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   2646589篇
  免费   199858篇
  国内免费   5031篇
耳鼻咽喉   37900篇
儿科学   84184篇
妇产科学   76198篇
基础医学   372189篇
口腔科学   79781篇
临床医学   230241篇
内科学   514046篇
皮肤病学   58564篇
神经病学   213543篇
特种医学   105742篇
外国民族医学   879篇
外科学   405180篇
综合类   64436篇
现状与发展   9篇
一般理论   923篇
预防医学   196482篇
眼科学   62362篇
药学   199874篇
  7篇
中国医学   5403篇
肿瘤学   143535篇
  2018年   24350篇
  2015年   24537篇
  2014年   34010篇
  2013年   52062篇
  2012年   69359篇
  2011年   73231篇
  2010年   43508篇
  2009年   41607篇
  2008年   70294篇
  2007年   75151篇
  2006年   76088篇
  2005年   73983篇
  2004年   72361篇
  2003年   69771篇
  2002年   68485篇
  2001年   122396篇
  2000年   126126篇
  1999年   107467篇
  1998年   29347篇
  1997年   26684篇
  1996年   26152篇
  1995年   25134篇
  1994年   23628篇
  1993年   22161篇
  1992年   86604篇
  1991年   83976篇
  1990年   82219篇
  1989年   80121篇
  1988年   74598篇
  1987年   73443篇
  1986年   70117篇
  1985年   67278篇
  1984年   50409篇
  1983年   43269篇
  1982年   25705篇
  1981年   23238篇
  1980年   21793篇
  1979年   48310篇
  1978年   34067篇
  1977年   29087篇
  1976年   26841篇
  1975年   29329篇
  1974年   35487篇
  1973年   34227篇
  1972年   32045篇
  1971年   30137篇
  1970年   28146篇
  1969年   26743篇
  1968年   24857篇
  1967年   22389篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
In cystic fibrosis (CF), perturbations of total daily energy expenditure (TDEE) may be a major determinant of altered nutrition and growth. Measurement of TDEE is problematic, though the flex-heart rate method (FHRM) provides a close estimation of TDEE, as compared to the cost-prohibitive, gold standard, the double-labeled water method, and permits estimates of the energy cost of daily activities (ECA) above resting energy expenditure (REE). We hypothesize that alterations in ECA affects TDEE in CF. PURPOSE: To measure components of TDEE in adolescents with CF and normal lung function compared with controls, and to determine whether ECA can be improved by diet and exercise. METHODS: Clinically stable CF subjects (aged 9-13, n=12) and age- and gender-matched controls (n=13) had repeated measurements of TDEE by FHRM, REE, and maximal cardiopulmonary exercise testing (CPET) during a 6-week exercise and diet program. RESULTS: While the mean REE was similar in both groups, ECA was significantly lower in CF adolescents as compared to controls (p=0.02). During CPET, maximal exercise in CF was characterized by hyperventilation, which was unrelated to ventilation-perfusion mismatching. There were no changes in REE after dietary intervention. CONCLUSION: ECA in CF adolescents with normal lung function is lower when compared to healthy controls. These findings support the hypothesis that clinically stable patients with CF have inefficient energy metabolism or alternatively conserve energy during activities of daily living.  相似文献   
43.
背景:Parkin基因(PRKN)突变可导致常染色体隐性遗传性早发帕金森病(EOPD)。目的:探讨EOPD白人家族PRKN突变的表现和基因型-表型关系。设计:对EOPD家族的3代20例成员进行基因分析,该家族有4例患者。应用直接基因组DNA测序、半定量聚合酶链反应、实时定量聚合酶链反应以及逆转录酶聚合酶链反应分析以确定PRKN突变。结果:4例早发患者(年龄30—38岁)被确定有PRKN复合杂合突变(T240M和EX5_6缺失),虽然PRKN的杂合T240M和纯合EX5_6缺失突变已有描述,但是据悉,本文为上述复合杂合突变的首次报道。患者的表型为典型常染色体隐性遗传性EOPD的表现,其特征是对左旋多巴治疗有效、相对缓慢的进展和运动障碍。所有杂合突变的基因携带者(T240M或EX5_6缺失)和1例56岁的复合杂合突变女性携带者(T240M和EX5_6缺失)无任何神经系统症状。结论:研究发现,PRKN基因复合杂合突变(T240M和EX5_6缺失)导致一个大的白人家族中4例成员发生常染色体隐性遗传性EOPD。另外1例成员具有相同的突变,比4例患者的平均发病年龄大10岁,并且无本病的临床表现。不完全的外显率对遗传咨询具有暗示作用,并且提示复杂的基因一环境交互作用在PRKN相关EOPD的发病机制中发挥作用。  相似文献   
44.
Low molecular weight heparins are widely used in the prophylaxis and treatment of thrombotic disorders. The effect of low molecular weight heparins on coagulation was examined ultrastructurally in an animal model. A test and a control group was formed, each consisting of five rabbits. Nadroparine (225 Institute of Chaoy Unit/kg twice daily) was applied to the test group for 10 days. The control group received 1 ml saline solution subcutaneously. Blood and vascular tissue samples collected at the end of the 10th day were evaluated under a JEM 100 B electron microscope. Platelet degranulation and agglutination was observed in the control group. Fibrin materials were detected in the cytoplasms and surroundings of degranulated platelets. Erythrocyte accumulation was remarkable on the vascular endothelium with intact coagulation periods. In the test group, outer membranes of platelets, hyalomere, and granular structures in the granulomeres were detected to be nearly intact. There were rare erythrocytes in the large vascular lumens. The aggregation phase had occurred but no agglutination was detected. Nadroparine seems to preserve consistency of lipoprotein membranes of platelets and granular structures containing enzymes, which contribute to the coagulation mechanisms.  相似文献   
45.
Summary: A female patient with isovaleric acidaemia had a successful outcome from pregnancy.  相似文献   
46.
47.
48.
49.
50.
To determine if impaired energy metabolism might contribute to some aspects of Alzheimer disease (AD), including the vulnerability of the CA1 region of the hippocampal formation and the altered cytoskeleton evident in neurofibrillary tangles, we examined the effects of metabolic poisons on neuronal damage and cytoskeletal disruption in the hippocampal formation. Intrahippocampal injection of 3-nitropropionic acid (3-NP) and malonic acid resulted in neuronal death, particularly in CA1. Cytoskeletal disruption included loss of dendritic MAP2, but sparing of axonal τ. MK-801 (a noncompetitive NMDA receptor antagonist) did not atenuate the lesions produced by intrahippocampal injection of malonate. MK-801, however, was effective against intrastriatal malonate. Acute systemic 3-NP resulted in neuronal damage and cytoskeletal disruption in the CA1 region of the hippocampal formation, including an extensive loss of MAP2 immuno-reactivity, but sparing of τ. The neuronal loss in CA1 was delayed as compared to striatum. Chronic intraventricular infusion of 3-NP produced a different pattern of neuronal damage. Loss of τ-1 immuno-reactivity was observed in CA3 and CA1 s. oriens, whereas MAP2 immunostaining was preserved. These results demonstrate that chronic and acute administration of metabolic inhibitors produce distinct patterns of neuronal damage and cytoskeletal disruption. The results further suggest a differential involvement of the NMDA receptor in malonate-induced neuronal damage in striatum as compared to the hippocampus. The pattern of neuronal damage and cytoskeletal disruption observed following acute metabolic impairment resembled some aspects of neurofibrillary pathology in AD, but did not result in τ hyperphosphorylation.  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