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   6254篇
  免费   731篇
  国内免费   1085篇
  2024年   15篇
  2023年   99篇
  2022年   201篇
  2021年   399篇
  2020年   316篇
  2019年   386篇
  2018年   363篇
  2017年   300篇
  2016年   323篇
  2015年   542篇
  2014年   581篇
  2013年   614篇
  2012年   743篇
  2011年   627篇
  2010年   399篇
  2009年   317篇
  2008年   360篇
  2007年   266篇
  2006年   234篇
  2005年   202篇
  2004年   165篇
  2003年   131篇
  2002年   116篇
  2001年   67篇
  2000年   61篇
  1999年   51篇
  1998年   33篇
  1997年   24篇
  1996年   13篇
  1995年   16篇
  1994年   25篇
  1993年   16篇
  1992年   14篇
  1991年   10篇
  1990年   6篇
  1989年   5篇
  1988年   7篇
  1987年   5篇
  1986年   1篇
  1985年   2篇
  1984年   4篇
  1983年   4篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1970年   1篇
  1950年   1篇
排序方式: 共有8070条查询结果,搜索用时 250 毫秒
51.
目的:探讨心房颤动(房颤)患者射频消融术后复发的风险因素,并依此构建个性化的风险评分系统。方法:选取2017年1~8月行射频消融术的房颤患者154例作为研究对象,依据术后3个月的随访结果将患者分为复发组及未复发组,采用单因素分析和Logistic回归分析对各风险因素进行分析,构建其评分系统,采用Hosmer-Lemeshow拟合优度检验和ROC曲线下面积评价评分系统的准确度及区分度。结果:术后随访3个月的结果显示共37例(24.03%)房颤患者出现复发,房颤类型、病程、体质量指数(BMI)、左房前后径(LAD)、左房容积(LAV)及超敏C反应蛋白(hs-CRP)水平均是房颤复发的独立风险因素(P<0.05)。构建的风险评分系统得分为0~26分,Hosmer-Lemeshow拟合优度检验:x^2=7.520,P=0.482;ROC曲线下面积为0.864(95%CI:0.837~0.891),预测评分值为15分时,约登指数最大(0.605),此时的敏感度和特异度分别为77.3%和83.2%。结论:房颤患者射频消融术后的复发率较高,依据风险因素构建的风险评分系统具有较高的预测效率和区分能力,可作为房颤患者射频消融术后复发风险评估的参考工具。  相似文献   
52.
目的:探讨血管紧张素转换酶抑制剂(Angiotensin-converting enzyme inhibitor,ACEI)联合无创呼吸机辅助治疗心衰合并阻塞性睡眠呼吸暂停低通气综合征(Obstructive sleep apnea hypopnea syndrome,OSAHS)疗效及对血清脑钠素(Brain natriuretic peptide,BNP)水平的影响。方法:抽取我院自2013年1月到2019年4月收治的98例心衰合并OSAHS患者,根据治疗方法分为对照组(49例,ACEI常规治疗)与实验组(49例,ACEI联合无创呼吸机辅助治疗),比较两组患者治疗前后红细胞生成素(Erythropoietin,EPO)、血红蛋白(hemoglobin,Hb)、红细胞计数(red blood cell,RBC)、平均红细胞蛋白含量(Mean corpuscular protein content,MCH)、血细胞比容(Hematocrit,HCT)、平均红细胞体积(Mean red blood cell volume,MCV)、夜间平均最低血氧合度(Lowest oxygen saturation,LSaO2)、睡眠呼吸暂停低通气指数(apnea hypopnea index,AHI)、血清脑钠素(Brain natriuretic peptide,BNP)水平、中心收缩压(systolic pressure,SP)及中心舒张压(diastolic pressure,DP)的变化。结果:治疗后,两组患者EPO、Hb、RBC、MCH、HCT、MCV水平均明显低于治疗前,且实验组患者的以上指标水平均显著低于对照组(P<0.05)。两组治疗后LSaO2高于明显高于治疗前,AHI水平低于治疗前,且实验组LSaO2高于对照组,AHI水平低于对照组(均P<0.05)。治疗后两组患者BNP、SP和DP明显低于治疗前(P<0.05),且实验组患者的以上指标水平低于对照组(P<0.05)。实验组患者的术后并发症发生率明显低于对照组(P<0.05)。结论:ACEI及无创呼吸机辅助治疗心衰合并OSAHS可改善患者的睡眠紊乱、睡眠呼吸障碍、心衰及高血压,具有临床推广应用的价值。  相似文献   
53.
目的:调查高血压患者饮食习惯以及传统制剂服用现状,并分析饮食习惯与高血压患病的关系以及传统制剂服用的影响因素。方法:按照简单随机抽样法,采用自制调查问卷对呼和浩特市3个镇共8个行政村成年常住农村村民进行问卷调查,调查内容包括人口学特征、饮食习惯等内容,并采用多因素logistic回归分析饮食习惯与高血压患病的关系以及高血压患者传统制剂服用的影响因素。结果:呼和浩特市高血压患病率为22.68%。多因素logistic回归结果显示,较高的BMI、高血压家族史、饮酒史、泡菜咸菜、油炸食品、红肉(猪/牛/羊肉)/动物内脏、海产品是高血压独立危险因素(OR=1.257、1.451、1.358、1.317、1.108、1.146、1.373,P<0.05),奶制品、豆制品、新鲜果蔬是高血压保护因素(OR=0.797、0.868、0.903,P<0.05)。高血压患者传统制剂服用率为16.90%。多因素logistic回归结果显示,年龄≥60岁、文化程度高中以下、不了解高血压知识是高血压患者传统制剂服用的危险因素(OR=1.342、1.545、1.142,P<0.05)。结论:呼和浩特市农村成年村民高血压患病率较高,不良饮食习惯(饮食偏咸、油腻等)是高血压独立危险因素,高龄、文化程度低、不了解高血压知识的高血压患者传统制剂服用率较高,应加强农村居民合理膳食、保持均衡饮食习惯的宣传教育以及农村高血压患者用药规范。  相似文献   
54.
The jasmonic acid (JA) pathway plays crucial roles in plant defence against pathogens and herbivores. Rice stripe virus (RSV) is the type member of the genus Tenuivirus. It is transmitted by the small brown planthopper (SBPH) and causes damaging epidemics in East Asia. The role(s) that JA may play in the tripartite interaction against RSV, its host, and vector are poorly understood. Here, we found that the JA pathway was induced by RSV infection and played a defence role against RSV. The coat protein (CP) was the major viral component responsible for inducing the JA pathway. Methyl jasmonate treatment attracted SBPHs to feed on rice plants while a JA-deficient mutant was less attractive than wild-type rice. SBPHs showed an obvious preference for feeding on transgenic rice lines expressing RSV CP. Our results demonstrate that CP is an inducer of the JA pathway that activates plant defence against RSV while also attracting SBPHs to feed and benefitting viral transmission. This is the first report of the function of JA in the tripartite interaction between RSV, its host, and its vector.  相似文献   
55.
Systemic necrosis often occurs during viral infection of plants and is thought mainly to be the result of long-term stress induced by viral infection. Potato virus X (PVX) encodes the P25 pathogenicity factor that triggers a necrotic reaction during PVX-potato virus Ysynergistic coinfection. In this study, we discovered that NbALY916, a multifunctional nuclear protein, could interact with P25. When NbALY916 expression was reduced by tobacco rattle virus (TRV)-based virus-induced gene silencing, the accumulation of P25 was increased, which would be expected to cause more severe necrosis. However, silencing of NbALY916 reduced the extent of cell death caused by P25. Furthermore, we found that overexpression of NbALY916 increased the accumulation of H2O2 and triggered more extensive cell death when coexpressed with P25, even though accumulation of P25 was itself reduced by the increased expression of NbALY916. Furthermore, transient expression of P25 specifically induced the expression of NbALY916 mRNA, but not the mRNAs of three other ALYs in Nicotiana benthamiana. In addition, we showed that silencing of NbALY916 or transient overexpression of NbALY916 affected the infection of PVX in N. benthamiana. Our results reveal that NbALY916 has an antiviral role that, in the case of PVX, operates by inducing the accumulation of H2O2 and mediating the degradation of P25.  相似文献   
56.
Traditional methods of identifying food‐borne pathogens are time consuming and laborious, so innovative methods for their rapid identification must be developed. Testing for bioluminescence pyrophosphate is a convenient and fast method of detecting pathogens without complex equipment. However, the sensitivity of the method is not as high as that of other methods, and it has a very high detection limit. In this study, the method was optimized to improve its sensitivity. The shortcomings of the method were first identified and corrected using dATPαS instead of dATP for the polymerase chain reaction (PCR), therefore reducing the background signal. Also, when the DNA template extracted from the food‐borne pathogens was purified, the new bioluminescence pyrophosphate assay had a limit of detection of <10 copy/μl or 10 colony‐forming units/ml, and its sensitivity was higher than that of fluorescent real‐time quantitative PCR. Moreover, a single copy of a food‐borne pathogen could be detected when a single DNA template was included in the PCR. Salmonella was detected in and isolated from 60 samples of broiler chicken, and the accuracy of the results was verified using a culture method (GB 4789.4–2010). These results showed that the new bioluminescence pyrophosphate assay has the advantages of an intuitive detection process, convenient operation, and rapid measurements. Therefore, it can be used for the rapid detection of pathogenic bacteria and probiotics in various fields.  相似文献   
57.
58.
Dysregulation of autophagy is associated with the neurodegenerative processes in Alzheimer's disease (AD), yet it remains controversial whether autophagy is a cause or consequence of AD. We have previously expressed the full‐length human APP in Drosophila and established a fly AD model that exhibits multiple AD‐like symptoms. Here we report that depletion of CHIP effectively palliated APP‐induced pathological symptoms, including morphological, behavioral, and cognitive defects. Mechanistically, CHIP is required for APP‐induced autophagy dysfunction, which promotes Aβ production via increased expression of BACE and Psn. Our findings suggest that aberrant autophagy is not only a consequence of abnormal APP activity, but also contributes to dysregulated APP metabolism and subsequent AD pathogenesis.  相似文献   
59.
Atherosclerosis is one of the most common and crucial heart diseases involving the heart and brain. At present, atherosclerosis and its major complications comprise the leading causes of death worldwide. Our purpose was to identify the role of ciRS‐7 in atherosclerosis. Tubulogenesis of HMEC‐1 cell was evaluated utilizing tube formation assay. Cell Counting Kit‐8 assay and flow cytometry were utilized to test viability and apoptosis. Migration assay was utilized to determine the migration capacity of experimental cells. Western blot was applied to examine apoptosis and tube formation‐associated protein expression. In addition, the above experiments were repeated when silencing ciRS‐7, overexpressing ciRS‐7, and upregulating miR‐26a‐5p. HMEC‐1 cells formed tube‐like structures over time. Silencing ciRS‐7 suppressed viability, migration, and tube formation but promoted apoptosis. Oppositely, overexpressing ciRS‐7 reversed the effect in HMEC‐1 cells. miR‐26a‐5p expression was elevated by silencing ciRS‐7 and reduced by overexpressing ciRS‐7. Moreover, overexpressing ciRS‐7 facilitated viability, migration, and tube formation via upregulating miR‐26a‐5p. Conclusively, overexpressing ciRS‐7 mobilized phosphoinositide 3‐kinase/protein kinase B (PI3K/AKT) pathway and suppressed c‐Jun N‐terminal kinase (JNK)/p38 pathway. ciRS‐7 exerted influence on apoptosis, viability, migration, and tube formation through mediating PI3K/AKT and JNK/p38 pathways by miR‐26a‐5p downregulation in HMEC‐1 cells.  相似文献   
60.
The progression of diabetic cardiomyopathy is related to cardiomyocyte dysfunction and apoptosis. Our previous studies showed that asporin (ASPN) was significantly increased in the myocardium of db/db mice through proteomics, and grape seed procyanidin B2 (GSPB2) significantly inhibited the expression of ASPN in the heart of db/db mice. We report here that ASPN played a critical role in glycated low‐density lipoproteins (gly‐LDL) induced‐cardiomyocyte apoptosis. We found that gly‐LDL upregulated ASPN expression. ASPN increased H9C2 cardiomyocyte apoptosis with down‐regulation of Bcl‐2, upregulation of transforming growth factor‐β1, Bax, collagen III, fibronectin, and phosphorylation of smad2 and smad3. However, GSPB2 treatment reversed ASPN‐induced impairments in H9C2 cardiomyocytes. These results provide evidence for the cardioprotective action of GSPB2 against ASPN injury, and thus suggest a new target for fighting against diabetic cardiomyopathy.  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