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   8521篇
  免费   488篇
  国内免费   1038篇
林业   940篇
农学   761篇
基础科学   897篇
  1346篇
综合类   3349篇
农作物   283篇
水产渔业   630篇
畜牧兽医   1383篇
园艺   150篇
植物保护   308篇
  2024年   36篇
  2023年   85篇
  2022年   185篇
  2021年   231篇
  2020年   260篇
  2019年   312篇
  2018年   235篇
  2017年   334篇
  2016年   415篇
  2015年   360篇
  2014年   430篇
  2013年   530篇
  2012年   706篇
  2011年   729篇
  2010年   547篇
  2009年   540篇
  2008年   491篇
  2007年   605篇
  2006年   539篇
  2005年   370篇
  2004年   292篇
  2003年   263篇
  2002年   186篇
  2001年   194篇
  2000年   139篇
  1999年   152篇
  1998年   120篇
  1997年   87篇
  1996年   94篇
  1995年   86篇
  1994年   86篇
  1993年   96篇
  1992年   73篇
  1991年   60篇
  1990年   51篇
  1989年   41篇
  1988年   38篇
  1987年   23篇
  1986年   10篇
  1985年   5篇
  1984年   4篇
  1983年   3篇
  1982年   2篇
  1962年   1篇
  1956年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
(1) Guanidinoacetic acid (GAA) is the single immediate endogenous precursor of creatine (Cr). It was hypothesised that dietary GAA would have different effects on performance and energy metabolites in breast muscle depending on the nutrient density (ND) of corn-soybean-based diets.

(2) A total of 540 one-day-old male Ross 308 broilers were allocated to 9 dietary treatments with 6 replicates (10 birds each) in a 3 × 3 factorial arrangement with three levels of ND (low, 2800; medium, 2950 and high, 3100 kcal metabolizable energy (ME)/kg; and with the other nutrients being constant relative to ME) and supplemented with three levels of GAA (0, 0.6 and 1.2 g/kg) in a 42-d feeding trial.

(3) In the starter and grower periods, increasing levels of ND improved body weight (BW), average daily gain (ADG), average daily feed intake (ADFI) and feed conversion ratio (FCR), with the exception of ADFI in the starter period. GAA supplementation did not affect performance characteristics. All performance indicators responded markedly to increasing ND in the finisher period, whereas the highest GAA level reduced ADFI compared to the unsupplemented control (156 vs. 162 g/d) and concomitantly FCR (1.81 vs. 1.93). No interactive effects were noted for any performance trait. The high ND diet resulted in more breast meat yield on d42, associated with higher fat content and darker colour compared to the other ND levels. The GAA supplementation did not affect carcass and breast traits. At the end of the experiment, Cr was elevated when feeding GAA at 1.2 g/kg (5455 vs. 4338 mg/kg fresh muscle).

(4) To conclude, ND had a substantial effect on performance and carcass traits, whereas any effect of GAA was limited to FCR in the finisher period and independent of diet ND level.  相似文献   

42.
This study was conducted to evaluate the effects of different levels of milk thistle meal on performance, blood biochemical indices, ileal bacterial counts and intestinal histology in laying hens fed diets containing different levels of metabolizable energy. A total number of 200 Leghorn laying hens (Hy‐Line W‐36) were randomly assigned to eight experimental treatments with five cage replicates of five birds each. Dietary treatments consisted of four levels of milk thistle meal (0%, 15%, 30% and 60%) and two levels of AMEn (11.09 and 12.34 MJ/kg) fed over a period of 80 days. In vitro studies revealed that the total phenolic component of milk thistle meal was 470.64 mg gallic acid equivalent/g of the sample, and its antioxidant activity for inhibiting the 2‐2‐diphenyl‐1‐picrichydrazyl free radical and reducing ferric ions was about 21% higher than that of butylated hydroxyltoluene (p < .05). Diets containing high level of AMEn led to improved egg production (p < .05), egg weight (< .05), egg mass (< .01) and feed conversion ratio (< .01). In addition, offering diets containing high energy significantly enhanced (< .01) serum triglyceride and malondialdehyde (MDA) concentrations as well as jejunal villus height. Dietary supplementation of 3% milk thistle meal resulted in the best feed conversion ratio (< .05), reduction of ileal Escherichia coli enumeration (< .01) and an enhancement in the villus height‐to‐crypt depth ratio (< .05). Furthermore, feeding incremental levels of this meal led to remarkable decrease in serum cholesterol, triglyceride and MDA (< .01) concentrations while significant increase in blood high‐density lipoprotein content and goblet cell numbers (< .05). The present findings indicate that milk thistle meal with high antioxidant and antibacterial properties in laying hen diets may improve health indices and productive performance.  相似文献   
43.
A Box–Behnken design (BBD) in a response surface methodology (RSM) was used to investigate the response of broiler chicks to in ovo feeding (IOF) of beta‐hydroxy beta‐methylbutyrate (HMB), dextrin and the timing of the first water and feed deprivation. On day 18th of incubation, 1,500 eggs were randomly assigned to 15 experimental runs of BBD, each with 4 replicates, as 3 levels IOF of HMB (0%, 0.5% and 1%) and dextrin (0%, 20% and 40%), and 3 levels of the first water and feed deprivation (6, 27 and 48 hr). Day‐old chicks from each replicate were then used to assess the effect of IOF and time first water and feed access on chick's responses. The IOF of dextrin leads to respectively 9.7%–15.5% lower hatchability for 20% and 40% inclusion (p < .05), whereas HMB inclusion appeared with no effect on hatchability (p > .05). Administration of dextrin or HMB into the amnion of embryos elevated length, width and surface area of villus, and increased glycogen content of liver and breast (p < .05). In all parameter models, the linear terms showed highest contribution (R2 = 0.81–0.97) to explain existing variation in chick's responses. The first water and feed deprivation had largest effect on BW2 and glycogen content of liver and breast. It is concluded that if possible, place chicks before 7 hr of hatch to preserve BW loss and have maximum response from IOF. If not possible, use IOF with 40% dextrin + 0.5% HMB to preserve gut integrity and energy status up to 48 hr. This should give advantage to chicks to recover fast after feeding, but that would have to be confirmed by trials growing birds to slaughter age.  相似文献   
44.
Overweight and obesity are multifactorial diseases caused by an imbalance in energy metabolism. An underlying genetic predisposition is often a factor in these conditions. In the cat breeding family of the Institute of Animal Nutrition at the Vetsuisse Faculty, University of Zurich, a segregating overweight phenotype with a genetic contribution was observed. From this breeding family, 26 kittens were followed from birth up to 8 months of age. During this time, food intake was measured using an automatic feeding station, and energy expenditure was investigated using indirect calorimetry at the ages of 4 and 6 months. Dual‐energy X‐ray absorptiometry (DEXA) was performed and blood glucose, leptin and insulin were measured at the ages of 4, 6 and 8 months. The kittens were also weighed daily for the first 2 weeks of life, every second day until weaning and once per week until 8 months of age. The body condition score (BCS) was evaluated monthly between 2 and 8 months of age. The main finding of this study is that a predisposition to overweight is connected to a higher food intake early in life, with no significant alterations in energy expenditure. The leptin blood levels were related to body fat percentage, and insulin sensitivity did not seem to be affected.  相似文献   
45.
Abstract – Standard metabolic rate (SMR, closely related to basal and resting metabolism) varies by up to threefold among juvenile Atlantic salmon, Salmo salar L., of similar size at common temperature. Here, consequences of this variation are predicted by combining empirically derived relationships between SMR, specific dynamic action, energy budgets, water velocity, food level in the environment and food availability to fish. The range of velocities across which growth is predicted to occur is inversely related to a fish’s SMR. Growth is positively related to SMR at high but negatively related to it at low‐food levels. The relationship between food level and the range of velocities over which lower SMR fish can grow but higher SMR fish cannot is asymmetrically bi‐phasic and peaked. It is predicted that maternal manipulation of offspring SMR would generate fitness benefits through bet‐hedging against unpredictability in food level and increases in the overall range of velocities that the family of offspring can occupy and thrive in.  相似文献   
46.
浅谈给水排水工程节能节水措施   总被引:1,自引:0,他引:1  
作者针对给排水系统工程特点并依据多年设计实践,总结了几点节能节水措施;阐明了通过减少不必要的浪费,可以达到节约水资源、节约能源的目的。  相似文献   
47.
48.
指出了太阳能吸附式制冷是极具发展前途的绿色环保、节能的制冷技术,为当前制冷技术研究中的热点和焦点。综合介绍了太阳能固体吸附式制冷技术的原理、现状、存在的问题及其解决的措施,并对其应用前景作了分析和展望。  相似文献   
49.
刘蕙兰  张建中 《安徽农业科学》2011,39(36):22457-22460
针对宁夏地区农民传统住宅抗震性差,建筑外围护结构保温性能差,采暖系统能源消耗量大,环境污染严重等问题,提出采用轻钢结构配以轻质保温板材的轻钢结构抗震节能体系,以期为宁夏农村住宅设计提供指导性建议。  相似文献   
50.
本试验旨在研究饲粮代谢能水平对14~17周龄不同性别北京油鸡育肥期生长性能、屠宰性能、肉品质及血清生化指标的影响,为确定北京油鸡适宜饲粮代谢能水平提供依据。本试验严格按照完全随机区组试验设计进行。选取13周龄北京油鸡600只,公母各占1/2,根据体重一致原则随机分为6组,其中3个组均为公鸡,另外3个组均为母鸡,每组5个重复,每个重复20只。3个组分别为低代谢能组(饲粮代谢能水平为12.20 MJ/kg)、中代谢能组(饲粮代谢能水平为12.64 MJ/kg)、高代谢能组(饲粮代谢能水平为13.08 MJ/kg)。预试期1周,正试期4周(14~17周龄)。结果显示:1)高代谢能组公鸡和母鸡的平均日增重显著高于其他2组(P <0.05),且高代谢能组母鸡的料重比显著低于其他2组(P <0.05),饲粮代谢能水平为13.08 MJ/kg时公鸡和母鸡有较好的生长性能。2)公鸡方面,低代谢能组的腿肌率显著高于其他2组(P<0.05);母鸡方面,低代谢能组的全净膛率显著高于高代谢能组(P<0.05),翅膀率显著低于高代谢能组(P <0.05)。低代谢能组公鸡和母鸡的皮脂...  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