全文获取类型
收费全文 | 13724篇 |
免费 | 941篇 |
国内免费 | 1篇 |
专业分类
林业 | 1350篇 |
农学 | 543篇 |
基础科学 | 79篇 |
3141篇 | |
综合类 | 807篇 |
农作物 | 598篇 |
水产渔业 | 1121篇 |
畜牧兽医 | 5411篇 |
园艺 | 354篇 |
植物保护 | 1262篇 |
出版年
2023年 | 115篇 |
2022年 | 176篇 |
2021年 | 308篇 |
2020年 | 306篇 |
2019年 | 263篇 |
2018年 | 671篇 |
2017年 | 602篇 |
2016年 | 559篇 |
2015年 | 446篇 |
2014年 | 502篇 |
2013年 | 787篇 |
2012年 | 1036篇 |
2011年 | 970篇 |
2010年 | 555篇 |
2009年 | 490篇 |
2008年 | 829篇 |
2007年 | 776篇 |
2006年 | 620篇 |
2005年 | 659篇 |
2004年 | 604篇 |
2003年 | 538篇 |
2002年 | 459篇 |
2001年 | 315篇 |
2000年 | 294篇 |
1999年 | 251篇 |
1998年 | 81篇 |
1997年 | 68篇 |
1996年 | 53篇 |
1995年 | 81篇 |
1994年 | 45篇 |
1993年 | 43篇 |
1992年 | 91篇 |
1991年 | 79篇 |
1990年 | 79篇 |
1989年 | 71篇 |
1988年 | 61篇 |
1987年 | 61篇 |
1986年 | 56篇 |
1985年 | 52篇 |
1984年 | 48篇 |
1983年 | 46篇 |
1980年 | 26篇 |
1979年 | 41篇 |
1974年 | 29篇 |
1972年 | 25篇 |
1971年 | 26篇 |
1970年 | 29篇 |
1969年 | 32篇 |
1968年 | 27篇 |
1967年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
951.
Antioxidant activity of olive pulp and olive oil phenolic compounds of the arbequina cultivar 总被引:3,自引:0,他引:3
Morelló JR Vuorela S Romero MP Motilva MJ Heinonen M 《Journal of agricultural and food chemistry》2005,53(6):2002-2008
The aim of this study was to characterize antioxidant activities of phenolic compounds that appear in olive pulp and olive oils using both radical scavenging and antioxidant activity tests. Antiradical and antioxidant activities of olive pulp and olive oil phenolic compounds were due mainly to the presence of a 3,4-dihydroxy moiety linked to an aromatic ring, and the effect depended on the polarity of the phenolic compound. Glucosides and more complex phenolics exhibited higher antioxidant activities toward oxidation of liposomes, whereas in bulk lipids aglycons were more potent antioxidants with the exception of oleuropein. Lignans acted as antioxidants only in liposomes, which could partly be due to their chelating activity, because liposome oxidation was initiated by cupric acetate. The antioxidant activity of virgin olive oil is principally due to the dialdehydic form of elenolic acid linked to hydroxytyrosol (3,4-DHPEA-EDA), a secoiridoid derivative (peak RT 36, structure unidentified), and luteolin. 相似文献
952.
Pérez-Gilabert M Sánchez-Felipe I García-Carmona F 《Journal of agricultural and food chemistry》2005,53(9):3666-3671
A lipoxygenase from Terfezia claveryi Chatin ascocarp, a mycorrhizal hypogeous fungus, is described for the first time. The higher proportion of PUFA in T. claveryi ascocarps makes lipid rancidity the main factor limiting its storage life. Thus, the studies on LOX from T. claveryi are important because this enzyme, among other roles, may be involved in an alteration of lipids leading to consumer rejection. The enzyme has been purified to apparent homogeneity by phase partitioning in the presence of Triton X-114, followed by two steps of cation-exchange chromatography. The purified T. claveryi LOX preparation consisted of a single major band with an apparent molecular mass of 66 kDa after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzymic activity exhibited a strong specificity toward linoleic and linolenic acids as substrates, while only 32% activity was observed using gamma-linolenic acid. The pH optimum of this enzyme was pH 7.0. When the enzyme reacted with linoleic acid, it produced a single peak, which comigrated with standard 13-hydroperoxy-octadecadienoic acid; 13-hydroperoxy-octadecatrienoic acid was produced during the reaction with linolenic acid. 相似文献
953.
Pérez-Gálvez A Rios JJ Mínguez-Mosquera MI 《Journal of agricultural and food chemistry》2005,53(12):4820-4826
The high-temperature treatment of paprika oleoresins (Capsicum annuum L.) modified the carotenoid profile, yielding several degradation products, which were analyzed by HPLC-APCI-MS. From the initial MS data, compounds were grouped in two sets. Set 1 grouped compounds with m/z 495, and set 2 included compounds with m/z 479, in both cases for the protonated molecular mass. Two compounds of the first set were tentatively identified as 9,10,11,12,13,14,19,20-octanor-capsorubin (compound II) and 9,10,11,12,13,14,19,20-octanor-5,6-epoxide-capsanthin (compound IV), after isolation by semipreparative HPLC and analysis by EI-MS. Compounds VII, VIII, and IX from set 2 were assigned as 9,10,11,12,13,14,19,20-octanor-capsanthin and isomers, respectively. As these compounds were the major products formed in the thermal process, it was possible to apply derivatization techniques (hydrogenation and silylation) to analyze them by EI-MS, before and after chemical derivatization. Taking into account structures of the degradation products, the cyclization of polyolefins could be considered as the general reaction pathway in thermally induced reactions, yielding in the present study xylene as byproduct and the corresponding nor-carotenoids. 相似文献
954.
Díaz-Maroto MC Díaz-Maroto Hidalgo IJ Sánchez-Palomo E Pérez-Coello MS 《Journal of agricultural and food chemistry》2005,53(13):5385-5389
Volatile oil extracts of fennel seeds (Foeniculum vulgare Mill.) and thyme leaves (Thymus vulgaris L.) were obtained by simultaneous distillation-extraction (SDE) and supercritical fluid extraction (SFE) and analyzed by gas chromatography-mass spectrometry (GC-MS). In general, fennel oil extracted by SDE and SFE showed similar compositions, with trans-anethole, estragole, and fenchone as the main components. In contrast, thymol and p-cymene, the most abundant compounds in thyme leaves, showed big differences, with generally higher amounts of monoterpenes obtained by SDE. However, in this case, the differences between the extracts were higher. Key odorants of fennel seeds determined by gas chromatography-olfactometry (GC-O) showed similar patterns when applying SDE and SFE. trans-Anethole (anise, licorice), estragole (anise, licorice, sweet), fenchone (mint, camphor, warm), and 1-octen-3-ol (mushroom) were the most intense odor compounds detected in fennel extracts. Thymol and carvacrol, with oregano, thyme, and spicy notes, were identified as key compounds contributing to the aroma of thyme leaves. 相似文献
955.
Horvatovich P Miesch M Hasselmann C Delincée H Marchioni E 《Journal of agricultural and food chemistry》2005,53(15):5836-5841
The 2-alkylcyclobutanones (2-ACBs) are formed from triglycerides by irradiation treatment and may be used as markers for this type of food processing. This paper describes a detection method for the analysis of monounsaturated alkyl side chain 2-ACBs, which is formed upon irradiation from monounsaturated fatty acids which frequently are the most abundant fatty acids in foods. The estimated radioproduction yields of the cis-2-(dodec-5'-enyl)-cyclobutanones (cis-2-dDeCB) and the cis-2-(tetradec-5'-enyl)-cyclobutanones (cis-2-tDeCB) were 1.0 +/- 0.5 and 0.9 +/- 0.2 nmol.mmol(-1) precursor fatty acid.kGy(-1), respectively, being similar to that of saturated 2-ACBs. The stability study of the s- and mu-2-ACBs in poultry meat samples irradiated at 10 kGy and stored for 3-4 weeks at 4 degrees C and 25 degrees C showed that these compounds undergo some transformation, their amounts being reduced by about 50%. These storage losses did not depend on the saturation state of the alkyl side chain. The EI-MS detection limit of 2-tDeCB is 3 times higher (0.6 pmol) than that of 2-dodecylcyclobutanone (0.2 pmol). Consequently, when the oleic acid content of the analyzed food exceeds the content of palmitic acid by a factor of 3, it would be of an advantage to apply 2-tDeCB as a marker for detection of the irradiation treatment. 相似文献
956.
Núñez-Delicado E Serrano-Megías M Pérez-López AJ López-Nicolás JM 《Journal of agricultural and food chemistry》2005,53(15):6087-6093
Dominga grape polyphenol oxidase (PPO) was extracted using phase partitioning with Triton X-114. The enzyme was obtained in latent state and could be optimally activated by the presence of 0.2% sodium dodecyl sulfate (SDS) at pH 6.0. In the absence of SDS, the enzyme showed maximum activity at acid pH. The kinetic parameters of the enzyme at pH 3.0 and 6.0 in the presence of SDS were calculated. The effect of several inhibitors was studied, tropolone being the most effective with a K(i) value of 18 muM. The effect of cyclodextrins was also studied, and the complexation constant K(c) between G(2)-beta-cyclodextrins and 4-tert-butylcatechol was calculated using the enzymatic method (K(c) = 13960 M(-)(1)). The evolution of the color parameters (L, a, b) of liquefied grape berries was inhibited by inhibitors of PPO activity, such as diethyldithiocarbamate, metabisulfite, and G(2)-beta-cyclodextrins, indicating that enzymatic browning by PPO is the main process involved in the browning of Dominga grape juice at room temperature. 相似文献
957.
Dupuy N Le Dréau Y Ollivier D Artaud J Pinatel C Kister J 《Journal of agricultural and food chemistry》2005,53(24):9361-9368
The authentication of virgin olive oil samples requires usually the use of sophisticated and very expensive analytical techniques, so there is a need for fast and inexpensive analytical techniques for use in a quality control methodology. Virgin olive oils present an intense fluorescence spectra. Synchronous excitation-emission fluorescence spectroscopy (SEEFS) was assessed for origin determination of virgin olive oil samples from five French registered designation of origins (RDOs) (Nyons, Vallée des Baux, Aix-en-Provence, Haute-Provence, and Nice). The spectra present bands between 600 and 700 nm in emission due to chlorophylls a and b and pheophytins a and b. The bands between 275 and 400 nm in emission were attributed to alpha-, beta-, and gamma-tocopherols and to phenolic compounds, which characterize the virgin olive oils compared to other edible oils. The chemometric treatment (PLS1) of synchronous excitation-emission fluorescence spectra allows one to determine the origin of the oils from five French RDOs (Baux, Aix, Haute-Provence, Nice, and Nyons). Results were quite satisfactory, despite the similarity between two denominations of origin (Baux and Aix) that are composed by some common cultivars (Aglandau and Salonenque). The interpretation of the regression coefficients shows that RDOs are correlated to chlorophylls, pheophytins, tocopherols, and phenols compounds, which are different for each origin. SEEFS is part of a global analytic methodology that associates spectroscopic and chromatographic techniques. This approach can be used for traceability and vindicates the RDOs. 相似文献
958.
959.
Mathieu Le Meur Emmanuelle Montargès-Pelletier Allan Bauer Renaud Gley Sylvie Migot Odile Barres Claire Delus Frédéric Villiéras 《Journal of Soils and Sediments》2016,16(5):1625-1642
Purpose
Suspended particulate matter (SPM) plays an important role in the transport and fate of contaminants in the environment. To better understand the relationships between contaminants and SPM, SPM properties, and their variations with flow regime, river size, land use, and season should be considered.Materials and methods
The grain size distribution, elemental composition, and mineralogy of SPM from different stations along the Moselle River (Lorraine, France) were investigated at the particle scale during different flow regimes. The resulting data were compared with the elemental composition of the dissolved compartment to understand the role of particles in element transport.Results and discussion
The grain size distribution, elemental composition, and mineralogy of SPM along the Moselle River and during different flow regimes showed only slight variations, except for the Fensch and Orne tributaries, two rivers that were impacted by inherited steel-making industrialization and different land use. In the Moselle River, SPM mainly consisted of clay minerals, while in Fensch and Orne Rivers, SPM mainly consisted of multiple types of anthropogenic particles. The diffuse urbanization gradient was hardly recognized based on the Trace Metal Element (TMEs) content in the river SPM, while the rivers impacted by the steel industries had greater TME contents. Finally, the TME content in the Moselle SPM was more strongly influenced by water flow than by the position of sampling on the linear reach of the Moselle River. The partitioning of TMEs in the particles and water at the main Moselle station (Frouard) revealed that SPM predominantly contributed to TMEs transport.Conclusions
This study confirmed that catchment geology greatly contributed to the SPM composition in the mean-sized rivers. In addition, the high anthropogenic pressure could be deciphered for small tributaries. Furthermore, this study allowed us to observe the high contribution of particles to TMEs and Rare Earth Element (REEs) transportation.960.
Sara Peres M. Clara F. Magalhães Maria Manuela Abreu Sara Leitão Ana Santos Maria José Cerejeira 《Journal of Soils and Sediments》2016,16(5):1612-1624