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   235842篇
  免费   14378篇
  国内免费   658篇
林业   23334篇
农学   13957篇
基础科学   2945篇
  42084篇
综合类   18527篇
农作物   17178篇
水产渔业   16401篇
畜牧兽医   86869篇
园艺   6318篇
植物保护   23265篇
  2021年   2463篇
  2020年   2876篇
  2019年   3666篇
  2018年   3915篇
  2017年   4242篇
  2016年   4716篇
  2015年   4291篇
  2014年   5640篇
  2013年   16217篇
  2012年   5858篇
  2011年   7729篇
  2010年   7199篇
  2009年   7804篇
  2008年   7117篇
  2007年   6186篇
  2006年   6821篇
  2005年   6032篇
  2004年   5954篇
  2003年   5664篇
  2002年   4993篇
  2001年   5441篇
  2000年   5198篇
  1999年   4963篇
  1998年   4086篇
  1997年   4133篇
  1996年   3880篇
  1995年   4431篇
  1994年   3792篇
  1993年   3488篇
  1992年   3913篇
  1991年   4105篇
  1990年   3784篇
  1989年   3667篇
  1988年   3276篇
  1987年   3367篇
  1986年   3185篇
  1985年   3556篇
  1984年   3385篇
  1983年   3219篇
  1982年   2705篇
  1981年   2642篇
  1980年   2622篇
  1979年   2811篇
  1978年   2592篇
  1977年   2432篇
  1976年   2284篇
  1975年   2079篇
  1974年   2162篇
  1973年   2110篇
  1972年   1846篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
1. The effects of feeding two fats with different degrees of saturation on skin tearing, carcase quality and body fat composition were examined in male and female chickens.

2. No differences in growth or efficiency of food utilisation were apparent on feeding the more saturated fat. Skin tearing was slightly reduced and carcase quality slightly improved on feeding the more saturated fat for 28 d.

3. Decreases in linoleic acid content in intra‐abdominal fat were apparent after 14 d feeding the diet containing saturated fat. These decreases were greater after feeding the saturated fat for 28 d.  相似文献   

992.
1. This article addresses the current and future role of artificial insemination (AI) in the broiler industry.

2. The application and success of AI programmes in commercial broiler breeder operations are largely dependent on efficient cage management (nutrition, lighting, environment, health programmes) of both males and females.

3. Artificial insemination will remain a viable alternative for the broiler industry, which competes within the economic constraints of least‐cost production.  相似文献   

993.
1. The effect of early exposure of heavy breed (HB) chicks to an anti‐oestrogen (tamoxifen—TAM) on later adiposity was studied.

2. TAM administration at the embryonic stage, but not at the day of hatching, reduced adiposity in females but not in males, at 8 to 9 weeks of age. This reduction in adiposity in females minimised or even alleviated the excess of fat in females compared to males.  相似文献   

994.
1. Some computer programs for least‐cost diet formulation include a facility for allowing variable diet density. A commonly used approach in such programs has been criticised for not maintaining nutrient proportions.

2. One proposed method of ensuring proportionality among nutrients involves numerous calculations during matrix construction, hampering matrix interpretation and revision.

3. An alternative, more convenient approach is presented and discussed.  相似文献   

995.
Fasted Brazilian squirrel monkeys (BrSMs) exhibited slightly higher serum bilirubin levels (0.30±0.05 mg/dl) than others in the fed state (0.13±0.01). The mean liver weight was 50% lower following a 22 h fast. The rate of bile flow was unaffected by fasting and averaged 13.8 l/min/kg and 47.5 l/min/100g liver in six BrSMs. No significant difference in mean bilirubin excretion/min was observed on a body weight basis following fasting. When the mean rate of bilirubin excretion was calculated as a function of liver weight, a two-fold higher rate was present in fasted monkeys, but only at the p=0.06 level of statistical significance. From data collected in this and earlier studies, it would appear that BrSMs represent the best animals studied to date to serve as experimental controls in comparative studies with Bovilian squirrel monkeys which exhibit a Gilbert-like syndrome.  相似文献   
996.
Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) cocentrations in milk and plasma samples from healthy and mastitic cows were determined by radioi-immunoassay and compared with prostaglandins (PGE2, PGF2 and thromboxane B2 [TXB2]), phospholipids and other relevant parameters in milk and blood. The concentrations of cAMP were about five times higher in plasma (p<0.01) than in milk, whereas the cGMP concentration in milk was three times higher (p<0.01) than that in plasma in both healthy and diseased animals. In mastitic milk, the cAMP and cGMP concentrations were 19% and 65% and in blood plasma 13% and 84% higher respectively than in healthy animals. In milk, cyclic nucleotide concentrations correlated with the markedly elevated cell count and also with the prostaglandin concentration and pH. In blood, cAMP correlated positively with phospholipids and cGMP with reduced glutathione (GSH). These changes are considered to be important in the disease process and, in particular, the increase in cGMP deserves further study.  相似文献   
997.
Randomized placebo-controlled crossover studies were carried out in dogs to evaluate how two non-steroidal anti-inflammatory drugs (NSAID) might modulate an acute post-traumatic inflammatory reaction. Two "identical" surgical interventions were performed on the forelimbs of each animal with an interval of 28 days, to enable a paired comparison of the inflammatory signs and the wound/bone healing processes. At one operation 8 dogs received 300 mg phenylbutazone twice daily for 8 days starting on the day before surgery, and at the other operation matching placebo tablets were given. In a similar placebo-controlled trial another group of 8 dogs received 5 mg indomethacin twice daily. With phenylbutazone the post-operative swelling was not significantly reduced compared to placebo, but there was less pain and limping. With indomethacin the swelling was somewhat reduced, but there was no consistent difference to placebo in the pain and limping assessments. None of the drugs appeared to distinctly effect the wound or fracture healing, as evaluated by clinical inspection, comparison of radiographs and comparison of bone sections from the sites of surgery. It proved difficult to select an appropriate dosage of indomethacin due to its high potential to induce GI ulceration and bleeding in dogs. In this experimental surgical model with an acute inflammation, neither phenylbutazone nor indomethacin showed impressive anti-inflammatory or analgesic properties. In the same model paracetamol has proved to significantly and more efficiently, reduce both swelling and pain without any noticeable adverse effects, and appears to be a better alternative than the two presently tested NSAID.  相似文献   
998.
999.
1000.
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