全文获取类型
收费全文 | 172303篇 |
免费 | 9256篇 |
国内免费 | 125篇 |
专业分类
林业 | 7780篇 |
农学 | 5819篇 |
基础科学 | 1082篇 |
22319篇 | |
综合类 | 26101篇 |
农作物 | 6840篇 |
水产渔业 | 8876篇 |
畜牧兽医 | 89309篇 |
园艺 | 2346篇 |
植物保护 | 11212篇 |
出版年
2019年 | 1687篇 |
2018年 | 2596篇 |
2017年 | 2949篇 |
2016年 | 2723篇 |
2015年 | 2293篇 |
2014年 | 2841篇 |
2013年 | 6849篇 |
2012年 | 5208篇 |
2011年 | 6421篇 |
2010年 | 4181篇 |
2009年 | 4243篇 |
2008年 | 6214篇 |
2007年 | 5912篇 |
2006年 | 5579篇 |
2005年 | 5224篇 |
2004年 | 4913篇 |
2003年 | 5051篇 |
2002年 | 4537篇 |
2001年 | 5592篇 |
2000年 | 5632篇 |
1999年 | 4485篇 |
1998年 | 1917篇 |
1997年 | 1817篇 |
1996年 | 1714篇 |
1995年 | 1995篇 |
1994年 | 1769篇 |
1993年 | 1636篇 |
1992年 | 3438篇 |
1991年 | 3650篇 |
1990年 | 3610篇 |
1989年 | 3526篇 |
1988年 | 3225篇 |
1987年 | 3216篇 |
1986年 | 3225篇 |
1985年 | 3122篇 |
1984年 | 2564篇 |
1983年 | 2216篇 |
1982年 | 1526篇 |
1979年 | 2332篇 |
1978年 | 1870篇 |
1977年 | 1505篇 |
1976年 | 1591篇 |
1975年 | 1649篇 |
1974年 | 1984篇 |
1973年 | 1977篇 |
1972年 | 1872篇 |
1971年 | 1773篇 |
1970年 | 1690篇 |
1969年 | 1693篇 |
1967年 | 1522篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
A D Ice A L Grant L K Clark T R Cline M E Einstein T G Martin M A Diekman 《American journal of veterinary research》1999,60(5):603-608
OBJECTIVE: To compare health and growth performance in barrows reared in all-in/all-out (AIAO) or continuous flow (CF) management systems. ANIMALS: 400 barrows. PROCEDURE: Barrows (approx 2 months old) were allotted to 4 replications (100 barrows each); barrows were housed in AIAO or CF rooms (10 pens/room), and 50 pigs/replicate received chlortetracycline (CTC, 110 mg/kg of feed). Barrows from each pen were slaughtered at 3, 4, 5, and 6 months old. RESULTS: Barrows in the AIAO room had greater total daily gain (TDG) and lean daily gain (LDG) than did barrows in the CF room. Addition of CTC did not improve TDG or LDG in either environment. Barrows in the AIAO room reached body weight of 104.5 kg in 169.7 days, compared with 177.3 days for barrows in the CF room. Feed-to-gain ratio was not affected by management or CTC. Lungs from barrows reared in AIAO facilities had a lower percentage of lesions than did lungs of barrows reared in CF facilities (1.74% vs 9.52%). Addition of CTC did not affect prevalence and extent of lung lesions. Extent of lung lesions was positively correlated with change in serum optical density (OD) to Mycoplasma hyopneumoniae (r = 0.35), but not with change in serum OD to Actinobacillus pleuropneumoniae. Lean growth and serum OD to M. hyopneumoniae and A. pleuropneumoniae were not correlated. CONCLUSIONS: Health and growth performance were better for barrows in an AIAO facility, compared with a CF facility, but addition of CTC to feed failed to enhance health or performance of barrows in either facility. 相似文献
993.
J. A. LEIGH 《Veterinary journal (London, England : 1997)》1999,157(3):225-238
The prevalence of bovine mastitis has been reduced over the past 25 years due to the implementation of a five-point control plan aimed at reducing exposure, duration and transmission of intramammary infections by bacteria. This has markedly reduced the incidence of bovine mastitis caused by bacteria which show a contagious route of transmission, but has had little effect on the incidence of mastitis due to bacteria which infect the gland from an environmental reservoir. Streptococcus uberis is one such bacterium which is responsible for a significant proportion of clinical mastitis worldwide.The inadequacies of the current methods of mastitis control have led to the search for additional measures, particularly vaccines to prevent intramammary infection by this bacterium. Such an approach requires detailed knowledge of the pathogenesis of intramammary infection. Our understanding of this area has grown in recent years but a lack of information still hampers disease control. Both live vaccines and, recently, crude sub-unit vaccines have shown promise against bovine mastitis due to S. uberis. Vaccines against mastitis must, however, be able to control infection without the participation of a marked inflammatory response. This review provides an overview of the recent advances which have been made in our understanding of host-pathogen interactions which promote infection and disease and highlights areas for strategic research aimed at controlling this bacterial infection. 相似文献
994.
995.
A double blind controlled trial was carried out on four commercial dairy herds, to investigate the effect of one 50 mg injection of selenium, 10 days before parturition, on the incidence of weak calves. Although the treatment marginally increased the selenium status of treated calves it did not decrease the incidence of the weak calf syndrome. 相似文献
996.
S Chema S Waghela A D James T T Dolan A S Young W N Masiga A D Irvin G H Mulela L S Wekesa 《The Veterinary record》1986,118(21):588-589
997.
Adult cockerels of a commercial egg-producing strain did not develop liver haemorrhages when maintained for 12 weeks on a diet containing 400 g rapeseed meal/kg food. Haemorrhages occurred in 43% of laying hens of the same strain as the cockerels and 33% of laying hens of another strain maintained on the same diet for the same period. Oestrogenisation of the male birds did not influence the incidence of haemorrhage. 相似文献
998.
Isolation of group eugonic fermenter-4 bacteria from a cat with multifocal suppurative pneumonia 总被引:1,自引:0,他引:1
R Drolet K B Kenefick M R Hakomaki G E Ward 《Journal of the American Veterinary Medical Association》1986,189(3):311-312
A pure growth of Group Eugonic Fermenter-4 bacteria (gram-negative) was isolated from the lungs of an 11-year-old male domestic cat that had been ill for 2 days before death. Clinical signs included anorexia, severe dyspnea, and salivation. The lungs contained several firm, slightly raised, yellowish-gray, spherical nodules of various sizes. Purulent exudate was found in the pericardial sac and left pleural cavity. Histologic evaluation revealed multifocal suppurative pneumonia. 相似文献
999.
1000.
A J Paul K S Todd J P Sundberg J A DiPietro J W McCall 《American journal of veterinary research》1986,47(4):883-884
Forty-two Beagles, 14 to 15 weeks of age, were injected subcutaneously with 50 infective larvae of Dirofilaria immitis and were allotted by weight, within sex, to 6 treatment groups. Group 1 served as nonmedicated vehicle-treated controls; groups 2 through 5 were given an oral tablet form of ivermectin at dosages of 0.3 micrograms/kg, 1.0 micrograms/kg, 2.0 micrograms/kg, and 3.3 micrograms/kg at 30 days after inoculation; group 6 was given the 2.0 micrograms/kg dosage at 45 days after inoculation. Dogs were euthanatized and necropsied 154 days after treatment (day 139 for dogs in group 6) and examined for heartworms. On the numerical bases of helminths recovered in the groups, the efficacies for preventing heartworm maturation were 0% (group 2), 53.2% (group 3), 97.2% (group 4), 98.1% (group 5), and 63.8% (group 6). Drug-related adverse reactions were not detected. 相似文献