全文获取类型
收费全文 | 17592篇 |
免费 | 917篇 |
国内免费 | 2044篇 |
专业分类
林业 | 1902篇 |
农学 | 2692篇 |
基础科学 | 1521篇 |
2694篇 | |
综合类 | 5823篇 |
农作物 | 920篇 |
水产渔业 | 593篇 |
畜牧兽医 | 2425篇 |
园艺 | 740篇 |
植物保护 | 1243篇 |
出版年
2024年 | 76篇 |
2023年 | 271篇 |
2022年 | 571篇 |
2021年 | 852篇 |
2020年 | 733篇 |
2019年 | 672篇 |
2018年 | 479篇 |
2017年 | 691篇 |
2016年 | 605篇 |
2015年 | 813篇 |
2014年 | 804篇 |
2013年 | 933篇 |
2012年 | 1209篇 |
2011年 | 1217篇 |
2010年 | 1084篇 |
2009年 | 1031篇 |
2008年 | 982篇 |
2007年 | 938篇 |
2006年 | 874篇 |
2005年 | 829篇 |
2004年 | 379篇 |
2003年 | 392篇 |
2002年 | 428篇 |
2001年 | 415篇 |
2000年 | 438篇 |
1999年 | 416篇 |
1998年 | 315篇 |
1997年 | 348篇 |
1996年 | 257篇 |
1995年 | 270篇 |
1994年 | 256篇 |
1993年 | 192篇 |
1992年 | 180篇 |
1991年 | 148篇 |
1990年 | 115篇 |
1989年 | 106篇 |
1988年 | 85篇 |
1987年 | 51篇 |
1986年 | 27篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1956年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
The limited space in farrowing crate imposes many challenges, such as prolonged farrowing duration and high piglet stillbirth rate. Although the features of farrowing pens compensate for the drawbacks of farrowing crates, they are associated with high piglet crushing mortality caused by the greater space afforded to sows and their rolling-over behaviour. Therefore, a freedom farrowing pen was designed to overcome the drawbacks of both farrowing crates and farrowing pens. The main features of the freedom farrowing pen are its left anti-crushing bar and detachable right anti-crushing bar on the sides of the sow lying area. It also has a 10 cm-high anti-crushing bar in the non-lying area. Eighteen healthy, multiparous Yorkshire sows (3-7 parity) were averaged and randomly assigned to farrowing crates, farrowing pens, and freedom farrowing pens to compare the effects of the farrowing systems on sow behaviour and performance. Results showed that the farrowing duration and the mean piglet birth intervals were longer for the sows in farrowing crates than for those in farrowing pens and freedom farrowing pens (P<0.05), but there was no difference between the sows in farrowing pens and those in freedom farrowing pens (P>0.05). The piglet stillbirth rate was higher for the sows in farrowing crates than for those in farrowing pens and freedom farrowing pens (P<0.001). Crushing mortality was higher among piglets in farrowing pens (P<0.001), but there was no difference between piglets in freedom farrowing pens and those in farrowing crates (P>0.05). The freedom farrowing pen and the farrowing pen allowed sows to turn around and move freely, but because of the different structures of their anti-crushing bars, the increase in sow movement did not cause higher piglet crushing mortality (P>0.05). Sows in freedom farrowing pens were found to be more protective of their piglets. 相似文献
43.
44.
磺胺二甲嘧啶在黑鲪体内的药物代谢动力学和残留消除研究 总被引:3,自引:0,他引:3
在(14±1)℃水温条件下,对黑鲪单次口灌100 mg/kg体重的磺胺二甲嘧啶,进行药物代谢动力学研究。在(20±2)℃水温条件下,按照《中华人民共和国水产行业标准磺胺类药物水产养殖使用规范》推荐剂量对黑鮶连续5天口灌给予磺胺二甲嘧啶,研究其在黑鮶体内的残留消除规律。血浆、肌肉和肝脏样品采用高效液相色谱检测,DAS2.0药物代谢动力学软件对数据进行处理分析。结果表明磺胺二甲嘧啶在黑鲪血浆、肌肉和肝脏中均符合一室模型,肝脏、血液和肌肉中药物达峰时间分别为6 h,8 h和10 h;峰值浓度分别为26.45μg/g、25.57μg/g和31.15μg/g;连续多次给药后,黑鮶血液、肌肉、肝脏中药物浓度分别在给药后12d、14d、15d后小于最大残留限量要求(0.1mg/kg)。 相似文献
45.
46.
Junzheng Du Shandian Gao Huiyun Chang Guozheng Cong Tong Lin Junjun Shao Zaixin Liu Xiangtao Liu Xuepeng Cai 《Veterinary immunology and immunopathology》2009,131(3-4):190-199
Integrins are heterodimeric adhesion receptors that participate in a variety of cell–cell and cell–extracellular matrix protein interactions. Many integrins recognize RGD sequences displayed on extracellular matrix proteins and the exposed loops of viral capsid proteins. Four members of the αv integrin family of cellular receptors, αvβ3, αvβ6, αvβ1 and αvβ8, have been identified as receptors for foot-and-mouth disease virus (FMDV) in vitro, and integrins are believed to be the receptors used to target epithelial cells in the infected animals. To analyse the roles of the αv integrins from a susceptible species as viral receptors, we have cloned Bactrian camel αv, β3 and β6 integrin cDNAs and compared them to those of other species. The coding sequences for Bactrian camel integrin αv, β3 and β6 were found to be 3165, 2289 and 2367 nucleotides in length, encoding 1054, 762 and 788 amino acids, respectively. The Bactrian camel αv, β3 and β6 subunits share many structural features with homologues of other species, including the ligand binding domain and cysteine-rich region. Phylogenetic trees and similarity analyses showed the close relationships of integrin genes from Bactrian camels, pigs and cattle, which are each susceptible to FMDV infection, that were distinct from the orders Rodentia, Primates, Perissodactyla, Carnivora, Galliformes and Xenopus. We postulate that host tropism of FMDV may in part be related to the divergence in integrin subunits among different species. 相似文献
47.
48.
49.
以马龙区荒野为研究对象,选取距聚居点的遥远度、距可达道路的遥远度、人口分布密度、生物物理自然度4项指标进行叠加分析,绘制了马龙区荒野的分布图,并对荒野面积的水平分布、垂直分布、景观格局以及荒野保护空间进行了分析评价。结果表明:马龙区荒野在水平空间上呈环带分布格局,中部区域荒野面积相对较大、荒野质量相对较高;其外围环带区域荒野面积较小、质量较低、“孤岛化”、“碎片化”较为严重;最外围环带荒野质量又显明提高,面积较为完整。马龙区高质量荒野的储量占比较大,主要集中分布于海拔1 957~2 178 m,面积占比52.92 %。其中一级荒野斑块连通性最好,二、三级荒野斑块的破碎程度较大,四级荒野的斑块形状最复杂;现有保护形式未能对高质荒野形成全面覆盖。马龙区应加强荒野保护区建设,提高对荒野的保护覆盖率,同时通过人工手段恢复和提高低质荒野质量。研究结果可为马龙区荒野保护工作的展开提供参考。 相似文献
50.