全文获取类型
收费全文 | 1500篇 |
免费 | 52篇 |
国内免费 | 6篇 |
专业分类
化学 | 902篇 |
晶体学 | 7篇 |
力学 | 29篇 |
数学 | 338篇 |
物理学 | 282篇 |
出版年
2021年 | 13篇 |
2020年 | 23篇 |
2019年 | 21篇 |
2018年 | 13篇 |
2016年 | 28篇 |
2015年 | 28篇 |
2014年 | 40篇 |
2013年 | 67篇 |
2012年 | 70篇 |
2011年 | 60篇 |
2010年 | 59篇 |
2009年 | 48篇 |
2008年 | 78篇 |
2007年 | 56篇 |
2006年 | 62篇 |
2005年 | 42篇 |
2004年 | 36篇 |
2003年 | 32篇 |
2002年 | 40篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 19篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 26篇 |
1992年 | 35篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 28篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1980年 | 21篇 |
1979年 | 17篇 |
1978年 | 26篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1974年 | 23篇 |
1971年 | 10篇 |
1970年 | 18篇 |
1969年 | 13篇 |
排序方式: 共有1558条查询结果,搜索用时 31 毫秒
21.
22.
Gert Brandl Fritz Kastner Rainer Fritsch Herbert Zinner Albrecht Mannschreck 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):1059-1069
Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke. 相似文献
23.
Some general expressions for the modeling of absorption band shapes and Raman excitation profiles are presented. These expressions are shown to be exact representations of the “transform” theory of Hizhnyakov and Tehver. Examples of a calculation are presented which utilize closed-form analytical solutions for the absorption band shape and resonance Raman excitation profile. 相似文献
24.
Mass spectra of 3,6,20β-trihydroxypregnanes differ greatly, depending upon the nature of the A/B ring fusion and the positions of the hydroxy groups. Of all the isomers only 3α,6β,20β-trihydroxy-5β-pregnane produces an intense, structurally significant, ion at m/e 263. For 3β,6α,20β-trihydroxy-5α-pregnane an ion of m/e 141 is typical. 相似文献
25.
W. G. Albrecht und K. Beyermann 《Fresenius' Journal of Analytical Chemistry》1977,286(1-2):102-106
Zusammenfassung Ein Gerät zur Diasolyse (Flüssig-flüssig Extraktion mit phasentrennender Membran) wird beschrieben, bei dem ein Silicongummischlauch als Membranmaterial dient. Der Einfluß einer Reihe von Parametern wurde untersucht (Pumpgeschwindigkeit, Schlauchlänge, Temperatur, pH, Volumen der wäßrigen Phase, Konzentration der zu bestimmenden Substanz, Quell- und Lösungsmittel, Fremdsubstanzen, kontinuierliche und diskontinuierliche Ausführung). Als Testsubstanzen wurden Barbiturate verwendet. Die Methode eignet sich zur Trennung von lipophilen und lipophoben Stoffen sowie zur Spurenanreicherung.
Separation by diasolysis by means of swollen silicone rubber membranes
An apparatus for diasolysis (liquid-liquid extraction with phase separation by membranes) is described, which employs silicone rubber tubes as membrane material. The effect of various parameters has been investigated (pumping rate, tube length, temperature, pH, volume of aqueous phase, concentration of substance to be determined, swelling agent, solvent, foreign substances, continuous and discontinuous mode of operation). Barbiturates served as testing substances. The method is suitable for the separation of lipophilic from lipophobic substances and also for the enrichment of traces.相似文献
26.
The syntheses of p-substituted 2-methyl-4-phenylbuten(1)-carboxylic acid derivatives are described, using Blanc's chloromethylation reaction, the Friedel-Crafts alkylation of unsaturated ketones or the Meerwein arylation; the formed intermediates react in subsequent steps to the title compounds. 相似文献
27.
Gudrun Albrecht 《Journal of Geometry》1994,50(1-2):1-10
In 1809 J. IVORY found a distance relation between any two confocal ellipsoids in Euclidean space E3. After that, the theorem of IVORY has been formulated for any two nondegenerate confocal quadrics of the same type. In this paper we succeed in completing these results and in formulating and proving them uniformly for any two quadrics of the same type belonging to a general system of confocal quadrics.
Herrn Prof. Dr. Oswald Giering zum 60. Geburtstag gewidmet 相似文献
Herrn Prof. Dr. Oswald Giering zum 60. Geburtstag gewidmet 相似文献
28.
29.
30.
Schalley CA Lützen A Albrecht M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(5):1072-1080
Functional molecules require a high degree of complexity which is difficult to achieve by covalent synthesis. This article discusses supramolecular approaches to the creation of larger architectures through noncovalent bonds, self-assembly, and template strategies. It highlights selected examples for the structural and conformational control of function and attempts to identify difficulties and challenges which may arise in future. 相似文献