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   1090篇
  免费   79篇
  国内免费   9篇
耳鼻咽喉   8篇
儿科学   37篇
妇产科学   31篇
基础医学   218篇
口腔科学   13篇
临床医学   82篇
内科学   195篇
皮肤病学   39篇
神经病学   174篇
特种医学   28篇
外科学   129篇
综合类   4篇
预防医学   43篇
眼科学   34篇
药学   58篇
肿瘤学   85篇
  2024年   5篇
  2023年   18篇
  2022年   10篇
  2021年   45篇
  2020年   37篇
  2019年   27篇
  2018年   35篇
  2017年   21篇
  2016年   53篇
  2015年   50篇
  2014年   55篇
  2013年   56篇
  2012年   92篇
  2011年   135篇
  2010年   52篇
  2009年   62篇
  2008年   81篇
  2007年   65篇
  2006年   54篇
  2005年   44篇
  2004年   41篇
  2003年   37篇
  2002年   36篇
  2001年   6篇
  2000年   5篇
  1999年   6篇
  1998年   6篇
  1997年   9篇
  1996年   3篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1992年   2篇
  1991年   1篇
  1990年   1篇
  1989年   4篇
  1988年   1篇
  1987年   1篇
  1986年   4篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1977年   1篇
  1974年   1篇
  1959年   1篇
  1932年   2篇
  1926年   1篇
  1903年   2篇
  1897年   1篇
排序方式: 共有1178条查询结果,搜索用时 1 毫秒
51.
Tuberculostearic acid (TBSA), a mycobacterial cell wall constituent, was measured in plasma samples using a highly sensitive high-performance liquid chromatography method. Plasma TBSA concentrations in patients with active tuberculosis (20 [0.5-347] nmol/l; n = 125) were higher than in patients with a variety of non-tuberculous pulmonary and extrapulmonary inflammatory conditions (0.1 [0-29] nmol/l; n = 116) and in healthy controls (0 [0-2] nmol/l; n = 102) (p = < 0.001). The calculated sensitivity, specificity, positive and negative predictive values for tuberculosis were 95.2%, 87.9%, 89.5% and 94.4%, respectively, indicating that assay of plasma TBSA might be a valuable complementary diagnostic tool.  相似文献   
52.
53.
The isolated form of femoral bowing is an important differential diagnosis of campomelia. Therefore, knowledge of isolated anomalies is fundamental for prenatal diagnosis, especially for the differential diagnosis from severe syndromes. Four cases are presented to discuss the differential diagnosis of femoral bowing including a review of the literature. We report four newborn babies with unilateral bowing and shortening of the femur. Three had no further anomaly; one child had additional abnormalities due to coumarin embryopathy. The radiological findings were shortened femora with bowing and varus deformity and cortical thickening on the concave side. All other parts showed normal bone structure. The aetiology of femoral bowing is unknown. Early damage of the cartilaginous model followed by remodelling with thickening on the concave side of the bone similar to the healing of malaligned fractures is suspected. The isolated form of femoral bowing without any other anomalies has to be differentiated from complex and more often severe congenital syndromes such as campomelia. Postpartum radiological examination should be reduced to a single exposure of the affected limb and follow-up should be done by clinical examination.  相似文献   
54.
High resolution pollen analysis of mid- to late-Holocene peat deposits from southwest Florida reveals a stepwise increase in wetland vegetation that points to an increased precipitation-driven fresh water flow during the past 5,000 years. The tight coupling between winter precipitation patterns in Florida and the strength of the El Ni?o-Southern Oscillation (ENSO) strongly suggests that the paleo-hydrology record reflects changes in ENSO intensity. A terrestrial subtropical record outside the Indo Pacific Warm Pool both documents ecosystem response to the known onset of modern-day ENSO periodicities, between approximately 7,000 and 5,000 years B.P., and subsequent ENSO intensification after 3,500 years B.P. The observed increases in "wetness" are sustained by a gradual rise in relative sea level that prevents a return to drier vegetation through natural succession.  相似文献   
55.
56.
57.
58.
OBJECTIVE: To characterize the ability of an automatic lung nodule segmentation algorithm to measure small nodule dimensions and growth rates. METHODS: A phantom of 20 sets of 6 balls each (11 different nylon balls and 9 acrylic balls) of 1 to 9.5 mm in diameter, in foam, was imaged using x-ray computed tomography with slice thicknesses of 5, 2.5, and 1.25 mm, pitches of 3 and 6, and standard and lung resolution. Measurements consisted of volume and maximum in-plane cross-sectional areas and their derived maximum and effective diameters. Growth rates were simulated using pairs of groups of balls. RESULTS: Volume measurements overestimate volume, more so for thicker slices. For the largest balls, the error is 60% for 5-mm slices and 20% for 1.25-mm slices. Effective diameter calculated from volume better approximates actual diameter. For area measurements, errors are 0% to 5% for the largest balls, and the effective and actual diameters are closely matched. CONCLUSIONS: Below 5 mm in diameter, changes in volume should reach 100% for reliable indication of growth. Above 6 mm, the threshold for detecting change is on the order of 25% growth. Even under ideal conditions, results indicate the need for caution when making a diagnosis of malignancy on the basis of volume change.  相似文献   
59.
60.
Multiple sclerosis (MS) is a chronic inflammatory and demyelinating disease of the central nervous system (CNS). Although the cause of MS is still uncertain, it is well accepted that both genetic and environmental factors are important for the development of disease. In this study, we focused on the Polio Virus Receptor (PVR) and Herpesvirus entry mediator B (HVEB) receptor genes, which are located on chromosome 19q13, a region previously linked to MS. Both receptors are expressed in the brain and immune system and play an important role for inter-cellular adhesion and entry of neurotropic viruses to the brain. We identified four new polymorphisms in the PVR gene, which were located in the promoter region and three different exons. All exonic polymorphisms altered the amino acid sequence of the receptor. No new polymorphisms were found in the HVEB gene, but we confirmed a previously identified intronic polymorphism. We analyzed the frequency of the polymorphisms by RFLP analysis in sporadic MS patients, MS families, and healthy controls and determined the surface expression of HVEB and PVR on peripheral blood monocytes. We did not find differences in the frequency of the polymorphisms or surface expression between MS patients and controls. Overall, our findings do not support a role of HVEB and PVR genes in the development of MS.  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