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   4689篇
  免费   372篇
  国内免费   34篇
耳鼻咽喉   32篇
儿科学   171篇
妇产科学   101篇
基础医学   588篇
口腔科学   115篇
临床医学   600篇
内科学   941篇
皮肤病学   49篇
神经病学   473篇
特种医学   364篇
外科学   565篇
综合类   96篇
一般理论   1篇
预防医学   363篇
眼科学   78篇
药学   332篇
中国医学   18篇
肿瘤学   208篇
  2022年   24篇
  2021年   55篇
  2020年   34篇
  2019年   60篇
  2018年   77篇
  2017年   47篇
  2016年   67篇
  2015年   75篇
  2014年   127篇
  2013年   156篇
  2012年   226篇
  2011年   218篇
  2010年   150篇
  2009年   120篇
  2008年   221篇
  2007年   222篇
  2006年   216篇
  2005年   190篇
  2004年   184篇
  2003年   204篇
  2002年   188篇
  2001年   173篇
  2000年   165篇
  1999年   129篇
  1998年   98篇
  1997年   105篇
  1996年   111篇
  1995年   77篇
  1994年   58篇
  1993年   75篇
  1992年   89篇
  1991年   86篇
  1990年   105篇
  1989年   120篇
  1988年   109篇
  1987年   94篇
  1986年   95篇
  1985年   85篇
  1984年   44篇
  1983年   48篇
  1982年   23篇
  1981年   33篇
  1980年   27篇
  1979年   30篇
  1978年   27篇
  1977年   23篇
  1976年   32篇
  1975年   19篇
  1973年   23篇
  1971年   17篇
排序方式: 共有5095条查询结果,搜索用时 551 毫秒
51.
BACKGROUND: Chronic cough often lasts for more than 1 year and is associated with airway inflammation. The effect of inhaled corticosteroids on symptom severity and inflammatory mediator levels in these patients is unknown. OBJECTIVE: We sought to determine whether inhaled corticosteroids reduce cough severity and sputum mediator concentrations in patients with chronic persistent cough. METHODS: We performed a double-blind, randomized, placebo-controlled crossover study with inhaled fluticasone, 500 microg twice daily, and placebo for 14 days in 88 patients with cough for more than 1 year, with normal chest radiography and spirometry results. Outcome measures were a daily cough visual analogue scale and induced sputum concentrations of eosinophilic cationic protein (ECP), myeloperoxidase, leukotriene B(4) (LTB(4)), leukotrienes C(4)/D(4)/E(4) (cysteinyl leukotrienes [Cys-LTs]), prostaglandin E(2) (PGE(2)), IL-8, and TNF-alpha. Sputum cell counts, exhaled nitric oxide levels, and carbon monoxide levels were also measured. RESULTS: There was a significant improvement in the cough visual analogue scale after inhaled fluticasone compared with placebo (mean difference, 1.0; 95% CI, 0.4-1.5; P <.001). LTB(4), Cys-LT, and PGE(2) levels were increased in all causes of cough. Sputum ECP counts, exhaled nitric oxide levels, and carbon monoxide levels decreased significantly after inhaled fluticasone. There was no change in sputum cell counts and other mediator concentrations. CONCLUSION: Cough severity and sputum ECP levels are modestly reduced by inhaled corticosteroids in patients with chronic cough persisting for more than 1 year. LTB(4), Cys-LT, PGE(2), IL-8, myeloperoxidase, and TNF-alpha levels are unaltered by this therapy. This raises the possibility that drugs targeted to reduce the effects of these mediators might be of benefit in chronic persistent cough.  相似文献   
52.
AIMS: To study the expression of Ki-67 and cytokeratin 20 (CK20) in a group of hyperplastic polyps (including a group with "atypical" features) with the aim of determining whether upper crypt Ki-67 staining and lower crypt CK20 staining correlated with these atypical features, as assessed by light microscopy. METHODS: Fifty seven formalin fixed, paraffin wax embedded hyperplastic colorectal polyps from 53 patients were selected on histological grounds; these comprised 26 typical polyps and 31 with atypical features, which included nuclear hyperchromatism, basal crowding, and increased mitotic activity. These polyps were examined using a standard immunohistochemical method with antibodies against CK20 and Ki-67. Comparisons were made with normal mucosa, adenomatous polyps, and carcinomas. RESULTS: Of the 26 typical polyps, 17 showed the usual pattern of lower crypt Ki-67 and upper crypt CK20 staining; one with upper crypt Ki-67 staining but normal surface CK20 staining; seven with Ki-67 confined to the lower half of crypts but with scattered lower crypt CK20; and one with both upper crypt Ki-67 staining, together with scattered CK20 basal staining. Of the 31 polyps with atypical features, 11 showed the usual staining pattern of lower crypt Ki-67 staining and surface staining with CK20; two showed Ki-67 staining extending into the upper half of crypts, but with a normal surface staining with CK20; 14 showed Ki-67 confined to the lower half of crypts, but scattered lower crypt staining with CK20; and four showed upper crypt Ki-67 staining together with scattered CK20 lower crypt staining. CONCLUSIONS: The normal pattern of lower crypt Ki-67 and upper crypt CK20 was seen in 28 of the 57 hyperplastic polyps and, in general, this corresponded with standard light microscopic appearances. Twenty one of the 57 polyps showed lower crypt mosaic CK20 staining, which in general corresponded with basal abnormalities on light microscopy, although seven specimens had normal appearances. Two smaller subsets emerged, one showing upper crypt Ki-67 staining in the presence of normal CK20 expression (three cases) and another in which a combination of lower crypt CK20 and upper crypt Ki-67 expression was seen (five cases). This last pattern was similar to that of neoplastic polyps and raises the possibility that a subgroup of hyperplastic polyps exists that may be a variant with malignant potential. Further studies with markers of mismatch repair genes and K-ras mutations may help to clarify this issue.  相似文献   
53.
54.
We examined the extent to which maternal antisocial behavior (ASB) is directly related to child conduct problems and social competence and assessed the potential mediating role of negative parenting. The sample included 93 adolescent mothers and their children (44 boys, 49 girls). Mothers retrospectively reported about their ASB since the child's birth, through Grade 2. Negative parenting was coded during a parent-child interaction task (PCIT) at Grade 2. Teachers assessed child outcomes at Grade 3. Maternal ASB during the child's life was directly related to parenting and both child outcomes. In the overall sample, negative parenting partially mediated the relation between maternal ASB and child conduct problems. However, the pattern of relations differed by sex. For boys, maternal ASB was directly related to conduct problems, independent of parenting. For girls, maternal ASB was strongly related to parenting but not conduct problems. Negative parenting did not mediate the relation between maternal ASB and child social competence. Implications for intervention and future research are discussed.  相似文献   
55.
Neuropeptides are found in specific subpopulations of primary afferent neurones. Peptide expression can be altered following axotomy or under the influence of nerve growth factor. Here we have examined the consequence of altering the peripheral target of afferent neurones. Many unmyelinated afferents from skin contain substance P-like immunoreactivity (SPLI) whilst those from muscle do not. We have found that fibres will innervate inappropriate tissue types. We have therefore cut and cross-anastomosed a skin and muscle hindlimb nerve in the rat and 10-12 weeks later analysed the regenerated nerves immunocytochemically for SPLI. Muscle afferents inappropriately reinnervating skin were found to contain many SPLI fibres in contrast to control nerves resutured to their own distal stumps. Conversely, skin afferents made to innervate muscle showed reduced levels of peptide staining. These results demonstrate the plasticity of peptide expression and suggest that factors in peripheral tissue or perhaps distal nerve sheaths exert a trophic influence on nervous system function.  相似文献   
56.
The allelic frequency of the gene for the K variant of butyrylcholinesterase (BCHE-K) was 0.17 in 74 subjects with late-onset (age > 65 years) histopathologically diagnosed Alzheimer's disease (AD), which was higher than the frequencies in 104 elderly control subjects (0.09), in 14 early-onset cases of confirmed AD (0.07) and in 29 confirmed cases of other dementia (0.10). The association of BCHE-K with late-onset AD was limited to carriers of the epsilon 4 allele of the apolipoprotein E gene (APOE), among whom the presence of BCHE-K gave an odds ratio of confirmed late-onset AD of 6.9 (95% C.I. 1.65-29) in subjects > 65 years and of 12.8 (1.9-86) in subjects > 75 years. In APOE epsilon 4 carriers over 75 years, only 1/22 controls, compared with 10/24 confirmed late-onset AD cases, had BCHE-K. We suggest that BCHE-K, or a nearby gene on chromosome 3, acts in synergy with APOE epsilon 4 as a susceptibility gene for late-onset AD.   相似文献   
57.
58.
The ocular tropism of adenovirus type 37 (Ad37) does not correlate with the wide distribution of the 46-kDa coxsackievirus and adenovirus receptor (CAR), the major receptor for most adenovirus serotypes. We previously found that Ad37 infects and binds well to conjunctival cells (Chang C), but poorly to lung epithelial (A549) cells that express CAR and hypothesized that this serotype uses a distinct receptor that is selectively expressed on conjunctival cells. To test this, we produced particles of a fiber-deleted Ad5 vector containing the Ad37 fiber protein. The "pseudotyped" vector infected Chang C cells better than A549 cells using a CAR-independent pathway. Ad37 binding was calcium-dependent and was abolished by protease digestion of cell surface proteins. Using a virus overlay protein blot assay (VOPBA), we detected calcium-dependent Ad37 binding to 50- and 60-kDa membrane proteins on permissive Chang C cells. In contrast, calcium-dependent binding was detected with only the 60-kDa protein on nonpermissive A549 cells. Ad19p, a closely related serotype that failed to bind to conjunctival cells, recognized the 60-kDa, but not the 50-kDa, protein. Ad37 has been reported to use sialic acid instead of CAR as a cell receptor on A549 cells. Pretreatment of Chang C cells with neuraminidase abolished Ad37 binding to only the 60-kDa protein, suggesting that sialic acid mediates Ad37 binding to the 60-kDa protein. The pseudotyped Ad37 vector was also able to infect neuraminidase-treated Chang C cells. Thus, subgroup D adenoviral binding to the 50-kDa protein is calcium-dependent and cell type- and serotype-specific, whereas binding to the 60-kDa protein is not necessary for infection of conjunctival cells. Together, these data suggest that the 50-kDa protein is the major receptor for Ad37 on conjunctival cells.  相似文献   
59.
60.
Summary Accurate volume determination of the encephalic ventricles is of importance in several clinical conditions, including Alzheimer's presenile dementia, schizophrenia, and benign intracranial hypertension. Previous studies have investigated the accuracy with which magnetic resonance imaging (MRI) can be used in clinical practice to evaluate the encephalic ventricles. However, adequate evaluation of pathological conditions depends on a sufficient amount of morphometric data from normal subjects. To begin establishing this data base for normal subjects, we evaluated the MRI scans of 38 subjects found to have no apparent pathology and calculated the ventricular volume in each case by using methods previously developed in our laboratory. The results were then compared with published volumes determined from studies that used either ventricular casts or computerized tomographic scans. The average total ventricular volume for all 38 subjects was 17.4 cm3, while that for males was 16.3 cm3 and that for females was 18.0 cm3. A small but significant correlation was found between age of subject and ventricular volume, with ventricular size increasing with age.
Evaluation du volume des ventricules cérébraux à partir des images obtenues en résonance magnétique nucléaire chez 38 sujets humains
Résumé La détermination exacte du volume des ventricules cérébraux est importante en clinique comme par exemple dans la démence présénile d'Alzheimer, la schizophrénie et l'hypertension intracrânienne bénigne. Des études antérieures ont étudié la fiabilité de la résonance magnétique nucléaire en pratique clinique pour évaluer le volume des ventricules cérébraux. Toutefois une évaluation correcte dans les conditions pathologiques implique une bonne connaissance des données morphométriques du sujet normal. Pour établir ces données sur « le sujet normal », nous avons étudié les coupes obtenues en IRM chez 38 sujets apparemment indemnes de toute pathologie; nous avons calculé le volume ventriculaire dans chaque cas en utilisant des méthodes mises au point auparavant dans notre laboratoire. Les résultats ont été ensuite comparés avec ceux obtenus par d'autres études utilisant soit des moules ventriculaires, soit des coupes tomographiques computérisées. Le volume ventriculaire total moyen chez 38 sujets est de 17,4 cm3, mais il est chez les sujets masculins de 16,3 cm3 et chez les sujets de sexe féminin de 18 cm3. Une corrélation faible mais significative a été trouvée entre l'âge du sujet et le volume ventriculaire, étant entendu que la taille du ventricule augmente avec l'âge.
  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