首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   268篇
  免费   16篇
  国内免费   1篇
林业   26篇
农学   9篇
  66篇
综合类   23篇
农作物   18篇
水产渔业   12篇
畜牧兽医   101篇
园艺   7篇
植物保护   23篇
  2024年   1篇
  2023年   2篇
  2022年   5篇
  2021年   8篇
  2020年   9篇
  2019年   9篇
  2018年   13篇
  2017年   11篇
  2016年   12篇
  2015年   13篇
  2014年   14篇
  2013年   18篇
  2012年   26篇
  2011年   17篇
  2010年   11篇
  2009年   16篇
  2008年   16篇
  2007年   13篇
  2006年   12篇
  2005年   13篇
  2004年   12篇
  2003年   13篇
  2002年   12篇
  2001年   3篇
  2000年   1篇
  1999年   1篇
  1997年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
排序方式: 共有285条查询结果,搜索用时 218 毫秒
101.

Purpose

Biochar has unique properties which make it a powerful tool to increase soil fertility and to contribute to the decrease of the amount of atmospheric carbon dioxide through the mechanisms of C sequestration in soils. Chemical and physical biochar characteristics depend upon the technique used for its production and the biomass nature. For this reason, biochar characterization is very important in order to address its use either for agricultural or environmental purposes.

Materials and methods

Three different biochars obtained from an industrial gasification process were selected in order to establish their chemical and physical peculiarities for a possible use in agronomical practices. They were obtained by charring residues from the wine-making industry (marc) and from poplar and conifer forests. Routine analyses such as pH measurements, elemental composition, and ash and metal contents were performed together with the evaluation of the cross-polarization magic angle spinning (CPMAS) 13C NMR spectra of all the biochar samples. Finally, relaxometry properties of water-saturated biochars were retrieved in order to obtain information on pore size distribution.

Results and discussion

All the biochars revealed basic pH values due to their large content of alkaline metals. The quality of CPMAS 13C NMR spectra, which showed the typical signal pattern for charred systems, was not affected by the presence of paramagnetic centers. Although paramagnetism was negligible for the acquisition of solid state spectra, it was effective in some of the relaxometry experiments. For this reason, no useful information could be retrieved about water dynamics in marc char. Conversely, both relaxograms and nuclear magnetic resonance dispersion profiles of poplar and conifer chars indicated that poplar char is richer in small-sized pores, while larger pores appear to be characteristic for the conifer char.

Conclusions

This study showed the potential of relaxometry in revealing chemical?Cphysical information on industrially produced biochar. This knowledge is of paramount importance to properly direct biochar agronomical uses.  相似文献   
102.
Celiac disease (CD) is an autoimmune permanent enteropathy that is triggered in susceptible individuals after the ingestion of gluten, a storage protein fraction presents in wheat, rye and barley endosperm. Specific gluten peptides can bind to HLA-DQ2/8 and induce lamina propria CD4+ T cell responses causing damage of the small intestine mucosa. Recent studies suggested that beside immunodominant and toxic epitopes, wheat gluten also contains epitopes capable of preventing the mucosal response in vitro. Among them, a decapeptide (QQPQDAVQPF) from wheat was reported to have an antagonist effect on the agglutination of K562(S) cells and celiac T-cell activation, although the corresponding nucleotidic sequence remained unknown. This study was therefore designed to clone the sequence encoding the protein carrying the decapetide with CD protective properties. A ω-secalin gene encoding containing the decapeptide QQPQRPQQPF was isolated. Although the decapeptide was not identical to the one previously described, QQPQRPQQPF showed the same capability to prevent K562(S) cell agglutination and celiac mucosa immune activation induced by toxic gliadins. The ω-secalin gene was found in wheat carrying the wheat–rye chromosomal translocations 1BL.1RS. The identification of this immunomodulatory gliadin sequence, naturally occurring in cultivars of wheat toxic for celiac patients, might offer new therapeutic strategies for CD.  相似文献   
103.
Water, Air, & Soil Pollution - In the present paper, electrocoagulation (EC) has been employed for the reduction of chemical oxygen demand (COD) reduction of a distillery wastewater...  相似文献   
104.
To evaluate the phytoremediation capability of some poplar and willow clones a hydroponic screening for cadmium tolerance, accumulation and translocation was performed. Rooted cuttings were exposed for 3 weeks to 50 μM cadmium sulphate in a growth chamber and morpho-physiological parameters and cadmium content distribution in various parts of the plant were evaluated. Total leaf area and root characteristics in clones and species were affected by cadmium treatment in different ways. Poplar clones showed a remarkable variability whereas willow clones were observed to be more homogeneous in cadmium accumulation and distribution. This behaviour was further confirmed by the calculation of the bio-concentration factor (BCF) and the translocation factor (Tf). Mean values of all the clones of the two Salicaceae species showed that willows had a far greater ability to tolerate cadmium than poplars, as indicated by the tolerance index (Ti), calculated on the dry weight of roots and shoots of plants. As far as the mean values of Tf was concerned, the capacity of willows to translocate was double that of poplars. On the contrary, the mean values of total BCF in poplar clones was far higher with respect to those in willows. The implications of these results in the selection of Salicaceae clones for phytoremediation purposes were discussed.  相似文献   
105.
OBJECTIVE: To investigate effects of isoflurane at approximately the minimum alveolar concentration (MAC) on the nociceptive withdrawal reflex (NWR) of the forelimb of ponies as a method for quantifying anesthetic potency. ANIMALS: 7 healthy adult Shetland ponies. PROCEDURE: Individual MAC (iMAC) for isoflurane was determined for each pony. Then, effects of isoflurane administered at 0.85, 0.95, and 1.05 iMAC on the NWR were assessed. At each concentration, the NWR threshold was defined electromyographically for the common digital extensor and deltoid muscles by stimulating the digital nerve; additional electrical stimulations (3, 5, 10, 20, 30, and 40 mA) were delivered, and the evoked activity was recorded and analyzed. After the end of anesthesia, the NWR threshold was assessed in standing ponies. RESULTS: Mean +/- SD MAC of isoflurane was 1.0 +/- 0.2%. The NWR thresholds for both muscles increased significantly in a concentration-dependent manner during anesthesia, whereas they decreased in awake ponies. Significantly higher thresholds were found for the deltoid muscle, compared with thresholds for the common digital extensor muscle, in anesthetized ponies. At each iMAC tested, amplitudes of the reflex responses from both muscles increased as stimulus intensities increased from 3 to 40 mA. A concentration-dependent depression of evoked reflexes with reduction in slopes of the stimulus-response functions was detected. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthetic-induced changes in sensory-motor processing in ponies anesthetized with isoflurane at concentrations of approximately 1.0 MAC can be detected by assessment of NWR. This method will permit comparison of effects of inhaled anesthetics or anesthetic combinations on spinal processing in equids.  相似文献   
106.
The objective of the study was to investigate and assess the impact of trainings on the levels of meat contamination produced from local livestock slaughter facilities in the North-West region of Somalia (Somaliland). The investigation considered slaughter facilities where workers had been trained or not. The survey was carried out in four local slaughter facilities. A pre-tested questionnaire on abattoir hygiene and food safety standards was administered to International Aid Organizations, government officials, abattoir workers and supervisors. In addition, a total of 320 surface meat swab samples were collected from randomly selected small ruminant carcasses slaughtered from four purposefully selected local slaughter facilities. The samples were analyzed at Analabs laboratories in Nairobi, Kenya, for total viable counts, total coliforms count and presence of Salmonella species. Meat contamination risk factors associated with hygiene practices based on training offered or not was identified. It was noted that slaughter facilities where abattoir workers had not received trainings on minimum meat hygiene standards and quality assurance systems of good hygiene practices and sanitary standard operating procedures produced carcasses with high levels of bacterial contamination in comparison with those where workers had received the said trainings. The laboratory results were in agreement with poor hygiene meat handling practices and lack of compliance with minimum meat hygiene and food safety standards in Berbera and Burao local livestock slaughter facilities where personnel had not been trained.  相似文献   
107.
Essential oil from flowers (FL) and vegetative parts (VP) of Achillea ligustica (Asteraceae), naturalized after cultivation in central Italy, was investigated by GC–FID and GC–MS. The most abundant components were linalool, viridiflorol, β-pinene, 1,8-cineole and terpinen-4-ol. The antioxidant assays (DPPH and ABTS radical scavenging assays, and β-carotene bleaching test) demonstrated a moderate activity of essential oils. The antimicrobial activity was evaluated by the broth micro-dilution method on 6 microbial strains and showed to be quite strong against the cariogenic Gram-positive Streptococcus mutans, suggesting that this essential oil could be a valid candidate for anti-cariogenic formulations. Moderate cytotoxic activity was observed in assays on four tumour cell lines by MTT assay.  相似文献   
108.
The aim of this study was to assess the effects of earliness (according to FAO class), maturity stage at harvest and environmental conditions on the ensilability of maize hybrids described by their fermentation products and by a fermentation quality index (FQI). Maize hybrids belonging to early (n = 14) and late (n = 15) FAO classes were grown in low, medium and high potential yield areas and harvested at an early (EH), medium (MH) and late maturity stage (LH), that is, at 1/3, 2/3 and 5 d after the 2/3 milk line stage, respectively, according to a split‐plot design. Upon harvest, each sample (n = 522) was analysed for dry matter (DM) and water‐soluble carbohydrates (WSC) before being ensiled in vacuum‐packed bags (n = 1,044). After 60 days of conservation, samples were analysed for DM and fermentation products. In the pre‐ensiling phase, DM was higher in early hybrids (p = .001), low yield areas (p < .001) and at LH maturity (p < .001), whereas WSC contents were higher in early hybrids (p < .001), medium yield areas (p < .001) and at EH maturity (p < .001). With regard to silages, early hybrids had a higher FQI (p < .001), which was highest in areas with a high yield potential (p < .01) and at EH maturity (p < .01). Late hybrids proved to be better suited for low yield areas compared with early hybrids (p < .01) and had a higher FQI at EH and MH than at LH maturity (p < .01).  相似文献   
109.
The promyelocytic leukemia (PML) tumor suppressor is a pleiotropic modulator of apoptosis. However, the molecular basis for such a diverse proapoptotic role is currently unknown. We show that extranuclear Pml was specifically enriched at the endoplasmic reticulum (ER) and at the mitochondria-associated membranes, signaling domains involved in ER-to-mitochondria calcium ion (Ca(2+)) transport and in induction of apoptosis. We found Pml in complexes of large molecular size with the inositol 1,4,5-trisphosphate receptor (IP(3)R), protein kinase Akt, and protein phosphatase 2a (PP2a). Pml was essential for Akt- and PP2a-dependent modulation of IP(3)R phosphorylation and in turn for IP(3)R-mediated Ca(2+) release from ER. Our findings provide a mechanistic explanation for the pleiotropic role of Pml in apoptosis and identify a pharmacological target for the modulation of Ca(2+) signals.  相似文献   
110.
Pedotransfer functions (PTFs) make use of routinely surveyed soil data to estimate soil properties but their application to soils different from those used for their development can yield inaccurate estimates. This investigation aimed at evaluating the water retention prediction accuracy of eight existing PTFs using a database of 217 Sicilian soils exploring 11 USDA textural classes. PTFs performance was assessed by root mean square differences (RMSD) and average differences (AD) between estimated and measured data. Extended Nonlinear Regression (ENR) technique was adopted to recalibrate or develop four new PTFs and Wind’s evaporation method was applied to validate the effectiveness of the relationships proposed. PTFs evaluation resulted in RMSD and AD values in the range 0.0630–0.0972 and 0.0021–0.0618 cm3 cm–3, respectively. Best and worst performances were obtained respectively by PTF-MI and PTF-ZW. ENR allowed to recalibrate PTF-MI and PTF-ZW with improvements of RMSD (0.0594 and 0.0508 cm3 cm–3) and to develop two relationships that improved RMSD by 75–78% as compared to PTF-MI. The results confirmed the potential of ENR technique in calibrating existing PTFs or developing new ones. Validation conducted with an independent dataset suggested that recalibrated/developed PTFs represent a viable alternative for water retention estimation of Sicilian soils.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号