全文获取类型
| 收费全文 | 146810篇 |
| 免费 | 8672篇 |
| 国内免费 | 676篇 |
专业分类
| 林业 | 5610篇 |
| 农学 | 4307篇 |
| 基础科学 | 1122篇 |
| 16924篇 | |
| 综合类 | 28452篇 |
| 农作物 | 5469篇 |
| 水产渔业 | 6881篇 |
| 畜牧兽医 | 76620篇 |
| 园艺 | 1861篇 |
| 植物保护 | 8912篇 |
出版年
| 2019年 | 1430篇 |
| 2018年 | 2054篇 |
| 2017年 | 2394篇 |
| 2016年 | 2154篇 |
| 2015年 | 1983篇 |
| 2014年 | 2317篇 |
| 2013年 | 5361篇 |
| 2012年 | 4371篇 |
| 2011年 | 5419篇 |
| 2010年 | 3520篇 |
| 2009年 | 3489篇 |
| 2008年 | 4983篇 |
| 2007年 | 4753篇 |
| 2006年 | 4428篇 |
| 2005年 | 4161篇 |
| 2004年 | 3812篇 |
| 2003年 | 3874篇 |
| 2002年 | 3674篇 |
| 2001年 | 4432篇 |
| 2000年 | 4571篇 |
| 1999年 | 3523篇 |
| 1998年 | 1429篇 |
| 1997年 | 1379篇 |
| 1995年 | 1561篇 |
| 1994年 | 1394篇 |
| 1993年 | 1346篇 |
| 1992年 | 2982篇 |
| 1991年 | 3241篇 |
| 1990年 | 3103篇 |
| 1989年 | 3053篇 |
| 1988年 | 2893篇 |
| 1987年 | 3019篇 |
| 1986年 | 3085篇 |
| 1985年 | 2845篇 |
| 1984年 | 2371篇 |
| 1983年 | 2031篇 |
| 1982年 | 1390篇 |
| 1979年 | 2151篇 |
| 1978年 | 1766篇 |
| 1977年 | 1503篇 |
| 1976年 | 1499篇 |
| 1975年 | 1567篇 |
| 1974年 | 2065篇 |
| 1973年 | 2041篇 |
| 1972年 | 1968篇 |
| 1971年 | 1798篇 |
| 1970年 | 1751篇 |
| 1969年 | 1623篇 |
| 1968年 | 1356篇 |
| 1967年 | 1433篇 |
排序方式： 共有10000条查询结果，搜索用时 62 毫秒
991.
Prevalence of gastrointestinal nematodes in dairy heifers in western Canada 总被引：3，自引：2，他引：1 
下载免费PDF全文
下载免费PDF全文 Cox WR Lemiski D 《The Canadian veterinary journal. La revue veterinaire canadienne》1989,30(8):666-668
A survey was conducted to estimate the prevalence of gastrointestinal nematodes in grazing dairy replacement heifers in western Canada. Fecal samples were collected from 566 animals on 34 farms distributed over the three prairie provinces. Fecal egg counts were performed using a modified Wisconsin centrifugation technique. The overall mean farm fecal egg count was 16.0 eggs per gram feces (range 0.7-78.1 epg). Gastrointestinal nematodes were demonstrated on every farm examined, and 93.3% of all individuals tested were positive. 相似文献
992.
993.
Glasser's disease and prevalence of subclinical infection with Haemophilus parasuis in swine in southern Ontario 下载免费PDF全文
下载免费PDF全文 Smart NL Miniats OP Rosendal S Friendship RM 《The Canadian veterinary journal. La revue veterinaire canadienne》1989,30(4):339-343
Glasser's disease accounted for less than 1% of total swine mortalities in an 11 year retrospective postmortem survey of swine submissions at three provincial government diagnostic laboratories in southern Ontario. However, Glasser's disease was suspected in 17 of 83 boar mortalities at the Record of Production Boar Test Station between 1983 and 1985 and was much more common in specific-pathogen-free (SPF) boars than in conventional boars. The prevalence of the causative organism, Haemophilus parasuis, was determined for 19 SPF herds in Ontario classified as "Excellent" under the Ontario Swine Herd Health Policy. Nasal swabs from two-month-old pigs were cultured on chocolate agar containing 1.5 mug/mL lincomycin, 5 mug/mL bacitracin, and 0.1 mug/mL crystal violet. Three herds were negative for H. parasuis infection; 16 herds contained clinically healthy carrier pigs. 相似文献
994.
Canine congenital aortic stenosis: A review of the literature and commentary 总被引：2，自引：0，他引：2 下载免费PDF全文
下载免费PDF全文 O'grady MR Holmberg DL Miller CW Cockshutt JR 《The Canadian veterinary journal. La revue veterinaire canadienne》1989,30(10):811-815
Congenital aortic stenosis usually affects the subvalvular region, and occurs mainly in Newfoundland, Golden Retriever, German Shepherd, and Boxer dogs. The disorder is inherited as a dominant trait with variable penetrance in Newfoundland dogs.
The prevalence of subaortic stenosis-like heart murmurs in Golden Retriever dogs appears to be very much greater than previously suspected.
Most cases of aortic stenosis represent mild lesions, are detected as incidental findings, and result in no loss of longevity or quality of life. Moderate or severe stenosis may result in exertional weakness, syncope, or sudden death. Signs of congestive heart failure are rare unless mitral valve insufficiency is present.
Generally, electrocardiography and radiography are unrevealing in this disorder. Doppler echocardiography may be the best diagnostic tool to detect even mild cases of aortic stenosis.
At present, therapy is limited due to the technical expertise and expense required. The prognosis depends on the severity of the lesion.
相似文献995.
996.
997.
998.
999.
1000.
The estimation of water flux through the stem of a plant by point estimates based on the heat pulse technique requires integration of the velocity profile. The polynomial integration method and the weighted average technique both assume radial symmetry about the bole. A method is introduced that solves the equations for the ellipse in the weighted average technique, and includes an optimizing algorithm for the placement of sensors. The sensitivity of sapflow estimates through stems to increasing eccentricity is examined by means of analytical solutions and simulation. The error in sap flux measurement resulting from the radial approximation of the sapwood conducting area is expressed analytically and shown to be small over the range of eccentricities (e < 0.8) expected in nature. Simulations where radial symmetry is assumed for elliptical stems show substantial error in mean velocity (and thus flux) with modest eccentricities (e > 0.4). 相似文献