全文获取类型
收费全文 | 201篇 |
免费 | 18篇 |
专业分类
林业 | 18篇 |
农学 | 4篇 |
39篇 | |
综合类 | 17篇 |
农作物 | 15篇 |
水产渔业 | 9篇 |
畜牧兽医 | 89篇 |
园艺 | 7篇 |
植物保护 | 21篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 1篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 12篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 23篇 |
2011年 | 11篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 17篇 |
2007年 | 9篇 |
2006年 | 14篇 |
2005年 | 4篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1938年 | 1篇 |
1937年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有219条查询结果,搜索用时 31 毫秒
151.
152.
153.
A little-leaf disease of Eucalyptus tereticornis, E. grandis and E. globulus characterized by stunting of plants and considerable reduction in size of leaves and internodes, was recorded during survey of nurseries and plantations in Kerala State. The survey indicated that though the little leaf disease was widespread, its incidence was quite low. Transmission of the symptoms by sap and graft techniques was unsuccessful. However, positive fluorescence and staining of phloem tissues by Dienes' stain indicates that this disease may be caused by mycoplasmalike organisms (MLO). 相似文献
154.
Florence Renou Úna Scallan Michael Keane E. P. Farrell 《European Journal of Forest Research》2007,126(4):545-554
The poor reputation of birch in Ireland is gradually changing, and the interest shown in it by foresters is growing, as is
the recognition of the many advantages that this genus offers, especially from an afforestation and ecosystem development
point of view. The potential of native birch species was investigated on industrial cutaway peatlands in the Irish midlands.
Field experiments were established to evaluate differences (in terms of survival, growth attributes and form) between B. pendula and B. pubescens, between bare-root and container planting, and between small and medium size seedlings. After five growing seasons, B. pendula was found to be the superior species especially on well drained and shallow peat sites. Bare-root B. pendula will grow faster with reasonable form but containerised birch may be favoured on more difficult sites (with deeper and wetter
peat). Larger seedlings performed better, regardless of species. This study demonstrated good growth potential for planted
birch on cutaway peatlands and that this species should be integrated in further planting programmes. 相似文献
155.
Varying amounts of humic acid (Na-salt; 0 to 10 ppm) were first equilibrated with a dilute suspension of H+ -Kaolin and then with spiked (high activity radioactive 64Cu) water. After filtration, through a 0.45 µm Millipore membrane, the amount of radioactivity on the filter and the filtrate was measured separately using a Gamma ray well counter. Adsorption of Cu (expressed as distribution coefficient — K d ) was plotted against humic acid concentration. K d values decreased sharply upto 1 ppm humic acid concentration and thereafter remained constant up to 10 ppm. 相似文献
156.
Quantitative mapping of soil types based on regression kriging of taxonomic distances with landform and land cover attributes 总被引:4,自引:0,他引:4
Nowadays, French soil scientists tend to gather new and existing soil data into a common database. The use of this database potentially allows for resolving environmental issues, largely through soil mapping. The purpose of this study is to present a methodology for mapping soil types illustrated by typical observations in the soil database, in this case from the La Rochelle area on the French Mid-Atlantic Coast. The main hypothesis underlying the method is that soil types result from environmental factors such as landform, parent material, and land cover. The method can be divided into four stages. The first step is to construct a local soil type classification from the database by a two-stage continuous classification procedure. The result of this procedure is that at each observation point, the soil is described by a vector of taxonomic distances to each of k centroidal soil types. In the example given, k=18. The second step involves fitting soil–environment equations, one for each centroidal soil type, by regressing taxonomic distances on layers of multivariate environmental data observed on a fine 20-m grid, by multiple linear regression. In this case, the layers are terrain attributes derived from a digital elevation model and land cover attributes derived from three bands of a SPOT image. The third step is to predict k maps or raster GIS layers representing taxonomic distances to soil types on the 20-m grid, using the soil–environment equations and the kriging of the residuals from the regressions. This results in many potential maps: a summary map depicting the nearest centroidal soil type (the soil type for which the taxonomic distance is least) at each location is possibly the most useful, and another one representing the minimum taxonomic distance which, if considered too large, might suggest locations for further field survey to refine the soil types. A map of standard errors of the kriged taxonomic distance residuals to the nearest centroidal soil type can be made to indicate spatial uncertainty. Continuous fuzzy membership maps can also be constructed from the distances. The fourth step involves validation with an independent soil data set allowing discovery of the nature of the actual prediction errors. Thirty-eight percent of sites in a validation sample of 1234 sites was unequivocally validated, 23% was equivocally validated, and the remainder was predicted wrongly by the method. 相似文献
157.
Varying amounts of CaCl2 or MgCl2 were first equilibrated with a dilute suspension of H+-kaolin and then with spiked (high activity radioactive 64Cu) water. After filtration, through 0.45 μm Millipore membrane the amount of radioactivity on the filter and the filtrate was measured separately using a Gamma ray well counter. Adsorption of Cu (expressed as distribution coefficient ?K d ) was plotted against Ca or Mg concentration. K d values decreased sharply at Ca or Mg concentration from 0 to 10 mg l?1 and changed only slightly from 10 to 200 mg l?1. Increase in the concentration of Ca or Mg reduces the Cu binding capacity of the clay. 相似文献
158.
159.
Onivaldo Randig Florence Deau Marcilene F. A. dos Santos Myrian S. Tigano Regina M. D. G. Carneiro Philippe Castagnone-Sereno 《European journal of plant pathology / European Foundation for Plant Pathology》2009,125(3):485-495
The root-knot nematode (RKN) Meloidogyne mayaguensis is considered as one of the most damaging RKN species because of its extremely wide host range. Recent surveys have shown
the rapid spread of this parasite in agro-ecosytems, often making crop cultivation not viable in the heavily infested areas.
Here, we report the identification, molecular cloning, genomic organisation and sequence analysis of a new satellite DNA (satDNA)
family from M. mayaguensis (named pMmPet). It is comprised of two groups of A+T rich, tandemly repeated units of 174 and 180 bp, respectively. Using
these sequences as targets, hybridisation and PCR experiments performed on a wide collection of 44 populations belonging to
15 RKN species showed that the pMmPet family could only be detected in the 16 M. mayaguensis populations tested. In addition, because of their repetitive nature, positive detection of pMmPet sequences was achieved
in single individual nematodes. Therefore, the repeated sequence described here possesses features that make it an excellent
candidate for use as a specific and extremely sensitive tool for the accurate detection and identification of this invasive
pest on a routine basis. Clearly, monitoring the occurrence and spread of M. mayaguensis at the domestic and international levels are needed to avoid wholesale loss of agricultural resources in the infested regions. 相似文献
160.
The MecaNiCAL model of carbon and nitrogen partitioning over a period of regrowth for a mean grass plant as described in Part 1 was fitted and evaluated against data from an experiment under controlled conditions with contrasting light and nitrogen nutrition. In the first investigation, the rate of nitrogen uptake was imposed to limit the compensation of errors between process. The root:shoot ratio was simulated well, with a good estimation of the nitrogen allocation to shoots. Some underestimation of the root weight after the cut and the final shoot weight under the low nitrogen treatment were consequences of both the lack of remobilisation and the high priority given to shoots. The good agreement obtained with the expected trend in simulations conducted with the simple nitrogen aborption submodel in extended conditions (contrasting initial content of nitrogen substrate and temperature change in regrowth) ensures the general consistency of the model in the limit of its area of validity. Partitioning to shoots and forage production seem to be sensitive mainly to the size of the carbohydrate substrate pool and its availibility, particularly under conditions of low light. Estimating the initial carbohydrate substrate pool by biochemical analysis may improve the accuracy of the model. Compared with more simple assumptions of partitioning, MecaNiCAL shows a higher level of agreement with the partitioning response to a wide range of environmental conditions. A simple assumption relating partitioning to plant nitrogen content does not seem to be sufficient to simulate the decrease in the root:shoot ratio observed under conditions of low light. Nevertheless, more data from experiments conducted under a wider range of contrasting conditions are required to estimate the validity of MecaNiCAL attached to the nitrogen absorption submodel and the advantage of its more complex assumptions with even greater accuracy. 相似文献