全文获取类型
收费全文 | 132481篇 |
免费 | 6910篇 |
国内免费 | 136篇 |
专业分类
林业 | 6121篇 |
农学 | 4237篇 |
基础科学 | 711篇 |
14840篇 | |
综合类 | 24331篇 |
农作物 | 5082篇 |
水产渔业 | 6258篇 |
畜牧兽医 | 68090篇 |
园艺 | 1596篇 |
植物保护 | 8261篇 |
出版年
2018年 | 1805篇 |
2017年 | 1885篇 |
2016年 | 1763篇 |
2015年 | 1584篇 |
2014年 | 1869篇 |
2013年 | 5125篇 |
2012年 | 3414篇 |
2011年 | 4125篇 |
2010年 | 2633篇 |
2009年 | 2565篇 |
2008年 | 3898篇 |
2007年 | 3913篇 |
2006年 | 3609篇 |
2005年 | 3402篇 |
2004年 | 3235篇 |
2003年 | 3252篇 |
2002年 | 3146篇 |
2001年 | 3813篇 |
2000年 | 3812篇 |
1999年 | 3147篇 |
1998年 | 1269篇 |
1997年 | 1241篇 |
1995年 | 1367篇 |
1994年 | 1180篇 |
1993年 | 1211篇 |
1992年 | 2562篇 |
1991年 | 2740篇 |
1990年 | 2710篇 |
1989年 | 2723篇 |
1988年 | 2510篇 |
1987年 | 2433篇 |
1986年 | 2508篇 |
1985年 | 2516篇 |
1984年 | 2054篇 |
1983年 | 1916篇 |
1982年 | 1279篇 |
1979年 | 2008篇 |
1978年 | 1586篇 |
1977年 | 1458篇 |
1976年 | 1422篇 |
1975年 | 1545篇 |
1974年 | 1934篇 |
1973年 | 1955篇 |
1972年 | 1922篇 |
1971年 | 1790篇 |
1970年 | 1753篇 |
1969年 | 1612篇 |
1968年 | 1415篇 |
1967年 | 1461篇 |
1966年 | 1283篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
S Katsuda H Hosomi M Shiomi Y Watanabe 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(4):669-673
Effects of atherosclerosis on the mean value and daily variation of arterial pressure were studied in 12 Watanabe-heritable hyperlipidemic (WHHL) rabbits aged 12 to 35 months and 25 normal Japanese white rabbits aged 6 to 30 months. A pressure catheter was inserted through the left subclavian artery under pentobarbital anesthesia. A few days after the catheterization, the mean arterial pressure (MAP) of the rabbits, which were active and in a good state of appetite, was recorded by an analogue-to-digital converter every second for about 6 hrs and stored in a computer. The mean (M) and standard deviation (SD) in the WHHL rabbit, calculated from each successive MAP record, ranged widely from 85.8 to 131.4 mmHg and 5.6 to 12.6 mmHg, respectively. There was no significant correlation between M and SD in the WHHL rabbit. M and variance (V) of MAP in the WHHL rabbit were significantly higher than those in the normal rabbit. M did not show any significant change with increasing ages, whereas SD increased significantly with aging in the WHHL rabbit. Concentrations of serum total cholesterol and triglyceride in the WHHL rabbit were 475 and 328 mg/dl, which were about nine and seven times as high as those in the normal rabbit, respectively. Macroscopic and histopathological examinations of the aorta revealed development and spread of sclerotic lesions with aging in the WHHL rabbit. We can conclude that development of atherosclerosis with aging in the WHHL rabbit causes malfunction of the baroreceptors, which contributes to hypertension and lability of arterial pressure. 相似文献
102.
Serum amyloid A protein concentration measured by radial immunodiffusion in Abyssinian and non-Abyssinian cats 总被引:1,自引:0,他引:1
S P DiBartola J A Reiter J B Cornacoff G J Kociba M D Benson 《American journal of veterinary research》1989,50(8):1414-1417
Serum amyloid A (SAA) protein concentration was determined by use of radial immunodiffusion (RID) in 4 groups of cats: Abyssinian cats with amyloidosis, healthy Abyssinian cats without clinical evidence of amyloidosis, hospitalized non-Abyssinian cats, and clinically normal non-Abyssinian cats. Mean SAA concentration in Abyssinian cats with amyloidosis was significantly (P = 0.05) higher than mean SAA concentration in healthy Abyssinian cats without clinical evidence of amyloidosis and in hospitalized non-Abyssinian cats. Mean SAA concentration in clinically normal non-Abyssinian cats was significantly (P = 0.05) lower than mean SAA concentration in healthy Abyssinian cats without clinical evidence of amyloidosis and in hospitalized non-Abyssinian cats. Affected and healthy Abyssinian cats, however, could not reliably be distinguished on the basis of SAA concentration, because of the wide range of SAA values in these 2 groups of cats. 相似文献
103.
Effects of epidural xylazine on EEG responses to surgical stimulation during isoflurane anaesthesia in dogs 总被引:1,自引:0,他引:1
K. A. Otto S. Piepenbrock B. Rischke C. Bötel† 《Veterinary anaesthesia and analgesia》1997,24(1):33-38
The effects of epidural administration of 250 μg/kg xylazine on EEG responses to surgical stimulation of 5 different intensities were evaluated during isoflurane anaesthesia for an experimental orthopaedic procedure in dogs. The dogs were assigned randomly to one of 2 treatment groups receiving either xylazine (n = 4) or equal volumes of sterile water (n = 4) (control group) epidurally. Intense surgical stimulation during removal of a bone graft from the dorsoiliac spine of the ileum was associated with a significantly (P = 0.0339) higher increase in EEG alpha/delta ratio after epidural administration of sterile water than after epidural injection of 250 μg/kg of xylazine. In addition, the preincision baseline values for 80% spectral edge frequency were significantly (P = 0.0339) lower in the xylazine group compared to control dogs. Our results suggest that epidural administration of 250 μg/kg of xylazine during orthopaedic procedures in dogs exerts antinociceptive effects which may be in part mediated by a supraspinal effect of xylazine. 相似文献
104.
J Jieyuan P B Spradbrow 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1992,39(5):388-390
Chickens were given various fowlpox vaccines on food pellets--a commercial vaccine (strain M), and the same strain after a single passage on chorio-allantoic membrane or in chicken embryo fibroblasts. All three oral vaccines induced antibodies at levels similar to those induced by commercial strain M administered to the wingweb. The oral vaccine derived from chorio-allantoic membrane gave protection similar to that obtained with vaccine administered by the wingweb, but this required a thousandfold more virus. 相似文献
105.
106.
H M Wens 《DTW. Deutsche tier?rztliche Wochenschrift》1992,99(6):264-265
This study examines LEIBNIZ' idea of Veterinary medicine in a biographical context. It is based on material from the Leibniz-Archives of the Nieders?chsische Landesbibliothek Hannover, primary sources as well as the correspondence between LEIBNIZ and F. HOFFMANN and B. RAMAZZINI. Critical analysis of LEIBNIZ' proposal to establish a medical administrative authority and an analysis of further sources corroborate the view of LEIBNIZ as a progressive thinker who included the epidemiology of veterinary medicine (the preventive approach) in his conception. In this way he conceived of veterinary medicine in scientific terms which is going to be the relevant approach today. 相似文献
107.
Two outbreaks of the egg drop syndrome were observed in quail flocks maintained on a farm together with chickens. The decrease in egg production ranged from 10.6 per cent to 50.6 per cent, and the number of soft-shelled eggs increased with the decline in egg production. In both the outbreaks haemagglutination inhibiting antibodies to EDS-76 virus were detected. Fluorescent viral antigen specific to EDS-76 virus was also detected in the lining epithelial and glandular cells of the uterus. 相似文献
108.
109.
110.
Water-stable macro-aggregate size fractions (>2.0 mm, 1.0–2.0 mm, 0.5–1.0 mm and 0.25–0.5 mm) and non-aggregated soil from a sandy loam under long-term clover-based pasture and from grass pasture were analysed to determine the role of acid- and water-extractable carbohydrate C, total hyphal length, microbial biomass, organic C and total and mycorrhizal root length in stabilization of the aggregates. Aggregates were examined by scanning electron microscopy (SEM) and the particle-size distribution of the size fractions was also determined. Macro-aggregation increased under grass, relative to clover-based pasture; however, the properties of the aggregate fractions measured did not reflect this difference. Microbial-biomass C, extractable-carbohydrate C, hyphal length, total and mycorrhizal root length and organic C content of the soils were poorly correlated with macro-aggregation. Within the aggregates, the proportion of 250–1000-km sand was smaller and clay, silt and fine sand (20–250 μm) were greater relative to non-aggregated soil, suggesting that the >250-μm sand in the non-aggregated soil limited the stabilization of macro-aggregates. Under SEM, no enmeshment of aggregates by hyphae and roots was apparent. Although 50–160 m hyphae g?1 soil was found within the aggregates, calculations showed that on average only 5 to 13 lengths of hyphae were associated with each 250-μm cube of soil within the aggregates, and suggested little potential to stabilize the aggregates by enmeshing. On average, all >2.0-mm aggregates contained less than 3.6 mm of roots and less than 50% by weight of <2.0-mm aggregates contained a single length of root. The findings cast doubt about the role of hyphae and fine roots in the stabilization of macro-aggregates through an enmeshing mechanism in sandy soils. 相似文献