全文获取类型
收费全文 | 446篇 |
免费 | 9篇 |
专业分类
林业 | 32篇 |
农学 | 21篇 |
基础科学 | 6篇 |
127篇 | |
综合类 | 45篇 |
农作物 | 12篇 |
水产渔业 | 30篇 |
畜牧兽医 | 145篇 |
园艺 | 11篇 |
植物保护 | 26篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 16篇 |
2013年 | 20篇 |
2012年 | 37篇 |
2011年 | 40篇 |
2010年 | 20篇 |
2009年 | 20篇 |
2008年 | 45篇 |
2007年 | 37篇 |
2006年 | 32篇 |
2005年 | 25篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 28篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有455条查询结果,搜索用时 0 毫秒
81.
Eduardo Segundo Dietrich E. Lesemann Germán Martín María P. Carmona Leticia Ruiz Isabel M. Cuadrado Leonardo Velasco Dirk Janssen 《European journal of plant pathology / European Foundation for Plant Pathology》2007,117(1):81-87
Amaranthus leaf mottle virus (AmLMV) was classified as a member of the genus Potyvirus on the basis of its particle morphology, serology, and biological properties (Casetta et al., 1986). Based on these properties, an Amaranthus viridis-infecting virus isolated in Spain, causing mottle and leaf blistering as well as reduced growth has been identified as AmLMV.
The 3′ terminal genomic region of this and a reference isolate from Italy has been sequenced and reveals a 95% nucleotide
identity between the two isolates. The sequenced part comprises the coat protein with 281 amino acids and 315 nucleotides
of the 3′ untranslated region (UTR) preceding a polyadenylated tail. Pairwise comparisons and phylogenetic analysis of the
nucleotide and deduced amino acid sequences of the CP and 3′ UTR of the cloned cDNAs with those of other potyviruses shows
that AmLMV is a distinct potyvirus closely related to Potato virus Y. 相似文献
82.
Thomas?HolstEmail author Helmut?Mayer Dirk?Schindler 《European Journal of Forest Research》2004,123(1):13-28
Within the framework of an interdisciplinary project on the effects of climate and forest management on beech-dominated deciduous forests (Swabian Jura, south-western Germany), forest meteorological investigations are carried out to analyse the influences of exposure and canopy density on the microclimate within various beech stands (Fagus sylvatica L.). This second paper of the series Microclimate within beech stands focuses on the thermal conditions that exist mainly in the near-surface layer at different test plots. They were analysed by air temperature, Ta, (at 1.5 m a.g.l) and soil temperature, Ts, at six depths measured continuously in the period 1999–2003. The main results can be summarized as follows. (1) The thermal situation within the beech stands described by Ta depended primarily on the turbulent air-mass exchange conditions which were based on the slope-specific energy balance of the forest floor and advective heat fluxes. (2) The thermal situation within the soil described by Ts at 3 and 20 cm depth was governed by the molecular heat transport. Therefore, the heating and cooling rates of Ts were always lower than for Ta. Higher Ta and Ts values for the test plots on the SW slope showed that the thermal conditions within the beech stands depended primarily on the exposure. (3) Based on slope-specific differences of daily extremes of Ta and Ts at 3 cm depth between the silviculturally treated and control plots, the influence of the more pronounced height growth of the understorey vegetation under the near-surface thermal conditions could be clearly verified for the NE slope.Abbreviations PAR Photosynthetically active radiation - PAI Plant area index - LAI Leaf area index 相似文献
83.
Hafezparast M Klocke R Ruhrberg C Marquardt A Ahmad-Annuar A Bowen S Lalli G Witherden AS Hummerich H Nicholson S Morgan PJ Oozageer R Priestley JV Averill S King VR Ball S Peters J Toda T Yamamoto A Hiraoka Y Augustin M Korthaus D Wattler S Wabnitz P Dickneite C Lampel S Boehme F Peraus G Popp A Rudelius M Schlegel J Fuchs H Hrabe de Angelis M Schiavo G Shima DT Russ AP Stumm G Martin JE Fisher EM 《Science (New York, N.Y.)》2003,300(5620):808-812
Degenerative disorders of motor neurons include a range of progressive fatal diseases such as amyotrophic lateral sclerosis (ALS), spinal-bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Although the causative genetic alterations are known for some cases, the molecular basis of many SMA and SBMA-like syndromes and most ALS cases is unknown. Here we show that missense point mutations in the cytoplasmic dynein heavy chain result in progressive motor neuron degeneration in heterozygous mice, and in homozygotes this is accompanied by the formation of Lewy-like inclusion bodies, thus resembling key features of human pathology. These mutations exclusively perturb neuron-specific functions of dynein. 相似文献
84.
To obtain crossing products, an efficient pollination and subsequent fertilization is essential. This efficient pollination is achieved by pollen germination and tube growth. Here, these pollen characteristics of 2 genetically differentiating cultivars of Anemone coronaria L. were investigated in vitro. For the essential components boron, calcium and an osmoticant, only calcium showed to be crucial for pollen germination. Boron concentrations influenced the pollen tube length with a concentration of 100 mg l?1 H3BO3 resulting in the longest pollen tubes. For the osmoticant sucrose, a concentration of 100 g l?1 caused a significant positive effect on both pollen germination and pollen tube length for the 2 cultivars. The cultivars reacted similarly with respect to the investigated compounds. Next to this, the pollen development was correlated with 8 different flower stages in A. coronaria. As a final point, the germination of an optimized pollen germination medium was compared with in vivo pollen germination in cross-pollinations within the same cultivar (identified by aniline blue staining). For ‘Mistral Wine’, pollen germination percentage was lower in vitro than in vivo, while ‘Wicabri Blue’ pollen showed no significant difference in germination rates in vivo and in vitro. To achieve fertilization a following requisite is that the stigma is receptive. To study this, the most receptive female flower stage of the 8 different flower stages for A. coronaria was characterized by aniline blue staining. A. coronaria clearly showed protogyny. 相似文献
85.
Aline Schäfer Rodrigues Silva Markus Noack Dirk Schlabing Silke Wieprecht 《Journal of Soils and Sediments》2018,18(10):3070-3081
Purpose
The critical shear stress of cohesive and mixed cohesive/non-cohesive sediments is affected by multiple interacting physical, chemical and biological parameters. There are various mathematical approaches in the scientific literature for computing critical shear stress. However, processes that influence sediment stability are still not fully understood, and available formulas differ considerably. These discrepancies in the literature arise from random system behaviour (natural variability of the sediments), different definitions of the critical shear stress, different measurement techniques and different model frameworks (scope of the parameters, undisturbed versus artificial sediment samples). While analytical approaches fail to address the involved uncertainties, fuzzy logic-based models integrate uncertainty and imprecision.Materials and methods
With this in mind, a data-driven neuro-fuzzy model (ANFIS) was used to determine the critical shear stress based on sediment characteristics such as wet bulk density and grain size distribution. In order to select model predictors systematically, an automated stepwise regression algorithm was applied. The database for this analysis consisted of 447 measurements of the critical shear stress originating from 64 undisturbed sediment samples.Results and discussion
The study identified clay content as the primarily controlling variable for erosion resistance. Depending on the characteristics of the sampling location, the bulk density was also selected as a model predictor. In comparison to analytical models that are available in the scientific literature, the fuzzy model achieved higher correlation coefficients between measured and predicted data.Conclusions
The neuro-fuzzy-model includes uncertainties of input variables and their interactions directly. Thus, it provides a reliable method for the prediction of erosion thresholds of cohesive/non-cohesive mixtures. It was also shown that this approach requires fewer measured variables as well as fewer assumptions than the models it was compared to.86.
Dirk Hoffmeister Guido Waldhoff Wolfgang Korres Constanze Curdt Georg Bareth 《Precision Agriculture》2016,17(3):296-312
Information on crop height, crop growth and biomass distribution is important for crop management and environmental modelling. For the determination of these parameters, terrestrial laser scanning in combination with real-time kinematic GPS (RTK–GPS) measurements was conducted in a multi-temporal approach in two consecutive years within a single field. Therefore, a time-of-flight laser scanner was mounted on a tripod. For georeferencing of the point clouds, all eight to nine positions of the laser scanner and several reflective targets were measured by RTK–GPS. The surveys were carried out three to four times during the growing periods of 2008 (sugar-beet) and 2009 (mainly winter barley). Crop surface models were established for every survey date with a horizontal resolution of 1 m, which can be used to derive maps of plant height and plant growth. The detected crop heights were consistent with observations from panoramic images and manual measurements (R2 = 0.53, RMSE = 0.1 m). Topographic and soil parameters were used for statistical analysis of the detected variability of crop height and significant correlations were found. Regression analysis (R2 < 0.31) emphasized the uncertainty of basic relations between the selected parameters and crop height variability within one field. Likewise, these patterns compared with the normalized difference vegetation index (NDVI) derived from satellite imagery show only minor significant correlations (r < 0.44). 相似文献
87.
88.
To date, models for simulating sap flow dynamics in individual trees with a direct link to stem diameter variation include only the diameter fluctuation driven by a change in stem water storage. This paper reports results obtained with a comprehensive flow and storage model using whole-tree leaf transpiration as the only input variable. The model includes radial stem growth based on Lockhart's equation for irreversible cell expansion. It was demonstrated that including growth is essential to obtaining good simulation results. To model sap flow dynamics, capacitance of storage tissues was assumed either constant (i.e., electrical analogue approach) or variable and dependent on the water content of the respective storage tissue (i.e., hydraulic system approach). These approaches resulted in different shapes for the desorption curve used to calculate the capacitance of storage tissues. Comparison of these methods allowed detection of specific differences in model simulation of sap flow at the stem base (F(stem)) and stem diameter variation (D). Sensitivity analysis was performed to select a limited subset of identifiable parameters driving most of the variability in model predictions of F(stem) and D Both the electrical analogue and the hydraulic system approach for the flow and storage model were successfully calibrated and validated for the case of a young beech tree (Fagus sylvatica L.). Use of an objective model selection criterion revealed that the flow and storage model based on the electrical analogue approach yielded better predictions. 相似文献
89.
Wilkins AL Rehmann N Torgersen T Rundberget T Keogh M Petersen D Hess P Rise F Miles CO 《Journal of agricultural and food chemistry》2006,54(15):5672-5678
Pectenotoxins from marine dinoflagellates of the genus Dinophysis are rapidly hydrolyzed by many shellfish to give pectenotoxin-2 seco acid, which isomerizes to 7-epi-pectenotoxin-2 seco acid. Three series of fatty acid esters of pectenotoxin-2 seco acid (PTX-2 seco acid) and 7-epi-PTX-2 seco acid were detected by LC-MS analysis of extracts from blue mussels (Mytilus edulis) from Ireland. The locations of the fatty acid ester linkages were identified by a combination of LC-MSn in positive- and negative-ion modes, LC-MS analysis of the products from reaction of the esters with sodium periodate, and NMR analysis of purified samples of the two most abundant ester derivatives. The 37-O-acyl esters of PTX-2 seco acid were the most abundant, followed by the corresponding 11-O-acyl esters, accompanied by low levels of the 33-O-acyl esters. The most abundant fatty acid esters in the fractionated sample were, in order, the 16:0, 22:6, 14:0, 16:1, 18:4, and 20:5 fatty acids, although a wide array of other PTX-2 seco acid fatty acid esters were also present at low levels. 相似文献
90.
The use of <Emphasis Type="Italic">Vp1</Emphasis> in real time RT-PCR to select for pre-harvest sprouting tolerance in triticale 总被引:1,自引:0,他引:1
In spite of the availability of laboratory and field tests there is still a major problem to select pre-harvest sprouting
(PHS) tolerant triticale varieties in a reliable, field-independent way. One approach to minimize the influence of environmental
conditions and physio-morphological traits on PHS detection is using molecular genetic tools. The ‘viviparous’ Vp1 gene has been repeatedly described to play an important role in dormancy in wheat. A quantitative RT-PCR assay based on the
expression of the Vp1 gene has been developed. Specific primers were designed for detecting Vp1 in both wheat and triticale. The expression levels of Vp1 were normalized using reference genes and relatively quantified with the comparative Ct-method. However, the first results indicate that the achieved Vp1 expression levels at 50 days post anthesis are not useful to select for PHS tolerance, both in wheat and triticale. This
negative outcome so far is possibly due to the existence of several splicing events or to the late assaying moment in the
kernel development, when Vp1 expression is found to be low. 相似文献