全文获取类型
收费全文 | 92001篇 |
免费 | 5659篇 |
国内免费 | 46篇 |
专业分类
林业 | 4265篇 |
农学 | 3497篇 |
基础科学 | 636篇 |
11761篇 | |
综合类 | 13680篇 |
农作物 | 3429篇 |
水产渔业 | 5007篇 |
畜牧兽医 | 48518篇 |
园艺 | 1204篇 |
植物保护 | 5709篇 |
出版年
2020年 | 765篇 |
2019年 | 970篇 |
2018年 | 1657篇 |
2017年 | 1915篇 |
2016年 | 1723篇 |
2015年 | 1450篇 |
2014年 | 1789篇 |
2013年 | 3871篇 |
2012年 | 3066篇 |
2011年 | 3709篇 |
2010年 | 2413篇 |
2009年 | 2393篇 |
2008年 | 3594篇 |
2007年 | 3331篇 |
2006年 | 3268篇 |
2005年 | 2785篇 |
2004年 | 2686篇 |
2003年 | 2703篇 |
2002年 | 2471篇 |
2001年 | 3459篇 |
2000年 | 3378篇 |
1999年 | 2588篇 |
1998年 | 1003篇 |
1997年 | 1069篇 |
1996年 | 899篇 |
1995年 | 1064篇 |
1994年 | 904篇 |
1993年 | 909篇 |
1992年 | 1857篇 |
1991年 | 1924篇 |
1990年 | 1874篇 |
1989年 | 1875篇 |
1988年 | 1616篇 |
1987年 | 1600篇 |
1986年 | 1638篇 |
1985年 | 1537篇 |
1984年 | 1236篇 |
1983年 | 1043篇 |
1982年 | 718篇 |
1979年 | 1065篇 |
1978年 | 827篇 |
1975年 | 823篇 |
1974年 | 899篇 |
1973年 | 868篇 |
1972年 | 808篇 |
1971年 | 798篇 |
1970年 | 807篇 |
1969年 | 784篇 |
1968年 | 708篇 |
1967年 | 736篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Transmission of porcine reproductive and respiratory syndrome virus from persistently infected sows to contact controls. 总被引:3,自引:0,他引:3 下载免费PDF全文
M D Bierk S A Dee K D Rossow S Otake J E Collins T W Molitor 《Canadian journal of veterinary research》2001,65(4):261-266
The objective of this study was to determine if porcine reproductive and respiratory syndrome virus (PRRSV) could persist in non-pregnant sows and if persistently infected sows could transmit virus to naive contact controls. Twelve PRRSV-naive, non-pregnant sows (index sows) were infected with a field isolate of PRRSV and housed in individual isolation rooms for 42 to 56 days postinfection. Following this period, 1 naive contact sow was placed in each room divided by a gate allowing nose-to-nose contact with a single index sow. Index sows were not viremic at the time of contact sow entry. Virus nucleic acid was detected by polymerase chain reaction, and infectious virus was detected by virus isolation in sera from 3 of the 12 contact sows at 49, 56, and 86 days postinfection. All 3 infected contacts developed PRRSV antibodies. Virus nucleic acid was detected in tissues of all of the 12 index sows at 72 or 86 days postinfection. Nucleic acid sequencing indicated that representative samples from index and infected contacts were homologous (> 99%) to the PRRSV used to infect index sows at the onset of the study. This study demonstrates that PRRSV can persist in sows and that persistently infected sows can transmit virus to naive contact animals. 相似文献
92.
93.
S. LEY A. WATERMAN A. LIVINGSTON 《Journal of veterinary pharmacology and therapeutics》1991,14(2):141-144
A comparison of the analgesic potency of the alpha 2-adrenoceptor agonist, xylazine, in control healthy sheep and sheep suffering chronic pain from footrot, indicated that the analgesic effectiveness of xylazine was significantly reduced in the animals experiencing chronic pain. This was measured by recording the threshold to a mechanically applied pressure stimulus. Furthermore, when the condition was apparently resolved, by conventional treatment over a period of 2 to 3 weeks, the decreased analgesic effectiveness of the alpha 2-agonist was still apparent although the animals were clinically cured of the footrot. 相似文献
94.
95.
Veterinary Research Communications - 相似文献
96.
97.
Since 1993, 14 cases of avian influenza from four different states in the U.S.A. have been diagnosed by virus isolation from eight avian species. Only 11 of the 14 avian influenza virus (AIV) primary isolations would have been successful if only the standard protocol for AIV isolation, i.e., inoculation of specific-pathogen-free embryonating chicken eggs (ECEs) by the chorioallantoic sac (CAS) route, had been followed. Primary isolation attempts were negative for AIV in three cases in which ECEs were inoculated by the CAS route; AIV could not be detected by hemagglutinating activity, agar gel immunodiffusion test or negative stain electron microscopy. However, in these three cases, primary isolations of AIV were achieved by inoculation of ECEs into either the yolk sac or onto the chorioallantoic membrane. 相似文献
98.
99.
M Kennedy S Citino T Dolorico A H McNabb A S Moffat S Kania 《Journal of zoo and wildlife medicine》2001,32(1):25-30
Feline coronavirus genetic elements were detected by polymerase chain reaction from blood, fecal samples, and effusive fluid collected from 33 cheetahs in the U.S.A. Feline coronavirus-specific serum antibodies were also measured by indirect immunofluorescence. Ten cheetahs were positive for viral shedding by polymerase chain reaction, whereas 13 were seropositive by immunofluorescence. Results of serology did not consistently correlate with shedding of virus, and the capture antigen used for detection of feline coronavirus-specific antibodies had a significant impact on results. Testing of samples from one population over a 1-yr period indicated chronic infection in some animals. These relatively healthy carrier animals were a source of virus for contact animals. Screening programs in cheetah populations for feline coronavirus infection may be most reliable if a combination of serologic analysis and viral detection by polymerase chain reaction is used. 相似文献
100.
Sean G. Sanders DVM Russell L. Tucker DVM Rodney S. Bagley DVM Patrick R. Gavin DVM PhD 《Veterinary radiology & ultrasound》2001,42(4):291-296
Magnetic resonance imaging (MR) was used to make a diagnosis of equine nigropallidal encephalomalacia in a horse. Equine nigropallidal encephalomalacia is a neurodegenerative disease that has many characteristics with Parkinson-like diseases in humans. Historically, horses were euthanized based on clinical signs and exposure to the toxic weed, yellow star thistle (Centaurea solstitialis). Previously, the disease has only been confirmed on necropsy. MR imaging can provide accurate and sensitive visualization of typical lesions seen in the brain of horses affected with equine nigropallidal encephalomalacia. Lesions were seen on T1-weighted, T2-weighted and proton density images. There was no contrast enhancement following Gd-DTPA administration. Lesions seen on MR were confirmed at necropsy. Using MR to confirm a diagnosis of equine nigropallidal encephalomalacia will prevent unnecessary suffering of horses and expense to owners that would otherwise incur, while further diagnostics are performed. 相似文献