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   188243篇
  免费   10428篇
  国内免费   862篇
林业   7812篇
农学   6090篇
基础科学   1407篇
  23917篇
综合类   33664篇
农作物   7499篇
水产渔业   9249篇
畜牧兽医   94925篇
园艺   2690篇
植物保护   12280篇
  2020年   1725篇
  2019年   2066篇
  2018年   2877篇
  2017年   3287篇
  2016年   2953篇
  2015年   2623篇
  2014年   3197篇
  2013年   7300篇
  2012年   5955篇
  2011年   7360篇
  2010年   4873篇
  2009年   4838篇
  2008年   6961篇
  2007年   6615篇
  2006年   6090篇
  2005年   5730篇
  2004年   5322篇
  2003年   5455篇
  2002年   4942篇
  2001年   5659篇
  2000年   5768篇
  1999年   4536篇
  1998年   1983篇
  1997年   1866篇
  1996年   1734篇
  1995年   2027篇
  1994年   1779篇
  1993年   1706篇
  1992年   3564篇
  1991年   3827篇
  1990年   3709篇
  1989年   3663篇
  1988年   3347篇
  1987年   3381篇
  1986年   3481篇
  1985年   3291篇
  1984年   2754篇
  1983年   2385篇
  1979年   2489篇
  1978年   2002篇
  1977年   1650篇
  1976年   1708篇
  1975年   1808篇
  1974年   2234篇
  1973年   2225篇
  1972年   2108篇
  1971年   1954篇
  1970年   1915篇
  1969年   1901篇
  1967年   1660篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Individual antigens of goats   总被引:1,自引:0,他引:1  
  相似文献   
102.
103.
Seven foci of pain (trigger points) were identified in the triceps brachii, infraspinatus, adductor-pectineus, peroneus longus, gluteus medius, ileocostorum lumborum, and quadriceps femoris muscles in 48 lame dogs. The dogs had been lame for 1 day to 150 weeks (mean, 24 weeks). Thirty-one dogs had been treated unsuccessfully with corticosteroids, nonsteroidal anti-inflammatory drugs, analgesics, or acupuncture. Palpating the trigger points induced severe pain. Treatment consisted of weekly stimulation of the trigger points by needling or injection of a local anesthetic. The mean treatment period was 2.8 weeks. Excellent results and complete recovery were observed in 34 dogs (60%).  相似文献   
104.
Samples of rapeseed from three Italian growing environments (Bologna, Perugia and Palermo) were analysed for glucose content and dry weight of 1000 seeds every three or four days starting from the end of flowering until complete ripening. In addition, the content of oil, soluble and total proteins, glucosinolates and myrosinase activity was determined in samples of mature seeds. The cultivars used were jet Neuf and Lingot (type 0) and Tandem, Jade and Santana (type 00). From the results it emerged that the point of intersection of the two branches of the linear regression plots for different glucose-consumption kinetics found during seed filling, in addition to being strongly affected by the climate of the test environment, is correlated with quantitative and qualitative production, independently of the genotype.  相似文献   
105.
106.
The effects of lipopolysaccharide ( Escherichia coli , O55:B5), administered 18 h after ovulation in the second oestrus after weaning on the hormonal profiles in 14 Swedish cross-bred (Landrace × Yorkshire) multiparous sows were studied. The endotoxin group (E-group) sows were administered with 300 ng/kg of lipopolysaccharide (LPS) whereas the control group (C-group) sows were administered 5 ml of saline intravenously via an indwelling jugular cannula. Blood samples for hormonal analyses were collected from all sows until slaughter. In the E-group, progesterone, cortisol and prostaglandin F metabolite levels increased significantly (p < 0.05) following LPS compared with the C-group. It can be concluded from this study that apart from elevating cortisol and prostaglandin F metabolite, LPS also elevates progesterone levels.  相似文献   
107.
108.
Canine thyroglobulin (cTg) has been isolated and purified. It has similar electrophoretic patterns as Tg from other mammalian species. The main fraction had a MW of 660,000, whereas also fractions of a MW of approximately 1,300,000 (dimer) and 330,000 (subunit) were present. The iodine content was 0.8 to 1.0 % (w/w). cTg did not cross-react with antibodies against human Tg to a degree that would allow the use of a radioimmunoassay for human Tg for the determination of cTg in serum or plasma. Therefore a polyclonal antiserum was raised against cTg and a homologous radioimmunoassay was developed, which was sensitive (0.4 μg/l) and specific (cross-reactivity in cTg assay of human Tg, goat Tg, T4, T3, and DIT < 0.01 %).

Plasma Tg levels in normal dogs of both sexes and aged 3–15 years amounted to 192 ± 73 μg/l (mean ± SD, n=30). There was no relation between plasma Tg and T4 levels.  相似文献   

109.
110.
Abstract. The repeated application of pig slurry to agricultural soils may result in an accumulation of salts and a risk of aquifer pollution due to nitrate leaching and salinization. Under Mediterranean conditions, a field experiment on a sandy loam soil (Typic Xerofluvent) was performed with maize (Zea mays) in 1998, 1999 and 2001 to study the effects of applying optimal (P1) and excessive rates (P3) of pig slurry on soil salinization, nitrate leaching and groundwater pollution. The rate of pig slurry was established considering the optimal N rate for maize in this soil (170, 162 and 176 kg N ha?1 for 1998, 1999 and 2001, respectively). Pig slurry treatments were compared to an optimal N rate supplied as urea (U) and a control treatment without N fertilizer (P0). The composition of the slurries showed great variability between years. Mean NO3? leaching losses from 1998 to 2001 were 329, 215, 173 and 78 kg N ha?1 for P3, P1, U and P0 treatments, respectively. The amount of total dissolved salts (TDS) added to the soil in slurry application between 1998 and 2001 was 2019 kg TDS ha?1 for the P1 treatment and 6058 kg TDS ha?1 for the P3 treatment. As a consequence, the electrical conductivity (EC) of the slurry‐treated soils was greater than that of the control soil. The EC correlated significantly with the sodium concentration of the soil solution. Over the entire experimental period, 2653, 2202 and 2110 kg Na ha?1 entered the aquifer from the P3, P1 and P0 treatments, respectively. The P3 treatment did not significantly increase grain production in 1999 and 2001 compared with that achieved with the optimal N rate treatment (P1). This behaviour shows the importance of establishing application guidelines for pig slurry that will reduce the risk of soil and groundwater pollution.  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