首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   32篇
  免费   1篇
林业   15篇
  17篇
综合类   1篇
  2020年   1篇
  2015年   1篇
  2009年   1篇
  2008年   3篇
  2007年   2篇
  2006年   2篇
  2005年   3篇
  2004年   2篇
  2003年   4篇
  2002年   2篇
  1999年   5篇
  1991年   1篇
  1990年   2篇
  1988年   1篇
  1985年   1篇
  1982年   1篇
  1980年   1篇
排序方式: 共有33条查询结果,搜索用时 15 毫秒
11.
Tropical forests contain many tree species that have supplied edible fruits for centuries.These fruits have contributed to human diets due to their richness in nutrients,vitamins,minerals,antioxidants and their low antinutrients content.We investigated the antioxidant,nutritional and anti-nutritional composition of Garcinia kola and Chrysophyllum albidum fruit parts.The nutritional,anti-nutritional and antioxidant compositions differed depending on the fruit part.Irrespective of fruit part,moisture content was high(72–93 %).While the edible part(fruit pulp) of C.albidum proved a better source of protein(4),fibre(17 %) and fat(2 %),the seed kernel was a better source of ash(2 %) and carbohydrate(15 %).Carbohydrate(22 %),protein(2 %),fat(1 %) and fibre(3 %) were higher in G.kola seed kernel(edible part) than in the pulp and pod.Anti-nutrient content in G.kola and C.albidum fruits was low,indicating that their consumption would not pose nutritional or health problems.The antioxidant compositions(especially phenolic content(10–21 mg g-1) and DPPH(1,1-diphenyl–2 picrylhydrazyl)(26–55 %)) of C.albidum fruit pulp and G.kola seed kernel were high,implying that they could be good sources of natural antioxidants and could be used as supplements in food manufacturing.  相似文献   
12.
Syringa vulgaris L. inflorescences, petals, and chloroplasts, isolated from lilac flower petals, were fed with aqueous solutions of (18)O-labeled linalool and [5,5-(2)H(2)]-deoxy-d-xylose (DOX). The chloroplasts of lilac flower petals were isolated after feeding experiments with labeled precursors. Volatiles from the chloroplasts were extracted by stir bar sorptive extraction (SBSE) and analyzed using enantioselective multidimensional gas chromatography-mass spectrometry (enantio-MDGC-MS). Feeding experiments with DOX indicate that the novel mevalonate-independent 1-deoxy-d-xylose 5-phosphate/2C-methyl-d-erythritol 4-phosphate (DOX/MEP) is the decisive pathway of lilac aldehyde and lilac alcohol, respectively. Bioconversion of [(18)O]linalool into lilac aldehyde and lilac alcohol during in vivo feeding experiments was monitored, and the metabolic pathways are discussed.  相似文献   
13.
陕北黄土高原森林植被的性质和当前森林培育的策略   总被引:2,自引:2,他引:2  
对比和分析了前人对陕北黄土高原植被的研究成果后认为陕北黄土高原的阔叶栎林为主的森林界限截止于渭北黄土高原北部,即陇县、彬县、宜君、铜川、黄龙一线。经过植被破坏和土壤侵蚀后土壤基质已经严重旱化和贫瘠化,通过重建植被土壤基质是可以逐步恢复的。植被的重建应该首选择先锋植物种类,造林后应及时进行改造,使其向接近该区天然林(植被)的方向发展,并需要建立一套可持续的森林经营体系。  相似文献   
14.
A novel enantioselective synthesis of nerol oxide (3, 6-dihydro-4-methyl-2-(2-methyl-1-propenyl)-2H-pyran) was used for the determination of the absolute configuration at C-2. The order of elution of the enantiomers on octakis-(2, 3-di-O-butyryl-6-O-tert-butyldimethylsilyl)-gamma-cyclodextrin in OV 1701-vi as the chiral stationary phase in enantioselective GC was determined as (2R) before (2S). Enantioselective multidimensional GC/MS (enantio-MDGC/MS) was used for the determination of the enantiomeric ratios of nerol oxide in different geranium oils. As a result, in all investigated oils nerol oxide occurs as a racemate. The biogenesis of nerol oxide in Pelargonium species was investigated by feeding experiments using deuterium-labeled neryl glucoside as the precursor. The Pelargonium plants were able to convert the fed precursor into racemic nerol oxide, which has to be considered as a "natural racemate".  相似文献   
15.
The biosynthesis of the monoterpene (S)-linalool and the sesquiterpene trans-(S)-nerolidol in fruits of Fragaria x ananassa Duch. cv. Eros and Florence and of the monoterpene (-)-alpha-pinene in Fragaria vesca was investigated by in vivo feeding experiments with [5,5-2H2]mevalonic acid lactone (d2-MVL) and [5,5-2H2]-1-deoxy-d-xylulose (d2-DOX). The feeding experiments indicate that (S)-linalool and trans-(S)-nerolidol in Fragaria x ananassa Duch. and (-)-alpha-pinene in F. vesca are exclusively synthesized via the cytosolic mevalonic acid pathway without any contribution from the plastidial 1-deoxy-D-xylulose/2-C-methyl-D-erythritol 4-phosphate (DOXP/MEP) route. Inhibition experiments revealed that even the presence of mevastatin, an export of plastid-derived isopentyl diphosphate/dimethylallyl diphosphate, cannot be induced. However, the enantioselective analysis shows that in Fragaria x ananassa Duch. cv. Eros and Florence both linalool enantiomers are present and that only (S)-linalool is labeled after administration of d2-MVL. Therefore, the origin of (R)-linalool in these fruits remains unknown. Contrarily, in Fragaria x ananassa Duch. foliage (R)-linalool is the dominant enantiomer. Feeding experiments revealed an incorporation of d2-MVL and d2-DOX at equal rates exclusively into (S)-linalool. Only in F. vesca foliage, where (R)-linalool is present at high enantiomeric purity (ee > 90%), is a de novo biosynthesis of the (R)-enantiomer via the DOXP/MEP pathway detectable. These results demonstrate a complex intraplant variation of (R)- and (S)-linalool biosynthesis via the cytosolic and plastidial route.  相似文献   
16.
通过对渭北黄土高原刺槐人工林最大林木的树干解析和年轮分析描述了林分最大两株林木的树高、直径和材积生长过程。结果表明,矮林树高初期生长迅速,“好”立地的最大木高生长大于“差”立地上的最大木,矮林和“差”立地上的乔林之间树高生长过程达到最高峰的年龄为4—8a,“好”立地上的乔林为12a左右。直径生长可以分为速生期和缓馒生长期,年轮波动在速生期幅度大,进入缓馒生长期后幅度小但频度加大。依据直径生长过程可以区分为两组:第一组为最大木和次大木速生期为造林后6—8a的林分;第二组林木的速生期可持续到25a左右。年轮宽度的灵敏度指数在林分内最大木和次大木之间和在林分间差异都较大,刺槐矮林趋于比乔林大。生长越迅速,受到的人为干扰越强,年轮变化对于扰的反映越敏感,年轮灵敏度指数就越高。抚育间伐时常常伐去了利用价值高的个体,林分现保留木常是先前的被压木。  相似文献   
17.
Direct seeding and planting of European beech (Fagus sylvaticaL.) are two common techniques for the conversion of pure Norwayspruce (Picea abies [L.] Karst.) stands into mixed stands. Thisstudy tested whether the growth of sown beech seedlings differsfrom that of planted seedlings of two stock types. Thereforeat two experimental sites repeated measurements were made ofheight, stem and first order branch diameter on sown and plantedseedlings over a period of nine years. The results showed thatthe growth responses of planted and sown seedlings to the environmentalconditions below the canopy of overstorey Norway spruce wererather similar. No differences between planted and sown seedlingswere found in their diameter and their estimated abovegrounddry weight. For all three batches the ratio between the estimatedbranch dry weight and the estimated main stem dry weight (branch-shoot-ratio(BSR)) was increased with age. Due to intraspecific competitionBSR was lowest for the sown seedlings irrespective of theirage. Differences in growth dynamics between planted and sownseedlings were found. For example, differences in the heightor the estimated aboveground woody dry weight between sown andplanted seedlings at a given age were not constant. Height,diameter and estimated dry mass of the seedlings in relationto age could be modelled precisely by a second-order polynomialfunction in the hitherto studied period.  相似文献   
18.
19.
Management of natural forests might be one option to reduce the high deforestation rate in Ecuador. We therefore evaluated the response of water and nutrient cycles in a natural tropical montane forest to improvement fellings with the aim of favoring economically valuable target trees which will later be harvested with additional ecosystem impacts not considered here.  相似文献   
20.
We used height growth data from a 7-year field experiment with European beech (Fagus sylvatica L.) seedlings to test the hypothesis that the effects of above- and belowground resources on height growth depend on seedling size and age. Photosynthetically active radiation (PAR) was determined by hemispheric photography, and estimates of fine root biomass of the overstory trees were used as an inverse proportional surrogate for belowground resource availability. For recently germinated seedlings growing under the canopy of Picea abies (L.) Karst., belowground resource availability affected height growth more than light. During subsequent stages of seedling development, apart from initial seedling size, PAR increasingly determined seedling growth. Besides initial size, seedling age determined the effects of above- and belowground resources on seedling height growth. In seedlings identical in initial size but differing in age, the increase in height growth with increasing PAR was greater in older seedlings than in younger seedlings. The ranking of seedling height by year showed that small differences in size at the end of the first growing season resulted in continuously increasing differences during the following years. Mortality data indicated that the chances of a seedling surviving intraspecific competition was strongly determined by its dominance ranking within the first 5 years after establishment.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号