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   36228篇
  免费   3814篇
  国内免费   124篇
耳鼻咽喉   291篇
儿科学   1362篇
妇产科学   903篇
基础医学   4925篇
口腔科学   708篇
临床医学   4981篇
内科学   7379篇
皮肤病学   719篇
神经病学   3807篇
特种医学   937篇
外国民族医学   4篇
外科学   4190篇
综合类   599篇
一般理论   35篇
预防医学   3531篇
眼科学   505篇
药学   2575篇
中国医学   26篇
肿瘤学   2689篇
  2023年   287篇
  2022年   363篇
  2021年   946篇
  2020年   739篇
  2019年   1128篇
  2018年   1225篇
  2017年   949篇
  2016年   1006篇
  2015年   1057篇
  2014年   1393篇
  2013年   1905篇
  2012年   2408篇
  2011年   2374篇
  2010年   1454篇
  2009年   1327篇
  2008年   2070篇
  2007年   2107篇
  2006年   1952篇
  2005年   1882篇
  2004年   1749篇
  2003年   1569篇
  2002年   1443篇
  2001年   635篇
  2000年   564篇
  1999年   570篇
  1998年   388篇
  1997年   291篇
  1996年   260篇
  1995年   265篇
  1994年   239篇
  1993年   219篇
  1992年   379篇
  1991年   358篇
  1990年   354篇
  1989年   330篇
  1988年   310篇
  1987年   299篇
  1986年   303篇
  1985年   285篇
  1984年   233篇
  1983年   206篇
  1982年   196篇
  1981年   171篇
  1980年   123篇
  1979年   148篇
  1976年   147篇
  1975年   123篇
  1974年   133篇
  1973年   141篇
  1972年   119篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.

Case Presentation:

A man with chronic paraplegia sustained a distal femur fracture following an unrelated fall while enrolled in a study examining musculoskeletal changes after 6 months of cycling with functional electrical stimulation (FES). After healing, he restarted and completed the study.

Management and Outcome:

Study measures included areal bone mineral density, trabecular bone microarchitecture, cortical bone macroarchitecture, serum bone formation/resorption markers, and muscle volume. The patient made small gains in bone- and muscle-related measures. Bone markers had not returned to baseline prior to restarting cycling, which may have impacted results.

Discussion:

This case shows that cycling with FES may be safely resumed after distal femur fracture.Key words: bone, cycling, fracture, functional electrical stimulation, spinal cord injuryCycling with functional electrical stimulation (FES) is an intervention for people with spinal cord injury (SCI) that is often used to improve overall health by targeting fitness, bone density, muscle volume, and other health indicators that impact risk for metabolic syndrome, diabetes, and cardiovascular disease.16 Inclusion in FES cycling programs is often impacted by bone status; programs and studies may exclude people with bone density that is a predetermined standard deviation below normal.7,8 Other programs base exclusion on lower extremity fracture history.9,10Even though people are excluded due to concerns about fractures during interventions, there is no evidence to support an increased fracture risk with FES cycling, with or without a fracture history. One study reported greater shear and less compressive forces at the knee with standing versus seated electrical stimulated exercise, suggesting greater risk with the knee flexed to 90°.11 However, the only fracture reported in the literature occurred during a high force flexed isometric contraction,12 not cycling. For people with SCI, lower extremity fractures typically occur during nontraumatic activities such as transfers13,14 and are labeled fragility fractures,15 with the majority occurring in the distal femur and proximal tibia.13,14 These fractures are thus caused by a different mechanism than what may occur during FES cycling. Furthermore, people with a history of low bone density and fragility fractures may have the greatest benefit from interventions such as FES cycling to decrease fracture risk by improving bone health.This case report describes the outcomes for a man with chronic paraplegia who sustained an unrelated distal femur fracture while enrolled in an FES cycling study. There are 2 objectives of this case report. The first is to demonstrate that FES cycling can be safely resumed following fracture healing, and the second is to discuss the subject’s musculoskeletal outcomes after he restarted the study once medically cleared after fracture healing.  相似文献   
992.
993.
994.
The prevention of hospital acquired pressure ulcers in critically ill patients remains a significant clinical challenge. The aim of this trial was to investigate the effectiveness of multi‐layered soft silicone foam dressings in preventing intensive care unit (ICU) pressure ulcers when applied in the emergency department to 440 trauma and critically ill patients. Intervention group patients (n = 219) had Mepilex® Border Sacrum and Mepilex® Heel dressings applied in the emergency department and maintained throughout their ICU stay. Results revealed that there were significantly fewer patients with pressure ulcers in the intervention group compared to the control group (5 versus 20, P = 0·001). This represented a 10% difference in incidence between the groups (3·1% versus 13·1%) and a number needed to treat of ten patients to prevent one pressure ulcer. Overall there were fewer sacral (2 versus 8, P = 0·05) and heel pressure ulcers (5 versus 19, P = 0·002) and pressure injuries overall (7 versus 27, P = 0·002) in interventions than in controls. The time to injury survival analysis indicated that intervention group patients had a hazard ratio of 0·19 (P = 0·002) compared to control group patients. We conclude that multi‐layered soft silicone foam dressings are effective in preventing pressure ulcers in critically ill patients when applied in the emergency department prior to ICU transfer.  相似文献   
995.

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   
996.

Introduction

As the human immunodeficiency virus (HIV)-positive population ages, issues concerning sexuality and fertility, among others, are becoming relevant. HIV is still surrounded by stigma and taboos, and there have been few studies conducted in industrialized settings concerning these questions. We therefore wanted to investigate the perception of sexuality and fertility in women living with HIV (WLWH) in an industrialized setting, using a questionnaire.

Methods

WLWH were recruited at their regular outpatient clinic visits, at the major Departments of Infectious Diseases in Denmark and Finland, from January 2012 to October 2013. A questionnaire was developed, study participants were informed of the nature of study and, if they agreed to participate and signed a consent form, they filled in the questionnaire. Demographic information on the participants was obtained from patient files (in Finland) or from a national HIV cohort (in Denmark). Statistical analysis was performed using STATA®, version 11.

Results

In total, 560 women were included in the study. The median age was 44 years. The majority were of white European origin, with fully suppressed HIV viral load, CD4 cell count >350 µL and mild or no symptoms of their HIV infection. A total of 62% were sexually active, stating condom use as their sole form of contraception. Of the sexually inactive women, one-third were in steady relationships. Eighty percent reported prior pregnancies, of which the majority had one or more children. Most children were born prior to the women''s HIV diagnosis and the mode of conception was predominantly natural. One-quarter of the participating women desired pregnancy, while more than half did not. The remaining quarter either stated that they already had the desired number of children or chose not to answer the question. Fourteen percent stated that their HIV diagnosis ended their wish for children; of these women, the median time of diagnosis was between 1995 and 1996. Pregnancy had been attempted unsuccessfully in one-quarter of study participants. The final question inquired what the risk of mother-to-child transmission was, with all precautions taken. Fifteen percent estimated the risk to be above two percent.

Conclusions

In conclusion, the majority of WLWH in industrialized settings in Denmark and Finland have few HIV-related symptoms, are sexually active and have a strong desire for children.  相似文献   
997.
998.
Cytokine receptors from the IL-6 receptor family are comprised of ligand specific alpha chains and a common signalling chain, gp-130, which is also required for high affinity binding. A cDNA library generated from the beta-TC3 SV40 T-antigen transformed insulinoma cell line was screened for members of this receptor family potentially relevant to both beta cell development and autoimmunity. Degenerate oligonucleotide primers to a consensus region of these receptors were used and the IL-11 receptor alpha chain was identified. Despite confirmation of IL-11 receptor mRNA expression, iodinated bioactive IL-11 did not bind specifically to beta-TC3 cells and gp-130-dependent cytokines did not elicit signalling events in beta cell lines. This was explained by absence of gp-130 protein or mRNA in the beta cell lines tested and in primary islets. We conclude from these results that the previously recognised effects of IL-6 family member cytokines on pancreatic islets must be indirect via other non-beta cells within the islet, rather than due to direct effects on beta cells themselves.  相似文献   
999.
Background: The incidence of sudden cardiac death is maximal in the morning hours. Although ventricular arrhythmias have been implicated as a potential mechanism, and several neurohumoral factors affecting myocardial excitability have been shown to be raised in the early morning hours, it is not known if there is any circadian variation in the dynamics of ventricular repolarization when studied on a beat-to-beat basis. The objective of this study was to examine the range, diurnal variations, and circadian distribution of the variability of the QT interval in healthy subjects. Method: We developed and validated a new method for continuous measurement of QT intervals from 24-hour Holter recordings. The QT intervals measured semi-automatically were corrected by a linear regression formula derived independently for each patient from his own QT and RR values in 32 healthy males (20 ± 0.4 years). QT variability was assessed by the mean standard deviation of the average of consecutive uncorrected QT intervals (SDA-QT Index) and corrected QT intervals (SDA-QTc index) over 5-minute segments. The rate-dependent changes of the QT interval were studied as a function of the slope of the regression line between the QT and RR values. Results: The average QTc range was mean (SD) 79 (± 28) ms; the average maximal QTc interval was 481 (± 24) ms. The 95% upper confidence limit for the mean 24-hour QTc interval was 443 ms. The RR, QT, and QTc intervals were longer, while the SDA-QT and SDA-QTc indices were shorter during sleep. Hourly averages of the SDA-QT and SDA- QTc index revealed a sudden increase in QT variability in the first hour of waking (P < 0.0001 and P = 0.006). Conclusion: The dynamic behavior of the QT interval shows significant diurnal variations. The maximal QTc interval over 24 hours is longer than previously assumed. The period shortly following awakening is characterized by a peak in the variability of the QT interval. These changes may be indicative of autonomic instability during the early waking hours and correspond with the peak incidence of sudden arrhythmic death.  相似文献   
1000.
Characteristics of various tissue and cell culture methods for studyingmaturation of human erythroblasts were reviewed and the basic assumptions required in their use were examined.

The relationship of maturation and proliferation of erythroblasts in different types of cultures was considered.

Criteria for selection of an in vitro model for studying maturation wereestablished. A new clot-free culture system in roller tubes was found tobe superior to those previously described because of convenience, replicabilityand adaptability to studies of proliferation.

The results of challenging the new culture system with various typesof cell-plasma relationships indicated that it was effective in distinguishingamong erythroblasts and plasmas of iron deficiency anemia, thalassemia,azotemia and erythrocytosis, and that the deductions arrived at were similarto those derived from the use of less convenient in vitro systems in whichdifferent parameters of maturation were used.

Experience with the new method suggests that it may be useful in thestudy of humoral factors affecting maturation of human erythroblasts.

The chief limitation of the proposed method, as for other in vitro methods,is that only direct effects of humoral agents on erythroblasts can be studied.

Submitted on December 17, 1958 Accepted on February 21, 1959  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