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   9336篇
  免费   447篇
  国内免费   95篇
耳鼻咽喉   95篇
儿科学   182篇
妇产科学   169篇
基础医学   1086篇
口腔科学   231篇
临床医学   804篇
内科学   2632篇
皮肤病学   164篇
神经病学   1035篇
特种医学   279篇
外科学   1165篇
综合类   28篇
预防医学   441篇
眼科学   110篇
药学   564篇
中国医学   43篇
肿瘤学   850篇
  2023年   72篇
  2022年   166篇
  2021年   283篇
  2020年   164篇
  2019年   201篇
  2018年   265篇
  2017年   180篇
  2016年   243篇
  2015年   294篇
  2014年   329篇
  2013年   507篇
  2012年   780篇
  2011年   677篇
  2010年   424篇
  2009年   399篇
  2008年   615篇
  2007年   656篇
  2006年   579篇
  2005年   629篇
  2004年   541篇
  2003年   446篇
  2002年   433篇
  2001年   66篇
  2000年   54篇
  1999年   54篇
  1998年   78篇
  1997年   73篇
  1996年   42篇
  1995年   50篇
  1994年   43篇
  1993年   36篇
  1992年   32篇
  1991年   39篇
  1990年   31篇
  1989年   29篇
  1988年   30篇
  1987年   28篇
  1986年   26篇
  1985年   30篇
  1984年   24篇
  1983年   19篇
  1982年   19篇
  1981年   24篇
  1980年   35篇
  1979年   13篇
  1978年   10篇
  1977年   12篇
  1976年   12篇
  1975年   12篇
  1974年   6篇
排序方式: 共有9878条查询结果,搜索用时 15 毫秒
981.
The Model for End-Stage Liver Disease (MELD) is widely used to predict the short-term mortality in patients with cirrhosis, but potential limitations of this score have been reported. The aim of this study was to improve the score's prognostic accuracy by assessing new objective variables. Data of 310 consecutive patients with cirrhosis who underwent elective transjugular intrahepatic portosystemic shunt placement between July 1995 and March 2005 were analyzed retrospectively. Bivariate and multivariate analyses were performed by proportional hazard Cox regression models. The area under the receiver operating characteristic curve (auROC) and the likelihood ratio test were used to evaluate the performance of the models for predicting early mortality. Findings were validated in a cohort of 451 consecutive patients with cirrhosis on waiting list for liver transplantation. Bivariate analyses showed that the following variables correlated with time to death: age, serum bilirubin, serum creatinine, international normalized ratio of prothrombin time, serum albumin, serum sodium, and MELD. Multivariate analysis revealed that MELD, serum sodium, and age were independently associated with the risk of death. The integrated MELD model (iMELD, incorporating serum sodium and age) was better than original MELD in predicting 12-month mortality: auROC increased by 13.4% and the likelihood ratio statistic from 23.5 to 48.2. The improved accuracy of iMELD was confirmed in the validation sample of 451 patients with cirrhosis on the waiting list for liver transplantation by increasing auROC (+8%) and likelihood ratio statistic (from 41.4 to 82.0). This study shows that in patients with cirrhosis, serum sodium and age are predictors of mortality independent of the MELD score. The incorporation of these variables into the original MELD formula improves the predictive accuracy of time to death.  相似文献   
982.

Purpose

To evaluate diagnostic accuracy of a noise-optimized virtual monoenergetic imaging (VMI+) reconstruction technique for detection of active arterial abdominal bleeding on dual-energy (DE) CT angiography compared with standard image reconstruction.

Materials and Methods

DE CT angiography data sets of 71 patients (46 men; age 63.6 y ± 13.3) with suspected arterial bleeding of the abdomen or pelvis were reconstructed with standard linearly blended (F_0.5), VMI+, and traditional virtual monoenergetic imaging (VMI) algorithms in 10-keV increments from 40 to 100 keV. Attenuation measurements were performed in the descending aorta, area of hemorrhage, and feeding artery to calculate contrast-to-noise ratios (CNRs) in patients with active arterial bleeding. Based on quantitative image quality results, the best series for each reconstruction technique were chosen to analyze the diagnostic performance of 3 blinded radiologists.

Results

DE CT angiography showed acute arterial bleeding in 36 patients. Mean CNR was superior in 40-keV VMI+ compared with VMI series (all P < .001), which showed highest CNRs in 70-keV VMI and F_0.5 (21.6 ± 7.9, 12.9 ± 4.7, and 10.4 ± 3.6) images. Area under the curve analysis for detection of arterial bleeding showed significantly superior (P < .001) results for 40-keV VMI+ (0.963) compared with 70-keV VMI (0.775) and F_0.5 (0.817) series.

Conclusions

Diagnostic accuracy in patients with active arterial bleeding of the abdomen can be significantly improved using VMI+ reconstructions at 40 keV compared with standard linearly blended and traditional VMI series in DE CT angiography.  相似文献   
983.
Patients with inflammatory bowel disease (IBD) have an increased risk of 10%-15% developing colorectal cancer (CRC) that is a common disease of high economic costs in developed countries. The CRC has been increasing in recent years and its mortality rates are very high. Multiple biological and biochemical factors are responsible for the onset and progression of this pathology. Moreover, it appears absolutely necessary to investigate the environmental factors favoring the onset of CRC and the promotion of colonic health. The gut microflora, or microbiota, has an extensive diversity both quantitatively and qualitatively. In utero, the intestine of the mammalian fetus is sterile. At birth, the intestinal microbiota is acquired by ingesting maternal anal or vaginal organisms, ultimately developing into a stable community, with marked variations in microbial composition between individuals. The development of IBD is often associated with qualitative and quantitative disorders of the intestinal microbial flora (dysbiosis). The healthy human gut harbours about 10 different bacterial species distributed in colony forming units which colonize the gastrointestinal tract. The intestinal microbiota plays a fundamental role in health and in the progression of diseases such as IBD and CRC. In healthy subjects, the main control of intestinal bacterial colonization occurs through gastric acidity but other factors such as endoluminal temperature, competition between different bacterial strains, peristalsis and drugs can influence the intestinal microenvironment. The microbiota exerts diverse physiological functions to include: growth inhibition of pathogenic microorganisms, synthesis of compounds useful for the trophism of colonic mucosa, regulation of intestinal lymphoid tissue and synthesis of amino acids. Furthermore, mucus seems to play an important role in protecting the intestinal mucosa and maintaining its integrity. Changes in the microbiota composition are mainly influenced by diet and age, as well as genetic factors. Increasing evidence indicates that dysbiosis favors the production of genotoxins and metabolites associated with carcinogenesis and induces dysregulation of the immune response which promotes and sustains inflammation in IBD leading to carcinogenesis. A disequilibrium in gut microflora composition leads to the specific activation of gut associated lymphoid tissue. The associated chronic inflammatory process associated increases the risk of developing CRC. Ulcerative colitis and Crohn’s disease are the two major IBDs characterized by an early onset and extraintestinal manifestations, such as rheumatoid arthritis. The pathogenesis of both diseases is complex and not yet fully known. However, it is widely accepted that an inappropriate immune response to microbial flora can play a pivotal role in IBD pathogenesis.  相似文献   
984.
Background and aimsContinuous glucose monitoring improves glycemic control in diabetes. This study compared the accuracy of the Dexcom G5 Mobile (Dexcom, San Diego, CA) transcutaneous sensor (DG5) and the first version of Eversense (Senseonics,Inc., Germantown, MD) implantable sensor (EVS).Methods and resultsSubjects with type 1 diabetes (T1D) and using EVS wore simultaneously DG5 for seven days. At day 3, patients were admitted to a clinical research center (CRC) to receive breakfast with delayed and increased insulin bolus to induce glucose excursions. At CRC, venous glucose was monitored every 15 min (or 5 min during hypoglycemia) for 6 h by YSI 2300 STAT PLUS? glucose and lactate analyzer. At home patients were requested to perform 4 fingerstick glucose measurements per day.Eleven patients (9 males, age 47.4 ± 11.3 years, M±SD) were enrolled. During home-stay the median [25th-75th percentile] absolute relative difference (ARD) over all CGM-fingerstick matched-pairs was 11.64% [5.38–20.65]% for the DG5 and 10.75% [5.15–19.74]% for the EVS (p-value = 0.58). At CRC, considering all the CGM-YSI matched-pairs, the DG5 showed overall smaller median ARD than EVS, 7.91% [4.14–14.30]% vs 11.4% [5.04–18.54]% (p-value<0.001). Considering accuracy during blood glucose swings, DG5 performed better than EVS when glucose rate-of-change was ?0.5 to ?1.5 mg/dL/min, with median ARD of 7.34% [3.71–12.76]% vs 13.59% [4.53–20.78]% (p-value<0.001), and for rate-of-change < -1.5 mg/dl/min, with median ARD of 5.23% [2.09–15.29]% vs 12.73% [4.14–20.82]% (p-value = 0.02).ConclusionsDG5 was more accurate than EVS at CRC, especially when glucose decreased. No differences were found at home.  相似文献   
985.
Sigma (σ) receptors have been implicated in the behavioral and motivational effects of alcohol and psychostimulants. Sigma receptor antagonists reduce the reinforcing effects of alcohol and excessive alcohol intake in both genetic (alcohol-preferring rats) and environmental (chronic alcohol-induced) models of alcoholism. The present study tested the hypothesis that pharmacological activation of σ-receptors facilitates ethanol reinforcement and induces excessive, binge-like ethanol intake. The effects of repeated subcutaneous treatment with the selective σ-receptor agonist 1,3-di-(2-tolyl)guanidine (DTG; 15 mg/kg, twice a day for 7 days) on operant ethanol (10%) self-administration were studied in Sardinian alcohol-preferring (sP) rats. To confirm that the effect of DTG was mediated by σ-receptors, the effects of pretreatment with the selective σ-receptor antagonist BD-1063 (7 mg/kg, subcutaneously) were determined. To assess the specificity of action, the effects of DTG on the self-administration of equally reinforcing solutions of saccharin or sucrose were also determined. Finally, gene expression of opioid receptors in brain areas implicated in ethanol reinforcement was analyzed in ethanol-naive sP rats treated acutely or repeatedly with DTG, because of the well-established role of the opioid system in alcohol reinforcement and addiction. Repeatedly administered DTG progressively and dramatically increased ethanol self-administration in sP rats and increased blood alcohol levels, which reached mean values close to 100 mg% in 1 h drinking sessions. Repeated DTG treatment also increased the rats'' motivation to work for alcohol under a progressive-ratio schedule of reinforcement. BD-1063 prevented the effects of DTG, confirming that σ-receptors mediate the effects of DTG. Repeated DTG treatment also increased the self-administration of the non-drug reinforcers saccharin and sucrose. Naive sP rats repeatedly treated with DTG showed increased mRNA expression of μ- and δ-opioid receptors in the ventral tegmental area. These results suggest a key facilitatory role for σ-receptors in the reinforcing effects of alcohol and identify a potential mechanism that contributes to binge-like and excessive drinking.  相似文献   
986.
BACKGROUND: In addition to detecting colorectal neoplasia, abdominal computed tomography (CT) with colonography technique (CTC) can also detect unsuspected extracolonic cancers and abdominal aortic aneurysms (AAA).The efficacy and cost-effectiveness of this combined abdominal CT screening strategy are unknown. METHODS: A computerized Markov model was constructed to simulate the occurrence of colorectal neoplasia, extracolonic malignant neoplasm, and AAA in a hypothetical cohort of 100,000 subjects from the United States who were 50 years of age. Simulated screening with CTC, using a 6-mm polyp size threshold for reporting, was compared with a competing model of optical colonoscopy (OC), both without and with abdominal ultrasonography for AAA detection (OC-US strategy). RESULTS: In the simulated population, CTC was the dominant screening strategy, gaining an additional 1458 and 462 life-years compared with the OC and OC-US strategies and being less costly, with a savings of $266 and $449 per person, respectively. The additional gains for CTC were largely due to a decrease in AAA-related deaths, whereas the modeled benefit from extracolonic cancer downstaging was a relatively minor factor. At sensitivity analysis, OC-US became more cost-effective only when the CTC sensitivity for large polyps dropped to 61% or when broad variations of costs were simulated, such as an increase in CTC cost from $814 to $1300 or a decrease in OC cost from $1100 to $500.With the OC-US approach, suboptimal compliance had a strong negative influence on efficacy and cost-effectiveness. The estimated mortality from CT-induced cancer was less than estimated colonoscopy-related mortality (8 vs 22 deaths), both of which were minor compared with the positive benefit from screening. CONCLUSION: When detection of extracolonic findings such as AAA and extracolonic cancer are considered in addition to colorectal neoplasia in our model simulation, CT colonography is a dominant screening strategy (ie, more clinically effective and more cost-effective) over both colonoscopy and colonoscopy with 1-time ultrasonography.  相似文献   
987.
Background and Aim: Sarcopenia is considered an important risk factor for morbidity and mortality in liver cirrhosis. Beta-hydroxy-beta-methylbutyrate (HMB) has the potential to increase muscle mass and performance by stimulating protein synthesis and reducing muscle catabolism. The present study aimed at evaluating the effect of HMB supplementation on muscle mass and function in patients with liver cirrhosis. Changes in frailty during the study were also estimated, and the safety of HMB supplementation was verified. Methods: This is a randomized, single-blind, placebo-controlled pilot trial. Twenty-four patients (14 HMB and 10 placebo) affected by liver cirrhosis were enrolled in the study. Each patient received dedicated counseling, which included nutrition and physical activity recommendations for chronic liver disease patients. Patients were randomized to receive 3 g/day of HMB or placebo (sorbitol powder) for 12 consecutive weeks. A diet interview, anthropometry, electrical bioimpedance analysis (BIA), quadriceps ultrasound, physical performance battery, Liver Frailty Index (LFI), and cognitive tests were completed at enrolment (T0), at 12 weeks (T1), and 24 weeks after enrolment (T2). Results: At baseline, the two groups were similar in demography, severity of liver disease, muscle mass, muscle function, and cognitive tests. LFI at baseline was higher in patients in the HMB group vs. those in the placebo group (4.1 ± 0.4 vs. 3.4 ± 0.6, p < 0.01). After treatment, a statistically significant increase in muscle function was seen in the HMB group (chair stand test: 14.2 ± 5 s vs. 11.7 ± 2.6 s, p < 0.05; six-minute walk test: 361.8 ± 68 m vs. 409.4 ± 58 m, p < 0.05). Quadriceps muscle mass measured by ultrasound also increased (4.9 ± 1.8 vs. 5.4 ± 1.8 mm, p < 0.05) after HMB, while LFI decreased (4.1 ± 0.4 vs. 3.7 ± 0.4, p < 0.05). HMB was well tolerated by patients, and no adverse events were documented. Conclusions: Our study suggests the efficacy of 12-week beta-hydroxy-beta-methylbutyrate supplementation in promoting improvements in muscle performance in compensated cirrhotic patients. LFI was also ameliorated. Further studies with a greater number of patients are required to reinforce this hypothesis.  相似文献   
988.
Piedmont is a region in northwestern Italy counting 4.2 million inhabitants. The purpose of our study was to update data on incidence and outcomes of hip fractures (HF) in our region to present days. The data of all patients affected by HF in 2003 in Piedmont (total: 5,386 patients) were analyzed, determining the incidence of HF, mean age, sex, fracture pattern and treatment adopted. Additionally, 564 patients underwent a questionnaire on comorbidities, complications, functional outcome and survivorship. Overall incidence of HF was 126.13/100,000 inhabitants-year. Mean hospitalization was 13.67 days. Mean time to surgery was 2.67 days. Survivorship was 94% at 3-month, 71.32% at 1-year and 60.21% at 3-year follow-up. These up-to-date data on HF in our region are in accordance with the international literature and could prove useful for Orthopaedic and Trauma surgeons for giving information to patients and their relatives.  相似文献   
989.
Metal implants corrode and release metal ions, cobalt and chromium, which, in turn, may cause systemic toxicity, mostly in the first few months from implantation of metal-on-metal hip arthroplasty. At the time of delivery, the placenta reduces the passage of cobalt and chromium ions released from metal-on-metal prosthesis. From a biomechanical view point, hip replacement should not be considered a contraindication for pregnancy or for spontaneous delivery, and does not seem to have any negative effects in terms of risk of dislocation, loosening, fracture, or revision surgery, neither negative effects on clinical and functional outcomes. The long-term biological consequences of exposure to Co–Cr particles and ions remain largely unknown.  相似文献   
990.
Integrated devices allow users to operate multiple pieces of assistive technology items from a single input device. Through this single input device, users with severe physical limitations are able to operate several other devices such as a wheelchair, telephone, computer, and communication aid. Twenty-four integrated control users completed a telephone survey to ascertain consumer satisfaction with integrated controls. Eighteen were either satisfied or very satisfied with the evaluation for an integrated control, one was neither satisfied nor dissatisfied, two were very dissatisfied, and three did not respond to the question. Twenty were very satisfied or satisfied and four were either dissatisfied or very dissatisfied with the training they received. Twenty-two respondents indicated they were either very satisfied or satisfied with their integrated control device, one was neither satisfied nor dissatisfied, and one was very dissatisfied. In general, respondents were satisfied with their integrated control devices. Specifically, respondents were satisfied with the increase in independence and the ability to control other equipment such as television sets and computers. Simplicity, touch sensitivity, and visual/auditory feedback appeared to play important roles in satisfaction.  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