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   6328篇
  免费   623篇
  国内免费   78篇
耳鼻咽喉   90篇
儿科学   186篇
妇产科学   193篇
基础医学   765篇
口腔科学   70篇
临床医学   653篇
内科学   1382篇
皮肤病学   90篇
神经病学   664篇
特种医学   158篇
外科学   969篇
综合类   172篇
一般理论   5篇
预防医学   703篇
眼科学   284篇
药学   462篇
中国医学   3篇
肿瘤学   180篇
  2023年   26篇
  2021年   91篇
  2020年   44篇
  2019年   96篇
  2018年   99篇
  2017年   94篇
  2016年   92篇
  2015年   94篇
  2014年   150篇
  2013年   283篇
  2012年   318篇
  2011年   405篇
  2010年   223篇
  2009年   226篇
  2008年   383篇
  2007年   407篇
  2006年   391篇
  2005年   436篇
  2004年   432篇
  2003年   372篇
  2002年   365篇
  2001年   72篇
  2000年   37篇
  1999年   65篇
  1998年   96篇
  1997年   84篇
  1996年   87篇
  1995年   59篇
  1994年   82篇
  1993年   59篇
  1992年   39篇
  1991年   46篇
  1990年   47篇
  1989年   38篇
  1988年   36篇
  1987年   29篇
  1986年   43篇
  1985年   61篇
  1984年   59篇
  1983年   51篇
  1982年   64篇
  1981年   53篇
  1980年   65篇
  1979年   36篇
  1978年   46篇
  1977年   29篇
  1976年   39篇
  1974年   37篇
  1973年   25篇
  1961年   20篇
排序方式: 共有7029条查询结果,搜索用时 15 毫秒
71.
72.
73.
Recent advances in clinical proteomics data acquisition have led to the generation of datasets of high complexity and dimensionality. We present here a visualization method for high-dimensionality datasets that makes use of neuronal vectors of a trained growing cell structure (GCS) network for the projection of data points onto two dimensions. The use of a GCS network enables the generation of the projection matrix deterministically rather than randomly as in random projection. Three datasets were used to benchmark the performance and to demonstrate the use of this deterministic projection approach in real-life scientific applications. Comparisons are made to an existing self-organizing map projection method and random projection. The results suggest that deterministic projection outperforms existing methods and is suitable for the visualization of datasets of very high dimensionality.  相似文献   
74.
Hugh  Firth Ian  Oswald 《Psychophysiology》1975,12(5):602-606
There are a number of reports suggesting an association between profusion of eye movements and active dreaming. It has however been suggested that this relationship might only be evident in comparisons across the night and would not be evident in comparisons within one REM period. Data from 20 subjects taking placebo, amylobarbitone, and nitrazepam were used to test this. Dream reports were collected from REM awakenings and rated blind as visually active or passive. Eye movement profusion (number of 2 sec epochs) was assessed for each REM period. Correlation between dream content and eye movement was low but significant in comparisons including the whole night, and including data from drug, withdrawal, and placebo conditions. A significant correlation was not consistently obtained, however, when data from each REMP were considered separately. Correlations based on data from non-drug nights only were also small and could have been due to chance effects alone. The low correlations were not explicable solely by poor reliability of content ratings. It is concluded that the relationship between visually active dreaming and eye movement is slight, and may not hold when time of night is adequately controlled.  相似文献   
75.
Human decidua has been shown to produce a number of cytokines. We hypothesized that decidual cytokine production influences cord blood mononuclear cell (CBMC) cytokine production and that cytokine profiles of decidua from allergic women differ from those of decidua from nonallergic women. Using enzyme-linked immunosorbent assay, we measured unstimulated and concanavalin A/phorbol myristate acetate-stimulated production of interleukin-4 (IL-4), IL-5, IL-10, IL-13 and interferon- gamma (IFN-gamma) by decidual explants from 59 healthy women delivered by unlabored cesarean section and from corresponding CBMCs in 39 of the 59. Except for IL-10, there was little or no unstimulated cytokine production. There was a strong correlation between stimulated decidual and stimulated CBMC IFN-gamma production (p = 0.01). In allergic women the ratio of IL-13 to IL-4 production was increased in stimulated explants (p = 0.03). Stimulated CBMCs from infants of allergic mothers were more likely to produce detectable levels of IL-5 than those from infants of nonallergic mothers (p = 0.04) and had a tendency toward higher IL-13 levels as well (p = 0.07). These results suggest that maternal and fetal IFN-gamma production is closely linked and that maternal allergy appears to influence cytokine production in the neonate for IL-5 and possibly IL-13.  相似文献   
76.
BACKGROUND: Chinese herbal medicine has a long history of human use. A novel herbal formula, anti-asthma herbal medicine intervention (ASHMI), has been shown to be an effective therapy in a murine model of allergic asthma. OBJECTIVE: This study was undertaken to compare the efficacy, safety, and immunomodulatory effects of ASHMI treatment in patients with moderate-severe, persistent asthma with prednisone therapy. METHODS: In a double-blind trial, 91 subjects underwent randomization. Forty-five subjects received oral ASHMI capsules and prednisone placebo tablets (ASHMI group) and 46 subjects received oral prednisone tablets and ASHMI placebo capsules (prednisone group) for 4 weeks. Spirometry measurements; symptom scores; side effects; and serum cortisol, cytokine, and IgE levels were evaluated before and after treatment. RESULTS: Posttreatment lung function was significantly improved in both groups as shown by increased FEV(1) and peak expiratory flow findings (P<.001). The improvement was slightly but significantly greater in the prednisone group (P<.05). Clinical symptom scores, use of beta(2)-bronchodilators, and serum IgE levels were reduced significantly, and to a similar degree in both groups (P<.001). T(H)2 cytokine levels were significantly reduced in both treated groups (P<.001) and were lower in the prednisone-treated group (P<.05). Serum IFN-gamma and cortisol levels were significantly decreased in the prednisone group (P<.001) but significantly increased in the ASHMI group (P<.001). No severe side effects were observed in either group. CONCLUSION: Anti-asthma herbal medicine intervention appears to be a safe and effective alternative medicine for treating asthma. In contrast with prednisone, ASHMI had no adverse effect on adrenal function and had a beneficial effect on T(H)1 and T(H)2 balance.  相似文献   
77.
In vivo gene transfer of lefty leads to implantation failure in mice   总被引:1,自引:0,他引:1  
BACKGROUND: Endometrium is a unique tissue that is prepared for implantation of blastocyst during each menstrual cycle. In humans, if implantation does not occur or fails, endometrium is shed. METHODS AND RESULTS: We identified ebaf/lefty, as a key cytokine, highly expressed in human endometrium during the non-receptive phase of tissue remodelling. Lefty was increased in the endometria of a number of patients with 'unexplained infertility' during the receptive phase, suggesting dysregulation of lefty as a potential factor contributing to infertility. Here, we showed that induction of a similar state of lefty overexpression in endometrium, by in vivo gene delivery, decreased implantation in pregnant mice. This state of overexpression could be induced by a retroviral vector transducing lefty or by liposome-mediated introduction of a lefty expression vector. Analysis of endometrium showed increased lefty after in vivo gene transfer. CONCLUSION: These findings suggest that induction of a state of lefty overexpression in endometrium leads to reduced implantation.  相似文献   
78.
The murine IL-4and IL-5genes encode hemopoietic growth factors involved in the stimulation, proliferation, and differentiation of cells of the T lymphocyte, B lymphocyte, and granulocyte lineages. We have mapped the Il-4 and Il-5 loci representing the structural genes for IL-4and IL-5,respectively, to mouse chromosome 11 using Chinese hamster ×mouse and rat × mouse somatic cell hybrids. Physical linkage studies of the IL-4and IL-5genes by pulsed field gel electrophoresis have shown that they are closely linked, being 110–180 kb apart. Since the Il-5 locus maps to the interface of bands A5 and B1 in the same location as the genes for IL-3and GM-CSF, this places these three cytokine genes, as well as the IL-4 gene, within a region of about 5000–10,000 kb. The present physical linkage studies indicate that the IL-4and IL-5genes are a minimum of 600 kb apart from the closely linked IL-3and GM-CSFgenes. The gene clustering, together with similarities in gene structure, regulation, and biological function, raises the possibility that the four genes may be part of a distantly related cytokine gene family.  相似文献   
79.
BACKGROUND: Detailed assessment of antibody responses to allergens reveals clinically relevant information about both host response and antigen structure. Microarray technology offers advantages of scale and parallel design over previous methods of epitope mapping. OBJECTIVE: We designed a redundant peptide microarray for IgE and IgG4 epitope mapping of the previously characterized peanut allergen, Ara h 2. METHODS: Six complete sets of overlapping peptides were commercially synthesized and site-specifically bound to epoxy-derivatized glass slides in triplicate. Peptides were 10, 15, or 20 amino acids in length with an offset of either 2 or 3 amino acids. A total of 10 control and 45 peanut-allergic sera were assayed. Specific IgE and IgG4 were detected by using fluorochrome-labeled monoclonal secondary antibodies. RESULTS: By using 15-mer and 20-mer peptides, we could define 11 antigenic regions, whereas only 5 were identifiable using 10-mers. Controls and patients produced IgG4 recognizing a comparable number of Ara h 2 peptides, although the dominant epitopes were distinct. As expected, patient IgE bound a larger number of Ara h 2 peptides (9.4% vs 0.9%). IgE and IgG4 epitopes recognized by patients were largely the same, and there was a positive association between IgE and IgG(4) signal, suggesting coordinate regulation. Cluster analysis of peptide binding patterns confirmed the specificity of antibody-peptide interactions and was used to define 9 core epitopes ranging from 6 to 16 residues in length-7 of which (78%) agreed with previous mapping. CONCLUSION: Epitope mapping by microarray peptide immunoassay and cluster analysis reveals interpatient heterogeneity and a more detailed map.  相似文献   
80.
An unexpected dose related increase in oral squamous cell carcinomas was observed in a standard 2-year carcinogenicity study with a novel calcium channel blocker, in which Wistar rats received daily doses of 0, 1.5, 7, 20, or 40 mg/kg of the compound mixed with a standard diet containing fibers from barley. This finding was associated with an increased incidence of severe (destructive) periodontitis and the formation of oro-nasal fistulae at the 2 highest doses. Five assays of the compound for genotoxicity were negative indicating that a genotoxic effect was highly improbable. To investigate the underlying pathogenic mechanisms a second 2-year study in the same strain of rats was initiated and the influence of the diet and/or a possible local irritancy by the drug was assessed. In this second study the compound was administered by oral gavage at daily doses of 0, 7, or 40 mg/kg (later reduced to 20 mg/kg due to systemic intolerance) to rats maintained either on the standard diet or on a low fiber diet assumed to be less aggressive in terms of inducing periodontal lesions. Dose dependent gingival overgrowth (a class-related effect) was observed in the incisor and molar teeth area of all treated groups but was independent of the diet used. No oral tumors were found in the standard diet or low fiber diet controls and all treatment groups fed the low fiber diet, whereas in the high-dose group fed the standard diet a total of 8 oral squamous cell carcinomas were detected in association with an increased incidence of severe periodontitis. These results indicate that the increased incidence of squamous cell carcinomas observed upon chronic administration of the compound is not due to a direct tumorigenic effect of the drug. Tumor formation is attributable to severe periodontal disease favored by the diet and class related gingival overgrowth.  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