全文获取类型
收费全文 | 145150篇 |
免费 | 7711篇 |
国内免费 | 102篇 |
专业分类
林业 | 6121篇 |
农学 | 4228篇 |
基础科学 | 884篇 |
15878篇 | |
综合类 | 27965篇 |
农作物 | 5574篇 |
水产渔业 | 6622篇 |
畜牧兽医 | 75209篇 |
园艺 | 1660篇 |
植物保护 | 8822篇 |
出版年
2018年 | 1722篇 |
2017年 | 1894篇 |
2016年 | 1768篇 |
2015年 | 1576篇 |
2014年 | 1914篇 |
2013年 | 5171篇 |
2012年 | 3393篇 |
2011年 | 4325篇 |
2010年 | 2759篇 |
2009年 | 2778篇 |
2008年 | 4185篇 |
2007年 | 4063篇 |
2006年 | 3911篇 |
2005年 | 3579篇 |
2004年 | 3453篇 |
2003年 | 3504篇 |
2002年 | 3319篇 |
2001年 | 4399篇 |
2000年 | 4509篇 |
1999年 | 3571篇 |
1997年 | 1397篇 |
1995年 | 1652篇 |
1994年 | 1413篇 |
1993年 | 1384篇 |
1992年 | 3063篇 |
1991年 | 3240篇 |
1990年 | 3199篇 |
1989年 | 3218篇 |
1988年 | 3001篇 |
1987年 | 3045篇 |
1986年 | 3108篇 |
1985年 | 3022篇 |
1984年 | 2455篇 |
1983年 | 2184篇 |
1982年 | 1488篇 |
1981年 | 1368篇 |
1979年 | 2360篇 |
1978年 | 1887篇 |
1977年 | 1656篇 |
1976年 | 1586篇 |
1975年 | 1727篇 |
1974年 | 2229篇 |
1973年 | 2296篇 |
1972年 | 2247篇 |
1971年 | 2092篇 |
1970年 | 1997篇 |
1969年 | 1787篇 |
1968年 | 1548篇 |
1967年 | 1611篇 |
1966年 | 1442篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
192.
193.
194.
195.
196.
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
197.
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
198.
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
199.
S. A. Selim K. M. S. Aziz A. J. Sarker H. Rahman 《Veterinary research communications》1991,15(4):327-333
Faecal samples from 434 calves under 1 year of age (307 diarrhoeal and 127 normal) were collected from three dairy farms and one village in selected areas of Bangladesh. The samples were tested by an enzyme-linked immunosorbent assay (ELISA) to detect the presence of rotavirus antigen. Of 402 dairy calves tested, 28 (7.0%) were positive, of which 21 (7.2%) were from diarrhoeic calves and 7 (6.3%) from non-diarrhoeic calves. Rotavirus infection varied from farm to farm (2.7–9.2%) and there was no positive response from any of the 32 village calves. Rotavirus was most commonly found in calves of 1 week of age or less (up to 22.2% in one group) but was not found in any calves later than 6 months of age. More than 80% of rotavirus-positive samples from diarrhoeic calves exhibited a titre of 128 or more (geometric mean 345±4.5), whereas non-diarrhoeal calves had titres less than or equal to 128 (geometric mean=29±1.9), suggesting that rotavirus infection in calves in Bangladesh was mostly associated with diarrhoea. 相似文献
200.
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