全文获取类型
收费全文 | 285篇 |
免费 | 14篇 |
国内免费 | 3篇 |
专业分类
林业 | 21篇 |
农学 | 4篇 |
基础科学 | 3篇 |
59篇 | |
综合类 | 31篇 |
农作物 | 8篇 |
水产渔业 | 15篇 |
畜牧兽医 | 148篇 |
园艺 | 5篇 |
植物保护 | 8篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 17篇 |
2012年 | 15篇 |
2011年 | 8篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 8篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1996年 | 5篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1941年 | 1篇 |
排序方式: 共有302条查询结果,搜索用时 812 毫秒
101.
Development and assessment of habitat suitability criteria for adult brown trout in southern New England rivers 总被引:2,自引:0,他引:2
Abstract – Habitat suitability criteria (HSC) for depth, mean velocity, nose velocity, substrate, embeddedness, and cover were developed for brown trout ≥170 mm ( Salmo trutta Linnaeus) on the West Branch Farmington River, CT, USA. Microhabitat data was collected by underwater observation using an equal effort habitat sampling design; HSC were constructed using nonparametric tolerance limits. Transferability of previously published HSC to the West Branch Farmington River was poor; only 1 of 13 HSC tested was considered transferable. The HSC developed for the West Branch Farmington River were tested for transferability to the East Branch Westfield River, Massachusetts. First, a composite suitability index (SI) score was calculated using the source HSC for each occupied and unoccupied location in the Westfield River. Then, χ 2 -tests were used to determine if optimal or suitable locations were occupied in greater proportion than usable or unsuitable locations. Composite SI scores based on total depth, mean velocity, and cover were not transferable, but composite SI scores based only on total depth and mean velocity were. A multivariate profile analysis was also used to test for transferability. In each test, only total depth, fish depth, and mean velocity HSC were successfully transferred. Transferability of depth and velocity HSC between rivers shows promise for applications to similar systems where brown trout occur. 相似文献
102.
Fruzsina?Szira Andreas?B?rner Kerstin?Neumann Khalil?Zaynali?Nezhad Gábor?Galiba András?Ferenc?BálintEmail author 《Euphytica》2011,178(3):373-391
To improve our knowledge on the genetic control of drought tolerance, the Oregon Wolfe Barleys (OWB), considered as a reference
population in genetic mapping, were subjected to various types of water deficit. Overall, when investigating numerous environments
and replications, 40 QTLs were identified in three developmental stages. Based on these loci five QTL clusters were separated,
which affect various drought-related traits in at least two developmental stages. Several candidate genes were identified
for each QTL cluster using an expressed sequence tag (EST)-based map with high marker density. The putative role of the candidates
in drought tolerance is discussed. The phenotypic effect of three of the five candidate genes was also tested on 39 barley
landraces and cultivars and a significant relationship was found between the allelic composition of these genes and yield
production under stress conditions. This study presents a relevant example of the use of reliable QTL data in the candidate
gene approach, while also demonstrating how the results could be practically utilized in marker-assisted selection (MAS). 相似文献
103.
Imran Muhammad Maria Kolla Römheld Volker Neumann Günter 《Journal of plant nutrition》2015,38(12):1803-1821
Effects of seed priming with zinc (Zn) plus manganese (Mn), boron (B), and phosphate (P) on growth and nutritional status of maize were studied. Nutrient seed priming significantly increased seed contents of primed nutrients. In nutrient solution (NS) lacking Zn and Mn, growth of maize plants primed with Zn?+?Mn increased by more than 50% and 100%, respectively, as compared to control treatment. The primed nutrients were efficiently translocated to the growing shoot and could maintain Zn and Mn supply for at least three weeks of the culture period. In soil culture, plants suffered from P and Zn deficiency, which was mitigated to some extent by P and Zn?+?Mn priming. Particularly, translocation of Zn seed reserves to the shoot tissue was negatively affected by the highly calcareous soil. In the field experiment, Zn?+?Mn seed priming increased grain yield by 15%, demonstrating the potential for long-lasting effects of nutrient seed priming. 相似文献
104.
Radio gaschromatography of carbohydrates, organic acids and amino acids A method for the radio-gaschromatographic determination of carbohydrates, organic acids and amino acids as well as the simultaneous recording of the specific activity of radioactive labelled compounds of these fractions is described and its application to the analysis of plant extracts or protein hydrolysates demonstrated. The application of 0.05–0.1 mCi 14C/g fresh weight of plant material is enough to obtain a sufficiently strong labelling even in short-term incubation experiments (15 sec.), as for example in photosynthesis research. 相似文献
105.
Kathleen Neumann Elke Stehfest Peter H. Verburg Stefan Siebert Christoph Müller Tom Veldkamp 《Agricultural Systems》2011,104(9):703-713
Globally, areas that are equipped for irrigation have almost doubled in size over the past 50 years and further expansions are expected for the future, to meet a growing food demand. For developing countries, the Food and Agriculture Organization of the United Nations (FAO) expects these areas to be expanded by 40 million ha, by 2030. Knowledge about the constraints to irrigation and spatially explicit information about the potential for irrigation expansion, however, are lacking on a global scale. The objective of our study was to explain the global pattern of irrigated croplands and to identify cropping regions where irrigation is likely to be expanded. We accounted for biophysical determinants, such as humidity and slope, mainly at grid-cell level. Socio-economic and governance determinants, for example, Gross Domestic Product (GDP) and control of corruption, were primarily considered on a country level, given the limitations in availability of sub-national data and the role of national level governance in irrigation decisions. To identify the variability of the determinants within these two spatial levels, we conducted a multilevel analysis. This is a method employing regression models that explicitly account for hierarchically structured data. Results show significant variability in terms of irrigation. While 56% of the global variance in irrigation occurs between countries, 44% occurs within countries. Our results suggest that it is necessary to consider biophysical, socio-economic and governance information for identifying cropland areas that are likely to be under irrigation. Under current conditions, conversion from rainfed to irrigated cropland is most likely in eastern China, northern Africa, and parts of the Mediterranean region. 相似文献
106.
In a seven year old male domestic cat diagnosis, therapy and healing of a nasal fibrosarcoma is described. After two surgical treatments no recurrence was seen in a time period of 10 months. Even with this unfavourable localization of the tumor a functionally and cosmetically satisfactory result was achieved. 相似文献
107.
108.
109.
AIMS: To determine the frequency with which porcine reproductive and respiratory syndrome (PRRS) virus (PRRSv) would become established in a non-commercial pig herd in New Zealand due to illegal feeding of uncooked food waste containing virus-contaminated pigmeat. To determine the likelihood of a single incursion resulting in a multi-farm outbreak of the disease, and describe the spatio-temporal characteristics of such an outbreak. METHODS: A Monte Carlo simulation model was constructed to determine the expected annual frequency of PRRSv infection being initiated in a non-commercial pig herd as a result of inadvertent feeding of pigmeat imported from countries endemically infected with the disease. Once the likelihood of PRRSv becoming established in a single pig herd was determined, stochastic spatially explicit infectious disease modelling software was utilised to model the temporal and spatial characteristics of the resulting epidemic. RESULTS: Assuming the proportion of imported pigmeat remained at current levels, consumption patterns of pigmeat in households in New Zealand remained steady, and limited compliance with recently reintroduced regulations to prevent feeding of uncooked food waste, at least 4.3 pig herds per year were predicted to become infected with PRRSv. Simulation modelling of PRRSv epidemics related to initial infection of a non-commercial farm produced an estimate that 36% of these incursions would spread from the initial herd, and that these outbreaks would involve 93 herds on average in the first year. By increasing the estimated persistence of PRRSv infection in small herds, an average of 205 herds became infected in the first year. CONCLUSIONS: Given a mean of 4.3 infected premises per year and a 36% probability of infection spreading beyond the initial infected herd, there was a 95% likelihood of a multi-farm PRRS outbreak occurring within 3 years. CLINICAL RELEVANCE: Introduction of PRRSv through importation of virus-contaminated pigmeat presents a high risk for establishment of the disease in the pig industry in New Zealand. 相似文献
110.
Neumann S Welling H Thuere S 《Journal of veterinary medicine. A, Physiology, pathology, clinical medicine》2007,54(10):612-617
Liver diseases are known to influence the serum concentration of insulin-like growth factor I (IGF-I) in humans, but such an effect has rarely been investigated in dogs. The aim of this study was to investigate serum IGF-I concentrations in dogs with primary liver diseases, in comparison with levels in healthy dogs and dogs with non-hepatic diseases. For this purpose, IGF-I serum concentrations were measured (DSL-5600 kit) in 36 dogs with various liver diseases and compared with 22 healthy controls and 20 dogs with non-hepatic diseases. The results showed that dogs with liver diseases had significantly lower IGF-I serum concentrations (P < 0.001) than clinical healthy dogs or dogs with non-hepatic diseases. But the results also indicate that the aetiology of liver disease has no influence on IGF-I serum concentration. 相似文献