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   4005篇
  免费   430篇
  国内免费   62篇
耳鼻咽喉   11篇
儿科学   51篇
妇产科学   165篇
基础医学   364篇
口腔科学   58篇
临床医学   357篇
内科学   340篇
皮肤病学   32篇
神经病学   153篇
特种医学   215篇
外科学   167篇
综合类   442篇
预防医学   1037篇
眼科学   28篇
药学   746篇
  8篇
中国医学   190篇
肿瘤学   133篇
  2024年   4篇
  2023年   62篇
  2022年   80篇
  2021年   150篇
  2020年   152篇
  2019年   126篇
  2018年   143篇
  2017年   132篇
  2016年   125篇
  2015年   184篇
  2014年   308篇
  2013年   308篇
  2012年   273篇
  2011年   297篇
  2010年   253篇
  2009年   241篇
  2008年   225篇
  2007年   218篇
  2006年   159篇
  2005年   122篇
  2004年   104篇
  2003年   94篇
  2002年   96篇
  2001年   70篇
  2000年   49篇
  1999年   47篇
  1998年   52篇
  1997年   55篇
  1996年   41篇
  1995年   27篇
  1994年   43篇
  1993年   26篇
  1992年   30篇
  1991年   26篇
  1990年   26篇
  1989年   20篇
  1988年   23篇
  1987年   21篇
  1986年   11篇
  1985年   26篇
  1984年   10篇
  1983年   3篇
  1982年   7篇
  1981年   6篇
  1980年   2篇
  1979年   3篇
  1978年   2篇
  1977年   5篇
  1975年   4篇
  1974年   2篇
排序方式: 共有4497条查询结果,搜索用时 15 毫秒
51.

Objectives

Data on the extent of drug use and associated HIV, hepatitis C and hepatitis B infection in West Africa are lacking. The objectives of ANRS12244 UDSEN study were to estimate the size of the heroin and/or cocaine drug user (DU) population living in the Dakar area (Senegal), and assess the prevalence and risk factors of HIV, hepatitis C virus (HCV) and hepatitis B virus (HBV), including behavioural determinants in this population, in order to set up an integrated prevention and treatment programme for DUs.

Design and methods

A capture-recapture method was applied for population size estimation, whereas the respondent-driven sampling (RDS) method was used to recruit a sample of DUs living in the Dakar area and determine HIV, HBV and HCV prevalence. Behavioural data were gathered during face-to-face interviews, and blood samples were collected on dried blood spots for analysis in a central laboratory. Data analysis was performed using the RDS analysis tool, and risk factors were determined by logistic regression. Access to laboratory results was organized for the participants.

Results

The size of the DU population in the Dakar area was estimated to reach 1324 (95% confidence interval (95% CI: 1281–1367)). Based on the 506 DUs included in the study, the HIV, HCV and HBV prevalence were 5.2% (95% CI: 3.8–6.3), 23.3% (95% CI: 21.2–25.2) and 7.9% (95% CI: 5.2–11.1), respectively. In people who inject drugs (PWID), prevalence levels increased to 9.4% for HIV and 38.9% for HCV (p=0.001 when compared to those who never injected). Women were more at risk of being HIV infected (prevalence: 13.04% versus 2.97% in males, p=0.001). Being PWID was a risk factor for HCV and HIV infection (odds ratio, OR: 2.7, 95% CI: 1.7–4.3, and OR: 4.3, 95% CI: 1.7–10.7, respectively), whereas older age and female sex were additional risk factors for HIV infection (10% increase per year of age, p=0.03 and OR: 4.9, 95% CI: 1.6–156, respectively). No specific determinant was associated with the risk of HBV infection.

Conclusions

High HIV and HCV prevalence were estimated in this population of DUs (including non-injectors) living in the Dakar area, Senegal, whereas HBV prevalence was close to that of the global Senegalese population, reflecting a risk of infection independent of drug use. Women seem to be highly vulnerable and deserve targeted interventions for decreasing exposure to HIV, while behavioural risk factors for HIV and HCV include the use of unsafe injections, reflecting the urgent need for developing harm reduction interventions and access to opioid substitution therapy services.  相似文献   
52.
In‐home salivary collection quality and adherence to a prescribed collection methodology for evaluation of dim light melatonin onset (DLMO) is unknown in children. Primary aims of this study were to 1) describe a novel family centered methodology for in‐home salivary collection; 2) determine the acceptance and feasibility of this methodology; 3) measure adherence to collection instructions; and 4) identify patterns between participants’ age and quality of samples collected. After receiving instructional handouts from the study team, families utilized in‐home salivary melatonin collection. Participants (N = 64) included 39 children (21 female, mean age 9.5 ± 1.61 years) and 25 adolescents (11 female, mean age 15.9 ± 2.12 years) with craniopharyngioma. Participants were 90% adherent to collection schedule, and 89% of the samples collected were of sufficient quantity and quality, with no differences found between age (child vs. adolescent) and melatonin sample quantity and quality. In‐home saliva collection provides an acceptable and feasible method to collect salivary melatonin and biomarkers in children and adolescents.  相似文献   
53.
54.
In conventional generalized autocalibrating partially parallel acquisitions, the autocalibration signal (ACS) lines are acquired with a frequency-encoding direction in parallel to other undersampled lines. In this study, a cross sampling method is proposed to acquire the ACS lines orthogonal to the undersampled lines. This cross sampling method increases the amount of calibration data along the direction, where k-space is undersampled, and especially improves the calibration accuracy when a small number of ACS lines are acquired. The cross sampling method is implemented with swapped frequency and phase encoding gradients. In addition, an iterative coregistration method is also developed to correct the inconsistency between the ACS and undersampled data, which are acquired separately in two orthogonal directions. The same calibration and reconstruction procedure as conventional generalized autocalibrating partially parallel acquisitions is then applied to the corrected data to recover the unacquired k-space data and obtain the final image. Reconstruction results from simulations, phantom and in vivo human brain experiments have distinctly demonstrated that the proposed method, named cross-sampled generalized autocalibrating partially parallel acquisitions, can effectively reduce the aliasing artifacts of conventional generalized autocalibrating partially parallel acquisitions when very few ACS lines are acquired, especially at high outer k-space reduction factors.  相似文献   
55.
56.
The hopelessness theory and Beck’s cognitive theory of depression were compared, controlling for other factors associated with mood change and stress reactivity. Using a high-risk design, 179 individuals were selected based on cognitive vulnerabilities and substance use frequency. Assessments of mood, daily events, and specific attributions were acquired using the Experience Sampling Method. Strong support was found for attributional style and sociotropy as indirect determinants of depressed mood, as well as for the notions of causal mediation and vulnerability specificity. Hopelessness theory explained a slightly larger portion of variance in depressed mood overall. The personality diatheses described by either theory were largely independent of each other and their mechanisms of action were not influenced by depression history or substance use.  相似文献   
57.
手术室空气微生物污染不同方法测定结果的比较   总被引:4,自引:0,他引:4  
为比较平板沉降不同时间采样及其相应判定标准的结果,对相同的无人员洁净手术室空气交替先后分别进行检测与判定结果。结果表明,对35间手术室空气采样5 min与30 min及按其相应判定标准的细菌数超标率分别为57.1%与14.3%。两者差异有统计学意义(P<0.01)。  相似文献   
58.

Background:

Cervical cancer is the most second common cancer among Iranian women. This study was carried out to compare the results of Pap smear method and Direct Visual Inspection (DVI) with 5% acetic acid in cervical cancer screening in Tabriz, Iran.

Material and Methods:

This cross-sectional study was carried out in Alzahra Therapeutic-Educational Centre, Tabriz, Iran in 2013 on 1000 women. First, Pap smear was done for all women, and then the cervix exposed with 5% acetic acid by cotton swab for 30 seconds and observed under adequate light. At the end, women with abnormal results in Pap smear or DVI method were referred to colposcopy and biopsy. Test''s sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), LR+, LR- and confidence interval (CI) were determined (P < 0.05).

Results:

Nine-hundred and seventy-four (94.7%) cases were normal and had no abnormal findings and 26 (2.6%) participants had positive results in Pap smear or DVI test. Twelve women had abnormal Pap smear (nine women with atypical squamous cells of undetermined significance, ASCUS, three women with dysplasia, atypical endocervical, and low-grade squamous intraepithelial lesion, LSIL results) and 14 women had positive DVI (four women with human papillomavirus, HPV or koilocyte,) and one women with abnormality in both method had carcinoma in biopsy that referred to oncologist. In this study the sensitivity, specificity, PPV and NPV for DVI were 71.4%, 50%, 35.7%, and 81.8% respectively in comparison with 14.3%, 50%, 10%, and 60% for Pap smear.

Conclusion:

As the DVI method has higher sensitivity and positive predictive value than Pap smear, it could be used as a useful method beside the Pap smear.  相似文献   
59.
African-American men who have sex with men (AA MSM) have been disproportionately infected with and affected by HIV and other STIs in San Francisco and the USA. The true scope and scale of the HIV epidemic in this population has not been quantified, in part because the size of this population remains unknown. We used the successive sampling population size estimation (SS-PSE) method, a new Bayesian approach to population size estimation that incorporates network size data routinely collected in respondent-driven sampling (RDS) studies, to estimate the number of AA MSM in San Francisco. This method was applied to data from a 2009 RDS study of AA MSM. An estimate from a separate study of local AA MSM was used to model the prior distribution of the population size. Two-hundred and fifty-six AA MSM were included in the RDS survey. The estimated population size was 4917 (95 % CI 1267–28,771), using a flat prior estimated 1882 (95 % CI 919–2463) as a lower acceptable bound, and a large prior estimated 6762 (95 % CI 1994–13,863) as an acceptable upper bound. Point estimates from the SS-PSE were consistent with estimates from multiplier methods using external data. The SS-PSE method is easily integrated into RDS studies and therefore provides a simple and appealing tool to rapidly produce estimates of the size of key populations otherwise difficult to reach and enumerate.  相似文献   
60.
Evidence suggests that respondent-driven sampling (RDS) is an efficient approach to sampling among varied populations of adult men who have sex with men (MSM) both in the USA and abroad, although no studies have yet evaluated its performance among younger MSM, a population with a steep rise in HIV infection in recent years. Young MSM (YMSM) may differ in terms of their connectedness to other YMSM (e.g., due to evolving sexual identity, internalization of sexual minority stigma, and lack of disclosure to others) and mobility (e.g., due to parental monitoring) which may inhibit the sampling process. The aims of this study were to evaluate the efficiency and effectiveness of RDS-based sampling among young urban MSM and to identify factors associated with recruitment success. We hypothesized that demographic, social, behavioral, and network factors, including racial/ethnic minority status, homelessness (i.e., as an indicator of socioeconomic marginalization), HIV-positive status, substance use problems, gay community connectedness, and network size would be positively related to recruitment productivity, while sexual minority stigmatization, environmental barriers (e.g., parental monitoring), and meeting sex partners on the internet (i.e., virtual venue) would be negatively related to recruitment productivity. Between December 2009 and February 2013, we used RDS to recruit a sample of 450 YMSM, ages 16–20. Findings suggest that the use of RDS for sampling among YMSM is challenging and may not be feasible based on the slow pace of recruitment and low recruitment productivity. A large number of seeds (38 % of the sample, n = 172) had to be added to the sample to maintain a reasonable pace of recruitment, which makes use of the sample for RDS-based population estimates questionable. In addition, the prevalence of short recruitment chains and segmentation in patterns of recruitment by race/ethnicity further hamper the network recruitment process. Thus, RDS was not particularly efficient in terms of the rate of recruitment or effective in generating a representative sample. Hypotheses regarding factors associated with recruitment success were supported for network size and internalized stigma (but not other factors), suggesting that participants with larger network sizes or high levels of internalized stigma may have more and less success recruiting others, respectively.  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