全文获取类型
收费全文 | 16606篇 |
免费 | 1246篇 |
国内免费 | 988篇 |
专业分类
林业 | 1483篇 |
农学 | 1851篇 |
基础科学 | 672篇 |
2985篇 | |
综合类 | 3052篇 |
农作物 | 850篇 |
水产渔业 | 942篇 |
畜牧兽医 | 5023篇 |
园艺 | 429篇 |
植物保护 | 1553篇 |
出版年
2023年 | 152篇 |
2022年 | 230篇 |
2021年 | 353篇 |
2020年 | 341篇 |
2019年 | 435篇 |
2018年 | 519篇 |
2017年 | 554篇 |
2016年 | 521篇 |
2015年 | 620篇 |
2014年 | 641篇 |
2013年 | 873篇 |
2012年 | 847篇 |
2011年 | 988篇 |
2010年 | 908篇 |
2009年 | 804篇 |
2008年 | 868篇 |
2007年 | 773篇 |
2006年 | 796篇 |
2005年 | 744篇 |
2004年 | 479篇 |
2003年 | 448篇 |
2002年 | 335篇 |
2001年 | 485篇 |
2000年 | 482篇 |
1999年 | 520篇 |
1998年 | 316篇 |
1997年 | 306篇 |
1996年 | 251篇 |
1995年 | 213篇 |
1994年 | 185篇 |
1993年 | 197篇 |
1992年 | 250篇 |
1991年 | 247篇 |
1990年 | 221篇 |
1989年 | 189篇 |
1988年 | 159篇 |
1987年 | 121篇 |
1986年 | 119篇 |
1985年 | 82篇 |
1984年 | 82篇 |
1983年 | 67篇 |
1981年 | 53篇 |
1980年 | 50篇 |
1979年 | 84篇 |
1978年 | 56篇 |
1977年 | 52篇 |
1976年 | 60篇 |
1975年 | 52篇 |
1974年 | 62篇 |
1973年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
GAL‐ and VIP‐Immunoreactive Nerve Structures in the Ileum and Large Intestine of Pigs with Dysentery
W. Sienkiewicz J. Kaleczyc Z. Pidsudko M. Akomy 《Anatomia, histologia, embryologia》2005,34(Z1):47-47
The morphology, neurochemistry and function of intramural nerve structures in the mammalian gastrointestinal tract are relatively well known, but in normal, healthy individuals. The present study was aimed at investigating the chemical coding of nerve structures in the wall of the ileum and large intestine in normal pigs (n = 3) and in pigs undergoing dysentery (n = 6). Dysentery was evoked by artificial infection of the clinically healthy animals per os with Brachyspira hyodysenteriae. All the animals were deeply anaesthetized and transcardially perfused with 4% paraformaldehyde. The cryostat sections of the intestines were processed for double‐labelling immunohistochemistry using antisera against PGP 9.5, GAL and VIP. In the intramural plexuses of the control pigs, the percentage of GAL‐immunoreactive (GAL‐IR) perykarya varied from 11% (descending colon) to 19% (centrifugal turns of the ascending colon) whereas in the dysenteric pigs, it was distinctly higher, reaching from 28% (ileum) up to 48% (cecum). In the control animals, the percentage of VIP‐IR neuronal somata varied from 3% (descending colon) to 19% (ileum). In dysenteric pigs, it was from 6% (descending colon) up to 28% (cecum). In the muscular coat (MC) and mucous membrane (MM) of the normal intestine, very numerous GAL‐ and VIP‐IR nerve fibres were observed. The nerve fibres in the myenteric plexus (MP) were even more numerous than those in the muscular coat while in the outer (OSP) and inner (ISP) submucous plexuses, they were less abundant. In the dysenteric pigs, the nerve fibres found in MC, MP and OSP were less numerous, whereas those observed in ISP and MM were more abundant than those in the control animals. The present results suggest that GAL and VIP are involved in the regulation of inflammatory processes developing in the porcine gastrointestinal tract during dysentery. 相似文献
82.
83.
84.
85.
本试验用外翻肠囊法研究高钙对肉仔鸡不同肠段(十二指肠、空肠和回肠)吸收不同形态锰的影响,以比较有机锰和无机锰在高钙条件下吸收特点的差异。采用单因子完全随机设计,培养液中添加的4种锰源分别为:硫酸锰、弱络合强度的蛋氨酸锰(Mn-MetE)、中等络合强度的氨基酸锰(Mn-AAA)和强络合强度的氨基酸锰(Mn-AAB)。为了扣除内源的影响,设置1个零添加锰水平处理。将40只31日龄AA肉公鸡随机分到以上5个组,每组8个重复,每个重复1只鸡,每只鸡的十二指肠、空肠和回肠分别作为相应肠段外翻肠囊的一个重复。结果表明:1)体外培养回肠肠囊对锰的吸收率显著高于十二指肠(P<0.01);2)回肠肠囊对强络合强度的Mn-AAB中锰的吸收率显著高于硫酸锰或中等络合强度的Mn-AAA(P<0.05)。本试验结果表明:在高钙条件下,络合形态的有机锰在体外培养的肉仔鸡肠囊中的吸收率显著高于无机形态的锰;强络合强度有机锰源中的锰能更强地抵抗小肠内的解离,比弱或中等络合强度的有机锰源更有利于锰的吸收。 相似文献
86.
Z. Ngoko K.F. Cardwell W.F.O. Marasas M.J. Wingfield R. Ndemah F. Schulthess 《European journal of plant pathology / European Foundation for Plant Pathology》2002,108(9):893-902
The aim was to identify biological and physical factors responsible for reducing maize yield in Cameroon. Two surveys were conducted in 137 fields in two agroecological zones in 1995–1997. In the Humid Forest (HF), Bipolaris maydis, Stenocarpella macrospora, Puccinia polysora, Rhizoctonia solani and soil fertility were factors that reduced maize production in 1995 and 1996. In the Western Highlands (WHL), Cercospora zeae-maydis, and the interaction between soil fertility and maize variety were the most important constraints to maize production in 1996. In 1997, C. zeae-maydis, S. macrospora, physiological spot and stem borer damage (Busseola fusca) were negatively related to ear weight. The combination of these biological factors (diseases and insects), and the physical parameter of soil fertility were responsible for reducing maize yield in these selected benchmarks of Cameroon. Maximum potential yield reductions were estimated at 68% due to B. maydis and 46% due to S. macrospora, respectively, in the HF in 1995. In 1996, maximum potential yield reductions in the HF were estimated at 34%, 41% and 30% due to S. macrospora, P. polysora and R. solani, respectively. In the WHL, C. zeae-maydis had the potential to cause a yield reduction of 79% in 1996. In the WHL in 1997, the interaction between C. zeae-maydis and B. fusca, stem diseases and the physiological spot caused potential reductions of 52%, 34% and 39%, respectively. 相似文献
87.
In controlled environment experiments, sporulation of Pyrenopeziza brassicae was observed on leaves of oilseed rape inoculated with ascospores or conidia at temperatures from 8 to 20°C at all leaf wetness durations from 6 to 72 h, except after 6 h leaf wetness duration at 8°C. The shortest times from inoculation to first observed sporulation ( l 0 ), for both ascospore and conidial inoculum, were 11–12 days at 16°C after 48 h wetness duration. For both ascospore and conidial inoculum (48 h wetness duration), the number of conidia produced per cm2 leaf area with sporulation was seven to eight times less at 20°C than at 8, 12 or 16°C. Values of Gompertz parameters c (maximum percentage leaf area with sporulation), r (maximum rate of increase in percentage leaf area with sporulation) and l 37 (days from inoculation to 37% of maximum sporulation), estimated by fitting the equation to the observed data, were linearly related to values predicted by inserting temperature and wetness duration treatment values into existing equations. The observed data were fitted better by logistic equations than by Gompertz equations (which overestimated at low temperatures). For both ascospore and conidial inoculum, the latent period derived from the logistic equation (days from inoculation to 50% of maximum sporulation, l 50 ) of P. brassicae was generally shortest at 16°C, and increased as temperature increased to 20°C or decreased to 8°C. Minimum numbers of spores needed to produce sporulation on leaves were ≈25 ascospores per leaf and ≈700 conidia per leaf, at 16°C after 48 h leaf wetness duration. 相似文献
88.
89.
90.
番石榴果实发育的初步研究 总被引:7,自引:0,他引:7
以东山月拔和二十一世纪这2个品种为试材,研究了番石榴(Psidium guajava L)果实的发育动态规律。结果表明:番石榴的果实发育呈现双“S”型;果实重量和果核重量的发育呈显著的正相关;推测果实发育后期为进行果实产期调控的关键时期;建议以果实发育的直径大小以及果实转蒂下垂作为确定进行产期调控的田间依据。 相似文献