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   5762篇
  免费   218篇
  国内免费   42篇
耳鼻咽喉   97篇
儿科学   143篇
妇产科学   90篇
基础医学   784篇
口腔科学   677篇
临床医学   421篇
内科学   1106篇
皮肤病学   140篇
神经病学   338篇
特种医学   190篇
外科学   612篇
综合类   37篇
一般理论   2篇
预防医学   676篇
眼科学   93篇
药学   380篇
  2篇
中国医学   58篇
肿瘤学   176篇
  2024年   32篇
  2023年   57篇
  2022年   130篇
  2021年   248篇
  2020年   158篇
  2019年   204篇
  2018年   273篇
  2017年   165篇
  2016年   216篇
  2015年   214篇
  2014年   288篇
  2013年   298篇
  2012年   463篇
  2011年   519篇
  2010年   318篇
  2009年   213篇
  2008年   330篇
  2007年   293篇
  2006年   242篇
  2005年   207篇
  2004年   165篇
  2003年   144篇
  2002年   132篇
  2001年   79篇
  2000年   78篇
  1999年   50篇
  1998年   49篇
  1997年   39篇
  1996年   33篇
  1995年   35篇
  1994年   24篇
  1993年   30篇
  1992年   26篇
  1991年   23篇
  1990年   21篇
  1989年   29篇
  1988年   22篇
  1987年   21篇
  1986年   22篇
  1985年   20篇
  1984年   11篇
  1983年   15篇
  1982年   9篇
  1981年   15篇
  1980年   7篇
  1979年   8篇
  1978年   6篇
  1977年   11篇
  1976年   7篇
  1969年   7篇
排序方式: 共有6022条查询结果,搜索用时 15 毫秒
91.
In human in-vitro fertilization (IVF), the oocytes are surrounded by cumulus and corona cells at the time of insemination so that their maturity cannot easily be evaluated. The best IVF results are obtained if the oocytes are inseminated 2-6 h after retrieval. In the intracytoplasmic sperm injection (ICSI) procedure, the oocytes are denuded by enzymatic and mechanical treatment in order to be able to perform the injection. As a consequence, the nuclear maturity of the oocytes can be evaluated and only those that have extruded the first polar body are injected. However, metaphase-II oocytes that have not yet reached cytoplasmic maturity cannot be recognized. The purpose of this study was to investigate the effect of different timing of cumulus- corona cell removal and injection on the outcome of ICSI. For this we allowed the oocytes to complete in-vitro cytoplasmic maturation in two different culture conditions: (i) surrounded by their cumulus and corona cells or (ii) totally denuded. We performed three different studies on sibling oocytes obtained after a standardized buserelin/human menopausal gonadotrophin (HMG) protocol. We investigated the effect of early (1-2 h after retrieval) and late (5-6 h after retrieval) oocyte denudation and injection on the survival and fertilization of the injected oocytes and on embryo cleavage after fertilization. We found no statistically significant differences between early and late injection, indicating that after a standardized buserelin/HMG protocol the metaphase-II oocytes do not need time for further cytoplasmic maturation. Furthermore, a different timing of cumulus-corona cell removal has no effect on the outcome of ICSI, suggesting that the surrounding cells are not necessary for survival, fertilization and cleavage after ICSI.   相似文献   
92.
Objective  To study associations between maternal dietary and supplement intake of antioxidants vitamin E, retinol and congenital heart defects (CHDs).
Design  Case–control study.
Setting  Erasmus MC, University Medical Center Rotterdam, the Netherlands.
Population  Participants were 276 case mothers of a child with CHD and 324 control mothers with their children.
Methods  Food frequency questionnaires covering the intake of the previous 4 weeks were filled out at 16 months after the index pregnancy. Data were compared between cases and controls using the Mann–Whitney U test. Risk estimates for the association between CHD and dietary intake of vitamin E and retinol were estimated in a multivariable logistic regression model.
Main outcome measures  Medians (5–95th percentile) and odds ratios with 95% CI.
Results  Dietary vitamin E intake was higher in case mothers than in controls, 13.3 (8.1–20.4) and 12.6 (8.5–19.8) mg/day ( P = 0.05). CHD risk increased with rising dietary vitamin E intakes ( P -trend = 0.01). Periconception use of vitamin E supplements in addition to a high dietary vitamin E intake above 14.9 mg/day up to nine-fold increased CHD risk. Retinol intakes were not significantly different between the groups and not associated with CHD risk.
Conclusions  High maternal vitamin E by diet and supplements is associated with an increased risk of CHD offspring.  相似文献   
93.
The activity of urea cycle enzymes was assayed in duodenal biopsy specimens obtained from a female infant who presented with neonatal hyperammonaemia. All enzyme levels were normal except N-acetyl glutamate-dependent carbamyl phosphate synthetase 1 (CPS1) which was half the mean activity in normal control specimens. A similar deficiency of CPS1 was also shown in duodenal specimens from the patient's mother who became slightly symptomatic after relatively high protein meals and during pregnancy, and had spontaneously modified her diet to one with protein restriction. The patient is growing normally on a dietary regimen similar to that spontaneously adopted by her mother. Urea cycle enzyme activity in the duodenal biopsy material from the controls was similar to that found in the normal human liver and appears to have distinct advantages as a means of assaying for urea cycle defects in patients with hyperammonaemia and their relatives.  相似文献   
94.
This study was designed to investigate: the prevalence of smokers among the UNIFESP nursing undergraduate students; some initial usage features; the smokers' dependence degree on nicotine. In order to compare the ratio of some variables, Pearson's Square Chi test was applied. The number of smokers among the nursing undergraduate students in the sample was 23 (8.2%) and 167 (59.9%) said they had never smoked a cigarette. Smokers' average age was 19.5 years old, and there is a significant difference between genders and only 2 (9.1%) smoking students may show a more severe discomfort while attempting to stop smoking, as showed the Fagerstr?m's Test.  相似文献   
95.
Alcohol related disorders often coexist with other psychiatric disorders and its incidence is increasing in last decades. Studies show that patients with comorbidity, specially those with severe psychiatric disorders, have higher rates of suicide, relapse, money spent in treatment, homeless and they use more medical service. Their evaluation must be meticulous because the differential diagnosis become complicated without a long period of alcohol withdrawal. These patients have a worse prognostic and their treatment is more difficult. Most of studies in this area have indicated that the integration of psychosocial and pharmacological techniques is more effective. The long term treatment must focus in the reduction of symptoms, improvement of social and familiar functioning, coping skills and relapse prevention.  相似文献   
96.
97.
98.
Glucose and glutamine metabolism of two microregions of human infiltrating ductile breast cancer, the center and the periphery, was studied and the results were compared with those of healthy mammary glands. In general, the activities of glycolytic enzymes and of phosphate-dependent glutaminase were as follows: center>periphery>mammary gland. Insulin caused a marked increase of glucose consumption and lactate production by incubated slices of mammary gland but had no effect on both microregions of the tumor. Therefore, human breast cancer presents metabolic microregions.  相似文献   
99.
100.
The need to use anaesthetised or restrained animals in acupuncture research in laboratory animals may represent a confounding variable, since both anaesthesia and stress alter the pain threshold and the activity of pain-related brain areas. In the current study we assessed the participation of the periaqueductal gray (PAG) in electroacupuncture's (EA) analgesic effects applied to the Zusanli point (36S) under carefully controlled stress conditions. Repeated immobilisation protocols (6 days, 1 h/day and 13 days, 2 h/day) were used to diminish the influence of acute immobilisation stress on c-Fos expression and analgesia (tail-flick test) induced by electroacupuncture on the 36S point (EA36S). Animals submitted to immobilisation alone (IMMO) or to electroacupuncture (100 Hz, 2-4 V, faradic wave) on a non-point region (EANP) were compared with animals submitted to electroacupuncture on the 36S point. In animals not previously submitted to repeated immobilisation, electroacupuncture on the 36S point induced analgesia and c-Fos expression in the PAG was not different from that induced by electroacupuncture at a non-acupuncture point. In animals submitted to repeated immobilisation (repeated immobilisation for 6 days or repeated immobilisation for 13 days), however, electroacupuncture on point 36S led to higher levels of analgesia and c-Fos expression, specifically in the ventrolateral PAG (vlPAG), as compared with animal groups subjected only to immobilisation or to electroacupuncture on a non-point. Our findings endorse previous results, and point to a specific part of the PAG involved in the effects of electroacupuncture at the Zusanli point.  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