全文获取类型
收费全文 | 391篇 |
免费 | 34篇 |
国内免费 | 1篇 |
专业分类
林业 | 21篇 |
农学 | 3篇 |
基础科学 | 1篇 |
90篇 | |
综合类 | 36篇 |
农作物 | 21篇 |
水产渔业 | 30篇 |
畜牧兽医 | 199篇 |
园艺 | 8篇 |
植物保护 | 17篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 4篇 |
2021年 | 24篇 |
2020年 | 20篇 |
2019年 | 29篇 |
2018年 | 17篇 |
2017年 | 15篇 |
2016年 | 18篇 |
2015年 | 16篇 |
2014年 | 15篇 |
2013年 | 16篇 |
2012年 | 24篇 |
2011年 | 19篇 |
2010年 | 20篇 |
2009年 | 14篇 |
2008年 | 20篇 |
2007年 | 15篇 |
2006年 | 21篇 |
2005年 | 17篇 |
2004年 | 10篇 |
2003年 | 10篇 |
2002年 | 17篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有426条查询结果,搜索用时 15 毫秒
151.
Emma M. Johansson Petra M.A. Fransson Patrick A.W. van Hees 《Soil biology & biochemistry》2009,41(6):1111-1116
Despite its potential impact on soil carbon flow, few studies have attempted to quantify the effects of elevated carbon dioxide (CO2) on production of exudates by mycorrhizal plants. In this study we quantified low molecular weight (LMW) organic compounds exuded by non-mycorrhizal (NM) and ectomycorrhizal (ECM) plants in relation to exposure to elevated CO2. Scots pine seedlings, either colonized by one of eight different ECM fungi or non-mycorrhizal (NM), were exposed to either ambient (350 ppm) or elevated (700 ppm) concentrations of CO2. Exudation of LMW organic acids (LMWOAs), amino acids, dissolved monosaccharides and total dissolved organic carbon (DOC) was determined and exudation rates were calculated per g root and fungal dry mass. CO2 had a significant impact on exudation. Under elevated CO2, exudation of total LMWOAs increased by 120-160%, amino acids by 250%, dissolved monosaccharides by 130-270% and DOC by 180-220% compared to ambient CO2 treatment. Net CO2 assimilation rates increased significantly by 41-47% for seedlings exposed to elevated CO2. Exuded C calculated as a percentage of assimilated CO2 increased by 41-88% in the elevated CO2 treatment compared to ambient CO2 treatment. 相似文献
152.
González-Barrio R Beltrán D Cantos E Gil MI Espín JC Tomás-Barberán FA 《Journal of agricultural and food chemistry》2006,54(12):4222-4228
Postharvest treatment of seedless white table grapes (var. 'Superior') with different gas ozone concentrations (3.88 and 1.67 g/h) for 1, 3, and 5 h induced an increase in stilbenoid biosynthesis [trans-resveratrol, piceatannol, and viniferinas (resveratrol dehydrodimers and dehydrotrimers)] during storage at 22 degrees C and 95% relative humidity. The maximal resveratrol concentration was reached after 2 days of storage, and this amount was similar to that induced by optimized UV-C treatments (1 min, 510 W, 40 cm). Although similar resveratrol concentrations accumulated in grapes after both UV-C and O3 treatments (maximum ozone production and time), the ozone treatment was more efficient in inducing viniferins accumulation in grape berries. A sequence in the biosynthesis of stilbenoids was observed, starting with the resveratrol monomer, continuing with the resveratrol dehydrodimers epsilon-viniferin and delta-viniferin, and ending with four different resveratrol dehydrotrimers. These trimers were different from alpha-viniferin, a trimer previously reported to be induced in grapes after biotic and abiotic stresses. Two alpha-viniferin isomers were also detected in the ozone-treated grapes, although at very low concentrations that prevented their quantification. 相似文献
153.
Wounds on the limbs of horses are notoriously difficult to heal, with over production of TGFβ1 thought to be responsible for excessive scarring; in contrast, wounds in the oral cavity heal rapidly with minimal scarring. This experiment aimed to determine the effect of TGFβ1 on the production of mRNA and proteins for various extracellular matrix components by two equine fibroblast cell lines isolated from the oral mucosa and distal limb. Fibronectin mRNA was up-regulated by TGFβ1 in the limb but not the oral cells. TGFβ1 increased the ratio of mRNA for collagen types I-III for the oral cells only. mRNA expression for TGFβ receptors-I and -II was significantly lower in limb fibroblasts, and treatment of either cell line with TGFβ1 down-regulated mRNA expression for both receptors. These differences may account for the improved healing seen in oral wounds compared to the excessive scarring seen in limb wounds. 相似文献
154.
155.
Felix F. Fru Emma T. Steenkamp Michael J. Wingfield Quentin C. Santana Jolanda Roux 《European journal of plant pathology / European Foundation for Plant Pathology》2017,148(1):97-107
Pitch canker of pines is caused by the fungus Fusarium circinatum. In South Africa, this pathogen has mostly been a nursery problem. From 2005, however, outbreaks of pitch canker have been reported from established Pinus radiata and P. greggii in the Western and Eastern Cape Provinces. Most recently, pitch canker-like symptoms were observed on 10-year-old P. greggii trees in a plantation in the midlands of the KwaZulu-Natal (KZN) Province. The aim of this study was to: (i) identify the causal agent of the observed symptoms, (ii) determine the genetic diversity, and (iii) the mode of reproduction of this fungal population. Furthermore, the aggressiveness of isolates from these trees was compared with that of isolates obtained previously from P. patula in South Africa. Isolates from the P. greggii trees in KZN were confirmed as F. circinatum based on both morphology and DNA sequence analyses. Microsatellite marker analyses revealed the presence of five genotypes of F. circinatum, not previously reported from other plantations in South Africa, with one of these genotypes being dominant. These genotypes were all pathogenic to P. patula and P. elliottii. No evidence of sexual reproduction was detected in the KZN population of the fungus. This was consistent with the fact that isolates from P. greggii were all of the MAT-2 mating type, in contrast to previously collected isolates from across South Africa that included both mating types. The results suggest that the outbreak of pitch canker on P. greggii in KZN represents a separate introduction of F. circinatum into the region with important implications for managing the disease. 相似文献
156.
157.
158.
Hecker K Read EK Vallevand A Krebs G Donszelmann D Muelling CK Freeman SL 《Journal of veterinary medical education》2010,37(4):395-402
The DVM program at the University of Calgary offers a Clinical Skills course each year for the first three years. The course is designed to teach students the procedural skills required for entry-level general veterinary practice. Objective Structured Clinical Examinations (OSCEs) were used to assess students' performance on these procedural skills. A series of three OSCEs were developed for the first year. Content was determined by an exam blueprint, exam scoring sheets were created, rater training was provided, a mock OSCE was performed with faculty and staff, and the criterion-referencing Ebel method was used to set cut scores for each station using two content experts. Each station and the overall exam were graded as pass or fail. Thirty first-year DVM students were assessed. Content validity was ensured by the exam blueprint and expert review. Reliability (coefficient α) of the stations from the three OSCE exams ranged from 0.0 to 0.71. The three exam reliabilities (Generalizability Theory) were, for OSCE 1, G=0.56; OSCE 2, G=0.37; and OSCE 3, G=0.32. Preliminary analysis has suggested that the OSCEs demonstrate face and content validity, and certain stations demonstrated adequate reliability. Overall exam reliability was low, which reflects issues with first-time exam delivery. Because this year was the first that this course was taught and this exam format was used, work continues in the program on the teaching of the procedural skills and the development and revision of OSCE stations and scoring checklists. 相似文献
159.
Emma V. Willcox George W. Tanner William M. Giuliano Robert McSorley 《Strength and Conditioning Journal》2010,63(2):203-222
Monoculture and mixed pastures in Florida provide habitat for a variety of resident and migratory bird species. The objectives of this study were to investigate the effects of grazing on vegetation structure and bird species richness and abundance in grazed monoculture and mixed pastures. Study pasture units were subject to four cattle grazing intensities: 0 = nongrazed (control), 15 = low, 20 = medium, or 35 = high animal units (AU) per pasture unit (no cattle, 1.3, 1.0, and 0.6 ha · AU?1, on monoculture pastures and no cattle, 2.1, 1.6, and 0.9 ha · AU?1, on mixed pastures). Monoculture pastures displayed a greater decrease in spatial heterogeneity of the vegetative community in the presence of grazing than mixed pastures. An increase in grazing intensity led to declines in total avian species richness and abundance and species richness within short-distance migrant, neotropical migrant, and permanent resident guilds on monoculture pastures. Declines in total species richness and abundance and neotropical migrant guild species richness and abundance were observed on mixed pastures subject to increasing grazing intensity. However, species richness within short-distance migrant and urban guilds and abundance within the grassland guild increased on this pasture type in the presence of grazing. Loss of spatial heterogeneity typically results in a lack of suitable habitat for birds that occupy the extremes of the vegetation structure gradient. This can lead to a loss of species richness and abundance. For the majority of avian guilds, a low grazing intensity of 1.3 ha · AU?1 and 2.1 ha · AU?1 on monoculture and mixed pasture, respectively, is recommended to maintain abundance. However, these grazing intensities may result in declines in species richness. Ultimately, if a range of avian species are to be supported on monoculture and mixed pastures, spatial heterogeneity of plant structure and composition must be maintained. 相似文献
160.
Manclús JJ Moreno MJ Plana E Montoya A 《Journal of agricultural and food chemistry》2008,56(19):8793-8800
Enzyme-linked immunosorbent assays (ELISAs) based on monoclonal antibodies for the detection of triazole fungicides have been developed. With this aim, hapten-protein conjugates, containing the common triazole and chlorinated aromatic moieties, were prepared. From mice immunized with these conjugates, several monoclonal antibodies (MAbs) with the ability to sensitively bind several triazoles with different specificity were obtained. Both analyte- and class-specific ELISAs were developed. The hexaconazole-specific immunoassay can determine this fungicide with a limit of detection of 0.3 mug/L in standard buffer. The so-called triazole-specific immunoassay allowed for the detection of tetraconazole, penconazole, cyproconazole, and myclobutanil, with limits of detection in the 0.1-0.7 mug/L range. These immunoassays were applied to the determination of triazoles in spiked fruit juices. Samples were adequately diluted to minimize the matrix effects. Coefficients of variation were below 30%, and recoveries ranged from 62 to 135%. Therefore, the developed immunoassays can determine triazole fungicides in fruit juices down to the maximum residue limits currently legislated, without any sample treatment other than dilution. 相似文献