全文获取类型
收费全文 | 281篇 |
免费 | 21篇 |
专业分类
林业 | 41篇 |
农学 | 5篇 |
基础科学 | 4篇 |
68篇 | |
综合类 | 47篇 |
农作物 | 9篇 |
水产渔业 | 16篇 |
畜牧兽医 | 76篇 |
园艺 | 6篇 |
植物保护 | 30篇 |
出版年
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 16篇 |
2012年 | 15篇 |
2011年 | 19篇 |
2010年 | 17篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 17篇 |
2006年 | 14篇 |
2005年 | 17篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1956年 | 1篇 |
1949年 | 1篇 |
1932年 | 1篇 |
1925年 | 1篇 |
1901年 | 2篇 |
1896年 | 2篇 |
排序方式: 共有302条查询结果,搜索用时 15 毫秒
91.
Martina Kasper Bernhard Freyer Kurt‐Jürgen Hülsbergen Harald Schmid Jürgen Kurt Friedel 《植物养料与土壤学杂志》2015,178(1):25-34
The importance of the soil humus content is indisputable. Soil humus plays an important role in preserving soil fertility and exerts great influence on plant production and yield potential. However, proofing that management‐related changes in the stock of soil organic matter (SOM) have taken place against the background of spatial and temporal variation is a difficult task. In most cases, sampling over a long period of time is needed to verify these changes. Alternatively, potential changes in the SOM stock can be estimated using humus balancing models, which help to identify the need for humus reproduction on a farm. In general, a humus balance is the difference between the humus demand of cultivated crops and humus supply through crops and organic fertilizers. In this study, the ‘Dynamic Humus Unit Method' within the modelling program REPRO was applied to calculate the humus balance for 29 model‐farms that are representative of most of the agricultural production in Austria. Each model‐farm represents a specific production type (PT) and farming system in a defined region or main production area (MPA). This approach gives an overview of the humus balances at a large scale and allows a general trend in Austria to be estimated. Besides differing between conventional and organic farming systems, specific site conditions can also be selected in the model. The constructed model‐farms belong to different PTs such as “forage production”, “cash crops”, “refinement”, and “permanent crops”. The PT “permanent crops” refers to the cultivation of wine. The cropping system of each PT was analyzed in detail, while livestock keeping was considered only when applicable. Positive humus balances were found for all PTs except for permanent crops. The results ranged from –122 to 890 kg C ha?1 y?1. Regions and farm structure, e.g., forage production compared to cash crop, were found to have a greater influence than the kind of farming system (i.e., organic vs. conventional farming). Comparing the different PTs, forage production had the highest positive humus balances (219 to 890 kg C ha?1 y?1), followed by cash crop (24 to 239 kg C ha?1 y?1), refinement (–64 to 402 kg C ha?1 y?1) and permanent crops (–122 to –38 kg C ha?1 y?1). Regarding the farming system, organic farming led to more humus accumulation than conventional farming due to a higher share of fodder legumes and catch crops and more diverse crop rotations. The results were within the range of available empirical data on SOM change, and it was therefore concluded that the results are reasonable. In general, humus reproduction can be regarded as sufficient for agricultural production. 相似文献
92.
Nuclear insulin-like growth factor 2 gene (IGF-2), growth hormone 1 gene (GH-1) and internal transcribed spacer 1 (ITS-1) of the ribosomal DNA as well as the mitochondrial NADH-3 and NADH-4 dehydrogenase genes (ND-3/4) exhibited species-specific restriction fragment patterns and three microsatellite loci (Sfo18, Ssa85 and Ssa197) had non-overlapping allele size ranges in Arctic charr and brook trout and were used as diagnostic markers for testing genetic purity of hatchery stocks and wild populations of Arctic charr and brook trout in Bavaria, Germany. Screening of four wild populations (three in Arctic charr and one in brook trout) revealed only a single hybrid (back-cross to brook trout) individual in L. Starnberg. In contrast, in three (out of five) hatchery stocks of Arctic charr and in both hatchery stocks of brook trout hybrids were detected with the frequency from 3 to 100%. Three hatchery stocks (SS2, SA and BS1) represent a hybrid swarm because they contained a very high proportion of hybrids (from 83 to 100%) and most or all hybrid individuals had alien alleles at only one or a few of six unlinked diagnostic loci, indicating that post-F1 hybrids represent the majority of individuals in these stocks and introgression has taken place. Release or escape of introgressed individuals from hatcheries into natural water bodies should be avoided in order to protect the biological diversity and genetic integrity of native fish populations. 相似文献
93.
Bernhard Vens-Cappell 《Aquacultural Engineering》1984,3(1):71-89
One feeding and two digestion experiments were performed in order to study the effect of feed processing by extrusion and pelleting on feed conversion and on the digestibility of energy, protein and amino acids. Feed conversion was 1·24 when trout was reared on an extruded diet as compared with 1·61 when reared on the same but pelleted diet. The specific growth rates of 1·56 and 1·55%, respectively, attained with both diets, were almost identical due to a depression of voluntary intake of the extruded diet. The effect of different daily feed intakes in percentage of body weight (NI, %) on the digestibility of energy (D, %) could be described using the following linear regression equations: D(%) = 78·3 ? 5·9 NI(%) for the pelleted diet and D(%) = 87·5 ? 3·9 NI(%) for the extruded diet. Though conversion of the extruded and pelleted diets differed significantly the digestible energy needed to produce 1 kg of gain was nearly the same, 17 370 kJ and 17 580 kJ respectively, indicating that differences in conversion were due to the digestible energy content. The digestion coefficients of the protein and amino acids were not influenced significantly (p < 0·05) by a change in the feed process, but different digestion coefficients for individual amino acids were observed. The use of digestible carbohydrate for trout nutrition is limited by the incidence of liver degeneration. 相似文献
94.
95.
Advances in fungal biosystematics and molecular genetics have clarified relationships among the wood‐decay fungi and are providing new tools for their detection and identification. Species complexes of forest pathogens, including those within Heterobasidion, Armillaria, Laetiporus, and Phellinus, are being resolved. The ability to isolate fungal DNA directly from wood without in intermediate culturing step will greatly facilitate sampling and disease detection and has applications in forest disease management, hazard tree assessment, invasive species detection, and carbon cycling, sequestration and climate change research. Recent changes in fungal nomenclature and their application to forest pathology are discussed. 相似文献
96.
The advanced backcross quantitative trait locus (AB-QTL) analysis has proven its usefulness to identify and localize favourable
alleles from exotic germplasm and to transfer those alleles into elite varieties. In a balanced design with up to six environments
and two nitrogen fertilization (N treatment) levels, a 4-factorial mixed model analysis of variance (ANOVA) was used to identify
QTL main effects, QTL × environment interaction effects and QTL × N treatment interaction effects in the spring barley BC2DH population S42. The yield-related traits studied were number of ears per m2, days until heading, plant height, thousand grain weight (TGW) and grain yield. In total, 82 QTLs were detected for all traits.
This finding was compared to a previous QTL study of the same population S42, where the current field data was reduced to
one half through restriction of the analysis to the standard N treatment level (von Korff et al., Theor Appl Genet 112: 1221–1231,
2006). These authors located 54 QTLs for the same traits by applying a 3-factorial mixed model similar to the current model but
excluding the factor N treatment. We found that QTL × environment interaction, alone or in combination, accounted for 24 of
the newly uncovered QTLs, whereas QTL × N treatment interaction was of lesser importance with six new cases in total. A valuable
QTL interacting with N treatment has been identified on chromosome 7H where lines carrying the wild barley allele were superior
in number of ears per m2 in either N treatment. We conclude that in population S42 the extension of the phenotype data set and the inclusion of N
treatment into the mixed model increased the power of QTL detection by providing an additional replication rather than by
revealing specific N treatment QTLs. 相似文献
97.
Validation of a 2-domain-model for the simulation of solute transfer in soils by laboratory and field experiments The simulation of water and solute transfer in the unsaturated zone on the basis of the classical convective dispersive model gives dissatisfactory results in many cases. Especially in the zone of evapotranspiration the observed penetration depths of surface-applied chemicals often exceed calculated values. This has been attributed to preferential flow in domains with accelerated flow. The aim of the investigations presented here was to extend the conventional theory of solute transfer in order to enable improved model predictions without introducing too much complexity to the model which might reduce its applicability. The mobile-immobile-concept of Coats and Smith (1964) was chosen to extend the model FLOTRA (Wagner et al., 1992), which is based on the convective dispersive approach. The model parameters additionally needed by the model are the immobile water content θim and the solute transfer coefficient α. The applicability of the model was tested on the basis of several laboratory and field experiments. It is shown, that with the mobile-immobile-approach modeling results of water and solute transfer in the top soil layers, which are most important in view of soil and groundwater protection, were improved compared to the calculations with the classical convective dispersive model. 相似文献
98.
Adsorption of Water, Ethylene Glycol Monoethyl Ether as well as Nitrogen and its Relation to Properties of German and Israeli Soil Samples To determine the specific surface area, samples taken from 140 soil horizons were selected and the significant physical and chemical properties were investigated. The specific surface area of the samples was determined by adsorption of H2O, ethylene glycol monoethyl ether (EGME) and N2. A comparison of the three methods shows that the specific surface area determined by the adsorption of H2O and EGME does not differ significantly. However, the specific surface determined by N2-adsorption differs markedly from the results obtained using the polar substances. As a dependent variable the specific surface area is mainly influenced by the clay content and clay mineral type. Further, the organic substance content as well as the iron- and manganoxide content have a more significant influence on the specific surface area the lower the clay content is, or the content of three layer minerals. As an independent variable, the specific surface area determined by adsorption of EGME, proved to be the characteristic soil factor which reflects the effective cation exchange capacity as well as the hygroscopicity with the highest degree of accuracy. 相似文献
99.
Mirzakhayot Ibrakhimov Christopher Martius J.P.A. Lamers Bernhard Tischbein 《Agricultural Water Management》2011,101(1):52-61
Salinization of irrigated agricultural land threatens ecological sustainability and livelihoods of people. Salinization is especially severe in the dry lowlands world-wide and in Central Asia where large amounts of salts accumulated in the soil profile, originating from shallow saline groundwater (GW). Analysis of the unique dataset of 2000 monitoring wells of GW table and salinity in lowland Khorezm region of Uzbekistan over the period of 1990 till 2006 showed shallow GW levels of 1.1-1.4 m (±0.48-0.66 m) at start of leaching periods and 0.9-1.4 (±0.43-0.63 m) in July during the annual growing seasons. While leaching efficiency is decreased, shallow GW in July is far above the optimum levels of 1.4-1.5 m. The effects of topography, soil texture, and irrigation and drainage networks were found to favor shallow GW forced by excessive water diversion. The drainage network, which is seen by many specialists as underdeveloped and its improvement necessary to arrest unacceptable GW levels, is being used under its full capacity. The solution to alleviate land degradation is not only an improved drainage, but better controlled and more flexible water management. 相似文献
100.
Zainul ABIDEEN Hans-Werner KOYRO Bernhard HUCHZERMEYER Bilquees GUL M. Ajmal KHAN 《土壤圈》2020,30(4):466-477
Soil water and nutrient status are both of major importance for plant appearance and growth performance. The objective of this study was to understand the effect of biochar (1.5%) and a biochar-compost mixture (1.5% biochar + 1.5% compost) on the performance of Phragmites karka plants grown on a synthetic nutrient-poor sandy clay soil (50% sand, 30% clay, and 20% gravel). Indicators of plant performance, such as growth, lignocellulosic biomass, water status (leaf water potential, osmotic potential, and turgor potential), mineral nutrition status, leaf gas exchange, and chlorophyll fluorescence, and soil respiration (carbon dioxide (CO2) flux) were assessed under greenhouse conditions. Biochar-treated plants had higher growth rates and lignocellulosic biomass production than control plants with no biochar and no compost. There was also a significant increase in soil respiration in the treatments with biochar, which stimulated microbial interactions. The increase in soil water-holding capacity after biochar amendment caused significant improvements in plant water status and plant ion (K+, Mg2+, and Ca2+) contents, leading to an increase in net photosynthesis and a higher energy-use efficiency of photosystem II. Biochar-treated plants had lower oxidative stress, increased water-use efficiency, and decreased soil respiration, and the biochar-compost mixture resulted in even greater improvements in growth, leaf turgor potential, photosynthesis, nutrient content, and soil gas exchange. Our results suggest that biochar and compost promote plant growth with respect to nutrient uptake, water balance, and photosynthetic system efficiency. In summary, both the soil amendments studied could increase opportunities for P. karka to sequester CO2 and produce more fodder bio-active compounds and biomass for bio-energy on nutrient-poor degraded soils. 相似文献