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   4981篇
  免费   448篇
  国内免费   181篇
耳鼻咽喉   47篇
儿科学   128篇
妇产科学   73篇
基础医学   698篇
口腔科学   139篇
临床医学   519篇
内科学   848篇
皮肤病学   99篇
神经病学   335篇
特种医学   163篇
外国民族医学   1篇
外科学   538篇
综合类   346篇
现状与发展   1篇
预防医学   378篇
眼科学   138篇
药学   475篇
  1篇
中国医学   82篇
肿瘤学   601篇
  2024年   6篇
  2023年   79篇
  2022年   213篇
  2021年   221篇
  2020年   151篇
  2019年   203篇
  2018年   181篇
  2017年   160篇
  2016年   179篇
  2015年   206篇
  2014年   233篇
  2013年   271篇
  2012年   335篇
  2011年   349篇
  2010年   191篇
  2009年   175篇
  2008年   249篇
  2007年   277篇
  2006年   237篇
  2005年   280篇
  2004年   201篇
  2003年   168篇
  2002年   153篇
  2001年   110篇
  2000年   99篇
  1999年   80篇
  1998年   53篇
  1997年   58篇
  1996年   38篇
  1995年   35篇
  1994年   32篇
  1993年   34篇
  1992年   49篇
  1991年   48篇
  1990年   30篇
  1989年   29篇
  1988年   33篇
  1987年   24篇
  1986年   22篇
  1985年   15篇
  1984年   8篇
  1982年   5篇
  1981年   5篇
  1979年   7篇
  1976年   4篇
  1974年   5篇
  1972年   8篇
  1970年   8篇
  1969年   8篇
  1939年   4篇
排序方式: 共有5610条查询结果,搜索用时 0 毫秒
21.
Background

Accurate accelerometer-based methods are required for assessment of 24-h physical behavior in young children. We aimed to summarize evidence on measurement properties of accelerometer-based methods for assessing 24-h physical behavior in young children.

Methods

We searched PubMed (MEDLINE) up to June 2021 for studies evaluating reliability or validity of accelerometer-based methods for assessing physical activity (PA), sedentary behavior (SB), or sleep in 0–5-year-olds. Studies using a subjective comparison measure or an accelerometer-based device that did not directly output time series data were excluded. We developed a Checklist for Assessing the Methodological Quality of studies using Accelerometer-based Methods (CAMQAM) inspired by COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN).

Results

Sixty-two studies were included, examining conventional cut-point-based methods or multi-parameter methods. For infants (0—12 months), several multi-parameter methods proved valid for classifying SB and PA. From three months of age, methods were valid for identifying sleep. In toddlers (1—3 years), cut-points appeared valid for distinguishing SB and light PA (LPA) from moderate-to-vigorous PA (MVPA). One multi-parameter method distinguished toddler specific SB. For sleep, no studies were found in toddlers. In preschoolers (3—5 years), valid hip and wrist cut-points for assessing SB, LPA, MVPA, and wrist cut-points for sleep were identified. Several multi-parameter methods proved valid for identifying SB, LPA, and MVPA, and sleep.

Despite promising results of multi-parameter methods, few models were open-source. While most studies used a single device or axis to measure physical behavior, more promising results were found when combining data derived from different sensor placements or multiple axes.

Conclusions

Up to age three, valid cut-points to assess 24-h physical behavior were lacking, while multi-parameter methods proved valid for distinguishing some waking behaviors. For preschoolers, valid cut-points and algorithms were identified for all physical behaviors. Overall, we recommend more high-quality studies evaluating 24-h accelerometer data from multiple sensor placements and axes for physical behavior assessment. Standardized protocols focusing on including well-defined physical behaviors in different settings representative for children’s developmental stage are required. Using our CAMQAM checklist may further improve methodological study quality.

PROSPERO Registration number

CRD42020184751.

  相似文献   
22.
23.
为改善技术论证的定量程度,作者用层析法对X-CT的选型操作进行了研究,并提出此方法可推广应用于一般医院的大型装备。  相似文献   
24.
Objective To detect new mutations among 29 glucose-6-phosphate dehydrogenase (G6PD) deficient individuals from Yunnan province. Methods The nitroblue tetrazolium (NBT) method was used to screen G6PD deficient individuals. Mutation was identified by single strand conformation polymorphism (SSCP), amplification created restriction site (ACRS), amplification refractory mutation system (ARMS) and DNA sequencing. Results Among 29 cases, 18 cases of G1388A, 1 case of C1004A, and 1 case of G1381A were identified. Nine cases remained to be defined. The G1381A mutation is a novel mis-sense mutation, with a substitution of threonine for alanine (A461T). The resultant G6PD had reduced enzymatic activity. In addition, G1381A caused a restriction site of Stu I to disappear, providing a rapid method for the detection of this mutation. Conclusion A novel mis-sense mutation G1381A was found. This mutation results in a substitution of threonine for alanine, producing enzyme with reduced activity. The loss of the Stu I restriction site offers a rapid method for the detection of this mutation.  相似文献   
25.
目的 研究偏头痛患儿的脑动脉血流动力学改变 ,探讨其在小儿偏头痛发生中的作用。方法 应用经颅多普勒 (TCD)技术 ,检测 90例 7~ 14岁头痛间歇期的偏头痛患儿和 80例健康同龄儿童脑动脉血管血流动力学指标。结果  90例偏头痛患儿中脑动脉血流动力学异常者 77例 (86 % ) ,其中 6 0例 (6 7% )流速增快 ,9例 (10 % )减慢 ,与对照组相比 ,差异具有显著性 (P <0 0 1) ;90例中 2 3例 (2 6 % )存在双侧同名动脉血流速度不对称 ,其中伴有血流速度异常者15例 ,血流速度正常者 8例 ,差异具有显著性 (P <0 0 1)。结论 脑动脉血流动力学因素异常改变 ,在小儿偏头痛的发生中具有重要作用。尤其值得注意的是 ,双侧同名动脉流速不对称的改变 ,在小儿偏头痛的发生中同样可能起着重要的作用。  相似文献   
26.
目的:探讨缬沙坦和氯沙坦治疗轻中度原发性高血压的临床疗效及安全性。方法:117例轻中度原发性高血压患者随机分为两组,缬沙坦(治疗)组59例,80~160mg/d,口服,疗程半年;氯沙坦(对照)组58例,50~100mg/d,口服,疗程半年。治疗前后测偶测血压、动态血压、肝肾功能、血脂、血糖、血尿酸,血浆肾素活性(PRA)、血管紧张素Ⅱ(AngⅡ)醛固酮(ALd)、内皮素(ET)等,并观察心脑事件发生情况。结果:治疗组总有效率74.6%(44/59例),降压幅度26.2/15.1mmHg,谷/峰(T/P)比值:收缩压(SBP)0.28、舒张压(DBP)0.78,与对照组总有效率74.1%(43/58例),降压幅度25.9/15.8mmHg,T/P比值:SBP 0.81、DBP 0.79均相似(P均>0.05)。两组治疗后PRA、AngⅡ均升高(P均<0.05);Ald、ET均降低(P均<0.05),但组间对照无显著性差异(P>0.05)。血尿酸也明显下降(P均<0.05),且基础值越高,降幅越大,对于治疗前高尿酸血症患者,对照组降压大于治疗组(P<0.05)。半年随访,两组心脑血管事件发生率相似(P>0.05),治疗组不良么应轻微。结论:缬沙坦是一种安全、作用持久、稳定、耐受性好、用药方便的治疗轻中度原发性高血压的新型AngⅡⅠ型受(AT1)拮抗药物之一,值得临床推广应用。  相似文献   
27.
目的:探讨L-精氨酸对病毒性心肌炎病理变化的影响。方法:将接种柯萨基病毒B3的Balb/c雄性小鼠随机分为饲服L-精氨酸组和对照组,于接种病毒后第5d测小鼠血清NO(NO2/NO3)和CK-MB,心肌组织病理学改变和超微结构变化。结果:血清NO(NO2/NO3)和血清CK-MB,L-精氨酸组高于对照组;心肌组织病理学检查可见L-精氨酸组小鼠心肌细胞有程度不等的空泡变性和坏死,病理损伤较对照组严重;  相似文献   
28.
目的:评价植入新型人工腰椎间盘的腰椎节段的稳定性和压缩力学性能。方法:将人工腰椎间盘植入6具新鲜青壮年尸体标本的L4-5椎间隙,进行三维运动范围和压缩刚度测试,并与植入前和髓核切除后进行比较。结果:新型人工腰椎间盘植入后,腰椎节段的三维运动范围为前屈146°,后伸66°,左侧弯79°,右侧弯89°,左轴向旋转85°,右轴向旋转87°。其压缩刚度比髓核切除后高(P<005)。结论:新型人工腰椎间盘植入后既保证了腰椎节段的三维运动功能,又起到了稳定脊柱的功能。  相似文献   
29.
 Cyclosporine is a powerful immunosuppressant with a narrow therapeutic window and considerable inter- and intrapatient variability. The pre-dose trough concentration (Cmin) is commonly used for therapeutic drug monitoring. With the new microemulsion (Neoral), intrapatient variability was reduced. However, the usefulness of Neoral Cmin was questioned. Firstly, because of the improved and more-rapid absorption, accidental intake before blood sampling has a greater impact on Cmin than with classic cyclosporine. Secondly, Cmin may be low despite high drug exposure, due to rapid clearance in children. A full pharmacokinetic (PK) profile with determination of the area under the curve (AUC) is expensive and cumbersome, and therefore a search for an abbreviated AUC began. Here, we present a retrospective analysis of 84 PK profiles from 78 pediatric renal transplant recipients. By analysis of rejection episodes and toxicity, we estimated a target AUC above 5,000 ng×h/ml in the early post-transplant period and 3,900 ng×h/ml beyond 100 days. The abbreviated AUC using the 2- and 6-h concentrations (C2 and C6) and a simple estimate derived from the 3-h concentration (C3) were equally well correlated with the AUC. From our data, we recommend a target C3 at approximately 800 ng/ml early after transplantation and 450–550 ng/ml beyond 100 days. Received: 28 January 1998 / Revised: 10 June 1998 / Accepted: 15 June 1998  相似文献   
30.
BACKGROUND/AIMS: Obstructive jaundice due to intraductal tumour growth is a rare symptom in association with hepatocellular carcinoma (HCC). METHODS: We report a 65-year-old white male who was admitted to our department with a 2-week history of progressive jaundice. At laparotomy, the liver showed advanced cirrhosis due to long-standing biliary obstruction. Cholangiography confirmed total obstruction of the main bifurcation of the hepatic duct by intraductal tumour growth. Combination treatment with surgical segment III drainage, transcatheter arterial embolization and radioembolization with yttrium-90 resin particles and endoscopic stenting was performed. This form of treatment has never been reported before. RESULTS: With these combined procedures, relief of jaundice and a survival time of 32 months could be achieved. CONCLUSION: The combination of palliative methods may relieve jaundice, ensure a good quality of life and possibly prolong survival in patients with mechanical tumour obstruction of the biliary tree by HCC.  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