全文获取类型
收费全文 | 1086篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 922篇 |
晶体学 | 6篇 |
力学 | 8篇 |
数学 | 60篇 |
物理学 | 106篇 |
出版年
2021年 | 10篇 |
2019年 | 8篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 16篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 29篇 |
2011年 | 26篇 |
2010年 | 16篇 |
2009年 | 13篇 |
2008年 | 20篇 |
2007年 | 24篇 |
2006年 | 17篇 |
2005年 | 24篇 |
2004年 | 19篇 |
2003年 | 17篇 |
2002年 | 18篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1984年 | 10篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1974年 | 8篇 |
1972年 | 7篇 |
1970年 | 8篇 |
1969年 | 5篇 |
1968年 | 59篇 |
1967年 | 42篇 |
1966年 | 41篇 |
1965年 | 100篇 |
1964年 | 42篇 |
1963年 | 99篇 |
1962年 | 109篇 |
1959年 | 5篇 |
1932年 | 5篇 |
排序方式: 共有1102条查询结果,搜索用时 31 毫秒
21.
Gavrilova AL Qin CJ Sommer RD Rheingold AL Bosnich B 《Journal of the American Chemical Society》2002,124(8):1714-1722
The di-Co(2+) complex, [Co(2+)(mu-OH)(oxapyme)Co(2+)(H(2)O)](+), contains an unsymmetrical binucleating ligand (oxapyme) which provides five- and six-coordinate metal sites when a hydroxide bridge is introduced. This complex absorbs 1 equiv of O(2) irreversibly in solution, producing an unstable di-Co(3+) oxygenated product. The oxygenated product has been studied at low temperatures, where its electronic absorption and (1)H NMR spectra were recorded. It is probable that the oxygenation reaction involves a one-site addition two-metal oxidation reaction to produce an end-on-bonded peroxide ligand at the available coordination site, giving the complex [Co(3+)(mu-OH)(oxapyme)Co(3+)(mu(1)-O(2))](+). Addition of 1 equiv of HClO(4) to this oxygenation product gives a stable peroxide complex, [Co(3+)(mu,eta(1):eta(2)-O(2))(oxapyme)Co(3+)](2+), where one of the oxygen atoms bridges the two metals and is sideways bonded to one of the metals. The formation of this stable complex involves expulsion of the OH(-) bridge. Addition of NO(2)(-) to the sideways-bonded peroxide complex leads to the formation of another stable complex, [Co(3+)(mu,eta(1):eta(1)-O(2))(oxapyme)Co(3+)(NO(2))](+), where the peroxide forms a classic di-end-on bridge to the two metals. Both of these complexes have been fully characterized. Addition of acid to this second stable dioxygen complex leads to the release of HNO(2) and the formation of the mu,eta(1):eta(2) sideways-bonded peroxide complex. 相似文献
22.
Udo Sommer 《Theoretical chemistry accounts》1967,9(1):26-37
Zusammenfassung Die Spin-Bahn-Kopplung der niedrigen elektronischen Anregungszustände von organischen Molekülen wird untersucht. Es wird gezeigt, daß die Zerstörung der aromatischen Ebene durch Torsionen oder Schwingungen zu nicht-verschwindenden Zweizentrenbeiträgen führt. Am Beispiel des Triphenylmethyl-Kations wird mit Hilfe der LCAO MO SCF-Methode die Größenordnung der auftretenden Wechselwirkungen ermittelt. Diese haben wahrscheinlich großen Einfluß auf die strahlungslosen Prozesse in Molekülen mit leicht beweglichen Gruppen.
Spin-orbit coupling of the lower excited electronic states of organic molecules has been investigated. It is shown that any destruction of the aromatic plane through torsions or vibrations leads to non-vanishing contributions from two-centre integrals. The order of magnitude of this type of interactions is determined for the triphenylmethyl-cation with the aid of the LCAO MO SCF method. These interactions probably have much influence on radiationless transitions in molecules containing mobile groups.
Résumé Etude du couplage spin-orbite dans les états électroniques exités les plus bas des molécules organiques. Toute non planéité aromatique créée par torsions ou vibrations entraîne une contribution non nulle de la part des intégrales bicentriques. L'ordre de grandeur de ce type d'interaction est detérminé, à l'aide de la méthode L.C.A.O. M.O. SCF, pour le cation triphenylméthyle. Ces interactions ont probablement beaucoup d'influence sur les transitions non radiatives dans les molécules contenant des groupements mobiles.相似文献
23.
K. Sommer und H. Kick 《Fresenius' Journal of Analytical Chemistry》1966,220(1):21-26
Zusammenfassung Zur spektrographischen 15N-Bestimmung wird für 15N-Konzentrationen von 0,38–20,0 At-% 15N ein Verfahren beschrieben, das mit UV-Spektrographen mit normaler Ausstattung ausgeführt werden kann. Die relative IsotopenhÄufigkeit wird mittels einer Eichkurve in leitprobengebundener oder leitprobenfreier Spektralanalyse bestimmt. Das Verfahren weist eine relative Standardabweichung der Analysenergebnisse zwischen 2,0 und 3,0% auf.
Summary A method for a spectrographic 15N determination in the atomconcentration range from 0.38 to 20.0% 15N is described. The method can be used with normal spectrographic equipment. The relative isotopic abundance is determined by means of a calibration curve. The relative standard deviation of the isotope determinations is between 2.0 and 3.0% for the method described.相似文献
24.
We study the dynamics of tethered chains of length N on adsorbing surfaces, considering the dilute case; for this we use the bond fluctuation model and scaling concepts. In particular, we focus on the mean-square displacement of single monomers and of the center of mass of the chains. The characteristic time tau of the fluctuations of a free chain in a good solvent grows as tau approximately N(a), where the coefficient a obeys a=2nu+1. We show that the same coefficient also holds at the critical point of adsorption. At intermediate time scales single monomers show subdiffusive behavior; this concurs with the behavior calculated from scaling arguments based on the dynamical exponent a. In the adsorbed state tau(perpendicular), the time scale for the relaxation in the direction perpendicular to the surface, becomes independent of N; tau(perpendicular) is then the relaxation time of an adsorption blob. In the direction parallel to the surface the motion is similar to that of a two-dimensional chain and is controlled by a time scale given by tau(parallel) approximately N(2nu(2)+1)L(-2Delta(nu/nu)), where nu(2) is the Flory exponent in two dimensions, nu is the Flory exponent in three dimensions, and Deltanu=nu(2)-nu. For the motion parallel to the surface we find dynamical scaling over a range of about four decades in time. 相似文献
25.
The influence of surface structure of technical materials on results and statements of surface analytical methods has been investigated. Especially surface roughness as a typical property of rolled products has been observed. For this purpose samples of steel (technical surface, roughness up to 5 m) and silicon wafers (polished surface) have been analyzed by SNMS and GDOS in order to get information about changes of the surface roughness as function of the sputtering time and their influence on the statements about the depth profiles obtained. 相似文献
26.
Lumír Sommer 《Fresenius' Journal of Analytical Chemistry》1958,164(3):299-309
Zusammenfassung Die Chromotropsäure ist ein analytisch wertvolles Reagens auf Eisen (III)23, Chrom (VI)9, Kupfer, Niob24 und besonders auf Titan (IV). Die Reaktion mit Chromotropsäure ist die empfindlichste (pD 5,9) und in Gegenwart von Ascorbinsäure weitgehend selektive Titanreaktion.In den Titan(IV)-lösungen bilden sich mit Chromotropsäure abhängig von der Zusammensetzung und dem pH-Wert der Lösung sowie von der Konzentration der Reaktionspartner stufenweise mehrere Chelate. In den Lösungen mit Reagensüberschuß liegen folgende Chelatgleichgewichte vor: TiO2+ + 2 H2R2 TiO(RH)2
4– + 2 H+ (Absorptionsmaximum470 m), PH 0–2; TiO2+ + 2 H2R2– TiOR2
6– + 4 H+ (470 m), pH1–3,5; TiOR2
6– + H2R2 TiOR3
10– + 2 H+ (420 m), pH 3,2–7,0; TiOR2
6 + 2H2R2– TiR4
12– + 2 H + H2O (470 m), pH 1,7–2,4.Die beiden stabilen Chelate TiOR2
6– und TiOR3
10– können bei begrenzten Reaktionsbedingungen zur spektrophotoinetrischen Titanbestimmung ausgenutzt werden. Die Bestimmung bei pH 2,9–3,2 und 467m in Gegenwart von Ascorbinsäure ermöglicht die Titanbestimmung neben einer Zahl von fremden Ionen. Sie ist die für die Praxis geeignetste Methode.Herrn Prof. Dr. A. Oká zum 55. Geburtstag gewidmet.Den Firmen E. Merck, Darmstadt und Reagencia, Kralupy, bin ich für das freundliche Überlassen der Präparate der Chromotropsäure mit herzlichem Dank verpflichtet. 相似文献
27.
Manfred Sommer 《Numerical Functional Analysis & Optimization》2013,34(2):213-234
The chief purpose of this paper is to study the problem of existence of continuous selections for the metric projection and of convergence of best Lp–approximations in subspaces of polynomial spline functions defined on a real compact interval I. Nürnberger-Sommer [8] have shown that there exists a continuous selection s if and only if the numberof knots k is less than or equal to the order m of the splines. Using their construction of s the author [12] has proved that the sequence of best Lp–approximations of f converges to s(f) as ρ→∞ for every continuous function f. The main results of this paper say that also in the case when k>m there exists always a continuous selection s (it is even pointwise-Lipschitz-continuous and quasi-linear) provided that the approximation problem is restricted to certain subsets Iepsilon; of I. In addition it is shown that anologously as for k≤m the sequence of best Lpapproximations of f converges to s(f) for every continuous function f on Iε 相似文献
28.
29.
Steffen Blaurock Thomas Koch Olaf Kühl Peter Lönnecke Felicite Majoumo René Sommer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1451-1456
Substituted bifunctional phosphorus-based ligands HX(CRR') n PR"H (or -PR" 2 ) [where X = O, S, NR', (substituted) cyclopentadienyl; n = 1, 2, 3; R, R', R" = alkyl, aryl, H] were employed as bridging ligands in the synthesis of early/late bridged transition metal complexes. Synthetic routes to the bifunctional ligands were also developed. First, mononuclear complexes, such as [TpZr(OCH 2 PPh 2 ) 3 ] (Tp = trispyrazolylborato), [Cp 2 Zr(1-O-2-PHR-C 6 H 10 )(Me)] (R = 2,4,6-Pr i 3 C 6 H 2 (Tipp)), [Cp 2 Zr(SCH 2 CH 2 PHR) 2 ] (R = Ph, Mes, Tipp), and phosphinoferrocene derivatives, were prepared. These complexes are suitable precursors for the introduction of a second metal (as in, for example, [TpZr( w -OCH 2 PPh 2 ) 3 Mo(CO) 3 ]). 相似文献
30.
Alain Chaintreau Wolfgang Fieber Horst Sommer Alexis Gilbert Keita Yamada Naohiro Yoshida Alain Pagelot Detlef Moskau Aitor Moreno Jürgen Schleucher Fabiano Reniero Margaret Holland Claude Guillou Virginie Silvestre Serge Akoka Gérald S. Remaud 《Analytica chimica acta》2013
Isotopic 13C NMR spectrometry, which is able to measure intra-molecular 13C composition, is of emerging demand because of the new information provided by the 13C site-specific content of a given molecule. A systematic evaluation of instrumental behaviour is of importance to envisage isotopic 13C NMR as a routine tool. This paper describes the first collaborative study of intra-molecular 13C composition by NMR. The main goals of the ring test were to establish intra- and inter-variability of the spectrometer response. Eight instruments with different configuration were retained for the exercise on the basis of a qualification test. Reproducibility at the natural abundance of isotopic 13C NMR was then assessed on vanillin from three different origins associated with specific δ13Ci profiles. The standard deviation was, on average, between 0.9 and 1.2‰ for intra-variability. The highest standard deviation for inter-variability was 2.1‰. This is significantly higher than the internal precision but could be considered good in respect of a first ring test on a new analytical method. The standard deviation of δ13Ci in vanillin was not homogeneous over the eight carbons, with no trend either for the carbon position or for the configuration of the spectrometer. However, since the repeatability for each instrument was satisfactory, correction factors for each carbon in vanillin could be calculated to harmonize the results. 相似文献