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   363篇
  免费   43篇
  国内免费   166篇
  2024年   6篇
  2023年   10篇
  2022年   17篇
  2021年   23篇
  2020年   20篇
  2019年   18篇
  2018年   23篇
  2017年   18篇
  2016年   19篇
  2015年   25篇
  2014年   22篇
  2013年   24篇
  2012年   42篇
  2011年   50篇
  2010年   30篇
  2009年   25篇
  2008年   33篇
  2007年   18篇
  2006年   28篇
  2005年   22篇
  2004年   12篇
  2003年   19篇
  2002年   16篇
  2001年   9篇
  2000年   4篇
  1999年   4篇
  1998年   3篇
  1997年   2篇
  1996年   3篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1990年   1篇
  1988年   2篇
  1987年   2篇
  1983年   1篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1977年   1篇
  1975年   1篇
  1970年   3篇
  1968年   1篇
  1967年   1篇
  1966年   1篇
  1965年   1篇
  1964年   4篇
排序方式: 共有572条查询结果,搜索用时 31 毫秒
141.
Subcutaneous transplantation of mesenchymal stromal cells (MSC) emerged as an alternative to intravenous administration because it avoids the pulmonary embolism and prolongs post‐transplantation lifetime. The goal of this study was to investigate the mechanisms by which these cells could affect remote organs. To this aim, murine bone marrow–derived MSC were subcutaneously transplanted in different anatomical regions and the survival and behaviour have been followed. The results showed that upon subcutaneous transplantation in mice, MSC formed multicellular aggregates and did not migrate significantly from the site of injection. Our data suggest an important role of hypoxia‐inducible signalling pathways in stimulating local angiogenesis and the ensuing modulation of the kinetics of circulating cytokines with putative protective effects at distant sites. These data expand the current understanding of cell behaviour after subcutaneous transplantation and contribute to the development of a non‐invasive cell‐based therapy for distant organ protection.  相似文献   
142.
Polymorphisms in IL6, ACE and ATR genes are associated with obesity. Torque Teno virus (TTV) seems to be able to interfere with production of some proinflammatory cytokines associated with obesity and related phenotypes. The aim of this study was to test the potential association between obesity, TTV infection and the IL6 G-174C (rs1800795), ACE I/D (rs4646994), AT1R A1166C (rs5186) polymorphisms. The polymorphisms and the presence of TTV were detected in blood samples from 150 obese and 150 normal-weight, healthy subjects using PCR based methods. IL6-174 CC genotype was more frequent in all obese patients (P=0.02) and in patients without TTV infections (P=0.03) than in controls. Obese women had more frequent TTV infections compared with normal-weight women (P=0.046). Obese subjects, regardless of gender (women P=0.03, men P=0.04), and healthy normal-weight men (P<0.01) carriers of AT1R C allele had higher triglycerides levels compared with non-carriers. The frequency of TTV in the control group (70.67%) was similar to data reported in other populations. The present study indicated that IL6-174 CC genotype and TTV infections in women could be associated with the common form of obesity.  相似文献   
143.
【目的】探明危害我国柑橘的实蝇种类以及柑橘大实蝇Bactrocera minax不同地理种群和不同寄主种群的遗传多样性。【方法】利用mtDNA COI基因对危害柑橘的果实蝇进行种类鉴定,采用MEGA软件对其中28个地理种群的535头果实蝇COI基因片段(约505 bp)序列进行比对,分析种间及种内遗传距离,构建系统发育树。使用DnaSP软件分析柑橘大实蝇不同地理种群和不同寄主种群的遗传多样性。【结果】从柑橘虫果内共鉴定出4种实蝇,分别为柑橘大实蝇B.minax、桔小实蝇B.dorsalis、蜜柑大实蝇B.tsuneonis和瑞丽果实蝇B.ruiliensis。这4种实蝇的种间遗传距离为0.0264~0.2410,种内遗传距离为0.0000~0.0140,种间与种内遗传距离没有重叠区域。单个柑橘虫果内一般仅有1种实蝇,极个别柑橘果实可同时被两种实蝇危害(4/43);在这些为害柑橘的实蝇种类中,以柑橘大实蝇的个体数量比例最大,占90.70%。柑橘大实蝇地理种群遗传多样性高,28个种群共有17个单倍型。【结论】柑橘大实蝇是所调查地区柑橘实蝇的绝对优势种,其种群遗传分化程度较高,扩散危害风险大。本研究结果对柑橘果实蝇类的监测和防控具有重要意义。  相似文献   
144.
145.
以郁金香的两个品种‘朱迪斯'(‘Judith Leyster')和‘大笑'(‘Big Smile')为材料,采用石蜡切片法确定其花芽分化进程,并测定花芽分化期鳞茎内碳水化合物和可溶性蛋白质含量的变化。结果表明,郁金香花芽分化过程中,两个品种的碳水化合物含量的变化趋势较为接近。随着鳞茎含水量的下降,可溶性总糖和可溶性蛋白含量均呈先增加后减少的趋势。淀粉含量的变化呈现波动性,而淀粉酶活性则持续增强并在后期达到稳定水平。鳞片中可溶性糖含量和淀粉酶活性同时增加是郁金香花芽形态分化启动的标志。相比于外层鳞片,内层鳞片是为花芽原基生长发育提供营养物质的首要场所。  相似文献   
146.
doi:10.1111/j.1741‐2358.2009.00318.x
Palatal and mandibular tori in a Romanian removable denture‐wearing population Objective: To establish the prevalence of palatal tori (TP) and mandibular tori (TM) in a Romanian denture‐wearing population in order to see how or if tori influenced the denture design or the treatment planning. Background data: There are no available data regarding tori in an elderly Romanian population and its implication for treatment planning. It could be considered a local factor influencing the quality of prosthetic treatment. Material and method: Tori prevalence was investigated in 251 patients, with an average age of 62 years. A statistical analysis was made, using odds ratio (OR) for the distribution related to gender and the Chi‐squared test for the differences in prevalence related to age groups. Treatment planning difficulties because of presence of tori were recorded. Results: Frequency of TP was significantly higher in both genders (OR = 2.0661 and p = 0.0446) and non‐significant frequency for distribution between genders for TM (OR = 0.9421 and p = 0.8273). The differences in age groups showed both tori types have a variable prevalence related to age. The most frequent location for TP was found in the posterior one‐third and two‐thirds of the palate and for TM in the canine and first premolar area presenting with different sizes. Conclusions: Tori prevalence in our study group is high and is significantly related to age (p < 0.05) having a peak at over 60 years. The preferential site of TP in the posterior palatal area and this location has an impact on decision making in treatment planning for the upper denture.  相似文献   
147.
A series of 82 5-aryl-2-thio-1,3,4-oxadiazole derivatives were screened for their anti-mycobacterial activities against Mycobacterium tuberculosis H37Rv. The synthesized compounds 30-37 appeared to be the most active derivatives exhibiting more than 90% inhibition of mycobacterial growth at 12.5 μg/mL. Structure-activity relationships study was performed for the given series by using the electronic-topological method combined with neural networks (ETM-NN). A system for the anti-mycobacterial activity prediction was developed as the result of training associative neural network (ASNN) with weights calculated from projections of a compound and each pharmacophoric fragment found on the elements of the Kohonen's self-organizing maps (SOMs). From the detailed analysis of all compounds under study, the necessary requirements for a compound to possess antituberculosis activity have been formulated. The analysis has shown that any requirement's violation for a molecule implies a considerable decrease or even complete loss of its activity. Molecular docking studies of the compounds allowed shedding light on the binding mode of these novel anti-mycobacterial inhibitors.  相似文献   
148.
目的:探讨老年男性原发性高血压(EH)患者脉压(PP)与动脉粥样硬化性颈动脉狭窄(CS)的关系。方法:对入选的157例伴有颈动脉粥样硬化的老年男性EH患者行颈动脉超声检查,并收集行颈动脉超声检查前1年内的多次血压水平及临床资料,根据颈动脉狭窄程度分为:CS〈50%组(n=66)及CS≥50%组(n=91),并进一步将颈动脉狭窄程度分级(I—V级),分析颈动脉狭窄的危险因素及与脉压的相关性。结果:①CS≥50%组收缩压(SBP)及PP显著高于CS〈50%组,而舒张压(DBP)显著低于CS〈50%组(P〈0.05),CS≥50%组的独立危险因素是外周动脉疾病(OR:4.543,95%CI:1.415.14.590)及脉压(OR:1.096,95%CI:1.038.1.157);②CS分级与PP(r=0.402,P〈0.01)及血浆纤维蛋白原(FIB)(r=0.200,P〈0.05)呈正相关,经校正年龄、体重指数(BMI)、SBP、DBP、总胆固醇(TO)、甘油三酯(TG)、高密度脂蛋白胆固醇(HDL-c)、低密度脂蛋白胆固醇(LDL-c)、D-二聚体(D-dimer)、血尿酸(UA)、空腹血糖(FBG)、氨基酸末端脑利钠肽前体(NT-proBNP)、总胆红素(TBIL)及直接胆红素(DBIL)等危险因素后,CS分级仍与PP及FIB有关。结论:老年男性原发性高血压患者脉压与颈动脉狭窄有关,治疗高血压的同时应当尽量减小脉压。  相似文献   
149.
永智丞  刘吉平  司薇 《生态学报》2020,40(20):7401-7409
向海自然保护区位于中国东北地区西部的半湿润半干旱气候区,是盐碱沼泽湿地集中分布区。近年来,受到气候变化和人类活动的影响,湿地退化严重,生物多样性下降。基于"压力-状态-响应"理论,利用层次分析方法构建湿地修复效果评估模型,构建了3个综合指标和19个评价因子在内的湿地评价指标体系,对退化湿地修复效果进行评估。结果表明,与2015年相比,2017年仙鹤岛修复示范区湿地植被盖度在原有基础上提高45.83%,水禽数量和种类分别提高40.41%和61.54%,水质综合污染指数下降了8.70%,土壤盐度指数下降了8.82%。与2015年的湿地评价值0.4481相比,2017年湿地评价值为0.5537,修复效果值提高了23.57%,向海湿地的退化状况得到明显改善,达到了湿地的修复效果,该研究对于湿地的恢复与管理具有一定意义。  相似文献   
150.
[目的]初步探讨不同浓度外源茉莉酸甲酯(MeJA)诱导大麦抗叶斑病效应差异及其分子机制,为应用MeJA防治大麦叶斑病提供理论依据。[方法]以‘蒙啤麦3号’大麦品种幼苗为材料,设置不接菌(无菌水处理叶片)、接菌(无菌水处理叶片接种麦根平脐蠕孢菌)和接菌+MeJA(0.5、1.0、1.5、2.0、2.5 mmol/L MeJA喷施叶片后接菌)3组处理,于三叶期调查叶斑病发病情况并据此筛选最适MeJA浓度,然后测定不接菌、接菌及接菌++ MeJA(最适浓度)处理不同处理时间叶片的抗氧化酶、抗病相关酶活性、丙二醛、渗透调节物质含量以及相关基因表达水平。[[结果]]:(1)叶面喷施外源MeJA提高了大麦对叶斑病的抗性,1.5 mmol/L MeJA处理叶片的病情指数较对照显著降低19.03%,诱导抗性效果最佳;(2)与单独接菌处理相比,1.5 mmol/L MeJA处理大麦叶片超氧化物歧化酶、过氧化物酶、过氧化氢酶、几丁质酶和β-,1,3-葡聚糖酶活性均显著提高,而其丙二醛、脯氨酸、可溶性糖和可溶性蛋白含量显著降低,同时其受MeJA调控转录因子及编码抗病相关酶的基因表达量显著上调。[结论]外源喷施1.5 mmol/L MeJA通过调节抗病相关酶活性和渗透调节物质含量,以及调控抗病相关酶基因及茉莉酸信号途径关键转录因子基因表达,进而提高大麦植株的叶斑病抗病性。  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