全文获取类型
收费全文 | 209篇 |
免费 | 13篇 |
专业分类
化学 | 152篇 |
晶体学 | 1篇 |
力学 | 7篇 |
数学 | 46篇 |
物理学 | 16篇 |
出版年
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2018年 | 7篇 |
2017年 | 1篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 12篇 |
2013年 | 9篇 |
2012年 | 14篇 |
2011年 | 16篇 |
2010年 | 12篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 13篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1954年 | 1篇 |
1941年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
71.
Thomas Bartelmann Frederik Gnannt Max Zitzmann Peter Mayer Henry Dube 《Chemical science》2021,12(10):3651
Introducing responsive elements into supramolecular recognition systems offers great advantages for the control of intermolecular interactions and represents an important stepping stone towards multi-purpose and reprogrammable synthetic systems. Of particular interest is implementation of light-responsiveness because of the unique ease and precision of this signal. Here we present visible light responsive hemithioindigo-based molecular tweezers that bear a highly polar sulfoxide function as an additional recognition unit inside their binding site. Sulfur oxidation allows to simultaneously enhance all crucial properties of this receptor type i.e. photoswitching capability, thermal stability of individual switching states, binding affinity, and binding modulation upon switching. With a novel titration method the thermodynamic binding parameters were determined using reduced sample amounts. Employing these strongly enhanced molecular tweezers allowed to demonstrate photocontrol of intermolecular charge transfer in a reversible manner.Hemithioindigo based molecular tweezers with a comprehensively improved property profile are obtained by simple oxidation of the sulfur atom. 相似文献
72.
Summary The separation of charged analytes by electrochromatography has been examined on porous-layer open tubular capillaries prepared
using the sol gel method. An electroosmotic flow of about 2.10×104 cm2V1s1 was obtained using between 10 and 30% acetonitrile in the mobile phase. Acidic diuretic drug compounds were successfully
separated at high pH as were theN-alkylanilines in their basic and neutral forms. The limitation of open tubular columns was observed on separating some basic
pharmaceutical drugs. These components showed severe peak tailing and were not resolved on a 20 μm i.d. porous silica layer
open tubular column. Strongly acidic components could not be detected on these columns due to their higher counter electromobilities.
The successful separation of neutral aryl alkyl ketones with an efficiency of 101,533 plates m1 for butyrophenone was an indication of the improved phase ratio on this type of open tubular columns. 相似文献
73.
G. Dube 《Accreditation and quality assurance》2001,6(1):3-7
The importance of analytical chemistry is increasing in many public fields, and the demand for reliable measurement results
is growing accordingly. A measurement result will be reliable only if its uncertainty has been quantified. This can be achieved
only by tracing the result back to a standard realizing the unit in which the measurement result is expressed. The National
Metrology Institutes (NMIs) can contribute to the reliability of the measurement results by developing measuring methods,
and by providing reference materials and standard measuring devices. In fields in which the comparability of measurement results
is of particular importance, they establish traceability structures. Responding to the globalization of trade and industry
the International Committee for Weights and Measures (CIPM) agreed on an arrangement on the mutual recognition of calibration
certificates (CIPM MRA) issued by the NMIs.
Received: 19 April 2000 / Accepted: 28 July 2000 相似文献
74.
Themba Dube 《Algebra Universalis》2008,58(2):181-202
If a frame satisfies a property which is some variant of realcompactness, then certain types of its subframes inherit the
property. Conversely, there are instances where a frame has a subframe satisfying some such property only if the frame itself
satisfies the property. We analyze these phenomena for the case of realcompactness, almost realcompactness, a-realcompactness, c-realcompactness and weak realcompactness vis-a-vis perfect subframes and flat subframes.
Received September 19, 2006; accepted in final form March 10, 2007. 相似文献
75.
76.
77.
S. N. Dube 《Proceedings Mathematical Sciences》1970,72(5):205-213
In the present paper an attempt is made to find the solution of the Navier-Stokes equations for the unsteady flow of a viscous incompressible fluid through a channel bounded by two parallel flat plates, the upper one in uniform motion and the other at rest, under the influence of pressure gradient (i) varying linearly with time, and (ii) decreasing exponentially with time. In the first case it is seen that the velocity of any point above the axis of the channel is more than the velocity of the point symmetrical to this below the axis of the channel. 相似文献
78.
Relative changes in the hydrophobicity and shape selectivity of standard analytes are shown to be a valuable method to monitor the reproducibility of the effective temperature experienced by the analytes in a chromatographic column in different ovens. Significant differences were observed between ovens with the same nominal temperature and could be a major cause of problems encountered in transferring methods between instruments or laboratories. By using two parameters, changes due to the column temperature can be distinguished from those caused by mobile phase composition differences. In addition marked increases in column efficiency were noted as the mobile phase temperature was reduced below the column temperature in contrast to claims that thermal equilibration is essential. 相似文献
79.
Summary The dual separation mechanism exhibited by capillary electrochromatography is demonstrated by the simultaneous separation
of sulfonamides as charged and neutral species over a pH range of 2.5 to 6.9. The neutral sulfonamides were separated according
to the difference in their hydrophobicities while charged components were separated by the differences in their electrophoretic
mobilities. The limitation of capillary electrochromatography for acidic components was also examined. 相似文献
80.
Photocontrol of Polar Aromatic Interactions by a Bis‐Hemithioindigo Based Helical Receptor
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Manuel Guentner Edgar Uhl Dr. Peter Mayer Dr. Henry Dube 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16433-16436
The first example of a bis‐hemithioindigo (bis‐HTI)‐based molecular receptor was realized. Its folding and selective binding affinity for aromatic guest molecules can be precisely controlled by visible light and heat. The thermodynamically stable state of the bis‐HTI is the s‐shaped planar Z,Z‐configuration. After irradiation with 420 nm light only the E,Z‐configuration is formed in a highly selective photoisomerization. The E,Z‐isomer adopts a helical conformation because of the implementation of repulsive steric interactions. The E,Z‐configured helix is able to recognize electron‐poor aromatic guests exclusively through polar aromatic interactions and also distinguishes between regioisomers. After heating, the Z,Z‐configuration is completely restored and the aromatic guest molecule is efficiently released. 相似文献