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排序方式: 共有252条查询结果,搜索用时 15 毫秒
1.
We investigate the dependence of the relaxation time of the current flowing in a nematic cell submitted to an external dc voltage on the physical properties of the substrate. We show that previously presented analyses of the same problem are not very useful for practical applications. We compare our theoretical predictions with experimental data, and show that the agreement is rather good. The influence of the adsorption-desorption phenomenon on the relaxation time is also discussed. 相似文献
2.
3.
Summary. The reaction of 2-chloroisobutyrophenones and nitromethanide anion gives stereoselectively (E)-3-nitro allylic alcohols. The Gibbs free enthalpies of reaction in DMSO for carbanion addition, epoxide formation, and rearrangement to 3-nitro allylic alcohol, as elementary steps for the reaction, were estimated from corresponding neutral gas reactions and using a thermodynamical approach to the transfer of gaseous compounds to DMSO. A criterion for assigning the sign of affinity of liquid compounds to DMSO was developed on the basis of the Gibbs enthalpies of liquefaction. The information obtained on reaction rate and thermodynamic viability of the steps indicates that carbanion addition is the rate-determining step.In memory of Prof. Dr. M. Ballester, deceased on April 6, 2005 相似文献
4.
The mean square tilt angle of a nematic slab with finite anchoring energy and periodic boundary conditions has been theoretically investigated, as a function of the slab geometry and of the reduced extrapolation length. If the anchoring strength is free-surfacelike, the contrast is affected by a loss 10% at room temperature if the ratio between the anchoring pitch and the cell thickness is 0.5.Glossary
anchoring pitch
-
h
cell thickness
-
/h
- ( = x/, = y/h)
reduced coordinates
-
(, )
local tilt angle
-
elastic constant
- wa
anchoring energy anisotropy
-
b=/w
a
de Gennes-Kleman extrapolation length
-
B=b/h
reduced extrapolation length
-
T
NI
nematic-isotropic transition temperature
-
:=(T/T
NI
) – 1
reduced temperature
-
easy axis direction
-
MAX
-
±
2
mean square tilt angle along the boundary
-
()
absorbance coefficients of the p-dye
-
r
/: dichroic ratio
-
c
contrast
-
G
contrast gain
-
S
order parameter 相似文献
5.
Zusammenfassung Die allgemeine Verwendbarkeit von modifizierten Bentone-Kolonnen zur Trennung von aromatischen Kohlenwasserstoffen, insbesondere Polyphenylen, wird gezeigt. Trennresultate auf festen Caesiumchlorid-Phasen, die bis 500° C verwendbar und praktisch unbegrenzt haltbar sind, werden gegenübergestellt.Als Beispiele für die Trennung substituierter Aromaten werden bromierte Bi- und Terphenyle angeführt. Es wurden nur gepackte Kolonnen verwendet.
Die vorliegende Arbeit wurde im Rahmen des ReaktorforschungsprogrammsOrgel ausgeführt.
Die Fa. Progil, Lyon, steuerte unter Euratom-Kontrakt wesentliche Ergebnisse und dank langjähriger Erfahrung auf dem Gebiet der Polyphenyle wertvolle fachliche Diskussionen bei.
Die Autoren danken auch Herrn Dr. W.Keess, der als Euratom-Forschungspraktikant insbesondere mit der Ausarbeitung von Analysenmethoden für die leichtersiedenden Anteile der Polyphenylgemische beauftragt war. 相似文献
Summary The general utility of modified Bentone-columns for the separation of aromatic hydrocarbons, especially of polyphenyls, is shown. The separation results are compared with those obtained on solid cesium chloride phases which guarantee an almost unlimited duration of life, even up to 500° C. Mixtures of brominated bi- and terphenyls figure as examples for the separation of substituted aromatics. Packed columns have been used exclusively.
Die vorliegende Arbeit wurde im Rahmen des ReaktorforschungsprogrammsOrgel ausgeführt.
Die Fa. Progil, Lyon, steuerte unter Euratom-Kontrakt wesentliche Ergebnisse und dank langjähriger Erfahrung auf dem Gebiet der Polyphenyle wertvolle fachliche Diskussionen bei.
Die Autoren danken auch Herrn Dr. W.Keess, der als Euratom-Forschungspraktikant insbesondere mit der Ausarbeitung von Analysenmethoden für die leichtersiedenden Anteile der Polyphenylgemische beauftragt war. 相似文献
6.
Abstract We present evidence for the flexo-electric effect in a hybrid aligned nematic cell containing 4-methoxybenzylidene-4'-n-butylaniline (MBBA) subject to d.c. excitation, by comparing the theoretical curve derived by including the flexo-electric term in the free energy with the experimental points. The agreement appears to be very good for MBBA doped with a small amount of an additive which shows reversible electrochemical reactions at very low redox potential; this allows us to determine the sum of the flexo-electric coefficients and the anchoring energy on the planar wall. For undoped MBBA the experimental results can be justified only by assuming a low voltage screening of the electric field, due to the presence of ionic impurities in the material. 相似文献
7.
8.
Diazonium salts, precisely arenediazonium o-benzenedisulfonimides, have been used for the first time as efficient electrophilic partners in Negishi coupling reactions. The synthetic protocol was general, easy and gave biaryls in satisfactory yields (34 examples, average yield 69%). o-Benzenedisulfonimide was recovered at the end of the reactions and reused to prepare the starting salts once again. 相似文献
9.
We report the operation of a 50 mW continuous-wave quantum cascade laser (QCL) in the 9.2 microm range, phase locked to a single-mode CO(2) laser with a tunable frequency offset. The wide free-running emission spectrum of the QCL (3-5 MHz) is strongly narrowed down to the kilohertz range, making it suitable for high-resolution molecular spectroscopy. 相似文献
10.
Bixue Xu Luca Unione Dr. Joao Sardinha Shaoping Wu Prof. Mélanie Ethève‐Quelquejeu Prof. Amelia Pilar Rauter Prof. Yves Blériot Dr. Yongmin Zhang Dr. Sonsoles Martín‐Santamaría Dr. Dolores Díaz Prof. Jesus Jiménez‐Barbero Prof. Matthieu Sollogoub 《Angewandte Chemie (International ed. in English)》2014,53(36):9597-9602
Molecular mimicry is an essential part of the development of drugs and molecular probes. In the chemical glycobiology field, although many glycomimetics have been developed in the past years, it has been considered that many failures in their use are related to the lack of the anomeric effects in these analogues. Additionally, the origin of the anomeric effects is still the subject of virulent scientific debates. Herein, by combining chemical synthesis, NMR methods, and theoretical calculations, we show that it is possible to restore the anomeric effect for an acetal when replacing one of the oxygen atoms by a CF2 group. This result provides key findings in chemical sciences. On the one hand, it strongly suggests the key relevance of the stereoelectronic component of the anomeric effect. On the other hand, the CF2 analogue adopts the natural glycoside conformation, which might provide new avenues for sugar‐based drug design. 相似文献