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   1527篇
  免费   89篇
  国内免费   181篇
林业   116篇
农学   189篇
基础科学   118篇
  170篇
综合类   619篇
农作物   83篇
水产渔业   71篇
畜牧兽医   308篇
园艺   44篇
植物保护   79篇
  2024年   7篇
  2023年   23篇
  2022年   57篇
  2021年   59篇
  2020年   60篇
  2019年   61篇
  2018年   44篇
  2017年   76篇
  2016年   74篇
  2015年   77篇
  2014年   90篇
  2013年   107篇
  2012年   121篇
  2011年   115篇
  2010年   90篇
  2009年   90篇
  2008年   72篇
  2007年   89篇
  2006年   65篇
  2005年   60篇
  2004年   43篇
  2003年   30篇
  2002年   32篇
  2001年   32篇
  2000年   24篇
  1999年   22篇
  1998年   26篇
  1997年   19篇
  1996年   20篇
  1995年   12篇
  1994年   12篇
  1993年   13篇
  1992年   19篇
  1991年   17篇
  1990年   7篇
  1989年   12篇
  1988年   12篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
排序方式: 共有1797条查询结果,搜索用时 296 毫秒
991.
This paper describes a UV detection method for the pesticides aldicarb and carbofuran, and some of their main metabolites, aldicarb-sulfoxide, aldicarb-sulfone and 3-hydroxy-carbofuran, in ground waters. Micellar electrokinetic chromatography (MEKC) with diode-array detection was developed for their determination at 210 nm. The experimental study was performed using sodium dodecyl sulfate (SDS) at a concentration level of 140 mM, and a buffer of borax/HCl 20 mM at pH 8 which gives the best resolution with an analysis time of less than 20 min. Different instrumental parameters such as voltage (23 kV), injection time (12 s) and temperature (25 degrees C) were optimized. The detection limits were in the range 2-7.4 microg glitre(-1) by solid-phase extraction (SPE) with a subsequent evaporation step. Groundwater spiked samples were pre-concentrated off-line with graphite carbon and subsequently analyzed by MEKC with diode-array detection yielding average recoveries between 77 and 97% (n = 4) with RSD between 2-7%.  相似文献   
992.
To establish the relationship between serum levels of three acute phase proteins, haptoglobin (Hp), C-reactive protein (CRP) and serum amyloid A (SAA), and the occurrence and severity of lesions at slaughter, a study was carried out using 70 fattening pigs from a finishing unit. Pigs were divided into three groups: Group 1 (25 pigs with clinical signs of disease), Group 2 (25 apparently healthy pigs with lesions at slaughter) and Group 3 (20 apparently healthy pigs with no lesions at slaughter). Serum levels of CRP, SAA and Hp were significantly higher in pigs with clinical signs of disease than in apparently healthy animals. Additionally, in apparently healthy pigs, serum levels of Hp and CRP were significantly higher in animals with lesions than those without lesions. The extent and severity of lung lesions were related to serum levels of Hp.  相似文献   
993.
采用超高效液相色谱一串联四极杆质谱,电喷雾电离(负离子模式),对肠衣中氯霉素残留量进行定性定量。试样用乙酸乙酯提取后正己烷脱脂,经Oasis HLB固相萃取小柱浓缩净化后,经Waters ACQUITY UPLC^TM BEH C18色谱柱分离,以乙腈和水为流动相进行梯度洗脱。在多反应监测采集模式下以保留时间和离子对(母离子和两个子离子)信息比较进行定性,以母离子和响应值高的子离子进行定量。该法的检出限为0.05μg/kg,定量限为0.1μg/kg。添加水平为0.05—2.0μg/kg时,加标回收率为91%-97%,相对标准偏差小于10%。  相似文献   
994.
BACKGROUND: Serum amyloid A (SAA) is an acute phase protein whose concentration increases in inflammatory, infectious, and neoplastic conditions in animals and human beings. Multicentric lymphoma is a common cancer in dogs, and chemotherapy is indicated to attain long-term survival. However, frequent relapses lead to changes in chemotherapeutic protocols. OBJECTIVES: The aims of this study were to evaluate SAA as a marker for relapse of multicentric lymphoma in dogs and to determine whether chemotherapy induces changes in the concentration of SAA during treatment. METHODS: SAA was measured by an ELISA test in healthy control dogs (n=20), in healthy dogs receiving chemotherapy (n=8), and in dogs with lymphoma (n=20). All dogs receiving chemotherapy were randomly assigned to 2 treatment groups, one receiving cyclophosphamide, vincristine, and prednisone (CVP) and the other receiving vincristine, cyclophosphamide, methotrexate, and L-asparaginase (VCMA) protocols. SAA concentration was determined before chemotherapy at weeks 1-4 in healthy dogs receiving chemotherapy and in dogs with lymphoma, then every 3 weeks for 4 months in healthy dogs, and at relapse and in the sample prior to relapse in dogs with lymphoma. SAA was measured only once in the healthy control dogs. Results were analyzed using repeated measures ANOVA followed by Tukey multiple comparison tests to compare groups and weeks of treatment. RESULTS: Mean SAA concentration was significantly higher in dogs with lymphoma before chemotherapy compared with healthy and chemotherapy control dogs. No increase in SAA concentration was found at relapse. No differences were observed in SAA concentration based on type of chemotherapy protocol. CONCLUSIONS: SAA is not a marker of relapse in dogs with multicentric lymphoma, nor does chemotherapy regimen affect SAA concentration.  相似文献   
995.
Serum amyloid A (SAA) is the major acute phase protein in horses. It is produced during the acute phase response (APR), a nonspecific systemic reaction to any type of tissue injury. In the blood of healthy horses, SAA concentration is very low, but it increases dramatically with inflammation. Due to the short half-life of SAA, changes in its concentration in blood closely reflect the onset of inflammation and, therefore, measurement of SAA useful in the diagnosis and monitoring of disease and response to treatment. Increases in SAA concentration have been described in equine digestive, reproductive and respiratory diseases and following surgical procedures. Moreover, SAA has proven useful for detection of some subclinical pathologies that can disturb training and competing in equine athletes. Increasing availability of diagnostic tests for both laboratory and field use adds to SAA's applicability as a reliable indicator of horses’ health status. This review article presents the current information on changes in SAA concentrations in the blood of healthy and diseased horses, focussing on clinical application of this biomarker.  相似文献   
996.
建立了分散固相萃取结合液相色谱串联质谱法检测牛肉、牛脂肪、牛肝和牛肾等可食性组织中的泰地罗新残留量的方法。取牛组织样品经50%(V/V)乙腈溶液提取,加入无水硫酸镁和氯化钠进行脱水和盐析,正己烷脱脂,高速离心分层后,取适量乙腈层溶液经0.1%(V/V)甲酸稀释后,用酸性氧化铝粉末进行样品净化并以10000 r/min离心取上清液,过0.22μm滤膜后上机测定。使用反相色谱柱进行分离,流动相为0.1%甲酸和乙腈溶液,采用梯度程序进行洗脱,三重四级杆质谱进行定性定量分析。结果表明,方法的最低检测限为5μg/kg,最低定量限为10μg/kg,添加含量在10~1000μg/kg范围内线性关系良好(r0.995),对应添加回收率为60%~110%,RSD10%,表明该方法具有较好的准确度与精密度。  相似文献   
997.
998.
氟苯尼考纳米乳制备及其抑菌效果观察   总被引:1,自引:1,他引:0  
为制备氟苯尼考纳米乳并了解其抑菌效果,本试验进行了处方筛选、物理性质考察、抑菌圈试验,通过测定氟苯尼考在多种油相中的溶解度,确定最佳油相;再以乳化剂-助乳化剂(Smix)体积比Kv值及Smix-油相体积比为考察指标,结合伪三元相图筛选最佳处方组成;利用染色法鉴别纳米乳类型,通过透射电镜观察纳米乳微观形态;通过激光粒度分析仪测定粒度分布、Zeta电位;采用离心及长期试验考察其稳定性;经抑菌圈试验观察氟苯尼考纳米乳对金黄色葡萄球菌、大肠埃希菌、微杆菌、枯草芽孢杆菌的体外抑菌效果。结果显示,橄榄油为最佳油相,EL-40为最佳乳化剂,丙三醇为最佳助乳化剂,优选的Smix体积比Kv值为2.0,Smix-油相体积比为8:2。氟苯尼考纳米乳最佳处方组成为:氟苯尼考120 mg,N,N-二甲基甲酰胺0.1 mL,橄榄油2 mL,EL-40 5.7 mL,丙三醇2.3 mL,水6 mL。氟苯尼考纳米乳为水包油(O/W)型,外观呈球形,大小均匀无黏连,平均粒径28 nm,粒径呈正态分布,Zeta电位为-0.454 mV,经离心试验及长期试验样品稳定,对4种常见菌体外抑菌效果强于同浓度氟苯尼考溶液。本试验结果表明,氟苯尼考纳米乳制备方法简单、可行,且纳米乳稳定,抑菌效果良好,在畜牧养殖中具有潜在应用价值。  相似文献   
999.
复合相变储能保温砂浆在日光温室中的应用效果   总被引:1,自引:3,他引:1  
周莹  王双喜 《农业工程学报》2017,33(20):190-196
为改善日光温室内作物生长的热环境,该文研制了一种适用于日光温室的石膏基石蜡/膨胀珍珠岩复合相变储能保温砂浆,其相变温度为25.6℃,相变潜热为89.8 k J/kg。并将50 mm的复合相变保温砂浆用于砖墙日光温室的后墙作为试验温室,与无相变材料的原砖墙温室(即对照温室)进行对比试验。在试验周期内,试验温室的室内日最低温度比对照温室平均高出1.5℃,最高可达2.4℃;其中,阴天试验温室的室内温度比对照温室平均高1.6℃;晴天试验温室的室内最高温度比对照温室低1.7℃,室内最大温差比对照温室低3.1℃,夜间(17:00-次日8:00)试验温室室温比对照温室平均高2.7℃;多云期间,试验温室的室内最高温比对照温室低1.4℃,最大温差比对照温室低3.5℃,夜间试验温室室温比对照温室平均高2.3℃;在相同栽培管理条件下,生长旺盛期和坐果期,试验温室的黄瓜植株高度比对照温室分别平均高出17.1和24.6 cm,试验温室内黄瓜的单果质量和单株结果数分别为对照温室的1.4倍和1.3倍,单株产量为对照温室的1.8倍。试验结果表明,复合相变储能保温砂浆具有良好的保温和蓄、放热效果,对日光温室内的热环境具有明显的改善效果,使其更适于黄瓜的生长。  相似文献   
1000.
液相色谱-串联质谱法测定水产饲料中喹乙醇残留量   总被引:3,自引:0,他引:3  
为测定水产饲料中喹乙醇的残留量,建立了高效液相色谱-串联质谱的测定方法.水产饲料经5%甲醇溶液提取,HLB固相萃取小柱净化后上机定量检测.采用Zorbax XDB C18色谱柱,并以O.2%乙酸水溶液+甲醇(60+40,体积分数)为流动相,色谱分离后直接进串联质谱器.采用电喷雾正离子,多反应监测模式检测,外标法定量.在1~20 mg/L浓度下具有良好的线性关系,方法的定量限为0.04 mg,/kg,添加浓度在1-20 mg/kg时的回收率为72.2%~98.5%,相对标准偏差小于7.9%.  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