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   134168篇
  免费   19660篇
  国内免费   31250篇
林业   16017篇
农学   18190篇
基础科学   13522篇
  40193篇
综合类   48829篇
农作物   9413篇
水产渔业   8204篇
畜牧兽医   16844篇
园艺   4132篇
植物保护   9734篇
  2024年   1079篇
  2023年   1660篇
  2022年   3020篇
  2021年   3793篇
  2020年   5072篇
  2019年   8125篇
  2018年   7224篇
  2017年   8526篇
  2016年   9018篇
  2015年   9675篇
  2014年   8900篇
  2013年   9963篇
  2012年   10331篇
  2011年   9928篇
  2010年   8805篇
  2009年   8064篇
  2008年   6993篇
  2007年   7112篇
  2006年   6726篇
  2005年   5946篇
  2004年   3982篇
  2003年   3553篇
  2002年   2966篇
  2001年   2784篇
  2000年   2828篇
  1999年   3105篇
  1998年   2967篇
  1997年   2675篇
  1996年   2400篇
  1995年   2395篇
  1994年   2236篇
  1993年   1915篇
  1992年   1763篇
  1991年   1492篇
  1990年   1217篇
  1989年   1102篇
  1988年   913篇
  1987年   611篇
  1986年   528篇
  1985年   281篇
  1984年   251篇
  1983年   229篇
  1982年   224篇
  1981年   259篇
  1980年   204篇
  1979年   160篇
  1978年   136篇
  1975年   111篇
  1965年   139篇
  1964年   147篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
中药抗炎机理研究进展   总被引:1,自引:1,他引:1  
中药对各种类型的炎症有不同程度的抑制效应,主要从调节下丘脑-垂体-肾上腺皮质轴功能,干扰花生四烯酸代谢,对炎症介质的作用,抑制白细胞趋化、移动和活化,抑制氧自由基的产生,影响细胞内第二信使以及抗血栓形成等方面抑制炎症。  相似文献   
992.
Along with other developed countries, Canada is interested in adopting the gamma interferon (IFN-γ) assay to test for bovine tuberculosis (TB). This study compared results of using the IFN-γ assay in a large number of field-tested cattle in Manitoba, some previously tested with a caudal fold test (CFT) only, and others injected with tuberculins for both a CFT and a comparative cervical test (CCT). Parallel testing further compared the IFN-γ assay and CCT results with the confirmed TB status of the animal (culture, histopathologic examination, polymerase chain reaction). Results from IFN-γ assays did not differ following the CFT versus CFT and CCT injections. Parallel testing demonstrated an apparent higher prevalence of tuberculosis for the IFN-γ assay versus CCT, which will assist in earlier removal of exposed animals and, ultimately, prevent populations from becoming infected.  相似文献   
993.
孕牛血清中早孕因子的分离纯化   总被引:2,自引:0,他引:2  
采用DEAE-Sepharose(DEAE-琼脂糖凝胶)、CM-Sepharose(CM-琼脂糖凝胶)等离子交换层析、抗孕牛全血清IgG-Sepharose 4B亲和层析等技术,分离纯化妊娠4-5个月健康孕牛全血清中的早孕因子(EPF),用玫瑰花环抑制实验对各阶段产物EPF活性进行检测。结果表明,经层析过柱后的CM-ⅡA提取物有EPF活性。经SDS-PAGE银染显色证实它含有分子量为21、67、80KD的蛋白,实验结果支持21KD的多肽为主要EPF活性物成分。同时实验表明了亲和层析对进一步纯化EPF是可行的。  相似文献   
994.
本研究针对鱼台县疑似患猪传染性胃肠炎的30~45日龄仔猪,通过临床症状、病理剖检和猪传染性胃肠炎病毒抗体检测ELISA诊断试剂盒确诊为猪传染性胃肠炎。随机抽取四圈57头患猪,按圈分成4组,分别用黄芪多糖-紫锥菊注射液+复方硫酸安普霉素注射液穴位注射、黄藤素注射液+氟苯尼考注射液、黄芪多糖注射液+烟酸诺氟沙星溶液、利巴韦林注射液+硫酸庆大霉素注射液治疗。试验结果表明:黄芪多糖-紫锥菊注射液+复方硫酸安普霉素注射液穴位注射的组方在该地区的治疗效果最好,其次是黄藤素注射液+氟苯尼考注射液的组方、黄芪多糖注射液+烟酸诺氟沙星溶液组方,利巴韦林注射液+硫酸庆大霉素注射液的组方的效果最差。  相似文献   
995.
Four goats (30.1 ± 1.3 kg) with common bile duct re‐entrant catheter and duodenal catheter were used to evaluate the effects of duodenal leucine infusion on pancreatic exocrine secretion and plasma parameters with two 4 × 4 Latin square design experiments. In the long‐term infusion experiment, goats were fed twice daily [700 g/day, dry matter (DM) basis] at 8:00 and 18:00 hours and were duodenally infused with 0, 3, 6, 9 g/day leucine for 14 days. Pancreatic juice and jugular blood samples were collected over 1‐h intervals for 6 h daily from d 11 to 14 days to encompass a 24‐h day. In the short‐term experiment, goats were infused leucine for 10 h continuously at the same infusion rate with Experiment 1 after feed deprivation for 24 h repeated every 10 days. Pancreatic juice and blood samples were collected at 0, 1, 2, 4, 6, 8 and 10 h of infusion. The results showed that the long‐term leucine infusion did not affect pancreatic juice secretion, protein output, trypsin and lipase secretion and plasma insulin concentration, but linearly increased α‐amylase secretion. No changes in pancreatic protein and lipase secretion were observed in the short‐term infusion. Pancreatic juice and α‐amylase secretion responded quadratically, with the greatest values observed in the 3 and 6 g/day leucine respectively. Trypsin secretion linearly decreased, while plasma insulin concentration increased linearly with increased leucine infusion. The results demonstrated that duodenal leucine infusion dose and time dependently regulated pancreatic enzyme secretion not associated with the change in plasma insulin concentration.  相似文献   
996.
In order to assess the survival of lactic acid bacteria (LAB) in whole crop maize silage in the gut of dairy cows, one representative silage sample and three different feces samples were collected from dairy cows on three dairy farms in Hua Bei, China and three dairy farms in Kyushu, Japan. The composition of the bacterial community was examined by denaturing gradient gel electrophoresis and quantitative polymerase chain reaction. Lactobacillus acetotolerans was detected in all bunker‐made maize silage samples, regardless of the dairy farm or sampling region from which they were sourced. A total of eight LAB species were detected in the maize silage samples, of which three (L. acetotolerans, L. pontis and L. casei) appeared to survive digestion. The populations of L. acetotolerans in silage and feces were 106–7 and 103–4 copies/g, respectively, indicating that, even for the LAB species showing potential survival in the gut, competition in this niche may be harsh and the population may substantially decrease during the digestion process. It may be difficult for silage LAB to survive in the gut of silage‐fed dairy cows, because marked decrease in population can take place during the digestion process, even for surviving species.  相似文献   
997.
998.
Feng, Q., Wu, G. H., Liang, T. M., Ji, H. Y., Jiang, X. J., Gu, W., Wang, W. Pharmacokinetics of oxytetracycline in hemolymph from the Chinese mitten crab, Eriocheir sinensis. J. vet. Pharmacol. Therap. 34 , 51–57. The purpose of this study was to investigate the hemolymph kinetics and depuration time of oxytetracycline following intramuscular administration at doses of 2, 8 and 40 mg/kg body weight, respectively. The concentration of OTC in hemolymph was assayed using solid phase extraction and high performance liquid chromatography. The elimination half‐life of the terminal part of the elimination phase (t1/2β) ranged from 87.9 to 114.3 h. The total body clearance (CLb) was 0.0430 L/kg/h at the lower dose, 0.0123 L/kg/h at the medium dose and 0.0013 L/kg/h at the higher dose. The apparent volume of the central compartment (Vc) was found to be 1.383, 0.699 and 0.143 L/kg respectively. The depuration time for each dose was 13.6, 29.6 and 57.6 days, respectively. Results from the present study suggest that the 40 mg/kg dose might have the best therapeutic efficacy following intramuscular administration.  相似文献   
999.
为评估湖南省某生猪批发市场猪群疫病的发生风险,找出可能的风险因素,便于提出针对性预防措施,采用自行设计的调查问卷,结合访谈和现场调查,对27户经营户进行了调查,并将调查结果和调运数据相结合进行了疫病传播风险定性评估。结果显示:该市场疫病传入的可能性"高",内部传播的可能性"中等",疫病传出的可能性"高"。生猪调运频次多、数量大,经纪人行为复杂,运输车辆清洗消毒不彻底是可能的风险因素。评估结果提示,应尽量减少经纪人行为影响,重点加强对运输车辆的清洗消毒。  相似文献   
1000.
王庆丰  倪成才  骆国民 《山东饲料》2013,(35):108-109,164
本研究的目的在于研究如何用SAS的proc mixed过程拟合线性代数差分模型。所用数据来源于148个集约经营火炬松人工林。直接拟合了一个胸高断面积的收获模型,而非代数差分生长模型。模型拟合过程如下:i).同时确定随林分变化的参数和最优拟合的方差结构模型;ii).依据AIC、BIC和极大似然比检验化简期望模型;iii).用代数差分法将拟合的收获模型转化为代数差分生长模型。  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