全文获取类型
收费全文 | 473篇 |
免费 | 21篇 |
国内免费 | 28篇 |
专业分类
林业 | 49篇 |
农学 | 25篇 |
基础科学 | 11篇 |
145篇 | |
综合类 | 131篇 |
农作物 | 32篇 |
水产渔业 | 33篇 |
畜牧兽医 | 52篇 |
园艺 | 30篇 |
植物保护 | 14篇 |
出版年
2024年 | 5篇 |
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 8篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 8篇 |
2017年 | 15篇 |
2016年 | 13篇 |
2015年 | 21篇 |
2014年 | 24篇 |
2013年 | 25篇 |
2012年 | 36篇 |
2011年 | 37篇 |
2010年 | 34篇 |
2009年 | 28篇 |
2008年 | 26篇 |
2007年 | 28篇 |
2006年 | 31篇 |
2005年 | 26篇 |
2004年 | 9篇 |
2003年 | 22篇 |
2002年 | 7篇 |
2001年 | 9篇 |
2000年 | 15篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有522条查询结果,搜索用时 640 毫秒
81.
《Communications in Soil Science and Plant Analysis》2012,43(11):1191-1215
Abstract The influence of limestone and N:P:K fertilizer rates on elemental composition of Coastal bermudagrass forage was determined to evaluate causes for high yield responses to dolomitic limestone at high N:P:K rates, as well as severe stand loss, and chlorosis of bermudagrass in the unlimed treatments. Increasing N:P:K fertilization resulted in severe Mg deficiency. Maximum yields (when limed with dolomitic limestone) were associated with Mg concentrations of 1.0 g/kg plant tops. Magnesium lost to plant removal, Mg loss to enhanced leaching under N fertilization, and K interference associated with excess K accumulation at high rates of NK inputs all contributed to Mg deficiency. However, the accumulation of excess K, which interfered with Mg uptake when high rates of N and K were applied, was considered to be the primary cause of the observed Mg deficiency. 相似文献
82.
《Communications in Soil Science and Plant Analysis》2012,43(15):1795-1812
Abstract Selected chemical properties of an artificially acidified agricultural soil from northern Idaho were evaluated in a laboratory study. Elemental S and Ca(OH)2were used to manipulate the soil pH of a Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll), which had an initial pH of 5.7. A 100 day incubation period resulted in a soil pH manipulation range of 3.3 to 7.0. Chemical properties evaluated included: N mineralization rate, extractable P, AI, Mn, Ca, Mg and K and CEC. N mineralization rate (assessed by anaerobic incubation) decreased with decreasing soil pH. Nitrification rate also decreased as NH4 +‐N accumulated under acid soil conditions. Sodium acetate extractable P was positively linearly correlated (R2= 0.87) with soil pH over the entire pH range evaluated. Potassium chloride extractable Al was less than 1.3 mg kg‐1of soil at pH values higher than 4.4. Consequently, potential Al toxicity problems in these soils are minimal. Extractable Mn increased with decreasing soil pH. Soil CEC, extractable Mg, and extractable K all decreased with increasing soil pH from 3.3 to 7.0. Extractable Ca levels were largely unaffected by changing soil pH. It is likely that the availability of N and P would be the most adversely affected parameters by soil acidification 相似文献
83.
《Communications in Soil Science and Plant Analysis》2012,43(15-16):2121-2128
Abstract The sequential extraction procedure currently used to measure magnesium (Mg) fertilizer dissolution in soils consists of removing dissolved Mg (step 1), and partially dissolved Mg (step 2), followed by an 18‐h extraction with 2 M HCl at room temperature to determine undissolved Mg (step 3). This procedure is satisfactory for soluble and moderately soluble Mg fertilizers but is not an accurate procedure for slightly soluble fertilizers, such as serpentine. When step 3 is replaced by a digestion procedure using 2 M HCl for 4 h at 90–95°C (improved step 3), the total serpentine Mg recovery (dissolved and undissolved Mg) from soil samples, either immediately after serpentine was added to soil or after a 21‐day incubation with moist soil, was about 100% compared to 40–50% by the original procedure. The improved procedure also increased the recovery of serpentine Mg applied to field soils. Therefore, this study recommends that the third step of the sequential extraction procedure be replaced by a 4 h digestion using 2 M HCl (90–95°C). 相似文献
84.
不同氮源与镁配施对甘蓝产量、品质和养分吸收的影响 总被引:5,自引:0,他引:5
采用田间试验和室内分析相结合的方法,研究不同氮源与镁配施对甘蓝(Brassica oleracea L.)产量、品质和养分吸收的影响。试验在等氮条件下设4个氮源,分别为不施氮肥、100%铵态氮、50%铵态氮+50%硝态氮、100%硝态氮;设4个硫酸镁施用量,分别为0、75 kg·hm-2、150 kg·hm-2、300 kg·hm-2。结果表明,100%硝态氮与中量(150 kg·hm-2)镁配施处理的甘蓝产量比不施肥处理、100%铵态氮与中量镁配施处理和50%铵态氮+50%硝态氮与中量镁配施处理分别增产56.9%、14.7%和5.2%。施用100%硝态氮处理的甘蓝产量略高于50%硝态氮+50%铵态氮处理,比施用100%铵态氮处理和不施肥处理分别增产13.0%和44.2%。施用低量(75kg·hm-2)镁肥的甘蓝产量比不施镁肥增产9.3%,而增加镁肥用量对甘蓝产量没有显著影响。施用100%硝态氮、50%铵态氮+50%硝态氮和100%铵态氮处理的甘蓝硝酸盐含量比不施氮肥处理分别增加84.4%、63.4%和6.9%。100%硝态氮与高量(300 kg·hm-2)镁肥配合施用的甘蓝硝酸盐含量比不施肥处理、100%铵态氮与高量镁肥配施处理和50%铵态氮+50%硝态氮与高镁肥配施处理分别增加101.4%、82.3%和14.1%。施用高量镁肥处理甘蓝硝酸盐含量比不施肥处理增加11.2%。随着硝态氮比例增加,甘蓝维生素C、还原糖、总氨基酸含量相应增加,镁肥施用量对甘蓝维生素C、还原糖、总氨基酸含量影响明显。随着硝态氮比例增加,甘蓝对磷、钾和钙吸收量显著增加;随着镁施用量增加,磷、钾和镁吸收量相应增加。不同氮源与镁肥相互作用对甘蓝维生素C含量,氮、磷、钾、钙和镁养分吸收均有明显的影响。本研究表明,50%硝态氮和50%铵态氮混合与适量镁肥配合施用,既能增加甘蓝产量,提高维生素C、还原糖和总氨基酸含量,又能减少硝酸盐含量,提高甘蓝品质。 相似文献
85.
袁洪州 《中国农村水利水电》2013,(8)
以《太湖流域水环境综合治理总体方案》提出的太湖2012年水质保护目标为基础,结合太湖分湖区实测水质浓度,确定太湖各湖区水质保护目标;提出太湖污染物限制排污总量曲线的概念,采用太湖二维水量水质模型,计算不同入湖水量条件下满足太湖2012年水质保护目标时的太湖污染物限制排污总量,结合入湖水量特征拟定太湖污染物限制排污总量曲线,并以实际入湖污染负荷量和太湖实测水质对太湖污染物限制排污总量曲线进行了检验,为严格限制纳污红线管理提供依据. 相似文献
86.
Towards an improved and more flexible representation of water stress in coupled photosynthesis-stomatal conductance models 总被引:1,自引:0,他引:1
Gregorio Egea Anne Verhoef Pier Luigi Vidale 《Agricultural and Forest Meteorology》2011,151(10):1370-1384
Coupled photosynthesis-stomatal conductance (A-gs) models are commonly used in ecosystem models to represent the exchange rate of CO2 and H2O between vegetation and the atmosphere. The ways these models account for water stress differ greatly among modelling schemes. This study provides insight into the impact of contrasting model configurations of water stress on the simulated leaf-level values of net photosynthesis (A), stomatal conductance (gs), the functional relationship among them and their ratio, the intrinsic water use efficiency (A/gs), as soil dries. A simple, yet versatile, normalized soil moisture dependent function was used to account for the effects of water stress on gs, on mesophyll conductance (gm) and on the biochemical capacity. Model output was compared to leaf-level values obtained from the literature. The sensitivity analyses emphasized the necessity to combine both stomatal and non-stomatal limitations of A in coupled A-gs models to accurately capture the observed functional relationships A vs. gs and A/gsvs. gs in response to drought. Accounting for water stress in coupled A-gs models by imposing either stomatal or biochemical limitations of A, as commonly practiced in most ecosystem models, failed to reproduce the observed functional relationship between key leaf gas exchange attributes. A quantitative limitation analysis revealed that the general pattern of C3 photosynthetic response to water stress may be well represented in coupled A-gs models by imposing the highest limitation strength to gm, then to gs and finally to the biochemical capacity. 相似文献
87.
88.
89.
镁对烤烟产量、质量、几个生理指标的影响 总被引:6,自引:2,他引:6
在酸性红壤条件下,通过土壤局部控制设计方法,研究 MgSO_4不同施用量对烤烟产量、品质、光合色素、光合强度、蒸腾速率的影响.结果指出:在供试土壤条件下,补充营养元素镁,可以提高烟叶产量,增加光合色素(尤其值得注意的是增加了烟叶香气物质类胡萝卜素的含量),增强了光合强度和蒸腾速率.镁与烟叶的外观质量和内在化学成份有关.镁肥的补充不是越多越好.两年研究结果一致表明,每亩施5Kg MgOS_4可以使烤烟达到优质适产水平.过多施用会导致总糖含量过高,烟碱和蛋白质含量过低,品质变劣. 相似文献
90.
The effect that different levels of molybdenum (11 μMand 111 μM) exert on nitrate reductase (E.C. 1.6.6.1–3) activity (NRA), and the content of total proteins in Nicotiana rustica was studied. Eleven μM and 111 μM of molybdenum increased the activity of nitrate reductase during the growth cycle of N. rustica. Likewise, total protein content (mg/g DW) was increased during the vegetative growth of the plants. 相似文献