全文获取类型
收费全文 | 2518篇 |
免费 | 64篇 |
国内免费 | 8篇 |
专业分类
化学 | 1636篇 |
晶体学 | 44篇 |
力学 | 87篇 |
数学 | 579篇 |
物理学 | 244篇 |
出版年
2023年 | 12篇 |
2022年 | 35篇 |
2021年 | 67篇 |
2020年 | 40篇 |
2019年 | 44篇 |
2018年 | 33篇 |
2017年 | 23篇 |
2016年 | 68篇 |
2015年 | 69篇 |
2014年 | 56篇 |
2013年 | 127篇 |
2012年 | 113篇 |
2011年 | 149篇 |
2010年 | 91篇 |
2009年 | 83篇 |
2008年 | 126篇 |
2007年 | 110篇 |
2006年 | 135篇 |
2005年 | 130篇 |
2004年 | 107篇 |
2003年 | 92篇 |
2002年 | 82篇 |
2001年 | 30篇 |
2000年 | 21篇 |
1999年 | 29篇 |
1998年 | 22篇 |
1997年 | 21篇 |
1996年 | 42篇 |
1995年 | 26篇 |
1994年 | 37篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 13篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 25篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1980年 | 31篇 |
1979年 | 28篇 |
1978年 | 17篇 |
1976年 | 16篇 |
1975年 | 12篇 |
1915年 | 9篇 |
1906年 | 7篇 |
排序方式: 共有2590条查询结果,搜索用时 703 毫秒
151.
Gialiana Biagi Irene Giorgi Oreste Livi Valerio Scartoni Silvia Velo Pier Luigi Barili 《Journal of heterocyclic chemistry》1996,33(6):1847-1853
A new 4-(benzotriazol-1-yl)-1,2,3-triazole structure was obtained by the diazotization reaction of either of 1-(2-aminophenyl)-4-carboxamido-5-amino-1H-1,2,3-triazole ( 1c ) or of the corresponding Dimroth isomer 1d . It underwent some common reactions to evaluate its chemical behaviour and structure. An analogous reaction sequence was carried out from the 2-nitro-4-methylphenyl azide, to assign the structure to the nitro derivatives prepared. The structure of the new compounds prepared was confirmed by chemical and spectroscopic methods. 相似文献
152.
Paolo Giusti Luigi Lazzeri Niccoletta Barbani Letizia Lelli Silvano De Petris Maria G. Cascone 《Macromolecular Symposia》1994,78(1):285-297
Blends of natural and synthetic polymers were studied for potential applications in the biomedical field. Collagen and hyaluronic acid were mixed in aqueous solution with poly(vinyl alcohol) and poly(acrylic acid). The properties of the blends were studied by differential scanning calorimetry and dynamic mechanical thermal analysis. Some methods were also investigated to enhance the miscibility of the polymers in these blends. 相似文献
153.
Saida Sissi Silvia Di Giacomo Claudio Ferrante Paola Angelini Alberto Macone Anna Maria Giusti Chiara Toniolo Annabella Vitalone Aghraz Abdellah Mustapha Larhsini Luigi Menghini Mohammed Markouk Gabriela Mazzanti Antonella Di Sotto 《Molecules (Basel, Switzerland)》2022,27(3)
In the present study, the phytochemical composition and bioactivities of A. maroccanus (AM) and A. radiatus (AR), two ecotypes collected in the Demnate road and Essaouira regions, respectively, were studied to highlight a pharmacological interest and to enable possible pharmaceutical development. To this end, methanolic and ethyl acetate extracts were prepared for each ecotype by fractionation; next, their phytochemical composition was evaluated by spectrophotometric and chromatographic analysis. Moreover, in line with the available evidence for Anacyclus spp. and their traditional use, a screening of bioactivities, including antioxidant, hypoglycemic, antiglycative, chelating, and antibacterial activities, was performed. The extracts were characterized by high amounts of polyphenols, tannins, and flavonoids, especially in the methanolic extracts; these samples were also enriched in carotenoids despite a lower chlorophyll content. Chlorogenic acid and rutin were the major identified compounds. The extracts also showed interesting hypoglycemic, antiglycative, and antibacterial properties, although with differences in efficacy and potency. Present results provide more scientific basis to the ethnopharmacological uses of Anacyclus spp. and suggest a further interest in AM and AR ecotypes as natural sources of bioactive compounds and/or phytocomplexes for possible pharmaceutical and nutraceutical developments. 相似文献
154.
155.
Emission of volatile sesquiterpenes and monoterpenes in grapevine genotypes following Plasmopara viticola inoculation in vitro 下载免费PDF全文
Alberto Algarra Alarcon Valentina Lazazzara Luca Cappellin Pier Luigi Bianchedi Rainer Schuhmacher Georg Wohlfahrt Ilaria Pertot Franco Biasioli Michele Perazzolli 《Journal of mass spectrometry : JMS》2015,50(8):1013-1022
The grapevine (Vitis vinifera) is one of the most widely cultivated fruit crops globally, and one of its most important diseases in terms of economic losses is downy mildew, caused by Plasmopara viticola. Several wild Vitis species have been found to be resistant to this pathogen and have been used in breeding programs to introduce resistance traits to susceptible cultivars. Plant defense is based on different mechanisms, and volatile organic compounds (VOCs) play a major role in the response to insects and pathogens. Although grapevine resistance mechanisms and the production of secondary metabolites have been widely characterized in resistant genotypes, the emission of VOCs has not yet been investigated following P. viticola inoculation. A Proton Transfer Reaction‐Time of Flight‐Mass Spectrometer (PTR‐ToF‐MS) was used to analyze the VOCs emitted by in vitro‐grown plants of grapevine genotypes with different levels of resistance. Downy mildew inoculation significantly increased the emission of monoterpenes and sesquiterpenes by the resistant SO4 and Kober 5BB genotypes, but not by the susceptible V. vinifera Pinot noir. Volatile terpenes were implicated in plant defense responses against pathogens, suggesting that they could play a major role in the resistance against downy mildew by direct toxicity or by inducing grapevine resistance. The grapevine genotypes differed in terms of the VOC emission pattern of both inoculated and uninoculated plants, indicating that PTR‐ToF‐MS could be used to screen hybrids with different levels of downy mildew resistance. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
156.
157.
Interaction of α,ω-dihaloalkanes with sulfide ion (eq. 1) is a common route for the synthesis in good yield of 5- and 6-membered polymethylene sulfides. 相似文献
158.
Luigi C. Berselli Roger Lewandowski 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2012
We consider a 3D Approximate Deconvolution Model ADM which belongs to the class of Large Eddy Simulation (LES) models. We aim at proving that the solution of the ADM converges towards a dissipative solution of the mean Navier–Stokes equations. The study holds for periodic boundary conditions. The convolution filter we first consider is the Helmholtz filter. We next consider generalized convolution filters for which the convergence property still holds. 相似文献
159.
L. Hennet V. Cristiglio J. Kozaily I. Pozdnyakova H. E. Fischer A. Bytchkov J. W. E. Drewitt M. Leydier D. Thiaudière S. Gruner S. Brassamin D. Zanghi G. J. Cuello M. Koza S. Magazù G. N. Greaves D. L. Price 《The European physical journal. Special topics》2011,196(1):151-165
Aerodynamic levitation is an effective way to suspend samples which can be heated with CO2 lasers. The advantages of this containerless technique are the simplicity and compactness of the device, making it possible to integrate it easily in different kinds of experiments. In addition, all types of materials can be used, including metals and oxides. The integration of aerodynamic levitation at synchrotron and neutron sources provides powerful tools to study the structure and dynamics of molten materials. We present here an overview of the existing techniques and of the developments made at the CEMHTI in Orléans, as well as a few examples of experimental results already obtained. 相似文献
160.