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   1213篇
  免费   58篇
  国内免费   5篇
耳鼻咽喉   15篇
儿科学   66篇
妇产科学   17篇
基础医学   169篇
口腔科学   61篇
临床医学   98篇
内科学   211篇
皮肤病学   13篇
神经病学   45篇
特种医学   51篇
外科学   183篇
综合类   27篇
一般理论   2篇
预防医学   42篇
眼科学   78篇
药学   97篇
  1篇
中国医学   6篇
肿瘤学   94篇
  2024年   3篇
  2023年   13篇
  2022年   32篇
  2021年   92篇
  2020年   57篇
  2019年   55篇
  2018年   59篇
  2017年   47篇
  2016年   48篇
  2015年   42篇
  2014年   52篇
  2013年   93篇
  2012年   113篇
  2011年   95篇
  2010年   56篇
  2009年   32篇
  2008年   55篇
  2007年   66篇
  2006年   71篇
  2005年   45篇
  2004年   47篇
  2003年   33篇
  2002年   17篇
  2001年   1篇
  1999年   2篇
  1998年   5篇
  1997年   4篇
  1996年   3篇
  1995年   7篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1991年   1篇
  1990年   4篇
  1989年   3篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   2篇
  1979年   1篇
  1978年   1篇
  1976年   3篇
  1973年   1篇
  1961年   3篇
  1960年   1篇
排序方式: 共有1276条查询结果,搜索用时 0 毫秒
21.
A retrospective analysis of endovenous glue-closure therapy (EVGC) performed in 76 greater saphenous veins (GSVs) from February 2016 to December 2017 was conducted to assess the incidence and characteristics of endovenous glue-induced thrombosis (EGIT), a phenomenon unique to nonthermal EVGC for GSV insufficiency. Kabnick and Lawrence classifications for endovenous heat-induced thrombosis were adopted. Seven instances of EGIT were detected among 54 patients (13%), with median/mode Kabnick and Lawrence classifications of 2/2 and 4/5, respectively. EGIT resolved with observation within an average of 5.2 wk after detection (range, 2–8 wk) without deep vein thrombosis or pulmonary embolism. EGIT was associated with significantly greater mean age (+7.75 y; P = .0308).  相似文献   
22.
Li B  Avinash GB  Hsieh J 《Medical physics》2007,34(10):3732-3738
Until recently, most studies addressing the trade-off between spatial resolution and quantum noise were performed in the context of single-slice CT. In this study, we extend the theoretical framework of previous works to volumetric CT and further extend it by taking into account the actual shapes of the preferred reconstruction kernels. In the experimental study, we also attempt to explore a three-dimensional approach for spatial resolution measurement, as opposed to the conventional two-dimensional approaches that were widely adopted in previously published studies. By scanning a finite-sized sphere phantom, the MTF was measured from the edge profile along the spherical surface. Cases of different resolutions (and noise levels) were generated by adjusting the reconstruction kernel. To reduce bias, the total photon fluxes were matched: 120 kVp, 200 mA, and 1 s per gantry rotation. All data sets were reconstructed using a modified FDK algorithm under the same condition: Scan field-of-view (SFOV) = 10 cm, and slice thickness = 0.625 mm. The theoretical analysis indicated that the variance of noise is proportional to > 4th power of the spatial resolution. Our experimental results supported this conclusion by showing the relationship is 4.6th (helical) or 5th (axial) power.  相似文献   
23.
Efficient delivery of viruses, proteins and biological macromelecules into a micrometer-sized focal spot of an XFEL beam for coherent diffraction imaging inspired new development in touch-free particle injection methods in gaseous and vacuum environments. This paper lays out our ongoing effort in constructing an all-optical particle delivery approach that uses piconewton photophoretic and femtonewton light-pressure forces to control particle delivery into the XFEL beam. We combine a spatial light modulator (SLM) and an electrically tunable lens (ETL) to construct a variable-divergence vortex beam providing dynamic and stable positioning of levitated micrometer-size particles, under normal atmospheric pressure. A sensorless wavefront correction approach is used to reduce optical aberrations to generate a high quality vortex beam for particle manipulation. As a proof of concept, stable manipulation of optically-controlled axial motion of trapped particles is demonstrated with a response time of 100ms. In addition, modulation of trapping intensity provides a measure of the mass of a single, isolated particle. The driving signal of this oscillatory motion can potentially be phase-locked to an external timing signal enabling synchronization of particle delivery into the x-ray focus with XFEL pulse train.OCIS codes: (140.7010) Laser trapping, (350.4855) Optical tweezers or optical manipulation  相似文献   
24.
We report a rare case of a 44-year-old male who underwent a diagnostic coronary angiogram following a non-ST elevation myocardial infarction complicated by an aortic valve leaflet tear requiring surgical intervention. Routine transthoracic echocardiogram demonstrated a mobile echogenic structure prolapsing into the left ventricular outflow tract. An intraoperative transesophageal echocardiogram confirmed that the structure originated from the ventricular side of left coronary cusp, causing malcoaptation between left and right coronary cusps, and subsequent moderate to severe aortic regurgitation.  相似文献   
25.
26.
27.
Population-based studies that assess long-term patterns of incidence, major aspects of treatment and survival are virtually lacking for Hodgkin lymphoma (HL) at a younger age. This study assessed the progress made for young patients with HL (<25 years at diagnosis) in the Netherlands during 1990–2015. Patient and tumour characteristics were extracted from the population-based Netherlands Cancer Registry. Time trends in incidence and mortality rates were evaluated with average annual percentage change (AAPC) analyses. Stage at diagnosis, initial treatments and site of treatment were studied in relation to observed overall survival (OS). A total of 2619 patients with HL were diagnosed between 1990 and 2015. Incidence rates increased for 18–24-year-old patients (AAPC + 1%, P = 0·01) only. Treatment regimens changed into less radiotherapy and more ‘chemotherapy only’, different for age group and stage. Patients aged 15–17 years were increasingly treated at a paediatric oncology centre. The 5-year OS for children was already high in the early 1990s (93%). For patients aged 15–17 and 18–24 years the 5-year OS improved from 84% and 90% in 1990–1994 to 96% and 97% in 2010–2015, respectively. Survival for patients aged 15–17 years was not affected by site of treatment. Our present data demonstrate that significant progress in HL treatment has been made in the Netherlands since 1990.  相似文献   
28.
Pulmonary complications are one of the most common causes of morbidity and mortality in patients undergoing peripheral blood stem cell transplantation. Both infective and non-infective etiologies can involve the lungs during this period and differentiating them clinically is a challenging task and management differs in each case. We present here a case of acute myeloid leukemia, in whom following allogeneic peripheral blood stem cell transplantation, diffuse alveolar hemorrhage developed.  相似文献   
29.
We report the growth of carbon dioxide (CO2) whiskers at low temperatures (−70 °C to −65 °C) and moderate pressure (4.4 to 1.0 bar). Their axial growth was assessed by optical video analysis. The identities of these whiskers were confirmed as CO2 solids by Raman spectroscopy. A vapor–solid growth mechanism was proposed based on the influence of the relative humidity on the growth.

Carbon dioxide (CO2) whiskers were reported to grow at low temperatures (−70 °C to −65 °C) and moderate pressure (4.4 to 1.0 bar).  相似文献   
30.
AIM: To identify their diagnostic and prognostic clinical characteristics in a large series.METHODS: Retrospective review of clinicopathologic and imaging characteristics of patients diagnosed with lymphoepithelial cysts and cystic lymphangiomas of the pancreas at Massachusetts General Hospital.RESULTS: Twelve patients were identified between 1/1/1997 and 8/1/2007. Their median age was 55.5 years(range 19-78 years), and 6 were females. The le-sion was incidentally discovered in half of the patients.Contrast enhanced computed tomography demonstrat-ed that the cysts had thin walls, without calcifications, pancreatic duct dilation or pancreatic parenchyma inva-sion. Endoscopic ultrasound with fine needle aspiration(EUS/FNA) confirmed the diagnosis of a lymphoepithe-lial cyst in 3 patients, one of whom was spared an op-eration and continues to do well after 6 years. Eleven patients had a resection: 3 pancreaticoduodenecto-mies, 7 distal pancreatectomies, and 1 enucleation. The median size of the cysts was 3 cm(range 2-20 cm). At a median follow-up of 57 mo no recurrences or other pancreas-related conditions occurred.CONCLUSION: Lymphoepithelial cysts and cystic lymphangiomas of the pancreas can be diagnosed with a combination of contrast-enhanced computed tomog-raphy scans and EUS/FNA. If the lesion is asymptom-atic, an operation might be avoided.  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