全文获取类型
收费全文 | 1389篇 |
免费 | 119篇 |
专业分类
林业 | 120篇 |
农学 | 38篇 |
基础科学 | 2篇 |
261篇 | |
综合类 | 97篇 |
农作物 | 66篇 |
水产渔业 | 117篇 |
畜牧兽医 | 664篇 |
园艺 | 37篇 |
植物保护 | 106篇 |
出版年
2024年 | 3篇 |
2023年 | 15篇 |
2022年 | 26篇 |
2021年 | 63篇 |
2020年 | 64篇 |
2019年 | 59篇 |
2018年 | 63篇 |
2017年 | 54篇 |
2016年 | 60篇 |
2015年 | 48篇 |
2014年 | 73篇 |
2013年 | 66篇 |
2012年 | 114篇 |
2011年 | 137篇 |
2010年 | 65篇 |
2009年 | 66篇 |
2008年 | 89篇 |
2007年 | 76篇 |
2006年 | 71篇 |
2005年 | 72篇 |
2004年 | 57篇 |
2003年 | 53篇 |
2002年 | 39篇 |
2001年 | 12篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1958年 | 3篇 |
1955年 | 1篇 |
排序方式: 共有1508条查询结果,搜索用时 15 毫秒
991.
Giuseppe Mandolino Andrea Carboni Manuela Bagatta V.M. Cristiana Moliterni Paolo Ranalli 《Euphytica》2002,126(2):211-218
DNA from female and male hemp (Cannabis sativa L.) plants belonging to nine different varieties were screened with180 RAPD primers in a search for sex-associated DNA markers.
About 1500bands were produced in total, nine primers were found yielding one or two DNA bands amplified in all nine male DNA
bulks and absent in all female DNA bulks. These putatively male-associated markers were then scored in three different F1progenies,
deriving from a cross between a common male parent and three different female plants. The sex of the progeny was accurately
scored on the basis of the floral phenotype, and the presence of the nine male-associated markers was verified by RAPD analysis.
In all three progenies examined, all the male plants showed the DNA markers previously identified by bulk segregant analysis
(BSA) on the hemp varieties, while all the female plants lacked them. The fact that the association between these markers
and the staminate phenotype is found when examining male plants of distantly related varieties, and that such linkage is never
broken when different progenies are examined, strongly supports the hypothesis that the markers found are physically located
on the Y chromosome, in a region excluded from recombination during meiosis. Another marker was shown to be present in the
male parent, in all the male plants of each progeny, and in 50% of the female progenies, while it was absent in the female
parent; the possible occurrence of markers deriving from multiple amplification sites of the genome is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
992.
Summary Callus induction, callus growth and organogenetic processes were investigated in hypocotyl and stem cultures of four species of Amaranthus each of which comprised several varieties. Callus formation occurred in almost all the varieties in 100% of explants. The combinations of naphtaleneacetic acid plus benzylaminopurine or 2,4-dichlorophenoxyacetic acid plus Kinetin were very effective in causing callus formation; the results for callus growth in presence of the same growth regulator combinations revealed in some cases significant differences among the varieties.As far organogenesis-based on a few varieties-only A. caudatus and A. hypochondriacus responded well forming shoots from callus when cultured in presence of indoleacetic acid plus Kinetin and/or indoleacetic acid plus benzylaminopurine. Root regeneration was also observed in several varieties. Complete plantlets were obtained from rooted shoots.The results are discussed in relation to hormonal effect and the genotype importance. 相似文献
993.
994.
995.
996.
Leonor Corrales-Retana Francesca Ciucci Giuseppe Conte Laura Casarosa Marcello Mele Andrea Serra 《Journal of animal physiology and animal nutrition》2021,105(2):326-335
The omega-3 fatty acid (FA) enrichment of yolk is a key means one of the main objectives to improve the nutraceutical properties of eggs. We evaluated the effect of the dietary inclusion of extruded linseed fed to laying hens on the fatty acid composition of the polar and non-polar lipid classes of the eggs. Two groups of 36 Lohmann White Leghorn layers (65 weeks old) were each fed one of two different diets for a period of 12 weeks. The two diets consisted of a conventional cereal-based diet concentrate (C) and a diet concentrate containing 5% linseed (L). The inclusion of linseed in the diet increased the content of α-linolenic (C18:3n-3), eicosapentaenoic (C20:5n-3) and docosahexaenoic (C22:6n-3) acids in neutral lipids, while a concomitant decrease in arachidonic acid (C20:4n-6) was observed. As regards the polar fraction, the fatty acid composition was slightly affected by the dietary treatments except for C18:0 (+1.14 fold), C18:2n-6 (+1.23 fold), C18:3n-3 (+2.8 fold) and C22:6n-3 (+1.41 fold). Principal component analysis demonstrated that very long-chain FAs were more representative of polar lipids, except for C20:5n-3, while neutral lipids were characterized by dietary n-3 FA (C18:3n-3). 相似文献
997.
Influence of tillage systems on biological properties of a Typic Argiudoll soil under continuous maize in central Argentina 总被引:2,自引:0,他引:2
Farmers are increasingly using zero tillage in Central Argentina to replace other tillage systems. Intensive tillage decreases soil organic matter content and causes physical degradation. The objective of this work was to evaluate changes in some soil biological properties induced by different tillage systems. A 6 year experiment in which continuous maize (Zea mays L.) was grown using three tillage systems (conventional tillage, reduced tillage and zero tillage) was carried out at Córdoba Province, Argentina, on a Typic Argiudoll. Variations in total organic C content, microbial biomass C, metabolic quotient (qCO2) and the proportion of the organic C present in the microbial biomass were evaluated at two sampling depths (0–5 and 5–15 cm). Additional samples from a nearby site (undisturbed grassland) were also taken and considered as a control. Concentrations of soil organic C and microbial biomass C were higher under zero tillage as compared with conventional tillage, at the 0–5 cm soil depth. Differences were not evident among tillage systems at the 5–15 cm soil depth. An analysis of the microbial biomass C content, in relation to the organic C, revealed higher values at the 0–5 cm soil depth only for those systems which provoke less disturbance of the soil (i.e. reduced tillage and zero tillage). Significantly greater amounts of CO2---C were released from zero tillage and reduced tillage soils than from conventionally tilled soils. This release was positively correlated with microbial biomass C. qCO2 values were not significantly different between tillage systems. Zero tillage proved to be more efficient in the conservation of organic C and microbial biomass C. The tillage system's impact on respiration was due to its effect on the microbial biomass. 相似文献
998.
In floodplain habitats inundation is a seasonally reoccurring phenomena. It represents a natural disturbance for the biocoenoses, causing their successional development to be reset. Collembola generally have developmental cycles that coincide with the yearly inundation incidences. They show perpetual regeneration, which is dependent on flooding intensity. Collembolan communities have been studied in floodplains of the Upper Rhine Valley since the mid-1990s. The development of collembolan communities was followed spatially in different floodplain levels in close vicinity to one another (with different inundation durations within the same year) as well as temporally within the same floodplain levels in different sites. Community development and structure depended mostly on inundation duration and differed from year to year in the same site. Through the differences in the population densities of the various species between sites as well as in different years, species groups, differing in their inundation tolerance, were distinguished. The species occurred either sympatrically or belonged to a common regional species pool (metacommunity). Which species dominated at individual sites depended on the inundation intensity of the individual site and year. The mixture of different inundation tolerances as well as regeneration strategies in the metacommunity, coupled with probable species exchange between patches, determines the composition and structure of local collembolan communities in floodplain forests. These communities are very heterogeneous at small spatial scales. They can thus differentially respond to different flooding intensities and maintain stabile metacommunities despite frequent, but irregular natural disturbances. 相似文献
999.
Paul D’Andrea Keith C. K. Lai Peter Kjeldsen Irene M. C. Lo 《Water, air, and soil pollution》2005,162(1-4):401-420
Although permeable reactive barriers (PRB) technology appears to be a very suitable and cost effective option, the extent to which remediation results will be realized, greatly depends on the long-term integrity of the system. The formation of mineral precipitates is possibly a major factor in the long-term performance of PRB. Precipitates may passivate reactive surfaces by blocking electron-transfer sites, and thereby reduce the long-term reactivity of the granular iron to degrade groundwater contaminants. To evaluate the potential passivation impacts of inorganic groundwater chemistry, column experiments containing zero-valent iron (Fe0) were performed under anoxic conditions to treat two contrasting Danish groundwater types spiked with trichloroethylene (TCE). For most of the experiments using Danish groundwater types, a soft low alkalinity groundwater produced slightly higher TCE dechlorination rate than did a hard high alkalinity groundwater. Compared to a soft low alkalinity baseline groundwater, it was also found the dechlorination of TCE in the column was enhanced in the presence of 1 mM CaCO3 and 1 mM NaHCO3. The dechlorination of TCE in the presence of 1 mM KNO3 and 1 mM Na2SiO3 was found to decrease considerably compared with the baseline solution. The results suggest that the composition of field groundwater is likely to strongly affect the ability of Fe0 barriers to degrade TCE. 相似文献
1000.
Development of a seven-target multiplex PCR for the simultaneous detection of transgenic soybean and maize in feeds and foods 总被引:16,自引:0,他引:16
Germini A Zanetti A Salati C Rossi S Forré C Schmid S Marchelli R Fogher C 《Journal of agricultural and food chemistry》2004,52(11):3275-3280
The detection of genetically modified organisms (GMOs) in food and feed is an important issue for all the subjects involved in raw material control, food industry, and distribution. Because the number of GMOs authorized in the EU increased during the past few years, there is a need for methods that allow a rapid screening of products. In this paper, we propose a method for the simultaneous detection of four transgenic maize (MON810, Bt11, Bt 176, and GA21) and one transgenic soybean (Roundup Ready), which allows routine control analyses to be sped up. DNA was extracted either from maize and soybean seeds and leaves or reference materials, and the recombinant DNA target sequences were detected with 7 primer pairs, accurately designed to be highly specific for each investigated transgene. Cross and negative controls were performed to ensure the specificity of each primer pair. The method was validated on an interlaboratory ring test and good analytical parameters were obtained (LOD = 0.25%, Repeatability, (r) = 1; Reproducibility, (R) = 0.9). The method was then applied to a model biscuit made of transgenic materials baked for the purpose and to real samples such as feed and foodstuffs. On account of the high recognition specificity and the good detection limits, this multiplex PCR represents a fast and reliable screening method directly applicable in all the laboratories involved in raw material and food control. 相似文献