全文获取类型
收费全文 | 340篇 |
免费 | 14篇 |
专业分类
林业 | 38篇 |
农学 | 4篇 |
基础科学 | 1篇 |
83篇 | |
综合类 | 33篇 |
农作物 | 14篇 |
水产渔业 | 26篇 |
畜牧兽医 | 124篇 |
园艺 | 17篇 |
植物保护 | 14篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 14篇 |
2015年 | 6篇 |
2014年 | 20篇 |
2013年 | 24篇 |
2012年 | 32篇 |
2011年 | 29篇 |
2010年 | 15篇 |
2009年 | 9篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 23篇 |
2005年 | 20篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1930年 | 2篇 |
1928年 | 1篇 |
排序方式: 共有354条查询结果,搜索用时 15 毫秒
71.
Kim H Hebelstrup Michael W Christiansen Massimiliano Carciofi Birgitte Tauris Henrik Brinch-Pedersen Preben B Holm 《Plant methods》2010,6(1):15
Background
Cloning of gene casettes and other DNA sequences into the conventional vectors for biolistic or Agrobacterium-mediated transformation is hampered by a limited amount of unique restriction sites and by the difficulties often encountered when ligating small single strand DNA overhangs. These problems are obviated by "The Uracil Specific Excision Reagent (USER™)" technology (New England Biolabs) which thus offers a new and very time-efficient method for engineering of big and complex plasmids. 相似文献72.
Ole K. Borggaard Christian Bender Koch Bo Elberling Henrik Breuning-Madsen Lars Stemmerik 《Geoderma》2012
Knowledge is scarce about the composition of soils on Bellona and other Pacific atolls. Such knowledge is important as it is closely related to sustainable land use of these special soils formed on carbonatic/phosphatic materials. Therefore, the micromorphological, chemical and mineralogical composition of samples from genetic horizons in three dominant Bellonese soils (Malanga, Kenge Ungi and Kenge Toaha) and underlying rock (Tanahu) were investigated. Tanahu mainly consists of dolomite, but this mineral is absent in the three soils, which are dominated by phosphate-containing minerals. The Malanga soil is strongly dominated by Ca and P with minor amounts of Al, F and Fe present in fluorapatite, hydroxyapatite and crandallite. In contrast, Al, Fe and P dominate in the Kenge Ungi and Kenge Toaha soils in accordance with a mineralogy consisting of crandallite together with aluminum oxides (gibbsite/boehmite) and iron oxides, mainly goethite with minor contents of hematite. The observed carbonate for phosphate substitution in the apatites and crandallite is important as it indicates an increased phosphate availability in the soils. All three soil samples contain ≤ 1% Si and very little K and Mg. Total contents of essential microelements are considered adequate, but the rather high contents of Sr and U, especially in the Kenge Ungi soil may be problematic. Although the composition of the soils suggests substantial fertility and resilience, the lack of K-containing weatherable minerals (silicate minerals) is in line with a very low K (and low Mg) content and explains why fertilization may be needed to sustain future cultivation of these special soils. Due to a possible low bioavailability of Fe, Mn and maybe other micronutrients at the circumneutral pH of these carbonatic/phosphatic soils as well as the rather high contents of Sr and U, it may be recommended to test element availability using appropriate chemical soil tests supplemented by plant experiments to ensure safe and sustainable (optimal) soil use. However, according to the local farmers, the Malanga, Kenge Toaha and Kenge Ungi soils are considered well suited for production of the preferred crops. 相似文献
73.
Lihui Xu Sabine Ravnskov John Larsen R. Henrik Nilsson Mogens Nicolaisen 《Soil biology & biochemistry》2012
Soil fungi and oomycetes (syn. peronosporomycetes) are the most common causes of pea diseases, and these pathogens often occur in complexes involving several species. Information on the dynamics within this complex of pathogens, and also between the complex of pathogens and other fungi in the development of root disease is limited. In this study, next-generation sequencing of nuclear ribosomal internal transcribed spacer-1 was used to characterize fungal communities in agricultural soils from nine pea fields, in which pea roots showed different degrees of disease. Fungal species richness, diversity, and community composition were analyzed and compared among the different pea soils. After filtering for quality and excluding non-fungal sequences, 55,460 sequences clustering into 434 operational taxonomic units (OTUs), were obtained from the nine soil samples. These sequences were found to correspond to 145–200 OTUs in each soil. The fungal communities in the nine soils were strongly dominated by Ascomycota and Basidiomycota. Phoma, Podospora, Pseudaleuria, and Veronaea, at genus level, correlated to the disease severity index of pea roots; Phoma was most abundant in soils with diseased plants, whereas Podospora, Pseudaleuria, and Veronaea were most abundant in healthy soils. No correlation was found between the disease severity index and the abundance of some of the other fungi and oomycetes normally considered as root pathogens in pea. 相似文献
74.
Molecular genetic approaches to increasing mineral availability and vitamin content of cereals 总被引:2,自引:0,他引:2
Henrik Brinch-Pedersen Sren Borg Birgitte Tauris Preben B. Holm 《Journal of Cereal Science》2007,46(3):308
The present paper summarizes the current state of knowledge on molecular genetic approaches to increasing iron and zinc availability and vitamin content in cereals. We have also attempted to integrate the scientific issues into the wider context of human nutrition. In the cereal grain, iron and zinc are preferentially stored together with phytate in membrane-enclosed globoids in the protein storage vacuole (PSV) found in the aleurone and the embryo scutellum. The PSV is accordingly central for understanding mineral deposition during grain filling and mobilization of minerals during germination. Recent studies in Arabidopsis have led to the first identification of iron and zinc transporters of the PSV and further illustrate some of the dynamics associated with mineral and phytate transport and deposition into the vacuole. This provides new opportunities for modulating iron and zinc deposition in the cereal grain. Current strategies towards increasing the iron content of the endosperm are largely based on the expression of legume ferritin genes in an endosperm-specific manner. However, it is apparent that this approach, at least in rice, only allows a two- to three-fold increase in the iron content of the grain due to exhaustion of the iron stores in leaves. Further increases thus have to rely on additional uptake and transport of iron from the root. Phytate is generally considered to be the single most important anti-nutritional factor for iron and zinc availability. In the current paper we summarize attempts to increase phytase activity in the grain by transformation and evaluate the potential of this approach as well as the reduction of phytate biosynthesis for improving the bioavailability of iron and zinc. Vitamins constitute the second important group of micronutrients in grain and we discuss current efforts to increase the amounts of provitamin A, vitamin C and vitamin E. 相似文献
75.
In 2008, Canada designed and implemented the Canadian Notifiable Avian Influenza Surveillance System (CanNAISS) with six surveillance activities in a phased-in approach. CanNAISS was a surveillance system because it had more than one surveillance activity or component in 2008: passive surveillance; pre-slaughter surveillance; and voluntary enhanced notifiable avian influenza surveillance. Our objectives were to give a short overview of two active surveillance components in CanNAISS; describe the CanNAISS scenario tree model and its application to estimation of probability of populations being free of NAI virus infection and sample size determination. Our data from the pre-slaughter surveillance component included diagnostic test results from 6296 serum samples representing 601 commercial chicken and turkey farms collected from 25 August 2008 to 29 January 2009. In addition, we included data from a sub-population of farms with high biosecurity standards: 36,164 samples from 55 farms sampled repeatedly over the 24 months study period from January 2007 to December 2008. All submissions were negative for Notifiable Avian Influenza (NAI) virus infection. We developed the CanNAISS scenario tree model, so that it will estimate the surveillance component sensitivity and the probability of a population being free of NAI at the 0.01 farm-level and 0.3 within-farm-level prevalences. We propose that a general model, such as the CanNAISS scenario tree model, may have a broader application than more detailed models that require disease specific input parameters, such as relative risk estimates. 相似文献
76.
Background
Current nature conservation in semi-natural grasslands often includes grazing and hay cutting, as well as the abandonment of draining. Semi-natural grassland and in particular meadows constitute important habitat type for a large number of animal species in today's fragmented and intensively cultivated landscape of Europe. Here we focus on the population characteristics of Common shrews Sorex araneus in relation to livestock grazing intensity in two wet meadows in western Denmark. 相似文献77.
Valuing forest recreation on the national level in a transition economy: The case of Poland 总被引:3,自引:0,他引:3
Anna Bartczak Henrik Lindhjem Stle Navrud Marianne Zandersen Tomasz ylicz 《Forest Policy and Economics》2008,10(7-8):467-472
Recreation benefits constitute a substantial part of the total economic value of forests, and are important for the choice of multi-functional forest policies. The application of methods valuing such benefits is in its infancy in transition economies in Central and Eastern Europe (CEE), so value estimates for policy use are sometimes transferred from Western Europe proportionally scaled down by GDP. However, little is known about how recreation values vary with income, and one risks underestimating benefits in CEE. This paper reports the findings of the first comprehensive, national-level study in any CEE country estimating annual and per trip forest recreation values in Poland using the Travel Cost (TC) and Contingent Valuation (CV) methods. Two in-person interview surveys of forest recreation behaviour were carried out. The first was administered on-site in ten representative forest areas, and the other in the homes of a national sample of adult Poles. Results show that forest recreation is highly valued in Poland, at Euros 0.64–6.93 per trip per person, depending on the valuation method. Both trip frequency and per trip values are higher than the average in Western Europe, despite a lower income level. Thus, a simple GDP-adjusted transfer from Western Europe would substantially undervalue forest recreation in Poland. Further, a comparison of TC consumer surplus estimates and GDP/capita in Europe shows no clear relationship, indicating that a range of cultural, institutional and other factors may be important. 相似文献
78.
79.
Activation of the Renin-Angiotensin System in Dogs With Asymptomatic and Mildly Symptomatic Mitral Valvular Insufficiency 总被引:1,自引:0,他引:1
Henrik D. Pedersen Jørgen Koch Knud Poulsen Asger L. Jensen Annette Flagstad 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1995,9(5):328-331
The renin-angiotensin system has important pathophysiologic implications in the development of congestive heart failure. The activity of the renin-angiotensin system early in the course of heart disease and heart failure in dogs was evaluated by measuring the plasma renin activity (PRA) and plasma aldosterone concentration (PAC) in 18 Cavalier King Charles Spaniels with asymptomatic or mildly symptomatic mitral valvular insufficiency, and in 18 healthy Cavalier King Charles Spaniels. All dogs were unmedicated and had no other diseases. The PRA was high in the dogs with mitral valvular insufficiency (median 3.44 ng/mL/h, interquartile interval 2.59 to 8.66 ng/mL/h) compared with the controls (median 2.51 ng/mL/h, interquartile interval 1.44 to 3.58 ng/mL/h). The PAC was also higher in the dogs with mitral insufficiency (median 53 pg/mL, interquartile interval 33 to 138 pg/mL) than in the control group (median 27 pg/mL, interquartile interval 11.5 to 54 pg/mL). However, there was considerable overlap between the 2 groups in both PRA and PAC. It was concluded from these data that there is early activation of the renin-angiotensin system in some Cavalier King Charles Spaniels with mitral valvular insufficiency. Further prospective studies are needed to determine if early intervention with angiotensin-converting enzyme inhibitors will be valuable in this group of patients. 相似文献
80.
Wenche Langseth Henrik Stenwig Lars Sogn Elisabet Mo 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(1):32-37
Abstract Studies were carried out on the growth of mould and the production of mycotoxins in grain during drying and storage. Various amounts of forced ambient air, 800, 600, 400, 200 and 0 m3 (air)/(hour ton), were used to dry wheat, which contained 32% moisture at harvest. Samples for mycological examination and determination of mycotoxins and moisture content were taken weekly. At harvest the mould flora consisted of various field fungi with less than 10% Fusarium spp. An increasing proportion of Aspergillius and Penicillium spp. were recorded in the bins at 0 and 200 m3 (air)/h t. The mycotoxin analysis indicated that the Fusarium spp. were also metabolically active until at least five weeks after the grain was put into the store room. The concentration of deoxynivalenol (DON) reached about 10 mg/kg after three weeks in the bins with no air flow, and about 2 mg/kg in the bins at 200 m3 (air)/h t. The zearalenone concentration also increased considerably, to about 5 mg/kg, in the bins with no air flow. The present results show that drying of grains using forced ambient air may produce good conditions for growth of field fungi as well as storage fungi if the flow of air is too low. 相似文献