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   4273篇
  免费   192篇
  国内免费   503篇
林业   546篇
农学   619篇
基础科学   352篇
  786篇
综合类   1195篇
农作物   203篇
水产渔业   191篇
畜牧兽医   608篇
园艺   163篇
植物保护   305篇
  2024年   14篇
  2023年   45篇
  2022年   119篇
  2021年   167篇
  2020年   145篇
  2019年   138篇
  2018年   100篇
  2017年   147篇
  2016年   150篇
  2015年   167篇
  2014年   175篇
  2013年   198篇
  2012年   291篇
  2011年   257篇
  2010年   244篇
  2009年   236篇
  2008年   209篇
  2007年   216篇
  2006年   229篇
  2005年   226篇
  2004年   92篇
  2003年   91篇
  2002年   92篇
  2001年   87篇
  2000年   110篇
  1999年   145篇
  1998年   131篇
  1997年   101篇
  1996年   89篇
  1995年   88篇
  1994年   71篇
  1993年   84篇
  1992年   64篇
  1991年   54篇
  1990年   63篇
  1989年   35篇
  1988年   28篇
  1987年   21篇
  1986年   16篇
  1985年   3篇
  1984年   8篇
  1983年   5篇
  1982年   1篇
  1981年   7篇
  1980年   4篇
  1979年   3篇
  1976年   1篇
  1974年   1篇
排序方式: 共有4968条查询结果,搜索用时 15 毫秒
21.
The peroxisome proliferator-activated receptors (PPARs) are the members of superfamily of nuclear hormone receptors. A great number of studies in rodent and human have shown that PPARs were involved in the lipids metabolism. The goal of the current study was to investigate the expression pattern of PPAR genes in various tissues of chicken. The tissue samples (heart, liver, spleen, lung, kidney, stomach, intestine, brain, breast muscle and adipose) were collected from six Arber Acres broilers (8 weeks old, male and female birds are half and half). Semi-quantitative RT-PCR and Northern blot were used to characterize the expression of PPAR-alpha and PPAR-gamma genes in the above tissues. By semi-quantitative RT-PCR, the results showed the expression level of PPAR-alpha gene was higher in brain, lung, kidney, heart and intestine, medium in stomach, liver and adipose than in spleen, and it did not express in breast muscle. The expression level of PPAR-gamma gene was higher in adipose, medium in brain and kidney than in spleen, heart, lung, stomach and intestine, but it did not express in liver and breast muscle. Northern blot results showed that PPAR-alpha gene expressed in heart, liver, kidney and stomach, and the intensity of hybridization signal was the stronger in liver and kidney than in other tissues, however, PPAR-gamma gene only expressed in adipose and kidney tissues. The results of this study showed the profile of PPAR gene expression in the chicken was similar to that in rodent, human and pig. However the expression profile of chicken also have its own specific trait, i.e. compared with mammals, PPAR-alpha gene can not be detected in skeletal muscle and PPAR-gamma gene can be stronger expressed in kidney tissues. This work will provide some basic data for the PPAR genes expression and lipids metabolism of birds.  相似文献   
22.
广东省饲料行业协会第四次会员代表大会的召开,是广东省饲料界的一件喜庆事,也是我们全饲料行业的一件喜庆事。我谨代表全国畜牧总站、中国饲料工业协会表示热烈的祝贺!热烈祝贺通过选举产生的广东省饲料行业协会新一届领导集体!热烈祝贺广东省饲料工业取得的巨大成就!热烈祝贺广东省饲料工业协会取得的出色业绩!热烈祝贺广东饲料行业对养殖业增产增效、对农民增收、对农业和农村经济建设和社会主义新农村建设做出的突出贡献!  相似文献   
23.
本文主要从苏丹红和饲料着色剂的化学结构、作用机理及毒性等方面说明饲料着色剂与苏丹红的天壤之别。  相似文献   
24.
1. An experiment was done under commercial conditions to investigate the physiological effects of isolating broody turkey hens, for 72 h, in sand and wire floored pens on the third, 10th and 16th weeks of production.

2. Hens identified as broody and removed from the flock had higher plasma prolactin concentrations than the laying hens at each of the three experimental stages.

3. Confinement in sand and wire floored pens, induced a decline in plasma prolactin concentrations. This decline probably impeded immediate development of broody behaviour. Alternately, levels of prolactin higher than those of laying hens were again measured 7 and 14 days after treatment during third week but not after the 10 th and 16th week of production.

4. Confinement did not induce consistent changes in luteinising hormone (LH) and progesterone concentrations from one period to an other.

5. An increase in the plasma concentration of D‐(/?)‐hydroxybutyrate was observed in the hens which had an egg present in the oviduct on day 2, 3 and/or 4 of the treatment. Subsequently, a decrease in ovulation rate was observed in the hens with higher concentrations of D‐(β)‐hydroxybutyrate while under treatment, during the 10th week of production.

6. These data confirm that the effectiveness of the traditional methods for broodiness prevention under commercial conditions is related to the induction of a decrease of prolactin.  相似文献   

25.
2018年8月开始,非洲猪瘟在我国快速多点发生,该病是高度接触性传染性疾病,目前无有效的疫苗和药物控制,各大公司和养殖户开始了猪场生物安全体系的升级改造。两年后我国大部分猪场的成功复产,全国生猪出栏量的大幅提升,证明了生物安全措施巨大效力;同时在严格的生物安全措施下创新了精准剔除、快速复产等操作,进一步证明了生物安全措施的有效作用。文章主要介绍猪场生物安全体系中入口(大门)和出口(后门)最为关键防线处的通道设计,方便所有的生物安全操作能够高效落实,切断病原轻易进出猪场的途径。  相似文献   
26.
采用单卵囊分离技术,分离肠艾美尔球虫。根据GenBank中发表的肠艾美尔球虫18SrDNA序列,设计一对引物,建立PCR方法对其基因片段扩增并测序、比对。结果成功分离肠艾美尔球虫,PCR扩增出清晰条带,大小为528bp,最低能检出27个孢子化卵囊。该序列测定结果与Genebank发表的肠艾美尔球虫18SrDNA比对,相似性达98.5%。  相似文献   
27.
Carcasses of 181 barrows, representing five genotypes, 1) H x HD, 2) SYN, 3) HD x L[YD], 4) L x YD, and 5) Y x L (H = Hampshire, D = Duroc, SYN = synthetic terminal sire line, L = Landrace, and Y = Yorkshire), and two levels of ractopamine (RAC) treatment (0 and 20 ppm) were completely dissected and the data were used to examine genotype and treatment (RAC) biases in estimation of fat-standardized lean weight and to evaluate accuracies and precisions realized by use of equations based on variables derived from different technologies. Independent variables used to establish regression equations represented technologies of direct carcass measurements, optical probe data, TOBEC (total body electrical conductivity) readings, and dissected (DHMLN) and fat-standardized (FSHMLN) ham lean. Genotype bias existed when any equation from a single technology was used and was minimized by combining FSHMLN with one TOBEC reading, carcass length, and the probe measurement of 10th rib fat depth. Large RAC biases appeared when equations from direct carcass measurements or optical probe data were used and were minimized by an equation using either DHMLN or FSHMLN. A practical equation with relatively high R2 value and small genotype and RAC biases were developed by combining TOBEC readings with direct carcass measurements of 10th rib fat depth and warm carcass weight.  相似文献   
28.
试验选用1日龄AA肉仔鸡180只,随机分为3组。Ⅰ组为对照组,添加硫酸锰(MnSO4·H2O)120mg/kg;Ⅱ组添加蛋氨酸螫合锰60mg/kg;Ⅲ组分别添加蛋氨酸螯合锰(Met-Mn)30mg/kg和硫酸锰(MnSO4·H2O)60mg/kg。研究不同方式添加锰对肉仔鸡生产性能的影响。结果表明.3种不同方式添加锰对肉仔鸡生产性能无显著影响(P〉0.05).但Ⅲ组的饲料成本有所降低。因此,在肉仔鸡日粮中以第3种方式添加效果最佳。  相似文献   
29.
尼帕病毒(Ni V)和亨德拉病毒(HeV)属于副黏病毒亚科的亨尼帕病毒属的成员。Ni V和HeV感染引起新的两种重要的人兽共患传染病。有关APMV-1(NDV)的发病和流行以及病原学研究认为APMV-1不断发生演化,新的基因型不断产生,对不同宿主的致病力不断变化,病毒感染的宿主谱不断扩大。本文简要介绍两种新的人兽共患传染病和APMV-1对鹅、鸭、猪的感染研究现状,就APMV-1宿主感染谱与演化加以分析,思考新的动物副黏病毒病防控对策。  相似文献   
30.
自从2018年8月我国报告首例非洲猪瘟疫情以来,经过3年多的艰难探索,我们面对非洲猪瘟疫情从最初的恐惧和束手无策,到现在的精准清除和“与狼共舞”,疫情防控从被动应对进入到常态化管理和无疫小区建设阶段;非洲猪瘟可防可控的预测得到了实践证明。但是由于我国幅员辽阔,养猪模式多样,疫情防控水平参差不齐;非洲猪瘟疫情零星散发的风险持续存在。下面就我们的观察和调查,对近年来非洲猪瘟防控上的一些经验和误区进行简要分析。  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