全文获取类型
收费全文 | 164236篇 |
免费 | 37722篇 |
国内免费 | 27772篇 |
专业分类
林业 | 18412篇 |
农学 | 16970篇 |
基础科学 | 15265篇 |
43658篇 | |
综合类 | 69435篇 |
农作物 | 12057篇 |
水产渔业 | 9527篇 |
畜牧兽医 | 24750篇 |
园艺 | 7522篇 |
植物保护 | 12134篇 |
出版年
2024年 | 3306篇 |
2023年 | 3333篇 |
2022年 | 5468篇 |
2021年 | 5965篇 |
2020年 | 6930篇 |
2019年 | 9725篇 |
2018年 | 8348篇 |
2017年 | 10297篇 |
2016年 | 10140篇 |
2015年 | 11462篇 |
2014年 | 10623篇 |
2013年 | 11838篇 |
2012年 | 13184篇 |
2011年 | 12899篇 |
2010年 | 11820篇 |
2009年 | 10890篇 |
2008年 | 9677篇 |
2007年 | 9813篇 |
2006年 | 8747篇 |
2005年 | 7717篇 |
2004年 | 4941篇 |
2003年 | 4269篇 |
2002年 | 3796篇 |
2001年 | 3434篇 |
2000年 | 3319篇 |
1999年 | 3212篇 |
1998年 | 2752篇 |
1997年 | 2564篇 |
1996年 | 2307篇 |
1995年 | 2248篇 |
1994年 | 2086篇 |
1993年 | 1815篇 |
1992年 | 1638篇 |
1991年 | 1417篇 |
1990年 | 1119篇 |
1989年 | 1003篇 |
1988年 | 836篇 |
1987年 | 583篇 |
1986年 | 498篇 |
1985年 | 263篇 |
1984年 | 230篇 |
1983年 | 218篇 |
1982年 | 221篇 |
1981年 | 266篇 |
1980年 | 205篇 |
1979年 | 157篇 |
1978年 | 132篇 |
1975年 | 115篇 |
1965年 | 141篇 |
1964年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
抗旱耐热白三叶新品种选育初报 总被引:5,自引:0,他引:5
鄂牧一号白三叶是以美国瑞加和路易斯安那两个白三叶品种为原始材料,经单株抗性造反份系比较鉴定,多系混合杂交,品种比较和区域试验选育而成,历时10年。该品种具有高产,抗旱,耐热和粗蛋白含量高等特性,是南方低山丘陵地区有推广应用前景的优良牧草和草坪植物。 相似文献
102.
103.
104.
Li C Basarab J Snelling WM Benkel B Kneeland J Murdoch B Hansen C Moore SS 《Journal of animal science》2004,82(4):967-972
Backfat thickness is one of the major quantitative traits that affects carcass quality in beef cattle. In this study, we identified and fine-mapped QTL for backfat EBV on bovine chromosomes 2, 5, 6, 19, 21, and 23 using an identical-by-descent haplotype-sharing analysis in a commercial line of Bos taurus. Eleven haplotypes were found to have significant associations with backfat EBV at the comparison-wise P-value threshold, and one at the chromosome-wise P-value threshold on bovine chromosomes 5, 6, 19, 21, and 23. On average, the 12 significant haplotypes had an effect of 0.62 SD on backfat EBV, ranging from 0.38 SD to 1.33 SD. The 12 significant haplotypes spanned nine chromosomal regions, one on chromosome 5 (65.4 to 70.0 cM), three on 6 (8.2 to 11.8 cM, 63.6 to 68.1 cM, and 81.5 to 83.0 cM), three on 19 (4.8 to 15.9 cM, 39.4 to 46.5 cM, and 65.7 to 99.5 cM), one on 21 (46.1 to 53.1 cM), and one on 23 (45.1 to 50.9 cM). Among the nine chromosomal regions, six were new QTL regions and three showed remarkable agreement with QTL regions that were previously reported. Eight of the nine QTL regions were localized to less than or close to 10 cM in genetic distance. The results provide a useful reference for further positional candidate gene research and marker-assisted selection for backfat. 相似文献
105.
牛病毒性腹泻病以发热、口腔及消化道粘膜糜烂、腹泻为主要症状,可引起怀孕母牛流产或产畸型胎儿,给养牛业造成巨大的经济损失,该病已成为当前严重危害我国养牛业的传染病之一。由于大部分感染BVDV的牛不表现特征性的临床症状和病理变化,而且引起腹泻和消化道黏膜糜烂或溃疡的疾病很多,所以确诊需进行实验室检查。目前实验室检测BVDV的主要方法是利用美国IDEXX公司ELISA诊断试剂盒,通过BVDV抗原和抗体的检测区别牛群持续感染牛。用于检测BVDV的样品种类有许多种,绝大多数是采集血液(血清)或牛奶样品进行检测。本试验对奶牛进行耳组织采样,同时采集血液和牛奶,用三种样品在相同条件下同时检测BVDV抗原,用血清和牛奶样品检测抗体,比较样品的检测结果。结果表明,这三种样品检测结果具有一致性,且耳组织采样更宜于大面积筛查。 相似文献
106.
Treatment of healthy dogs with the butyrophenone derivative, lenperone hydrochloride, at two different doses significantly decreased gastroesophageal sphincter pressure (GESP). No dose-related effect was identified. Individual variation in the response to lenperone hydrochloride was noted which was consistent on a day-to-day basis. Lenperone hydrochloride is unsuitable for chemical restraint of dogs undergoing esophageal manometry because it decreases GESP and because the magnitude of the decrease varies considerably between dogs. 相似文献
107.
Jiang YN Wu CY Huang CY Chu HP Ke MW Kung MS Li KY Wang CH Li SH Wang Y Ju YT 《Journal of animal science》2008,86(10):2461-2470
The Lanyu pig is an indigenous breed from the Lanyu Islet, which is southeast of Taiwan. Two herds of Lanyu pigs were introduced from the Lanyu Islet into Taiwan in 1975 and 1980. The current population of conserved Lanyu pigs consists of only 44 animals with unknown genetic lineage. The Lanyu pig possesses a distinct maternal genetic lineage remote from Asian and European pigs. The present study aimed to understand the phylogenetic relationship among conserved Lanyu, Asian, and European type pigs based on the cytochrome b coding gene, to ascertain the maternal lineage and genetic diversity within the conserved Lanyu pigs, and to address whether genetic introgression from exotic or Formosan wild pigs had occurred in the conserved Lanyu pigs. Entire mitochondrial genomes of both types of Lanyu pig comprised 2 ribosomal RNA, 22 transfer RNA, and 13 protein-coding genes. Only 2 haplotypes of the mitochondrial DNA (mtDNA) control region and cytochrome b were identified in the conserved Lanyu pig herds. When maximum likelihood trees were constructed, the Type I Lanyu mitochondrial genes formed a unique clade with a large pairwise distance of both cytochrome b and the control region from Asian and European type breeds, Formosan wild pigs, and exotic breeds. Significant loss of genetic diversity of mtDNA within the conserved Lanyu pigs was demonstrated by low haplotype and nucleotide diversities, supported by Fu and Li's D* neutrality test (1.44055; P < 0.05). The mtDNA control region sequences of extant pigs in the Lanyu Islet, however, showed high haplotype and nucleotide diversity, and clustered with exotic pigs. These results indicate no maternal lineage mtD-NA gene introgression from Formosan wild pigs and introduced exotic pigs to conserved Type I Lanyu pigs, and a severe loss of heterozygosity of mtDNA in conserved Lanyu pigs. The remaining extant pigs on the Lanyu Islet have been introgressed with exotic breeds. Strategies for future conservation of native Lanyu pigs are now even more urgent and important. 相似文献
108.
记者:公安部警犬技术学校被业界喻为中国警犬技术人才培养的摇篮,作为校长,请您介绍一下学校在办学方面有哪些特色?南会林:我校经历了几十年的办学实践,已经形成了培养优秀的警犬技术专业人才与训练优良警犬相结合的鲜明特色. 相似文献
109.
110.