全文获取类型
收费全文 | 220301篇 |
免费 | 12456篇 |
国内免费 | 395篇 |
专业分类
林业 | 8445篇 |
农学 | 6905篇 |
基础科学 | 1559篇 |
26625篇 | |
综合类 | 40473篇 |
农作物 | 8547篇 |
水产渔业 | 10900篇 |
畜牧兽医 | 111589篇 |
园艺 | 2864篇 |
植物保护 | 15245篇 |
出版年
2018年 | 2936篇 |
2017年 | 3258篇 |
2016年 | 3086篇 |
2015年 | 2594篇 |
2014年 | 3271篇 |
2013年 | 8645篇 |
2012年 | 6011篇 |
2011年 | 7358篇 |
2010年 | 4794篇 |
2009年 | 4750篇 |
2008年 | 7121篇 |
2007年 | 6842篇 |
2006年 | 6519篇 |
2005年 | 6005篇 |
2004年 | 5798篇 |
2003年 | 5832篇 |
2002年 | 5625篇 |
2001年 | 6825篇 |
2000年 | 6610篇 |
1999年 | 5313篇 |
1998年 | 2260篇 |
1997年 | 2220篇 |
1996年 | 2074篇 |
1995年 | 2483篇 |
1994年 | 2251篇 |
1993年 | 2201篇 |
1992年 | 4447篇 |
1991年 | 4711篇 |
1990年 | 4606篇 |
1989年 | 4675篇 |
1988年 | 4272篇 |
1987年 | 4395篇 |
1986年 | 4539篇 |
1985年 | 4338篇 |
1984年 | 3636篇 |
1983年 | 3248篇 |
1982年 | 2278篇 |
1981年 | 2152篇 |
1979年 | 3353篇 |
1978年 | 2754篇 |
1977年 | 2374篇 |
1976年 | 2184篇 |
1975年 | 2310篇 |
1974年 | 2941篇 |
1973年 | 3062篇 |
1972年 | 2939篇 |
1971年 | 2625篇 |
1970年 | 2518篇 |
1969年 | 2380篇 |
1967年 | 2023篇 |
排序方式: 共有10000条查询结果,搜索用时 968 毫秒
241.
242.
Spealman CR 《Science (New York, N.Y.)》1941,93(2408):187-188
The rate of the frog or guinea pig heart preparation was not significantly influenced by the H-ion concentration when this was kept within limits which allowed the heart to continue beating. The theory that the H-ion concentration is intimately concerned with the origination of the heart beat is not supported by the results of this investigation. 相似文献
243.
J. E. Reubranb 《European Journal of Forest Research》1870,14(1):137-139
Ohne Zusammenfassung 相似文献
244.
245.
Lockyer JN 《Science (New York, N.Y.)》1886,7(169):386-387
246.
247.
The vulvar labia of ewes naturally infected with ureaplasma were significantly more swollen and red than those of uninfected ewes. Similar changes were observed following experimental infection of previously uninfected ewes. These differences, although statistically significant, were not sufficiently marked to be useful in diagnosing infection by clinical examination. 相似文献
248.
Intrajugular injection of a purified E. coli lipopolysaccharide induced a biphasic fever in sheep after a latent period of 12 to 20 min. The changes in the blood flow from the liver and from the viscera drained by the portal vein were: (a) in the latent period, decreases in total hepatic blood flow (THF) due to decreased portal venous blood flow (PVF); (b) during the first febrile phase, increases in THF due to increased hepatic arterial blood flow and, (c) in the second febrile phase, increases in THF due to decreased PVF. Although there were large variations in the oxygen supply to the viscera drained by the portal vein and to the liver, there were relatively small or no changes in their oxygen consumption. 相似文献
249.
The 1998 Report of the American Association of Feline Practitioners and Academy of Feline Medicine Advisory Panel on Feline Vaccines was developed to help veterinary practitioners formulate vaccination protocols for cats. The current panel report updates information, addresses questions, and speaks to concerns raised by the 1998 report. In addition it reviews vaccine licensing, labeling, and liability issues and suggests ways to successfully incorporate vaccination protocol changes into a private practice setting. 相似文献
250.
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