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   101篇
  免费   4篇
林业   16篇
农学   4篇
基础科学   1篇
  32篇
综合类   7篇
农作物   8篇
水产渔业   13篇
畜牧兽医   22篇
园艺   1篇
植物保护   1篇
  2023年   1篇
  2022年   1篇
  2021年   3篇
  2020年   4篇
  2019年   3篇
  2018年   1篇
  2017年   3篇
  2016年   5篇
  2015年   6篇
  2014年   3篇
  2013年   5篇
  2012年   8篇
  2011年   14篇
  2010年   6篇
  2009年   2篇
  2008年   9篇
  2007年   9篇
  2006年   7篇
  2005年   3篇
  2004年   3篇
  2003年   6篇
  2002年   3篇
排序方式: 共有105条查询结果,搜索用时 31 毫秒
81.
This work addresses the most relevant advances in the breeding and rearing of marine ornamental species. The main breakthroughs in marine ornamental fish culture are discussed, with seahorses deserving a section of their own as a result of their conservation status and unique biology. Details on spawning, embryo development, larval rearing, plankton culturing, and tank design are presented. In addition, with the increase in popularity of ornamental invertebrates in reef aquariums, details on the culturing techniques of some of the most traded invertebrate groups (e.g., live rocks, corals, anemones, polychaetes, mollusks, decapod crustaceans and echinoderms) are also discussed. Finally, the last part of this work highlights the concerns toward the establishment of sustainable collection, production, and trading practices for marine ornamentals as well as the urgent need to develop reliable traceability protocols to distinguish sustainably caught and/or cultured specimens from wild ones. This work represents not only an exhaustive and updated bibliographical source but also a starting point for all those who want to contribute to the development of this fascinating research field.  相似文献   
82.
83.
Adults from spider crab, Maja brachydactyla, Balss, 1922 were kept in captivity for up to 2 years. Haemolymph of ten females was extracted monthly for monitoring several metabolites and the presence of Vibrionacea bacteria. A neurotoxic marker and hepatic metabolic and digestive enzyme capacities were contrasted between wild specimens and those reared in captivity. As a result, no differences were observed in hepatosomatic index (HSI) between males and females, but captive animals presented lower HSI than the wild ones. After 2 years of confinement, no changes in quantities of haemolymph microflora and metabolites were observed and this was considered indicative of adaptation of the broodstock to confinement. Spider crab also showed a large plasticity in their hepatopancreatic digestive capabilities suggested by the adaptation to the food supplied in captivity. Moreover, captivity conditions did not seem to negatively alter their antioxidant defences, xenobiotic capacity or neuromuscular activity, as no enhanced oxidative stress damage was shown in either males or females. These results indicate that although the confinement conditions used in this study do not mimic those from the wild, they could be considered as adequate for rearing M. brachydactyla in captivity, at least with regard to the set of parameters assessed.  相似文献   
84.
This study aims to describe changes in the activity of digestive enzymes of the zebra cichlid, Archocentrus nigrofasciatus, from hatching until 30 d after hatch (d.a.h.), and to evaluate the effects of feeding diets with different levels of fishmeal (FM) substitution with alternative nonanimal protein sources from 30 d.a.h. up to the age of 60 d.a.h. Results indicated that the developmental patterns of digestive enzymes from the exocrine pancreas and intestine are similar to those of other phylogenetically close cichlids, although they seemed to develop faster than other species as indicated by the peaks in enzyme activity, which were detected at younger stages of development. The 100% FM replacement with different alternative nonanimal protein sources had a negative impact on the growth performance of A. nigrofasciatus juveniles, whereas fish fed the diet with a 50% FM replacement showed similar results to those fed the 100% FM diet. Fish showing the lowest growth rate had also the lowest enzyme activity, especially in relation to the intestinal brush border enzymes. This study assesses the digestive capabilities and nutritional condition of the zebra cichlid fish and provides knowledge on the potential for FM substitution in their feeds.  相似文献   
85.
Four anthocyanin-pyruvic adducts were synthesized through the reaction of cyanidin 3-O-glucoside, cyanidin 3-O-rutinoside, cyanidin 3-O-sophoroside, and cyanidin 3-O-sambubioside with pyruvic acid, structurally characterized by liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR), and their chromatic properties were studied (pH and SO2 stability assays). Overall, these pigments were shown to have a higher resistance to discoloration toward pH variations and also in the presence of SO2, being that this resistance to discoloration was explained by a higher protection of the chromophore group against the water or bisulfite nucleophilic attack that gives rise to the colorless hemiacetal form. Only slight differences in the protection against the nucleophilic attack of water and bisulfite were found to occur between all of the cyanidin-pyruvic acid adducts studied. Indeed, anthocyanin-pyruvic acid adducts with glucose or sambubiose attached to the 3-O position of the flavylium moiety were shown to have smaller bleaching constants compared with similar pigments that possess a rutinosyl or sophorosyl moiety. The study of the pigments (A-D and cyanidin-3-O-glucoside) color parameters, namely, chroma (C), lightness (L), and the hue angle (h(a,b)), obtained from the CIELAB system, revealed that different patterns of sugars in the anthocyanin-pyruvic acid adduct moiety affected the referred three parameters of color. The loss of saturation (DeltaC < 0) and the increase of lightness (DeltaL > 0) presented by the cyanidin-pyruvic acid adduct solutions at acidic pH values (1.0 and 2.0) showed that they are much less colored than the cyanidin-3-O-glucoside. For higher pH values (5.0 and 7.0), the reverse trend was observed. This means that the cyanidin-pyruvic acid adducts A-D are much more colored than the anthocyanin at these pH values. The higher coloring capacity of these pigments at higher pH values may be an important feature, indicating a putative application of these compounds in food products.  相似文献   
86.
Procyanidins as antioxidants and tumor cell growth modulators   总被引:2,自引:0,他引:2  
Five procyanidin fractions with different structural complexities were obtained after fractionation of a grape seed extract. The procyanidin fraction's abilities to inhibit lipid peroxidation induced by 2,2'-azobis-2-methyl-propanimidamide dihydrochloride in a liposomal membrane system were examined. The antioxidant capacities of all fractions were evaluated through monitoring oxygen consumption and by measuring the formation of conjugated dienes. All tested fractions provided protection of membranes against peroxyl radicals by increasing the induction time of oxidation. This effect increased up to fraction II but decreased with the increase of the structural complexity of further procyanidin fractions, possibly due to steric hindrance effects exhibited by the more complex fractions. In addition, the antiradical properties and the reducing power of these fractions were determined by using 2,2-diphenyl-1-picrylhydrazyl and ferric reducing/antioxidant power methods, respectively. Moreover, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide reduction and DNA synthesis were measured in Michigan Cancer Foundation 7 (MCF-7), a human breast cancer cell line, treated with catechin or procyanidin fractions in order to evaluate the effect of these compounds on cell viability and proliferation. The results obtained showed that at 30 microg/mL, fractions I and II decreased cell viability and proliferation, which was not observed with 60 microg/mL of the same fractions. Catechin was also able to decrease cell viability and proliferation at 30 and 60 microg/mL. It is interesting to notice that the procyanidin fractions that exhibited higher antioxidant activity were the same to affect cell viability and proliferation.  相似文献   
87.
Three newly formed Port wine pigments were isolated by Toyopearl HW-40(s) gel chromatography and semipreparative HPLC. Furthermore, the pigments were identified by mass spectrometry (LC/MS) and NMR techniques (1D and 2D). These anthocyanin-derived pigments showed UV-visible spectra different from those of the original grape anthocyanins. These pigments correspond to malvidin 3-glucoside linked through a vinyl bond to either (+)-catechin, (-)-epicatechin, or procyanidin dimer B3 [(+)-catechin-(+)-catechin]. NMR data of these pigments are reported for the first time.  相似文献   
88.
Tannins are well-known food polyphenols that interact with proteins, namely, salivary proteins. This interaction is an important factor in relation to their bioavailability and is considered the basis of several important properties of tannins, namely, the development of astringency. It has been generally accepted that astringency is due to the tannin-induced complexation and/or precipitation of salivary proline-rich proteins (PRPs) in the oral cavity. However, this complexation is thought to provide protection against dietary tannins. Neverthless, there is no concrete evidence and agreement about which PRP families (acidic, basic, and glycosylated) are responsible for the interaction with condensed tannins. In the present work, human saliva was isolated, and the proteins existing in saliva were characterized by chromatographic and proteomic approaches (HPLC-DAD, ESI-MS, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and MALDI-TOF). These approaches were also adapted to study the affinity of the different families of salivary proteins to condensed tannins by the interaction of saliva with grape seed procyanidins. The results obtained when all the main families of salivary proteins are present in a competitive assay, like in the oral cavity, demonstrate that condensed tannins interact first with acidic PRPs and statherin and thereafter with histatins, glycosylated PRPs, and bPRPs.  相似文献   
89.
A rapid, specific, and sensitive method based on the Quick Easy Cheap Effective Rugged and Safe (QuEChERS) method and a cleanup using dispersive solid-phase extraction with MgSO(4), PSA, and C18 sorbents has been developed for the routine analysis of 14 pesticides in strawberries. The analyses were performed by three different analytical methodologies: gas chromatography (GC) with electron capture detection (ECD), mass spectrometry (MS), and tandem mass spectrometry (MS/MS). The recoveries for all the pesticides studied were from 46 to 128%, with relative standard deviation of <15% in the concentration range of 0.005-0.250 mg/kg. The limit of detection (LOD) for all compounds met maximum residue limits (MRL) accepted in Portugal for organochlorine pesticides (OCP). A survey study of strawberries produced in Portugal in the years 2009-2010 obtained from organic farming (OF) and integrated pest management (IPM) was developed. Lindane and β-endosulfan were detected above the MRL in OF and IPM. Other OCP (aldrin, o,p'-DDT and their metabolites, and methoxychlor) were found below the MRL. The OCP residues detected decreased from 2009 to 2010. The QuEChERS method was successfully applied to the analysis of strawberry samples.  相似文献   
90.
Agricultural reform and infrastructural development are among the major drivers of biodiversity loss and landscape homogenization worldwide. Ponds and other small stagnant water bodies are crucial for maintaining regional biodiversity, yet they are vulnerable to human induced landscape change. We investigated for 199 ponds in the ‘département’ Pas-de-Calais in north-western France if pond persistence (n = 86, 43%) or disappearance (n = 113, 57%) was related to wider changes in the landscape, over the period 1975–2006. Landscape data were obtained from aerial photographs (1963), two ASTER satellite images (2001 and 2003) and observations on the ground (1975 and 2006) and land use around the ponds was described over concentric circles with five different radii in the 100–1000 m range. Overall, pond disappearance was associated with a decrease in grassland and an increase in arable fields around the ponds. We found that the small, man-made cattle ponds, with either natural substrate or concrete drinking troughs, were more often affected than the larger, semi-natural ponds. Since the cattle ponds are regularly used for amphibian reproduction, their massive abandonment therewith weakens the population network and puts the local occurrence of some of the rarer species at risk. Spatial extrapolation of models on pond persistence allowed the identification of areas most at risk of further pond loss. We suggest that local amphibian conservation efforts will be the most effective if the focus is on the marshes and dune areas and on pond preservation in the remaining grasslands.  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