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   4169篇
  免费   86篇
  国内免费   114篇
林业   321篇
农学   269篇
基础科学   233篇
  574篇
综合类   1547篇
农作物   217篇
水产渔业   250篇
畜牧兽医   510篇
园艺   334篇
植物保护   114篇
  2024年   1篇
  2023年   31篇
  2022年   37篇
  2021年   33篇
  2020年   31篇
  2019年   29篇
  2018年   33篇
  2017年   46篇
  2016年   73篇
  2015年   60篇
  2014年   641篇
  2013年   463篇
  2012年   454篇
  2011年   569篇
  2010年   601篇
  2009年   496篇
  2008年   211篇
  2007年   69篇
  2006年   33篇
  2005年   31篇
  2004年   39篇
  2003年   32篇
  2002年   22篇
  2001年   27篇
  2000年   53篇
  1999年   33篇
  1998年   20篇
  1997年   24篇
  1996年   21篇
  1995年   30篇
  1994年   13篇
  1993年   12篇
  1992年   10篇
  1991年   13篇
  1990年   9篇
  1989年   11篇
  1988年   3篇
  1987年   8篇
  1986年   6篇
  1985年   3篇
  1984年   4篇
  1983年   2篇
  1982年   4篇
  1981年   9篇
  1980年   4篇
  1979年   6篇
  1978年   2篇
  1977年   2篇
  1955年   4篇
  1944年   1篇
排序方式: 共有4369条查询结果,搜索用时 31 毫秒
11.
为了确定秃疮花水溶性外用制剂的临床应用剂量标准,试验用甘肃省畜牧兽医研究所研制的秃疮花水溶性外用制剂,以Reed-Muench法进行了体外抗病毒试验。试验结果表明秃疮花水溶性外用制剂对GPV的IC50=2-6.5倍个外用制剂试验单位(8.8mg/mL外用制剂干物质);对CPDV的IC50=2-7.2倍个外用制剂试验单位(5.4mg/mL外用制剂干物质)。这说明秃疮花水溶性外用制剂对GPV和CPDV有一定的抑制功能。  相似文献   
12.
胰岛素样生长因子Ⅰ(IGF-Ⅰ)是胰岛素类激素家族中的成员之一,是一种在分子结构上与胰岛素类似的多肽蛋白物质.IGF-I在人体及动物体内具有极其重要并且丰富的生物学功能,如促生长、促分化、参与糖代谢、蛋白质代谢和脂肪代谢等,并对消化系统、泌乳及生殖有一定的影响.文章就IGF-I的来源,分子结构及生物学功能作一简单概述.  相似文献   
13.
The objective of this study was to develop equations for estimating ileal digestible crude protein (CP) and metabolizable energy (ME) contents of meat meal (MM) and meat and bone meal (MBM) as feed ingredients for pigs based on in vitro assays. Test ingredients were 4 sources of MM and 3 sources of MBM. Ash and CP contents of the ingredients ranged from 3.8% to 33.1% and 46.8% to 82.9% (as-is basis), respectively. In vitro ileal disappearance (IVID) of CP was determined and ileal digestible CP content was calculated by multiplying CP content by IVID of CP. In vitro total tract disappearance (IVTTD) of dry matter (DM) was determined and ME was calculated using gross energy, CP contents, and IVTTD of DM. The IVID of CP and IVTTD of DM ranged from 77.2% to 88.7% and from 82.7% to 92.4%, respectively. Calculated ileal digestible CP and ME contents ranged from 37.8% to 73.5% DM and 2,405 to 3,905 kcal/kg DM, respectively. Ash contents were negatively correlated (P < 0.001) with CP (r = −0.99), in vitro ileal digestible CP (r = −0.97), gross energy (r = −1.00), in vitro digestible energy (r = −0.97), and adjusted ME (r = −0.97). The most fitting equations for ileal digestible CP and adjusted ME were: ileal digestible CP (% DM) = 11.91 − 0.90 × Ash (% DM) + 0.74 × IVID of CP (%) (R2 = 0.99) and adjusted ME (kcal/kg DM) = 130.85 − 50.90 × ash (% DM) + 47.06 × IVTTD of DM (%) (R2 = 0.99). To validate the accuracy of the prediction equations for ME, mean bias and linear bias were determined using a regression analysis. Calculated ME values of MM and MBM were in a good agreement with data obtained from animal experiments based on a statistically insignificant bias in the models. In conclusion, ME concentrations of MM and MBM as swine feed ingredients can be calculated using ash concentration and in vitro disappearance of dry matter.  相似文献   
14.
以Visual Basic 6.0这种高级语言开发多要素系统为例,主要介绍在处理具有相关性的各要素组成多要素系统时需要注意的问题及其解决方法,同时阐述了系统相关ActiveX控件的调用及其使用方法。此外,本多要素系统也实现了外部应用程序Microsoft Office对象库Access 2000的引用,同时完成与本多要素系统相关的程序代码。  相似文献   
15.
16.
Gene expression in black tiger prawns (Penaeus monodon) was studied following intra-muscular injection of CMVGal plasmid into the second abdominal segment. We used an in situ staining technique to detect -gal expression in one- and three-month-old injected prawns. We found that only one of the three-month-old prawns expressed the marker gene (2 days after injection), and the site of expression was confined to the sixth abdominal segment away from the injection site. We repeated the experiment on a new batch of three-month-old prawns, but using fluorometric determination technique. This time we found that -gal expression was detected (6/42) at the site of injection after 2, 7, and 14 days. In two other test samples, transgene expression was detected in the sixth abdominal segment only, further confirming the possibility of injected DNA dispersal. The results of the study also suggest that direct gene transfer is a feasible technique in black tiger prawns.  相似文献   
17.
本文利用生物信息学软件分析了鲤(Cyprinus carpio)基因组中同源框基因Hoxa3a与多种鱼类及其它生物的同源性,构建了分子进化树。结果表明:鲤与斑马鱼(Danio rerio)的序列同源性最高为95%,与大西洋鲑(Salmo salar)等四种鱼类的同源性次之为84%,与米氏叶吻银鲛(Callorhinch...  相似文献   
18.
This study was conducted to evaluate the effects of different concentrations of dietary lipids on body composition and liver function in juvenile red drum, Sciaenops ocellatus. Diets were formulated to contain 40% crude protein from solvent-extracted menhaden fish meal and 0, 7, 14 or 21% lipid from menhaden fish oil. The basal diet, without supplemental fish oil, contained lipid at 0.4% of dry weight. The diets were fed to groups of 25 juvenile red drum initially averaging 7.3 ± 0.18 g fish–1 in a recirculating culture system for 8 weeks and weight gain was recorded. After an additional 8 weeks, 16 fish from each treatment were sacrificed and the following measurements were recorded: hepatosomatic index (HSI), intraperitoneal fat (IPF) ratio, and liver -tocopherol, malondialdehyde (MDA) formation, and cytochrome P-4501A activity (measured as 7-ethoxyresorufin O-deethylase (EROD) activity). The activity of alanine and aspartate aminotransferases and concentrations of -tocopherol also were measured in plasma.Weight gain was significantly (p<0.05) affected by dietary lipid concentration, with values ranging from 361% of initial weight for fish fed the basal diet to 527% of initial weight for fish fed the diet containing 7% lipid. The HSI and IPF ratio values also were significantly affected by lipid with the lowest values recorded for fish fed the basal diet and the highest values observed in fish fed the diet containing 21% lipid. Increasing dietary lipid significantly increased oxidative stress as reflected in reduced -tocopherol in liver and plasma and increased MDA formation in the liver, although no overt pathological signs were observed. These findings suggest that lipid concentrations between 7 and 14%, when the diet contains 60 IU vitamin E kg–1, are likely to limit oxidative stress and result in normal physiological responses of red drum.  相似文献   
19.
本研究采用注射可视嵌入性荧光、剪附肢两种手段对不同期别的三疣梭子蟹进行标记,以研究标记的适用性及对个体生长的影响。对不同发育阶段三疣梭子蟹进行两个部位荧光注射,统计蜕壳后可识别率。结果显示,Ⅱ、Ⅲ期幼蟹适合腹面区域注射,Ⅳ期以后幼蟹适合游泳足基节和头胸甲背面的薄膜关节注射;标记后,经过两次蜕壳,识别率在80%以上,但经3次蜕壳后,识别率较低;根据标记组、未标记组生长数据,通过单因素方差分析发现,标记对三疣梭子蟹个体生长无显著性影响。Ⅶ期以后的幼蟹,更适合剪附肢法,该法操作简单、识别率高,对个体生长、存活无显著性影响(P〉0.05)。  相似文献   
20.
虎掌菌酶解提取物抑菌试验研究   总被引:3,自引:0,他引:3  
采用木瓜蛋白酶、纤维素酶对虎掌菌进行酶解提取,并检测提取物对大肠杆菌、金黄色葡萄球菌、酵母菌、青霉菌和黑曲霉的抑菌效果。结果表明,不同提取方法所得粗提物都有不同程度的抑菌效果,提取液对黑曲霉和青霉菌的抑菌效果最明显,对酵母菌抑菌效果最不明显。  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