全文获取类型
收费全文 | 348篇 |
免费 | 15篇 |
国内免费 | 8篇 |
专业分类
林业 | 26篇 |
农学 | 8篇 |
基础科学 | 6篇 |
22篇 | |
综合类 | 211篇 |
农作物 | 29篇 |
水产渔业 | 15篇 |
畜牧兽医 | 36篇 |
园艺 | 12篇 |
植物保护 | 6篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 8篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 35篇 |
2012年 | 22篇 |
2011年 | 54篇 |
2010年 | 29篇 |
2009年 | 23篇 |
2008年 | 16篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 8篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有371条查询结果,搜索用时 15 毫秒
1.
本文探讨通过富硒饲料饲养的富硒鸡不同部位中硒含量及脂肪酸组成。分别取富硒饲养鸡不同部位,包括皮、褐色脂肪、白色脂肪、胸肌、腿肌、肌胃、心脏、肾脏、肝脏、蛋;各样本采用微波消解法(MD)消解,然后用电感耦合等离子体质谱法(ICP-MS)检测硒含量。以正己烷抽提样本中脂肪,经三氯化硼-甲醇甲酯化后,采用GC-MS进行脂肪酸组成进行分析。各检测部位中,硒含量依次为:肌胃>白色脂肪>皮>蛋>肾脏>肝脏>腿肌>心脏>褐色脂肪>胸肌。肌胃中硒含量最高为2639.19 ng/g,胸肌中硒含量最低为129.76 ng/g。脂肪酸组成分析结果显示,白色脂肪中饱和脂肪酸含量最高为88.07%,胸肌不饱和脂肪酸含量最高为68.44%。本次检测结果显示富硒饲料在母鸡不同部位硒含量不同,不同部位脂肪酸组成也不相同,本实验结果对富硒鸡中营养成分的利用提供参考。 相似文献
2.
3.
4.
歙县枇杷产业化的发展与对策 总被引:3,自引:0,他引:3
主要介绍了枇杷的生物学特性和营养价值、药用价值,在分析了歙县枇杷生产现状的基础上,指出了歙县枇杷产业化发展存在的问题,并提出了发展枇杷产业需要通过采取适度规模化生产、合理品种组成、加强产后服务、实现产品深加工和综合利用等对策。 相似文献
5.
Yan Yin Yang BiSongjiang Chen Yongcai LiYi Wang Yonghong GeBo Ding Yingchao LiZhong Zhang 《Scientia Horticulturae》2011
In order to understand the cuticular wax properties of Asian pear fruits (cv. Pingguoli), a series of assays was conducted on extraction, fractionation and determination of composition. The results showed that the maximum yield of wax from the fruit was obtained by chloroform/methanol (3:1), and then by chloroform extraction. Polar and low polar fractions occupied 64.3% and 26.9% of total crude wax by column chromatography. 54 and 22 components were identified in polar and low polar fractions by GC/MS, respectively. Long-chain fatty acids and triterpenoids predominated in polar fraction and n-alkanes were predominant in low polar fraction. In vitro tests indicated that polar fraction, low polar fraction and total crude wax inhibited spore germination and mycelial growth of Alternaria alternata, which is a causal agent of Alternaria rot of pears, and the maximum inhibition was obtained by polar fraction. These findings indicated that n-alkanes in low polar fraction and triterpenoids, fatty acid in polar fraction might have contributed to the antifungal properties of pear fruit cuticular waxes. 相似文献
6.
We examined patterns of variation in richness, diversity, and composition of understory vascular plant communities in mixedwood boreal forests of varying composition (broadleaf, mixedwood, conifer) in Alberta, Canada, before and for 2 years following variable-retention harvesting (clearcut, 20 and 75% dispersed green tree retention, control). Broadleaf-dominated forests differed from mixedwood or conifer-dominated forests in that they had greater canopy cover, litter depth, soil nitrogen, warmer soils, as well as greater shrub cover, herb and shrub richness and diversity (plot scale). In contrast, conifer, and to a lesser extent mixedwood, forest had greater β diversity than broadleaf forest. Overall, mixedwood and conifer forests were similar to one another, both differed from broadleaf forest. Several species were found to be significant indicators of broadleaf forest but most of these also occurred in the other forest types. Understory composition was related to canopy composition and edaphic conditions. Variable-retention harvesting had little effect on understory cover, richness, or diversity but resulted in reduced richness and β diversity at a larger scale. The clearcut and 20% treatments affected composition in all forest types. Early successional species and those common in disturbed sites were indicators of harvesting while evergreen, shade-tolerant understory herbs were indicators of the control forest and 75% retention harvest. We conclude that it is important to maintain a range of variation in canopy composition of mixedwood forests in order to conserve the associated understory communities. The presence of conifers in these forests has a particularly important influence on understory communities. The threshold for a lifeboat effect of variable-retention harvesting is between 20 and 75% retention. Examination of richness and β diversity at a variety of scales can provide interesting information on effects of harvesting on spatial reorganization and homogenization of understory plant communities. 相似文献
7.
Rapid conversion of lodgepole pine (Pinus contorta) dominated landscapes in western Alberta to a mosaic of successional stand ages has long-term implications for elk populations in the region that have not been fully assessed. We developed stand-level models of forage succession using data from 159 cutblocks to simulate forage and cover availability within the home range of an elk under “even-flow” and “pulsed” timber cutting scenarios that are common in this area. We found forage biomass peaked approximately 9 years following felling for both herbaceous (graminoids and forbs) and palatable browse forage. Forage production was determined primarily by the age of the cutblock (time since felling) and to a lesser extent elevation, compound topographic index (a measure of site wetness), and the distance to the nearest deciduous forest patch. Forbs became increasingly abundant as stands matured. Browse composition shifted from palatable species to unpalatable species after approximately 30 years. Within an elk home range (100 km2), we found that simulating an “even-flow” cutting regime resulted in forage availability that was always higher than under the current conditions of 90% forests when more than 10 ha were harvested per year. Further, forest cover (>30-year-old stands) was never less than the guideline of 60% of the area needed to provide adequate thermal and hiding cover. In contrast, when a “pulsed” harvest scenario was simulated, similar to what occurs for mountain pine beetle control, forage availability changed dramatically over time as a large cohort of harvested timber aged. Without further harvesting the stand conditions in the home range eventually returned to a state of pre-harvest risk for mountain pine beetle outbreak. We demonstrated several additional harvesting scenarios that avoided the potential risk and produced a much higher level of forage than currently exists. 相似文献
8.
在贵州省黔东南地区雷山、施秉、镇远三县调查了三种不同类型的灌丛,对样地内灌木树种和草本植物的种类、密度、覆盖度、水平及垂直分布等结构特点进行了分析.并对其演替及利用前景进行了评价。 相似文献
9.
INTRoDUCTIoNAnthasbeenusedasmedicineandhealthprotectionproductsfora1ongtime-Theant(PolyrhachisvicinaRoger)ismostincommon.TheyaremainlylivinginGuangxiProvince.Theyareablack,irri-tateacidityanddelicatefragranceinsects.ThereisakindofantinWandaMountain,Daxing'anMountain,andXiaoxing'anMountain.Itisabig(aboutmorethanl-ocmlong),strongandnonpollutioninsect.alotofbigandblackantswerecollectedfromWandaMountain.Itwasappraisedbyantexpertstobeantfami1yandantcategory.ItwasnamedFormicacuniculariaLa… 相似文献
10.
Weston F. Mwase Åsmund Bjørnstad James M. Bokosi Moses B. Kwapata Brita Stedje 《New Forests》2007,33(3):297-307
Biodiversity is declining throughout southern African miombo woodlands due to poor land use practices that are detrimental
to soil, vegetation and habitat. We aimed at examining tree and shrub species diversity and distribution in Uapaca kirkiana-dominated woodlands under three land tenure types; forest reserves, customary and leasehold land. The study was conducted
at different forest sites within similar agroecological zone in southern Malawi. Study sites were located at a range of altitudes
between 900 and 1,200 m a.s.l. Three circular plots each with 32.60 m radius were established at each study site to sample
tree and shrub species composition, structure and distribution under three land tenure types. We found that forest reserves
had higher species diversity with an average of 16 tree families, 27 genera and 34 species as compared to only 10 tree families,
6 genera and 6 species on customary forest lands. Comparisons of diameter at breast height size class distributions showed
that customary land had significantly low numbers of small (5.0–10.0 cm) and very large (≥30 cm) diameter classes suggesting
lower levels of regeneration and high rate of anthropogenic activities. The high species diversity and richness in forest
reserves and leasehold land indicate high potential for protected lands to restore tree species diversity. It is concluded
that levels of human activities as influenced by land tenure type reduce tree species diversity, composition and distribution
at the different sites, and this confirms the hypothesis that open access lands are not compatible with conservation of tree
and shrub species diversity because of high anthropogenic activities. 相似文献