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   8632篇
  免费   598篇
  国内免费   30篇
耳鼻咽喉   74篇
儿科学   270篇
妇产科学   204篇
基础医学   1249篇
口腔科学   93篇
临床医学   1284篇
内科学   1711篇
皮肤病学   121篇
神经病学   834篇
特种医学   342篇
外科学   746篇
综合类   138篇
一般理论   8篇
预防医学   1004篇
眼科学   125篇
药学   501篇
中国医学   15篇
肿瘤学   541篇
  2023年   72篇
  2022年   121篇
  2021年   226篇
  2020年   131篇
  2019年   214篇
  2018年   244篇
  2017年   181篇
  2016年   205篇
  2015年   243篇
  2014年   277篇
  2013年   388篇
  2012年   595篇
  2011年   551篇
  2010年   327篇
  2009年   311篇
  2008年   479篇
  2007年   536篇
  2006年   455篇
  2005年   477篇
  2004年   459篇
  2003年   452篇
  2002年   385篇
  2001年   106篇
  2000年   90篇
  1999年   109篇
  1998年   125篇
  1997年   96篇
  1996年   100篇
  1995年   89篇
  1994年   57篇
  1993年   76篇
  1992年   51篇
  1991年   55篇
  1990年   57篇
  1989年   44篇
  1988年   67篇
  1987年   50篇
  1986年   50篇
  1985年   63篇
  1984年   55篇
  1983年   42篇
  1982年   42篇
  1981年   29篇
  1980年   33篇
  1978年   22篇
  1977年   22篇
  1976年   37篇
  1974年   25篇
  1973年   22篇
  1971年   23篇
排序方式: 共有9260条查询结果,搜索用时 15 毫秒
61.
Background: This paper is part of a prospective, epidemiologic study concerning postpartum depression (PPD). The women were first examined during pregnancy; after delivery they were seen with their infants at 3 and 18 months. The present study focuses on the 3-months-postpartum results. Methods: A sample of 570 women and their infants were examined 3 months after delivery. Using the EPDS (Edinburgh Postnatal Depression Scale; Cox et al., 1987. Br. J. Psychiatry 150:782–786), 10.2% of these new mothers presented PPD. The focus of the study concerned the effects of this neurotic disorder on the mother, the infant and on the mother–infant relationship. Results: The deleterious effects concerning the infant were functional disorders such as eating or sleeping difficulties. The ‘depressed’ dyads presented less vocal and visual communications, less corporal interactions and less smiling. Conditions surrounding delivery and tiredness at 3 months are linked to difficulties in mother–infant relationship for the non-depressed mothers. Logistic models showed that primiparous PPD mothers have difficulties bathing their infants, whereas multiparous PPD mothers are more tired. Limitation: This study did not take into account either protective factors or the effects of the infant himself. Clinical relevance: Knowledge of the mothers’ and infants’ difficulties may help caregivers to detect these at-risk dyads and initiate therapeutic measures.  相似文献   
62.
Hereditary cerebral hemorrhage with amyloidosis - Dutch type (HCHWA-D) is an autosomal dominant disease caused by deposition of β-amyloid in the leptomeningeal arteries and cortical arterioles, in addition to preamyloid deposits and amyloid plaques in the brain parenchyma.
The disease is due to a point mutation at codon 693 of the amyloid precursor protein (βPP) gene at chromosome 21. Since this point mutation is diagnostic for HCHWA-D, presymptomatic testing is feasible and offered, together with genetic counselling and psychological support, to subjects at risk. HCHWA-D is clinically characterized by recurrent strokes, in addition to dementia, which can occur after the first stroke but also preceding it. Radiological studies revealed focal lesions (hemorrhages, hemorrhagic and non-hemorrhagic infarctions) and diffuse white matter damage. Diffuse white matter hyperintensities on MRI are an early symptom of HCHWA-D since they have been found on MRI scans of subjects who had not suffered a stroke.
The presence of the diagnostic point mutation makes HCHWA-D a useful model to study the effects of cerebral amyloid angiopathy in vivo. The characteristic pathological abnormalities and its implications for Alzheimer's disease will be discussed in Part II of this article  相似文献   
63.
Fas was recently demonstrated to be the major target molecule engaged by CD4+ cytolytic T lymphocytes (CTL). We examined Fas expression on various cloned T cell subpopulations and their susceptibility to lysis by CD4+ or CD8+ CTL. A reciprocal relationship in Fas and Fas-ligand expression was observed in CD4+ T helper (Th)1- and Th2-type clones, and Fas mRNA was predominantly detected in Th2 clones, whereas Fas-ligand mRNA was principally found in Th1 clones. The two Th0 clones tested expressed both Fas and Fas-ligand, but only one exhibited cytolytic activity, whereas both were sensitive to CD4-mediated lysis. A functional consequence of the inverse Fas-Fas-ligand expression pattern was that Th2 and Th0 cells were sensitive to lysis by both Th1 CD4+ CTL and a CD8+ CTL clone in a Fas-dependent manner. These results suggest that cytolytic CD4+ Th1 cells may play an immunomodulatory role, regulating a Th2/Th0 response by Fas-mediated lysis.  相似文献   
64.
The invasion of red blood cells (RBCs) by Plasmodium falciparum is dependent on multiple molecular interactions between erythrocyte receptors and parasite ligands. Invasion studies using culture-adapted parasite strains have indicated significant receptor heterogeneity. It is not known whether this heterogeneity reflects the parasite invasion arsenal in the field. We have studied the invasion phenotypes of 14 distinct field isolates from the Legal Amazon areas of Brazil by using erythrocyte invasion assays to investigate invasion into normal, enzyme-treated, and clinical-mutant RBCs. Analysis of these isolates revealed four distinct invasion profiles. Using En(a-) cells to get an unequivocal estimate of the use of glycophorin A (GPA) as a receptor, we found that the 175-kDa erythrocyte-binding antigen (EBA-175)/GPA pathway was used by a minority of the parasite isolates studied. Although polymorphism of region II domains at specific amino acid positions in both EBA-140 and EBA-181 was found in these field isolates, this did not correlate with invasion profiles and thus receptor selectivity. These studies have further confirmed the existence of a significant diversity of invasion pathways in nature and suggest that additional parasite ligands will have to be targeted to devise global vaccines that will work in the field.  相似文献   
65.
Preliminary data have suggested that female infertility due to corpus luteum insufficiency may be caused by subclinical hypothyroidism [exaggerated thyroid-stimulating hormone (TSH) response to thyrotrophin- releasing hormone (TRH) stimulation]. L-Thyroxine supplementation has been recommended to achieve pregnancies in subclinical hypothyroid women. This controlled study was carried out in order to investigate the biochemical diagnosis of subclinical hypothyroidism as a possible infertility factor. Five infertile patients (aged 25-36 years) with subclinical hypothyroidism (n = 4, stimulated TSH >20 microU/ml) or primary hypothyroidism (n = 1) and five healthy controls (aged 22-39 years) with normal thyroid function (stimulated TSH <15 microU/ml), regular cycles and no history of infertility were studied in the early follicular phase. In the pre-study evaluation, eight of 23 volunteers (34.8%) had to be excluded because of subclinical hypothyroidism with stimulated TSH values (TSHs) >15 microU/ml. Cycle function of patients and controls was compared by the method of LH pulse pattern analysis. Therefore blood samples were drawn every 10 min during a 24 h period. Sleep was recorded from midnight to 7 a.m. Repetition of the TRH tests at the end of the 24 h blood sampling period confirmed the difference in stimulated TSH values of the two study groups. Pulse analysis for luteinizing hormone (LH), TSH and prolactin showed no differences between patients and controls for pulse frequency, amplitude, height, length, area under curve (AUC) and the 24 h mean. Even the hypothyroid patient had a normal LH pulse pattern. Additional measurement of melatonin in pooled sera every 30 min gave the well-documented diurnal profiles during day and night for both groups. Patients had significantly higher melatonin values at seven time points during the night. Peaks for LH, TSH, prolactin and cortisol were correlated with the sleep stages wake, rapid eye movement, 1 + 2 and 3 + 4. We concluded that corpus luteum insufficiency in female infertility cannot be explained by subclinical hypothyroidism and thus should not be treated with L-thyroxine for fertility reasons.   相似文献   
66.
67.
The ligand for the T cell antigen CD2 is CD48 in rodents, but CD58 in humans. The extracelluar parts of these three antigens are structurally related in that all contain two immunoglobulin superfamily (IgSF) domains. There have been reports of alternative ligands for CD2 in the human, but not so far in rodents. We describe the analysis of ligands for rat CD2 and CD48 using fluorescent beads capable of displaying a high ligand density and detecting low-affinity interactions like that of CD2 with CD48 (Kd = 60 ? 90 μM). Monovalent chimeric proteins containing the two IgSF domains of rat CD48 or CD2 and domains 3 and 4 of rat CD4 (CD4d3+4) were anchored to fluorescent covaspheresTM via a CD4 monoclonal antibody (mAb) with the CD48 or CD2 domains available for ligand binding. Multivalent CD48-CD4d3 + 4 covaspheresTM gave strong specific binding to rat CD2 expressed on the surface of transfected Jurkat cells. CD48-CD4d3+4 was compared with CD48-IgG and CD48-IgM as tools for detecting binding at the cell surface. Soluble divalent CD48-IgG and decavalent CD48-IgM bound to soluble CD2 with a Koff of around 10?3 s?1 as determined using a BIAcoreTM biosensor. However, binding to cells by CD48-IgG and CD48-IgM was only detectable when they were immobilized on covaspheresTM and represented no increase in sensitivity over CD48-CD4 covaspheresTM when tested for binding to cells expressing high and low levels of CD2. CD48-CD4d3 + 4 covaspheresTM only bound to rat cells expressing CD2. In the reverse orientation, binding of CD2-CD4d3 + 4 covaspheresTM was dependent on expression of CD48. Pre-incubation of cells with CD2 or CD48 mAb abolished all binding of CD48-CD4d3 + 4 or CD2-CD4d3 + 4, respectively. The data provide no evidence for an alternative ligand for rat CD2 or CD48.  相似文献   
68.
Expression of the interleukin (IL)-2 receptor β chain in the IL-7-dependent pre-B cell line I × N/2B permitted growth in presence of either IL-2 or IL-7, allowing for a direct comparison of intracellular signaling events. Protein tyrosine phosphorylation was essential for IL-2- and IL-7-induced signal transduction since the tyrosine kinase inhibitor herbimycin A blocked proliferation in response to both factors. Western blot analysis of tyrosine-phosphorylated proteins revealed that both IL-2 and IL-7 stimulation led to enhanced phosphorylation of proteins of 170-, 145, 115- and 99-kDa, as well as induction of phosphorylation of a 96-kDa protein. However, a 55- and a 155-kDa protein were only phosphorylated after IL-2 stimulation. The 55-kDa protein specifically phosphorylated by IL-2 could be identified as p52shc which has recently been shown to be critically involved in Ras activation. Shc tyrosine phosphorylation as a result of IL-2 stimulation was consistently found in CTLL-2 cells and human T lymphoblasts. Taken together our results indicate that the IL-2- and IL-7-stimulated intracellular pathways are partially different and that Shc is a target of IL2-, but not IL-7-, stimulated tyrosine phosphorylation.  相似文献   
69.
Some studies have reported associations between COMT and MAO genotypes and aggression, though results have been inconsistent. We examined the relationship between Overt aggression scale (OAS) scores, and both MAOA and MAOB polymorphisms in a well-powered sample of 346 subjects with schizophrenia. We also examined COMT in a Stage II replication sample of 150 individuals, and combined these results with our previously reported (Stage I) findings for COMT. We found no evidence of any associations between OAS ratings and any of the polymorphisms investigated under different genetic models. There was no evidence of epistatic interaction between MAOA and COMT on OAS scores. These results fail to support the theory that functional polymorphisms within the MAOA, MAOB, or COMT genes, as determinants of catecholamine enzymatic activity, are risk factors for aggressive behavior.  相似文献   
70.
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