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   522篇
  免费   116篇
  国内免费   10篇
耳鼻咽喉   9篇
儿科学   7篇
妇产科学   28篇
基础医学   45篇
口腔科学   5篇
临床医学   37篇
内科学   134篇
皮肤病学   5篇
神经病学   22篇
特种医学   13篇
外科学   25篇
综合类   63篇
预防医学   183篇
眼科学   4篇
药学   46篇
  3篇
中国医学   5篇
肿瘤学   14篇
  2023年   8篇
  2022年   12篇
  2021年   33篇
  2020年   51篇
  2019年   39篇
  2018年   88篇
  2017年   88篇
  2016年   64篇
  2015年   80篇
  2014年   107篇
  2013年   27篇
  2012年   7篇
  2011年   3篇
  2010年   7篇
  2009年   10篇
  2008年   1篇
  2007年   2篇
  2005年   1篇
  2003年   1篇
  2001年   2篇
  2000年   1篇
  1999年   2篇
  1998年   5篇
  1997年   1篇
  1996年   3篇
  1995年   3篇
  1994年   1篇
  1993年   1篇
排序方式: 共有648条查询结果,搜索用时 15 毫秒
61.
Microbial transformation of the oleanolic acid (1) using Trichothecium roseum (pers.) Link (M 95.56) has resulted in the isolation of two new hydroxylated type metabolites, characterized as 15α-hydroxy-3-oxo-olean-12-en-28-oic acid (2) and 7β,15α-dihydroxy-3-oxo-olean-12-en-28-oic acid (3). The structure elucidation of these metabolites was based primarily on HR-EIMS, 1D NMR, and 2D NMR analyses.  相似文献   
62.
Discrimination of people living with HIV/AIDS (PLWHA) is a persistent issue in China, which affects their psychological health. However, the association between psychological factors and adherence to highly active antiretroviral therapy (HAART) has not been systematically investigated before. Therefore, this study examined the impact of social support, depression, and medication-taking self-efficacy on ART adherence among PLWHA based on Cha et al.’s model, and included “stigma” to the original model to explain the psychological mechanism. Of the 504 participants receiving HAART, 37.8% had mild-to-severe depression. According to structural equation modeling, social support was directly associated with depression, stigma, and adherence; depression partially mediated the positive relationship between social support and adherence self-efficacy and the negative association between stigma and self-efficacy. The modified and extended Cha et al.’s model had a satisfactory fit. Interventions to improve mental health through mental health services, social support, and enhancement of adherence self-efficacy beliefs are required.  相似文献   
63.
横断面研究能否进行因果推断   总被引:2,自引:1,他引:1       下载免费PDF全文
基于变量调查(或测量)的共时性、统计学关联及幸存者偏倚等原因,横断面研究被认为不能进行因果推断,这是当前的"共识"。本文基于因果思维,借助因果图,首先明确定义真实截面和测量截面,并识别截面概念仅存在于理论的特性。实际横断面研究中,测量变量的共时性并不存在,而是无一例外地表现为非共时性时序,其实质上相当于测量变量间互为独立性假设,或不存在有差别错分偏倚。类似于累积病例对照研究和历史性队列研究,横断面研究均为暴露和结局已存在或发生后进行的测量,这种测量相当于对变量值的历史重建或"考古"。这类研究进行因果推断的共性前提条件之一是,测量变量与其历史变量间必须存在着因果律。测量变量均为真实变量的替代者,测量变量间的时序在因果推断上并不重要。应加强对横断面研究分析性角色的认识。  相似文献   
64.
65.
基于大自然时间轴的测量时序分类法   总被引:2,自引:2,他引:0       下载免费PDF全文
因果推断中,时序(或方向性)的概念尚未完全明确。本文从因果思维出发,以真实因和真实果的发生时间将大自然时间轴划分为3个时域和2个时点,从而锚定了因果推断只能实现于第3时域。测量时序可分为5种类型:跨第1和3时域纵向时序(实验性时序)、跨第2和3时域纵向时序、同时域纵向时序、同时域逆纵向时序和同时域横向时序(观察性时序)。这种分类法适用于首次或多次测量、及时和延后测量等所有测量策略。除了实验中真实因的测量(或干预措施)在其发生之前(第1时域)或观察和实验中真实因的测量在真实果发生之前(第2时域)的情形外,所有其他测量策略类似于历史重建或"考古",测量时序的重要性次于测量的准确性。从研究设计应整合偏倚设计的观点来看,本文提出基于大自然时间轴的测量时序五分类法,概念清楚并将有助于判断研究过程中可能出现的偏倚,为正确进行因果推断研究奠定基础。  相似文献   
66.
The utilization of computed tomography is beneficial for the analysis of skeletal remains and it has important advantages for anthropometric studies. The present study investigated morphometry of left tibia using CT images of a contemporary Turkish population. Seven parameters were measured on 203 individuals (124 males and 79 females) within the 19–92-years age group. The first objective of this study was to provide population-specific sex estimation equations for the contemporary Turkish population based on CT images. A second objective was to test the sex estimation formulae on Southern Europeans by Kranioti and Apostol (2015). Univariate discriminant functions resulted in classification accuracy that ranged from 66 to 86%. The best single variable was found to be upper epiphyseal breadth (86%) followed by lower epiphyseal breadth (85%). Multivariate discriminant functions resulted in classification accuracy for cross-validated data ranged from 79 to 86%. Applying the multivariate sex estimation formulae on Southern Europeans (SE) by Kranioti and Apostol in our sample resulted in very high classification accuracy ranging from 81 to 88%. In addition, 35.5–47% of the total Turkish sample is correctly classified with over 95% posterior probability, which is actually higher than the one reported for the original sample (25–43%). We conclude that the tibia is a very useful bone for sex estimation in the contemporary Turkish population. Moreover, our test results support the hypothesis that the SE formulae are sufficient for the contemporary Turkish population and they can be used safely for criminal investigations when posterior probabilities are over 95%.  相似文献   
67.
Gonadotropin induces masculinization and spermatogenesis in men with congenital hypogonadotropic hypogonadism (CHH). However, large cohort studies for the efficacy and reliable predictors of this therapy need to be conducted. The aim of this study was to investigate the efficacy of gonadotropin treatment in a large cohort of male CHH patients and analyze putative predictors for successful spermatogenesis.This retrospective study included 223 CHH azoospermic patients without puberty development treated between 2005 and 2014. All patients received combined human chorionic gonadotropin (HCG) and human menopausal gonadotropin (HMG) and were followed up for >6 months (5109 person-months). Serum total testosterone level, testicular size, spermatogenesis, and pregnancy outcome were recorded at each visit.After gonadotropin therapy, testicular size was enlarged from 2.1 ± 1.6 to 8.1 ± 4.6 mL (P < 0.001) and serum total testosterone was elevated from 0.9 ± 0.5 to 15.1 ± 8.2 nmol/L (P < 0.001). Spermatogenesis (>0/mL) occurred at a median period of 15 months (95% confidence interval 13.5–16.5). Larger basal testicular volume (P = 0.012) and noncryptorchidism history (P = 0.028) are independent predictors for earlier sperm appearance. Sixty four percent (143/223) of patients succeeded in producing sperms and the average time for initial sperm detection was 14 ± 8 months. However, their sperm concentrations (11.7 [2.1, 24.4] million/mL) and sperm progressive motility (A + B 36.9% ± 20.2%) are significantly lower than World Health Organization standards. Of the 34 patients who desired for fathering children, 19 patients impregnanted their partners during the treatment.Gonadotropin therapy induces spermatogenesis in male CHH patients. A larger basal testicular size and noncryptorchidism history are favorable indicators for earlier spermatogenesis.  相似文献   
68.
Objectives: The goal of this study was to evaluate the effects of middle ear packing agents (MEPA) on post-operative hearing improvement and complications after tympanoplasty in patients with adhesive otitis media (OM).

Materials and methods: Patients with adhesive OM who underwent tympanoplasty surgery were enrolled in the study between January 2012 and January 2015. A total of 205 patients who received canal wall-down tympanoplasty with ossicular chain reconstruction were randomized into one of the three groups with different MEPA. Group 1 (n?=?72) received MeroGel as the MEPA, Group 2 (n?=?64) cartilage, and Group 3 (n?=?69) both. Air conduction (AC) and bone conduction (BC) thresholds at 0.5, 1, 2, and 4?kHz were measured, and air-bone gaps (ABG) were analyzed before and after the surgery for each patient.

Results: Mean pre- and post-operative ABG was 30.9?dB and 17.6?dB in Group 1, 31.4?dB and 21.9?dB in Group 2, and 32.2?dB and 19.1?dB in Group 3. The ABG closure was 13.3?±?7.5 in Group 1, 9.5?±?5.9 in Group 2, and 13.1?±?9.3 in Group 3. The improvement of ABG after surgery was statistically significant in all three groups (p?p?Conclusions: Tympanoplasty using esterified hyaluronic acid (i.e. MeroGel) or cartilage as the MEPA resulted in improved hearing for patients with conductive hearing loss due to adhesive OM. Using MeroGel as the MEPA appeared to achieve a better post-operative outcome than using cartilage.  相似文献   
69.
目的 系统评价腹腔镜根治性子宫切除术(LRH)与开腹根治性子宫切除术(ARH)治疗早期宫颈癌的疗效与安全性,为临床工作中对宫颈癌的诊治和为患者选择合理手术方式提供决策依据。方法 检索Pub Med、EMbase、Cochrane Library、CBM、CNKI、万方和维普数据库,采用Revman 5.3软件对入选的随机对照试验研究文献进行综合定量分析。结果 本研究共有11篇文献符合入选标准,包括944例早期宫颈癌患者,其中,LRH组患者472例,ARH组患者472例。Meta分析结果显示:与ARH组比较,LRH组治疗早期宫颈癌可以减少术中失血量[MD=-60.53,95%CI(-73.09,-47.97),P<0.00001];LRH组淋巴结清除数目明显多于ARH组,且差异有统计学意义[MD=4.25,95%CI(1.75,6.76),P=0.0009];LRH组可以缩短术后肛门排气时间[MD=-14.12,95%CI(-16.26,-11.97),P<0.00001]。在手术时间、术中并发症发生率、术后并发症发生率、术后随访2~5年宫颈癌复发率以及生存率方面,两组间差异均无统计学意义。结论 LRH与ARH相比,LRH治疗早期宫颈癌在近期疗效、手术创伤和术后疾病的恢复方面具有一定的积极作用。但是,对于远期疗效的作用还不明确,尚需开展更多研究予以验证。  相似文献   
70.
《Vaccine》2020,38(5):963-978
BackgroundData on the safety of inadvertent rubella vaccination in pregnancy is important for rubella vaccination programs aimed at preventing congenital rubella syndrome.MethodsThe association between monovalent rubella or combination vaccinations in or shortly before pregnancy and potential harm to the foetus was examined by conducting a systematic review and meta-analysis using fixed effect methods and simulation.ResultsFour cohort studies of inadvertently vaccinated and unvaccinated women were found, 15 cohorts of pregnant women who were rubella susceptible at time of inadvertent vaccination and 9 cohort studies with no information on susceptibility and case series. No case of vaccine associated congenital rubella syndrome (CRS) was identified. Cohort studies with an unvaccinated comparison group were limited in number and size, and based on these only a theoretical additional risk of 6 or more cases of CRS per 1000 vaccinated women (0% observed, upper 95% CI 0.6%) could be excluded. Based on cohorts of vaccinated rubella susceptible pregnant women a maximum theoretical risk of 1 CRS case in 1008 vaccinated women (0% observed, upper 95% CI 0.099%) was estimated. Asymptomatic rubella vaccine virus infection of the neonate was also noted (fixed effects estimate of risk overall 1.74%, 95% CI 1.21, 2.28).ConclusionThere is no evidence that CRS is caused by rubella-containing vaccines but transplacental vaccine virus infection can occur. CRS is effectively prevented by vaccination, thus the risk/benefit balance is unequivocally in favour of vaccination. The data confirm previous recommendations that inadvertent vaccination during pregnancy is not an indication for termination of pregnancy.  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