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   1561篇
  免费   160篇
  国内免费   2篇
耳鼻咽喉   12篇
儿科学   68篇
妇产科学   27篇
基础医学   247篇
口腔科学   28篇
临床医学   214篇
内科学   271篇
皮肤病学   32篇
神经病学   136篇
特种医学   137篇
外科学   169篇
综合类   63篇
预防医学   116篇
眼科学   17篇
药学   110篇
中国医学   7篇
肿瘤学   69篇
  2021年   18篇
  2020年   13篇
  2019年   16篇
  2018年   20篇
  2017年   22篇
  2016年   17篇
  2015年   20篇
  2014年   31篇
  2013年   69篇
  2012年   48篇
  2011年   62篇
  2010年   59篇
  2009年   54篇
  2008年   61篇
  2007年   60篇
  2006年   70篇
  2005年   47篇
  2004年   51篇
  2003年   44篇
  2002年   54篇
  2001年   42篇
  2000年   40篇
  1999年   30篇
  1998年   29篇
  1997年   57篇
  1996年   42篇
  1995年   29篇
  1994年   33篇
  1993年   28篇
  1992年   24篇
  1991年   17篇
  1990年   27篇
  1989年   50篇
  1988年   36篇
  1987年   33篇
  1986年   28篇
  1985年   36篇
  1984年   20篇
  1983年   17篇
  1982年   10篇
  1981年   23篇
  1980年   12篇
  1979年   23篇
  1978年   20篇
  1977年   24篇
  1976年   18篇
  1975年   14篇
  1974年   18篇
  1971年   10篇
  1968年   9篇
排序方式: 共有1723条查询结果,搜索用时 203 毫秒
11.
12.
Peritoneal desmoplastic small round cell tumors with divergent differentiation are recently described highly aggressive neoplasms with characteristic clinical, morphologic, and immunohistochemical features. This review covers 38 cases that have been reported in the literature. The average age of patients is 18.4 years, and males are affected twice as frequently as females. Tumors generally present as multiple peritoneal nodules without obvious organ involvement. Histology shows islands of small cells set in dense desmoplastic stroma. Immunohistochemical stains are usually positive for cytokeratins, epithelial membrane antigen, desmin, and vimentin. Many cases also stain for neuron-specific enolase but rarely for other neuroepithelial markers. Ultrastructural appearances range from undifferentiated small cells to larger epithelial elements. Paranuclear aggregates of intermediate filaments are characteristic. Dense-core granules and other neuroendocrine features have been described in a minority of cases. Some tumors respond to chemotherapy, but most patients die within months to a few years. The histogenesis of these tumors is uncertain.  相似文献   
13.
STUDY OBJECTIVES: Oleamide and anandamide are fatty acid amides implicated in the regulatory mechanisms of sleep processes. However, due to their prompt catabolism by fatty acid amide hydrolase (FAAH), their pharmacologic and behavioral effects, in vivo, disappear rapidly. To determine if, in the absence of FAAH, the hypnogenic fatty acid amides induce an increase of sleep, we characterized the sleep-wake patters in FAAH-knockout mice [FAAH (-/-)] before and after sleep deprivation. DESIGN: FAAH (-/-), FAAH (+/-), and FAAH (+/+) mice were implanted chronically for sleep, body temperature (Tb), and locomotor activity (LMA) recordings. Sleep-wake states were recorded during a 24-hour baseline session followed by 8 hours of sleep deprivation. Recovery recordings were done during the 16 hours following sleep deprivation. Total amount of wake, slow-wave sleep, and rapid eye movement sleep were calculated and compared between genotypes. The electroencephalographic spectral analysis was performed by fast Fourier transform analysis. Telemetry recordings of Tb and LMA were carried out continuously during 4 days under baseline conditions. SETTING: N/A. PATIENTS OR PARTICIPANTS: FAAH (-/-) mice and their heterozygote (+/-) and control (+/+) littermates were used. INTERVENTIONS: Sleep deprivation. MEASUREMENTS AND RESULTS: FAAH (-/-) mice possess higher values of slow-wave sleep and more intense episodes of slow-wave sleep than do control littermates under baseline conditions that are not related to differences in Tb and LMA. A rebound of slow-wave sleep and rapid eye movement sleep as well an increase in the levels of slow-wave activity were observed after sleep deprivation in all genotypes. CONCLUSION: These findings support the role of fatty acid amides as possible modulators of sleep and indicate that the homeostatic mechanisms of sleep in FAAH (-/-) mice are not disrupted.  相似文献   
14.
创伤病人的手术与焦虑状态调查   总被引:6,自引:0,他引:6  
采用状态——特质焦虑问卷及10项躯体性焦虑测试题,对40例外科创伤病人手术前后的焦虑状态调查显示:术前状态焦虑量表评分显著高于术后;术前躯体性焦虑评分显著高于术后;高特质焦虑评分亚组与低特质焦虑评分亚组术前状态焦虑评分无显著差异,但术后则前者显著高于后者;急诊手术者手术前后状态焦虑评分显著高于择期手术者。  相似文献   
15.
16.
In this study, we report two developments for studies of ion transport in cultured epithelial cells. First, a convenient method is presented for measuring apparent cell height using fluorescent microbeads as high-contrast landmarks of the apical and basal cell surfaces. The apparent cell height is then used as an indicator to monitor the time course of changes in cell volume in response to osmotic perturbations. Second, an Ussing-type chamber design for the inverted fluorescence microscope is presented, which allows determination of transepithelial electrical properties. Using these two methods, we obtained simultaneous measurements of cell height and transepithelial electrical parameters for cultured renal (A6) epithelium. Cell height was measured by alternately focusing the microscope between microbeads marking the apical and basal surfaces. The distance between these two surfaces was measured electrically from the voltage output of a potentiometer that was mechanically coupled to the fine-focusing knob of the microscope. Following decreases in the bathing solution osmolality, the cell height and transepithelial Na+ transport rate (measured as short-circuit current, I SC) increased. The increase in cell height preceded changes in I SC by several minutes, suggesting a lack of direct linkage between changes in cell volume and transepithelial Na+ transport. Both the fluorescent microbead cell height method and the Ussing-type chamber can be used in conjunction with patch-clamp techniques, intracellular microelectrode impalements, or fluorescent probes of intracellular composition. Therefore, this system may be advantageous for studies of epithelial cell volume and channel regulation.  相似文献   
17.
A study is reported of the estimation of plasma calcium fractions and the calcium-binding affinity of plasma proteins in a total sample of 59 people, which included 29 normal subjects and 30 patients with either hypercalcaemia or hypocalcaemia. It was demonstrated that when the sample was considered as a whole there was a significant correlation between the total plasma calcium concentration and the ultrafiltrable, ionized, and protein-bound calcium fractions and between the ultrafiltrable and ionized fractions. We have also demonstrated that in patients with either hypercalcaemia or hypocalcaemia, including acidotic uraemics, the calcium-binding affinity of the plasma proteins did not differ significantly from that in normal subjects. A significant correlation was also found between the total plasma calcium concentration and the ultrafiltrable, ionized and protein-bound calcium fractions when the normal subjects and the groups of patients with hypercalcaemia and hypocalcaemia due to chronic renal failure were considered as separate groups. The group of patients with hypercalcaemia included patients both with hyperparathyroidism and with hypercalcaemia due to other causes.  相似文献   
18.
The proportion of human peripheral blood CD8+ T cells that are CD57+ CD28- is low at birth but increases with age and in individuals infected with human cytomegalovirus (HCMV) or human immunodeficiency virus (HIV). These CD57+ CD28- CD8+ T cells contain large oligoclonal T-cell expansions whose antigen specificity is unknown. We identified clonal expansions of virus-specific memory cytotoxic T-lymphocyte precursors (CTLp) in both healthy carriers of HCMV and in asymptomatic HIV-infected subjects. In each subject, from the T-cell receptor (TCR) beta-chain hypervariable sequence of each immunodominant CTL clone, we designed complementary oligonucleotide probes to quantify the size and phenotypic segregation of individual virus-specific CTL clones in highly purified populations of peripheral blood CD8+ T cells. We found large clonal expansions of virus-specific CTL clonotypes in CD57+ CD28- CD8+ T cells. Using limiting dilution analysis, we found functional peptide-specific CTLp at high frequency in CD57+ CD28- cells. Thus, memory CTL specific for persistent viruses account for many oligoclonal expansions within CD57+ CD28- CD8+ T cells.  相似文献   
19.
Spurious hyperkalaemia   总被引:1,自引:1,他引:1       下载免费PDF全文
In a patient with acute lymphoblastic leukaemia, the plasma was found to have a potassium level of 10·4 mEq./1. Investigations showed that plasma from patients with leukaemia may be found to have falsely high potassium levels because of breakdown of leucocytes between the venepuncture and separation of the plasma.  相似文献   
20.
The morphological changes in a patient with a generalized storage disease characterized by the intracellular deposition of neutral lipid are described. There is widespread accumulation of lipid in the cytoplasm of many cells and in occasional nuclei. Diagnosis may be facilitated by the recognition of clear vacuoles in the cytoplasm of granulocytes in blood films. In jejunal biopsies vacuolation of the epithelial cells may simulate the appearances of a-betalipoproteinaemia. The lipid inclusions consist largely of normal triglycerides and are free in the cytoplasm, unassociated with any organelle. The biochemical basis of the lesions is uncertain. Although there are lipoprotein abnormalities the primary defect appears to be intrinsic to the cell and may involve either a defective cytoplasmic lipase or an impaired uptake and utilization of fatty acids by mitochondria.  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