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   1698篇
  免费   250篇
  国内免费   29篇
  2024年   5篇
  2023年   31篇
  2022年   49篇
  2021年   81篇
  2020年   54篇
  2019年   104篇
  2018年   68篇
  2017年   71篇
  2016年   62篇
  2015年   81篇
  2014年   173篇
  2013年   173篇
  2012年   123篇
  2011年   117篇
  2010年   54篇
  2009年   73篇
  2008年   73篇
  2007年   68篇
  2006年   68篇
  2005年   51篇
  2004年   42篇
  2003年   38篇
  2002年   36篇
  2001年   35篇
  2000年   36篇
  1999年   24篇
  1998年   30篇
  1997年   18篇
  1996年   14篇
  1995年   15篇
  1994年   17篇
  1993年   16篇
  1992年   12篇
  1991年   6篇
  1990年   10篇
  1989年   7篇
  1988年   1篇
  1987年   4篇
  1986年   2篇
  1985年   2篇
  1984年   4篇
  1983年   6篇
  1982年   5篇
  1981年   3篇
  1980年   5篇
  1979年   2篇
  1978年   4篇
  1977年   2篇
  1975年   1篇
  1970年   1篇
排序方式: 共有1977条查询结果,搜索用时 171 毫秒
21.
内皮素-1对缺氧肺动脉平滑肌细胞的增殖作用   总被引:2,自引:0,他引:2  
内皮素(ET)是至今所发现的最强的内源性血管收缩肽,近年来发现ET-1能促进血管平滑肌细胞增殖。本研究表明ET-1对缺氧培养的肺动脉平滑肌细胞(PASMC)有剂量依赖的增殖作用,缺氧可促进PASMC的DNA合成且增加ET-1的丝裂原作用。ET-1的丝裂原作用主要由其A型受体(ETR_A)所介导,ETR_A的特异拮抗剂BQ123可显著抑制缺氧以及缺氧与ET-1协同所产生的增殖作用,而且发现ETR_A在缺氧培养的PASMC中的表达显著高于常氧对照组PASMC。本研究表明ET-1参与了缺氧性肺动脉结构重组,而缺氧可增强PASMC对ET-1的增殖反应性。  相似文献   
22.
In the last-larval instar of the tobacco hornworm, Manduca sexta, a switch from excretion of uric acid to storage in the fat body occurs during transition from the feeding to the wandering stage. Neuroendocrine control of this change from excretion to storage was demonstrated by neck-ligation experiments with synchronously reared larvae. Results indicate that a neurohormone is released from the head 24–30 hr before the initiation of wandering and coincident with the first release of ecdysone that initiates metamorphosis. Direct involvement of the moulting hormone was shown by the effects of multiple injections of 20-hydroxyecdysone into the abdomen of larvae that had been ligated before the release of hormone. Urate levels in the fat body were 20- to 100-fold higher from hormone-injected larvae as from saline inject controls. Topically applied juvenile hormone or methoprene reversed the 20-hydroxyecdysone-induced storage of urate. Increased levels of uric acid in the haemolymph during pupal development result from the presence of juvenile hormone, and the abrupt decrease in uric acid concentration in the haemolymph just prior to pupal ecdysis results from a decreased titre of juvenile hormone. Applications of methoprene prevented the decrease in uric acid levels in the haemolymph.  相似文献   
23.
Summary Endothelia of the anterior cerebral arteries in rats aged 1 to 3 days were studied. Thin (about 50–90 Å) and thick (about 100–110 Å) filaments are present in the endothelia. Numerous spherical- or rod-shaped bodies, measuring approximately 0.07 to 0.3 m in diameter and up to 0.6 m in length occur in the endothelial cells. These bodies contain a tubular structure. The diameter of the individual tubules is about 200 Å. The present observations suggest that spherical- or rod-shaped inclusions are first synthesized in the rough endoplasmic reticulum and thereafter these materials are transported into the Golgi complex for maturation. A small number of the inclusions, however, may originate directly from the rough endoplasmic reticulum and not pass through the Golgi apparatus.A part of this study was demonstrated at the 70th Versammlung der Anatomischen Gesellschaft in Düsseldorf, April, 1–5, 1975The author thanks Mr. Tatsuro Fukushima for preparation of photographs  相似文献   
24.
The unregulated activity of inteins during expression and consequent side reactions during work‐up limits their widespread use in biotechnology and chemical biology. Therefore, we exploited a mechanism‐based approach to regulate intein autocatalysis for biotechnological application. The system, inspired by our previous structural studies, is based on reversible trapping of the intein's catalytic cysteine residue through a disulfide bond. Using standard mutagenesis, the disulfide trap can be implemented to impart redox control over different inteins and for a variety of applications both in vitro and in Escherichia coli. Thereby, we first enhanced the output for bioconjugation in intein‐mediated protein ligation, also referred to as expressed protein ligation, where precursor recovery and product yield were augmented fourfold to sixfold. Second, in bioseparation experiments, the redox trap boosted precursor recovery and product yield twofold. Finally, the disulfide‐trap intein technology stimulated development of a novel bacterial redox sensor. This sensor reliably identified hyperoxic E. coli harboring mutations that disrupt the reductive pathways for thioredoxin and glutathione, against a background of wild‐type cells. Biotechnol. Bioeng. 2013; 110: 1565–1573. © 2012 Wiley Periodicals, Inc.  相似文献   
25.
《Reproductive biology》2020,20(3):408-416
Sepsis is defined as a systemic inflammatory response to infection. This study is aimed to evaluate the effects of experimental sepsis on the proliferation and apoptosis of granulosa and theca cells in the rat ovary.28-day-old immature Wistar-Albino female rats were treated with pregnant mare serum gonadotrophin to develop the first generation of preovulatory follicles. Sepsis was induced by cecal ligation and puncture (CLP). Following in vivo 5-Bromo-2-deoxyuridine (BrdU) labeling, animals were sacrificed and ovaries were embedded in paraffin and Epon. Besides electron microscopic evaluation, BrdU, cleaved caspase-3, p27 immunostaining, and TUNEL labeling were performed.In CLP-operated animals, cleaved caspase-3 immunoreactivity was significantly increased in Graafian follicles. TUNEL and BrdU labeling in the ovarian follicles were not statistically different between CLP and sham-operated rats. In septic animals, p27 immunoreactivity was increased significantly in the nuclei of oocytes and decreased in the cytoplasm of granulosa and theca cells in multilaminar primary follicles compared to the sham group. In ultrastructural evaluation, increased apoptosis was observed in theca interna and granulosa cells in both the early and late stages of follicles in the CLP group.In conclusion, experimentally-induced sepsis leads to apoptosis in ovarian follicles at advanced stages of development. Our data suggest that although sepsis may not cause a potential threat to developing follicles at least in the short term, more severe damage may occur during advanced stages of follicle development.  相似文献   
26.
Coronary artery disease (CAD) is one of the biggest threats to human life. Circulating microRNAs (miRNAs) have been reported to be linked to the pathogenesis of CAD, indicating the possible role in CAD diagnosis. The present study aimed to explore the expression profile of plasma miRNAs and estimate their value in diagnosis for CAD. 67 Non‐CAD control subjects and 88 CAD patients were enrolled. We conducted careful evaluation by RT‐PCR analysis, Spearman rank correlation coefficients analysis, Receiver Operating Characteristic (ROC) curves analysis and so on. The plasma levels of six miRNAs known to be related to CAD were measured and three of them showed obvious expression change. Circulating miR‐29a‐3p, miR‐574‐3p and miR‐574‐5p were all significantly increased. ROC analysis revealed the probability of the three miRNAs as biomarkers with AUCs (areas under the ROC curve) of 0.830, 0.792 and 0.789, respectively. They were significantly correlated with each other in CAD patients, suggesting the possibility of joint diagnosis. The combined AUC was 0.915, much higher than each single miRNA. Therefore, our study revealed three promising biomarkers for early diagnosis of CAD. The combination of these miRNAs may act more effectively than individual ones for CAD diagnosis.  相似文献   
27.
The current standard biomarker for myocardial infarction (MI) is high‐sensitive troponin. Although powerful in clinical setting, search for new markers is warranted as early diagnosis of MI is associated with improved outcomes. Extracellular vesicles (EVs) attracted considerable interest as new blood biomarkers. A training cohort used for diagnostic modelling included 30 patients with STEMI, 38 with stable angina (SA) and 30 matched‐controls. Extracellular vesicle concentration was assessed by nanoparticle tracking analysis. Extracellular vesicle surface‐epitopes were measured by flow cytometry. Diagnostic models were developed using machine learning algorithms and validated on an independent cohort of 80 patients. Serum EV concentration from STEMI patients was increased as compared to controls and SA. EV levels of CD62P, CD42a, CD41b, CD31 and CD40 increased in STEMI, and to a lesser extent in SA patients. An aggregate marker including EV concentration and CD62P/CD42a levels achieved non‐inferiority to troponin, discriminating STEMI from controls (AUC = 0.969). A random forest model based on EV biomarkers discriminated the two groups with 100% accuracy. EV markers and RF model confirmed high diagnostic performance at validation. In conclusion, patients with acute MI or SA exhibit characteristic EV biomarker profiles. EV biomarkers hold great potential as early markers for the management of patients with MI.  相似文献   
28.
Numerous studies have demonstrated that thioredoxin-interacting protein (TXNIP) expression of peripheral blood leucocytes is increased in coronary artery disease (CAD). However, the molecular mechanism of this phenomenon remained unclear. DNA methylation plays important roles in the regulation of gene expression. Therefore, we speculated there might be a close association between the expression of TXNIP and methylation. In this study, we found that compared with controls, DNA methylation at cg19693031 was decreased in CAD, while mRNA expressions of TXNIP and inflammatory factors, NLRP3, IL-1β, IL-18, were increased. Methylation at cg19693031 was negatively associated with TXNIP expression in the cohort, THP-1 and macrophages/foam cells. Furthermore, Transwell assay and co-cultured adhesion assay were performed to investigate functions of TXNIP on the migration of THP-1 or the adhesion of THP-1 on the surface of endothelial cells, respectively. Notably, overexpressed TXNIP promoted the migration and adhesion of THP-1 cells and expressions of NLRP3, IL-18 and IL-1β. Oppositely, knock-down TXNIP inhibited the migration and adhesion of THP-1 and expressions of NLRP3, IL-18. In conclusion, increased TXNIP expression, related to cg19693031 demethylation orientates monocytes towards an inflammatory status through the NLRP3 inflammasome pathway involved in the development of CAD.  相似文献   
29.
目的:探究Interlock可解脱弹簧圈在脾动脉瘤的腔内治疗中的应用价值。方法:回顾性分析2016年2月至2019年2月于本中心使用Interlock可解脱弹簧圈治疗的36例脾动脉瘤患者的临床资料,包括10例男性,26例女性,31例真性动脉瘤,5例假性脾动脉瘤,术前均行超声或CTA明确诊断。术中栓塞后,立即血管造影以明确技术成功率。围手术期及术后2周、3个月和6个月监测血常规、胰淀粉酶和主动脉CTA,观察并发症的发生情况。结果:6例患者弹簧圈栓塞动脉瘤远近端及瘤腔,其余仅栓塞脾动脉瘤瘤腔。术中DSA血管造影提示即刻脾动脉瘤栓塞闭塞率为97%以上,术中共使用128枚Interlock弹簧圈,其中104枚为钻石型,24枚为普通2D型。弹簧圈平均直径为6.3±4.2(2-12)mm,平均长度为16±13.5(3-32)mm,瘤体平均尺寸为40.6±12.5(15-70) mm。围手术期无并发症发生。平均随访10.0±3.2(6-15)个月,1月后2例出现脾梗死,7例发生轻微腹痛及低热等症状,所有病例均未见瘤腔再通和瘤体增大。结论:Interlock可解脱弹簧圈可以安全有效地治疗脾动脉瘤,但其远期疗效需长期随访观察。  相似文献   
30.
目的:探讨乌司他丁对非停跳冠脉搭桥术患者的心肺保护作用。方法:选取2017年12月-2019年4月我院收治的非停跳冠脉搭桥术患者76例,根据使用的药物不同分为两组,对照组应用常规方法,研究组应用乌司他丁,在麻醉之后切皮之前为T1,旁路血管开放时时间点为T2,手术结束为T3,手术之后的8 h为T4。比较两组治疗前后的心肺功能指标、动脉血气分析及血浆炎症因子、氧合指数术后恢复。结果:和T1进行对比时,两组T3、T4中的气道阻力(Air way Resistance,Raw)、呼吸指数(Respiratory Index,RI)、肺泡-动脉血氧分压差P(A-a)DO2均有所升高,在T2、T4中(PVR)有所升高,在T2、T3、T4中肺顺应性(Compliance of Lung,CL)有所降低。和对照组进行对比时,研究组在T3、T4中肺循环阻力(pulmonary vascular resistance, PVR)、RI、P(A-a)DO2有所降低,在T2、T3、T4中通气死腔百分比(VD/VT)有所降低(P0.05),在T2中CL有所升高(P0.05);治疗前,两组BNP、TNF-α、IL-6、IL-8无统计学意义(P0.05),治疗后BNP、肿瘤坏死因子(tumor necrosis factor-α,TNF-α)、白细胞介素-6 (Interleukin-6,IL-6)、白细胞介素-8 (Interleukin-8,IL-8)在T1、T2、T3、T4中低于对照组(P0.05),肌钙蛋白(cardiac troponin,cTnI)在T1中和对照组没有明显差异(P0.05),T2、T3、T4中研究组明显低于对照组(P0.05),研究组氧合指数高于对照组(P0.05);研究组T1、T2、T3、T4时平均动脉压(mean artery pressure,MBP)均高于对照组(P0.05),T1、T2、T3、T4时心率均低于对照组(P0.05);研究组ICU停留时间、ICU带气管插管时间、ICU机械通气时间、肺部并发症均低于对照组(P0.05)。结论:乌司他丁用于非停跳冠脉搭桥术的效果较好,可以保护患者的心肺功能。  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