全文获取类型
收费全文 | 402篇 |
免费 | 36篇 |
专业分类
林业 | 18篇 |
农学 | 9篇 |
基础科学 | 1篇 |
64篇 | |
综合类 | 29篇 |
农作物 | 4篇 |
水产渔业 | 17篇 |
畜牧兽医 | 257篇 |
园艺 | 9篇 |
植物保护 | 30篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 21篇 |
2014年 | 12篇 |
2013年 | 39篇 |
2012年 | 11篇 |
2011年 | 34篇 |
2010年 | 26篇 |
2009年 | 17篇 |
2008年 | 26篇 |
2007年 | 11篇 |
2006年 | 9篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1967年 | 3篇 |
1966年 | 4篇 |
1952年 | 1篇 |
1951年 | 1篇 |
1950年 | 2篇 |
1949年 | 2篇 |
1948年 | 3篇 |
1946年 | 1篇 |
排序方式: 共有438条查询结果,搜索用时 15 毫秒
1.
E A ter Laak J H Noordergraaf R P Dieltjes 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1992,39(8):553-562
The prevalence of mycoplasmas in the respiratory tracts of 148 pneumonic calves originating from 25 herds in the Netherlands is reported. Four types of culture media were used to isolate mycoplasmas: solid modified Edward medium, 2 types of Friis media, and A7B differential agar medium. Mycoplasmas were isolated both from nasal swab specimens and lung lavage fluids collected from live calves and from nasal mucosa and lung tissue specimens collected post mortem. All of the mycoplasma strains isolated could be identified as either Ureaplasma diversum (isolated from 80% of 25 herds), Mycoplasma dispar (92%), M. bovirhinis (88%), M. bovis (20%), M. bovigenitalium (4%), M. arginini (16%), or M. canis (12%). Isolation rates of M. dispar and U. diversum were considerably higher from lung lavage fluids than from nasal swab specimens. M. bovis was detected only in fattening herds and not in dairy herds. The respiratory tracts of 75% of the calves examined contained at least 2 mycoplasma species. In total, 25 different combinations of mycoplasma species were detected in specimens collected from noses and lungs. The pathogenic species U. diversum and M. dispar had not been isolated before in the Netherlands. 相似文献
2.
Ter Haar D 《Science (New York, N.Y.)》1948,107(2782):405-411
3.
4.
5.
6.
7.
8.
9.
Increasing abundance of Juncus effusus (soft rush) and Juncus conglomeratus (compact rush) in pastures and meadows in western Norway has caused reductions in forage yield and quality in recent decades. Understanding plant development and regrowth following cutting is essential in devising cost‐effective means to control rushes. In a field experiment in western Norway, we investigated development of above‐ and below‐ground fractions of rush from seedlings to three‐year‐old plants, including the impact on vigour of disturbing growth by different cutting frequencies during the period 2009–2012. Each year, the plants were exposed to one or two annual cuts or left untreated and five destructive samplings were performed from March to early December. Juncus effusus showed significantly more vigorous growth than Juncus conglomeratus in the last two years of the study period. The above‐ground:below‐ground biomass ratio of both species increased mainly in spring and early summer and was reduced in late summer and autumn. Removal of aerial shoots also reduced the below‐ground fraction of both species. One annual cut in July effectively reduced biomass production in both species by 30–82%, which was only a slightly smaller reduction than with two annual cuts, in June and August. Mechanical control measures such as cutting can thus effectively reduce rush vigour when performed late in the growing season. 相似文献
10.
Kormann Urs G. Scherber Christoph Tscharntke Teja Batáry Péter Rösch Verena 《Landscape Ecology》2019,34(5):1045-1056
Landscape Ecology - Global change pressures (GCPs) imperil species and associated ecosystem functions, but studies investigating interactions of landscape-scale pressures remain scarce. Loss of... 相似文献