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1.
Land-use change from forest to agriculture in the volcanic ash-derived soils of Mexico has increased over recent decades. It is likely that land uses and management practices, particularly fertilizer use have affected phosphorus (P) distribution and availability. The objective of this study was to evaluate the effects of land-use types (native forest and maize mono-cropping), and the related P addition, on the forms and distribution of soil P and their isotopic exchangeability. An Andisol, sampled from a cropping site, along with the contiguous area under native forest was treated with 32P-labelled potassium phosphate (KH232PO4). The soil samples were extracted after incubation times of 7, 21, 35 and 49 days. Phosphorus content and 32P recovery in fractions sequentially extracted were assessed for each incubation time. Total soil P was dominated by inorganic fractions (79 to 86%) in both land-use types. Resin-Pi, bicarbonate extractable inorganic P (Bic-Pi) and sodium hydroxide extractable inorganic P (NaOH0.1-Pi) were all raised with P addition. However, the proportion of organic P fraction was reduced under cropped soil. The recovery of 32P in soils with P addition indicates that resin-Pi, Bic-Pi and NaOH0.1-Pi comprised nearly all the exchangeable P. In native soils with no P addition, more than 19% of the 32P was recovered in Bic-Po and NaOH0.1-Po forms. This finding indicates that organic P cycling is crucial when soil Pi reserves are presented in an inadequate amount. Ecologically based management has to be designed for replenishment and succeeding maintenance of soil organic P compounds to increase sustainable agricultural production.  相似文献   
2.
Soil organic carbon(SOC) plays a key role in improving soil quality and optimizing crop yield. Yet little is known about the fate of macroaggregates(0.25 mm) under long-term fertilization and their relative importance in SOC sequestration in reclaimed calcareous soil. Therefore, the effects of mineral fertilizers and organic manure on the mechanisms of organic carbon(OC) stabilization in macroaggregates were investigated in this study. Four treatments were used: unfertilized control(CK), mineral fertilizer(NPK), compost chicken manure alone(M), and mineral fertilizers plus manure(MNPK). Samples from the 0–20 cm layer of soil receiving 11-year-long fertilization were separated into four fractions based on the macroaggregates present(unprotected coarse and fine particulate organic matter, cPOM and fPOM; physically protected intra-microaggregate POM, i POM; and biochemically protected mineral associated OM, MOM) by the physical fractionation method. Compared with the control, the long-term application of NPK had little effect on SOC content, total nitrogen(TN) content, and OC and TN contents of macroaggregate fractions. In contrast, incorporation of organic manure(MNPK) significantly increased SOC(45.7%) and TN(24.3%) contents. Application of MNPK increased OC contents within macroaggregate-extracted fractions of cPOM(292.2%), fPOM(136.0%) and iPOM(124.0%), and TN contents within cPOM(607.1%), fPOM(242.5%) and iPOM(127.6%), but not the mineral associated organic carbon(MOM-C) and nitrogen(MOM-N) contents. Unprotected C fractions were more strongly and positively correlated with SOC increase than protected C fractions, especially for cPOM-C, indicating that SOC sequestration mainly occurred via cPOM-C in the studied calcareous soil. In conclusion, MNPK increased the quantity and stability of SOC by increasing the contents of cPOM-C and cPOM-N, suggesting that this management practice(MNPK) is an effective strategy to develop sustainable agriculture.  相似文献   
3.
为探究不同发育期及授粉方式对设施甜瓜稳定同位素比值变化的影响,本研究基于元素分析——稳定同位素比率质谱(EA-IRMS),测定在不同发育期和授粉方式中设施甜瓜的4种稳定同位素比值(δ13C、δ15N、δ18O和δ2H),采用单因素方差分析法解析激素授粉和中华蜜蜂授粉对甜瓜稳定同位素比值的差异性。结果表明,在相同的种植和环境条件下,自然分馏效应导致设施甜瓜在不同发育时期的同位素差异。在甜瓜发育期间,不同授粉方式设施甜瓜的δ13C、δ15N和δ18O值较稳定,无显著差异(P>0.05),而在发育30 d时激素授粉与蜜蜂授粉甜瓜的δ2H值分别为-43.63‰和-53.50‰,存在显著差异(P<0.05)。本研究初步揭示了稳定同位素在甜瓜发育过程中以及不同授粉方式下的分馏情况,其中δ2H值可作为甜瓜授粉方式的一项标识性指标,对丰富设施甜瓜溯源体系具有重要意义。  相似文献   
4.
A greenhouse experiment was conducted in North-west India to study the effect of soil applied boron on yield of berseem (Trifolium alexandrium L.) and soil boron fractions in boron deficient calcareous soils. Three soils with varying calcium carbonate content viz. 0.75% (Soil I), 2.6% (Soil II), and 5.7% (Soil III) were collected from different sites of Ludhiana, Bathinda, and Shri Muktsar Sahib districts, Punjab, India. The treatments consisted of six levels of soil applied boron viz. 0.5, 0.75, 1.0, 1.25, 1.5, and 2.0 mg B kg?1 along with control. The green fodder yield and dry matter yield increased significantly at 0.75 mg B kg?1 soil treatment level in the first cutting, while these were significant at 1.0 mg B kg?1 soil treatment level in all soils at second, third, and fourth cuttings. Among all three calcareous soils, Soil I with lower calcium carbonate was the best soil in respect of mean yield in comparison to Soil II and Soil III. Combined effect of boron level and soils had significant effect on yield of berseem. There was a significant increase in mean dry root biomass at 1.0 mg B kg?1 soil level over control and then remained non-significant with further high levels of soil applied boron. The mean dry root biomass decreased significantly for the soils having 0.75%, 2.6%, and 5.7% calcium carbonate levels. Readily soluble fraction is considered to be easily available fraction of B for plant uptake and consisted of 0.47–0.62% in Soil I, 0.31–0.43% in Soil II, and 0.24–0.34% in Soil III of the total boron. Among all B fractions, mean readily soluble, specifically adsorbed, and oxide-bound fractions got increased significantly with increase in B levels. Readily soluble and organically bound B fractions were more in Soil I as compared to Soil II and Soil III. Specifically adsorbed boron, oxide bound fraction, residual and total boron were more in Soil III in comparison to Soil I and Soil II. Among all fractions, residual fraction accounted for the major portion of the total B. It comprised of 92.71–93.90% in Soil I, 94.51–95.40% in Soil II, and 94.91–95.25% in Soil III of the total boron.  相似文献   
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6.
Plants have developed different mechanisms to absorb and solubilize phosphorus (P) in the soil, especially in environments with low P availability. This study evaluated the effects of different winter cover crops on soil P availability in a clayey subtropical (Hapludox) soil receiving soluble P fertilizer and a rock phosphate applied to the summer crop, under no‐tillage. The experiment was carried out over 3 yrs (2009–2011) with five different cover crop species: common vetch, fodder radish, ryegrass, black oat, white clover and fallow as control. The soil was sampled after the third year of cover crop cultivation and analysed for inorganic and organic P forms according to the well‐established Hedley fractionation procedure. Phosphate fertilizers promoted accumulation of both labile and nonlabile P pools in soil in the near surface layer, especially under rock phosphate. Fertilizer applications were not able to change P fractions in deeper layers, emphasizing that the Brazilian clayey soils are a sink of P from fertilizer and its mobility is almost nil. Although the cover crops recycled a great amount of P in tissue, in a short‐term evaluation (3 yrs) they only changed the content of moderately labile P in soil, indicating that long‐term studies are needed for more conclusive results.  相似文献   
7.
为了探究牛肉及副产物中稳定碳、氮同位素在加工过程中的变化规律,确证稳定碳、氮同位素在牛肉加工制品产地溯源中的稳定性和有效性。本试验通过对牛肉进行不同时间的水煮、烤制和油炸3种处理,其中水煮和烤制加工时间分别为5、10、15、20、25和30 min,油炸加工时间分别为1、2、3、4和5 min;采用元素分析仪-稳定同位素比率质谱仪(EA-IRMS)测定脱脂牛肉、粗脂肪及副产物中δ13C和δ15N值。结果表明,脱脂牛肉中δ13C值在水煮、烤制和油炸3种加工方式不同加工时间之间均无显著差异,水煮和烤制后粗脂肪中δ13C值无显著变化,油炸后的牛肉粗脂肪δ13C值主要受植物油的影响,加工方式及加工时间对其无显著影响;水煮脱脂牛肉δ15N值在加工25、30 min时与对照组牛肉存在显著差异,但平均差值仅为0.3‰~0.9‰。牛肉稳定碳、氮同位素在不同加工过程中分馏效应较小,可有效用于牛肉加工半成品及成品的原产地溯源。  相似文献   
8.
Hedley labile phosphorus(P)pools in soil tend to be several times larger than annual forest requirements,even in highly weathered soils characterized by P limitation.The discrepancy between plant and soil P status could be partly attributable to the frequently adopted air-drying pretreatment that tends to increase soil P solubility.In this study,the effects of air-drying on the distribution of Hedley P fractions were examined using soils collected under 4 forest types at Gongga Mountain,southwestern China.The results showed that the microbial biomass P(Pmic)in the organic horizon decreased markedly after air-drying.The concentrations of Hedley labile P in the air-dried samples were 31%–73%more than those in the field-moist samples.Consequently,the air-drying-induced increments of Hedley labile P pools in the surface soil horizons were 0.8–3.8 times the annual plant P requirements.The organic horizon was more susceptible to the air-drying-induced increases in Hedley labile P than the mineral horizon,probably because of the stronger release of Pmicand disruption of soil organic matter.The quality of P,indexed by the ratio of Hedley labile P to slowly cycling P,shifted in favor of the Hedley labile fractions after air-drying,further revealing that air-drying changed the distribution of Hedley P pools in forest soils.These indicated that the effects of air-drying could not be ignored when interpreting the discrepancy between the P status of plants and the Hedley labile P pools in forest soils.To more efficiently evaluate the P status in forest soils via the Hedley fractionation procedure,the use of field-moist soils is recommended.  相似文献   
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