首页 | 官方网站   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   24723篇
  免费   2063篇
  国内免费   48篇
医药卫生   26834篇
  2021年   345篇
  2020年   221篇
  2019年   356篇
  2018年   408篇
  2017年   299篇
  2016年   296篇
  2015年   357篇
  2014年   490篇
  2013年   750篇
  2012年   1106篇
  2011年   1096篇
  2010年   615篇
  2009年   538篇
  2008年   1014篇
  2007年   1106篇
  2006年   976篇
  2005年   960篇
  2004年   993篇
  2003年   906篇
  2002年   861篇
  2001年   875篇
  2000年   869篇
  1999年   725篇
  1998年   375篇
  1997年   350篇
  1996年   340篇
  1995年   317篇
  1994年   217篇
  1993年   191篇
  1992年   603篇
  1991年   522篇
  1990年   510篇
  1989年   501篇
  1988年   494篇
  1987年   435篇
  1986年   472篇
  1985年   465篇
  1984年   366篇
  1983年   303篇
  1982年   209篇
  1981年   197篇
  1980年   214篇
  1979年   347篇
  1978年   237篇
  1977年   229篇
  1975年   189篇
  1974年   227篇
  1973年   204篇
  1972年   199篇
  1969年   198篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
BACKGROUND: Abnormalities in the limbic-hypothalamic-pituitary-adrenal (LHPA) axis have been implicated in the pathogenesis of obsessive-compulsive disorder (OCD). To our knowledge, however, no prior study has measured pituitary gland volume in OCD. METHODS: Volumetric magnetic resonance imaging studies were conducted in 31 psychotropic drug-na?ve children (10 boys, 21 girls) aged 8-17 years and 31 case-matched healthy comparison subjects. RESULTS: Pituitary volume was significantly smaller in patients with OCD as compared with healthy control subjects (11% smaller). Smaller pituitary volume in patients with OCD was associated with increased compulsive but not obsessive symptom severity. Boys with OCD had smaller pituitary gland volumes compared with control boys (20% smaller). No significant differences in pituitary volume were observed between girls with OCD and control girls. Boys with OCD had significantly smaller pituitary volumes than girls with OCD (31% smaller), whereas control boys also had smaller pituitary gland volumes compared with control girls (21% smaller). CONCLUSIONS: These findings provide new evidence of reduced pituitary volume in pediatric OCD that seems to be more prominent in male patients. The observed alterations in pituitary volume are consistent with neuroendocrine studies that have reported abnormalities in the LHPA axis in OCD.  相似文献   
92.
Symptoms of obstructive lung disease in domestic cleaners have been related to the use of bleach and other irritant cleaning products. The short-term effects of cleaning exposures on respiratory symptoms and peak expiratory flow (PEF) were investigated in domestic cleaners with respiratory disorders. In a panel study, 43 female domestic cleaners with a recent history of asthma and/or chronic bronchitis completed a 2-week diary, collecting information on respiratory symptoms, PEF and cleaning exposures. Mixed regression models were used to assess daily changes in symptoms and PEF associated with specific cleaning exposures. The probability of having work-related asthma was individually assessed by a computerised diagnostic system and an occupational asthma expert. Lower respiratory tract symptoms were more common on working days and were predominantly associated with exposure to diluted bleach, degreasing sprays/atomisers and air fresheners. Associations with upper respiratory tract symptoms and PEF were less apparent. Eleven (30%) subjects scored positively for work-related asthma. It is concluded that exposure to certain irritant cleaning products aggravates lower respiratory tract symptoms in female domestic cleaners with asthma or chronic bronchitis.  相似文献   
93.
Recent protocols have allowed successful positive crossmatch (+XM) and ABO incompatible (ABOI) kidney transplantation, although their long-term outcome is not clear. To begin to assess this issue we compared protocol biopsies performed 12 months posttransplant in 37 +XM, 24 ABOI and 198 conventional allografts. Although the majority in all three groups had only minimal histologic changes, transplant glomerulopathy (TG) was significantly increased in +XM (22% vs. 13% ABOI vs. 8% conventional, p = 0.015), and correlated with prior humoral rejection (HR) by multivariate analysis (odds ratio 17.5, p < or = 0.0001). Patients with a prior history of HR also had a significant increase in interstitial fibrosis (No HR 54% vs. HR 86%, p = 0.045). In the absence of HR no difference in histologic changes was seen between groups, although all three groups had a demonstrable mild increase in interstitial fibrosis from biopsies performed at the time of transplant. Thus, although HR is associated with an increase in TG, in its absence allograft histology is similar in +XM, ABOI and conventional allografts 1 year posttransplant.  相似文献   
94.
We report the genetic, clinical, electrophysiological, and imaging studies in a family with bilateral striopallidodentate calcinosis (Fahr's disease). The intracerebral calcium deposits occurred before onset of the symptoms in the third decade of life. Progressive neurological deterioration occurred in the fifth decade of life in the proband. Cerebrospinal fluid homocarnosine, a central nervous system-specific peptide, was increased twofold in patients with autosomal dominant bilateral stripallidodentate calcinosis; in sporadic cases, there was no detectable homocarnosine and a decreased level of histidine. With advancing age, the amount of calcification increases, but it has not been determined if a critical amount must be reached before symptoms occur. Computerized tomography is superior to magnetic resonance imaging for radiological diagnosis. Despite diffuse striatal calcification, striatal 6-[18F]fluoro-L-dopa uptake did not reveal any difference between patients and control subjects, from which we infer persisting integrity of the nigrostriatal dopaminergic pathway.  相似文献   
95.
96.
In this study we evaluated the association between cytomegalovirus infection alone or in relation to human leukocyte antigen matching and the development of vanishing bile duct syndrome, a form of chronic hepatic allograft rejection. A total of 81 consecutive liver transplant recipients were studied. Cytomegalovirus infection developed in 46 recipients (57%), and vanishing bile duct syndrome occurred in 9 recipients (11%). Cytomegalovirus infection developed in only five of the nine patients with vanishing bile duct syndrome. Univariate analysis of pretransplant recipient/donor cytomegalovirus serological tests and human leukocyte antigen typing showed they were not significant risk factors for the development of vanishing bile duct syndrome. Time-dependent analysis of cytomegalovirus infection after transplantation as a risk factor for vanishing bile duct syndrome, in a multivariate analysis with human leukocyte antigen match, showed no statistical significance. In our study, no association was found between cytomegalovirus infection alone or in relation to class I or II human leukocyte antigen match and the subsequent development of vanishing bile duct syndrome.  相似文献   
97.
Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a potent stimulator of macrophages and neutrophils and plays a role in inflammatory diseases. In this article, we report that mouse brain-derived microvascular smooth muscle cells (SM) and endothelial cells (En) in coculture with splenocytes support the colony proliferation of immature granulocyte-macrophage-like (GM) cells. Unstimulated SM and En cells release GM-CSF as shown by ELISA assay and SM expresses mRNA for GM-CSF by polymerase chain reaction (PCR). Stimulation of SM and En by a nonspecific activator (lipopolysaccharide) results in upregulation of GM-CSF production. GM colonies cannot be grown on cultured astrocytes or on extracellular matrix alone prepared from smooth muscle or endothelium. However, colonies form on the extracellular matrix and on astrocytes, either in the presence of SM- or En-conditioned medium or after the addition of recombinant GM-CSF. The GM cells are positive for nonspecific esterase, peroxidase, and MAC-1 markers but are negative for FC gamma receptors and for Thy 1.2, CD8, CD4, MHC class II, and Asialo GM1 markers. These observations emphasize the possibility for active participation of brain microvasculature SM and En in acute inflammatory reactions of the central nervous system.  相似文献   
98.
99.
All cases of acute intermittent porphyria (AIP) are believed to be caused by a mutation in the gene encoding for porphobilinogen deaminase, a rate-limiting enzyme in the haem synthetic pathway. This gene has been mapped to the long arm of chromosome 11, a region of the genome that has recently attracted considerable attention as a possible location for genes implicated in major mental disorder. This study was designed to show whether major mental illness co-segregated with acute intermittent porphyria in families where the two conditions are found. The study also investigated the relation between clinical mental symptoms and biochemical parameters of acute intermittent porphyria. The case records of 344 consecutive patients admitted to the Porphyrias Research Group in the Western Infirmary in Glasgow between 1950 and 1988 with acute intermittent porphyria were examined for evidence of psychiatric contact. Of 16 individuals identified, 12 were available for the study. Forty relatives of these 12 probands, including 9 who were asymptomatic carriers of AIP, were interviewed for lifetime history of mental illness and current symptoms. Comparisons were made between 4 groups of patients based on urinary porphyrin levels and erythrocyte enzyme activity; 1) manifest acute intermittent porphyria, 2) latent acute intermittent porphyria, 3) normal relatives and 4) total acute intermittent porphyria (latent and manifest combined). No association was found between AIP and schizophrenia or manic-depressive illness. Only one patient with schizophrenia was found in the sample of 344 case notes, and in 2 families bipolar illness was found but did not segregate with acute intermittent porphyria. The commonest psychiatric diagnosis in patients was generalized anxiety. In the total AIP group (latent and manifest), compared with normals, the rating scale measures of anxiety were significantly correlated with the level of porphyrin metabolites in the urine at the time of rating. This was true even in subjects with latent AIP, who were not at the time of testing aware that they were asymptomatic carriers of the illness. AIP should be considered in the differential diagnosis of generalized anxiety disorder.  相似文献   
100.
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-23

京公网安备 11010802026262号