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   1961篇
  免费   86篇
  国内免费   10篇
耳鼻咽喉   11篇
儿科学   167篇
妇产科学   32篇
基础医学   230篇
口腔科学   54篇
临床医学   155篇
内科学   288篇
皮肤病学   44篇
神经病学   163篇
特种医学   89篇
外科学   211篇
综合类   13篇
预防医学   140篇
眼科学   189篇
药学   129篇
中国医学   1篇
肿瘤学   141篇
  2023年   10篇
  2022年   19篇
  2021年   29篇
  2020年   21篇
  2019年   30篇
  2018年   39篇
  2017年   23篇
  2016年   35篇
  2015年   38篇
  2014年   46篇
  2013年   76篇
  2012年   109篇
  2011年   150篇
  2010年   56篇
  2009年   69篇
  2008年   117篇
  2007年   124篇
  2006年   154篇
  2005年   145篇
  2004年   110篇
  2003年   116篇
  2002年   101篇
  2001年   45篇
  2000年   40篇
  1999年   34篇
  1998年   21篇
  1997年   17篇
  1996年   9篇
  1995年   12篇
  1994年   11篇
  1993年   9篇
  1992年   23篇
  1991年   14篇
  1990年   14篇
  1989年   16篇
  1988年   9篇
  1987年   13篇
  1986年   7篇
  1985年   8篇
  1984年   4篇
  1983年   11篇
  1982年   12篇
  1981年   4篇
  1979年   8篇
  1974年   4篇
  1970年   5篇
  1955年   7篇
  1949年   4篇
  1925年   3篇
  1904年   3篇
排序方式: 共有2057条查询结果,搜索用时 15 毫秒
51.

Introduction

This study was designed to compare rates of alcohol, marijuana, and cigarette use in Cambodian-American adolescents with norms from nationally- and regionally-representative peers.

Methods

Substance use data from 439 10th grade Cambodian-American adolescents in Long Beach, California were compared to grade- and gender-matched nationally representative data from the Monitoring the Future study and data from the California Healthy Kids Survey of students within the same school district.

Results

Overall, the Cambodian-American youth were less likely than nationally- and regionally-representative youth to use alcohol, marijuana, and cigarettes. Specifically, relative to estimates obtained for the general population and students attending school in the same school district, Cambodian-American youth were significantly less likely to use alcohol and marijuana. Cambodian-American youth were also less likely than youth in the general population to smoke cigarettes, but did not differ statistically from youth within their same school district.

Conclusions

As a group, Cambodian-American youth may not be at especially high risk for substance use. As is the case with virtually all populations, some individuals within the Cambodian-American group are likely to have more difficulty than others with substance use concerns. Thus, additional research is needed to identify factors that might help to identify high users with potential service needs.  相似文献   
52.

Background

Suboptimal vitamin B status might affect cognitive performance in early childhood. We tested the hypothesis that short-term supplementation with folic acid and selected B vitamins improves cognitive function in healthy children in a population with relatively low folate status.

Methods

We screened 1,002 kindergarten children for suboptimal folate status by assessing the total urinary para-aminobenzoylglutamate excretion. Two hundred and fifty low ranking subjects were recruited into a double blind, randomized, controlled trial to receive daily a sachet containing 220 μg folic acid, 1.1 mg vitamin B2, 0.73 mg B6, 1.2 μg B12 and 130 mg calcium, or calcium only for 3 months. Primary outcomes were changes in verbal IQ, short-term memory and processing speed between baseline and study end. Secondary outcomes were urinary markers of folate and vitamin B12 status, acetyl-para-aminobenzoylglutamate and methylmalonic acid, respectively, and, in a subgroup of 120 participants, blood folate and plasma homocysteine.

Results

Pre- and post-intervention cognitive measurements were completed by 115 children in the intervention and 122 in the control group. Compared to control, median blood folate increased by about 50 % (P for difference, P < 0.0001). Homocysteine decreased by 1.1 μmol/L compared to baseline, no change was seen in the control group (P for difference P < 0.0001) and acetyl-para-aminobenzoylglutamate was 4 nmol/mmol higher compared to control at the end of the intervention (P < 0.0001). We found no relevant differences between the groups for the cognitive measures.

Conclusion

Short-term improvement of folate and homocysteine status in healthy children does not appear to affect cognitive performance.  相似文献   
53.
54.
55.
A double-cone coil with large angled windings has been developed to modulate deeper brain areas such as the anterior cingulate cortex (ACC). Abnormal resting state activity in the pregenual ACC (pgACC), dorsal ACC (dACC) and subgenual ACC (sgACC) has been observed in depression. A patient with medication resistant chronic depression received ten sessions of transcranial magnetic stimulation (TMS) (10 Hz, 2000 stimuli/session) using a double-cone coil placed over the supplementary motor area, targeting the anterior cingulate. Source localized EEG recordings were conducted pre- and post-TMS. The Beck Depression Inventory (BDI-II) improved by 27%, and the two subscales of the Hospital Anxiety Depression Scale (HADS), namely depression (40%) and anxiety (33%) improved as well. Along with the clinical improvement eletrophysiological resting state activity changed in the dACC and sgACC in this patient in comparison to a normative group. The results of this case report further support the involvement of pgACC, dACC and sgACC activity in the pathophysiology of depression and indicate that modulation of neural activity in this area by high frequency TMS with a double-cone coil might represent a new promising approach in the treatment of medication resistant chronic depression.  相似文献   
56.

Purpose

Myofibroma is a rare benign spindle cell neoplasm, and the aim of the present study was to carry out a literature review and present a clinical case of a patient with a myofibroma in the submandibular region and its management.

Conclusions

Diagnosis of myofibroma can be reached by a histopathologic and immunohistochemical analysis and surgical excision is the treatment of choice.  相似文献   
57.
Monatsschrift Kinderheilkunde - Eine adäquate Energie- und Nährstoffversorgung ist Grundlage für ein gesundes Wachstum und Voraussetzung für die Erhaltung von Gesundheit und...  相似文献   
58.
Normal rabbit spinal cord was homogenized in sucrose and fractionated by centrifugation in a sucrose density gradient system slightly modified after the Norton-Poduslo method for the isolation of myelin. The following fractions were recovered: the fraction floating on 0.32 M sucrose, the myelin fraction at the 0.32 M/0.85 M interface and the pellet. After fixation in glutaraldehyde the fractions were subjected to Marchi staining, a histochemical method used for the demonstration of degenerating myelin. The floating fraction was enriched in Marchi-positive bodies as compared to the homogenate while the myelin fraction and the pellet contained low amounts. No esterified cholesterol was found in the floating fraction. Since histochemical and electron microscopical studies have shown that Marchi-positive myelinoid bodies in the normal CNS are associated with node-paranode regions our results indicate a possibility to isolate and biochemically characterize a presumably closely myelin-related fraction of known anatomical origin. The absence of esterified cholesterol in the floating fraction shows that biochemical or biophysical properties other than a content of esterified cholesterol may give rise to a positive Marchi reaction.  相似文献   
59.
60.
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