全文获取类型
收费全文 | 6614篇 |
免费 | 542篇 |
国内免费 | 61篇 |
专业分类
林业 | 352篇 |
农学 | 482篇 |
基础科学 | 86篇 |
1019篇 | |
综合类 | 770篇 |
农作物 | 290篇 |
水产渔业 | 398篇 |
畜牧兽医 | 3051篇 |
园艺 | 109篇 |
植物保护 | 660篇 |
出版年
2023年 | 47篇 |
2020年 | 68篇 |
2019年 | 125篇 |
2018年 | 220篇 |
2017年 | 224篇 |
2016年 | 186篇 |
2015年 | 208篇 |
2014年 | 200篇 |
2013年 | 352篇 |
2012年 | 277篇 |
2011年 | 325篇 |
2010年 | 262篇 |
2009年 | 218篇 |
2008年 | 318篇 |
2007年 | 280篇 |
2006年 | 247篇 |
2005年 | 211篇 |
2004年 | 199篇 |
2003年 | 199篇 |
2002年 | 151篇 |
2001年 | 241篇 |
2000年 | 184篇 |
1999年 | 182篇 |
1998年 | 74篇 |
1997年 | 76篇 |
1996年 | 57篇 |
1995年 | 65篇 |
1994年 | 50篇 |
1993年 | 55篇 |
1992年 | 105篇 |
1991年 | 112篇 |
1990年 | 109篇 |
1989年 | 109篇 |
1988年 | 87篇 |
1987年 | 82篇 |
1986年 | 75篇 |
1985年 | 59篇 |
1984年 | 64篇 |
1983年 | 52篇 |
1981年 | 44篇 |
1980年 | 48篇 |
1979年 | 72篇 |
1978年 | 52篇 |
1977年 | 52篇 |
1976年 | 59篇 |
1975年 | 52篇 |
1974年 | 61篇 |
1973年 | 75篇 |
1972年 | 44篇 |
1971年 | 45篇 |
排序方式: 共有7217条查询结果,搜索用时 0 毫秒
901.
902.
The effect of cultural conditions on the production of leukotoxin by biotypes A and B of F. necrophorum was investigated. Biotypes A and B were grown in prereduced, anaerobically sterilized, brain-heart infusion (BHI) broth. The average leukotoxin titer of culture supernatant was 18 times higher from biotype A strains than from biotype B strains. Leukotoxin activity peaked during the late-log and early-stationary phases of growth, then declined precipitously in both biotypes. F. necrophorum biotype A was grown in different media (BHI, liver infusion, and Eugon broths), at various pH (6.6, 7.3, 7.7, and 8.2), incubation temperatures (30, 35, 39, and 43 degrees C), redox potentials (-352 to +375 mV), and iron concentrations (less than 0.2, 4.2, 42.1, and 361.4 microM). Anaerobic BHI broth with pH from 6.6 to 7.7 at 39 degrees C incubation temperature supported maximal F. necrophorum growth and leukotoxin production. The optimum redox potential for F. necrophorum growth was in the range of -230 to -280 mV. However, the presence of titanium III citrate or dithiothreitol (7.78 mM) in the medium decreased (P less than 0.05) the leukotoxicity of F. necrophorum. Low iron concentration (less than 0.2 microM) decreased (P less than 0.05) growth rate but not leukotoxin activity of F. necrophorum, whereas high iron concentration inhibited the leukotoxin activity. 相似文献
903.
Attempts were made to induce an intestinal hypersensitivity response to weaner diet by feeding pigs with small quantities of this material before weaning. In two trials using different weaner diets piglets subjected to this regimen showed no significant differences in small intestinal structure, in ability to absorb xylose, in bodyweight gain, in incidence of diarrhoea or excretion of enteropathogens after weaning compared with pigs not given any of the diet before weaning, or fed with a different diet before weaning. When post-weaning diarrhoea occurred it was associated with an earlier, more prolonged and greater proliferation of enterotoxigenic Escherichia coli in the small intestines than occurred in healthy pigs after weaning. The greater proliferation in pigs which developed diarrhoea could not be attributed either to an excessive dietary intake after weaning, or to a specific proliferation of rotaviruses. 相似文献
904.
The occurrence of chlortetracycline residues in the meat of slaughter calves in 62% herds under study (the additive of the medicated premix AUREOVIT to feed without observing the withdrawal times) did not influence significantly the Gram-negative resistant and R+ microflora isolated from the same material, in comparison with control herds that were administered no antibiotics. Neither was the spectrum of donors and transferring R plasmids influenced significantly nor the incidence of different resistance determinants. The effect of chlortetracycline addition to feed was negative (at P = 0.05) only in the occurrence of R+ microflora isolated from stable environment where the slaughtered calves had been housed. 相似文献
905.
906.
907.
908.
909.
The diagnostic value of laboratory examination methods was assessed in the diagnosis of avian encephalomyelitis in seven to twenty-two days old chickens. Histological examination and immunofluorescent test are expedient methods meeting the requirements for timely application of infection-control measures. The agreement of histological examination with the over-all laboratory examination is 70 to 81% and the agreement of the immunofluorescence test is 76%. Bioassay on chickens followed by a histological examination appears to be the best method, providing results with the highest significance. However, it is lengthy, applicable to the necessary demonstration of a virus or to cases when the histological or immunofluorescence examinations are dubious. With the over-all laboratory evaluation the method shows agreement in 95 to 100% of cases. The diagnostic value of the method of virus isolation in chick embryos is reduced by the fact that intercurrent viruses (adenoviruses, IB and others) may be passaged at the same time. 相似文献
910.
Cultures of the fungus Penicillium italicum can extract Fe from powdered stainless steels, including highly corrosion-resistant alloys containing 11 to 13 % Ni. Physical contact of fungus with metal is unnecessary, but acidification alone fails to account for the phenomenon. Evidence from other sources suggests that fungal metabolites are involved. 相似文献