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   193篇
  免费   7篇
林业   14篇
农学   15篇
基础科学   1篇
  45篇
农作物   56篇
水产渔业   17篇
畜牧兽医   34篇
园艺   4篇
植物保护   14篇
  2023年   2篇
  2022年   6篇
  2021年   15篇
  2020年   12篇
  2019年   14篇
  2018年   13篇
  2017年   16篇
  2016年   13篇
  2015年   13篇
  2014年   12篇
  2013年   18篇
  2012年   12篇
  2011年   13篇
  2010年   12篇
  2009年   6篇
  2008年   12篇
  2007年   2篇
  2006年   1篇
  2005年   2篇
  2004年   3篇
  2003年   3篇
排序方式: 共有200条查询结果,搜索用时 31 毫秒
41.
Sandy soils, with low productivity, could be improved by compost application to sustain crop production. This study aimed to examine the effect of three compost types (vegetable, fruit and yard waste compost, garden waste compost, and spent mushroom compost) on basic properties of a loamy sand and greenhouse tomato productivity. Disturbed and intact soil samples were taken from a decade-long compost field experiment on loamy sand with three compost types at application rate of 30 m3 ha?1 yr?1 (7.5 ton ha?1 yr?1). The soils were characterized for chemical and physical properties. Tomato was planted in a greenhouse using soil samples from the field and vegetative and yield parameters (plant height, stem diameter, leaf number, and fruit yield), water productivity, and harvest index were evaluated. All compost types significantly increased soil total carbon, total nitrogen, pH, electrical conductivity and significantly decreased bulk density, with no effect on plant available water compared to the control. Fresh and dry fruit weights were significantly increased after compost addition. Plant height, leaf number, stem diameter, and total biomass did not significantly improve after compost addition. Spent mushroom compost had greater effect in improving tomato productivity. A decade-long application of composts on loamy sand improved basic chemical and physical properties which were reflected in increased fruit yield in tomato. Since no negative effect of compost was observed, we suggest that sandy soils may serve as a safe end use option for these composts and potentially support crop growth.  相似文献   
42.
Property rights, the agricultural price index, forest area, population, income and timber price are important factors in the deforestation process. The aim of this study was to test the impact of these factors on deforestation in Iran using an environmental Kuznets curve (EKC). The autoregressive distributed lag approach was also used to estimate the deforestation function. The existence of an inverted U-shaped EKC for deforestation in Iran was confirmed. In addition, there is evidence of a relationship between deforestation and property rights, forest area, agricultural price index and terms of trade. It is concluded that improvement of secure property rights and environmental policies can improve compliance regarding forest land use and reduce the deforestation rate in Iran.  相似文献   
43.
The aim of this study was to investigate the cytotoxic and anticancer activities of stylosin, a monoterpene extracted from an edible plant, Ferula ovina, on 5637 and HFF3 cells using MTT and comet assays and DAPI staining.To assess stylosin effects, cells were cultured in the presence of various concentrations of stylosin during three days; the IC50 of stylosin on cancerous 5637 cells was less than its value on HFF3 normal cells, indicating that it might have anticancer properties. Investigating the mechanism of stylosin action revealed that it quickly induced DNA lesions and increased the number of apoptotic cells.  相似文献   
44.
1. Systemic listeriosis was induced in 14-d-old Chukar partridge chicks, Alectoris chukar, by intravenous injection of a suspension containing 106 cfu/ml of viable Listeria monocytogenes organisms to study the course of infection.

2. Septicaemic and encephalitic forms of listeriosis were observed in all birds. Infection resulted in a fever response 8-h post-inoculation. Disease rapidly developed over a 24-h period with decreased activity, lethargy, ruffled feathers, huddling, listlessness, inability to stand, wing droop, decreased feed and water consumption, growth depression, neural disturbances and finally death. Gross and histopathological changes were observed in the myocardium, proventriculus, gizzard, intestine, pancreas, kidney, liver, spleen, lung, meninges and joints.

3. The diversity of these clinical signs and lesions suggests a high susceptibility of Chukar partridge chicks to systemic listeriosis.  相似文献   

45.
The effects of zinc–methionine (Zn‐Met) supplementation on growth, blood metabolites and gastrointestinal development were investigated in two experiments with sheep. The objective of Experiment 1 was to determine the effects of Zn‐Met supplementation on hormones and metabolites involved in growth and energy balance regulation, while Experiment 2 aimed to determine the effects of Zn‐Met on feed intake, body weight, gastrointestinal development and liver glycogen concentration in lamb. The animals were assigned to groups with different concentrations of dietary Zn‐Met (0, 0.4, 0.8 and 1.2 g/day) in both experiments. In Experiment 1, feeding different doses of Zn‐Met increased plasma insulin‐like growth factor 1 (IGF‐1) concentration, but it linearly decreased plasma growth hormone (GH). No differences were observed in blood cortisol, insulin and glucose concentrations among the treatments. In Experiment 2, addition of Zn‐Met to the diets did not lead to changes in the body weights of the lambs. Both average daily gain and dry matter intake (DMI) increased linearly with increasing concentrations of dietary Zn‐Met. Lambs receiving Zn‐Met showed higher liver glycogen concentrations than the control. While significant increases were observed in the villus height and crypt depth in the duodenum and jejunum as a result of Zn‐Met supplementation, no change was detected in blood glucose concentrations (p > 0.05). Our findings suggest that dietary Zn‐Met may improve growth, energy balance and gastrointestinal development in sheep.  相似文献   
46.
47.
Chronic inflammation, as reflected by increased level of acute phase protein such as C-reactive Protein (CRP) is highly prevalent in hemodialysis patients. CRP is a strong predictor of overall and cardiovascular mortality and morbidity in hemodialysis patients. This research was conducted to determine the C-reactive Protein (CRP) levels and its correlation to demographic and clinical characteristics and Laboratory values in hemodialysis patients in Sari, Iran. In a cross sectional study, 147 hemodialysis patients were studied. Patients' demographic and clinical data were recorded and also serum CRP, Cholesterol, Albumin, Phosphorous, Calcium, Hemoglobin and Hematocrit levels were measured. Overall, the mean CRP concentration was 15.8 mg L(-1). With considering to the different cutoff point (5, 6.2, 10 mg L(-1)) for CRP level, 107 patients (72.8%) had CRP level >5 mg L(-1), 99 patients (67.3%) had CRP level > 6.2 mg L(-1) and 77 patients (52.4%) had CRP level >10 nmg L(-1). The CRP levels greater than 6.2, had a direct statistically significant correlation with duration of hemodialysis and phosphorus level (p = 0.01). Also, CRP levels above 10 mg L(-1) had a direct statistically significant correlation with age and phosphorus levels (p = 0.02). According to the prevalence of high CRP level and it's correlation with age, duration ofhemodialysis and phosphorus level in hemodialysis patients, CRP level should be screened in this group of patients routinely because of its prognostic importance.  相似文献   
48.
The supercritical fluid extraction (SFE) of the aerial parts of Perovskia atriplicifolia Benth. was studied. The effect of different parameters such as pressure, temperature, modifier identity, and modifier volume on the SFE of the plant was investigated. The extracts were analyzed by GC and GC-MS and compared with the essential oil obtained from P. atriplicifolia Benth by steam distillation. The supercritical extracts and the steam-distilled products had very different compositions. The main constituents of the oil obtained by steam distillation were 1,8-cineole, limonene, camphor, beta-caryophyllene, alpha-pinene, camphene, and alpha-humulene. On the other hand, the major components of SFE extracts were 1,8-cineole, limonene, camphor, beta-caryophyllene, gamma-cadinene, alpha-pinene, and alpha-terpinyl acetate. The results showed that increasing the temperature from 35 to 65 degrees C (at a constant pressure of 100 atm) drastically reduced the number of extracted components. Also, the number of extracted constituents and the percent of main analytes increased when lower pressures were used. Using different modifiers (e.g., methanol, ethanol, dichloromethane, and hexane) for the extraction of the plant at low pressure (100 atm) and temperature (35 degrees C) showed that hexane was more selective than the other modifiers.  相似文献   
49.
Genetic Resources and Crop Evolution - Marrubium L., is a problematic genus of Lamiaceae family with approximately 40 taxa that some of its species grow in Iran. In the current study, we studied...  相似文献   
50.
Background:hESCs-MSCs open a new insight into future cell therapy applications, due to their unique characteristics, including immunomodulatory features, proliferation, and differentiation. Methods:Herein, hESCs-MSCs were characterized by IF technique with CD105 and FIBRONECTIN as markers and FIBRONECTIN, VIMENTIN, CD10, CD105, and CD14 genes using RT-PCR technique. FACS was performed for CD44, CD73, CD90, and CD105 markers. Moreover, these fibroblast-like cells, due to multipotent characteristics, differentiated to the osteoblast. Results:MSCs were derived from diploid and triploid hESC lines using sequential 3D and 2D cultures and characterized with the specific markers. IF showed the expression of FIBRONECTIN and CD105 in hESCs-MSCs. Flow cytometry data indicated no significant difference in the expression of MSC markers after 6 and 13 passages. Interestingly, gene expression profiles revealed slight differences between MSCs from diploid and triploid hESCs. The hESCs-MSCs displayed osteogenic differentiation capacity, which was confirmed by Alizarin red staining. Conclusion:Our findings reveal that both diploid and triploid hESC lines are capable of forming MSCs; however, there are some differences in their gene expression profiles. Generation of MSCs from hESCs, as a non-invasive procedure in large scale, will lend itself for the future cell-based therapeutic applications. Key Words: Human embryonic stem cells, Mesenchymal stem/stromal cells, Regenerative medicine  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