全文获取类型
收费全文 | 1364篇 |
免费 | 38篇 |
国内免费 | 3篇 |
专业分类
化学 | 879篇 |
晶体学 | 13篇 |
力学 | 75篇 |
数学 | 251篇 |
物理学 | 187篇 |
出版年
2022年 | 12篇 |
2021年 | 32篇 |
2020年 | 19篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 18篇 |
2016年 | 46篇 |
2015年 | 32篇 |
2014年 | 49篇 |
2013年 | 82篇 |
2012年 | 74篇 |
2011年 | 82篇 |
2010年 | 44篇 |
2009年 | 46篇 |
2008年 | 80篇 |
2007年 | 87篇 |
2006年 | 63篇 |
2005年 | 55篇 |
2004年 | 56篇 |
2003年 | 33篇 |
2002年 | 45篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 10篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 23篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1975年 | 18篇 |
1974年 | 9篇 |
1973年 | 12篇 |
1972年 | 6篇 |
排序方式: 共有1405条查询结果,搜索用时 125 毫秒
991.
Polverino Arianna Longo Angela Donizetti Aldo Drongitis Denise Frucci Maria Schiavo Loredana Carotenuto Gianfranco Nicolais Luigi Piscopo Marina Vitale Emilia Fucci Laura 《Journal of nanoparticle research》2014,16(7):1-13
Reduced graphene oxide (RGO) sheet was functionalized with nanocrystalline cellulose (NCC) via click coupling between azide-functionalized graphene oxide (GO-N3) and terminal propargyl-functionalized nanocrystalline cellulose (PG-NCC). First, the reactive azide groups were introduced on the surface of GO with azidation of 2-chloroethyl isocyanate-treated graphene oxide (GO-Cl). Then, the resulted compounds were reacted with PG-NCC utilizing copper-catalyzed azide-alkyne cycloaddition. During the click reaction, GO was simultaneously reduced to graphene. The coupling was confirmed by Fourier transform infrared, Raman, DEPT135, and 13C NMR spectroscopy, and the complete exfoliation of graphene in the NCC matrix was confirmed with X-ray diffraction measurement. The degree of functionalization from the gradual mass loss of RGO-NCC suggests that around 23 mass % has been functionalized covalently. The size of both NCC and GO was found to be in nanometric range, which decreased after click reaction. 相似文献
992.
Alessia Bacchi Ivano Bilotti Aldo Brillante Domenico Crocco Raffaele G. Della Valle Alberto Girlando Matteo Masino Paolo Pelagatti Elisabetta Venuti 《Journal of Raman spectroscopy : JRS》2013,44(6):905-908
We present a Raman investigation of polymorphism in 1,1,4,4‐tetraphenyl‐butadiene (TPB), a well‐known blue luminescent molecule, which retains its emissive properties in the solid state. The use of low‐wavenumber (10–150 cm−1) Raman microscopy, very sensitive to the crystal packing, allows us to single and pick up four different polymorphs. X‐ray analysis shows that the TPB molecules assume different conformations in the various polymorphs, a fact revealed also by the Raman spectra in the region of intra‐molecular vibrations. Lattice dynamics calculations yield a preliminary assignment of the low‐wavenumber Raman spectra and provide information of the relative stability of the phases. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
993.
Lorenzo Brasco Carlo Nitsch Aldo Pratelli 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2013,64(3):591-597
Denoting by ${\varepsilon\subseteq\mathbb{R}^2}$ the set of the pairs ${(\lambda_1(\Omega),\,\lambda_2(\Omega))}$ for all the open sets ${\Omega\subseteq\mathbb{R}^N}$ with unit measure, and by ${\Theta\subseteq\mathbb{R}^N}$ the union of two disjoint balls of half measure, we give an elementary proof of the fact that ${\partial\varepsilon}$ has horizontal tangent at its lowest point ${(\lambda_1(\Theta),\,\lambda_2(\Theta))}$ . 相似文献
994.
Gianfranco Mamone Salvatore De Caro Aldo Di Luccia Francesco Addeo Pasquale Ferranti 《Journal of mass spectrometry : JMS》2009,44(12):1709-1723
One of the main objectives of wheat glutenin subunit (GS) analysis is the identification of protein components linked to wheat quality. The proteomic characterization of glutenin has to consider the relatively low levels of arginine and lysine residues and the close sequence similarity among the different groups of these subunits, which hinders or even prevents the identification of the GS. In this study, a proteomic approach has been applied to resolve the heterogeneity of wheat glutenin components. Proteins extracted from Triticum durum flour were first analyzed by two‐dimensional gel electrophoresis, which greatly reduced glutenin complexity. The identity of each spot was confirmed by nano liquid chromatography tandem mass spectrometry analysis of tryptic peptides. In parallel, measurements of the high mass range by matrix‐assisted laser desorption/ionization time‐of‐flight analysis allowed detection of the large tryptic peptides. Gathering all data from search engine interrogation, very high sequence coverage was obtained for high molecular weight GS, including Bx7 and By8, in agreement with the known genetic profile of durum wheat. In addition, a truncated form of By8, never detected before, was also found. Low molecular weight GS (LMW‐GS) B‐type was identified with reasonable sequence coverage, while a clear identification of LWM‐GS C‐ and D‐type was hindered by the incompleteness of the wheat DNA databases. This study represents the first comprehensive analysis of the glutenin proteome and provides a reliable method for classifying wheat varieties according to their glutenin profile. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
995.
Barbara Roda Sonia Casolari Pierluigi Reschiglian Mara Mirasoli Patrizia Simoni Aldo Roda 《Analytical and bioanalytical chemistry》2009,394(4):953-961
In this work, the biospecific recognition antigen–antibody reaction was implemented in gravitational field-flow fractionation
(GrFFF), a flow-assisted separation technique for micron-sized particles, in order to realize a hybrid immunomodulated GrFFF
system in which two different principles are combined to achieve highly versatile fractionation. Micron-sized polystyrene
beads coated with horseradish peroxidase (HRP) were used as a model sample, and anti-HRP antibodies were immobilized on the
accumulation wall of the GrFFF channel. Ultrasensitive chemiluminescence imaging was employed to visualize the beads during
elution and to optimize experimental conditions. The same principle was then applied to real biological samples composed by
Yersinia enterocolitica and Escherichia coli cells. Results show the possibility to modify the elution of selected sample components and even to retain them into the
channel. The hybrid immunomodulated GrFFF system is a step towards the development of a module that could be integrated in
a lab-on-a-chip-based point-of-care testing device which includes sample pre-analytical cleanup and analysis. 相似文献
996.
Simona De Marino Maria Valeria D'Auria Sylvain Petek Rosa María Andrés Miguel Payá 《Tetrahedron》2009,65(15):2905-1811
Investigation of the marine sponge Coscinoderma mathewsi led to the isolation of two novel nitrogen-containing cheilanthane sesterterpenoids, coscinolactams A and B, together with known suvanine. The structures were elucidated by extensive spectroscopic measurements including NOE experiments to deduce the stereochemistry. The natural compounds, as well as a semisynthetic derivative, showed moderate anti-inflammatory activity measured as their capability to inhibit PGE2 and NO production. The suvanine aldehyde derivative 4 inhibited inducible nitric oxide protein expression with an IC50 value of 7.3 μM. 相似文献
997.
Deprotonations of α-benzoyl ketene dithiomethylacetals with LDA/HMPA resulted in kinetic deprotonations at three different sites depending on the other α-substituents. 相似文献
998.
Bianchi L Dell'Erba C Maccagno M Mugnoli A Novi M Petrillo G Sancassan F Tavani C 《The Journal of organic chemistry》2003,68(13):5254-5260
Within an overall ring-opening/ring-forming protocol, the (E,E)-4-methylthio-2-nitro-3-phenylsulfonyl-1-pyrrolidino-1,3-butadiene (7) [derived from the initial opening of 3-nitro-4-(phenylsulfonyl)thiophene (6) with pyrrolidine and silver nitrate in EtOH] is revealed to be an excellent precursor of nitro(phenylsulfonyl) derivatives of ring-fused aromatic (naphthalene, phenanthrene) or heteroaromatic (benzothiophene) compounds whose substitution pattern cannot be easily achieved by conventional methods. The key step is represented by a thermal electrocyclic rearrangement of (E,E)-1-aryl-4-methylsulfonyl-2-nitro-3-phenylsulfonyl-1,3-butadienes (9), which, thanks to proper geometric and electronic factors, occurs in unprecedentedly mild conditions and is followed by an irreversible, concerted syn beta-elimination of methanesulfinic acid to aromatize the newly formed cyclohexadienic ring. 相似文献
999.
Polarization holographic gratings in sp configuration are written at 488 nm in photorefractive organic-inorganic films based on SiO2. The films, prepared by a solgel technique, contain Disperse Red 1, carbazole units, and 2,4,7-trinitro-9-fluorenone. The gratings are characterized by their diffraction efficiency for a 632.8-nm probe. The polarization gratings act as a half-wave plate, and the diffraction efficiency is independent of the polarization direction of the probe. 相似文献
1000.