全文获取类型
收费全文 | 231954篇 |
免费 | 14031篇 |
国内免费 | 658篇 |
专业分类
林业 | 23147篇 |
农学 | 13905篇 |
基础科学 | 2935篇 |
41321篇 | |
综合类 | 19344篇 |
农作物 | 17063篇 |
水产渔业 | 16093篇 |
畜牧兽医 | 83603篇 |
园艺 | 6192篇 |
植物保护 | 23040篇 |
出版年
2021年 | 2434篇 |
2020年 | 2802篇 |
2019年 | 3612篇 |
2018年 | 3794篇 |
2017年 | 4159篇 |
2016年 | 4629篇 |
2015年 | 4220篇 |
2014年 | 5563篇 |
2013年 | 16110篇 |
2012年 | 5566篇 |
2011年 | 7238篇 |
2010年 | 6995篇 |
2009年 | 7678篇 |
2008年 | 6703篇 |
2007年 | 5762篇 |
2006年 | 6485篇 |
2005年 | 5745篇 |
2004年 | 5591篇 |
2003年 | 5367篇 |
2002年 | 4727篇 |
2001年 | 5031篇 |
2000年 | 4668篇 |
1999年 | 4621篇 |
1998年 | 4036篇 |
1997年 | 4082篇 |
1996年 | 3833篇 |
1995年 | 4398篇 |
1994年 | 3778篇 |
1993年 | 3496篇 |
1992年 | 3679篇 |
1991年 | 3804篇 |
1990年 | 3527篇 |
1989年 | 3493篇 |
1988年 | 3075篇 |
1987年 | 3204篇 |
1986年 | 3065篇 |
1985年 | 3442篇 |
1984年 | 3312篇 |
1983年 | 3138篇 |
1982年 | 2686篇 |
1981年 | 2648篇 |
1980年 | 2602篇 |
1979年 | 2788篇 |
1978年 | 2613篇 |
1977年 | 2431篇 |
1976年 | 2290篇 |
1975年 | 2100篇 |
1974年 | 2259篇 |
1973年 | 2153篇 |
1971年 | 1960篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
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
112.
113.
114.
A.J.A. Vinten D.R. Lewis D.R. Fenlon K.A. Leach R. Howard I. Svoboda I. Ogden 《Soil Use and Management》2002,18(3):223-231
Abstract. Slurry from farm animals may contaminate water supplies, rivers and bathing waters with faecal coliforms, such as Escherichia coli . Where animals harbour the O157 strain the hazard to human health is particularly high, but both the hazard level, and the low incidence and sporadic nature of the excretion of E. coli O157 make it difficult to study this strain under field conditions. The survival of total E. coli and of E. coli O157 were compared in the laboratory for two soils under controlled temperature and moisture. E. coli O157 die-off rate was the same as or quicker than for total E. coli . This result meant that field experiments studying the fate of total E. coli should give a satisfactory evaluation of the risk of water contamination by the O157 strain. In four field experiments at three sites, slurry containing total E. coli numbers of 2.2 × 104 to 5.7 × 105 colony forming units per mL (c.f.u. mL–1 ) was applied to drained field plots. Field die-off was faster than expected from laboratory experiments, especially in one experiment where two weeks dry weather followed application. In all but this experiment, the first drain flow events after slurry application led to very high E. coli concentrations in the drains (103 to 104 c.f.u. mL–1 ). E. coli O157 was present in the slurry used for two of the experiments (33 c.f.u. per 100 mL in each case). However the proportion of E.coli O157 was very low (about 1 in 105 ) and it was not detected in the drainage water. After the first week E. coli drainage water numbers decreased rapidly but they were 1–10 c.f.u. mL–1 for much of the sampling period after slurry application (1–3 months). 相似文献
115.
116.
Intramuscular and oral disposition of enrofloxacin in African grey parrots following single and multiple doses 总被引:5,自引:0,他引:5
K. FLAMMER D. P. AUCOIN D. A. WHITT 《Journal of veterinary pharmacology and therapeutics》1991,14(4):359-366
The intramuscular (IM) and oral (PO) disposition of enrofloxacin, a new fluoroquinolone antimicrobial drug, were evaluated in African grey parrots. Peak enrofloxacin concentration, mean (+/- SEM), at 1 h following a 15-mg/kg IM dose was 3.87 (+/- 0.27) micrograms/ml and declined with a mean residence time of 3.05 h. Peak enrofloxacin plasma concentrations at 2 to 4 h following oral doses of 3, 15, and 30 mg/kg were 0.31 (+/- 0.11), 1.12 (+/- 0.11), and 1.69 (+/- 0.23) micrograms/ml, respectively, and declined with a mean residence time of 3.44-5.28 h. The relative bioavailability of the 15-mg/kg oral dose was 48%. An equipotent metabolite, ciprofloxacin, was detected in plasma at concentrations ranging from 3 to 78% of those of enrofloxacin. Enrofloxacin concentrations and area under the curve were significantly lower, the mean residence time significantly shorter and the ciprofloxacin/enrofloxacin ratios higher, following 10 days of oral treatment at 30 mg/kg every 12 h. Following 10 days of treatment, no significant biochemical changes were noted; however, polydipsia and polyuria occurred in treated birds, but resolved quickly upon discontinuation of enrofloxacin administration. These studies indicate that a rational starting dose for enrofloxacin in psittacines (7.5-30 mg/kg BID) should be higher than those in other domestic animals. 相似文献
117.
I.-S. Park G. C. Choi D. S. Kim Y. K. Nam 《Journal of the World Aquaculture Society》2002,33(4):494-500
For the evaluation of hormonal control of spermiation in fish, a method to quanify the spermiation response of mature Rhynchocypris oxycephalus (Sauvage and Dabry) to hormonal therapy is described. Spermatocrit was determined after 7 min centrifugation at 18,000 ± g and sperm density was estimated by a standard hemocytomer method. Sperm density can be predicted from spermatocrit since their relationship is linear as described by the regression equation, Y = 3.68X - 27.18 ( R 2 = 0.82, N = 50). where Y is spermatocrit and × is sperm density. Milt production by mature R. oxycephalus was highest at 24 h after injection of 1,000 IU human chorionic gonadotropin (HCG) and 50 μg luteinizing hormone-releasing hormone analogue (LHRHa) per kg body weight. Increased milt production coincided with low spermatocrit and sperm density levels. These results demonstrate that spermiation in mature R. oxycephalus can be reliably evaluated by a spermatocrit method and that HCG and LHRHa are effective in stimulating of spermiation in this species. 相似文献
118.
119.
Karen E. Bateman DVM MSc Pamela A. Catton Paul W. Pennock Stephen A. Kruth 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(4):267-272
Eighteen dogs with malignant melanoma of the oral cavity were treated with high-dose per fraction (0–7–21) radiation therapy. Eight hundred cGy was administered on days 0, 7, and 21 for a total dose of 2,400 cGy in 3 weeks. Of 17 dogs evaluated, 9 (53%) had a complete remission and 5 (30%) achieved a partial remission with an overall response rate of 83%. Local failure occurred in 2 of the 9 dogs where a complete response was initially observed. One dog died of intercurrent disease, and one died of metastatic disease without evidence of local recurrence. Five dogs are alive and free of disease 9 to nineteen months from the initiation of therapy. The 0–7–21 protocol was well-tolerated, and acute radiation reactions were low-grade and limited to the skin. The results of this study demonstrate that oral melanomas in dogs are responsive to radiation. 0–7–21 radiation therapy offers a viable alternative to radical excision, especially when tumor volume or location would require cosmetically or functionally debilitating surgery. 相似文献
120.