首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   210篇
  免费   11篇
林业   7篇
农学   10篇
  96篇
综合类   20篇
农作物   4篇
水产渔业   7篇
畜牧兽医   51篇
园艺   7篇
植物保护   19篇
  2023年   2篇
  2022年   2篇
  2021年   11篇
  2020年   6篇
  2019年   6篇
  2018年   7篇
  2017年   6篇
  2016年   8篇
  2015年   6篇
  2014年   9篇
  2013年   10篇
  2012年   10篇
  2011年   11篇
  2010年   8篇
  2009年   9篇
  2008年   9篇
  2007年   14篇
  2006年   5篇
  2005年   9篇
  2004年   14篇
  2003年   7篇
  2002年   2篇
  2001年   2篇
  2000年   2篇
  1999年   1篇
  1998年   1篇
  1996年   1篇
  1995年   2篇
  1994年   1篇
  1992年   3篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1988年   5篇
  1987年   1篇
  1986年   3篇
  1985年   3篇
  1984年   8篇
  1983年   3篇
  1982年   2篇
  1981年   3篇
  1980年   1篇
  1973年   1篇
  1971年   1篇
  1964年   1篇
  1956年   1篇
排序方式: 共有221条查询结果,搜索用时 62 毫秒
101.
A total of 12 fatty acid esters of Z- and E-p-coumaryl alcohol were isolated from cv. Annurca apple fruit and characterized. This apple variety is widely cultivated in the south of Italy, and the fruits typically undergoe a reddening treatment after harvest. Structures of the p-coumaryl esters were elucidated by GC-MS and (1)H and (13)C NMR after purification of individual compounds by HPLC. It was found that the esters are localized in the fruit peel. During reddening of the fruit, there was a substantial increase in the amount of esters and particularly in molecular species with unsaturated fatty acids. The individual compounds were tested for antioxidant activity, and over half were shown to be at least as effective as alpha-tocopherol.  相似文献   
102.
The winding process leading to the formation of rolled-up spermatozoa in Collembola is described. It is a phenomenon common to all collembolan species examined so far and it starts with the organization of a cytoplasmic flattened evagination beneath the head of the elongated spermatid, which gives rise to an extracellular cavity. Within this cavity secretory material produced by the epithelial cells of testes is progressively stored. The spermatozoon, whose cytoplasm is reduced to a thin layer, enrolls around this material. The final appearance is that of a spheroidal or lenticular structure containing dense material in the central extracellular cavity; this cavity is surrounded by the flattened sperm in whose cytoplasm the sperm components forms several spires. The material into the extracellular cavity becomes progressively denser and has a different appearance in the species examined.  相似文献   
103.
Summary In continuation of collecting activities in the last six years a further mission has been carried out in South Italy jointly by staff members of the Istituto del Germoplasma, Bari, and the Zentralinstitut für Genetik und Kulturpflanzenforschung, Gatersleben, in September 1986 for exploring and collecting plant genetic resources. In this year South-eastern parts of Calabria and the Ìsole Ègadi have been covered. 90 samples, mainly of vegetables, grain legumes and some cereals, could be collected. The material represents variable land-races and wild relatives of crop plants. From the last groupBrassica, Beta and some wild cereals, asSecale, Aegilops andDasypyrum, should be mentioned. With this mission the exploration of South Italy is nearly completed. Further activities will concentrate to some selected regions.
Sammlung pflanzlicher und genetischer Ressourcen in Süditalien 1986
Zusammenfassung In Fortführung von Sammlungsaktivitäten der letzten sechs Jahre, wurde im September 1986 eine weitere Sammelreise, gemeinsam von Mitarbeitern des Istituto del Germoplasma, Bari, und des Zentralinstituts für Genetik und Kulturpflanzenforschung, Gatersleben, unternommen, die dem Studium und der Sammlung pflanzlicher genetischer Ressourcen diente. In diesem Jahr wurden südöstliche Teile Kalabriens und die Ìsole Ègadi erfaßt. 90 Proben, besonders von Gemüsen, Körnerleguminosen und einigen Getreiden, konnten gesammelt werden. Das Material besteht aus variablen Landsorten und wildwachsenden Verwandten der Kulturpflanzen. Aus der letztgenannten Gruppe sindBrassica, Beta und einige Wildgetreide, wieSecale, Aegilops undDasypyrum, zu nennen. Mit dieser Sammelreise ist die Exploration Süditaliens im wesentlichen abgeschlossen. Weitere Aktivitäten werden sich auf einige ausgewählte Gebiete beschränken.

1986
, () (), 1986 , . - . 90 , , , . . Brassica, Beta , Secale, Aegilops Dasypyrum. . .
  相似文献   
104.
Olive oil mill wastewaters (OMWs) show significant polluting properties due to their content of organic substances, and because of their high toxicity toward several biological systems. Wastewaters' toxicity has been attributed to their phenolic constituents. A chemical study of wastewaters from a Ligurian oil mill characterized phenolic products such as 1,2-dihydroxybenzene (catechol), derivatives of benzoic acid, phenylacetic acid, phenylethanol, and cinnamic acid. The OMWs were fractioned by ultrafiltration and reverse osmosis techniques and tested for toxicity on aquatic organisms from different trophic levels: the alga Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum); the rotifer Brachionus calyciflorus; and two crustaceans, the cladoceran Daphnia magna and the anostracan Thamnocephalus platyurus. The fraction most toxic to the test organisms was that from reverse osmosis containing compounds of low molecular weight (<350 Da), and this was especially due to the presence of catechol and hydroxytyrosol, the most abundant components of the fraction.  相似文献   
105.
106.
BACKGROUND: In addition to their possible direct biological effects, plasma carotenoids can be used as biochemical markers of fruit and vegetable consumption for identifying diet-disease associations in epidemiological studies. Few studies have compared levels of these carotenoids between countries in Europe. OBJECTIVE: Our aim was to assess the variability of plasma carotenoid levels within the cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC). METHODS: Plasma levels of six carotenoids--alpha-carotene, beta-carotene, beta-cryptoxanthin, lycopene, lutein and zeaxanthin--were measured cross-sectionally in 3043 study subjects from 16 regions in nine European countries. We investigated the relative influence of gender, season, age, body mass index (BMI), alcohol intake and smoking status on plasma levels of the carotenoids. RESULTS: Mean plasma level of the sum of the six carotenoids varied twofold between regions (1.35 micromol l(-1) for men in Malm?, Sweden vs. 2.79 micromol l(-1) for men in Ragusa/Naples, Italy; 1.61 micromol l(-1) for women in The Netherlands vs. 3.52 micromol l(-1) in Ragusa/Naples, Italy). Mean levels of individual carotenoids varied up to fourfold (alpha-carotene: 0.06 micromol l(-1) for men in Murcia, Spain vs. 0.25 micromol l(-1) for vegetarian men living in the UK). In multivariate regression analyses, region was the most important predictor of total plasma carotenoid level (partial R(2)=27.3%), followed by BMI (partial R(2)=5.2%), gender (partial R(2)=2.7%) and smoking status (partial R(2)=2.8%). Females had higher total carotenoid levels than males across Europe. CONCLUSIONS: Plasma levels of carotenoids vary substantially between 16 different regions in Italy, Greece, Spain, France, Germany, the UK, Sweden, Denmark and The Netherlands. Compared with region of residence, the other demographic and lifestyle factors and laboratory measurements have limited predictive value for plasma carotenoid levels in Europe.  相似文献   
107.
Summary Exploration and collection of plant genetic resources were continued in central Italy 1989—regions Abruzzo, Umbria, Marche, Toscana.Triticum dicoccon was used as an indicator for traditional agriculture. 169 accessions were collected, mainly of cereals, vegetables and grain legumes. Worth mentioning are land-races ofTriticum aestivum, T. durum, Secale cereale, Pisum sativum, Lactuca sativa andCucurbita maxima. Brassica oleracea var.palmifolia, the palm-leaved kale, is an important vegetable in the Toscana. Several other rare crops could be also collected.
Sammlung pflanzlicher genetischer Ressourcen in Italien 1989
Zusammenfassung Die Exploration und Sammlung pflanzlicher genetischer Ressourcen wurden 1989 in Mittelitalien fortgesetzt — Regionen Abruzzo, Umbria, Marche, Toscana.Triticum dicoccon wurde als Indikator für traditionelle Landwirtschaft verwendet. 169 Proben wurden gesammelt, hauptsächlich von Getreiden, Gemüsen und Körnerleguminosen. Erwähnenswert sind Landsorten vonTriticum aestivum, T. durum, Secale cereale, Pisum sativum undCucurbita maxima. Brassica oleracea var.palmifolia, der Palmkohl, ist ein wichtiges Gemüse in der Toscana. Verschiedene andere seltene Fruchtarten konnten ebenfalls gesammelt werden.

1989
1989 , , , .Triticum dicoccon . 169 , , . Triticum aestivum, T. durum, Secale cereale, Pisum sativum Cucurbita maxima. Brassica oleracea var.palmifolia, , . .
  相似文献   
108.
Fluoroquinolone antibacterial drugs are currently used in reptilian medicine because of their broad spectrum of activity including the most frequent pathogens of these species. The disposition kinetics of marbofloxacin (MBX) at a single dose of 2 mg/kg were determined in healthy red-eared sliders after intravenous (IV) and intramuscular (IM) administration. The influence of renal portal system on the bioavailability of the drug was investigated by using forelimb and hindlimb as IM injection sites. Apparent volume of distribution at steady-state (Vss) and systemic clearance (Cl) of marbofloxacin after IV administration were estimated to be 48.21 ± 5.42 ml/kg and 23.38 ± 2.90 ml/hr·kg, respectively. The absolute bioavailabilities after IM route were 45.96% (forelimb) and 52.09% (hindlimb). The lack of statistically significant differences in most of the pharmacokinetic parameters after the two IM injection sites suggests a negligible influence of renal portal system in clinical use of MBX, although the Cmax after IMfore administration is advantageous, having into account the concentration-dependent action of this antibiotic. The absence of visible adverse reactions in the animals and the advantageous pharmacokinetic properties suggest the possibility of its safe and effective clinical use in red-eared sliders.  相似文献   
109.
A single antibody was shown to adopt different binding-site conformations and thereby bind unrelated antigens. Analysis by both x-ray crystallography and pre-steady-state kinetics revealed an equilibrium between different preexisting isomers, one of which possessed a promiscuous, low-affinity binding site for aromatic ligands, including the immunizing hapten. A subsequent induced-fit isomerization led to high-affinity complexes with a deep and narrow binding site. A protein antigen identified by repertoire selection made use of an unrelated antibody isomer with a wide, shallow binding site. Conformational diversity, whereby one sequence adopts multiple structures and multiple functions, can increase the effective size of the antibody repertoire but may also lead to autoimmunity and allergy.  相似文献   
110.
Dondina  Olivia  Orioli  Valerio  Tirozzi  Pietro  Bani  Luciano 《Landscape Ecology》2022,37(6):1543-1558
Landscape Ecology - Nestedness is a common pattern of species assemblages in fragmented landscapes. The spatial pattern and ecological drivers of nested communities have been widely explored, but...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号