全文获取类型
收费全文 | 857篇 |
免费 | 28篇 |
国内免费 | 2篇 |
专业分类
化学 | 634篇 |
晶体学 | 5篇 |
力学 | 15篇 |
数学 | 106篇 |
物理学 | 127篇 |
出版年
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 24篇 |
2015年 | 23篇 |
2014年 | 34篇 |
2013年 | 31篇 |
2012年 | 37篇 |
2011年 | 45篇 |
2010年 | 28篇 |
2009年 | 42篇 |
2008年 | 36篇 |
2007年 | 44篇 |
2006年 | 27篇 |
2005年 | 48篇 |
2004年 | 38篇 |
2003年 | 32篇 |
2002年 | 35篇 |
2001年 | 20篇 |
2000年 | 19篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 12篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1971年 | 7篇 |
1970年 | 9篇 |
排序方式: 共有887条查询结果,搜索用时 15 毫秒
1.
S. Schrader A. Penzkofer W. Holzer R. Velagapudi B. Grimm 《Journal of luminescence》2004,110(4):303-308
Optical, structural and morphological properties of thin films of polyparaphenylenevinylene (PPV) formed by an alkyl sulfinyl precursor route have been studied. Thin films were fabricated on an optical glass and on quartz glass either by spin-coating of the precursor solution or by layer-by-layer deposition using Langmuir–Blodgett technique. PPV precursor films were also spin-coated on gold-coated glass in order to study thin-film optical parameters by surface plasmon spectroscopy. We have been successful in forming about 40 precursor mono layers on quartz glass by Langmuir–Blodgett technique using optimized surface pressure and dipping conditions. After thermal conversion of the precursor layers good quality fluorescent PPV films of yellow colour have been obtained. Optical characterization of the films was carried out by linear absorption and emission spectroscopy, ellipsometry, and surface plasmon spectroscopy. Structural and morphological studies on the thin films were carried out by using X-ray scattering and atomic force microscopy. Wave-guided travelling-wave laser action has been achieved in a PPV film on quartz glass. The sample was transversally pumped with picosecond laser pulses (wavelength 347.15 nm, duration 35 ps). Laser emission occurred at 550 nm for pump pulse energy densities above . 相似文献
2.
Peter Esser Bettina Pohlmann Hans-Dieter Scharf 《Angewandte Chemie (International ed. in English)》1994,33(20):2009-2023
The light of the sun can be used directly for changing chemical structures photochemically. Any industrial application must conform to the limitations imposed by the spectral distribution of the photons from the sun, the interruptions to the radiation due to the day/night rhythm, and the weather. In this review, we describe the photochemical potential of the sun, give a fundamental treatment of the concept of photoreactors driven by sunlight (abbreviated to solar photoreactors), and give an account of the realization of this concept in the first pilot plant on the “Plataforma Solar de Almeria” in southern Spain and in other activities in this field. Based on experimental data from photochemical investigations on the pilot plant scale, possibilities, limitations, and the potential growth of solar photochemistry are described. Solar photochemistry, in our opinion, is a technique which could make a contribution to the chemistry of the future because of its photochemical synthesis potential, the avoidance of waste products, and the direct utilization of the sun, not only as a primary energy source, but also as a reaction partner. 相似文献
3.
We discuss supersymmetric scattering theory and employ Krein's theory of spectral shift functions to investigate supersymmetric scattering systems. This is the basis for the derivation of relative index theorems on some classes of open manifolds. As an example we discuss the de Rham complex for obstacles in
N
and asymptotically flat manifolds. It is shown that the absolute or relative Euler characteristic of an obstacle in
N
may be obtained from scattering data for the Laplace operator on forms with absolute or relative boundary conditions respectively. In the case of asymptotically flat manifolds we obtain the Chern-Gauss-Bonnet theorem for theL
2-Euler characteristic.On leave of absence from Institute of Physics, Leningrad State University, Leningrad 相似文献
4.
Helmut Sprdizer Andrea Pichler Wolfgang Holzer Irene Toth Bettina Zuchart 《Helvetica chimica acta》1997,80(1):139-145
Khusimone (1), one of the main odor-donating compounds of vetiver oil is subject of the following study on structure/odor relationship. The omittance of the ethano bridge of the tricyclic khusimone leads to a bicyclic system. The stereoselective approach to this degraded structure is described, and the olfactory properties are studied. The key step of the synthesis of the hydrindane nucleus is based on a highly diastereoselective conjugate addition to a chiral oxo-cyclopentene-2-carboxylate. 相似文献
5.
Reinhard Schubert Achim Ansmann Paul Bleckmann Bernhard Schrader 《Journal of Molecular Structure》1975,26(2):429-438
By using the values of the vibrational frequencies of normal and deuterated cyclopropenone (II-d0 , II-d2 ) and 16 O-and 18 O-substituted dimethylcyclopropenone (III) as -well as the infrared and Raman intensities of II a consistent set of force constants has been derived for the cyclopropenone skeleton. The derived values show that the zwitterionic form makes a substantial contribution to the electronic ground state of the molecule. The combined frequency and intensity calculation - simulation of the infrared and the Raman spectrum - is shown to be a good method for making a proper assignment of calculated and observed vibrations and deriving realistic sets of force constants. 相似文献
6.
7.
Zwickl H Traxler E Staettner S Parzefall W Grasl-Kraupp B Karner J Schulte-Hermann R Gerner C 《Electrophoresis》2005,26(14):2779-2785
The secretome of cells and tissues may reflect a broad variety of pathological conditions and thus represents a rich source of biomarkers. The identity of secreted proteins, usually isolated from cell supernatants or body fluids, is hardly accessible by direct proteome analysis, because these proteins are often masked by high amounts of proteins actually not secreted by the investigated cells. Here, we present a novel method for the specific detection of proteins secreted by human tissue specimen as well as cultured cells and chose liver as a model. The method is based on the metabolic labelling of proteins synthesized during a limited incubation period. Then, the cell supernatant is filtered, precipitated, and subjected to two-dimensional gel electrophoresis. Whereas fluorography detected a large number of proteins derived from residual plasma and dead cells, the autoradiographs selectively displayed genuinely secreted proteins. We demonstrate the feasibility of this approach by means of the secretomes of the hepatocellular carcinoma-derived cell line HepG2 and human liver slices. The selective identification of cell- and tissue-specific protein secretion profiles may help to identify novel sets of biomarkers for wide clinical applications. 相似文献
8.
Beate Hager Bettina Schwarzinger Heinz Falk 《Monatshefte für Chemie / Chemical Monthly》2006,137(2):163-168
Summary. Two model compounds for the green fluorescent protein chromophore were prepared. One of them incorporates the natural 4-hydroxybenzylidene
group of the natural tyrosin derived chromophore, the other one bears a methyl group instead of the hydroxy group. Whereas
the photochemically prepared (E)-diastereomer of the first compound very effectively reverted thermally (room temperature) to the thermodynamically stable
(Z)-diastereomer, the (E)-diastereomer of the second derivative proved to be stable even at elevated temperatures for more than a day. This finding
can be rationalized by constructing the appropriate resonance structures showing that only in the first case an effective
delocalization enables partial single bond character of the benzylidene double bond. From the standpoint of chemical etiology,
only Nature’s choice of the tyrosin derived chromophore of the green fluorescent protein provides an efficient radiationless
thermal relaxation channel for the unwanted photo-diastereomerization product formed after excitation besides the dominating
fluorescence channel of its chromophore. 相似文献
9.
B. Schrader und E. Steigner 《Fresenius' Journal of Analytical Chemistry》1971,254(3):177-183
Zusammenfassung Aus digitalisierten Raman- und Infrarotspekten von 70 Steroiden wurden die Summenspektren der Substanzen mit übereinstimmenden Strukturmerkmalen berechnet. In diesen Spektren sind Banden geringer Standardabweichung dann charakteristisch für ein Strukturmerkmal, wenn sie bei anderen Strukturmerkmalen fehlen. Sie sind dann für die Strukturaufklärung von Substanzen unbekannter Struktur geeignet.
Wir danken Herrn Dipl.-Phys. H. Barentzen für die Aufstellung des Computerprogramms sowie Frl. G. Pannek und Frau E. von Bühlow für die Hilfe bei der Verschlüsselung und Aufbereitung der Daten. — Der Deutschen Forschungsgemeinschaft und dem Landesamt für Forschung, Nordrhein-Westfalen, danken wir für Sachbeihilfen. 相似文献
Raman spectroscopy and molecular structureIII. Selection of characteristic bands of polyatomic molecules by means of a computer
Digitized Raman and infrared spectra of 70 steroids are used for the calculation of summarized spectra of all substances with the same structural details. In these spectra bands with low standard deviation are characteristic for the structural detail if they are absent in the other groups of spectra. They can be used for the elucidation of unknown structures.
Wir danken Herrn Dipl.-Phys. H. Barentzen für die Aufstellung des Computerprogramms sowie Frl. G. Pannek und Frau E. von Bühlow für die Hilfe bei der Verschlüsselung und Aufbereitung der Daten. — Der Deutschen Forschungsgemeinschaft und dem Landesamt für Forschung, Nordrhein-Westfalen, danken wir für Sachbeihilfen. 相似文献
10.
Solid solutions in the system zinc sulfide/zinc phosphide (Zn(2+)(x)S(2-2xP(2x)) were investigated using the cyclic cluster model within the semiempirical MSINDO method. Results of cyclic cluster calculations for binding energies of the perfect ZnS and Zn(3)P(2) are presented and compared with the experimental data. The miscibility of ZnS and Zn(3)P(2) over the whole composition range of 0 < x < 1 was investigated by calculating the Gibbs free energy of mixing Delta(M)G for different values of x. A miscibility gap was found at both ends of the composition range and compared with experimental data. 相似文献