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   213篇
  免费   22篇
林业   17篇
农学   4篇
基础科学   5篇
  52篇
综合类   10篇
农作物   24篇
水产渔业   37篇
畜牧兽医   64篇
园艺   4篇
植物保护   18篇
  2024年   1篇
  2023年   2篇
  2022年   7篇
  2021年   15篇
  2020年   8篇
  2019年   11篇
  2018年   10篇
  2017年   14篇
  2016年   10篇
  2015年   10篇
  2014年   14篇
  2013年   13篇
  2012年   11篇
  2011年   19篇
  2010年   8篇
  2009年   7篇
  2008年   13篇
  2007年   11篇
  2006年   4篇
  2005年   8篇
  2004年   5篇
  2003年   7篇
  2002年   8篇
  2001年   3篇
  1999年   5篇
  1996年   1篇
  1993年   2篇
  1992年   2篇
  1988年   1篇
  1987年   1篇
  1986年   2篇
  1984年   1篇
  1968年   1篇
排序方式: 共有235条查询结果,搜索用时 140 毫秒
191.
The concept of nutritional programming raises the interesting possibility of directing specific metabolic pathways or functions in juvenile fish, for example, to improve the use of substitutes to fishmeal and oil, and hence to promote sustainability in aquaculture. The aim of the study was to determine effects of early nutritional stimuli of gilthead seabream larvae and check if nutritional programming of gilthead sea bream is possible between 16 days post hatching (dph) and 26 dph. A trial was conducted to determine the effects of early nutritional stimuli of gilthead seabream larvae. Five experimental microdiets (pellet size <250 μm) were formulated containing five different proportions of a marine lipid source rich in long‐chain polyunsaturated fatty acids (LC‐PUFA) and two vegetable lipid sources rich in linolenic and linoleic acids. The results of this study demonstrate that dietary n‐3 LC‐PUFA levels increased larval growth and survival affecting Δ6 desaturase gen (fads2) expression and retinal neurons density. However, the high mortalities obtained along on‐growing in fish fed low n‐3 LC‐PUFA at 16 dph constrained the feasibility of nutritional programming of gilthead seabream during this late developmental window and needs to be further investigated.  相似文献   
192.
Phytoplankton cultures of Chlorella sp., Tetraselmis sp. and Isochrysis galbana were used alone as feed to rear separate batches of newly caught milkfish (Chanos chanos) fry (about 21 days old). Ultrastructural studies of fry hepatocytes and pancreatic acinar cells indicated that they cannot directly utilize Chlorella, which has a rigid cell wall. The fry can directly utilize Tetraselmis and Isochrysis, but neither is nutritionally adequate for growth and survival if used as the only feed. Tetraselmis is nutritionally inferior to Isochrysis.  相似文献   
193.
Melanomacrophage centres (MMCs), located in different organs of non‐mammalian vertebrates, play a role in the destruction, detoxification or recycling of endogenous and exogenous materials. Cytochrome P450 monoxygenase 1A (CYP1A) is involved in xenobiotics biotransformation, and its liver expression is considered as a biomarker for detecting exposure to environmental pollutants. Atlantic bluefin tuna (ABFT), Thunnus thynnus L., liver samples were collected from: wild animals caught in the eastern Atlantic; juveniles reared in the central Adriatic; juveniles reared in the northern Adriatic; adults reared in the western Mediterranean. The samples were processed for basic histology, histochemistry and for CYP1A immunodetection. An unexpected high density of MMCs, containing ferric iron and lipofuscin–ceroids, was detected in the juveniles sampled in the northern Adriatic Sea. These individuals showed also a strong anti‐CYP1A immunopositivity in hepatocytes and in the epithelium of bile ducts. This study supports the utility of MMCs as biomarkers of fish ‘health status’ and gives concern for a potential contaminant accumulation in ABFT.  相似文献   
194.
The object of this work was to study the effects of crossbreeding on meat quality and fatty acid profile of Holstein calves. Samples were taken from Longissimus thoracis (LT) muscle of 36 calves of three different groups (Holstein crossed with Rubia Gallega (HF×RG), Holstein crossed with Limousine (HF×LI) and Holstein crossed with Belgian Blue (HF×BB)). Significant differences were observed in carcass weight and killing out percentage (P < 0.001) among, groups reaching the highest values in the HF×BB group (228 kg and 59.4%, respectively), while the cross with Limousine presented the lowest values for carcass weight (191 kg) and the cross with Rubia Gallega showed the lowest killing out percentages (54.9%). Meat from HF×RG animals was redder (a* 13.31) and lightest (L* 39.55) than meat from HF×LI and HF×BB groups. With regard to fatty acid profile, the saturated fatty acids were the most abundant fatty acid, followed by monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids in the three groups. Crossbreeding did not affect the proportion of fatty acid. Finally, live weight, cold carcass weight, killing out, shear force, L* from LT, b*from LT, a* from fat, b* from fat, C14:0, C15:0, C16:0, C18:0, C18:3n‐6, MUFA and price‐to‐sales ratio were the selected variables from discriminant analysis to classify the types of crossbreeding.  相似文献   
195.
The objective of this work was to characterize and identify among the passion fruit hybrids of the second generation backcross (BC2: BC1 × P. edulis), resistance to passion fruit woodiness disease (CABMV) with desirable agronomic attributes. Ninety‐two progeny of BC2 hybrids were evaluated for severity of the virus in conditions of field, physical and chemical characterization of the fruits and precocity of the plant in relation to the vegetative and reproductive phases. The data were analysed using multivariate statistics and mixed models (REML/BLUP) to estimate genetic parameters. The was conditioned by and , for number of fruits, fruit and peel weight and soluble solids and the effect of for virus severity to CABMV and effect of on the variables fruit length, fruit diameter, peel thickness and pulp weight. For the titratable acidity it had no . The progeny BC2‐A, BC2‐C, BC2‐E, BC2‐F and BC2‐H families can be selected for use in passion fruit breeding programmes by adding high vegetative vigour, early fruit production, resistance to CABMV and also desirable agronomic attributes.  相似文献   
196.
Supplements with corn grain, molasses cane, and different nitrogen sources were evaluated in 16 growing Hosltein heifers [227 ± 33 kg body weight (BW)] grazing kikuyu (Pennisetum clandestinum) pasture in a 10-ha sward (rotational grazing with electric fences) during 90 days in the summer season. The nitrogen sources were urea (U); urea and blood meal (U + BM); and urea, blood meal, and rumen-protected methionine (U + BM + RPM). Heifers were randomly assigned to four experimental supplements defined as follows: control (no supplementation), U, U + BM, and U + BM + RPM. Two kilograms (as fed) of supplement was offered daily. The final BW of heifers fed U + BM + RPM was higher (P < 0.05) than heifers not supplemented. The total and average daily weight gain of heifers supplemented with U + BM + RPM were higher than heifers not supplemented or supplemented with U and U + BM (P < 0.05). The average daily gain of heifers supplemented with U and U + BM were higher than heifers not supplemented (P < 0.05). Grass intake was not affected by supplementation, but total dry matter intake was increased by supplements with U, U + BM, and U + BM + RPM (P < 0.05). Feed conversion was improved by U + BM + RPM (P < 0.05). Total tract digestion was not affected by supplements. Blood urea nitrogen concentrations of heifers supplemented with U, U + BM, and U + BM + RPM were higher than heifers not supplemented (P < 0.05). It is concluded that supplements with U + BM + RPM improved growth performance and feed conversion in heifers grazing kikuyu pasture.  相似文献   
197.
The aim of this paper was to genetically characterize Toxoplasma gondii isolates from free range chickens in regions of Brazilian territory in the state of Mato Grosso do Sul (MS) where T. gondii strains have never been studied. In total, T. gondii isolates from 22 free range chickens were included in this study. Fifty chickens from Eldorado, thirty from Rio Verde and ten from Aquidauana were sampled between January and April 2007. In relation to the genetic diversity of T. gondii isolates from chickens in MS, the magnitude of the diversity in the isolates sampled in this study was comparable to the overall diversity in a composite data set. These 22 isolates in MS revealed 11 genotypes, whereas the 321 isolates ever genotyped in Brazil have revealed 95 genotypes. The values of Simpson's Diversity Index for the whole population of T. gondii isolates in Brazil, the whole population of T. gondii isolates from chickens in Brazil and the population surveyed in this study were 0.97, 0.95 and 0.90, respectively. Seven of the 11 genotypes revealed from chicken isolates from MS are newly described genotypes and six of them each have a single isolate. In conclusion, the results obtained from isolates in MS corroborate previous studies on T. gondii isolates in Brazil, thus confirming their diversity and atypicality. Nonetheless, the applicability of PCR-RFLP markers for epidemiological inferences remains controversial.  相似文献   
198.
The present study aimed to evaluate the effect of three culture systems on caprine primordial follicle activation in vitro: follicles cultured either in the isolated form within alginate (Isolated follicles + Alginate treatment), or enclosed in ovarian tissue (in situ), with or without alginate (Fragment + Alginate, and Fragment alone treatments, respectively). After culture, the Isolated follicles + Alginate treatment presented a percentage of morphologically normal follicles (MNF) similar to both the non-cultured control and the Fragment Alone treatments. Nevertheless, Fragment + Alginate treatment showed a significant reduction in the number of MNF when compared to the other treatments. Regarding follicle development, our results showed that regardless of the alginate, the presence of ovarian tissue limited primordial follicle activation during in vitro culture. Remarkably, the Isolated primordial follicle + Alginate treatment was the only one that significantly promoted follicle activation and increased both follicle and oocyte diameters during IVFC, pointing out a higher cell proliferation. In conclusion, the presence of ovarian tissue with or without alginate limited follicle development (activation) after culture. Nevertheless, when primordial follicles were isolated and encapsulated in alginate they presented suitable survival rates, higher rates of follicle activation and continued to grow throughout the culture period.  相似文献   
199.
Alzheimer’s disease (AD) is a devastating neurodegenerative disease and the most common cause of dementia. It has been confirmed that the pathological processes that intervene in AD development are linked with oxidative damage to neurons, neuroinflammation, tau phosphorylation, amyloid beta (Aβ) aggregation, glutamate excitotoxicity, and cholinergic deficit. Still, there is no available therapy that can cure AD. Available therapies only manage some of the AD symptoms at the early stages of AD. Various studies have revealed that bioactive compounds derived from marine organisms and plants can exert neuroprotective activities with fewer adverse events, as compared with synthetic drugs. Furthermore, marine organisms have been identified as a source of novel compounds with therapeutic potential. Thus, there is a growing interest regarding bioactive compounds derived from marine sources that have anti-AD potentials. Various marine drugs including bryostatin-1, homotaurine, anabaseine and its derivative, rifampicins, anhydroexfoliamycin, undecylprodigioisin, gracilins, 13-desmethyl spirolide-C, and dictyostatin displayed excellent bioavailability and efficacy against AD. Most of these marine drugs were found to be well-tolerated in AD patients, along with no significant drug-associated adverse events. In this review, we focus on the drugs derived from marine life that can be useful in AD treatment and also summarize the therapeutic agents that are currently used to treat AD.  相似文献   
200.
The effect of phenolic-rich extracts from avocado peel on the formation of cholesterol oxidation products (COPs) in porcine patties subjected to cooking and chill storage was studied. Eight COPs (7α-hydroxycholesterol, 7β-hydroxycholesterol, 7-ketocholesterol, 20α-hydroxycholesterol, 25-hydroxycholesterol, cholestanetriol, 5,6β-epoxycholesterol, and 5,6α-epoxycholesterol) were identified and quantified by GC-MS. The addition of avocado extracts (~600 GAE/kg patty) to patties significantly inhibited the formation of COPs during cooking. Cooked control (C) patties contained a larger variety and greater amounts of COPs than the avocado-treated (T) counterparts. COPs sharply increased in cooked patties during the subsequent chilled storage. This increase was significantly higher in C patties than in the T patties. Interestingly, the amount of COPs in cooked and chilled T patties was similar to those found in cooked C patties. The mechanisms implicated in cholesterol oxidation in a processed meat product, the protective effect of avocado phenolics, and the potential implication of lipid and protein oxidation are thoroughly described in the present paper.  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