全文获取类型
收费全文 | 105438篇 |
免费 | 5520篇 |
国内免费 | 51篇 |
专业分类
林业 | 4308篇 |
农学 | 3038篇 |
基础科学 | 729篇 |
11678篇 | |
综合类 | 20717篇 |
农作物 | 4292篇 |
水产渔业 | 4616篇 |
畜牧兽医 | 54321篇 |
园艺 | 1195篇 |
植物保护 | 6115篇 |
出版年
2018年 | 1204篇 |
2017年 | 1331篇 |
2016年 | 1284篇 |
2015年 | 1090篇 |
2014年 | 1260篇 |
2013年 | 3931篇 |
2012年 | 2564篇 |
2011年 | 3184篇 |
2010年 | 2077篇 |
2009年 | 2054篇 |
2008年 | 3205篇 |
2007年 | 2937篇 |
2006年 | 2801篇 |
2005年 | 2636篇 |
2004年 | 2744篇 |
2003年 | 2678篇 |
2002年 | 2621篇 |
2001年 | 3272篇 |
2000年 | 3288篇 |
1999年 | 2440篇 |
1998年 | 1069篇 |
1997年 | 1081篇 |
1995年 | 1251篇 |
1994年 | 1164篇 |
1993年 | 1121篇 |
1992年 | 2362篇 |
1991年 | 2530篇 |
1990年 | 2438篇 |
1989年 | 2493篇 |
1988年 | 2272篇 |
1987年 | 2349篇 |
1986年 | 2484篇 |
1985年 | 2394篇 |
1984年 | 1918篇 |
1983年 | 1773篇 |
1982年 | 1165篇 |
1981年 | 1123篇 |
1980年 | 1025篇 |
1979年 | 1762篇 |
1978年 | 1424篇 |
1977年 | 1146篇 |
1976年 | 1130篇 |
1975年 | 1165篇 |
1974年 | 1524篇 |
1973年 | 1610篇 |
1972年 | 1584篇 |
1971年 | 1515篇 |
1970年 | 1408篇 |
1969年 | 1262篇 |
1967年 | 1094篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
871.
Langenfeld M Kaczmarczyk J Caputa-Jurasz L Tuz R Galos M 《Archivum veterinarium Polonicum / Polish Academy of Sciences, Committee of Veterinary Sciences》1993,33(3-4):189-195
On 27 German Landrace boars studies were conducted to describe the effect of feeding level during the growth period on the microscopic picture of vesicular glands in boars at 5, 6 and 7 months of age. Investigations have shown that differentiation of feeding level during the growth period affected the development of internal structures of the parenchyma in the boars' vesicular glands. The size of the tubules, their number within the field of vision and height of glandular epithelium lining the tubules were the highest in the group of animals fed at increased level. 相似文献
872.
SUMMARY: Two-hundred random pedigrees of cows and fifty of sires born in 1987 from the Gir herdbook of the Brazilian Association of Zebu Breeders were analized. The bull Chave de Ouro DGR no. 2851 was the most influential animal with a 7% direct relationship to the breed. Total average inbreeding was 3.62 and 3.25 for the female and male sample, respectively. The subdivision of total inbreeding into current and non-current components resulted in values of 1.62, 1.25, 2.00 and 2.00 for the female and male sample, respectively. Long-term inbreeding was the principal component of non-current inbreeding, with values of 1.52% and 1.26%, respectively. Inbreeding due to strain formation strain due formation was less important (0.48% and 0.74%, respectively). The average generation interval was 8.02 years. The breed appears not yet to be subdivided into strains but this process may be starting. The average generation interval for the pedigree population was very high. Culling of old bulls could decrease this interval. ZUSAMMENFASSUNG: Verwandtschaft, Inzucht und Generationsintervall bei Gir Herdbuchrindern in Brasilien 200 zuf?llige Stammb?ume von Kühen und 50 von 1987 geborenen Stieren wurden vom Gir Herdbuch des brasilianischen Zebu Zuchtverbandes genommen. Der Stier Chave de Ouro DGR Nr. 2851 war das einflu?reichste Tier mit einer 7%igen direkten Verwandtschaft zur Rasse. Der gesamte Inzuchtkoeffizient war 3.6 und 3.25% für die weibliche und m?nnliche Stichprobe. Die Unterteilung der gesamten Inzucht in laufende und nicht laufende Komponenten resultierte in Werten von 1.62, 1.25, 2.0, 2.0 für die weibliche und die m?nnliche Stichprobe. Langfristige Inzucht war die Hauptursache für Nicht-Rezente Inzucht mit Werten von 1.5 und 1.26. Inzucht aufgrund von Linienbildung war weniger wichtig (0.48% und 0.74%). Das durchschnittliche Generationsintervall war 8.02 Jahre. Die Rasse scheint noch nicht in Linien unterteilt zu sein, aber dieser Proze? k?nnte begonnen haben. Das durchschnittliche Generationsintervall ist mit 8.02 Jahren sehr hoch. Nichtverwendung alter Stiere k?nnte dieses Intervall verkürzen. 相似文献
873.
874.
875.
876.
The effects of offspring sex, weight, age, and level of interaction with the dam on responses to weaning were examined to assist in the development of a weaning protocol for alpacas. In the first study, preand post-weaning activities, and weight change over Days -12-0,0-7 and 7-16 with respect to weaning, were recorded for 20 dam-offspring (hembra-cria) pairs aged 81-200 days. Pre-weaning changes in dam and offspring weights were positively related (P<0.05). Although heavier crias tended to be found closer to their dams than lighter crias (P<0.05) no additional effect of age on the dam-offspring relationship was found. Following weaning, cria growth rates were low over Days 0-7 but improved over Days 7-16, and hembra weight change followed the same pattern. Over Days 0-2, grazing and sitting activities of hembras and crias were replaced by standing and walking along paddock fencelines, although by Day 2 fenceline activities had decreased (P<0.05). Crias which were more frequently observed at fencelines had lower post-weaning growth rates (P<0.05). In the second study, pre-weaning sucking behaviour, and weight change over Days -30-0, 0-8 and 8-16 with respect to weaning, were recorded for 19 hembra-cria pairs aged 124-160 days. During 10 hours of observation on Days -5 and -4, the total duration of sucking by individual crias varied from 0-18 minutes, and the mean +/- SEM duration of sucking was 1.94 +/- 0.113 minutes. Cria sucking behaviour was positively related to growth rate prior to and weight at weaning (P<0.05). As in the first study, pre-weaning changes in dam and offspring weights were positively related (P<0.05). Following weaning, growth rates of the crias were depressed and the hembras lost weight over Days 0-8 and 8-16. The changes in growth rate and behaviour in Studies 1 and 2 indicated that weaning can be stressful for hembras and crias. However, there was no evidence from either study that pre-weaning behavioural or physical characteristics were related to the changes. 相似文献
877.
878.
879.
Schneider RR Hunter DB 《The Canadian veterinary journal. La revue veterinaire canadienne》1993,34(2):103-108
A study of the pattern and relative frequency of diseases in adult female mink during the lactation period was undertaken. All adult females that died between parturition (April/May) and July 1, 1990, from 48 farms in southern Ontario were selected for study, and the cause of death was determined by gross necropsy. In addition, the cause of death was determined by gross necropsy for all adults and weaned kits that died on one farm between April 1988 and March 1989.
The mortality rate among farms in the 1990 study, for adult females during the lactation period, ranged from 0.2% to 10.1%, with a median of 1.9%. Nursing disease (56%) was the most common diagnosis, followed by mastitis (11%), metritis (8%), and dystocia (7%). Escherichia coli and Staphylococcus spp. were the most frequent isolates from the cases of mastitis. In the 1988/1989 study, the mortality rate was highest from May to July, with a large increase in June as a result of nursing disease.
相似文献880.