全文获取类型
收费全文 | 4927篇 |
免费 | 326篇 |
国内免费 | 337篇 |
专业分类
林业 | 394篇 |
农学 | 383篇 |
基础科学 | 165篇 |
459篇 | |
综合类 | 2140篇 |
农作物 | 183篇 |
水产渔业 | 325篇 |
畜牧兽医 | 1102篇 |
园艺 | 108篇 |
植物保护 | 331篇 |
出版年
2024年 | 62篇 |
2023年 | 144篇 |
2022年 | 168篇 |
2021年 | 208篇 |
2020年 | 208篇 |
2019年 | 256篇 |
2018年 | 122篇 |
2017年 | 223篇 |
2016年 | 228篇 |
2015年 | 194篇 |
2014年 | 344篇 |
2013年 | 334篇 |
2012年 | 403篇 |
2011年 | 339篇 |
2010年 | 308篇 |
2009年 | 289篇 |
2008年 | 234篇 |
2007年 | 228篇 |
2006年 | 207篇 |
2005年 | 156篇 |
2004年 | 128篇 |
2003年 | 119篇 |
2002年 | 94篇 |
2001年 | 63篇 |
2000年 | 63篇 |
1999年 | 45篇 |
1998年 | 37篇 |
1997年 | 24篇 |
1996年 | 148篇 |
1995年 | 19篇 |
1994年 | 31篇 |
1993年 | 21篇 |
1992年 | 22篇 |
1991年 | 25篇 |
1990年 | 22篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
排序方式: 共有5590条查询结果,搜索用时 15 毫秒
51.
《动物营养(英文)》2019,5(2):174-178
This paper reflects the results of a short experiment conducted in parallel with a larger trial which aimed to test the assumption that ‘consumption of feed by broiler chickens during periods of darkness is largely negligible’. To that effect, on d 31, feeders of birds raised under intermittent lighting (IL), i.e. 1 h of light [1L]:3 h of dark (3D):1L:3D:1L:3D:1L:3D:2L:6D, were weighed at the onset and at the end of each period of darkness (or scotoperiod). Moreover, in order to compare the feeding behavior of IL birds with that of broilers raised under continuous lighting (CL, i.e. 18L:6D), their feeders were weighed in parallel and at the same time points. On d 31, feed intake of IL birds during scotoperiods represented 45% of their 24 h feed intake. Both CL and IL birds presented anticipatory feed intake prior to the long nocturnal period of darkness (6D), as well as higher feed intake right at the onset of lighting at 06:00. Feed intake of CL birds during the 6D nocturnal scotoperiod was negligible at around 2% of their total feed intake. Intermittent lighting birds exhibited excitement at the start of each hour-length scotoperiod and, within that time, ingested around 2.5 times the amount of feed ingested by CL birds. Although short, this study revealed several interesting observations which might be worth further exploring in a larger, lengthier, behavior-focused experiment. Amongst other factors, it might be interesting to understand whether the high feed intake observed during scotoperiods for IL birds in reflective of the whole flock or rather a coping mechanism developed mainly by hierarchically lower-ranking birds to achieve their daily feed intakes requirements. 相似文献
52.
Murrah buffaloes, best breed for milk production are native of Haryana state. They contributes significantly to the farmer’s income, livelihood and food (milk and meat) security, in the semi-tropical regions of North India. Johne’s disease though endemic in the domestic livestock of the country, but reports are not available in the buffaloes suffering from morbidity due to progressive weakness and diarrhoea. We estimated the status of JD in diarrhoeic buffaloes and cattle reporting at Veterinary Clinical Complex of Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar, Haryana, India, using conventional, serological and PCR assays.141 buffaloes suffering from chronic diarrhoea were screened to estimate sero-prevalence of MAP and 50.0 % young and 53.52 % adult animals were positive. Of 14 cattle screened, none of the young and 66.6 % adult cows were positive. In buffaloes, 66.1 and 6.77 %, fecal samples were positive in microscopy and IS900 PCR, respectively. Sero-prevalence of JD was very high in diarrhoeic buffaloes and cattle from Haryana state of India.Buffaloes positive for Mycobacterium avium subspecies paratuberculosis (MAP) infection had reduced total leukocyte count and lymphocytes. 相似文献
53.
为探究热加工方式对牛乳过敏原αs1-酪蛋白构象和抗原性的影响,利用间接竞争酶联免疫吸附测定方法、
免疫印迹方法分析不同加热条件下αs1-酪蛋白免疫原性的变化,进而通过8-苯胺-1-萘磺酸荧光探针和圆二色谱分
析其二级结构变化,初步揭示热处理调控过敏原αs1-酪蛋白抗原性的机制。结果表明:在80 ℃、60 min,90 ℃、
10 min,90 ℃、60 min条件下热处理后,αs1-酪蛋白中α-螺旋结构含量显著低于未加热αs1-酪蛋白,在70 ℃、
20 min,80 ℃、20 min,90 ℃、20 min条件下热处理后,αs1-酪蛋白中无规卷曲含量显著增加,70~100 ℃加热
20 min条件下表面荧光强度最强,其他温度-时间条件下二级结构含量变化不显著;αs1-酪蛋白构象的变化导致αs1-酪
蛋白的抗原性显著降低,间接竞争酶联免疫吸附测定显示,在70~100 ℃加热20 min条件下,αs1-酪蛋白的抗原残留
量均较高,而免疫印迹方法显示不同温度-时间条件下αs1-酪蛋白仍具有免疫反应特性,建议进一步通过动物实验揭
示热处理调控αs1-酪蛋白抗原性的机制。 相似文献
54.
环境因素对丹顶鹤越冬行为的影响 总被引:3,自引:0,他引:3
丹顶鹤在盐城越冬期间各种环境因素对其行为都将产生一定的影响,对此我们进行了观察记录。该项工作主要用8×40、10×50双筒和20倍单筒望远镜实地观察、照相机摄影等直接记录丹顶鹤的各种行为;种群数量计算为直接计数法;气候因子则根据各级气象部门的预报结果,结合观察点温度计等手段测算。结果表明丹顶鹤越冬期间,气候因子的变化是对其行为产生直接影响的主要因素,温度、雨、雾、雪、风等发生大幅度变化时,都将导致越冬期丹顶鹤的行为发生相应的适应性变化,对迁徙行为的影响则更为明显。而食物和水源则通过气候因子的变化和安全度的影响再次反应到丹顶鹤的越冬行为中来。本文最后提出了减轻灾害性天气对丹顶鹤越冬行为的影响建议。 相似文献
55.
56.
白头鹤是长江中下游的大型越冬水鸟,安徽升金湖是其在国内主要的越冬地之一。近年来,由于生境退化,越冬种群的数量在萎缩,种群的越冬生态研究十分必要。2007年10月~2008年4月,我们在升金湖对白头鹤的主要分布地点进行了调查,并对集群情况进行了观察。升金湖白头鹤觅食地主要分布于湖区外围的稻田,夜栖于上湖核心区内。整个越冬期,白头鹤大部分以5只以上的群类型觅食,以家庭集群活动仅占越冬集群数的29.14%。随着越冬期的变化,集群大小发生改变:越冬前期,越冬鹤以家族群活动频率最高,占集群的35.64%,30~49只集群频率最低,仅为6.38%;越冬中期,家庭集群及5~9只集群频率相对于越冬前期减少,10只以上集群频率增加;越冬后期,以≥50只以上集群频率最高,占28.77%。此外,我们还观察到1对成年鹤占有一定面积的稻田并积极保护,表现领域行为。 相似文献
57.
58.
I Kakoma C.A Carson M Ristic 《Comparative immunology, microbiology and infectious diseases》1980,3(3):291-298
Erlichia canis, a rickettsial pathogen which infects monocytes, induces generalized lymphocyte activation. Activated T lymphocytes differentiate into effector cells capable of destroying infected and uninfected monocytes and platelets. Activated B lymphocytes differentiate into plasma cells associated with plasmocytosis, hypergammaglobulinemia with high levels of specific antibody and a platelet migration inhibition factor. These effector mechanisms, aimed at parasite destruction, contribute to the pathogenesis of acute tropical canine pancytopenia and do not completely eliminate the etiologic agent. A carrier state of ‘infection-immunity’ exists between the immunocompetent host and virulent parasite. E. canis has evolved mechanisms of ‘tolerant-symbiosis’ with hostile macrophages and other effector cells in the immune host. 相似文献
59.
60.
Yuko TAJIMA Kaori MAEDA Tadasu K. YAMADA 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2015,77(1):45-51
One hundred and twenty
stranding events of Stejneger’s beaked whales were reported in Japan between 1999 and
2011. The purpose of this study is to introduce pathological data and to discuss probable
causes of death for 44 Stejneger’s beaked whales among them. The significant pathological
findings were the pulmonary edema, parasitic granulomatous nephritis, emaciation,
amyloidosis, suppurative bronchopneumonia and so on. The probable causes of death were
categorized as noninfectious in 43 of the cases, which included drowning, starvation and
secondary amyloidosis. One individual was diagnosed with septicemia, which was the only
example of an infectious disease. Because we could not always perform advanced analyses,
such as microbiology tests, biotoxin examinations or contaminant analyses, the finality of
our findings may be impaired. However, the present study has broad implications on the
causes of death of Stejneger’s beaked whales of the seas around Japan, which are valuable
for the future studies and for the detection of emerging diseases. 相似文献