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   179篇
  免费   50篇
  国内免费   16篇
  2024年   1篇
  2023年   8篇
  2022年   11篇
  2021年   13篇
  2020年   17篇
  2019年   9篇
  2018年   6篇
  2017年   13篇
  2016年   3篇
  2015年   7篇
  2014年   12篇
  2013年   17篇
  2012年   12篇
  2011年   11篇
  2010年   14篇
  2009年   17篇
  2008年   10篇
  2007年   11篇
  2006年   5篇
  2005年   8篇
  2004年   9篇
  2003年   3篇
  2002年   3篇
  2001年   4篇
  1999年   1篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1995年   7篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
排序方式: 共有245条查询结果,搜索用时 15 毫秒
1.
Dendrobium wangliangii is an epiphytic orchid distributed in the Jinshajiang dry‐hot valley in Luquan County, Yunnan Province, China. Most Dendrobium spp. typically have a low fruit set, but this orchid shows a higher fruit set under natural conditions despite the lack of effective pollinators. The pollination biology of the critically endangered D. wangliangii was investigated in this study. A fruit set rate of 33.33 ± 4.71% was observed after bagging treatment in 2017 and a high fruit set rate (65.72 ± 4.44% in 2011; 50.79 ± 5.44% in 2017) was observed under natural conditions, indicating that D. wangliangii is characterized by spontaneous self‐pollination. The anther cap blocked the growing pollinium; thus, the pollinium slid down and reached the stigmatic cavity, leading to autogamous self‐pollination. Specifically, 51.50% of 162 unopened flowers (total 257 flowers) of this Dendrobium species under extreme water‐deficit conditions developed into fruits, suggesting the presence of cleistogamy in D. wangliangii. Here, cleistogamy may represent the primary mode of pollination for this orchid. Spontaneous self‐pollination and specific cleistogamous autogamy could represent major adaptions to the drought and pollinator‐scarce habitat in the Jinshajiang dry‐hot valley.  相似文献   
2.
目的 从微生态学角度研究石斛多糖治疗肠道微生态失调小鼠的作用及初步机制.方法 盐酸林可霉素灌胃制备肠道菌群失调小鼠模型,应用石斛多糖进行治疗,同时设正常对照组、丽珠肠乐组、阴性对照组,给药7d后处死小鼠,应用PCR-DGGE法检测肠道菌群丰富度、血清IL-2.结果 应用盐酸林可霉素灌胃3d后,小鼠肠道菌群丰富度、血清IL-2降低,持续治疗7d后,石斛多糖治疗小鼠肠道菌群丰富度、血清IL-2增高.结论 石斛多糖具有扶植肠道正常菌群生长,调整菌群失调,提高机体免疫力的作用.  相似文献   
3.
氮源和真菌诱导子对铁皮石斛原球茎悬浮培养的影响   总被引:2,自引:0,他引:2  
利用正交实验设计研究不同种类和浓度的氮源对铁皮石斛原球茎生长的影响,利用完全随机实验设计研究不同真菌诱导子对铁皮石斛原球茎生长和多糖积累的影响.结果表明硝态氮促进铁皮石斛原球茎鲜重和干重的增加( P <0.05);铵态氮促进铁皮石斛原球茎鲜重增加( P <0.05).无论鲜重还是干重,硝态氮和铵态氮的影响均不存在互作,最佳组合为:67-V培养液 100 mg/L (NH4)2SO4 800 mg/L KNO3 30 g/L蔗糖 200 g/L马铃薯提取汁.F检验的结果表明,14种真菌诱导子对铁皮石斛原球茎生物量的增加(鲜重与干重)均无显著性影响( P >0.05).但与对照铁皮石斛原球茎的多糖含量相比,真菌诱导子g6、g14、g5、g4处理可使其多糖含量分别提高14%、9%、6%、4%.本研究获得了有利于铁皮石斛原球茎生长的硝态氮和铵态氮的最佳搭配方案以及有利于铁皮石斛原球茎积累多糖的四种真菌诱导子,表明通过液体悬浮培养生产铁皮石斛原球茎及其多糖成分具有较好的开发应用前景.  相似文献   
4.
细叶石斛有效成分分析及其水溶性提取物的血管舒张活性   总被引:8,自引:0,他引:8  
对细叶石斛(DendrobiumhancockiiRofle)茎上部、茎中部、茎下部和根中的多糖、生物碱和矿质元素含量进行了分析,并研究了其水溶性提取物对SD大鼠胸主动脉血管的舒张效应。结果表明,细叶石斛中总多糖含量较高,并含有较多的钾、钙、镁、铁、锰、锶、钛和铜等元素,与细茎石斛〔D.moniliforme(L.)Sw.〕及铁皮石斛(D.officinaleKimuraetMigo)相比,其水溶性多糖和生物碱的含量较低,而且不同部位中的含量存在差异。细叶石斛水溶性提取物强烈拮抗苯肾上腺素所致的大鼠胸主动脉血管收缩作用,对内皮完整和无内皮功能的2种样本均引起类似的浓度依赖性舒张效应,相关系数有显著意义(>r0.01),两者的IC50分别为0.309和0.404g L。  相似文献   
5.
A water-soluble polysaccharide DNP-W2 composed of glucose, mannose, and galactose in the molar ratio of 6.1:2.9:2.0 had been isolated from the stems of Dendrobium nobile. Its molecular weight was 1.8 × 104 Da determined by HPGPC. Structural features of DNP-W2 were investigated by a combination of chemical and instrumental analysis, including FTIR, GC, GC-MS, periodate oxidation-Smith degradation, methylation analysis, partial acid hydrolysis, and NMR spectroscopy. The results showed that DNP-W2 is a 2-O-acetylgalactomannoglucan and has a backbone consisting of (1→4)-linked β-d-Glcp, (1→6)-linked β-d-Glcp, and (1→4)-linked β-d-Manp, with branches at O-6 of (1→4)-linked β-d-Glcp and β-d-Manp. The branches are composed of α-d-Galp. The acetyl groups are substituted at O-2 of (1→4)-linked Manp. Preliminary tests in vitro reveals that DNP-W2 can stimulate ConA- and LPS-induced T and B lymphocyte proliferation.  相似文献   
6.
Dendrobium officinale has been considered over past centuries to be extremely valuable for use as an herbal medicine in South Asian countries. In this work, the chemical profiles of D. officinale from different habitats were systematically characterized using ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-Q-TOF-MS) and multivariate analysis. The principal component analysis (PCA), partial least squares discriminate analysis (PLS-DA) and orthogonal partial least squares analysis (OPLS-DA) of UPLC-Q-TOF-MS data displayed an obvious separation. Several flavonoids and terpenoids derivatives contribute to the quantitative chemotypic variation within and between the samples as observed. These findings lead to a better understanding of the phytochemical variation of D. officinale which can aid in quality control of raw material.  相似文献   
7.
Vegetative anatomy and systematics of subtribe Dendrobiinae (Orchidaceae)   总被引:5,自引:0,他引:5  
Anatomy of leaf, stem, and root of more than 100 species in subtribe Dendrobiinae (Orchidaceae) was studied with the light microscope to provide a comparative anatomical treatment of these organs, to serve as an independent source of evidence that might be taxonomically important, and to recommend such reinterpretations of existing classifications as are suggested by a phylogenetic assessment of data. We based our classification on that of Rudolf Schlechter as the most complete and widely accepted today. We found that the anatomy of plants in subtribe Dendrobiinae reflects a high degree of morphological diversity, and many of the anatomical characters appear to be homoplasous. When these anatomical data are used to interpret the systematic relationships among the genera, they indicate that Dendrobium is not monophyletic and that Cadetia and Pseuderia are apparently nested within the structure of Dendrobium when section Grastidium is chosen as a functional outgroup. Lack of resolution in the strict consensus tree illustrates the difficulty of determining the phylogenetic relationships of many of Schlechter's sections using anatomical characters. Nevertheless, we recommend that his sectional classification, with appropriate modifications based on available data, be retained for the present, pending a more detailed understanding of the phylogeny of Dendrobiinae based on morphology, micromorphology, anatomy, and DNA studies.  相似文献   
8.
对采自广西、云南和广东的美花石斛(Dendrobium loddigesii Rolfe)野生植株根、茎和叶内的内生细菌进行分离并测定其促生特性,采用扩增核糖体DNA限制性酶切分析(ARDRA)与UPGMA聚类分析相结合的方法对内生细菌菌株进行分类并确定优势属;在此基础上,对具有解磷、解钾和产生长素能力的菌株进行促生潜力评价。结果显示:从不同产地美花石斛植株不同部位共分离得到67株内生细菌菌株,其分布呈现出组织与地区的特异性;其中,来源于广西的植株中菌株数量最多(42株),分离自茎的菌株数量最多(34株)。67株内生细菌菌株可分为31个ARDRA簇,经16S rDNA序列比对鉴定为12个属,包括假单胞菌属(Pseudomonas)、微杆菌属(Microbacterium)、肠杆菌属(Enterobacter)、芽孢杆菌属(Bacillus)、鞘氨醇单胞菌属(Sphingomonas)、葡萄球菌属(Staphylococcus)、嗜冷杆菌属(Psychrobacter)、短波单胞菌属(Brevundimonas)、涅斯捷连科氏菌属(Nesterenkonia)、副球菌属(Paracoccus)、泛菌属(Pantoea)和沙雷氏菌属(Serratia),其中芽孢杆菌属、微杆菌属和肠杆菌属为优势属;来源于广西的植株中内生细菌的丰度与多样性均高于其他两地。在67株内生细菌菌株中,有30株菌株具有解无机磷和解有机磷的双重能力、22株具有解钾能力、24株具有产生长素能力,其中仅8株菌株兼具3种促生能力。组培实验结果显示:在培养基中接种1×106CFU·mL-1芽孢杆菌DLB20菌株,对株高2~3 cm和3~4 cm的美花石斛试管苗生长有促进作用,且更有利于株高3~4 cm试管苗的生根,表明具有解磷、解钾和产生长素能力的菌株对美花石斛试管苗有一定的促生潜力。  相似文献   
9.
超微铁皮石斛对脾虚便秘小鼠肠道微生物及酶活的影响   总被引:1,自引:0,他引:1  
目的探讨超微铁皮石斛对脾虚便秘小鼠肠道微生物及酶活性的影响。方法采用灌胃番泻叶水煎液7 d后控制饮食,饥饱失常8 d,进行小鼠脾虚便秘造模。设模型组、正常组和治疗组,模型组和正常组灌胃无菌水,治疗组分别灌胃给药铁皮石斛传统汤剂、超微全量汤剂、超微50%量汤剂和超微25%量汤剂,共7 d,然后采集肠道内容物分析肠道菌群及酶活。结果模型组五类可培养微生物(细菌总数、大肠埃希菌、乳酸菌、双歧杆菌和真菌)数量与正常组比较差异均有统计学意义(P〈0.01);铁皮石斛传统汤剂组大肠埃希菌数,铁皮石斛超微50%量汤剂组细菌总数、大肠埃希菌和真菌数,超微25%量汤剂组细菌总数和大肠埃希菌数均达到正常组水平(P〉0.05);铁皮石斛超微全量汤剂组和超微50%量汤剂组对纤维素酶的影响作用相当,均达到正常组水平(P〉0.05),铁皮石斛三种不同剂量的超微汤剂对木聚糖酶活性的影响作用相当(P〉0.05),铁皮石斛超微全量汤剂组淀粉酶活性与正常组相当(P〉0.05)。结论铁皮石斛传统汤剂、超微全量汤剂和超微50%量汤剂对脾虚便秘均有很好的疗效,能够调控肠道微生态平衡及肠道酶活性。  相似文献   
10.
中国石斛属一新种   总被引:5,自引:0,他引:5  
Dendrobium fanjingshanense Z. H. Tsi ex X. H. Jin et Y. W. Zhang, sp. nov. Fig. 1 Habitu D. wilsonii Rolfe simile, a quo tepalis revolutis fulvis, lobo labelli intermedii infra medium macula una flabellata purpurea ornato. Epiphyticum; caulis teres, 20~40 cm altus, 2~3 mm crassus, caespitosus, superne 5~6-foliatus, internodiis 1~1.5 cm longis. Folia oblongo-lanceolata, subcoriacea, 2~5 cm longa, 5~15 mm lata, apice obtusa et plus minusve hamata, basi vaginis tubulatis membranaceis obtecta. Inflorescentiae e lateribus partium superarum caulium annotinorum defoliatorum nascentes, versus apicem caulis laterales, 1~2-florae; pedunculi 2~3 mm longi, ca. 1 mm crassi, basi vaginis 3~4 membranaceis 3~4 mm longis instructi; bracteae ovato-triangulatae, 3~5 mm longae, apice acutae, macula atro-fusca ornatae. Flores patentes; pedicelli cum ovario ca. 2~3 cm longi; tepala revoluta, fulva, apice obtusa; sepalum intermedium oblongum 2 cm longum, medio 6~7 mm latum, apice fere obtusum; sepala lateralia paulo oblique ovato-lanceolata, sepalo intermedio aequilonga sed medio paulo angustiora, apice obtusa, basi cum pede columnae mentum obconoideum ca. 8 mm longum 6 mm latum apice obtusum formantia; petala subelliptica, ca. 2 cm longa, medio 6 mm lata, apice subobtusa; labellum fulvum, basi purpureum et dense velutinum, obscure trilobatum, lobis lateralibus semiorbiculatis erectis, basi (inter lobos laterales) callo uno purpureo praeditis, lobo intermedio ovato, ca. 1 cm longo, 7 mm lato, apice subacuto et recurvo, supra medio carinato, glabro; columna alba, ca. 3 mm longa, basi in pedem ca. 9 mm longum producta, pede medio purpurato, glabro; operculum antherae album, ambitu rhombicum, glabrum; pollinia 4.  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