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   110篇
  免费   3篇
  国内免费   17篇
  2021年   1篇
  2020年   1篇
  2019年   2篇
  2018年   16篇
  2017年   8篇
  2016年   5篇
  2014年   4篇
  2013年   3篇
  2012年   5篇
  2011年   7篇
  2010年   3篇
  2009年   8篇
  2008年   5篇
  2007年   9篇
  2006年   2篇
  2005年   1篇
  2004年   3篇
  2003年   2篇
  2002年   9篇
  2001年   4篇
  2000年   3篇
  1999年   5篇
  1998年   4篇
  1997年   3篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1992年   2篇
  1991年   1篇
  1989年   1篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1981年   1篇
  1975年   1篇
排序方式: 共有130条查询结果,搜索用时 31 毫秒
61.
Rühl T  Böttcher C  Hennig L  Burger K 《Amino acids》2004,27(3-4):285-290
Summary. Hexafluoroacetone was applied as a bidentate protecting and activating agent for the syntheses of RGD-peptide mimetics starting from iminodiacetic acid in solution and on solid phase.  相似文献   
62.
中国竹亚科镰序竹属一新种——匍匐镰序竹   总被引:3,自引:0,他引:3  
报道了福建厦门园林植物园发现的中国竹亚科Bambusoideae镰序竹属一新种——匍匐镰序竹Drepanostchvum stotonfrme S.H.Chen&Z.Z.Wang。该种与坝怕D.microphyllum(Hsueh&Yi)Keng f.ex Y相似,区别在于本种植株藤本状极明显,竿匍匐状,较细,竿直径3-6mm,竿壁厚约lmm;全竿25-55节.竿基部数节节间长5-9cm,中部节间长13-18cm,节内长l-2mm;箨舌高约O.5mm,具长约2mm的纤毛:叶舌高约3mm,具长约4mm纤毛;叶片较小,在成竹时长2-6cm,宽O.3-0.6cm,叶片次脉3-4对。  相似文献   
63.
Choi SB  Wha JD  Park S 《Life sciences》2004,75(22):2653-2664
In the present study, we screened candidates for enhancing insulin action, using glucose uptake as an indicator, from Liriope platyphylla Wang et Tang (LPWT) extract, Liliaceae, in 3T3-L1 adipocytes. The mechanism of insulin sensitizing action in the fractions was also investigated. LPWT extract with 70% MeOH was sequentially separated with Diaion HP-20 and silica gel column chromatography. The 9:1 fraction from silica gel column chromatography increased glucose uptake with 1 ng/mL up to glucose uptake with 50 ng/mL insulin. The 9:1 fraction, determined as homoisoflavone-enriched fraction, worked as an insulin sensitizer. It increased insulin stimulated glucose uptake in 3T3-L1 adipocytes, insulin responsive cells, through increased glucose transporter 4 (GLUT4) contents in the plasma membrane. GLUT4 translocation was increased through insulin receptor substrate 1 (IRS1)-PI3 kinase-Akt signaling mechanism. Thus, homoisoflavone-enriched fraction in LPWT extract played an important role as an insulin sensitizer in adipocytes.  相似文献   
64.
65.
The inflammatory microenvironment plays a critical role in the development and progression of malignancies. In the present study, we aimed to evaluate the prognostic value of lymphocyte-related inflammation and immune-based prognostic scores in patients with chordoma after radical resection, including the neutrophil-lymphocyte ratio (NLR), platelet-lymphocyte ratio (PLR), monocyte-lymphocyte ratio (MLR), and systemic immune-inflammation index (SII). A total of 172 consecutive patients with chordoma who underwent radical resection were reviewed. R software was used to randomly select 86 chordoma patients as a training set and 86 chordoma patients as a validation set. Potential prognostic factors were also identified, including age, sex, tumor localization, KPS, Enneking stage, tumor size, and tumor metastasis. Overall survival (OS) was calculated using the Kaplan–Meier method and multivariate Cox regression analyses. NLR, PLR, SII, Enneking stage, tumor differentiation and tumor metastasis were identified as significant factors from the univariate analysis in both the training and validation sets and were subjected to multivariate Cox proportional hazards analysis. The univariate analysis showed that NLR ≥1.65, PLR ≥121, and SII ≥370×109/L were significantly associated with poor OS. In the multivariate Cox proportional hazard analysis, SII, Enneking stage and tumor metastasis were significantly associated with OS. As noninvasive, low-cost, reproducible prognostic biomarkers, NLR, PLR and SII could help predict poor prognosis in patients with chordoma after radical resection. This finding may contribute to the development of more effective tailored therapy according to the characteristics of individual tumors.  相似文献   
66.
BACKGROUND: Increasing bodies of evidence suggest that metformin may be beneficial in the primary prevention of colorectal cancer (CRC), and a dose–response relationship has been reported. However, long-term epidemiological observations between the treatment period, cumulative dose, and intensity of metformin and CRC are rarely reported. The aim of this study was to identify the association between the effect of metformin and CRC development in a nationwide cohort study. METHODS: This nationwide population-based study examined a cohort of 1,000,000 patients randomly sampled from individuals enrolled in the Taiwan National Health Insurance system. Patients with newly diagnosed type 2 diabetes mellitus (DM) between 1997 and 2007 were enrolled. A statistical variables, including the demographic data, treatment period, cumulative dose, and intensity of metformin use, was compared between patients developing CRC and those without CRC. RESULTS: This study included 47,597 patients. The mean follow-time was 7.17 ± 3.21 years. After adjustment, metformin use was an independent protective factor against CRC development (P < .001). Although the protective ability of metformin against CRC development was reduced during long-term therapy, the risk of CRC decreased progressively with a higher cumulative dose or higher intensity of metformin use (both P < .001). CONCLUSION: This study revealed that metformin use significantly reduced the risk of CRC in a dose-dependent manner in patients with type 2 DM in the Taiwanese population. However, a gradual decline in medication adherence may reduce the protective ability of metformin against CRC development during long-term therapy.  相似文献   
67.
OBJECTIVES: To report the long-term outcome and toxicity of locoregionally advanced nasopharyngeal carcinoma (LA NPC) treated with nimotuzumab (h-R3) plus intensity-modulated radiotherapy (IMRT) with or without chemotherapy. METHODS: From May 2008 to March 2014, 3022 newly histology-proven, nonmetastatic NPC patients were retrospectively reviewed; among them, 257 patients treated with h-R3 were enrolled in this study. The patients' age range was between 10 and 76 years. The distribution of patients by disease stage was 150 (58.4%) in stage III, 88 (34.2%) in stage IV A, and 19 (7.4%) in stage IV B. All the patients received the treatment of h-R3 plus IMRT, and from them, 239 cases were also treated with cisplatin-based chemotherapy. Acute and late radiation-related toxicities were graded according to the Acute and Late Radiation Morbidity Scoring Criteria of Radiation Therapy Oncology Group. The accumulated survival was calculated according to the Kaplan-Meier method. Log-rank test was used to compare the survival difference. Multivariate analysis was performed using Cox's proportional-hazard model. RESULTS: All 257 patients had completed combined treatment; 231 patients received h-R3 plus IMRT with induction chemotherapy (IC), while 26 patients received only h-R3 plus IMRT. With a median follow-up of 48 months (range, 13-75 months), the estimated 5-year local recurrence-free survival, regional recurrence-free survival, distant metastases-free survival, progression-free survival, and overall survival (OS) rates were 94.3%, 94.8%, 91.9%, 83.4%, and 86.2%, respectively. Univariate analysis showed that age, T stage, clinical stage, and IC were related with OS. Multivariate analysis indicated that T stage and IC were independent prognostic factors for OS. The incidence of grade 3 to 4 acute mucositis and leukocytopenia was 10.9% and 19.8%, respectively, with no cases of skin rash and infusion reaction. Xerostomia was the most common late complication, and the degree of dry mouth in most survivors was mild to moderate at the last follow-up time. CONCLUSION: h-R3 plus IMRT with or without chemotherapy showed promising outcomes in terms of locoregional control and survival without increasing the incidence of radiation-related toxicities for patients.  相似文献   
68.
银缕梅物种濒危度的定量分析   总被引:12,自引:0,他引:12  
采用二级模糊综合评判法进一步分析现存个体和居群数均极少的中国金缕梅科一新属种──银缕梅的物种濒危度。首先挑选对小种群绝灭有影响的随机干扰因素,建立了包括20个评价指标在内的因素集。然后通过对评价指标定量化和权分配一系列处理,并通过最初一、二层的综合评判,求得濒危度和保护等级,进而确定物种的濒危状态及其在省级和国家级的保护序次。研究结果表明,二级模糊综合评判的方法十分灵敏,可操作性强,它能比较准确地反映植物物种实际濒危状况。  相似文献   
69.
采用SSR分子标记分析延胡索的遗传多样性,筛选出多态性高、稳定性好的12对引物,对19个居群360份延胡索样品进行了群体遗传分析。结果表明:(1)12对SSR引物共扩增出多态性位点227个,检测到4~9个等位基因,平均等位基因数目为5.25个,表现出丰富的多态性;延胡索居群具有较高的遗传多样性(Na=5.25,I=1.192 6,H=0.387 9),物种间遗传分化程度高(Fst=0.388 3),基因流较弱(Nm=0.393 8)。(2)UPGMA聚类分析和贝叶斯距离分析结果表明,19个居群明显聚为4大支;Mantle Test结果(r=0.326,P=0.01)表明,地理位置相近的种群亲缘关系更近。研究认为,延胡索的遗传结构是该物种自交为主的繁育系统、克隆生长、地理隔离以及居群间有限的基因流共同作用的结果,故对该物种的保护应以就地保护为主。  相似文献   
70.
通过野外调查和随机取样法,对仅产于陕西勉县的中国特有濒危植物秦岭石蝴蝶( Petrocosmea qinlingensis W. T. Wang)群落的维管植物组成、垂直结构和分布区类型及其种群特征和土壤化学性质进行了调查和分析;在此基础上,初步探讨了该种类的濒危原因。调查结果显示:秦岭石蝴蝶为喜阴植物,仅分布于山体海拔约640 m的区域,种群面积仅约42 m2;土壤为黄棕壤,呈中性(pH 6.50),土壤中有机质含量较高,全氮、全磷和全钾含量较低,有效铁、有效镁、有效钠和有效钙含量则较高;秦岭石蝴蝶种群中个体数量约1000株,多生长于覆有土壤或苔藓的岩石上,也有部分成年个体生长在裸露且瘠薄的岩石上。秦岭石蝴蝶群落中共有维管植物28种,隶属于23科28属;其中,蕨类植物3科4属4种,裸子植物1科1属1种,被子植物19科23属23种,优势科和优势属不明显。秦岭石蝴蝶群落垂直结构明显,可分为乔木层、灌木层和草本层,其中,乔木层优势种为杜仲( Eucommia ulmoides Oliver),灌木层优势种为华西小石积( Osteomeles schwerinae Schneid.),草本层优势种为裂叶荨麻( Urtica lobatifolia S. S. Ying)。该群落维管植物科的分布型以热带分布型科为主,其中泛热带分布型科占明显优势;属的分布型以温带分布型属为主,其中北温带分布型属占优势;中国特有分布的科和属均很少;总体上看,该群落具有暖温带向亚热带过渡的特点。在秦岭石蝴蝶种群的不同样方中,成年个体和幼苗数量均有一定差异,成年个体占14.6%~37.5%,幼苗占61.3%~80.0%,幼苗数量明显高于成年个体;各样方的单株叶片数为7~9,冠幅为6.0~7.2 cm,大多数样方的单株结实量小于4,表明在同一个种群的不同生境中秦岭石蝴蝶的分布和生长状况有明显差异。根据调查结果,推测种群规模较小、分布范围狭窄以及人为干扰可能是造成秦岭石蝴蝶濒危的主要原因,而人为干扰是其中的重要原因。  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