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   2593篇
  免费   156篇
  国内免费   6篇
耳鼻咽喉   18篇
儿科学   70篇
妇产科学   144篇
基础医学   403篇
口腔科学   77篇
临床医学   195篇
内科学   608篇
皮肤病学   20篇
神经病学   202篇
特种医学   53篇
外科学   410篇
综合类   17篇
预防医学   119篇
眼科学   95篇
药学   138篇
中国医学   1篇
肿瘤学   185篇
  2022年   13篇
  2021年   45篇
  2020年   29篇
  2019年   30篇
  2018年   50篇
  2017年   44篇
  2016年   61篇
  2015年   63篇
  2014年   108篇
  2013年   93篇
  2012年   135篇
  2011年   161篇
  2010年   108篇
  2009年   92篇
  2008年   197篇
  2007年   200篇
  2006年   178篇
  2005年   196篇
  2004年   150篇
  2003年   162篇
  2002年   133篇
  2001年   33篇
  2000年   20篇
  1999年   30篇
  1998年   22篇
  1997年   29篇
  1996年   36篇
  1995年   26篇
  1994年   18篇
  1993年   20篇
  1992年   17篇
  1991年   9篇
  1990年   11篇
  1989年   10篇
  1988年   15篇
  1987年   13篇
  1986年   14篇
  1985年   15篇
  1984年   17篇
  1983年   11篇
  1982年   16篇
  1981年   9篇
  1980年   9篇
  1979年   9篇
  1978年   9篇
  1977年   11篇
  1973年   9篇
  1971年   10篇
  1970年   9篇
  1969年   12篇
排序方式: 共有2755条查询结果,搜索用时 15 毫秒
991.
Myxopapillary ependymomas (MPE) are considered benign (World Health Organization (WHO) grade I) neoplasms with favorable prognosis. However, malignant behavior occurs in a small subset. To our knowledge, only five anaplastic MPEs have been reported without consensus on diagnostic criteria. We retrieved 14 anaplastic MPEs from the pathology archives of six institutions. Each tumor included at least two of the following features: ≥5 mitoses per 10 high power fields, Ki‐67 labeling index (LI) ≥10%, microvascular proliferation (MVP) and spontaneous necrosis. These features were typically encountered in the foci of hypercellularity and reduced mucin. There were eight male and six female patients (age range 6–57 years, median = 16.5). Ten tumors displayed anaplasia at initial resection, and 4 were anaplastic at a second surgery for recurrence (ranging from 9 months to 14 years following initial resection). The Ki‐67 LI ranged between 8% and 40% in the anaplastic foci and <3% in the foci of classic MPE. There was documented cerebrospinal fluid (CSF) dissemination in seven cases, recurrence following an anaplastic diagnosis in three cases and bone or soft tissue invasion in two cases. One patient suffered lung metastases. Two cases evaluated by targeted next‐generation sequencing and one evaluated by fluorescence in situ hybridization (FISH) showed nonspecific chromosomal gains. We conclude that although rare, anaplastic MPE occurs in both pediatric and adult patients, similar to other ependymomas. At a minimum, closer follow‐up is recommended, given the concern for aggressive biologic potential. Further study is needed to determine WHO grading criteria and genetic indicators of tumor progression.  相似文献   
992.
cIMPACT‐NOW (the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy) was established to provide a forum to evaluate and recommend proposed changes to future CNS tumor classifications. From 2016 to 2019 (Round 1), cIMPACT published four updates. Update 1 clarified the use of the term NOS (Not Otherwise Specified) and proposed use of the additional term NEC (Not Elsewhere Classified). Update 2 issued clarifications regarding two diagnoses: Diffuse Midline Glioma, H3 K27M‐mutant and Diffuse Astrocytoma/Anaplastic Astrocytoma, IDH‐mutant. Update 3 proposed molecular criteria that could be used in the setting of an IDH‐wildtype diffuse or anaplastic astrocytic glioma without histological features of glioblastoma to infer that the tumor would behave similarly to a grade IV glioblastoma. Update 4 suggested that, in children and young adults, subtypes of IDH‐wildtype/H3‐wildtype diffuse gliomas may have distinct clinical features in the setting of a BRAFV600E mutation, FGFR1 alteration, other MAPK pathway alteration, or a MYB or MYBL1 rearrangement. The practical diagnostic relevance of these cIMPACT proposals is highlighted in this summary.  相似文献   
993.
Ring chromosomes are rare cytogenetic findings and are associated at phenotypic level with mental retardation and congenital abnormalities. Features specific for ring chromosome syndromes often overlap with the features of terminal deletions for the corresponding chromosomes. Here, we report a case of a ring chromosome 14 which was identified by conventional cytogenetics and shown to have a terminal deletion and an additional inverted duplication with a triplication by using large insert clone and oligo array-comparative genomic hybridization (array-CGH), fluorescence in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA). The combination of an inverted duplication with a terminal deletion in a ring chromosome is of special interest for the described syndromes of chromosome 14. The presented findings might explain partly overlapping clinical features described in terminal deletion, duplication and ring chromosome 14 cases, as these rearrangements can be easily overlooked when performing GTG-banding only. Furthermore, we suggest that ring chromosome formation can act as an alternative chromosome rescue next to telomere healing and capture, particularly for acrocentric chromosomes. To our knowledge, this is the first time an inverted duplication with a terminal deletion in a ring chromosome is identified and characterized using high-resolution molecular karyotyping. Systematic evaluation of ring chromosomes by array-CGH might be especially useful in distinguishing cases with a duplication/deletion from those with a deletion only.  相似文献   
994.
Congenital central nervous system (CNS) tumors are uncommon, accounting for 1% of all childhood brain tumors. They present clinically either at birth or within the first 3 months. Glioblastoma (GBM) only rarely occurs congenitally and has not been fully characterized. We examined clinicopathologic features and genetic alterations of six congenital GBMs. Tumors were seen by neuroimaging as large, complex cerebral hemispheric masses. All showed classic GBM histopathology, including diffuse infiltration, dense cellularity, GFAP-positivity, high mitotic activity, endothelial proliferation and pseudopalisading necrosis. Neurosurgical procedures and adjuvant therapies varied. Survivals ranged from 4 days to 7.5 years; two of the three long-term survivors received chemotherapy, whereas the three short-term survivors did not. Paraffin-embedded tissue sections were used for FISH analysis of EGFR, chromosomes 9p21 (p16/CDKN2A) and 10q ( PTEN/DMBT1); sequencing of PTEN and TP53; and immunohistochemistry for EGFR and p53. We uncovered 10q deletions in two cases. No EGFR amplifications, 9p21 deletions, or mutations of TP53 or PTEN were noted; however, nuclear p53 immunoreactivity was strong in 5/6 cases. Tumors were either minimally immunoreactive (n = 3) or negative (n = 3) for EGFR. We conclude that congenital GBMs show highly variable survivals. They are genetically distinct from their adult counterparts and show a low frequency of known genetic alterations. Nonetheless, the strong nuclear expression of p53 in these and other pediatric GBMs could indicate that p53 dysregulation is important to tumorigenesis.  相似文献   
995.

Objectives

Continuous noninvasive blood pressure (BP) measurement enables us to observe rapid changes in BP and to study underlying hemodynamic mechanisms. This study aimed to gain insight into the pathophysiological mechanisms underlying short-term orthostatic BP recovery patterns in a real-world clinical setting with (pre)syncope patients.

Setting and Participants

In a prospective cohort study, the active lying-to-standing test was performed in suspected (pre)syncope patients in the emergency department with continuous noninvasive finger arterial BP measurement.

Measures

Changes in systolic BP, cardiac output (CO), and systemic vascular resistance (SVR) were studied in normal BP recovery, initial orthostatic hypotension, delayed BP recovery, and sustained orthostatic hypotension.

Results

In normal recovery (n = 47), ΔBP at nadir was ?24 (23) mmHg, with a CO change of +10 (21%) and SVR of ?23 (21%). In initial orthostatic hypotension (n = 7) ΔBP at nadir was ?49 (17) mmHg and CO and SVR change was ?5 (46%) and ?29 (58%), respectively. Delayed recovery (n = 12) differed significantly from normal recovery 30 seconds after standing, with a ΔBP of ?32 (19) vs 1 (16) mmHg, respectively. Delayed recovery was associated with a significant difference in SVR changes compared to normal recovery, ?17 (26%) vs +4 (20%), respectively. There was no difference in CO changes. In sustained orthostatic hypotension (n = 16), ΔBP at 180 seconds after standing was ?39 (21) mmHg, with changes in CO of ?16 (31%) and SVR of ?9 (20%).

Conclusions/Implications

Hemodynamic patterns following active standing are heterogeneous and differ across orthostatic BP recovery patterns, suggesting that volume status, medication use, and autonomic dysfunction should all be taken into account when evaluating these patients. Moreover, results suggest that a delayed BP recovery is associated with an impaired increase in SVR in a significant proportion of individuals, implying that physicians treating older adults with hypertension should consider the possible negative effect of intensive hypertension treatment on initial orthostatic blood pressure control.  相似文献   
996.
OBJECTIVE: To examine the errorless learning approach using a procedural memory task (i.e. learning of actual routes) in patients with amnesia, as compared to trial-and-error learning. DESIGN: Counterbalanced self-controlled cases series. SETTING: Psychiatric hospital (Korsakoff clinic). SUBJECTS: A convenience sample of 10 patients with the Korsakoff amnestic syndrome. INTERVENTION: All patients learned a route in four sessions on separate days using an errorless approach and a different route using trial-and-error. MAIN MEASURES: Error rate was scored during route learning and standard neuro-psychological tests were administered (i.e. subtest route recall of the Rivermead Behavioural Memory Test (RBMT) and the Dutch version of the California Verbal Learning Test (VLGT)). RESULTS: A significant learning effect was found in the trial-and-error condition over consecutive sessions (P = 0.006), but no performance difference was found between errorless and trial-and-error learning of the routes. VLGT performance was significantly correlated with a trial-and-error advantage (P < 0.05); no significant correlation was found between the RBMT subtest and the learning conditions. CONCLUSION: Errorless learning was no more successful than trial-and-error learning of a procedural spatial task in patients with the Korsakoff syndrome (severe amnesia).  相似文献   
997.
998.

Introduction

The male-to-female transgender (waria) is part of a key population at higher risk for HIV. This study aims to test whether psychosocial determinants as defined by the theory of planned behaviour (TPB) can explain behaviours related to condom use among waria. Three preparatory behaviours (getting, carrying, and offering a condom) and two condom use behaviours (during receptive and insertive anal sex) were assessed.

Methods

The study involved 209 waria, recruited from five districts in Jakarta and interviewed by using structured questionnaires. Specific measures were developed to study attitudes, subjective norms and perceived behavioural control (PBC) in order to predict intentions and behaviours.

Results

The explained variance between intentions with regard to three preparatory behaviours and two condom uses ranged between 30 and 57%, and the variance between the actual preparatory behaviours of three preparatory and two condom uses ranged between 21 and 42%. In our study, as with several previous studies of the TPB on HIV protection behaviours, the TPB variables differed in their predictive power. With regard to intention, attitude and PBC were consistently significant predictors; attitude was the strongest predictor of intention for all three preparatory behaviours, and PBC was the strongest predictor of intention for condom use, both during receptive and insertive anal sex. TPB variables were also significantly related to the second parameter of future behaviour: actual (past) behaviour. TPB variables were differentially related to the five behaviours. Attitude was predictive in three behaviours, PBC in three behaviours and subjective norms in two behaviours.

Conclusions

Our results have implications for the development of interventions to target preparatory behaviours and condom use behaviours. Five behaviours and three psychological factors as defined in the TPB are to be targeted.  相似文献   
999.
Distal embolic event is one of the major limitations of coronary and non‐coronary vascular interventions. Balloon and filter‐based Embolic Protection Devices (EPDs) are a new class of interventional devices, used to prevent consequential morbidity and mortality of the distal embolic events. Data from first generation EPD supply proof of concept and show approximately 40% reduction in mortality and morbidity, when EPDs are used during saphenous vein grafts (SVGs) interventions. Current limitations of all first generation EPD technology taper their penetration. With breakthroughs in embolic protection technology, it is estimated that, in the near future, EPDs will be used with stenting in all high‐risk lesions (SVGs, carotid arteries and acute coronary syndromes), become the standard of care and even be used in low risk cases.  相似文献   
1000.
The use of an arteriovenous graft as vascular access for hemodialysis is associated with a high rate of patency loss. The influence of timing of the first cannulation of the graft on graft survival has not been sufficiently studied. The purpose of this study was to investigate an association between the timing of the first cannulation of the polytetrafluoroethylene arteriovenous graft and the incidence of 12‐month failure. This is a retrospective study on a cohort of chronic hemodialysis patients treated in a single center. According to the time, in weeks, between graft construction and its first successful cannulation, the grafts were divided into six groups: 2nd, 3rd, 4th, 5th, 6th and 7th or more week after surgery. The primary outcome was primary graft failure at 12 months, defined as the first occurrence of graft thrombosis or any invasive access procedure. The secondary outcome was cumulative graft failure at 12 months, defined as complete loss of the access site for dialysis. Fifty‐eight patients with 64 newly‐created arteriovenous grafts were included in the study. In the whole cohort, the incidence of primary graft failure at 12 months was 72.2%, and the incidence of cumulative graft failure at 12 months was 40.7%. The incidences of primary graft failure and cumulative graft failure at 12 months did not differ significantly between the study groups. In our study, timing of the first cannulation of a new arteriovenous polytetrafluoroethylene graft had no significant impact on graft survival.  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