全文获取类型
收费全文 | 181202篇 |
免费 | 10009篇 |
国内免费 | 117篇 |
专业分类
林业 | 7781篇 |
农学 | 5876篇 |
基础科学 | 1168篇 |
22873篇 | |
综合类 | 30098篇 |
农作物 | 7156篇 |
水产渔业 | 9052篇 |
畜牧兽医 | 92603篇 |
园艺 | 2421篇 |
植物保护 | 12300篇 |
出版年
2019年 | 1706篇 |
2018年 | 2571篇 |
2017年 | 2918篇 |
2016年 | 2678篇 |
2015年 | 2276篇 |
2014年 | 2847篇 |
2013年 | 7103篇 |
2012年 | 5218篇 |
2011年 | 6444篇 |
2010年 | 4187篇 |
2009年 | 4319篇 |
2008年 | 6318篇 |
2007年 | 5986篇 |
2006年 | 5565篇 |
2005年 | 5259篇 |
2004年 | 4988篇 |
2003年 | 5195篇 |
2002年 | 4709篇 |
2001年 | 5543篇 |
2000年 | 5541篇 |
1999年 | 4447篇 |
1998年 | 1952篇 |
1997年 | 1906篇 |
1996年 | 1745篇 |
1995年 | 2104篇 |
1994年 | 1838篇 |
1993年 | 1734篇 |
1992年 | 3527篇 |
1991年 | 3774篇 |
1990年 | 3667篇 |
1989年 | 3705篇 |
1988年 | 3398篇 |
1987年 | 3329篇 |
1986年 | 3469篇 |
1985年 | 3325篇 |
1984年 | 2777篇 |
1983年 | 2434篇 |
1982年 | 1690篇 |
1979年 | 2569篇 |
1978年 | 2022篇 |
1977年 | 1772篇 |
1976年 | 1792篇 |
1975年 | 1901篇 |
1974年 | 2254篇 |
1973年 | 2311篇 |
1972年 | 2170篇 |
1971年 | 2048篇 |
1970年 | 1975篇 |
1969年 | 1951篇 |
1967年 | 1764篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
In a large pig breeding herd with high prevalence of post-parturient diseases of the sows, weaned sows of different parity groups with (n = 663) or without (n = 1125) recidiving mastitis metritis agalactia (MMA) in their previous history were subjected to ultrasonography. A total of 114 of 663 sows with recidiving MMA in their previous history and with ultrasonographic visible mammary gland changes, and 157 of sows without recidiving MMA in their previous history were culled and subjected to gross pathological and bacteriological examination of their mammary glands. The sows having suffered MMA had more (p < 0.001) hyperechogenic images in their mammary glands compared with the sow having suffered no recidiving MMA. Abdominal glands were more (p < 0.01) prone to pathological changes compared with the pectoral ones. Sows of high parity had more hyperechogenic images and gross pathological changes in their mammary glands compared with the sows of low parity. 相似文献
203.
Canine distal renal tubular acidosis and urolithiasis 总被引:1,自引:0,他引:1
D J Polzin C A Osborne F W Bell 《Veterinary Clinics of North America: Small Animal Practice》1986,16(2):241-250
Distal RTA is characterized by decreased distal renal tubular hydrogen ion secretion, decreased ability to acidify urine, hypercalciuria, hyperphosphaturia, hypocitraturia, and metabolic acidosis. Because of the resulting alterations in urine composition and pH, patients with distal RTA are predisposed to urolithiasis and renal calcification. Diagnosis of distal RTA is important because it is a potentially reversible disorder that, left untreated, may cause nephrocalcinosis, recurrent urolith formation, moderate to severe metabolic acidosis, and renal failure. 相似文献
204.
Abstract – Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974–1991 and in summer (late June to early July) in 1992–2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series. 相似文献
205.
A E van de Braak A T van 't Klooster A Malestein J A Faber 《The Veterinary quarterly》1986,8(1):12-23
Forty-one dairy cows were fed a low (LCa-13 g/d) and a high (HCa-83.5 g/d) calcium ration in the 8 weeks prior to parturition and the effect on the Ca mobilization rate around parturition was studied. Plasma Ca values were stable in the LCa group around parturition. In the older cows of the HCa group a very slight decrease in the mean plasma Ca was observed: 2.58 mmol/l at 12-36 h ante partum decreased to 2.38 mmol/l at parturition. Hypocalcaemia, which commonly occurs around parturition, did not occur in 40 of the cows. A subclinical hypocalcaemia (1.8 mmol/l) occurred in one cow (parity 10) from the HCa group. To assess the efficiency of Ca mobilization, a severe hypocalcaemia (1.0 mmol/l) with clinical signs was induced by means of Na2EDTA infusion (0.90 mmol/min), starting at 10 h post-partum. The older cows in the LCa group required more Na2EDTA than those in the HCa group. Higher urinary hydroxyproline excretion in the week before parturition in the LCa than in the HCa group suggested a higher bone turnover. Plasma PTH levels around parturition were not significantly different between the groups. The amount of colostrum milked out in the first 10 h post-partum did not influence Ca homeostasis around parturition. The results contradict those of many other experiments in which hypocalcaemia was observed in cows ingesting high levels of Ca. It is concluded that the restricted feed intake prepartum possibly had a favourable effect on Ca homeostasis. 相似文献
206.
Serum samples collected from 687 indigenous chickens located in small scattered groups in four states of Nigeria were examined for antibodies to infectious bursal disease (IBD) virus by the agar-gel precipitation (AGPT) and counterimmunoelectrophoresis (CIEOP) tests. 51 of the positive samples were further titrated by each of the two techniques. CIEOP detected more positive reactors (74.59%) than AGPT (58.95%). CIEOP also detected higher antibody levels among the reactors [geometric mean titre (GMT) of 51 samples was 23.02] when compared to AGPT. GMT of the same 51 samples was 21.8. The prevalence of antibodies to IBD virus in the indigenous chickens ranged from 64.7 to 77.7% CIEOP reactors between states. Since reports of IBD outbreaks among these chickens are rare unlike the situation among commercial poultry flocks, it was concluded that local chickens probably act as carriers of IBD virus. 相似文献
207.
208.
209.
210.