全文获取类型
收费全文 | 430篇 |
免费 | 19篇 |
专业分类
林业 | 29篇 |
农学 | 18篇 |
基础科学 | 3篇 |
131篇 | |
综合类 | 39篇 |
农作物 | 51篇 |
水产渔业 | 23篇 |
畜牧兽医 | 111篇 |
园艺 | 4篇 |
植物保护 | 40篇 |
出版年
2023年 | 5篇 |
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 28篇 |
2017年 | 18篇 |
2016年 | 15篇 |
2015年 | 3篇 |
2014年 | 16篇 |
2013年 | 24篇 |
2012年 | 28篇 |
2011年 | 39篇 |
2010年 | 13篇 |
2009年 | 13篇 |
2008年 | 46篇 |
2007年 | 26篇 |
2006年 | 14篇 |
2005年 | 15篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 20篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1926年 | 2篇 |
排序方式: 共有449条查询结果,搜索用时 12 毫秒
81.
Paolo Bazzoffi Sergio Pellegrini Andrea Rocchini Miranda Morandi Olga Grasselli 《Soil & Tillage Research》1998,48(4):918-286
Application of urban refuse compost to agricultural soil could help to solve municipalities' problems related to the increasing production of waste only if soil property improvement and environmental conservation can be demonstrated. The use of low-pressure tractor tyres is another proposal in modern agriculture for reducing soil compaction. This study thus aimed to detect the effects of both compost and low-pressure tractor tyres on soil loss, runoff, aggregate stability, bulk density, penetrometer resistance and maize (Zea mays L.) yield. A 3-year field experiment was carried out on a hilly (15% slope) clay loam soil in central Italy. Twelve plots (200 m2 each) were monitored with tipping-pot devices for runoff and soil erosion measurement. Treatments were: compost addition (64 Mg ha−1), mineral fertilisation, use of low-pressure tyres, use of traditional tyres, with three replicates, in a fully randomised block design. Compost was applied once at the beginning of the experiment. Runoff reduction due to compost ranged between 7 and 399 m3 ha−1 during seasons, while soil erosion was reduced between 0.2 and 2.4 Mg ha−1. Mean weight diameter (MWD) of stable aggregates, measured on wheel tracks, increased by 2.19 mm, then progressively decreased. Compost significantly increased bulk density by 0.08 Mg m−3 due to its inert fraction content. This effect was less evident in the second and third year, probably due to harrowing. Maize yields were slightly, but significantly, reduced in composted plots by 1.72 Mg ha−1 in the third year. Low-pressure tyres significantly reduced soil loss in the third year by 1 Mg ha−1. Furthermore, they did not significantly influence runoff volumes and soil structural stability. Low-pressure tyres or compost addition were singly able to prevent an increase in penetrometer resistance due to agricultural machinery traffic. Low-pressure tyres increased the maize yield during the 3 years and the difference (0.4 Mg ha−1) became significant in the third year. In conclusion, results show the positive lasting effect of compost in ameliorating soil physical properties and reducing runoff and soil erosion. Low-pressure tyres appear justifiable both for the observed increase of grain production and reduction of soil compaction. This latter effect is, nevertheless, masked by compost addition which is also able to reduce penetrometer resistance. Further research is required to explain the causes of the slight inhibition of grain yield observed when compost was compared with mineral fertilisation. 相似文献
82.
83.
Olga Babourina Konstantin Voltchanskii Ian Newman Zed Rengel 《Soil Science and Plant Nutrition》2005,51(5):733-736
Potassium transport was investigated in the root elongation zone of Arabidopsis seedlings during the first minutes of Al3+ exposure, using the non-invasive MIFE microelectrode technique. To prevent pH changes during Al3+ application, and to separate aluminium from acidic stress, plants were pre-treated with 5 mM homoPIPES before addition of AlCl3 (pH 4.2). The 30-min treatment with 50 or 500 μM AlCl3 led to a significant increase in K+ efflux in solutions containing 100 μM CaCl2 . This efflux was suppressed by high concentrations of Ca2+ (10 mM) in the bathing solution. Our results suggest that elevated external Ca2+ activities can sustain K+ influx in the root elongation zone during Al3+ exposure either by maintaining [Ca2+ ]cyt or by affecting Al3+ uptake across the plasma membrane. 相似文献
84.
Olga E. Scholten Lee W. Panella Theo S.M. De Bock Wouter Lange 《European journal of plant pathology / European Foundation for Plant Pathology》2001,107(2):161-166
Rhizoctonia solani Kühn is a serious plant pathogenic fungus, causing various types of damage to sugar beet (Beta vulgaris L.). In Europe, the disease is spreading and becoming a threat for the growing of this crop. Plant resistance seems to be the most practical and economical way to control the disease. Experiments were carried out to optimise a greenhouse procedure to screen plants of sugar beet for resistance to R. solani. In the first experiment, two susceptible accessions were evaluated for root and leaf symptoms, after being grown in seven different soil mixtures and inoculated with R. solani. The fungus infected all plants. It was concluded that leaf symptoms were not reliable for the rating of disease severity. Statistically significant differences between the soil mixtures were observed, and there were no significant differences between the two accessions. The two soil mixtures, showing the most severe disease symptoms, were selected for a second experiment, including both resistant and susceptible accessions. As in the first experiment, root symptoms were recorded using a 1–7 scale, and a significant expression of resistance was observed. The average severity of the disease in the greenhouse experiment generally was comparable with the infection in field experiments, and the ranking of the accessions was the same in the two types of experiments. It was concluded that evaluation procedures in the greenhouse could be used as a rapid assay to screen sugar beet plants for resistance to R. solani. 相似文献
85.
M. Pilar Gómez-Serranillos Sara Martín Teresa Ortega Olga M. Palomino Marín Prodanov Visitación Vacas Teresa Hernández Isabel Estrella M. Emilia Carretero 《Plant foods for human nutrition (Dordrecht, Netherlands)》2009,64(4):238-243
Phenolic composition of wine depends not only on the grape variety from which it is made, but on some external factors such
as winemaking technology. Red wine possesses the most antioxidant effect because of its high polyphenolic content. The aim
of this work is to study for the first time, the neuroprotective activity of four monovarietal Spanish red wines (Merlot (ME),
Tempranillo (T), Garnacha (G) and Cabernet-Sauvignon (CS)) through its antioxidant ability, and to relate this neuroprotection
to its polyphenolic composition, if possible. The wine effect on neuroprotection was studied through its effect as free radical
scavenger against FeSO4, H2O2 and FeSO4 + H2O2. Effect on cell survival was determined by 3(4,5-dimethyltiazol-2-il)-2,5-diphenyltetrazolium reduction assay (MTT) and lactate
dehydrogenase (LDH) release assay on astrocytes cultures. Results showed that most of the studied wine varieties induced neuroprotection
through their antioxidant ability in astrocytes, Merlot being the most active; this variety is especially rich in phenolic
compounds, mainly catechins and oligomeric proanthocyanidins. Our results show that red wine exerts a protection against oxidative
stress generated by different toxic agents and that the observed neuroprotective activity is related to their polyphenolic
content. 相似文献
86.
Matías Santini Elsa Lucila Camadro Olga Noemí Marcellán Luis Ernesto Erazzú 《American Journal of Potato Research》2000,77(4):211-218
Five diploid hybrid families derived from crosses between haploids of three Argentinian cultivars and three diploid wild species,Solanum gourlayi, S. chacoense andS. spegazzinii, were evaluated in a field experiment in Balcarce. All plants were androsterile and, thus, could not be screened for 2n pollen production. Data on agronomic tuber traits were statistically analyzed. Differences among families were non-significant for tuber number/plant, but were significant for tuber weight/plant and dry matter content (with values above 21.0% in two of them). The relative frequencies of tubers in the categories established for size, skin texture, and eye depth were family dependent, but they were familiy independent in the categories established for tuber shape and skin color. Great morphological variability was detected for all the traits studied, and plants with high yield and high dry matter content were identified. These families can be used as sources of germplasm in breeding and to explore heterotic responses in 2x × 4x crosses, given the capacity of some plants to produce 2n eggs, as found in a related investigation. 相似文献
87.
Kottaridi C Nomikou K Teodori L Savini G Lelli R Markoulatos P Mangana O 《Veterinary microbiology》2006,116(4):310-316
Thirteen orf virus isolates obtained during the time period between 1995 and 2004 from crusted scab lesions of nine sheep and four goats from different geographical areas of Greece and Italy with suspected contagious ecthyma infection were analyzed. DNA of all isolates was successfully amplified by PCR with the primers 045F-045R and identified them as parapox virus. Partial DNA sequence of orf virus interferon resistant (VIR) gene, phylogenetic analysis of the available isolates and amino acid comparison of the interferon resistance protein encoded by this genomic region was carried out. According to the results of the present report a precise characterisation of the genomic region studied might provide evidence for the genetic variation and movement of the circulating orf virus strains. 相似文献
88.
Petra FRÝDLOVÁ Jan HNÍZDO Lenka CHYLÍKOVÁ Olga ŠIMKOVÁ Veronika CIKÁNOVÁ Petr VELENSKÝ Daniel FRYNTA 《Integrative zoology》2013,8(Z1):39-45
Blood cell morphology and count are not uniform across species. Recently, between‐species comparisons revealed that the size of red blood cells is associated with body size in some lizard taxa, and this finding was interpreted in the context of the metabolic theory. In the present study, we examined the numbers and the size of blood cells in 2 species of monitor lizards, the mangrove‐dwelling monitor (Varanus indicus) and the savannah monitor (V. exanthematicus), and we compared these traits in individuals of different body size. The results revealed that during the course of ontogeny, the size of red blood cells increases with body mass. Because the mass‐specific metabolic rate decreases with body size and the cell volume‐to‐surface ratio decreases with the cell size, changes in the erythrocyte size might be the result of oxygen transport adjustment. 相似文献
89.
Milica Marković Tea Zuliani Snežana Belanović Simić Zorana Mataruga Olga Kostić Snežana Jarić Janja Vidmar Radmila Milačič Janez Ščančar Miroslava Mitrović Pavle Pavlović 《Journal of Soils and Sediments》2018,18(12):3404-3414
Purpose
Riparian zone contamination is a growing problem for several European catchments due to high anthropogenic pressures. This study investigates As, Cd, Cr, Cu, Ni, Pb, and Zn concentrations in the Sava River riparian zone, characterized by wide agricultural areas, various geological substrates, and different types of industrial pollution. The accumulation and mobility of these elements were studied because they are listed as priority substances in the Water Framework Directive and environmental objectives for surface waters.Materials and methods
Sampling was performed during the sampling campaign of the EU 7th FW-funded GLOBAQUA project in September 2015 during a low-water event. Soil samples were collected along the Sava River at 12 selected sampling sites, from a depth of 0–30 cm, at a distance of 10–15 m from the river bank. The extent of pollution was estimated by determining total and readily soluble element concentrations in the soils. Potential ecological risk and the source of the selected elements in the soils was determined using the enrichment factor (EF), potential ecological risk index (RI), and statistical methods such as the principal component analysis (PCA) and multiple linear regression analysis (MLRA).Results and discussion
This study showed that concentrations of the selected elements increase along the Sava. In terms of origin, PCA and MLRA indicated that Cr and Ni in soils are predominantly lithogenic, while As, Cd, Pb, and Zn are both lithogenic and anthropogenic (ore deposits, industry, and agriculture). PCA singled out Cu since its origin in soil is most probably from specific point-source pollution. EF was generally minor to moderate for most of the examined elements, apart from Cu, for which the EF was significant at one sampling site. Overall ecological risk (RI) fell within the low-risk category for most sites, apart from Belgrade sampling site (BEO), where high total Cd content affected individual and overall ecological risk indicators, indicating Cd could represent a considerable ecological risk for the downstream riparian zone.Conclusions
At downstream sites, there was a noticeable increase in PTE content, with Cd, Cr, Ni, and Zn exceeding the proposed threshold values for European soils, indicating rising contamination in riparian soils. In terms of the ecological risk, only Cd could pose a potential ecological threat for the downstream riparian zone.90.
Busche MA Eichhoff G Adelsberger H Abramowski D Wiederhold KH Haass C Staufenbiel M Konnerth A Garaschuk O 《Science (New York, N.Y.)》2008,321(5896):1686-1689
The neurodegeneration observed in Alzheimer's disease has been associated with synaptic dismantling and progressive decrease in neuronal activity. We tested this hypothesis in vivo by using two-photon Ca2+ imaging in a mouse model of Alzheimer's disease. Although a decrease in neuronal activity was seen in 29% of layer 2/3 cortical neurons, 21% of neurons displayed an unexpected increase in the frequency of spontaneous Ca2+ transients. These "hyperactive" neurons were found exclusively near the plaques of amyloid beta-depositing mice. The hyperactivity appeared to be due to a relative decrease in synaptic inhibition. Thus, we suggest that a redistribution of synaptic drive between silent and hyperactive neurons, rather than an overall decrease in synaptic activity, provides a mechanism for the disturbed cortical function in Alzheimer's disease. 相似文献