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   3072篇
  免费   206篇
  国内免费   11篇
耳鼻咽喉   14篇
儿科学   51篇
妇产科学   82篇
基础医学   647篇
口腔科学   84篇
临床医学   251篇
内科学   615篇
皮肤病学   23篇
神经病学   428篇
特种医学   136篇
外科学   284篇
综合类   12篇
一般理论   2篇
预防医学   238篇
眼科学   73篇
药学   149篇
中国医学   5篇
肿瘤学   195篇
  2022年   29篇
  2021年   35篇
  2020年   37篇
  2019年   38篇
  2018年   46篇
  2017年   47篇
  2016年   54篇
  2015年   52篇
  2014年   83篇
  2013年   120篇
  2012年   182篇
  2011年   184篇
  2010年   102篇
  2009年   107篇
  2008年   162篇
  2007年   161篇
  2006年   163篇
  2005年   145篇
  2004年   133篇
  2003年   135篇
  2002年   144篇
  2001年   74篇
  2000年   89篇
  1999年   75篇
  1998年   44篇
  1997年   41篇
  1996年   38篇
  1995年   30篇
  1994年   31篇
  1993年   29篇
  1992年   46篇
  1991年   60篇
  1990年   31篇
  1989年   33篇
  1988年   35篇
  1987年   44篇
  1986年   29篇
  1985年   35篇
  1984年   26篇
  1983年   17篇
  1982年   14篇
  1981年   29篇
  1980年   19篇
  1979年   45篇
  1978年   17篇
  1975年   14篇
  1974年   13篇
  1973年   15篇
  1970年   14篇
  1969年   16篇
排序方式: 共有3289条查询结果,搜索用时 562 毫秒
1.
2.
3.
Study Objective . To determine albuterol delivery by metered-dose inhaler (MDI) in an in vitro pediatric mechanical ventilatory circuit model. The influence of a spacing device, endotracheal tube (ETT) diameter and length, and air humidity was also investigated. Design . An albuterol MDI canister was connected to an AeroVent spacer or Airlife MDI adapter and ETT 4.0, 5.0, or 6.0 mm at commercially available and equal lengths. The ETT tip was attached to an in-line filter holder with a 1-μm type A/E glass fiber filter. Ventilator settings were fractional concentration of inspired oxygen 50%, tidal volume 250 ml, inspiratory:expiratory (I:E) ratio 1:3, rate 25 breaths/minute, temperature 35°C, and a decelerating flow pattern. Ten albuterol canisters were activated two times each (total 2000 μg) into dry (4.0-, 5.0-, and 6.0-mm ETT) and humidified air (4.0- and 6.0-mm ETT) and repeated in triplicate. Percentage MDI output was determined by weighing the filter before and after drug administration (balance sensitivity 10 μg). Significant differences (p≤0.05) among the groups with and without a spacer and in dry and humidified air were determined by ANOVA with Scheffe's multiple comparison test. Multiple regression was used to determine significant associations between ETT diameter and length and delivery. Main Results . With the AeroVent spacer in humidified air, delivery with the 4.0- and 6.0-mm ETT was approximately 2.3% and 5%, respectively. The spacer and dry air significantly improved delivery. Conclusions . In humidified air, the dose of albuterol by MDI with an AeroVent spacer should be doubled for children intubated with 6.0-mm ETT, and four puffs administered for every one puff desired for 4.0-mm ETT. The results of this investigation should prove useful in initial clinical trials of albuterol MDI in ventilator-dependent infants and children.  相似文献   
4.
(18)F-FDG PET is an important diagnostic tool for detecting myocardial viability in patients with coronary artery disease. In combination with perfusion scanning, (18)F-FDG PET allows differentiation between reversibly and irreversibly damaged myocardium and selection of patients likely to benefit from revascularization. Viability PET is usually performed in two-dimensional (2D) mode. Taking into account the rising number of three-dimensional (3D)-only scanners, a validation of 3D acquisition is required. METHODS: Twenty-one patients with coronary artery disease referred for (18)F-FDG PET underwent an imaging protocol of nongated 2D (2D-NG) and gated 2D (2D-G) acquisitions for 15 min each, followed by 3D gated acquisitions for 10 min (3D-10) and 5 min (3D-5), using an ECAT Exact HR+ scanner. Results were analyzed using a 20-segment polar map in terms of activity concentration (Bq/mL), viability (50% uptake threshold), regional activity distribution, visual assessment of viability based on a 3-point rating scale, and left ventricular ejection fraction. RESULTS: Activity concentration measured in each segment with 2D-G, 3D-10, and 3D-5 showed a good linear correlation with 2D-NG. Quantitative viability assessment with 3D-5 gave a sensitivity of 84% and a specificity of 98%, compared with 2D-NG. No differences in regional activity distribution and visual viability assessment were found between the various protocols. Left ventricular ejection fractions obtained with 3D-10 and 3D-5 showed a good linear correlation with those measured with 2D-G. CONCLUSION: An ECG-gated 3D imaging protocol gave results comparable to those of 2D acquisition with regard to absolute and regional myocardial activity distribution, left ventricular function, and visual viability assessment. Sensitivity for viability assessment with a 50% uptake threshold was significantly less with 3D, but specificity was maintained. This protocol delivers a clinical performance nearly equivalent to that of 2D acquisition.  相似文献   
5.
Abstract From August to October 1991, the periodontal status of 1001 Yemenis representing the age groups 12-14, 15-19, 20-24 and 35-44 years was recorded and evaluated with preference to the CPITN, the calculus index and clinical attachment levels. The impact of chewing khat, the leaves of a cultivated, alkaloid shrub, and of using the traditional miswak chewing stick for oral hygiene purposes were investigated. The results show that 6.9% of the juvenile probands (15-19 years) had healthy periodontal tissue (CPITN 0). whereas bleeding on probing and calculus (CPITN 1+2) were registered in 86.2%. In the 35-44 year age group. 1.7% were periodontally healthy, whereas 84.5% displayed plaque retention or shallow pocketing (CPITN 2-3) and 12.5% deep pocketing (CPITN 4). The treatment needs in all age groups are confined primarily to calculus removal and instruction in oral hygiene. The clinical attachment level and the calculus index revealed age-related attachment loss and calculus formation, primarily among male probands. The higher khat consumption among the male population is reflected in its detrimental effect on the periodontal tissue, especially among younger probands. Oral hygiene aids have also an influence on periodontal status, with a toothbrush proving more efficient than the miswak. WHO efforts directed towards prophylactic programs need to be intensified but can be staffed by dental hygienists.  相似文献   
6.
Fetal tissues from 16 spontaneous abortions, two terminations, and one perinatal death, 18 of which were associated with maternal human parvovirus B19 infection, were examined for B19 infection by histology and in situ hybridization using a digoxigenin-labeled B19-DNA probe. In 15 spontaneous abortions and one termination, erythroblasts with intranuclear inclusions (lantern cells) reacted with B19-DNA by in situ hybridization. No internal or external fetal malformations were observed. Because 13 (86.7%) spontaneous abortions with lantern cells occurred between the 20th and 28th weeks of gestation, it is postulated that B19 infection may be a particular threat to the fetus during this stage of gestation.  相似文献   
7.
Gamma interferon plays an important role in regulating the functional properties of mononuclear phagocytes. In the present study, the role of activated protein kinases in the mechanism of action of gamma interferon cell signaling in human peripheral blood monocytes was investigated. Analysis in vitro of 100,000 x g cytosolic fractions from untreated and interferon-treated cells showed that agonist treatment resulted in time- and concentration-dependent increases in phosphotransferase activity when myelin basic protein (MBP) was used as the substrate. Anion-exchange chromatography of high-speed supernatants prepared from detergent extracts of interferon-treated cells revealed two discrete peaks of MBP phosphotransferase activity. Immunoblotting of fractions from these peaks with antiphosphotyrosine antibodies and with antibodies that specifically recognize the family of mitogen-activated protein (MAP) kinases detected a MAP kinase with a subunit M(r) of 42,000 in the earliest-eluting peak (peak 1). Phosphorylation of the 42,000-M(r) protein on tyrosine was observed only after treatment of cells with interferon. The contribution of MAP kinase to the interferon-stimulated activity in peak 1 was confirmed by quantitative immunoprecipitation with anti-MAP kinase and antiphosphotyrosine antibodies. The conclusion that the interferon-activated MBP kinase in peak 1 could be accounted for by an activated MAP kinase was also supported by the finding that fractions from Mono Q peak 1 demonstrated activity towards a MAP kinase-specific substrate. The later-eluting peak of interferon-activated MBP phosphotransferase activity appeared to be accounted for by an activated protein kinase C (PKC). This conclusion is based upon analyses of immunoblotting and immunoprecipitation experiments with antibodies to PKC and was also supported by the observed inhibition of this kinase with a PKC pseudosubstrate peptide. The interferon-stimulated PKC present in Mono Q peak 2 was active in the absence of calcium ions, suggesting that it is a calcium-independent isoform of PKC.  相似文献   
8.
The association is well established between congenital heart disease and spinal deformities such as scoliosis or kyphosis, but data are not available for risks and the outcome of heart surgery in patients with spinal deformities. We report a case of successful orthotopic heart lung transplantation in a patient with complex congenital heart disease and severe chest deformity who had undergone previous spinal fusion surgery for progressive right convex thoracic kyphoscoliosis.  相似文献   
9.
Nonuniform soft-tissue attenuation affects the diagnostic accuracy of SPECT in myocardial perfusion imaging. The attenuation map required for attenuation correction can be acquired using x-ray tomography (CT). Frequent findings in attenuation-corrected images are defects in the apical and anterior myocardial wall. We assume that these are artifacts produced by misalignment of SPECT images and the attenuation map. METHODS: One hundred forty patients underwent myocardial perfusion imaging with 99mTc-methoxyisobutylisonitrile. Twenty-seven of 140 showed pronounced defects in the apical or anterior wall only after CT-based attenuation correction. SPECT and corresponding CT slices were examined for misalignment in the ventrodorsal direction (y-direction) visually and by threshold-based delineation of the body surface. Mismatched studies were realigned and image reconstruction and analysis were redone. The effect of the correction was assessed visually and by semiquantitative analysis based on a 20-segment model using 4D-MSPECT. RESULTS: In 15 of 27 patients, the improved coregistration led to smaller and less-pronounced defects in the regions mentioned. In 6 of 27 patients, former defects were judged as normal. No improvement was seen in only 4 patients. In these 4 subjects, the mismatch in the y-direction was <1 pixel (7 mm), and visual inspection suggested a coincident mismatch in the craniocaudal direction. In 2 cases, coregistration was not possible because the body outline extended beyond the CT field of view. Semiquantitative analysis revealed a significant increase of the relative uptake in the apex; in the apical segments of the anterior, septal, and inferior wall; and in the mid-anterior and mid-anteroseptal segment. Basal segments of the anterolateral, lateral, and inferolateral wall and the middle inferolateral segment showed a significant decrease of relative uptake. CONCLUSION: Misalignment in the y-direction between SPECT and the attenuation map can lead to artifacts in the apical, septal, and anterior wall, which will appear as defects. It also can cause overcorrection in the basal inferior and lateral segments. There is evidence that mismatches along the other directions may have a similar effect. The coregistration of SPECT and the attenuation map needs to be verified for every patient, even when using integrated dual-modality imaging devices.  相似文献   
10.
Two techniques are currently available for the creation of low anterior rectal stapled anastomoses. The first technique requires the placement of a pursestring suture at the superior margin of the rectal cuff, which is technically difficult. In the second technique, the rectal cuff is closed with a linear stapler. The circular end-to-end stapler, with the anvil removed, is then passed through an enterotomy in the rectal remnant. We describe an easy and safe method that obviates difficulties during the transanal passage of the stapler and minimizes the risk of injury to the rectum. This method uses an inexpensive and readily available rubber catheter and metal guide.  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