全文获取类型
收费全文 | 2694篇 |
免费 | 113篇 |
国内免费 | 7篇 |
专业分类
化学 | 2101篇 |
晶体学 | 7篇 |
力学 | 41篇 |
数学 | 384篇 |
物理学 | 281篇 |
出版年
2023年 | 21篇 |
2022年 | 53篇 |
2021年 | 93篇 |
2020年 | 71篇 |
2019年 | 76篇 |
2018年 | 37篇 |
2017年 | 42篇 |
2016年 | 109篇 |
2015年 | 96篇 |
2014年 | 102篇 |
2013年 | 166篇 |
2012年 | 195篇 |
2011年 | 201篇 |
2010年 | 153篇 |
2009年 | 113篇 |
2008年 | 169篇 |
2007年 | 150篇 |
2006年 | 136篇 |
2005年 | 136篇 |
2004年 | 130篇 |
2003年 | 103篇 |
2002年 | 99篇 |
2001年 | 35篇 |
2000年 | 43篇 |
1999年 | 31篇 |
1998年 | 26篇 |
1997年 | 25篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有2814条查询结果,搜索用时 31 毫秒
911.
Sossio Cimmino Ezio Martuscelli Clara Silvestre Maurizio Canetti Claudia De Lalla Alberto Seves 《Journal of Polymer Science.Polymer Physics》1989,27(9):1781-1794
Results of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant Kn are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account. 相似文献
912.
Daniela Goldmann Dietmar Janietz Reinhard Festag Claudia Schmidt Joachim H. Wendorff 《Liquid crystals》1996,21(5):619-623
New disc-shaped triarylamino-1,3,5-triazines were prepared by reaction of cyanuric chloride with two-fold alkoxy substituted anilines. Each of the triarylmelamines exhibits an enanti-otropic mesophase. X-ray investigations reveal the formation of columnar liquid crystalline structures with either a hexagonal or a rectangular lattice. The lattice parameters, as well as the intracolumnar ordering, depend on the length of the flexible lateral side chains. The new melamines form Langmuir monolayers at the air/water interface due to their amphiphilic nature. The monolayer organization is characterized by a side-on arrangement of the molecules. The polar central molecular parts lie flat on the water, whereas the lateral alkyl chains are oriented perpendicular to the water surface. 相似文献
913.
914.
Claudia Draxl 《Few-Body Systems》1987,2(3):N49-N49
915.
A partially observable control problem for an R
d
-valued jump process with counting observations is studied. The state and the observations may be strongly dependent and, in particular, the two processes may jump together. An equivalent separated problem is introduced and the existence of an optimal control for the separated problem is obtained in the class of relaxed and generalized controls. Equivalence between the initial problem and the relaxed generalized separated control problem is discussed. 相似文献
916.
Alessandro Venditti Claudia Lattanzi Luigi Ornano Filippo Maggi Cinzia Sanna Mauro Ballero 《Natural product research》2016,30(7):789-795
In this study, we reported the analysis of the medium polarity fraction obtained from an accession of Helichrysum microphyllum subsp. tyrrhenicum from La Maddalena Island. Besides several compounds already evidenced in this species and related genera, i.e. micropyrone (1), arzanol (2), helipyrone (3), acetyl-bitalin derivatives (4, 5), gnaphaliol (6), caffeic acid (7), ursolic acid (8), 7-O-β-(d-glucopyranosyl)-5-methoxy-1(3H)-isobenzofuranone (9), gnaphaliol-9-O-β-d-glucopyranoside (11) and gnaphaliol-3-O-β-d-glucopyranoside (12), the presence of a new glycosidic phthalide, 6-O-β-(d-glucopyranosyl)-4-methoxy-1(3H)-benzofuranone (10), was evidenced for the first time, which resulted in a structural isomer of compound (9). The occurrence of this new benzofuranone derivative is an additional evidence of the deep intraspecific variability expressed by this species, which was also stated for the non-volatile components, and may be a distinctive trait of the population growing on La Maddalena Island. 相似文献
917.
Perna canaliculus is a nutritional supplement recently studied and highly recommended for its anti-inflammatory effects in both animals and humans. In this study, the physicochemical properties, the microbiological quality, the total lipid content and fatty acids composition of three commercial samples of Perna powder were determined. Subsequently, three simple formulations of extemporaneous oral pastes containing Perna were prepared and designed for veterinary use. Their microbiological stability was assessed after 1-month storage at either room temperature or 35 °C. The results demonstrated that commercial Perna samples lack homogeneity, in regard to some technological properties and fatty acid composition; therefore, a preliminary characterisation of commercial Perna samples is recommended to assure the quality of formulations containing this nutritional supplement. Oral paste formulations are easy and simple to prepare and show good physical and microbiological stability, suggesting their large-scale production. 相似文献
918.
Claudia Rodrigues Alzir A. Batista Ricardo Q. Auclio Letícia R. Teixeira Lorenzo do Canto Visentin Heloisa Beraldo 《Polyhedron》2008,27(14):3061-3066
N4-Methyl-4-nitrobenzaldehyde thiosemicarbazone (H4NO2Fo4M), N4-methyl-4-nitrobenzophenone thiosemicarbazone (H4NO2Bz4M) and their ruthenium(II) complexes [Ru(4NO2Fo4M)2(PPh3)2] (1), [Ru(4NO2Bz4M)2(PPh3)2] (2), [Ru(4NO2Fo4M)2(dppb)] (3) and [Ru(4NO2Bz4M)2(dppb)] (4) (dppb = 1,4-bis(diphenylphospine)butane) were obtained and characterized. The crystal structure of H4NO2Fo4M has been determined. Electrochemical studies have shown that the nitro anion radical, one of the proposed intermediates in the mechanism of action of nitro-containing anti-trypanosomal drugs, is formed at approximately −1.00 V in the free thiosemicarbazones as well as in their corresponding ruthenium(II) complexes, suggesting their potential to act as antitrypanosomal drugs. The natural fluorescence of H4NO2Fo4M, H4NO2Bz4M and complexes (1)–(4) provides a way to identify and to monitor their concentration in biological systems. 相似文献
919.
Peter Puschnig Claudia Ambrosch-Draxl 《Monatshefte für Chemie / Chemical Monthly》2008,139(4):389-399
We show how ab initio calculations based on density functional theory contribute to the understanding of the electronic and optical properties of organic semiconducting materials, which form the active layers in many opto-electronic applications. As a textbook example, we present the electronic structure and the optical properties of the oligo-phenylenes as evolving from their benzene-constituents. Thereby we discuss the dependence on the molecular length and introduce the modifications in the opto-electronic properties due to intermolecular interactions which are inherently present in the bulk phase. 相似文献
920.
Giovanni Bagnasco Claudia Cammarano Maria Turco Serena Esposito Antonio Aronne Pasquale Pernice 《Thermochimica Acta》2008,471(1-2):51-54
Cobalt–silicon mixed oxides with Co/Si ratio of 10/90 (10Co), 20/80 (20Co) and 30/70 (30Co) were prepared by a modified sol–gel method. The materials treated in air at 400 and 600 °C were characterized by SEM and TPR/TPO techniques. TPR measurements showed that in all samples only a fraction of Co was present as Co3O4 and as amorphous silicate and was reducible by H2 within 800 °C, while a part was not reducible under TPR conditions. The fraction of Co not reducible decreased with increasing Co content. A TPO/TPR cycle gave rise to an increase of the fraction of not reducible Co. 相似文献