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   413篇
  免费   15篇
  国内免费   1篇
林业   25篇
农学   4篇
基础科学   1篇
  119篇
综合类   17篇
农作物   35篇
水产渔业   16篇
畜牧兽医   183篇
园艺   10篇
植物保护   19篇
  2024年   1篇
  2023年   4篇
  2022年   7篇
  2021年   17篇
  2020年   12篇
  2019年   28篇
  2018年   18篇
  2017年   12篇
  2016年   17篇
  2015年   13篇
  2014年   18篇
  2013年   24篇
  2012年   33篇
  2011年   35篇
  2010年   14篇
  2009年   14篇
  2008年   31篇
  2007年   24篇
  2006年   23篇
  2005年   20篇
  2004年   26篇
  2003年   16篇
  2002年   15篇
  2001年   1篇
  1996年   1篇
  1993年   2篇
  1991年   1篇
  1988年   1篇
  1984年   1篇
排序方式: 共有429条查询结果,搜索用时 31 毫秒
81.
A study was conducted to evaluate the effect of pinolene-based film-forming Vapor Gard (VG) emulsion (di-1-p-menthene), a commercial antitranspirant, on the response of the sensitive bean (Phaseolus vulgaris cv. Pinto) plants to realistic ozone fumigations. Plants treated with the chemical were significantly less damaged in comparison with untreated controls when exposed to as much as 150 ppb of ozone in the atmosphere for 4 h. In unozonated plants, photosynthesis as well as stomatal conductance was significantly depressed by the antitranspirant. In VG-treated individuals, (1) visible injury is strongly reduced; (2) membrane damage is counteracted; (3) photosynthetic activity is unchanged, as well as the stomatal conductance and the store of CO2 in substomatal chamber; (4) F v/F m and the other parameters of chlorophyll fluorescence reveal a stability of the photochemical apparatus; and (v) antioxidant defence is not stimulated. Unexpectedly, our results highlighted a dramatic difference between the protective effects towards ozone damage induced by VG, depending on its mode of distribution. As reported above, when entire plants (??both leaves??) are treated or untreated with VG, those individuals wherein VG was not applied showed severe alterations in phenomenological, biochemical and ecophysiological parameters investigated due to ozone toxicity. This is not true in the cases where ??single primary leaves?? or selected regions (??half leaves??) are treated with VG. Even if visible injury is present after ozone fumigation, physiological parameters, such as A max and G w, in ozonated and VG-treated single leaves and half leaves are similar to unfumigated controls. Similar results were obtained for chlorophyll fluorescence parameters. A membrane-protective action is observed in half-leaves treatment. It appears that the presence of regions (single leaves or half leaves), which are treated with VG, modifies the behaviour to ozone of untreated regions. Possible explanations of the observed phenomenon are discussed. The antitranspirant di-1-p-menthene proved to be a low-cost, low-technology tool for assessing ozone injury in the field.  相似文献   
82.
Tropical Animal Health and Production - A cross-sectional study was conducted to determine the seroprevalence and the risk factors associated with C. burnetii infection in cattle in the state of...  相似文献   
83.
This study aimed to assess radiographic and tomographic cardiac parameters, including width and length of the heart, and the ratio of heart width to coelom width of blue-fronted Amazon parrots (Amazona aestiva) with varying body condition scores. Thirty-five captive birds were included in the study and were allocated into one of three groups according to their respective body condition score: lean, ideal and obese. No differences were observed among the groups with regard to radiographic and tomographic measurements. Computed tomography enabled better identification of the structures of the cardiovascular system without interference from the overlying structures of the celomatic cavity observed in radiographic images. However, radiographic examinations should still be considered the standard screening method to identify cardiac alterations, such as increased or reduced organ dimensions. Standardizing the techniques and measurements performed in this study may serve as a basis for further research in the field.  相似文献   
84.
ABSTRACT

The corn-grass intercropping system began to be used in the dry season, as it provides increased straw production for the no-tillage system. However, corn and grass are plants demanding in nitrogen. The corn cultivated in the dry season is called out-of-season corn in Brazil. The objective of this study was to evaluate the productivity and nutrients concentrations of out-of-season corn and Congo-grass intercropped in the no-tillage system, as a function of the nitrogen rates applied in sidedressing. The treatments were four nitrogen rates, 0, 30, 60 and 90?kg?ha?1. The experimental design was randomised complete blocks with four replicates. The experimental period corresponded to the harvests of 2015 and 2016. There were evaluated: corn grain yield, dry mass production and nutrient concentration in the shoots of the plants intercropped. The evaluations were carried out at the physiological maturity stage of the corn and at the time of desiccation of the grass. Nitrogen increased grain yield and dry mass production of the plants intercropped. Nitrogen maximised the magnesium concentration in out-of-season corn and the nitrogen, calcium, magnesium and sulphur concentrations in Congo grass. Excess nitrogen promoted reduction of the phosphorus in the Corn-Congo grass intercropping system in the dry season.  相似文献   
85.
Three new monoterpene glycosides named 4-O-methyl-paeoniflorin (1), isopaeoniflorin (2), and isobenzoylpaeoniflorin (3), together with two known monoterpene glycosides, paeoniflorin (4) and benzoylpaeoniflorin (5), were isolated from the roots of Paeonia lactiflora. Their structures were established on the basis of spectral and chemical evidence.  相似文献   
86.
The essential oil obtained from the seeds of Momordica charantia was analyzed by GC/MS. Twenty-five components, representing 90.9% of the oil, were identified. The main constituents were trans-nerolidol, apiole, cis-dihydrocarveol and germacrene D. Furthermore, the oil was tested for its antibacterial and antifungal activities. Staphylococcus aureus was found to be the most sensitive microorganism with MIC values <500 microg/ml.  相似文献   
87.
88.
Recent studies highlighted the role of autophagy as a cardinal regulatory system for homeostasis and cancer‐related signalling pathways. In this context, the deregulated expression of p62 – Sequestosome1 (p62/SQSTM1) – a protein acting both as an autophagy receptor and signalling hub, has been associated with tumour development and chronic inflammation. Multiple clinical studies test drugs targeting autophagy, and even more research is on the way to clinical trials. However, no comparative investigations have been carried out to identify adequate preclinical models to assess p62‐based medicine. In veterinary oncology the role of p62 in cancer‐related pathways has been largely ignored. We compared p62 sequences in multiple organisms and found that canine p62 significantly diverges from the humans and from other animals sequences. Then, we chart by immunohistochemistry the expression levels of p62 in canine mammary tumours. A total of 66 tumours and 10 non‐neoplastic mammary samples were examined. The expression of p62 was higher in normal tissue and adenomas than carcinomas, with lowest levels of p62 protein detected in high grade carcinomas. In all cases examined the tumour stroma appeared to be p62‐negative. Taken together our results would suggest that in dogs the association between p62 expression and cancer cells overturns that reported in human breast carcinoma, where p62 accumulates in malignant cells as compared to normal epithelium. Thus, at least in canine mammary tumours, p62 should be not considered a tumour‐rejection antigen for an anti‐cancer immunotherapy.  相似文献   
89.
Xanthomonas arboricola pv. juglandis is the causal agent of walnut blight, one of the most important and widespread diseases of Persian (English) walnut (Juglans regiaL.), causing severe damage to leaves, twigs and nuts. To investigate the genomic variability of X. arboricolapv. juglandis, 66 isolates obtained from different countries (England, France, Italy, The Netherlands, Romania, Spain, USA, and New Zealand) were analysed using the Amplified Fragment Length Polymorphism (AFLP) technique. EcoRI and MseI were used as restriction endonucleases. Primers with a core sequence including endonuclease recognition sites and a 3prime-terminal cytosine selective base for MseI primer, or no selective base for EcoRI primer, were used. Data were analysed by means of a multiple correspondence analysis. A total of 76 amplified polymorphic DNA fragments were used to compute relationships among isolates. The AFLP profiles of X. arboricola pv. juglandis isolates appeared to be reliably distinguishable from X. arboricola pv. pruni and X. arboricola pv. corylina, and from other Xanthomonas species, i.e. X. campestris pv. campestris, X. fragariae, X. hortorum, X. axonopodis pv. vesicatoria. Though this pathogen is associated with one single host genus, a high level of genomic diversity was found. This diversity might be partly explained by the geographic origin. Nevertheless, isolates with different patterns were collected within one country, and similar molecular patterns were found in isolates collected at different sites. However, genetic diversity might be influenced by exchanging vegetative material from different countries. Mixing of X. arboricola pv. juglandis isolates might have partly concealed the influence of the geographic location from which the bacteria were isolated.  相似文献   
90.
In this study, we investigated the dynamics of Mycoplasma hyopneumoniae infections in 66 pig farms, with different production systems (one-, two-, and three-site systems), and considered different risk factors. Serological assay was used to detect serum antibodies against M. hyopneumoniae and real time polymerase chain reaction (RT–PCR) was performed to detect M. hyopneumoniae DNA in tracheobronchial swabs. Results demonstrated that M. hyopneumoniae infection status was predominantly influenced by the age of the animals and the type of production system. Infection rates were higher in older animals and the prevalence was higher in the one- and two-site systems than in the three-site systems. Dynamics of infection by RT-PCR showed that earlier M. hyopneumoniae infection on one-site farms occurs earlier, while on two- and three-site farms occurs later but spreads faster, suggesting that contact between animals of different age favors the transmission.  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