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   4246篇
  免费   333篇
  国内免费   313篇
林业   200篇
农学   215篇
基础科学   204篇
  259篇
综合类   1293篇
农作物   151篇
水产渔业   1316篇
畜牧兽医   941篇
园艺   141篇
植物保护   172篇
  2024年   20篇
  2023年   53篇
  2022年   118篇
  2021年   127篇
  2020年   165篇
  2019年   179篇
  2018年   125篇
  2017年   219篇
  2016年   187篇
  2015年   157篇
  2014年   225篇
  2013年   282篇
  2012年   332篇
  2011年   296篇
  2010年   260篇
  2009年   234篇
  2008年   229篇
  2007年   234篇
  2006年   213篇
  2005年   162篇
  2004年   153篇
  2003年   145篇
  2002年   104篇
  2001年   95篇
  2000年   83篇
  1999年   79篇
  1998年   52篇
  1997年   76篇
  1996年   47篇
  1995年   54篇
  1994年   36篇
  1993年   30篇
  1992年   19篇
  1991年   24篇
  1990年   14篇
  1989年   25篇
  1988年   13篇
  1987年   10篇
  1986年   7篇
  1985年   1篇
  1984年   1篇
  1983年   3篇
  1981年   2篇
  1980年   1篇
  1976年   1篇
排序方式: 共有4892条查询结果,搜索用时 15 毫秒
881.
为研究复合植物提取物对妊娠母猪繁殖性能的影响,试验选取40头妊娠85 d大长二元母猪,随机分为对照组、植物提取物组(1000 mg/kg),每头猪为一个重复,试验期为妊娠85 d至分娩。结果表明:植物提取物组仔猪初生重较对照组提高7.6%(P<0.05),并且植物提取物组高初生重仔猪的比例增加(P<0.01),低初生重仔猪的比例减少(P<0.05)。综上,复合植物提取物可提高仔猪初生重,改善仔猪均匀度,提高母猪的繁殖性能。  相似文献   
882.
[目的]探讨海水胁迫下海带甲醇提取物对豇豆的生长效应。[方法]将海水稀释成7种浓度梯度液培养豇豆种子,用25%海水将海带甲醇提取物分别稀释50、200、800和1200倍后培养豇豆种子,10 d后测定幼苗的各项生长指标。[结果]豇豆成苗率随着海水浓度的增加而下降,25%海水的成苗率为22.22%,确定海水的临界浓度为25%。海带甲醇提取物200倍液对豇豆成苗率的提高最明显,比对照提高64.71%。该提取物50倍液对豇豆的生长效果优于其他浓度,其主根长、总鲜重、根鲜重、叶鲜重、叶绿素a与b含量和叶绿素总量分别比对照提高了23.08%、18.27%、31.89%、44.87%、1.29%、1.43%和1.79%。[结论]在25%海水胁迫下海带甲醇提取物对豇豆幼苗生长具有较明显的作用。  相似文献   
883.
884.
The present study aimed to determine the pharmacokinetic profiles of ceftiofur (as measured by ceftiofur and its active metabolites concentrations) in a small-size dog breed, Peekapoo, following a single intravenous or subcutaneous injection of ceftiofur sodium. The study population comprised of five clinically healthy Peekapoo dogs with an average body weight (BW) of 3.4 kg. Each dog received either intravenous or subcutaneous injection, both at 5 mg/kg BW (calculated as pure ceftiofur). Plasma samples were collected at different time points after the administration. Ceftiofur and its active metabolites were extracted from plasma samples, derivatized, and further quantified by high-performance liquid chromatography. The concentrations versus time data were subjected to noncompartmental analysis to obtain the pharmacokinetic parameters. The terminal half-life (t1/2λz) was calculated as 7.40 ± 0.79 and 7.91 ± 1.53 hr following intravenous and subcutaneous injections, respectively. After intravenous treatment, the total body clearance (Cl) and volume of distribution at steady-state (VSS) were determined as 39.91 ± 4.04 ml hr−1 kg−1 and 345.71 ± 28.66 ml/kg, respectively. After subcutaneous injection, the peak concentration (Cmax; 10.50 ± 0.22 μg/ml) was observed at 3.2 ± 1.1 hr, and the absorption half-life (t1/2ka) and absolute bioavailability (F) were calculated as 0.74 ± 0.23 hr and 91.70%±7.34%, respectively. The pharmacokinetic profiles of ceftiofur and its related metabolites demonstrated their quick and excellent absorption after subcutaneous administration, in addition to poor distribution and slow elimination in Peekapoo dogs. Based on the time of concentration above minimum inhibitory concentration (T > MIC) values calculated here, an intravenous or subcutaneous dose at 5 mg/kg of ceftiofur sodium once every 12 hr is predicted to be effective for treating canine bacteria with a MIC value of ≤4.0 μg/ml.  相似文献   
885.
The Atlantic salmon (Salmo salar) is a freshwater and marine fish of the family Salmonidae, widely farmed in aquaculture facilities in several countries. The salmon are carnivorous, but in aquaculture, alternative foods have been experienced. It is well known that feeding in captivity should cause adaptation and modifications of the morphological characteristics of the oral cavity, especially of tongue; therefore, the aim of this study was to investigate, by light, laser confocal and scanning electron microscopy, the morphological characteristics of the tongue dorsal surface, considering the importance of the correlations between feeding habits and the anatomy of the tongue. Scanning electron microscopy demonstrates the presence of caniniform teeth with oro-aboral orientation surrounded by numerous filiform papillae, single, fused or arranged in row. Oro-aborally, the papillae show an appearance like a rosette and they disappear at level of the root. Light and laser confocal microscopy demonstrates that the mucosa is covered by a non-keratinized stratified pavement epithelium with, in the deepest layer, the presence of a triangular structure whose apex is cranially directed and base facing aborally. In this structure, spindle-shaped cells are present, with a vimentin immunoreactivity, that for their characteristics could be adult mesenchymal stem cells. The obtained data could be useful not only for further studies on the nutrition, but it is interesting the detection of tissues typical of the embryo-fetal phase in the adult specimens tongue, thus giving a basis for studies of potential applications, if any, regarding cell therapies for different clinical indications.  相似文献   
886.
通过最佳注入量设计和岩心不同剩余油饱和度的降压试验研究,认为表面活性剂应用于低渗油藏降压增注,影响作用效果的因素除地层的孔喉特征、合适的表面活性剂等固有因素外,其主要影响因素是储层的剩余油饱和度。  相似文献   
887.
为了探索和验证聚合物分子尺寸与岩石孔喉尺寸的配伍关系,以河南油田东部老油区稀油油田为例,应用数学方法、微孔滤膜过滤方法和动态光散射方法,对开展聚合物驱条件下拟使用的聚合物的分子尺寸进行试验测定,得到了双河油田不同渗透率岩石能够匹配的聚合物分子量。  相似文献   
888.
[目的]研究"乳炎康注射液"对奶牛乳房炎主要致病菌耐药性的消除作用。[方法]观察奶牛乳房炎主要致病菌对氨苄青霉素等5种β-内酰胺类抗生素的耐药性,并通过筛选耐药菌,研究"乳炎康注射液"对其耐药性的消除作用。[结果]奶牛乳房炎主要致病菌对先锋霉素V高敏,对羧苄青霉素比较敏感,对氨苄青霉素、阿莫西林、青霉素G的敏感性低,并且产生了不同程度的耐药性。经"乳炎康注射液"感触后,奶牛乳房炎主要致病菌对β-内酰胺类抗生素的耐药率明显下降,且原来敏感药物的抑菌圈扩大了1.2~2.3 mm。[结论]"乳炎康注射液"对奶牛乳房炎主要致病菌对β-内酰胺类抗生素的耐药性有一定的消除作用。  相似文献   
889.
为了探讨一种以软骨提取物、姜黄、葛根粉和薏苡仁粉为主要组分制成的压片糖果的改善膝骨关节炎临床疗效。该试验采用人体试食试验,通过对比试食压片糖果(试验组)和安慰剂(对照组)两组受试人群在试验前后的视觉模拟评分(visual analogue scale, VAS)、西安大略和麦克马斯特大学骨关节炎指数(WOMAC)、临床症状积分和血清白细胞介素-6(interleukin-6, IL-6)、超敏C反应蛋白(high-sensitivity C reactive protein, hs-CRP)水平等试验结果,发现试验组的VAS评分、WOMAC评分中疼痛、关节僵硬、生理功能评分和总分均在试食结束后显著降低(P < 0.01),明显低于对照组;且临床症状评分中关节疼痛、压痛、晨僵时间、肿胀评分和总评分均得到显著减低(P < 0.01),并呈现出较高的有效率(61.02%),显著高于对照组(有效率15.25%)(P < 0.01);此外,试食后试验组的IL-6水平显著降低(P < 0.05),且试食期间未见不良反应和安全性指标异常。由此可见,该压片糖果具有明显改善膝骨关节炎的疗效,能够缓解膝关节疼痛和肿胀、改善膝关节功能和活动度,控制病情,且可能与调节炎症因子IL-6有关,是一种安全有效改善膝骨关节炎症状的健康食品。  相似文献   
890.
The effects of swine manure extract (SME) as foliar fertilizer (FSME), soil fertilizer (SSME), and both soil and foliar fertilizer (FNSSME) on leaf nitrogen (N) concentration, chlorophyll content, total potassium (K) in plant parts and starch content in the fresh roots, compared to a conventional, chemical fertilizer (CF) were studied in cassava cultivar ‘Hauybong 60’. The results showed that plants on FNSSME had the highest chlorophyll contents and SPAD values at four months after planting (MAP). Cassava plants treated with SSME and FNSSME had highest starch content and was significantly higher than in plants treated with CF and a FSME. There was a strong, positive relationship between the leaf nitrogen concentration and chlorophyll content in cassava at 6 MAP. The results of the study indicated that an application of FNSSME to cassava plants could provide a higher chlorophyll content and higher tuber quality of the plants than those applied with chemical fertilizer.  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