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   393篇
  免费   27篇
林业   28篇
农学   11篇
  85篇
综合类   31篇
农作物   18篇
水产渔业   8篇
畜牧兽医   203篇
园艺   15篇
植物保护   21篇
  2023年   2篇
  2022年   3篇
  2021年   17篇
  2020年   8篇
  2019年   17篇
  2018年   12篇
  2017年   15篇
  2016年   8篇
  2015年   18篇
  2014年   17篇
  2013年   8篇
  2012年   38篇
  2011年   45篇
  2010年   13篇
  2009年   21篇
  2008年   35篇
  2007年   30篇
  2006年   18篇
  2005年   30篇
  2004年   28篇
  2003年   13篇
  2002年   15篇
  2001年   1篇
  1999年   2篇
  1998年   2篇
  1997年   1篇
  1993年   1篇
  1992年   1篇
  1972年   1篇
排序方式: 共有420条查询结果,搜索用时 15 毫秒
1.
In an attempt to obtain shelf-stable litchi fruit with preserved nutritional quality and good sensory features, quarters of peeled and pitted fruits were vacuum dried at 50, 60 and 70 °C at a constant pressure of 8.0 kPa. The product was assessed for its vitamin C, total phenolics and texture (hardness). In addition, the product with the best texture was assessed for its shelf-life by means of accelerated testing. Results suggest that vacuum dried litchi retained almost 70% of the vitamin C and total phenolics when compared to frozen fruits (control). Vitamin C and phenolic compounds content significantly decreased with drying, while no difference was found between different drying temperatures. Hardness increased with drying temperature. The sample dried at 70 °C presented crispness, which is a desired quality feature in dried fruit products. This sample was subjected to shelf-life evaluation, whose result suggests a shelf-life of eight months at 23 °C. Total color change (CIE ΔE00) was the expiry criterion. Vacuum drying was a suitable technique for producing shelf-stable litchi fruit with good texture while preserving its desirable original nutrients. Consumption of vacuum dried litchi may be beneficial to health due to its remarkable content of phenolic compounds and vitamin C.  相似文献   
2.
Recent literature and public discourse emphasize the role of craft breweries in the revitalization process of economically distressed neighborhoods across the U.S. With this, many are reporting rising property values in areas surrounding craft breweries. This research examines the impacts of craft breweries on both residential and commercial property values in a case study of Charlotte, North Carolina. Estimating a series of hedonic models which incorporate a difference‐in‐difference estimator, we find that craft breweries have a positive impact on residential property values. While many areas in close proximity to a craft brewery appear to have been associated with relatively higher price premiums even before the opening of the brewery, breweries tend to add to this premium, especially in center‐city neighborhoods. We find no significant impacts on commercial property values. These results are informative to policy makers considering revising zoning laws and other regulations in efforts to promote the growth of craft breweries and spur economic development in their local economies.  相似文献   
3.
A 3.5-year-old spayed female ferret, fed a diet high in refined sugar, was referred for lethargy, polyuria, polydipsia, and polyphagia. Diabetic ketoacidosis was diagnosed. Treatment included insulin therapy and a low carbohydrate diet. Diabetes mellitus resolved 54 d later, and insulin therapy was discontinued. There has been no recurrence of the diabetes mellitus.  相似文献   
4.
5.
6.
Interspecific hybrids between Trifolium uniflorum and cultivated white clover (Trifolium repens) have highly useful characteristics for temperate pastoral systems derived from both parent species. However, the early hybrids (F1 and BC1) also have unacceptably poor seed production for commerce. This study analysed the basis for the poor seed production and investigated breeding strategies for overcoming the problem. The BC1F1 generation produced lower‐than‐expected numbers of heads per plant and seeds per floret. Backcrossing of selected hybrids to white clover corrected these deficiencies and created new variation. Seed numbers were also returned to near target levels by recurrent selection within the BC1 generation. Thus, it was possible to retain a theoretical average of 25% of T. uniflorum genome and still achieve high seed production per plant. The BC1F2 and BC2F1 generations produced high seed numbers per plant, along with reasonable variation. Both of these second‐generation hybrid forms have high reproductive potential and should be the focus for the selection of the desired combinations of agronomic and seed production traits.  相似文献   
7.
To select the best microalgae for Ostrea edulis conditioning, four single species diets were fed to batches of broodstock, which were then compared using physiological and biochemical approaches. Ingestion and absorption were first studied, showing that Chaetoceros gracilis and Skeletonema marinoï were efficiently ingested (4.9–5.3 mg g?1 h?1) and absorbed (1.9–2.5 mg g?1 h?1) while Tetraselmis suecica led to the lowest physiological responses (0.36 and 0.12 mg g?1 h?1 respectively). When O. edulis were fed any microalgae except T‐ISO with only 79 mg g?1, gonads accumulated carbohydrates from 116 to 141 mg g?1 and the extent of accumulation depended on the species supplied in the order T. suecica<C. gracilis<S. marinoï. When oysters were fed either of the diatoms (C. gracilis or S. marinoï), an efficient transfer of 20:5(n‐3) to all tissues, including the gonads, was recorded while no enrichment in 22:6(n‐3) occurred in all tissues (polar fraction) when oysters were fed T‐ISO. In contrast (22:5(n‐6)), a characteristic fatty acid of T‐ISO accumulated in all tissues, confirming its allocation despite particularly low ingestion (1.66 mg g?1 h?1) and absorption (0.32 mg g?1 h?1). When oysters were fed C. gracilis or S. marinoï an efficient transfer of cholesterol and campesterol from diatoms to the gonads was observed, while no sterol accumulation occurred in the gonad when fed T. suecica. Because of low ingestion, absorption and poor biochemical compounds' transfer, T. suecica is not recommended for O. edulis conditioning. T‐ISO also exhibited low physiological performances but due to a specific 22:6(n‐3) enrichment in the gonad neutral fraction (16.1%), its potential role in reproduction should be considered. Chaetoceros gracilis is highly recommended for O. edulis broodstock while a source of DHA other than that provided by T‐ISO should be found due to its poor absorption. Because a mixed diet has been shown to be more efficient for O. edulis broodstock conditioning, complementary trials dealing with the effects of other species rich in 22:6(n‐3) such as Rhodomonas salina or Pavlova lutheri should be performed.  相似文献   
8.
9.
Seasonal and diurnal changes in water-soluble carbohydrates (WSC) and ethanol-soluble carbohydrates (ESC), as well as in chromatographic profiles of the sugars comprising these categories, were studied in orchardgrass pastures at one location in the Piedmont region of Virginia. Grass from four experimental plots was sampled weekly in the morning and afternoon over an 8-week period (early to late spring). Tissue was air-dried to simulate hay, or frozen to preserve the sugar profiles of fresh pasture. WSC and ESC were assayed colorimetrically. To profile sugars, boiled-water extracts were separated by high-performance liquid chromatography coupled to pulsed amperometric detection. Fructan, glucose, fructose, and sucrose were quantified by high-performance liquid chromatography. All sugar concentrations were highest in the early spring in both fresh and dried tissue. Fructan chain length was highest in early spring as well. Significant diurnal differences were observed for WSC and fructan, on some dates (P < .0001 and P = .024, respectively), and for ESC, glucose, and sucrose averaged over the entire period (P = .0002, .004, and <.0001, respectively). Sucrose was barely detectable in fresh tissue but reached 1.6% to 12% dry matter in dried tissue. These results demonstrate changes in orchardgrass carbohydrates over a season, within a day, and between dried and fresh herbage. Understanding these changes may be helpful in the management of horses with a history of insulin resistance and laminitis.  相似文献   
10.
Seasonal and diurnal patterns of sugar accumulation in bermudagrass (Cynodon dactylon) pastures were monitored to evaluate risk factors for pasture-associated laminitis of ponies and horses. Bermudagrass was collected from four plots in the morning and afternoon on a weekly basis, from mid-July until late August. Tissue was air-dried to simulate hay, or frozen to retain the sugar profiles of fresh pasture. Samples were analyzed colorimetrically for total water-soluble and ethanol-soluble carbohydrates, and electrochemically for starch. In addition, sugars were separated and quantified by high-performance liquid chromatography coupled to pulsed amperometric detection. The dominant sugars in extracts were glucose, fructose, and sucrose. Some minor peaks, corresponding to tri- and tetrasaccharides, were also detected in some extracts. Starch increased over time in fresh and dried tissue, and concentrations varied diurnally in fresh, but not in dried tissue (P = .021). Sucrose in dried tissue decreased and then increased, with higher concentrations than in fresh tissue on all sampling dates (P = .024). Glucose and fructose exhibited diurnal variation on one and two dates, respectively (P = .034 and .0028, respectively). These results reveal trends in carbohydrate concentrations and profiles that may help to evaluate the likelihood of equine laminitis outbreaks on bermudagrass.  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