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   134篇
  免费   1篇
林业   13篇
农学   2篇
  51篇
综合类   17篇
农作物   10篇
畜牧兽医   23篇
园艺   3篇
植物保护   16篇
  2023年   1篇
  2022年   3篇
  2021年   5篇
  2020年   4篇
  2019年   4篇
  2017年   1篇
  2016年   1篇
  2015年   3篇
  2014年   10篇
  2013年   10篇
  2012年   9篇
  2011年   17篇
  2010年   6篇
  2009年   6篇
  2008年   9篇
  2007年   10篇
  2006年   4篇
  2005年   7篇
  2004年   6篇
  2003年   3篇
  2002年   6篇
  2001年   1篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1995年   2篇
  1994年   1篇
  1992年   1篇
  1991年   1篇
  1978年   1篇
排序方式: 共有135条查询结果,搜索用时 23 毫秒
101.
Coatings fulfill an important function in providing functionality and service life to wood surfaces. In the present study, the potential of nanocellulosic fillers toward improving waterborne wood coating mechanics is evaluated using free-standing coating films. At 2% filler content, significant improvements in static and dynamic mechanical properties were observed. The extent of these improvements was different depending on whether high-aspect-ratio cellulose nanofibrils of short cellulose nanocrystals were used. Chemical surface modification of cellulose nanofibrils did not provide further improvement. The water–vapor sorption properties of the coating films, which were also evaluated, did not show significant effects due to addition of nanocellulose, while optical transparency slightly decreased.  相似文献   
102.
The pathogen Fusarium oxysporum f. sp. cepae inducing the Fusarium basal rot mainly spreads in warmer cultivation regions due to its adaptibility to high temperature. Meanwhile the pathogen occurs in Germany as well, especially in years with relatively high average temperature during the growing season. Phytopathological investigations of 300 symptomless onion bulbs showed a contamination rate of approximately 10% with regard to Fusarium spp, with F.?oxysporum proving to be the predominant species. Onion sets planted in these fields were latently infected with F.?oxysporum at rates of 19?C98%. Unexpectedly, the contaminated sets did not indispensably lead to a high occurrence of plants exhibiting characteristic symptoms of Fusarium basal rot such as wet and dry rot. Presumably, the development of symptoms is particularly affected by given climatic conditions. The results of pathogenicity tests of isolated Fusarium spp. isolates under controlled conditions support this assumption. The inoculation of the substrate with selected Fusarium spp. isolates resulted in a reduction of emergence by up to 70% under controlled conditions, which are suboptimal with regard to the cultivation of onions. The emergence of plants was not affected by Fusarium spp. under optimal cultivation of onions. However, under optimal cultivation conditions a reduction of plant growth occurred in a subsequent growth stage. Beside F.?oxysporum, F.?proliferatum could be detected in onion bulbs as well as seeds. The proportion of contaminated seeds accounted to 62%. Both species F.?oxysporum and F.?proliferatum proved to be pathogenic in onion although their isolates varied much in their virulence.  相似文献   
103.

Context

Clustering forest harvest stands reduces the movements of the harvesters, forwarders and staff. Moreover, it simplifies the subsequent log transport, when compared with dispersed stands.

Aims

Harvesting activities are generally based on silvicultural motivated planning data. The development of an analytical method to cluster harvest stands with respect to the spatial network of roads should improve the harvesting effort.

Material and method

The clustering of harvest stands was developed for Aracruz (Brazil) in 2004, where it is used there successfully since. The hierarchical method ??single linkage cluster analysis?? is applied. As a distance function, the Euclidian distance was substituted by the shortest path on the spatial network.

Result

The clustering method is based on the minimum spanning tree, which is the spatial equivalent to the dendrogram of an ordinary cluster analysis. Applying the Delaunay triangulation to fill the distance matrix reduces the distance calculation time from O(n 2) to O(n). The method is illustrated by a planning district of the Aracruz enterprise.

Conclusion

Harvesting units are properly clustered spatially by the discussed method. Topographic obstacles are automatically avoided and the need to relocate machinery is reduced as well as the total driving distance.  相似文献   
104.
Many cash-poor households in the semi-arid tropics strongly depend on non-timber forest products (NTFPs) for livelihood. Increasing threats on NTFP-providing tree species, due to land-use intensification, require ecological studies as well as additional information about species?? uses and management provided by local people. The objectives of our study were to (i) document uses and management of the baobab (Adansonia digitata L.), (ii) investigate knowledge distribution among genders and different villages, and (iii) assess the population status of the baobab in eastern Burkina Faso. We conducted an ethnobotanical survey among Gulimanceba people and performed a quantitative analysis using different measures of knowledge. Interviews reveal that the baobab is harvested by local people for 25 use-types. The fruits are the most important plant part and baobab products are of special importance for nutritional uses. Local management of baobab seems to be so far sufficient to maintain baobab populations. The fact that we found some differences in uses and management of baobab between genders and villages emphasizes the importance of gender- and region-related management recommendation. People are able to use and manage the baobab in a relative sustainable way as human population density is relatively low and as they have relatively good access to the forest compared to other regions of Burkina Faso. However, in the light of land-use and climate changes, adapted management strategies are required. We conclude that ethnobotanical studies on a small-scale level are of high importance in order to develop management strategies that are reliable in a specific region.  相似文献   
105.

Background

A large number of different plant lines are produced and maintained in a typical plant research laboratory, both as seed stocks and in active growth. These collections need careful and consistent management to track and maintain them properly, and this is a particularly pressing issue in laboratories undertaking research involving genetic manipulation due to regulatory requirements. Researchers and PIs need to access these data and collections, and therefore an easy-to-use plant-oriented laboratory information management system that implements, maintains and displays the information in a simple and visual format would be of great help in both the daily work in the lab and in ensuring regulatory compliance.

Results

Here, we introduce ??Phytotracker??, a laboratory management system designed specifically to organise and track plasmids, seeds and growing plants that can be used in mixed platform environments. Phytotracker is designed with simplicity of user operation and ease of installation and management as the major factor, whilst providing tracking tools that cover the full range of activities in molecular genetics labs. It utilises the cross-platform Filemaker relational database, which allows it to be run as a stand-alone or as a server-based networked solution available across all workstations in a lab that can be internet accessible if desired. It can also be readily modified or customised further. Phytotracker provides cataloguing and search functions for plasmids, seed batches, seed stocks and plants growing in pots or trays, and allows tracking of each plant from seed sowing, through harvest to the new seed batch and can print appropriate labels at each stage. The system enters seed information as it is transferred from the previous harvest data, and allows both selfing and hybridization (crossing) to be defined and tracked. Transgenic lines can be linked to their plasmid DNA source. This ease of use and flexibility helps users to reduce their time needed to organise their plants, seeds and plasmids and to maintain laboratory continuity involving multiple workers.

Conclusion

We have developed and used Phytotracker for over five years and have found it has been an intuitive, powerful and flexible research tool in organising our plasmid, seed and plant collections requiring minimal maintenance and training for users. It has been developed in an Arabidopsis molecular genetics environment, but can be readily adapted for almost any plant laboratory research.  相似文献   
106.
The degenerative wear and pathologic damage of the joints are reasons for total endoprotheses in man as well as in dogs. The main problem is the aseptic loosening of the protheses. By usig the finite-element-method, the total endoprothesis is designed with new features, with the purpose of preventing loosening and being better adapted to load transmission. In order to simulate the femur of the dog for the numerical analysis, a material law is developed. By taking into account the anisotropy and the local density of the cancellous bone in the femoral head, the young's modules are experimentally determined. The measurements are performed by ultrasonic methods on femoral heads of euthanised dogs. The results show planar isotropic cancellous bone.  相似文献   
107.
In the following investigations, the LH secretion of cells from pituitaries in heifers on days 16-18 of their oestrous cycle (n = 14) was analysed. Cells were dissociated with trypsin and collagenase and maintained in a static culture system. For the estimation of LH release, the cells were incubated with various concentrations of mammalian GnRH (Lutrelef) for 6 h. To determine the action of Antarelix (GnRH antagonist), the cells were preincubated for 1 h with concentrations of 10(-5) or 10(-4) M Antarelix followed by 10(-6) M GnRH coincubation for a further 6 h. At the end of each incubation, the medium was collected for LH analysis. Parallel, intracellular LH was qualitatively detected by immunocytochemistry. Changes in the intensity of LH staining within the cells in dependence of different GnRH concentrations were not observed, but a significant increase LH secretion in pituitary cells was measured at 10(-6) M GnRH. Antarelix had no effect on basal LH secretion at concentrations of 10(-4) and 10(-5) M. After coincubation of pituitary cells with Antarelix and GnRH, Antarelix blocked the GnRH-stimulated LH secretion with a maximal effect of 10(-4) M, but the staining of immunoreactive intracellular LH was detected at approximately the same level compared to the pituitary cells treated with exogenous GnRH alone. These data demonstrate that Antarelix is effective in influencing the GnRH-stimulated LH secretion of pituitary cells in vitro. After administration of Antarelix in vivo, the GnRH-stimulated LH secretion of cultured pituitary cells was not inhibited.  相似文献   
108.
In north-west Germany Fusarium head blight of wheat (FHB) is frequently caused by Fusarium culmorum and F. graminearum. This damage has, however, mainly been caused by infections during flowering; the incidence of FHB has increased steadily for many years in crop rotations without maize. The authors postulate that F. culmorum can cause systemic infections in wheat. In 2003 they used real-time PCR to analyse more than 1?100 tissue samples from wheat fields in order to determine whether F. culmorum was present in the internodes and spikes of the wheat plants. More than 30% of all analysed samples contained F. culmorum-DNA, and many wheat stems were completely or nearly completely systemically colonized by F. culmorum. These findings are consistent with those of other researchers who have detected a systemic growth of F. culmorum during experiments under controlled conditions. It cannot be automatically assumed that the fungus spreads from the wheat head during flowering; the plant could have become infected through chlamydospores or mycelium on residual plant debris in the soil. Therefore this pathogen must be regarded as a crop rotation disease. F. culmorum is able to severely infect wheat through the roots and stem bases, especially when the soil is dry and warm. Thus, spraying fungicides during flowering is ineffective.  相似文献   
109.
Pesticide movement to subsurface drains was monitored in two typical crop production areas in Germany. Field trials were conducted on two subsurfacedrained soils, a silt loam and a poorly structured sandy soil, under different climatic conditions. Over a period of one year, the drainflow was measured and the drain water was analysed for all applied herbicides. Different leaching behaviour was observed at the two field sites. Following autumn application of pendimethalin and isoproturon to the Soester Börde soil, maximum concentrations of about 62 μg litre?1 for isoproturon and 0.7 μg litre?1 for pendimethalin were observed in drainflow from this silt loam. The early occurrence of both herbicides in the drain water only two days after application is consistent with fast flow through macropores. In contrast, on the subsurfacedrained sandy soil in Brandenburg, isoproturon did not reach the drains until two months after autumn application and was found at maximum concentrations of only 1.4 μg litre?1; pendimethalin was not detected in the drain water. Pesticide movement after spring application seemed to be of minor importance. At both locations, spring application led to low concentrations of pesticides in the drainflow (pendimethalin < 0.01 μ litre?1; metolachlor ? 0.05 μ litre?1; chloridazon ? 0.15 μ litre?1; metamitron ? 0.02 μg litre?1; terbuthylazine ? 1.4 μ litre?1).  相似文献   
110.
Canine pituitary hyperadrenocorticism (Cushing's disease) caused by neoplasia of the corticotrope cells is one of the most common endocrine diseases especially in smaller dog breeds. Cushing's disease was diagnosed in eleven wire-haired Dachshunds and for further six wire-haired Dachshunds Cushing's disease was suspected on the basis of clinical signs. A joined pedigree could be ascertained for all these 17 dogs. Eleven of these dogs were so closely related to each other, that they were summarized in four nucleus families. Two fullsiblings were examined by means of clinical, laboratory diagnostic and morphological methods. The main lesions consisted of atrophic dermatosis with alopecia, increase of activity of liver enzymes in plasma and bilateral adrenocortical hyperplasia and therefore corresponded to the typical signs of a secondary hyperadrenocorticism. A rather unusual finding was the pituitary carcinoma in one of these dogs. Similarly to human patients affected by hyperadrenocorticism, real-time PCR analysis showed a 2.9-fold increase of expression of the canine MDR1 gene in the liver of one affected wirehaired Dachshund. This study documents the first familial occurrence of pituitary-dependent hyperadrenocorticism in wirehaired Dachshunds, the overexpression of the MDR1 gene in the dog and the third case of familial hyperadrenocorticism in dogs ever described.  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