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   29642篇
  免费   387篇
  国内免费   572篇
林业   2239篇
农学   1004篇
基础科学   976篇
  2814篇
综合类   9304篇
农作物   1268篇
水产渔业   709篇
畜牧兽医   10248篇
园艺   1217篇
植物保护   822篇
  2024年   95篇
  2023年   325篇
  2022年   400篇
  2021年   425篇
  2020年   335篇
  2019年   504篇
  2018年   466篇
  2017年   261篇
  2016年   308篇
  2015年   359篇
  2014年   820篇
  2013年   623篇
  2012年   1754篇
  2011年   1885篇
  2010年   890篇
  2009年   837篇
  2008年   1672篇
  2007年   1777篇
  2006年   1700篇
  2005年   1684篇
  2004年   1587篇
  2003年   1418篇
  2002年   1310篇
  2001年   968篇
  2000年   1248篇
  1999年   760篇
  1998年   462篇
  1997年   462篇
  1996年   399篇
  1995年   359篇
  1994年   440篇
  1993年   478篇
  1992年   458篇
  1991年   383篇
  1990年   397篇
  1989年   320篇
  1988年   204篇
  1987年   163篇
  1986年   147篇
  1985年   174篇
  1984年   162篇
  1983年   135篇
  1982年   136篇
  1981年   86篇
  1980年   94篇
  1979年   52篇
  1978年   41篇
  1966年   29篇
  1963年   34篇
  1959年   30篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
南美洲有草地面积844.5万km^2,饲养着草食家畜4.2亿头,其中牛为2.62亿头。热带稀树草原、亚热带温带潘帕斯草原、温带半荒漠、热带荒漠、热带干燥疏林与灌丛、热带雨林区的人工草地是主要草地类型。巴西和阿根廷是南美洲两个重要的草地资源大国,分别有草地面积1.69亿hm^2和1.42亿hm^2。  相似文献   
132.
亚洲的草地资源及其评价   总被引:3,自引:0,他引:3  
亚洲有草地面积20.78亿hm^2。中国、俄罗斯(亚洲部分)、哈萨克斯坦和蒙古国是亚洲的4个草地资源大国,它们的草地面积都在1亿hm^2以上。亚洲的天然草地类型繁多,从资源的角度看,主要是热带稀树草原,亚热带荒漠,温带荒漠,温带草原,温带草甸,高寒草甸和冻原等。  相似文献   
133.
134.
连续四年试验观察,证明集群放牧饲养的黄牛具有合群、护群、亲和、模仿、习惯等习性;其反刍、歇息、应激等行为亦进行了必要的阐述。  相似文献   
135.
近年来,美国蛋的平均消费量持续下降。部分原因是由于人们厌食早餐,生活方式的改变。可是,在很大程度上是由于人们认为食品中的胆固醇会引起冠心病,从而影响了蛋的消费。因此,任何降低蛋中胆固醇含量的方法,都有助于养禽业。美国和其他国家的许多学者,对降低蛋中胆固醇含量进行了大量研究,试用了多种化学制剂,认为丙丁酚〔4,4’—(异丙叉二硫)—双(2,6—二特丁基酚)〕对降低蛋中胆固醇含量最有效。为研究丙丁酚对蛋鸡生产性能及蛋中胆固醇的影响,作者把72只40周龄星杂蛋鸡养在个体笼内(30.5×45.7cm)。试验设6种日粮处理,每种日粮设2个重复,每重复6只鸡。  相似文献   
136.
蛋鸡饮水中添加88-C微生物制剂对产蛋性能的影响牟玉清,李诗洪(四川农业大学625014)李克弦,方盛荣,亢正生(大邑县畜牧局)“88-C微生物”制剂,是一种高效生物增产剂。该制剂具有改善生物营养,调节生物生理机能,防病抗病,增加生物产量,改善产品品...  相似文献   
137.
据实际调查,运用层次分析法,将疫病传入的各外界风险因素指标划分为目标层、准则层和分准则层三个层次。采用EXCEL软件进行数据统计,依次编辑各层次结构模型,构建各层次的判断矩阵和一致性检验。结果表明:猪场的管理措施、生物安全、场址是疫病传入的主要风险因素。据此确立了I级指标和II级指标,从而构建疫病传入的风险因素指标体系。  相似文献   
138.
Re-emergence of bluetongue in northern Europe in 2007   总被引:2,自引:0,他引:2  
  相似文献   
139.
Determination and kinetics of enrofloxacin and ciprofloxacin in Tra catfish (Pangasianodon hypophthalmus) and giant freshwater prawn (Macrobrachium rosenbergii) using a liquid chromatography/mass spectrometry method. J. vet. Pharmacol. Therap. 34, 142-152. The fluoroquinolones enrofloxacin (EF) and ciprofloxacin (CF) residues were investigated in the edible tissues of two important Asian aquacultured species such as Tra catfish (Pangasianodon hypophthalmus) and giant freshwater prawn (Macrobrachium rosenbergii) using a sensitive liquid chromatography-electrospray ionization-tandem mass spectrometry method. Fish and prawn were treated with medicated feed with multiple doses of EF, in field conditions. A validation study of the analytical method was realized in terms of linearity, specificity, precision (repeatability and within-laboratory reproducibility), recovery and decision limit (CCα). The time needed before the antibiotic disappears from animal tissues or reach the maximum residue limit (MRL, 100μg/kg) was assessed. The concentration values of EF detected in Tra catfish tissue were between the MRL and 2×MRL concentrations, according to the fish density, 7days following the end of the enrofloxacin treatment (20mg/kg body weight per day, for seven consecutive days). The concentration value of ER in prawn tissue was lower than the MRL and the limit of quantification (LOQ, 14μg/kg) 5 and 7days after the stop of the EF treatment (50mg/kg body weight per day, for five consecutive days), respectively. The mean detected levels of CF was much lower in comparison with that of EF, indicating that only a small part of EF is metabolized into CF (<5%) in both Tra catfish and prawn.  相似文献   
140.
Boar taint is characterized by an unpleasant taste or odor in intact male pigs and is primarily attributed to increased concentrations of androstenone and skatole and to a lesser extent by increased indole. The boar taint compounds skatole and indole are produced by gut bacteria, metabolized in the liver, and stored in the fat tissue. Androstenone, on the other hand, is synthesized in the testis along with testosterone and estrogens, which are known to be important factors affecting fertility. The main goal of this study was to investigate the relationship between genetic factors involved in the primary boar taint compounds in an attempt to discover ways to reduce boar taint without decreasing fertility-related compounds. Heritabilities and genetic correlations between traits were estimated for compounds related to boar taint (androstenone, skatole, indole) and reproduction (testosterone, 17β-estradiol, and estrone sulfate). Heritabilities in the range of 0.47 to 0.67 were detected for androstenone concentrations in both fat and plasma, whereas those for skatole and indole were slightly less (0.27 to 0.41). The genetic correlations between androstenone in plasma and fat were extremely high (0.91 to 0.98) in Duroc and Landrace. In addition, genetic correlations between androstenone (both plasma and fat) and the other sex steroids (estrone sulfate, 17β-estradiol, and testosterone) were very high, in the range of 0.80 to 0.95. Furthermore, a genome-wide association study (GWA) and a combined linkage disequilibrium and linkage analysis (LDLA) were conducted on 1,533 purebred Landrace and 1,027 purebred Duroc to find genome regions involved in genetic control of the boar taint compounds androstenone, skatole, and indole, and sex hormones related to fertility traits. Up to 3,297 informative SNP markers were included for both breeds, including SNP from several boar taint candidate genes. From the GWA study, we found that altogether 27 regions were significant at a genome-wide level (P < 0.05) and an additional 7 regions were significant at a chromosomal level. From the LDLA study, 7 regions were significant on a genome-wide level and an additional 7 regions were significant at a chromosomal level. The most convincing associations were obtained in 6 regions affecting skatole and indole in fat on chromosomes 1, 2, 3, 7, 13, and 14, 1 region on chromosome 6 affecting androstenone in plasma only, and 5 regions on chromosomes 3, 4, 13, and 15 affecting androstenone, testosterone, and estrogens.  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