全文获取类型
收费全文 | 6015篇 |
免费 | 348篇 |
专业分类
林业 | 1121篇 |
农学 | 164篇 |
基础科学 | 11篇 |
1328篇 | |
综合类 | 577篇 |
农作物 | 161篇 |
水产渔业 | 192篇 |
畜牧兽医 | 2252篇 |
园艺 | 134篇 |
植物保护 | 423篇 |
出版年
2023年 | 45篇 |
2022年 | 44篇 |
2021年 | 93篇 |
2020年 | 94篇 |
2019年 | 61篇 |
2018年 | 203篇 |
2017年 | 185篇 |
2016年 | 170篇 |
2015年 | 145篇 |
2014年 | 162篇 |
2013年 | 377篇 |
2012年 | 348篇 |
2011年 | 379篇 |
2010年 | 188篇 |
2009年 | 168篇 |
2008年 | 309篇 |
2007年 | 326篇 |
2006年 | 330篇 |
2005年 | 276篇 |
2004年 | 271篇 |
2003年 | 280篇 |
2002年 | 229篇 |
2001年 | 187篇 |
2000年 | 176篇 |
1999年 | 108篇 |
1998年 | 36篇 |
1997年 | 38篇 |
1996年 | 45篇 |
1995年 | 74篇 |
1994年 | 45篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 23篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 25篇 |
1987年 | 17篇 |
1986年 | 33篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1980年 | 26篇 |
1977年 | 22篇 |
1970年 | 16篇 |
1968年 | 14篇 |
1966年 | 19篇 |
1955年 | 14篇 |
1941年 | 16篇 |
1939年 | 14篇 |
1937年 | 15篇 |
排序方式: 共有6363条查询结果,搜索用时 15 毫秒
1.
The cultivation of perennial instead of annual energy crops has received growing interest. Previous studies identified numerous beneficial effects of perennial energy crop (PEC) cultivation for the agricultural landscape such as promotion of agrobiodiversity, reduced requirements for agrochemicals and fertilizers as well as a large potential for carbon accumulation in soil. However, the mere presence of soil organic matter (SOM) accumulation gives no indication about the persistence of the SOM for example after a recultivation of the stands. Therefore, this study focused on SOM pools of different density fractions and soil microbial parameters. Six different PECs were tested against a typical benchmark system as feedstock for anaerobic digestion. The study has shown that all PEC species increased soil microbial activity and provided an insight how they sequester carbon in soil. Moreover, significant modifications in basic soil properties caused by plant growth were observed. For example, the cultivation of giant knotweed has lowered the soil pH by more than 0.5 pH units compared to the benchmark system. After 5 years of PEC cultivation, total soil organic carbon stocks were increased between 1,500 ± 400 and 4,500 ± 1,500 kg C ha-1 for the upper 10 centimetres of soil. The distribution among different soil fractions showed species-specific patterns. Tall wheatgrass and Virginia mallow showed particular high accumulation rates in the mineral-associated SOM fraction which indicates long residence times of the SOM after a possible recultivation of the fields. 相似文献
2.
T. Pudert A. Weyrich F. Geburek C. Herden M. Röcken 《Equine Veterinary Education》2021,33(11):e386-e392
Thymoma is a rare condition in horses. This case of a 24-year-old Warmblood gelding that was presented with oedema and signs of vascular congestion of the left forelimb caused by a thoracic mass is described. The diagnostic work-up included blood chemistry, cytology of pleural effusion, ultrasonography, radiography and the visualisation and collection of a tissue sample by thoracoscopy. Finally, post-mortem findings and histopathology revealed thymic epithelial neoplasia with histomorphologic features previously unreported in horses. The unique mixture of spindle-shaped and epithelioid tumour cells in combination with clear features of malignancy suggested the application of the Moran and Suster histological classification system for thymomas in humans (Moran and Suster, 2008, Curr. Treat. Options Oncol., 9, 288), which has not been reported in an equine case before and fits well to the present case. 相似文献
3.
4.
B. Götz 《Journal of pest science》1938,14(8):92-93
Ohne Zusammenfassung 相似文献
5.
6.
Revierförfter von Mühlen zu Solitude 《European Journal of Forest Research》1868,12(1):340-342
Ohne Zusammenfassung
Bergleiche Auguftheft diefer Bl?tter, in melchem gleichfalls auf die Wichtigfeit diefes Qegenftandes hingemiefen murde. Die
Red. 相似文献
7.
8.
G Breves R Zitnan B Schr?der C Winckler H Hagemeister K Failing J Voigt 《Archives of Animal Nutrition》2002,56(5):371-377
In a previous study we found a positive correlation between early weaning in calves and morphological parameters which were indicative of ruminal development, i.e. the length and width of the papillae. The objective of the present study was to determine to what extent this observation could be reflected by modulations of absorptive and secretory functions of the rumen mucosa. For this purpose the short-circuit currents (Isc) as a measure of electrogenic net ion fluxes and the transepithelial conductances (G(T)) as a measure of the overall tissue permeability were measured in vitro applying the Ussing-chamber technique. Simultaneously, the unidirectional flux rates of sodium and chloride across rumen wall epithelia were determined in the absence of electrochemical gradients. Under these conditions, significant positive net flux rates (Jnet) clearly indicate active mechanisms for electrolyte absorption. For the experiments 12 male Holstein calves 7 d of age were assigned to three groups of 4 animals each: milk group (I, slaughtered after 6 weeks of age), late weaning group (II, slaughtered after 9 weeks of age) and early weaning group (II, weaned after 6 weeks of age and slaughtered after 9 weeks of age). Whereas G(T) values remained unaffected by different age and feeding, Isc values were significantly affected by early weaning but were not influenced by age. Irrespective of weaning time active absorption of Na+ tended to be higher by about 60% in 9 weeks old animals. Active absorption of chloride was significantly increased in milk fed 9 weeke old calves and this effect was further stimulated by early weaning. In conclusion, the data show an increasing active Na+ absorption with age in calf rumen that could not be influenced by early weaning. Similarly, active Cl- absorption was initially increased during postnatal development and this effect could be stimulated further by early weaning. 相似文献
9.
10.
Dr. G. Götze 《Journal of pest science》1929,5(6):73-75
Ohne Zusammenfassung 相似文献