全文获取类型
收费全文 | 163篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
林业 | 18篇 |
农学 | 1篇 |
基础科学 | 8篇 |
102篇 | |
综合类 | 31篇 |
农作物 | 5篇 |
水产渔业 | 1篇 |
畜牧兽医 | 4篇 |
园艺 | 3篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 19篇 |
2012年 | 21篇 |
2011年 | 9篇 |
2010年 | 4篇 |
2009年 | 13篇 |
2008年 | 4篇 |
2007年 | 5篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1988年 | 1篇 |
排序方式: 共有173条查询结果,搜索用时 252 毫秒
41.
Pedro García-Caparrós Alfonso Llanderal 《Communications in Soil Science and Plant Analysis》2016,47(20):2306-2314
The ability to produce native plants well adapted to the saline conditions without the production of nutrient-rich runoff will be a boon to nurseries hoping to reduce their environmental contamination impact and water use while at the same time producing quality plants to be used in the restoration of saline lands. Sarcocornia fruticosa plants were grown for 8 weeks in plastic containers with a source of sphagnum peat moss and perlite (80:20 v/v) to evaluate the effect of two salinity levels (2.0 (low-salinity treatment) and 7.5 dS m?1 (high-salinity treatment)) on plant growth, nutrient concentration in leachate and water and nutrient uptake efficiency and their losses. Leachate was collected to determine the runoff volume and composition, which included nitrate-nitrogen (NO3–N), phosphate-phosphorus (PO43–P) and potassium (K+) concentrations. Plant dry weight (DW) and nutrient content were determined in plants at the beginning and at the end of the experiment to establish the nutrient balance. Increasing salinity levels of irrigation water did not reduce either the plant DW or the water-use efficiency (WUE), but increased the volume of leachate per plant. The nutrient concentrations in leachates without significant differences between salt treatments exceeded the thresholds established by environmental guidelines, leading to a great risk of pollution. Based on nutrient balance, the irrigation with a higher salinity level reduced the plant nutrient uptake efficiency (10%, 18% and 12% for nitrogen (N), phosphorus (P) and potassium (K), respectively) and increased the nutrient losses (6% N, 7% P and 8% K), resulting in the recommendation to grow this species with the low salinity level based on the highest nutrient-use efficiency and the lowest levels of nutrient losses. 相似文献
42.
43.
Bulk precipitation and throughfall analyses in 50–100-year-old Scots pine stands revealed decreasing sulphur, nitrogen, calcium and magnesium deposition gradients, which extend from the St. Petersburg-Leningrad region and N.-E. Estonia to S.-E. Finland. The Ca and Mg deposition alleviate the acidifying effect of sulphur and nitrogen. The Scots pine canopies acted as a sink for ammonium and nitrate, while the canopy interactions increased sulphur, calcium and magnesium content in throughfall. Foliar S, N and Ca concentrations correlated positively with the corresponding deposition loads. In contrast, low foliar magnesium concentrations were detected in the vicinity of St. Petersburg. The results indicate that the sulphur and calcium deposition may have increased soil leachate S and Ca concentrations in the most polluted Scots pine stands. 相似文献
44.
A meta-analysis of the effects of nitrogen additions on base cations: Implications for plants, soils, and streams 总被引:2,自引:0,他引:2
R.W. Lucas J. KlaminderM.N. Futter K.H. Bishop G. EgnellH. Laudon P. Högberg 《Forest Ecology and Management》2011,262(2):95-104
The dominant base cations (BC; i.e., Ca2+, Mg2+, K+, and Na+) are important in buffering soil and water acidity in both terrestrial and aquatic ecosystems. Ca2+, Mg2+, and K+ are also important in many plant physiological functions. Because BC availability is affected by changes in the nitrogen (N) cycle, we conducted a meta-analysis of previously published data to determine if N fertilization alters the availability of BC in terrestrial and stream ecosystems across biomes. We include data from 107 independent studies published in 62 different articles, taking a holistic perspective on BC by examining their responses to added N in plant foliage, bulk soil, soil solution, and stream water. Our results suggest N fertilization may accelerate BC loss from terrestrial ecosystems over time periods less than five years. We found that N additions resulted in an overall 24% decrease in the availability of exchangeable Ca2+, Mg2+, and K+ in the bulk soil of boreal forest, temperate forest, and grassland biomes. Collectively, responses of BC in boreal forest, temperate forest, tropical forest, and grassland biomes increased following N fertilization by about 71% in soil solution and 48% in stream waters. Additionally, BC responses in foliage decreased in boreal forest and temperate forest biomes following N additions over time periods less than five years, but there were no significant changes over longer time periods. Despite large short-term shifts in BC responses following N additions, we did not find evidence of widespread negative impacts on ecosystems over time periods greater than five years. This analysis suggests effects of N addition on the availability of exchangeable BC may diminish over time. Although the effects on BC can be substantial over periods less than five years, there is little available evidence that N fertilization has had large-scale detrimental effects on the availability of BC needed for plant growth within terrestrial or aquatic ecosystems. 相似文献
45.
46.
本文系统剖析了熊毅-傅积平改进区分的土壤结合态腐殖质的形成特点,胡,富组成及其结合特征。结果表明:(1)用0.1mol/LNaOH及0.1mol/LNaOH+0.1mol/LNa4P2O7混合液连续浸提的松结态(H1)和稳结态(H2)腐殖质所占的比例随土壤pH升高分别呈减少和增加趋势。统计分析显示H1与游离态铁,铝呈极显著的正相关,与交换性钙呈极显著负相关,H2则与交换性钙呈极显著正相关,而与游离 相似文献
47.
Taïeb Tounekti Ahmedou Mohammed Vadel Mustapha Ennajeh Habib Khemira Sergi Munné‐Bosch 《植物养料与土壤学杂志》2011,174(3):504-514
In this study, we evaluated how increased cation supply can alleviate the toxic effects of NaCl on plants and how it affects essential oils (EOs) and phenolic diterpene composition in leaves of rosemary (Rosmarinus officinalis L.) plants grown in pots. Two concentrations of the chloride salts KCl, CaCl2, MgCl2, and FeCl3 were used together with 100 mM NaCl to study the effects of these nutrients on plant mineral nutrition and leaf monoterpene, phenolic diterpene, and EO composition. The addition of 100 mM NaCl, which decreased K+, Ca2+, and Mg2+ concentrations with increasing Na+ in leaves, significantly altered secondary metabolite accumulation. Addition of MgCl2 and FeCl3 altered leaf EO composition in 100 mM NaCl–treated rosemary plants while KCl and CaCl2 did not. Furthermore, addition of CaCl2 promoted the accumulation of the major phenolic diterpene, carnosic acid, in the leaves. The carnosol concentration was reduced by the addition of KCl to salt‐stressed plants. It is concluded that different salt applications in combination with NaCl treatment may have a pronounced effect on phenolic diterpene and EO composition in rosemary leaves thus indicating that ionic interactions may be carefully considered in the cultivation of these species to achieve the desired concentrations of these secondary metabolites. 相似文献
48.
农业废弃物及其制备的生物质炭对酸性土壤的改良作用 总被引:13,自引:0,他引:13
The liming potential of some crop residues and their biochars on an acid Ultisol was investigated using incubation experiments. Rice hulls showed greater liming potential than rice hull biochar, while soybean and pea straws had less liming potential than their biochars. Due to their higher alkalinity, biochars from legume materials increased soil pH much compared to biochars from non-legume materials. The alkalinity of biochars was a key factor aflecting their liming potential, and the greater alkalinity of biochars led to greater reductions in soil acidity. The incorporation of biochars decreased soil exchangeable acidity and increased soil exchangeable base cations and base saturation, thus improving soil fertility. 相似文献
49.
Gong Zhang Guang-Ming Zeng Guo-He Huang Yi-Min Jiang Jia-Mei Yao Chun-Yan Du Ru Jiang Chang Zhang 《Journal of Forest Research》2006,11(6):389-396
The effects of dry deposition, canopy leaching, precipitation ion concentration, and precipitation H+ concentration on net throughfall flux (NTF, throughfall minus bulk precipitation) were evaluated on a seasonal basis by using
a multiple regression analysis approach based on an observation period of 4 years in Shaoshan subtropical mixed evergreen
forest, south-central China. Regression analysis results indicated that the estimated canopy exchange flux was the dominant
factor regulating the NTF and the calculated dry deposition was a minor term. The seasonal dry deposition of base cations
accounted for 15%–43% of the NTF. The NTF analysis showed that K+, Ca2+, Mg2+, Na+, and weak acids in throughfall were derived from foliar leaching and the canopy uptakes of H+, NH4
+, and NO3
− were from precipitation. The retention rate of proton (H+ and NH4
+) in the canopy was close to the canopy leaching rate of base cations when corrected for weak acids because weak acid-induced
canopy leaching did not exchange with protons, which suggested that the canopy leaching processes neutralized acid precipitation
in Shaoshan forest. 相似文献
50.
Rongjie Wu Bingqing Liu Bin Xue Ruili Gao George M. Ndzana Rentao Liu Juying Huang Hui An Lingtong Du Muhammad Kamran 《Soil Use and Management》2023,39(3):1109-1124
Different land use and management actions can affect soil aggregates (SAs) and nutrient stocks, which are crucial for sustainable agriculture. The impacts of various chrono-sequences on the soil aggregate structure, soil organic carbon (SOC) and nutrients associated with aggregate fractions in wolfberry (Lycium barbarum L.) plantations are still not fully understood. This study examined the composition and stability of SAs, SOC, total nitrogen (TN), available phosphorus (AP) and exchangeable cations (K+, Na+, Ca2+ and Mg2+) in bulk soil and various aggregate-size fractions from five wolfberry plantations with varying ages (1, 4, 6, 10 and 13 years) and a corn field (0 years) in the arid region of northwest Ningxia in China. The results indicated that silt–clay (<53 μm) fractions were dominant in the soil, accounting for 51%–66%, under different plantation ages. The proportion of the macro-aggregates (>250 μm) increased significantly, by 40%–47%, over the 4 years of wolfberry plantation. Likewise, the soil aggregate stability was improved, and total exchangeable bases (TEB) along with numerous cations concentrations (K+, Na+, Ca2+ and Mg2+) in SAs were significantly reduced as the wolfberry plantings became older. Both concentrations of SOC and TN in the soil aggregates peaked in the 13th year. The silt–clay fractions stored a considerable amount of SOC and nutrients. However, short-term (under 6 years) cultivation of wolfberry reduced the stocks of SOC, TN and AP in the soil, while long-term (over 10 years) cultivation increased them, particularly in macro-aggregates. These findings indicated that long-term wolfberry farming had several advantages, such as enhancing soil structure, accumulating SOC and nutrients and ameliorating alkaline soils, especially after 10 years, in the arid northwest of China. 相似文献