全文获取类型
收费全文 | 5714篇 |
免费 | 325篇 |
国内免费 | 1篇 |
专业分类
林业 | 1061篇 |
农学 | 163篇 |
基础科学 | 10篇 |
1235篇 | |
综合类 | 539篇 |
农作物 | 148篇 |
水产渔业 | 196篇 |
畜牧兽医 | 2170篇 |
园艺 | 123篇 |
植物保护 | 395篇 |
出版年
2023年 | 34篇 |
2022年 | 37篇 |
2021年 | 84篇 |
2020年 | 82篇 |
2019年 | 48篇 |
2018年 | 189篇 |
2017年 | 172篇 |
2016年 | 155篇 |
2015年 | 137篇 |
2014年 | 156篇 |
2013年 | 365篇 |
2012年 | 321篇 |
2011年 | 359篇 |
2010年 | 168篇 |
2009年 | 148篇 |
2008年 | 289篇 |
2007年 | 310篇 |
2006年 | 315篇 |
2005年 | 271篇 |
2004年 | 260篇 |
2003年 | 277篇 |
2002年 | 218篇 |
2001年 | 184篇 |
2000年 | 179篇 |
1999年 | 104篇 |
1998年 | 41篇 |
1997年 | 39篇 |
1996年 | 46篇 |
1995年 | 74篇 |
1994年 | 44篇 |
1993年 | 23篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 23篇 |
1987年 | 16篇 |
1986年 | 32篇 |
1985年 | 29篇 |
1984年 | 23篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1980年 | 28篇 |
1977年 | 22篇 |
1966年 | 14篇 |
1964年 | 14篇 |
1961年 | 13篇 |
1955年 | 14篇 |
1941年 | 14篇 |
1857年 | 13篇 |
排序方式: 共有6040条查询结果,搜索用时 0 毫秒
61.
Hadi Manghabati Wendelin Weis Axel Göttlein 《European Journal of Forest Research》2018,137(5):631-642
Phosphorus is an essential nutrient for forest growth. In this study, we assessed the impact of soil extractable phosphorus using two simple extraction methods on nutrition and productivity of Norway spruce in sixteen mature forest stands on different bedrocks and soils in Bavaria, Southern Germany. Representative trees were sampled for needles, twigs, branches, stem bark, and stem wood. Total phosphorus content in the tree parts and soil phosphorus stock extractable with citric acid and sodium bicarbonate up to a soil depth of 80 cm were determined. We found that easily soil extractable phosphorus is a suitable indicator for estimating phosphorus uptake and stand productivity in Norway spruce. In contrast, organic layer phosphorus showed no significant correlation with aboveground biomass phosphorus contents. In the biomass, the highest phosphorus contents were measured in young needles and twigs, but the highest correlation with soil phosphorus was detected for phosphorus contents in needles and bark. The stock of phosphorus extracted by citric acid down to 40 cm soil depth revealed the best correlation with phosphorus in needles and bark. Therefore, as a supplemental or alternative method to needle analysis, our study suggests the use of phosphorus contents in stem bark to evaluate tree phosphorus nutrition. These results highlight the suitability of the citric acid soil extraction method to characterize plant available phosphorus in Norway spruce ecosystems. 相似文献
62.
Huawei Ji Jiahao Wen Baoming Du Ningxiao Sun Björn Berg Chunjiang Liu 《Annals of Forest Science》2018,75(2):59
Key message
Foliar phosphorus (P) resorption in Quercus variabilis Blume was significantly lower at a P-rich than at a P-deficient site. Moreover, P resorption strongly decreased, and nitrogen:phosphorus and carbon:phosphorus resorption ratios increased with soil P content. This demonstrates a strong link between foliar P resorption and P content in soils, and emphasizes the importance of P resorption in leaves of trees growing in soils with contrasted P content.Context
Subtropical ecosystems are generally characterized by P-deficient soils. However, P-rich soils develop in phosphate rock areas.Aims
We compared the patterns of nutrient resorption, in terms of ecological stoichiometry, for two sites naturally varying in soil P content.Methods
The resorption efficiency (percentage of a nutrient recovered from senescing leaves) and proficiency (level to which nutrient concentration is reduced in senesced leaves) of 12 elements were determined in two oak (Q. variabilis) populations growing at a P-rich or a P-deficient site in subtropical China.Results
P resorption efficiency dominated the intraspecific variation in nutrient resorption between the two sites. Q. variabilis exhibited a low P resorption at the P-rich site and a high P resorption at the P-deficient site. Both P resorption efficiency and proficiency strongly decreased with soil P content only and were positively related to the N:P and C:P ratios in green and senesced leaves. Moreover, resorption efficiency ratios of both N:P and C:P were positively associated with soil P.Conclusion
These results revealed a strong link between P resorption and P stoichiometry in response to a P deficiency in the soil, and a single- and limiting-element control pattern of P resorption. Hence, these results provide new insights into the role of P resorption in plant adaptations to geologic variations of P in the subtropics.63.
Karl Gösswald 《Journal of pest science》1943,19(3):30-34
Ohne Zusammenfassung
Mit 10 Abbildungen 相似文献
64.
65.
66.
67.
H. W. Fassbender L. Alpízar J. Heuveldop H. Fölster G. Enríquez 《Agroforestry Systems》1988,6(1-3):49-62
Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems
of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica.
For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference
between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests)
of the system are considered.
The implications of the models are discussed in detail.
Aspects of net primary production in the systems studied are considered.
N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall
patterns and pruning of theE. poeppigiana.
For part I see Vol. 4, No. 3, 1986 For part II see this issue
Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesellschaft für Technische Zusammenarbeit),
Turrialba, Costa Rica 相似文献
68.
The current study investigated the effects of oyster mushroom Pleurotus ostreatus, extract on immunological and hematological parameters of rainbow trout, Oncorhynchus mykiss. The fish were fed diets containing 0 (control), 1, and 2% supplementation of the oyster mushroom extract for 6 wk. Blood samples were collected weekly for the first 6 weeks. After 6 wk of feeding, the fish were challenged with Lactococcus garvieae and mortality was recorded. The results of this study showed that feeding rainbow trout an oyster mushroom extract–supplemented diet stimulated phagocytic activity of phagocytic cells, lysozyme activity, and myeloperoxidase activity in serum, but it did not significantly affect the total serum immunoglobulin level. At the same time, a significant increase was found in the number of neutrophils, monocytes, and total white blood cells. Fish fed the diet supplemented with oyster mushroom extract showed reduced mortalities following L. garvieae infection compared with controls. These results show that supplementation of fish diets with oyster mushroom extract at 1 and 2% concentrations significantly imrpoves hematological parameters and modulates the immune response against L. garvieae in rainbow trout. 相似文献
69.
F. Zöhrer 《European Journal of Forest Research》1969,88(1):41-63
Ohne Zusammenfassung 相似文献
70.
L. Alpízar Professor H. W. Fassbender Coordinator J. Heuveldop Professor H. Fölster G. Enríquez 《Agroforestry Systems》1986,4(3):175-189
The agroforestry systems of cacao (Theobroma cacao) under laurel (Cordia alliodora) and cacao under poro (Erythrina poeppigiana) were studied at CATIE, Turrialba, Costa Rica. An inventory was taken of the organic matter and nutrients (N, P, K, Ca, and Mg) separating the species into their compartments (leaves, branches, trunks and roots). Studies of the litter and of the mineral soil (0–45 cm) yielded these results:
Patterns of nutrient accumulation are discussed in relation to the characteristics of these agroforestry systems. 相似文献