全文获取类型
收费全文 | 149篇 |
免费 | 10篇 |
国内免费 | 27篇 |
专业分类
186篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 8篇 |
2012年 | 2篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 3篇 |
2008年 | 10篇 |
2007年 | 5篇 |
2006年 | 9篇 |
2004年 | 5篇 |
2003年 | 11篇 |
2002年 | 1篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有186条查询结果,搜索用时 15 毫秒
81.
树木根系中1级根在养分和水分吸收方面发挥着重要作用。研究1级根的形态结构与功能的联系,对了解1级根的生理功能和寿命,以及森林生态系统碳和养分的循环具有重要的理论意义。但是,1级根在根系统中,因着生的位置不同,可能表现出不同的生理生态功能。该研究以胡桃楸(Juglans mandshurica)、黄波罗(Phellodendron amurense)和水曲柳(Fraxinus mandshurica)人工林根系的1级根为研究对象,研究了不同着生位置的1级根的形态、解剖结构和组织化学特征。将1级根按着生位置的不同分成3类:Ar类根为2级根上的1级根;Br类根为2级–4级根的根尖;Cr类根为3级–5级根上的1级根。结果表明:不同着生位置的1级根,形态、解剖结构和组织化学方面都具有高度的异质性。3类1级根中,Ar类根数量多、根长较短、直径细,N含量高,皮层比例高、维根比低,主要由二原型原生木质部的根组成;Br类和Cr类根数量较少、单根较长、直径粗,N含量低,皮层比例低、维根比高,主要由多原型原生木质部的根组成。研究结果对了解不同着生位置的1级根的吸收功能和寿命具有重要的理论意义。 相似文献
82.
The basal diameter of the annual shoot (1YD) affects vegetative growth and fruiting of the walnut trees. In order to determine interdependency between the 1YD and the older parent wood, 64 walnut genotypes belonging to four different branching and fruiting habits (morphotypes M-I, M-II, M-III and M-IV) were investigated. Year-to-year stability of 1YD was tested with the architectural analysis of a 3-year-old fruiting branch and its constituents (a 3-year-old bearer + corresponding 2-year-old + annual shoots) during 3 successive years. Based on Pearson's correlation coefficients and the multiple regression analysis of 12 quantitative traits, 12 models (four morphotype in 3 successive years) of 1YD were formed. They were compared with the standard model which was calculated on the basis of 1-year measurements of 1Y with no respect to the branching and fruiting type and comprises three quantitative traits, i.e. basal diameter of a 2-year-old parent shoot (2YD), the length of 2Y shoot (2YL), and the length of annual shoot (1YL). In a single year, the 1YD was influenced by two–five parameters. Five out of 12 models agreed with the standard model: in the lateral fruiting genotypes (M-IV), 1YD was always under the influence of the 2Y diameter, and the 1Y length. In addition, the number of nodes of the 2Y parent shoot had an important influence on 1Y diameter. In the terminal bearers (M-I), the impact of 2YD on the 1YD slightly increased with the tree age, and some other parameters, like 1Ynumber and 1Ynodes, which became to be important for 1YD. In the intermediate genotypes with mezotonic ramification (M-II), the number of vegetative buds per 1Y and angles of 1Y had significant effects on 1YD. In the intermediate bearers with acrotonic ramification (M-III), one to four other parameters were included into the model each year beside the 1Y number. Since the traits of a 2-year-old parent shoot have a great influence on the 1YD, the information from the year N can be used for the prediction of the annual shoot development in the year N+1. Such a prediction is more reliable in M-I and M-IV than in M-II and M-III. When we deal with the intermediate fruiting cultivars, 1Y number has to be considered in prediction of 1Y diameter beside 2YD and 1YL. 相似文献
83.
核桃楸青果皮提取液对植物生长的影响 总被引:2,自引:0,他引:2
用核桃楸青果皮的氯仿、苯、正丁醇提取液,对萝卜、莴苣、稗草、马唐的发芽和生长的影响以及对黄瓜子叶叶绿素的形成的影响进行了试验。结果表明:氯仿、苯提取液抑制供试植物发芽和生长和叶绿素的形成,不同浓度的正丁醇提取液对供试植物显示抑制或促进作用。 相似文献
84.
Unusual Fine Root Distributions of Two Deciduous Tree Species in Southern France: What Consequences for Modelling of Tree Root Dynamics? 总被引:3,自引:0,他引:3
The spatial distribution of fine roots of two deciduous tree species was investigated in contrasting growing conditions in
southern France. Hybrid walnut trees (Juglans regia×nigra cv. NG23) and hybrid poplars (Populus euramericana cv. I214) were both cultivated with or without annual winter intercrops for 10 years on deep alluvial soils. Soil samples
for measuring the fine root distribution of both trees and crops were obtained by soil coring down to 3-m depth at several
distances and orientations from the tree trunk. The distribution of live fine roots from walnut and poplar trees was patchy
and sometimes unexpected. In the tree-only stands, fine root profiles followed the expected pattern, as fine root density
decreased with increasing depth and distance from the tree trunk. However, many fine root profiles under intercropped trees
were uniform with depth, and some inverse profiles were observed. These distributions may result from a high degree of plasticity
of tree root systems to sense and adapt to fluctuating and heterogeneous soil conditions. The distortion of the tree root
system was more pronounced for the walnut trees that only partially explored the soil volume: in the tree-only stand, the
walnut rooting pattern was very superficial, but in the intercropped stand walnut trees developed a deep and dense fine root
network below the crop rooting zone. The larger poplars explored the whole available soil volume, but the intercrop significantly
displaced the root density from the topsoil to layers below 1 m depth. Most tree root growth models assume a decreasing fine
root density with depth and distance from the tree stem. These models would not predict correctly tree–tree and tree–understorey
competition for water and nutrients in 3D heterogeneous soil conditions that prevail under low-density tree stands. To account
for the integrated response of tree root systems to such transient gradients in soils, we need a dynamic model that would
allow for both genotypic plasticity and transient environmental local soil conditions. 相似文献
85.
GC/MS法分析核桃叶挥发油化学成分 总被引:9,自引:0,他引:9
利用水蒸气蒸馏方法从陕西栽培的核桃品种西洛3号提取了核桃叶挥发性物质,用GC/MS法分离确定出20种化学成分,其中主要成分(相对含量)为萜类(84.89%)、芳香烃(3.9%)和酯类(1.34%)化合物,占总检出量约90.84%。 相似文献
86.
Sean M. Hoban Tim S. McCleary Scott E. Schlarbaum Jeanne Romero-Severson 《Biology letters》2009,5(3):324-327
We investigate the question of naturally occurring interspecific hybrids between two forest trees: the native North American butternut (Juglans cinerea L.) and the introduced Japanese walnut (Juglans ailantifolia Carrière). Using nuclear and chloroplast DNA markers, we provide evidence for 29 F1 and 22 advanced generation hybrids in seven locations across the eastern and southern range of the native species. Two locations show extensive admixture (95% J. ailantifolia and hybrids) while other locations show limited admixture. Hybridization appears to be asymmetrical with 90.9 per cent of hybrids having J. ailantifolia as the maternal parent. This is, to our knowledge, the first genetic data supporting natural hybridization between these species. The long-term outcome of introgression could include loss of native diversity, but could also include transfer of useful traits from the introduced species. 相似文献
87.
采用超声波辅助提取方法,以胡桃楸为原料,在单因素实验的基础上研究一年内不同月份胡桃楸不同部位总黄酮、总酚的含量变化,同时对胡桃楸提取物体外抗肿瘤活性进行初步评价。结果显示,乙醇浓度60%,超声时间40 min,料液比1:20,提取温度30℃为最佳提取参数。在此条件下,不同采摘时期胡桃楸不同部位的总黄酮、总酚含量存在显著差异。5~7月份叶和小枝的总黄酮及总酚含量明显高于8~10月份,其中7月份叶的总黄酮总酚含量最高,分别为12.56±0.33和76.98±3.73 mg·g-1,然而茎皮总黄酮、总酚含量随月份增加呈持续下降趋势。体外抗肿瘤研究表明胡桃楸叶提取物对人肝癌细胞SMMC-7721、人乳腺癌细胞MCF-7和人口腔表皮样癌细胞KB的增殖抑制作用,其中7月份胡桃楸叶提取物对人乳腺癌MCF-7细胞增殖抑制作用更明显,其IC50值为0.24 mg·mL-1。本研究为胡桃楸资源的合理开发及利用提供一定的理论基础。 相似文献
88.
以新疆地区种植的4个核桃(Juglans regia Linn.)栽培品种(包括新栽培品种'温185'和'新新2'以及老栽培品种'新丰'和'扎343')及巩留野核桃自然保护区生长的野生核桃为研究对象,对其cpDNA的psbK-psbI区间和mtDNA的COX2 intronⅠ区间以及nrDNA的ITS和ETS区间的DNA片段序列进行了比较分析,并对其MP、ML和UPGMA系统发育树进行了分析;此外,还基于SSR分子标记结果对其进行了遗传多样性指数、UPGMA系统发育树和遗传分组分析.结果表明:野生种与4个栽培品种的cpDNA和mtDNA片段序列无碱基变异,而其nrDNA的片段序列却存在3个碱基变异,但4个栽培品种间无碱基变异.以麻核桃(J.hopeiensis Hu)为外类群,基于上述4个DNA片段序列构建的MP、ML和UPGMA系统发育树的聚类结果一致,均表现为4个栽培品种聚为一组,而野生种和麻核桃则分别单独聚为一组.野生种的观测杂合度、预期杂合度和固定指数分别为0.383、0.448和0.153,4个栽培品种的上述3个遗传多样性指数分别为0.428~0.576、0.423~0.619和-0.043~0.234.基于SSR分子标记结果的UPGMA系统发育树和分组数为5的遗传分组结果均表明:野生种和品种'温185'分别单独为一组;品种'新新2'和'新丰'为一组;而品种'扎343'也单独为一组,但与品种'新新2'和'新丰'遗传关系较近.遗传分组结果还表明:分组数为3更利于明确品种'扎343'的分组地位,此时,其与品种'新新2'和'新丰'为一组.综合分析结果表明:核桃4个栽培品种间的遗传差异较小,且老栽培品种的遗传多样性总体上高于新栽培品种;野生种与栽培品种间具有明显的遗传差异,说明在育种或栽培过程中核桃种质资源的遗传多样性可能会逐渐降低,并且,该野生种可为核桃的分子育种提供天然的基因库资源. 相似文献
89.
Kourosh Vahdati Shima Bayat Hassan Ebrahimzadeh Maryam Jariteh Masoud Mirmasoumi 《Plant Cell, Tissue and Organ Culture》2008,93(2):163-171
Low efficiency of embryo maturation, germination and conversion to plantlets is a major problem in many species including
Persian walnut. We studied the effects of abscisic acid (ABA) and sucrose, on the maturation and germination of Persian walnut
(Juglans regia) somatic embryos. Individual globular somatic embryos were grown on a maturation medium supplemented with different combinations
of ABA and sucrose for ca. 1 month, until shoot meristems and radicles had developed. White and opaque embryos in late cotyledonary
stage were subjected to desiccation after the culture period on maturation media. The number of germinated somatic embryos
was influenced by the concentrations of ABA in the maturation medium. The best treatment for germination, in which both shoot
and root were developed contained 2 mg l−1 ABA and resulted in 41% conversion of embryos into plantlets. Regeneration was reduced at higher levels of ABA. While ABA
always reduced the rate of secondary embryogenesis, treatments containing 4.0% sucrose significantly increased the number
of secondary embryos. On the other hand, sucrose had little influence on maturation. Normal and abnormal embryos were verified
anatomically. 相似文献
90.