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   16910篇
  免费   896篇
  国内免费   1502篇
林业   1408篇
农学   1434篇
基础科学   832篇
  1879篇
综合类   7299篇
农作物   1184篇
水产渔业   749篇
畜牧兽医   2523篇
园艺   1185篇
植物保护   815篇
  2024年   107篇
  2023年   301篇
  2022年   698篇
  2021年   785篇
  2020年   696篇
  2019年   671篇
  2018年   527篇
  2017年   745篇
  2016年   563篇
  2015年   800篇
  2014年   917篇
  2013年   1080篇
  2012年   1374篇
  2011年   1444篇
  2010年   1343篇
  2009年   1203篇
  2008年   1148篇
  2007年   1028篇
  2006年   827篇
  2005年   702篇
  2004年   395篇
  2003年   329篇
  2002年   345篇
  2001年   275篇
  2000年   254篇
  1999年   149篇
  1998年   110篇
  1997年   90篇
  1996年   87篇
  1995年   58篇
  1994年   54篇
  1993年   41篇
  1992年   42篇
  1991年   25篇
  1990年   21篇
  1989年   17篇
  1988年   19篇
  1987年   6篇
  1986年   4篇
  1985年   3篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1981年   5篇
  1969年   1篇
  1964年   1篇
  1962年   2篇
  1959年   1篇
  1956年   8篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
51.
Sanguinarine (SA) and chelerythrine (CHE) are the main active components of the phytogenic livestock feed additive, Sangrovit®. However, little information is available on the pharmacokinetics of Sangrovit® in poultry. The goal of this work was to study the pharmacokinetics of SA, CHE, and their metabolites, dihydrosanguinarine (DHSA) and dihydrochelerythrine (DHCHE), in 10 healthy female broiler chickens following oral (p.o.) administration of Sangrovit® and intravenous (i.v.) administration of a mixture of SA and CHE. The plasma samples were processed using two different simple protein precipitation methods because the parent drugs and metabolites are stable under different pH conditions. The absorption and metabolism of SA following p.o. administration were fast, with half‐life (t1/2) values of 1.05 ± 0.18 hr and 0.83 ± 0.10 hr for SA and DHSA, respectively. The maximum concentration (Cmax) of DHSA (2.49 ± 1.4 μg/L) was higher that of SA (1.89 ± 0.8 μg/L). The area under the concentration vs. time curve (AUC) values for SA and DHSA were 9.92 ± 5.4 and 6.08 ± 3.49 ng/ml hr, respectively. Following i.v. administration, the clearance (CL) of SA was 6.79 ± 0.63 (L·h?1·kg?1) with a t1/2 of 0.34 ± 0.13 hr. The AUC values for DHSA and DHCHE were 7.48 ± 1.05 and 0.52 ± 0.09 (ng/ml hr), respectively. These data suggested that Sangrovit® had low absorption and bioavailability in broiler chickens. The work reported here provides useful information on the pharmacokinetic behavior of Sangrovit® after p.o. and i.v. administration in broiler chickens, which is important for the evaluation of its use in poultry.  相似文献   
52.
A liquid chromatography–tandem mass spectrometry method was developed to confirm the presence of androstenedione-19-oic acid in intact male equine plasma and to show the source of 19-norandrostenedione in equine plasma. Androstenedione-19-oic acid was recovered from acidified plasma by liquid–liquid extraction using methyl tert-butyl ether and separated on an Ace 5 C8 column. A triple quadrupole mass spectrometer was used to detect the analytes in negative electrospray ionization mode. Limits of detection, quantification, and confirmation of the method were 0.1, 0.5, and 1.0 ng/mL, respectively. The linear dynamic range of quantification was 0.5–50 ng/mL. The presence of androstenedione-19-oic acid was confirmed in all plasma samples obtained from intact male horses but not those from gelded and female horses; the average concentration was 3.1 ± 1.6 ng/mL, suggesting androstenedione-19-oic acid is an endogenous compound only in intact male horse plasma samples. The conversion of androstenedione-19-oic acid to 19-norandrostenedione in equine plasma was demonstrated by spiking androstenedione-19-oic acid into blank plasma and monitoring the generation of 19-norandrostenedione and its increase in concentration during storage. Results indicated that androstenedione-19-oic acid was readily converted into 19-norandrostenedione; the higher the storage temperature, the faster the conversion. The conversion was not affected by the types of plasma samples collected from gelded and female horses or by anticoagulants used in blood collection to harvest plasma. Compared with other matrices such as water, methanol, and phosphate-buffered saline, the conversion of androstenedione-19-oic to 19-norandrostenedione in equine plasma was faster, suggesting that there is an unknown factor(s) in equine plasma that enhances the conversion.  相似文献   
53.
This study was conducted to investigate the pattern of DNA methylation in pronuclearstage mouse embryos derived from vitrified-warmed oocytes.Mouse oocytes at metaphase Ⅱ (MⅡ) stage of meiosis were all...  相似文献   
54.
Peripartal cows often experience negative energy balance, and are therefore prone to suffering from metabolic diseases such as hyperketonemia, which causes financial losses in dairy farms. This study aimed to investigate the effect of green tea polyphenol (GTP) supplementation during the periparturient period on production performance, oxidative stress and immunometabolism in dairy cows with hyperketonemia. One hundred Holstein cows were assigned to GTP (0.2 g/kg DM; n = 50) or control (without GTP; n = 50) group based on body weight, previous milk yield, and parity on d 15 before expected parturition. Subsequently, 10 cows with hyperketonemia were selected from each group, according to blood β-hydroxybutyric acid (BHBA) concentration between 1.2 and 2.9 mmol/L from 2 to 3 d postpartum. All cows were fed a close-up diet and a lactation diet with or without GTP supply from 15 d prepartum until 30 d postpartum. Milk and blood samples were obtained from 20 cows selected with hyperketonemia on 10, 20, and 30 d postpartum. Compared with control cows, greater milk yield and lower somatic cell count were observed in GTP cows. The GTP group had lower concentrations of BHBA, free fatty acids, cholesterol, triglyceride, reactive oxygen species, malondialdehyde, and hydrogen peroxide, greater concentrations of glucose, lower activities of aspartate aminotransferase, alanine aminotransferase, and glutamyl transpeptidase, alongside greater activities of superoxide dismutase, glutathione peroxidase, and total antioxidant capacity. Additionally, GTP supplementation up-regulated concentrations of interleukin-6 and interleukin-10, but down-regulated concentrations of tumor necrosis factor-α, interleukin-1β, interleukin-2, interleukin-8, and interferon-γ in plasma. Greater concentrations of plasma immunoglobulin G were also detected in the GTP group. Overall, the data suggested that GTP supplementation from 15 d prepartum to 30 d postpartum improved the milk yield and health status in cows with hyperketonemia during early lactation.  相似文献   
55.
邢颖  董瑜  杨艳萍 《中国饲料》2019,(19):114-119
本研究围绕苜蓿种植、加工、利用等产业链上的相关技术进行国际专利态势分析,研判苜蓿产业技术的研发态势,为促进我国饲草料研发提供参考。研究采用文献计量方法,重点针对主要技术研发领域、研发热点及重要国家、机构的研发产出和布局开展深入分析。分析表明,从20世纪90年代中期开始,苜蓿产业技术专利产出快速增加;其中,育种技术的专利申请数量及核心专利数量最多,转基因相关技术是热点研发主题;美国和中国专利数量领先,美国主要布局在育种、病虫草害防控和收获加工工艺与设备领域,中国主要布局在饲料与饲养、肥料和栽培农艺领域;重要专利申请机构主要来自美国、德国和中国。大型农业跨国公司是最主要的专利申请主体。育种、病虫草害防控和收获加工工艺与设备等领域的专利基本由大型跨国公司把控,绝大多数核心专利也基本来自大型跨国公司。研究表明,我国苜蓿领域专利研发发展迅速,但专利技术水平和专利研发布局仍有提高优化空间,应大力推动核心技术领域的研发。  相似文献   
56.
A cluster of Chlamydia psittaci (C. psittaci) cases was reported in Zhejiang Province, China, 2019. This study evaluates the extent of the outbreak and determines the source of infection. Real-time PCR and sequencing of the ompA gene of C. psittaci were performed to identify the cases, the domesticated poultry and close contacts. The index patient was a 76-year-old woman with chronic vertigo, and Case 2 was a 64-year-old female farmer with herpes zoster. Both women bought psittaci-infected chickens or ducks from the same mobile street vendor and raised them for 10 days and 23 days before fever onset. There were no direct contact between the two women. C. psittaci test was positive for the two patients, one sick chicken, three healthy ducks and the vendor's chicken cage. Phylogenetic analysis showed that all seven C. psittaci positive samples carried identical ompA genotype A of C. psittaci. Of all of the patients' 148 close contacts, none tested positive for C. psittaci, or developed acute respiratory symptoms. Both patients were discharged after a 4-week hospital stay. In conclusion, the source of this cluster was the poultry infected with C. psittaci, which occasionally cause infections in farmers, but inter-human transmission seems unlikely.  相似文献   
57.
通过对仙游县2014年秋季猪O型口蹄疫免疫抗体检测,了解和掌握仙游县猪口蹄疫免疫效果,以更好地指导今后动物疫病防控工作。  相似文献   
58.
鸡肝脏交感传入神经元的定位研究   总被引:1,自引:0,他引:1  
用霍乱毒素结合辣根过氧化物酶(CT-HRP)逆行追踪法,研究了支配家禽肝脏的交感传入神经元定位。选用体重1.5 kg~2.5 kg的成年母鸡7只,将CT-HRP溶液注入肝门区,动物存活3 d~4 d后,经左心室灌流固定,取胸、腰和荐段各脊神经节,制成50μm的连续冰冻切片,TMB法呈色反应,置明视野显微镜下观察统计。结果发现,支配鸡肝脏的交感传入神经元胞体位于T2~T7脊神经节,其峰值位于T5、T6脊神经节。说明支配鸡肝脏的交感传入神经元胞体仅位于胸段脊神经节。  相似文献   
59.
蚕蛹油微胶囊的制备   总被引:3,自引:0,他引:3  
为了改善蚕蛹油的加工性能和延长其保质期,以大豆蛋白和β-环状糊精为壁材,采用喷雾干燥法制备蚕蛹油微胶囊。依据蚕蛹油微胶囊乳状液的稳定性检测指标,确定壁材大豆蛋白和β-环状糊精的质量比为1∶1。通过正交试验确定制备蚕蛹油微胶囊的最佳工艺条件为:芯材(蚕蛹油)与壁材的质量比为1∶2,乳状液中固形物的质量分数为20%,均质压力25MPa,喷雾干燥的进风温度190℃。在此工艺条件下制备蚕蛹油微胶囊的包埋率为91.2%。  相似文献   
60.

Objects:  

This study aimed to investigate the immunoprotection of the recombinant Eg.myophilin (rEg.myophilin) and tentatively analyze mechanism of this protection.  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