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   15576篇
  免费   782篇
  国内免费   83篇
耳鼻咽喉   156篇
儿科学   347篇
妇产科学   199篇
基础医学   1819篇
口腔科学   515篇
临床医学   1087篇
内科学   4547篇
皮肤病学   124篇
神经病学   944篇
特种医学   533篇
外科学   2600篇
综合类   55篇
预防医学   404篇
眼科学   211篇
药学   1060篇
中国医学   16篇
肿瘤学   1824篇
  2023年   101篇
  2022年   193篇
  2021年   303篇
  2020年   168篇
  2019年   206篇
  2018年   275篇
  2017年   242篇
  2016年   293篇
  2015年   339篇
  2014年   375篇
  2013年   472篇
  2012年   801篇
  2011年   901篇
  2010年   545篇
  2009年   456篇
  2008年   861篇
  2007年   880篇
  2006年   870篇
  2005年   842篇
  2004年   855篇
  2003年   868篇
  2002年   823篇
  2001年   380篇
  2000年   377篇
  1999年   390篇
  1998年   204篇
  1997年   168篇
  1996年   141篇
  1995年   143篇
  1994年   120篇
  1993年   153篇
  1992年   297篇
  1991年   256篇
  1990年   222篇
  1989年   196篇
  1988年   199篇
  1987年   189篇
  1986年   166篇
  1985年   164篇
  1984年   121篇
  1983年   93篇
  1982年   65篇
  1981年   63篇
  1979年   67篇
  1978年   63篇
  1977年   43篇
  1975年   51篇
  1974年   55篇
  1971年   42篇
  1969年   48篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Endoscopic resection has been accepted as the standard treatment for intramucosal gastric tumors of differentiated type. However, the indication was limited to small tumors to achieve en bloc resection and prevent local recurrence in cases of conventional endoscopic mucosal resection (EMR) such as the strip biopsy and the cap technique. To avoid multi‐fragmental resection, we have developed endoscopic submucosal dissection (ESD) as a new endoscopic resection technique. ESD is a remarkable technique, because we make it possible to remove the lesions en bloc regardless of size, shape, coexisting ulcer, and location. However, it is difficult or impossible to resect recurrent tumors en bloc in conventional EMR owing to hard fibrosis, and some patients need laparotomy. Using ESD, we can dissect the submucosal layer as we directly look at the submucosa, and remove the lesion safely and reliably even in cases of hard fibrosis. The key to treatment of recurrent tumors in ESD are as follows: (i) using enough submucosal injection solution (we use a mixture of Glyceol and 1% 1900 kDa hyaluronic acid preparation); (ii) incising the mucosa without fibrosis; (iii) understanding characteristics of various cutting devices, and changing other devices in difficult situations. In these ways we can remove the majority of the recurrent tumors en bloc. Hence, we consider that ESD is a very effective treatment which achieves excellent en bloc and complete resection rates and enables patients with intramucosal gastric tumors to a recurrent‐free survival even in recurrent tumors.  相似文献   
52.
AIM: The role of air plethysmography (APG) in the diagnosis of chronic venous insufficiency has not been well established. The purpose of this study was to elucidate the relationship between APG parameters and clinical severity in patients with chronic venous insufficiency. METHODS: Two hundred and ninety-four limbs in 154 patients with primary varicose veins were evaluated by APG. Limbs were categorized according to the clinical classification of chronic venous disease suggested by the Ad Hoc Committee on Reporting Standards in Venous Disease of the North American Chapter of the Society for Vascular Surgery and International Society for Cardiovascular Surgery (SVS/ ISCVS). RESULTS: The venous filling index (VFI) was significantly higher in classes 2, 3, 4, and 5+6 than in class 0 or 1, and did not differ among classes 2, 3, 4, 5+6. The ejection fraction did not differ significantly among the 6 classes, and the residual volume fraction was significantly higher in classes 2, 3, 5+6 than in class 0. CONCLUSIONS: APG is a reasonable method for distinguishing the presence or absence of chronic venous insufficiency, but it cannot discriminate the clinical severity. Among APG parameters, the VFI is the most useful diagnostic parameter in the evaluation of chronic venous insufficiency.  相似文献   
53.
Human urotensin-II (U-II) is the most potent vasoactive peptide identified to date, and may be involved in hypertension and atherosclerosis. We investigated the effects of the interactions between U-II or other vasoactive agents and mildly oxidized low-density lipoprotein (mox-LDL) or hydrogen peroxide (H2O2) on the induction of vascular smooth muscle cell (VSMC) proliferation. Growth-arrested rabbit VSMCs were incubated with vasoactive agents (U-II, endothelin-1, angiotensin-II, serotonin, or thromboxane-A2) in the presence or absence of mox-LDL or H2O2. [3H]Thymidine incorporation into DNA was measured as an index of VSMC proliferation. On interaction with mox-LDL or H2O2, U-II induced the greatest increase in [3H]thymidine incorporation among these vasoactive agents. A low concentration of U-II (10 nmol/l) enhanced the potential mitogenic effect of low concentrations of mox-LDL (120 to 337%) and H2O2 (177 to 226%). U-II at 50 nmol/l showed the maximal mitogenic effect (161%), which was abolished by G protein inactivator (GDP-beta-S), c-Src tyrosine kinase inhibitor (radicicol), protein kinase C (PKC) inhibitor (Ro31-8220), extracellular signal-regulated kinase (ERK) kinase inhibitor (PD98059), or Rho kinase inhibitor (Y27632). Mox-LDL at 5 microg/ml showed the maximal mitogenic effect (211%), which was inhibited by free radical scavenger (catalase), intracellular and extracellular antioxidants (N-acetylcysteine and probucol), nicotinamide adenine dinucleotide phosphate oxidase inhibitor (diphenylene iodonium), or c-Jun N-terminal kinase (JNK) inhibitor (SP600125). These results suggested that U-II acts in synergy with mox-LDL in inducing VSMC DNA synthesis at the highest rate among these vasoactive agents. Activation of the G protein/c-Src/PKC/ERK and Rho kinase pathways by U-II together with the redox-sensitive JNK pathway by mox-LDL may explain the synergistic interaction between these agents.  相似文献   
54.
55.
Background:   The aim of this study is to construct a simple screening test for the risk of falls in community-dwelling elder persons.
Methods:   A total of 1378 community-dwelling people aged 65 years and older in five different communities in Japan were asked to answer a self rated questionnaire including 22 items covering physical, cognitive, emotional and social aspects of functioning and environmental factors. At a six-month follow-up, the outcome of fall occurrence and the number of falls was ascertained by social workers, health visitors or nurses.
Results:   Five out of 22 items were selected using a logistic regression model. Using this five-item version, a screening test was constructed, and at the best cut-off point, the sensitivity and specificity were 68% and 70%, respectively. The validity of this scale was tested on persons with cognitive dysfunction.
Conclusion:   The simplicity and the predictive validity of the screening test support the use of this test in health check ups or general outpatient facilities.  相似文献   
56.
The primed status of T cells is markedly different among liver transplant recipients, due to a lifetime of antigen exposure and reduced thymopoiesis by aging, and diseases. This study aims to characterize the preoperative immunological status of CD8+ T cell subpopulations and relate it to the outcome for liver transplant recipients. We classified 112 liver transplant recipients into 5 groups, based on hierarchical clustering of the CD8+CD45 isoform proportion of T cells. In Groups I and II (pediatric), the naive T cell proportion was more than 50%. In adult recipients, Group III was characterized by a naive T cell proportion of 50%, Group IV had the greatest effector/memory T cells (EM), and Group V had the greatest proportion of effector T cells. In Groups IV and V, the effector T cell proportion was considerably higher, and was accompanied by marked downregulation of the CD27+CD28+ subsets and upregulation of interferon gamma (IFN)-gamma, tumor necrosis factor-alpha, and perforin expression. Group V recipients tended to be complicated postoperatively, with a significantly reduced survival rate (1 yr, 66.8%) and markedly reduced Eastern Cooperative Oncology Group performance status.  相似文献   
57.
Objectives It is known that, in fluorine-18 fluorodeoxyglucose Positron Emission Tomography (FDG PET) for the diagnosis of oral cancer, FDG uptake may vary even among different cases of the same squamous cell carcinoma. However, the details of this phenomenon have not yet been elucidated. In this study, we analyzed the relationship between histopathological findings in oral squamous cell cancer and PET findings on FDG uptake. Methods We examined 45 patients with oral squamous cell carcinoma who had undergone FDG PET before treatment. FDG uptake was assessed by a standardized uptake value (SUV) calculated according to the PET-measured tissue concentration of FDG, the administered dose of radionuclide, and the body weight of the patient. The relationship between the mean SUV and each of the following parameters was examined: histological grade of malignancy, degree of cell differentiation, size and/or local extent of the primary lesion, and cell density of the tumor. Results The mean SUV of FDG uptake did not depend on the histological grade of malignancy or on the degree of cell differentiation, but tended to be greater the larger the primary lesion. SUV also depended on cell density, increasing with the percentage of tumor parenchyma. Conclusions It is concluded that cancer cell density greatly influences the SUV of FDG, in that a tumor with fewer cellular elements in cancer tissue tends to become a false negative.  相似文献   
58.
Summary Biomineralization was investigated using embryonic mouse mandibular first molars (M1) cultured in the presence or absence of fetal calf serum. Metabolic features including cell division and Ca2+ and phosphate incorporation into dentine and enamel extracellular matrices were analyzed. The relative timing and magnitude of DNA synthesis for serumless cultures was comparable toin vivo controls. Isotopic calcium and phosphate incorporation into the mineral phase of dentine and enamel matrices, in the absence of serum, fluctuated during development. Molar tooth morphogenesis, cytodifferentiation, and extracellular matrix formation approximated late crown-stage development in serumless cultures. Von Kossa histochemical staining indicated calcium phosphate salt formation in serumless cultures. Analysis of anhydrous fixation-prepared enamel and dentine representing serumless cultured explants indicated that crystal size and orientation were comparable toin vivo enamel and dentine. In contrast, serum-supplemented cultures showed atypical crystal size and orientation. Calcium/phosphorous (Ca/P) ratio values for serumless cultures after 21 days showed Ca/P enamel values of 2.03 (SD±0.04, p<0.025) and dentine values of 1.89 (SD±0.01, p<0.025). Electron diffraction patterns of enamel and dentine formed in serumless cultures were principally those of highly-ordered crystalline hydroxyapatite. Our results suggest that tissue-specific dentine and enamel biomineralization is regulated by endogenous factors intrinsic to the developmental program of embryonic tooth organs during serumless culture.  相似文献   
59.
Porcine teschovirus (PTV) antigens were detected by a streptavidin‐biotin complex method in formalin‐fixed paraffin‐embedded tissues of 3‐week‐old pigs that had been inoculated intravenously with PTV Talfan strain. PTV antigens were detected in cytoplasm of nerve cells, glial cells and endothelial cells in the cerebellar nuclei, the grey matter of the midbrain, pons and medulla oblongata and the ventral horn of the spinal cord and of ganglion cells in the spinal ganglion corresponding to those lesions characterized as non‐suppurative encephalomyelitis and ganglionitis. The results of this study suggest that nerve cells of the brain stem and spinal cord and ganglion cells of the spinal ganglion permit PTV replication and represent the main target cell population of PTV. This is the first study to demonstrate PTV antigen by immunohistochemistry in formalin‐fixed paraffin‐embedded tissue specimens from pigs infected with PTV.  相似文献   
60.
Background : We have previously shown that eradication of Helicobacter pylori increases acid secretion in H. pylori -associated enlarged fold gastritis.
Aim : To investigate whether locally produced interleukin-1β is possibly involved in the inhibition of acid secretion in H. pylori gastritis.
Methods : IL-1β release from the gastric body mucosa was determined by short-term culture of biopsy specimens in 13 patients with enlarged fold gastritis (all H. pylori -positive), five H. pylori -positive and 10 H. pylori -negative patients without enlarged folds. The acid-inhibitory effect of locally produced IL-1β was examined by [14C]-aminopyrine uptake assay using isolated rabbit gastric glands.
Results : IL-1β release was significantly greater in patients with enlarged fold gastritis, significantly correlated with both basal and tetragastrin-stimulated acid outputs in the H. pylori -positive patients ( r  = −0.591 and r  = −0.641, respectively; P  < 0.01), and significantly decreased with concomitant increases in acid secretions after eradication of H. pylori . [14C]-aminopyrine uptake was inhibited by IL-1β in a dose-dependent manner.
Conclusions : Increased production of IL-1β caused by H. pylori infection is possibly involved in the inhibition of acid secretion in enlarged fold gastritis.  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