全文获取类型
收费全文 | 386篇 |
免费 | 16篇 |
国内免费 | 5篇 |
专业分类
化学 | 244篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 90篇 |
物理学 | 60篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 15篇 |
2012年 | 29篇 |
2011年 | 26篇 |
2010年 | 18篇 |
2009年 | 13篇 |
2008年 | 25篇 |
2007年 | 21篇 |
2006年 | 24篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 25篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有407条查询结果,搜索用时 15 毫秒
21.
Domingo Chinea 《Rendiconti del Circolo Matematico di Palermo》1984,33(3):319-330
In this paper we study the Riemannian submersions between manifolds belonging to those classes of almost contact metric manifolds which can be assembled under the common denomination of quasi-K-cosymplectic manifolds. 相似文献
22.
Wolf-Rüdiger Leupold Concepcion Domingo Werner Niggemann Bernhard Schrader 《Fresenius' Journal of Analytical Chemistry》1980,303(5):337-348
Summary The automatic interpretation of digital recorded infrared and Raman spectra is described. The procedure starts with the automatic correction for an approximated base line. In the case of Raman spectra the spectral response of the spectrometer is corrected, too. Subsequently, the spectra are reduced to band lists, conserving the position, intensity and half-widths of the bands. These band lists are the input in an interpretation algorithm for the combined evaluation of infrared and Raman spectra by testing presence or absence of characteristic bands or groups of bands. The algorithm was tested with 300 substances. A balance of the interpretation results shows that the abscence of structural elements is found more safely than the presence. The algorithm may be modified for special purposes: evaluation of infrared or Raman spectra alone or application to special classes of substances.
Automatische Reduktion und Auswertung von IR- und Raman-SpektrenI. Interpretation charakteristischer Banden
Zusammenfassung Ziel dieser Arbeit ist die automatische Interpretation von Infrarot- und Raman-Spektren mit Hilfe charakteristischer Banden. Die Bearbeitung der Spektren beginnt mit der Korrektur der digital registrierten Spektren auf eine angenÄherte Grundlinie. Bei Raman-Spektren wird zusÄtzlich die spektrale Empfindlichkeit des Spektrometers korrigiert. Die Spektren werden auf Bandenlisten reduziert, in denen die Lage, IntensitÄt und Halbwertsbreite der einzelnen Banden enthalten sind. Diese Bandenlisten dienen als Eingabe in einen Interpretationsalgorithmus mit dem durch Prüfung der Lage und IntensitÄt einzelner charakteristischer Banden und Bandengruppen auf Anwesenheit oder Abwesenheit von Strukturmerkmalen geschlossen wird. Der Algorithmus wurde an 300 Substanzen getestet. Die Aussage über das Fehlen bestimmter Gruppen ist sicherer als die über deren Vorhandensein. Die Struktur des Auswertealgorithmus erlaubt ein einfaches Anpassen an verschiedene Anwendungsgebiete: Auswertung von Infrarot-oder Raman-Spektrum allein, bzw. Anwendung bei speziellen Substanzklassen.相似文献
23.
Domingo A. Herrero 《Mathematische Annalen》1974,207(4):271-279
24.
Laveissière G Todor L Degrande N Jaminion S Jutier C Di Salvo R Van Hoorebeke L Alexa LC Anderson BD Aniol KA Arundell K Audit G Auerbach L Baker FT Baylac M Berthot J Bertin PY Bertozzi W Bimbot L Boeglin WU Brash EJ Breton V Breuer H Burtin E Calarco JR Cardman LS Cavata C Chang CC Chen JP Chudakov E Cisbani E Dale DS de Jager CW De Leo R Deur A d'Hose N Dodge GE Domingo JJ Elouadrhiri L Epstein MB Ewell LA Finn JM Fissum KG Fonvieille H Fournier G Frois B Frullani S Furget C Gao H Gao J 《Physical review letters》2004,93(12):122001
We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states. 相似文献
25.
26.
Intramolecular Diels-Alder reactions of 2-azadiene models have been studied quantum chemically at the B3LYP/6-31G level in order to elucidate the stereochemical features of the cyclization step involved in the biosynthesis of paraherquamide A and VM99955. These cycloadditions take place through concerted transition states associated with [4 + 2] processes. Analysis of the energies along the competitive paths reveals that while the cycloadditions of the oxindoles present a large anti selectivity, the indoles show a low syn selectivity for the formation of the C20 stereogenic center that is larger for the reduced tertiary amide form. The presence of the C14 methyl of the beta-methylproline ring produces a low hindrance along the reaction coordinate for the syn approach of the isoprene framework, in agreement with the low facial selectivity found experimentally. An analysis of the electrophilicity and activation parameters for experimental models of the inter- and intramolecular Diels-Alder reactions reveals several significant factors controlling these biosynthetic cyclizations. The results are in reasonable agreement with the available experimental data. 相似文献
27.
A theozyme for antibody aldolases has been studied at the MP2/6-31G** computational level. Formation of two cooperative hydrogen-bonds between the acidic hydrogen atoms of the enamine and of a methanol molecule with the oxygen atom of the aldol acceptor markedly favors the C-C bond-formation associated with the aldol reaction. A comparative analysis of the geometry, the charge distribution and the shape of the molecular electrostatic potential of the transition structure (TS) with the covalent adduct, resulting from the reaction of methylamine and the beta-diketone used as a hapten allows us to characterize the transition-state analogue (TSA) generated at immunization. This finding allows us to propose a hapten based on a chiral beta-ketosulfoxide that could give the formation of a TSA that addresses the tetrahedral geometry of the TS. 相似文献
28.
Maspoch D Domingo N Ruiz-Molina D Wurst K Hernández JM Vaughan G Rovira C Lloret F Tejada J Veciana J 《Chemical communications (Cambridge, England)》2005,(40):5035-5037
A metal-organic open-framework with an unprecedented (6,3)-helical topology, large channels and mixed ferro- and antiferromagnetic interactions has been synthesized using a three-connecting tricarboxylic polychlorotriphenylmethyl radical and Co(ii) ions. 相似文献
29.
The generation of acetoxyphenylketene (4) in the cold in the presence of biacetyl yields the single β-lactone , which undergoes a novel rearrangement to the tricyclic orthoester lactone above 130°. 相似文献
30.
Transition structures associated with the C-C bond-formation step of the proline-catalyzed intermolecular aldol reaction
between acetone and isobutyraldehyde have been studies using density functional theory methods at the B3LYP/6-31G** computational
level. A continuum model has been selected to represent solvent effects. For this step, which is the stereocontrolling and
rate-determining step, four reactive channels corresponding to the syn and anti arrangement of the active methylene of the
enamine relative to the carboxylic acid group of l-proline and the re and si attack modes to both faces of the aldehyde carbonyl group have been analyzed. The B3LYP/6-31G**
energies are in good agreement with experiment, allowing us to explain the origin of the catalysis and stereoselectivity for
these proline-catalyzed aldol reactions.
Received: 2 April 2002 / Accepted: 18 July 2002 / Published online: 11 October 2002
Acknowledgements. This work was supported by research funds provided by the Ministerio de Educación y Cultura of the Spanish Government by
DGICYT (project PB98–1429). All the calculations were performed on a Cray–Silicon Graphics Origin 2000 of the Servicio de
Informática de la Universidad de Valencia. We are most indebted to this center for providing us with computer capabilities.
Correspondence to: L. R. Domingo e-mail: domingo@utopia.uv.es 相似文献