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   24917篇
  免费   1445篇
  国内免费   136篇
耳鼻咽喉   250篇
儿科学   633篇
妇产科学   510篇
基础医学   3740篇
口腔科学   1073篇
临床医学   2204篇
内科学   5786篇
皮肤病学   677篇
神经病学   2231篇
特种医学   587篇
外科学   2246篇
综合类   54篇
一般理论   11篇
预防医学   2362篇
眼科学   483篇
药学   1696篇
中国医学   113篇
肿瘤学   1842篇
  2024年   33篇
  2023年   256篇
  2022年   604篇
  2021年   1029篇
  2020年   615篇
  2019年   826篇
  2018年   934篇
  2017年   648篇
  2016年   778篇
  2015年   849篇
  2014年   1118篇
  2013年   1416篇
  2012年   2204篇
  2011年   2308篇
  2010年   1207篇
  2009年   993篇
  2008年   1703篇
  2007年   1641篇
  2006年   1490篇
  2005年   1376篇
  2004年   1210篇
  2003年   1021篇
  2002年   909篇
  2001年   113篇
  2000年   79篇
  1999年   98篇
  1998年   125篇
  1997年   108篇
  1996年   92篇
  1995年   67篇
  1994年   59篇
  1993年   61篇
  1992年   65篇
  1991年   55篇
  1990年   38篇
  1989年   43篇
  1988年   31篇
  1987年   21篇
  1986年   33篇
  1985年   28篇
  1984年   29篇
  1983年   18篇
  1982年   19篇
  1981年   15篇
  1979年   16篇
  1978年   9篇
  1977年   10篇
  1969年   14篇
  1968年   11篇
  1967年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
During the 30 months of surveillance period, 85 pAmpC-producing isolates were detected (prevalence 0.56% overall): blaCMY-2 gene in 70 E. coli, 2 K. pneumoniae and 6 P. mirabilis isolates; and the blaDHA-1 gene in 4 E. coli and 3 K. pneumoniae. In 8.23% of them, other β-lactamases (predominantly OXA-1) were identified. All pAmpC-producing isolates were susceptible to carbapenems, whereas high resistance to nalidixic acid, ciprofloxacin and trimethoprim-sulfamethoxazole was observed among pAmpC-producing isolates (80%, 60%, and 44.7%, respectively). In hospital patients, predisposing factors such as prior antibiotic use, previous hospitalization, presence of an indwelling device, invasive urinary tract procedures and mechanical ventilation were observed. In the community setting, urinary tract infection was the most common type of infection related to pAmpC-producing isolates. A wide heterogeneity of clones was found among our E. coli isolates by PFGE, suggesting that this mechanism of resistance is not due to the dissemination of a clonal strain. Surveillance of these resistance mechanisms in the community is thus needed. Awareness of pAmpC dynamic is required to prevent introduction into hospitals and to control the spread of this emerging resistance within the community.  相似文献   
992.

OBJECTIVE:

To evaluate the effects of the levels of glycemic control on the frequency of clinical complications following invasive dental treatments in type 2 diabetic patients and suggest appropriate levels of fasting blood glucose and glycated hemoglobin considered to be safe to avoid these complications.

METHOD:

Type 2 diabetic patients and non-diabetic patients were selected and divided into three groups. Group I consisted of 13 type 2 diabetic patients with adequate glycemic control (fasting blood glucose levels <140 mg/dl and glycated hemoglobin (HbA1c) levels <7%). Group II consisted of 15 type 2 diabetic patients with inadequate glycemic control (fasting blood glucose levels >140 mg/dl and HbA1c levels >7%). Group III consisted of 18 non-diabetic patients (no symptoms and fasting blood glucose levels <100 mg/dl). The levels of fasting blood glucose, glycated HbA1c, and fingerstick capillary glycemia were evaluated in diabetic patients prior to performing dental procedures. Seven days after the dental procedure, the frequency of clinical complications (surgery site infections and systemic infections) was examined and compared between the three study groups. In addition, correlations between the occurrence of these outcomes and the glycemic control of diabetes mellitus were evaluated.

RESULTS:

The frequency of clinical outcomes was low (4/43; 8.6%), and no significant differences between the outcome frequencies of the various study groups were observed (p>0.05). However, a significant association was observed between clinical complications and dental extractions (p = 0.02).

CONCLUSIONS:

Because of the low frequency of clinical outcomes, it was not possible to determine whether fasting blood glucose or glycated HbA1c levels are important for these clinical outcomes.  相似文献   
993.
Assessing cytomegalovirus (CMV)-specific cell-mediated immunity (CMI) represents an appealing strategy for identifying transplant recipients at risk of infection. In this study, we compared two gamma interferon-releasing assays (IGRAs), Quantiferon-CMV and CMV enzyme-linked immunosorbent spot (ELISPOT), to determine the ability of each test to predict protective CMV-specific T-cell responses. Two hundred twenty-one Quantiferon-CMV and ELISPOT tests were conducted on 120 adult kidney transplant recipients (KTRs), including 100 CMV-seropositive transplant recipients (R+) and 20 CMV-seronegative transplant recipients of a CMV-positive donor (D+/R). As a control cohort, 39 healthy adult subjects (including 33 CMV-seropositive and 6 CMV-seronegative subjects) were enrolled. CMV IgG serology was used as a reference for both tests. In the CMV-seropositive individuals, the ELISPOT and Quantiferon-CMV assays provided 46% concordance with the serology, 12% discordance, 18% disagreement between ELISPOT or Quantiferon-CMV and the serology, and 24% gray areas when one or both tests resulted in weak positives. None of the CMV-seronegative subjects showed detectable responses in the ELISPOT or the Quantiferon-CMV test. In transplant recipients, both the ELISPOT and Quantiferon-CMV assays positively correlated with each other and negatively correlated with CMV DNAemia in a significant way (P < 0.05). During the antiviral prophylaxis, all 20 D+/R KTRs we examined displayed undetectable Quantiferon-CMV and ELISPOT results, and there was no evidence of CMV seroconversion. The receiving operator curve (ROC) statistical analysis revealed similar specificities and sensitivities in predicting detectable viremia (areas under the curve [AUC], 0.66 and 0.62 for Quantiferon-CMV and ELISPOT, respectively). ELISPOT and Quantiferon-CMV values of >150 spots/200,000 peripheral blood mononuclear cells (PBMCs) and >1 to 6 IU gamma interferon (IFN-γ) were associated with protection from CMV infection (odds ratios [OR], 5 and 8.75, respectively). In transplant recipients, the two tests displayed similar abilities for predicting CMV infection. Both the ELISPOT and Quantiferon-CMV assays require several ameliorations to avoid false-negative results.  相似文献   
994.
Because the fibroblast has a remarkable capability of phenotypic modulations, reflected in both morphologic and immunohistochemical (IHC) changes, ultrastructural studiesare mandatory to identify the variants of fibroblasts. Myofibroblasts or histiofibroblasts are such examples, demonstrating chimeric ultrastructural features of fibroblastic cells in common with smooth muscle cells or with histiocytes, respectively. The presence of epithelioid fibroblastic cells sharing morphologic features with epithelial or plasma cells has not been yet characterized. The authors identified 4 cases of fibrosarcomas (FS) characterized by an unusual phenotype and associated with peculiar ultrastructural findings. The electron microscopic (EM) findings were correlated with the histologic appearance and immunoprofile. All tumors were located in the extremities, 3 in soft tissues and 1 in the bone. By light microscopy 2 cases were composed predominantly by round uniform cells with a striking plasmacytoid appearance. One case mimicked carcinoma, composed predominantly by epithelioid cells and scattered giant tumor cells. The fourth case showed a mixture of plasmacytoid-like and epithelioid cells. By IHC, tumor cells were positive for vimentin and in 2 cases also for epithelial membrane antigen. Kappa/lambda light chain and cytokeratins markers were negative. By EM all 4 tumors showed in addition to classic features of fibroblasts, unusual epithelial-type features, such as secretory granules of "neurosecretory-type" (3 cases), rudimentary cell junctions (3 cases), microvilli (2 cases), and lumen-like structures (1 case). One plasmacytoid-type tumor showed finely granular extracellular deposits. The study describe 4 examples of fibrosarcomas with unusual features at the ultrastructural level, which are associated microscopically with a peculiar phenotype, mimicking plasmacytoma or carcinoma. These findings broaden the spectrum of fibroblastic cell variants in neoplasia.  相似文献   
995.
996.
The representation of serial position in sequences is an important topic in a variety of cognitive areas including the domains of language, memory, and motor control. In the neuropsychological literature, serial position data have often been normalized across different lengths, and an improved procedure for this has recently been reported by Machtynger and Shallice (2009) Machtynger, J. and Shallice, T. 2009. Normalizing serial position analyses: The Proportional Accountability algorithm. Cognitive Neuropsychology, 26: 217222. [Taylor & Francis Online], [Web of Science ®] [Google Scholar]. Effects of length and a U-shaped normalized serial position curve have been criteria for identifying working memory deficits. We present simulations and analyses to illustrate some of the issues that arise when relating serial position data to specific theories. We show that critical distinctions are often difficult to make based on normalized data. We suggest that curves for different lengths are best presented in their raw form and that binomial regression can be used to answer specific questions about the effects of length, position, and linear or nonlinear shape that are critical to making theoretical distinctions.  相似文献   
997.
Quantitative detection of human cytomegalovirus (HCMV) DNA on whole blood is currently the primary choice for virological monitoring in transplant patients and for determining the appropriate antiviral strategy, however specific issues of variability remain in terms of extraction methods, amplification efficiency, and variability. This study compared the performance characteristics of two nucleic acid extraction and testing systems for HCMV-DNA quantitation, the artus® CMV QS-RGQ kit, associated with a fully automated DNA extraction and assay set up by Qiagen (system 1) and the Q-CMV Real Time Complete kit by Nanogen, associated with a semiautomated nucleic acid extraction system by Biomérieux (system 2) in 189 specimens from transplant patients and 10 from 2012 HCMV Quality Control for Molecular Diagnostics (QCMD). The two systems exhibited a 80.4% concordance. Differences between the two systems were within ±1 log10 copies/ml of the averaged log10 results for 88.9% of the tested specimens. For all qualitatively discordant specimens, mean viral load was ≤3 log10 copies/ml. Considering viral load measurement, system 1 gave earlier positives that system 2, with a 14.8% of specimens resulted positive at low viral loads with system 1 and negative with system 2. In QCMD specimens, difference was below 0.7 log10 copies/ml for both the systems.  相似文献   
998.
Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a life-saving procedure used for the treatment of selected hematological malignancies, inborn errors of metabolism, and bone marrow failures. The role of neutrophils in alloHSCT has been traditionally evaluated only in the context of their ability to act as a first line of defense against infection. However, recent evidence has highlighted neutrophils as key effectors of innate and adaptive immune responses through a wide array of newly discovered functions. Accordingly, neutrophils are emerging as highly versatile cells that are able to acquire different, often opposite, functional capacities depending on the microenvironment and their differentiation status. Herein, we review the current knowledge on the multiple functions that neutrophils exhibit through the different stages of alloHSCT, from the hematopoietic stem cell (HSC) mobilization in the donor to the immunological reconstitution that occurs in the recipient following HSC infusion. We also discuss the influence exerted on neutrophils by the immunosuppressive drugs delivered in the course of alloHSCT as part of graft-versus-host disease (GVHD) prophylaxis. Finally, the potential involvement of neutrophils in alloHSCT-related complications, such as transplant-associated thrombotic microangiopathy (TA-TMA), acute and chronic GVHD, and cytomegalovirus (CMV) reactivation, is also discussed. Based on the data reviewed herein, the role played by neutrophils in alloHSCT is far greater than a simple antimicrobial role. However, much remains to be investigated in terms of the potential functions that neutrophils might exert during a highly complex procedure such as alloHSCT.  相似文献   
999.

Acute gastroenteritis (AGE) is a leading cause of disease worldwide. The aim of this prospective observational study is to describe the epidemiology of AGE in closed and semi-closed institutions in Catalonia. In 2017, 151 outbreaks were reported; 30.5% occurred in closed and semi-closed institutions; 71.7% caused by norovirus (NoV) (1532) cases. Person-to-person transmission accounted for 75.8% of NoV outbreaks vs 46.1% in non-NoV outbreaks (p?<?0.001). Attack rate for NoV outbreaks was 33.1% vs 14.3% for non-NoV outbreaks (RR?=?2.3; 95%CI: 2.0–2.7). The high number of affected underscores prompt and intense preventive measures to avoid the extension and perpetuation of outbreaks in these settings.

  相似文献   
1000.
Journal of Digital Imaging - The recent introduction of wireless head-mounted displays (HMD) promises to enhance 3D image visualization by immersing the user into 3D morphology. This work...  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