全文获取类型
收费全文 | 286108篇 |
免费 | 16097篇 |
国内免费 | 1411篇 |
专业分类
林业 | 23951篇 |
农学 | 14402篇 |
基础科学 | 3208篇 |
45003篇 | |
综合类 | 37633篇 |
农作物 | 17409篇 |
水产渔业 | 17158篇 |
畜牧兽医 | 113654篇 |
园艺 | 6627篇 |
植物保护 | 24571篇 |
出版年
2020年 | 3059篇 |
2019年 | 3840篇 |
2018年 | 4171篇 |
2017年 | 4629篇 |
2016年 | 4942篇 |
2015年 | 4569篇 |
2014年 | 5877篇 |
2013年 | 16530篇 |
2012年 | 7210篇 |
2011年 | 9283篇 |
2010年 | 7895篇 |
2009年 | 8297篇 |
2008年 | 8441篇 |
2007年 | 7598篇 |
2006年 | 8057篇 |
2005年 | 7404篇 |
2004年 | 7056篇 |
2003年 | 6901篇 |
2002年 | 6260篇 |
2001年 | 6588篇 |
2000年 | 6406篇 |
1999年 | 5787篇 |
1998年 | 4218篇 |
1997年 | 4239篇 |
1996年 | 3999篇 |
1995年 | 4520篇 |
1994年 | 3984篇 |
1993年 | 3698篇 |
1992年 | 4888篇 |
1991年 | 5187篇 |
1990年 | 4938篇 |
1989年 | 4911篇 |
1988年 | 4445篇 |
1987年 | 4477篇 |
1986年 | 4413篇 |
1985年 | 4586篇 |
1984年 | 4219篇 |
1983年 | 3894篇 |
1982年 | 3154篇 |
1981年 | 3039篇 |
1980年 | 2987篇 |
1979年 | 3751篇 |
1978年 | 3322篇 |
1977年 | 3010篇 |
1976年 | 2925篇 |
1975年 | 2822篇 |
1974年 | 3249篇 |
1973年 | 3138篇 |
1972年 | 2991篇 |
1971年 | 2905篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
Modell W 《Science (New York, N.Y.)》1939,89(2311):349-350
144.
Glock WS 《Science (New York, N.Y.)》1922,56(1452):484-485
145.
146.
147.
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
148.
149.
In New Zealand, the brushtail possum (Trichosurus vulpecula) is the principal wildlife vector of bovine tuberculosis. Control of infected possum populations contributes to the control of tuberculosis in domestic livestock. Vaccination is potentially a complementary strategy to population control, but to be cost-effective, administration of the vaccine to possums would need to be from an appropriately designed automatic vaccinator. Possums themselves would activate the vaccinator so that it would deliver an aerosol spray of vaccine. There would be no direct way to prevent possums receiving multiple doses of vaccine. This study examined the effect on protective immunity of repeated vaccination. Captive possums were vaccinated with BCG strain pasteur 1173P2 either 12 times at weekly intervals, twice at 6-weekly intervals, or once. Vaccination was by a combination of intranasal aerosol and conjunctival instillation. Eight weeks after the last dose of vaccine, all possums were challenged intratracheally with Mycobacterium bovis strain 83/6235. Vaccination induced a significant immune response as measured by the lymphocyte proliferation assay (LPA). A significant level of protection, as measured by the response to challenge, developed in all the vaccinated possum groups, but protection was greatest in the group vaccinated 12 times. It was concluded that protection would be enhanced if vaccinations were repeated at short intervals (weekly), but no benefit or detriment resulted from revaccination after longer intervals (1-2 months). 相似文献
150.
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