb{Q}}} $ is of the form $\widetilde{\mathbb{Q}[x]}$ with x in $ \widetilde{\overline{\mathbb{Q}}} $.  相似文献   
3.
We introduce the notion of n-nuanced MV-algebra by performing a Łukasiewicz–Moisil nuancing construction on top of MV-algebras. These structures extend both MV-algebras and Łukasiewicz–Moisil algebras, thus unifying two important types of structures in the algebra of logic. On a logical level, n-nuanced MV-algebras amalgamate two distinct approaches to many valuedness: that of the infinitely valued Łukasiewicz logic, more related in spirit to the fuzzy approach, and that of Moisil n-nuanced logic, which is more concerned with nuances of truth rather than truth degree. We study n-nuanced MV-algebras mainly from the algebraic and categorical points of view, and also consider some basic model-theoretic aspects. The relationship with a suitable notion of n-nuanced ordered group via an extension of the Γ construction is also analyzed.  相似文献   
4.
Summary A separated filtered ring has a maximally complete immediate extension. This is an analogue of Krull Theorem from valuation ring theory in the frame of filtered rings.
Riassunto Un anello separato filtrato ha una immediata estensione massimale completa. Questo risultato è un analogo del teorema di Krull della teoria degli anelli di valutazione nell’ambito degli anelli filtrati.
  相似文献   
5.
6.
7.
This work discusses the synthesis and the fragmentation patterns for 2-(p-acetylaminosulfonamido)-2-thiono-(5,5-dimethyl-1,3,2-dioxaphosphorinane)(1) and for the p-acetylaminosulfonylamides of O,O-diethylthiophosphoric acid (2), O,O-diphenylthiophosphoric acid (3), dimethylaminocyclohexylthiophosphoric acid (4), and diethylaminophenylthiophosphoric acid (5). A thionamidic-thiolimidic structure was attributed to compounds 1-5, consistent with their IR and NMR spectra. EI mass spectra at 70 eV, high resolution (HR) mass measurements and metastable ion spectra were used to elucidate the fragmentation processes and to determine the kinetic energy release values associated with the metastable ion dissociations. HR accurate mass measurements were used to confirm the compositions of the more abundant ions.  相似文献   
8.
Vanadium Doped Sol-Gel TiO2 Coatings   总被引:1,自引:0,他引:1  
A study of the experimental conditions required to obtain vanadium doped sol-gel TiO2 coatings is presented. Tetraethyl orthotitanate was employed as the TiO2 source and VCl3, VOSO4 · H2O and VOSO4 dissolved H2SO4 where employed as vanadium sources.Dip coating has been used to produce coatings on silicon wafers, spectral carbon electrodes and titanium electrodes. Both supported and unsupported films have been studied by UV-Vis spectra, IR spectroscopy and X-ray diffraction (XRD). The measurements have been made on samples as prepared and treated thermally at temperatures between 100°C and 300°C. The thermal treatment temperatures have been established from DTA/TGA measurements.The vanadium doped sol-gel TiO2 coatings have been tested as sensors for redox potential measurements in electrochemical processes. The influence of both the thickness of films and the nature of substrate has been investigated.  相似文献   
9.
Phenylpyruvic acid reacts with p-nitroaniline to yield the 3-hydroxypyrrolinone2a, and with anilines bearing+M substituents in the p-position to yield the 3-enaminopyrrolinones1b-1e.

Mit 1 Abbildung

5. Mitt.:M. Ruse, E. Hamburg undM. Petri, Chem. Ber.103, 3727 (1970).  相似文献   
10.
Zusammenfassung Es wurden 34 neue Komplexsalze durch doppelte Umsetzung aus wäßr.-alkohol. Lösungen der folgenden Reineckeat-Analoga: [Cr(NCS)4(m-xylidin)2], [Cr(NCS)4(p-xyl)2] und Hexammin-, Monoacido-pentammin- und Diacido-tetramminkobalt(III)-komplexsalze erhalten. Es wurden in einigen Fällen Unterschiede in physiko-chemischen Eigenschaften, wie Farbtönung, Kristallform, Löslichkeit und papierchromatographischeR f-Werte, bei den stellungsisomeren Salzen vom Typus: Kation · [Cr(NCS)4(xyl)2] und auch bei den Koordinationsisomerpaaren: [Co(DH)2(m-xyl)2] [Cr(NCS)4(p-xyl)2] und [Co(DH)2(p-xyl)2] [Cr(NCS)4(m-xyl)2] usw. beobachtet.
Cobalt(III)ammine derivatives of some reineckate analogues with xylidines
34 new complex salts were prepared by double conversion of the reineckate analogues [Cr(NCS)4(m-xylidine)2], [Cr(NCS)4(p-xyl)2], with the hexammine-, monoacido-pentammine- and diacidotetrammine-complexes of Co(III). In some of the position and coordination isomeres differences of the standard physico-chemical properties, i.e. color, crystal form, solubility and paper chromatographyR f-values were observed.
  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