全文获取类型
| 收费全文 | 4680篇 |
| 免费 | 235篇 |
| 国内免费 | 466篇 |
专业分类
| 林业 | 306篇 |
| 农学 | 516篇 |
| 基础科学 | 137篇 |
| 456篇 | |
| 综合类 | 2221篇 |
| 农作物 | 444篇 |
| 水产渔业 | 100篇 |
| 畜牧兽医 | 705篇 |
| 园艺 | 181篇 |
| 植物保护 | 315篇 |
出版年
| 2024年 | 27篇 |
| 2023年 | 104篇 |
| 2022年 | 166篇 |
| 2021年 | 211篇 |
| 2020年 | 168篇 |
| 2019年 | 217篇 |
| 2018年 | 137篇 |
| 2017年 | 203篇 |
| 2016年 | 230篇 |
| 2015年 | 218篇 |
| 2014年 | 316篇 |
| 2013年 | 280篇 |
| 2012年 | 385篇 |
| 2011年 | 322篇 |
| 2010年 | 279篇 |
| 2009年 | 276篇 |
| 2008年 | 214篇 |
| 2007年 | 257篇 |
| 2006年 | 183篇 |
| 2005年 | 158篇 |
| 2004年 | 125篇 |
| 2003年 | 121篇 |
| 2002年 | 74篇 |
| 2001年 | 82篇 |
| 2000年 | 79篇 |
| 1999年 | 58篇 |
| 1998年 | 65篇 |
| 1997年 | 66篇 |
| 1996年 | 59篇 |
| 1995年 | 61篇 |
| 1994年 | 35篇 |
| 1993年 | 39篇 |
| 1992年 | 22篇 |
| 1991年 | 31篇 |
| 1990年 | 30篇 |
| 1989年 | 30篇 |
| 1988年 | 15篇 |
| 1987年 | 15篇 |
| 1986年 | 6篇 |
| 1985年 | 4篇 |
| 1982年 | 1篇 |
| 1981年 | 2篇 |
| 1980年 | 1篇 |
| 1978年 | 2篇 |
| 1977年 | 1篇 |
| 1976年 | 5篇 |
| 1956年 | 1篇 |
排序方式： 共有5381条查询结果，搜索用时 125 毫秒
51.
为探讨返青期休牧对退化高寒草地植被特征及优势种光合生理的影响,本研究在祁连山区选择已实施返青期休牧6年的高寒草甸开展了植被特征及优势种光合生理相关指标的调查研究。结果表明：返青期休牧6年后,高寒草甸的植被盖度、地上生物量、地下生物量和土壤含水量较未休牧区分别增加了38.44%,985.00%,209.56%和62.62%,其优势禾草垂穗披碱草（Elymus nutans）株高、叶片净光合速率、光化学量子效率、呼吸速率、叶面积、相对叶绿素含量和叶片氮含量分别提高了965.77%,139.86%,4.92%,269.37%,254.13%,197.02%和96.24%（P<0.05）,其地上地下生物量与除叶温和光化学猝灭系数外的指标显著相关,叶片净光合速率与除叶温外的指标显著相关。因此,返青期休牧可显著增强高寒草地优势禾草的光合作用和呼吸作用,促进植物生长及退化草地的恢复。本研究为推广实施返青期休牧这一措施来恢复退化高寒草地植被提供了理论基础。 相似文献
52.
奶牛围产期的饲养管理是规模化奶牛场生产环节中的重中之重,该项工作不仅影响奶牛泌乳量和生鲜乳品质,还直接决定新生犊牛的健康水平和奶牛的产后恢复情况。因此,各牧场需要加强奶牛围产期的饲养管理,让奶牛在分娩前后平稳过渡。本文从营养需要、分群、饲养和环境等方面介绍了奶牛围产前期和围产后期的管理需要,以期为围产期奶牛的科学饲养管理提供理论参考。 相似文献
53.
Yanfen Ma Ying Feng Liwen Song Muyang Li Hongyu Dai Hua Bao Guijie Zhang Lei Zhao Chunhua Zhang Jing Yi Yusheng Liang 《动物营养（英文）》2021,7(1):206
Peripartal cows often experience negative energy balance, and are therefore prone to suffering from metabolic diseases such as hyperketonemia, which causes financial losses in dairy farms. This study aimed to investigate the effect of green tea polyphenol (GTP) supplementation during the periparturient period on production performance, oxidative stress and immunometabolism in dairy cows with hyperketonemia. One hundred Holstein cows were assigned to GTP (0.2 g/kg DM; n = 50) or control (without GTP; n = 50) group based on body weight, previous milk yield, and parity on d 15 before expected parturition. Subsequently, 10 cows with hyperketonemia were selected from each group, according to blood β-hydroxybutyric acid (BHBA) concentration between 1.2 and 2.9 mmol/L from 2 to 3 d postpartum. All cows were fed a close-up diet and a lactation diet with or without GTP supply from 15 d prepartum until 30 d postpartum. Milk and blood samples were obtained from 20 cows selected with hyperketonemia on 10, 20, and 30 d postpartum. Compared with control cows, greater milk yield and lower somatic cell count were observed in GTP cows. The GTP group had lower concentrations of BHBA, free fatty acids, cholesterol, triglyceride, reactive oxygen species, malondialdehyde, and hydrogen peroxide, greater concentrations of glucose, lower activities of aspartate aminotransferase, alanine aminotransferase, and glutamyl transpeptidase, alongside greater activities of superoxide dismutase, glutathione peroxidase, and total antioxidant capacity. Additionally, GTP supplementation up-regulated concentrations of interleukin-6 and interleukin-10, but down-regulated concentrations of tumor necrosis factor-α, interleukin-1β, interleukin-2, interleukin-8, and interferon-γ in plasma. Greater concentrations of plasma immunoglobulin G were also detected in the GTP group. Overall, the data suggested that GTP supplementation from 15 d prepartum to 30 d postpartum improved the milk yield and health status in cows with hyperketonemia during early lactation. 相似文献
54.
55.
Association of oxidative status and insulin sensitivity in periparturient dairy cattle: an observational study 
下载免费PDF全文
下载免费PDF全文 A. Abuelo J. Hernández J. L. Benedito C. Castillo 《Journal of animal physiology and animal nutrition》2016,100(2):279-286
Post‐parturient insulin resistance (IR) is a common feature in all mammalian animals. However, in dairy cows, it can be exacerbated because of high milk yield, leading to excessive negative energy balance, which is related with increased disease incidence, reduced milk production and worsened reproductive performance. IR has been extensively investigated in humans suffering from diabetes mellitus. In these subjects, it is known that oxidative stress (OS) plays a causative role in the onset of IR. Although OS occurs in transitional dairy cattle, there are yet no studies that investigated the association between IR and OS in dairy cattle. Therefore, the aim of this study was to investigate whether there is a relationship between OS and IR in dairy cattle. Serum samples were taken repeatedly from 22 dairy cows from 2 months prior to the expected calving date to 2 months after calving and were analysed for markers of metabolic and redox balance. Surrogate indices of insulin sensitivity were also calculated. Generalised linear mixed models revealed an effect of the oxidative status on peripheral insulin concentration and on indices of insulin sensitivity. Hence, field trials should investigate the effectiveness of antioxidant therapy on insulin sensitivity in peripheral tissues during the transition period of dairy cattle. 相似文献
56.
为研究沉水植物在不同水深和生长时期对不同种类入侵植物的响应,选取2种湿地入侵植物凤眼莲Eichhornia crassipes、水盾草Cabomba caroliniana和2种常见本地沉水植物黑藻Hydrillaverticillata、菹草Potamogeton crispus为研究对象,通过模拟试验探究在不同水深（0.2、0.4 m）和生长时期（生长初期和生长旺期）的本地沉水植物对2种入侵植物的响应。结果显示,当水深为0.4 m时更有利于黑藻的生长,并可削弱入侵植物对黑藻生长的消极作用,而水深对菹草的生长无显著影响;入侵植物种类对本地沉水植物的生长无显著影响,但影响方式却存在差异,其中水盾草倾向于直接抑制本地沉水植物的生长,而凤眼莲可以通过降低水体透明度以及总磷含量进而间接抑制本地沉水植物的生长。此外,外来植物在本地沉水植物生长初期入侵对本地沉水植物产生的消极影响较生长旺期入侵时更显著。表明凤眼莲及水盾草入侵对本地沉水植物生长的影响机制存在差异,本地沉水植物在适宜水深和生长旺期对2种入侵植物具有更强的抵抗能力。 相似文献
57.
2022年3月25日,欧盟药品管理局(EMA)兽医药品委员会(CVMP)发布了食品动物注射部位兽药残留指南,并于2022年8月1日正式生效。该指南代替旧版的注射部位兽药残留指南(EMA/CVMP/542/03-FINAL)。本文就新发布指南的背景、适用范围、法律依据、评价方法、残留研究及相关定义等内容进行介绍。 相似文献
58.
59.
60.