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   7757篇
  免费   519篇
  国内免费   30篇
耳鼻咽喉   73篇
儿科学   180篇
妇产科学   210篇
基础医学   1072篇
口腔科学   373篇
临床医学   864篇
内科学   1533篇
皮肤病学   172篇
神经病学   861篇
特种医学   163篇
外科学   699篇
综合类   44篇
一般理论   9篇
预防医学   869篇
眼科学   105篇
药学   548篇
中国医学   24篇
肿瘤学   507篇
  2024年   45篇
  2023年   131篇
  2022年   219篇
  2021年   417篇
  2020年   251篇
  2019年   308篇
  2018年   333篇
  2017年   267篇
  2016年   266篇
  2015年   324篇
  2014年   433篇
  2013年   489篇
  2012年   775篇
  2011年   758篇
  2010年   391篇
  2009年   323篇
  2008年   476篇
  2007年   485篇
  2006年   405篇
  2005年   355篇
  2004年   254篇
  2003年   217篇
  2002年   203篇
  2001年   25篇
  2000年   11篇
  1999年   25篇
  1998年   19篇
  1997年   15篇
  1996年   12篇
  1995年   7篇
  1994年   5篇
  1993年   11篇
  1992年   3篇
  1991年   4篇
  1990年   6篇
  1989年   3篇
  1988年   4篇
  1986年   5篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1978年   4篇
  1976年   2篇
  1975年   2篇
  1971年   3篇
  1968年   1篇
  1967年   1篇
  1965年   1篇
  1963年   1篇
  1930年   1篇
排序方式: 共有8306条查询结果,搜索用时 15 毫秒
21.
This qualitative study explores the experiences of emerging adults with serious mental health conditions (e.g., bipolar disorder, posttraumatic stress disorder) before and after they emancipate from the child welfare system and exit a transitional living program. Sixteen participants were interviewed before and 13 were interviewed after aging out. Findings suggest that transitional living programs services were appreciated for the relationships and safety net they fostered. Future plans were positive, but vague, and worries about the future were prevalent. Struggles with independence post-emancipation were common despite adult service use. Additional research is needed to understand how to best support these at-risk emerging adults.  相似文献   
22.
23.
24.

Introduction

Teeth are often included in the radiation field during head and neck radiotherapy, and recent clinical evidence suggests that dental pulp is negatively affected by the direct effects of radiation, leading to impaired sensitivity of the dental pulp. Therefore, this study aimed to investigate the direct effects of radiation on the microvasculature, innervation, and extracellular matrix of the dental pulp of patients who have undergone head and neck radiotherapy.

Methods

Twenty-three samples of dental pulp from patients who finished head and neck radiotherapy were analyzed. Samples were histologically processed and stained with hematoxylin-eosin for morphologic evaluation of the microvasculature, innervation, and extracellular matrix. Subsequently, immunohistochemical analysis of proteins related to vascularization (CD34 and smooth muscle actin), innervation (S-100, NCAM/CD56, and neurofilament), and extracellular matrix (vimentin) of the dental pulp was performed.

Results

The morphologic study identified preservation of the microvasculature, nerve bundles, and components of the extracellular matrix in all studied samples. The immunohistochemical analysis confirmed the morphologic findings and showed a normal pattern of expression for the studied proteins in all samples.

Conclusions

Direct effects of radiotherapy are not able to generate morphologic changes in the microvasculature, innervation, and extracellular matrix components of the dental pulp in head and neck cancer patients.  相似文献   
25.

Introduction

Effective root canal disinfection is a fundamental component of successful root canal treatment. Photodynamic therapy (PDT) has been proposed as a new adjunctive method for additional disinfection of the root canal system with the possibility of improved treatment outcomes. The aim of this systematic review was to investigate the effect of PDT on bacterial load reduction during root canal disinfection.

Methods

Two reviewers independently conducted a comprehensive literature search using a combination of medical subject heading terms and key words to identify studies relevant to the Population Intervention Control Outcome question. The selection of articles for inclusion was performed in 2 phases based on predetermined eligibility criteria according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Inter-reviewer agreement for each phase was recorded. The effect of PDT on bacterial load reduction during root canal disinfection was evaluated as the primary outcome variable during data extraction.

Results

The literature search provided 57 titles and abstracts. Three articles met the inclusion criteria and were selected for this systematic review. The reasons for study exclusion in each phase were recorded. Because of the heterogeneity in clinical indications and PDT protocols among the included studies, a meta-analysis could not be performed. All included studies showed a positive effect of PDT in the reduction of microbial load in root canal treatment ranging from 91.3%–100%.

Conclusions

Limited clinical information is currently available on the use of PDT in root canal disinfection. If supported by future clinical research, PDT may have efficacy for additional root canal disinfection, especially in the presence of multi–drug-resistant bacteria.  相似文献   
26.
27.

Background

Characterized as a sudden and temporary loss of consciousness and postural tone, with quick and spontaneous recovery, syncope is caused by an acute reduction of systemic arterial pressure and, therefore, of cerebral blood flow. Unsatisfactory results with the use of drugs allowed the nonpharmacological treatment of neurocardiogenic syncope was contemplated as the first therapeutic option.

Objectives

To compare, in patients with neurocardiogenic syncope, the impact of a moderate intensity aerobic physical training (AFT) and a control intervention on the positivity of head-up tilting test (HUT) and orthostatic tolerance time.

Methods

Were studied 21 patients with a history of recurrent neurocardiogenic syncope and HUT. The patients were randomized into: trained group (TG), n = 11, and control group (CG), n = 10. The TG was submitted to 12 weeks of AFT supervised, in cycle ergometer, and the CG to a control procedure that consisted in 15 minutes of stretching and 15 minutes of light walk.

Results

The TG had a positive effect to physical training, with a significant increase in peak oxygen consumption. The CG did not show any statistically significant change before and after the intervention. After the intervention period, 72.7% of the TG sample had negative results to the HUT, not having syncope in the revaluation.

Conclusion

The program of supervised aerobic physical training for 12 weeks was able to reduce the number of positive HUT, as it was able to increase tolerance time in orthostatic position during the HUT after the intervention period.  相似文献   
28.
There has been little investigation of the natural course of evidence‐based treatments (EBTs) over time following the draw‐down of initial implementation efforts. Thus, we undertook qualitative interviews with the providers at 38 U.S. Department of Veterans Affairs’ residential treatment programs for posttraumatic stress disorder (PTSD) to understand implementation and adaptation of 2 EBTs, prolonged exposure (PE), and cognitive processing therapy (CPT), at 2 time points over a 4‐year period. The number of providers trained in the therapies and level of training improved over time. At baseline, of the 179 providers eligible per VA training requirements, 65 (36.4%) had received VA training in PE and 111 (62.0%) in CPT with 17 (9.5%) completing case consultation or becoming national trainers in both PE and CPT. By follow‐up, of the increased number of 190 eligible providers, 87 (45.8%) had received VA training in PE and 135 (71.1%) in CPT, with 69 (36.3%) and 81 (42.6%) achieving certification, respectively. Twenty‐two programs (57.9%) reported no change in PE use between baseline and follow‐up, whereas 16 (42.1%) reported an increase. Twenty‐four (63.2%) programs reported no change in their use of CPT between baseline and follow‐up, 12 (31.6%) programs experienced an increase, and 2 (5.2%) programs experienced a decrease in use. A significant number of providers indicated that they made modifications to the manuals (e.g., tailoring, lengthening). Reasons for adaptations are discussed. The need to dedicate time and resources toward the implementation of EBTs is noted.  相似文献   
29.
Despite the pressing need for an AIDS vaccine, the determinants of protective immunity to HIV remain concealed within the complexity of adaptive immune responses. We dissected immunodominant virus-specific CD8+ T cell populations in Mamu-A*01+ rhesus macaques with primary SIV infection to elucidate the hallmarks of effective immunity at the level of individual constituent clonotypes, which were identified according to the expression of distinct T cell receptors (TCRs). The number of public clonotypes, defined as those that expressed identical TCR β-chain amino acid sequences and recurred in multiple individuals, contained within the acute phase CD8+ T cell population specific for the biologically constrained Gag CM9 (CTPYDINQM; residues 181–189) epitope correlated negatively with the virus load set point. This independent molecular signature of protection was confirmed in a prospective vaccine trial, in which clonotype engagement was governed by the nature of the antigen rather than the context of exposure and public clonotype usage was associated with enhanced recognition of epitope variants. Thus, the pattern of antigen-specific clonotype recruitment within a protective CD8+ T cell population is a prognostic indicator of vaccine efficacy and biological outcome in an AIDS virus infection.The global HIV pandemic demands an effective vaccine. However, while immunogenic vectors enter advanced clinical trials, the parameters on which to base measurements of efficacious immunity in a prospective manner remain unclear. Indeed, the recent Merck STEP trial failure has exposed our rudimentary understanding of protective determinants within the adaptive T cell response to HIV (13). It is established that specific CD8+ T cell immunity suppresses HIV replication in vivo and that certain patterns with respect to antigen targeting and MHC class I restriction are consistently associated with low levels of virus load (46). However, simple quantitative correlates, at least in peripheral blood, have proved elusive (7, 8). This paradox is exemplified by the SIV model, in which CD8+ T cell responses to the structurally constrained Gag CM9 epitope restricted by Mamu-A*01 are protective yet insufficient in terms of magnitude alone to define outcome (9, 10).In the absence of consistent numerical correlates of immune control, recent observational studies have focused on functional profiling in attempts to identify the properties that demarcate effective HIV-specific CD8+ T cell responses (1115). Indeed, a broad consensus indicates that polyfunctionality within pathogen-specific T cell populations, which is related to the sensitivity of antigen recognition among other parameters, correlates with improved outcome measures (3, 16). However, the qualitative properties of CD8+ T cell populations are clearly affected by viral replication, and the extent to which such functional associates reflect deterministic attributes remains uncertain. Similarly, phenotypic analyses of HIV-specific CD8+ T cell populations have yet to provide definitive indicators of immune control (3). At a more fundamental level, a given cognate T cell response is defined by the nature of its constituent clonotypes, which are defined on the basis of their expressed TCRs and can be considered the elemental units of any antigen-specific T cell population. Thus, the primary interface between the virus and adaptive T cell immunity occurs at the level of TCR-mediated recognition of peptide-MHC antigen; these signal transduction events, in turn, dictate the ontogeny and biological characteristics of individual cognate T cells in vivo. Given the seminal importance of clonotype-dependent TCR-mediated recognition events, it is not unreasonable to propose that the potential efficacy of a composite virus-specific CD8+ T cell population might depend on the idiosyncrasies with which individual cognate TCRs engage the targeted viral antigen.In a previous study, we examined the clonotypic composition of immunodominant CD8+ T cell populations in acute SIV infection to illuminate the role of TCR usage in the process of mutational immune escape (17). In the present study, we conducted a detailed prospective study of vaccine-induced SIV-specific CD8+ T cell responses to the same immunodominant epitopes to establish whether the mobilized antigen-specific TCR repertoire can influence virologic outcome.  相似文献   
30.
The aim of this study was to evaluate in vitro the influence of high-power lasers (Nd:YAG and diode 980 nm) associated with mineral coal as fotopotencializer on bond strength of an epoxy resin-based root canal sealer to root dentin, using the pushout test, and on the dentin/filling material interface, using confocal laser microscopy. For this purposes, 50 canines were instrumented with Mtwo rotary system up to #50.04 instrument and randomly assigned to five groups (n = 10): group I—control EDTAC; group II—EDTAC and Nd:YAG laser; group III—EDTAC and diode laser 980 nm; group IV—EDTAC, Nd:YAG laser and mineral coal 5 g/100 mL; and group V—EDTAC, diode laser 980 nm and mineral coal 5 g/100 mL. All data were analyzed by ANOVA (at 5% significance level) following the Kruskal-Wallis, Dunn and Tukey tests. The group I increased more bond strength of the sealer to root dentin that treated with only EDTAC 17% (17.21 ± 21.75 MPa), similar to the group II (12.21 ± 18.20 MPa) and group IV (14.92 ± 28.06 MPa), both treated with Nd:YAG laser, with the exception of group IV, which was added to mineral coal. The group V (8.75 ± 13.42 MPa) had similar results to the groups II and IV, but the same similarity were found when compared with group III (7.11 + 11.28 MPa), with lower results. Regarding the root thirds, the apical third (23.27 ± 29.21 MPa) presented a statistically higher value on bond strength than the cervical third (5.92 ± 5.33 MPa) and middle third (6.93 ± 7, 11 MPa) (p > 0.05). Group II (86.27 μm) showed the highest tags penetration values, with a statistically difference to the group III (51.57 μm), IV (36.77 μm) and V (32.37 μm) (p < 0.05). Group I (71.63 μm) was statistically similar to groups II and III (p > 0.05). Group IV had the lowest values and was statistically similarity to groups III and V (p > 0.05). It was concluded that the treatment with Nd:YAG laser provides better results than the diode 980 nm laser, except when was added mineral coal. The control and diode 980 nm laser groups presented less adhesive failures and more mists failures than the other groups. Both lasers did not interfere negatively compared to the control group.  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