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   1539篇
  免费   55篇
  国内免费   11篇
耳鼻咽喉   30篇
儿科学   39篇
妇产科学   22篇
基础医学   133篇
口腔科学   44篇
临床医学   111篇
内科学   337篇
皮肤病学   19篇
神经病学   76篇
特种医学   105篇
外科学   331篇
综合类   9篇
一般理论   1篇
预防医学   80篇
眼科学   14篇
药学   125篇
中国医学   8篇
肿瘤学   121篇
  2023年   6篇
  2022年   19篇
  2021年   35篇
  2020年   18篇
  2019年   32篇
  2018年   43篇
  2017年   31篇
  2016年   33篇
  2015年   38篇
  2014年   42篇
  2013年   86篇
  2012年   112篇
  2011年   138篇
  2010年   87篇
  2009年   100篇
  2008年   155篇
  2007年   147篇
  2006年   101篇
  2005年   87篇
  2004年   73篇
  2003年   87篇
  2002年   55篇
  2001年   7篇
  2000年   5篇
  1999年   9篇
  1998年   10篇
  1997年   6篇
  1996年   10篇
  1995年   6篇
  1994年   4篇
  1992年   2篇
  1990年   3篇
  1989年   3篇
  1988年   1篇
  1987年   2篇
  1986年   3篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1980年   3篇
  1978年   1篇
  1975年   1篇
排序方式: 共有1605条查询结果,搜索用时 78 毫秒
1.
Chordoma is a rare tumor, arising from notochord remnants, which usually occurs in the axial skeleton and rarely metastasizes. Although there have been 3 previous reports of metastatic disease to the facial bones from sacrococcygeal chordoma, this is the first to describe spread to the mandible from a vertebral primary chordoma.  相似文献   
2.
Ultrasonographic assessment of human skeletal muscle size   总被引:7,自引:0,他引:7  
The measurement of human muscle size is essential when assessing the effects of training, disuse and ageing. The considered gold standard for cross-sectional area measurements of muscle size is magnetic resonance imaging (MRI). However, MRI is costly and often inaccessible. The aim of the present study was to test the reproducibility and validity of a more accessible alternative method using ultrasonography (ULT). We examined the cross-sectional areas in the vastus lateralis muscle of six individuals. Axial-plane ULT scans were taken at given levels along the entire muscle length. The ULT scanning was repeated on different days (reliability) and validated against MRI-based measurements. Mean intraclass correlation coefficients were 0.998 for the reliability of ULT and 0.999 for the validity of ULT against MRI. The coefficient of variation values for cross-sectional area measurements assessed by six different experimenters were 2.1% and 0.8% for images obtained with ULT and MRI, respectively. The ULT method is a valid and reliable alternative tool for assessing cross-sectional areas of large individual human muscles. The present findings justify the application of the ULT method for the detection of changes throughout large muscles in response to training, disuse or as a consequence of sarcopenia.  相似文献   
3.
4.
The relationship between sex and outcome after laparoscopic surgery for symptomatic cholelithiasis remains unclear. The purpose of this study was to determine the influence of sex on the clinical presentation of patients with symptomatic gallstone disease and the clinical outcomes of laparoscopic cholecystectomy. The rates of conversion to open cholecystectomy, complication rates, operative times, and lengths of hospital stay were compared between the sexes. Compared with female patients, males were significantly older and more likely to have coexisting cardiovascular disease, previous upper abdominal surgery, previous hospitalization for acute cholecystitis and pancreatitis, acute cholecystitis, and suppurative cholecystitis (such as empyema), conversions, and complications. The mortality rate was nil. Analyses revealed an independent effect of sex on the prevalence of complications, even when including all of the major confounding factors in the model. In contrast, the effect of sex on conversion to open cholecystectomy was not significant when controlling for patient age. Operative time and postoperative hospital stay were significantly longer in males than in females. The tendency of male patients to have cholecystitis of greater severity should remind surgeons of the need to inform patients about the higher conversion rate among male patients, to reduce the disappointment of a large laparotomy wound or prolonged recovery period. On the other hand, there may be an increased need for surgeons to strongly advice male patients with symptomatic cholelithiasis to undergo early intervention.  相似文献   
5.
BACKGROUND: Members of the European Society of Paediatric Nephrology (ESPN) initiated a study of the demography and policy of paediatric renal care among European countries at the end of the 20th century. METHODS: A questionnaire was mailed to the presidents of each of 43 national renal paediatric societies or working groups in Europe. Data on each country's population, income as reflected by its gross national product and infant mortality rate, were obtained from the United Nations. The paediatric health care systems were previously divided into three types: general practitioner care system, paediatric care system and combined care system (CCS). RESULTS: In 1998, 842 specialized paediatric nephrologists worked in hospitals in 42 European countries. The median number of paediatric nephrologists per million child population (pmcp) was 4.9 (range 0-15). The median number of children served per paediatric nephrologist was significantly higher in countries with the general practitioner care system than in those with the paediatric or combined care system (CCS), namely 370 747 vs 169 456 and 191 788, respectively. In addition to specially trained paediatric nephrologists, there were 1087 paediatricians with a part-time interest/activity in paediatric nephrology in hospitals in 34 European countries. Eastern European countries had significantly more general paediatricians with part-time nephrological activities than countries belonging to the European Union (EU), 16.7 vs 6.6 pmcp. In 1998, 92% of 42 European countries offered paediatric dialysis facilities for acute renal failure and 90% for chronic renal failure and 55% offered paediatric renal transplantation (RTx). Only 30% of Eastern European countries (central omitted) offered paediatric RTx vs 87% of EU countries. The availability of paediatric RTx was associated significantly with the countries' gross national product (r = 0.53, P<0.001). The median number of paediatric hospitals offering dialysis for childhood chronic renal failure was 1.5 pmcp (range 0-5.0) and the median number of paediatric hospitals offering paediatric RTx was 0.4 pmcp (range 0-3.5). Fewer children were on dialysis or were transplanted in Eastern European countries than in the EU. CONCLUSIONS: At the end of the 20th century, there was a marked variation in delivery of paediatric renal care within Europe. This was related to factors such as size of the population, geographical and political situation, the type of primary paediatric care system and economic situation. European countries were far from equal with regard to access of renal replacement therapy for children. Improvement of the economic situation is beyond the capabilities of paediatric nephrologists. However, in these days of world-wide globalization paediatricians in greater Europe should be able to achieve better cooperation and exchange of ideas and information which would be the first step towards equality of renal care for children.  相似文献   
6.
Introduction We used an experimental hip model to assess the mechanical stability of a hip prosthesis, and compared the femoral medullary canal preparation techniques of reaming and broaching.

Methods 15 pairs of cadaveric femora had a simulated replacement, the right femur with a reaming technique and the left with a broaching technique. Both femurs were radiographed to assess component positioning and cement mantle. The femurs were osteotomized 30 days after the procedure. The shear strength of the interface was studied at 4 different levels along an aluminum rod during push-out tests.

Results The overall mean value of the interface failure load was 15% lower with the reaming technique (6.5 kN for the reaming technique versus 7.7 kN for the broaching technique; p = 0.02).

Interpretation Broaching was superior to reaming for the preparation of the femoral canal, and should be used in order to increase primary stability. Further in vivo studies are required to account for factors such as intramedullary pressure, bleeding and surgical variations, which could not be accounted for in our study.  相似文献   
7.
We have validated ECG-gated emission tomography using technetium-99m methoxyisobutylisonitrile for the assessment of regional ventricular function by comparing it with cine magnetic resonance imaging (MRI). Gated tomography was performed at rest in 24 patients referred for myocardial perfusion imaging [17 males and seven females with a mean age of 58 years, nine of whom had had a previous myocardial infarction (MI)]. Scores were assigned to each of nine myocardial segments for wall motion and for thickening. Cine MRI was analysed in an identical fashion. Four out of 216 (2%) segments were uninterpretable by gated tomography because of inadequate tracer uptake. In eight patients without coronary artery disease (CAD), wall motion and thickening were normal by both methods. Gated tomography showed abnormal wall motion or thickening in all patients with previous MI and in five of seven patients with CAD but no prior MI. Association between wall motion and thickening was good (r s=0.86). Overall, there was good agreement between gated tomography and MRI for both wall motion (178/212 segments, =0.66) and wall thickening (184/212 segments, =0.69). In segments with severely reduced perfusion, however, there was poorer agreement (=0.31). Interobserver and intraobserver agreement was high ( from 0.61 to 0.78). Thus, in patients investigated for CAD, there is good overall agreement between gated tomography and MRI but the agreement is lower in segments with severe perfusion defects.  相似文献   
8.

Purpose

To quantify radiation exposure to the primary operator and staff during PET/CT-guided interventional procedures.

Methods

In this prospective study, 12 patients underwent PET/CT-guided interventions over a 6 month period. Radiation exposure was measured for the primary operator, the radiology technologist, and the nurse anesthetist by means of optically stimulated luminescence dosimeters. Radiation exposure was correlated with the procedure time and the use of in-room image guidance (CT fluoroscopy or ultrasound).

Results

The median effective dose was 0.02 (range 0–0.13) mSv for the primary operator, 0.01 (range 0–0.05) mSv for the nurse anesthetist, and 0.02 (range 0–0.05) mSv for the radiology technologist. The median extremity dose equivalent for the operator was 0.05 (range 0–0.62) mSv. Radiation exposure correlated with procedure duration and with the use of in-room image guidance. The median operator effective dose for the procedure was 0.015 mSv when conventional biopsy mode CT was used, compared to 0.06 mSv for in-room image guidance, although this did not achieve statistical significance as a result of the small sample size (p = 0.06).

Conclusion

The operator dose from PET/CT-guided procedures is not significantly different than typical doses from fluoroscopically guided procedures. The major determinant of radiation exposure to the operator from PET/CT-guided interventional procedures is time spent in close proximity to the patient.  相似文献   
9.
Henoch-Schönlein purpura (HSP)-associated stenosing ureteritis represents a rare complication of the disease, typically presenting with severe manifestations. This article reports on a 3.5-year-old boy with HSP and severe nephritis who developed a unilateral stenosing ureteritis with atypical manifestations, resulting in a nonfunctional kidney and consequent nephrectomy. The urinary tract ultrasound was normal in the first week of illness, and the diagnosis was made during follow-up 8 months after onset. The predominance of nephritic manifestations may have masked any signs of ureteritis, leading to the delay in diagnosis. To clarify the clinical spectrum of this complication, an extensive review of the literature was performed. We emphasize the necessity of repeated urinary tract ultrasound both early and later in the course of HSP, especially in cases with renal involvement, so that an early diagnosis of this complication can prevent a potentially serious renal outcome.  相似文献   
10.
OBJECTIVE: To evaluate the clinical usefulness of serum vascular endothelial growth factor (VEGF) levels in gastric cancer patients. SUMMARY BACKGROUND DATA: Vascular endothelial growth factor plays an important role in the formation of new blood vessels involved in the growth and metastatic spread of solid tumors, but there is limited information regarding the clinical significance of serum VEGF levels in cancer patients. METHODS: Serum VEGF concentrations were measured by an enzyme linked immunosorbent assay in 61 healthy controls and in 58 gastric cancer patients before surgery, and then again at 7 and 30 days after surgery. The association between preoperative serum VEGF levels, clinicopathological features and patient survival, and their changes following surgery were evaluated. RESULTS: Serum VEGF levels in gastric cancer patients were significantly higher than those in controls. There was a significant association between serum VEGF levels and disease stage, as well as invasion depth of the tumor and the presence of distant metastases. Serum VEGF levels decreased significantly after radical resection of the primary tumor and increased in patients with unresectable tumors. Multivariate regression analysis showed that serum VEGF level is an independent prognostic factor for survival. CONCLUSIONS: Serum VEGF levels in gastric patients are significantly higher compared with normal controls and correlate with local tumor extent, disease stage, and the presence of distant metastases. Preoperative serum VEGF concentration decreases significantly after radical resection of the primary tumor and is an independent prognostic factor for patient survival suggesting that determination of serum VEGF levels may be clinically useful.  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