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   9847篇
  免费   482篇
  国内免费   96篇
耳鼻咽喉   95篇
儿科学   187篇
妇产科学   171篇
基础医学   1138篇
口腔科学   237篇
临床医学   853篇
内科学   2802篇
皮肤病学   165篇
神经病学   1063篇
特种医学   317篇
外科学   1202篇
综合类   28篇
预防医学   456篇
眼科学   114篇
药学   629篇
中国医学   43篇
肿瘤学   925篇
  2023年   72篇
  2022年   168篇
  2021年   289篇
  2020年   169篇
  2019年   208篇
  2018年   275篇
  2017年   188篇
  2016年   245篇
  2015年   303篇
  2014年   342篇
  2013年   525篇
  2012年   804篇
  2011年   707篇
  2010年   438篇
  2009年   421篇
  2008年   637篇
  2007年   679篇
  2006年   596篇
  2005年   662篇
  2004年   565篇
  2003年   476篇
  2002年   456篇
  2001年   94篇
  2000年   85篇
  1999年   73篇
  1998年   94篇
  1997年   78篇
  1996年   45篇
  1995年   53篇
  1994年   47篇
  1993年   36篇
  1992年   44篇
  1991年   50篇
  1990年   40篇
  1989年   38篇
  1988年   37篇
  1987年   40篇
  1986年   32篇
  1985年   38篇
  1984年   26篇
  1983年   22篇
  1982年   21篇
  1981年   25篇
  1980年   37篇
  1979年   15篇
  1978年   11篇
  1977年   12篇
  1976年   12篇
  1975年   13篇
  1974年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Available results highlight the lack of good level of evidence studies on the pure prognostic value of histological grade. In the present study, the prognostic relevance of histological grade and of its three components, tubule formation, nuclear pleomorphism and mitotic count, was analyzed in a series of 372 patients with node-negative breast cancer treated with locoregional therapy alone until early relapse. Histological grade was determined blindly by two observers and discordance between evaluations was resolved after joint review using a multihead microscope. No relation was observed between histological grade and any of its three components and disease-free survival. Conversely, a significant relation was observed between histological grade and distant metastasis-free survival (at 6 years, 94, 86 and 76% for grades 1, 2 and 3, respectively, P=0.013) as well as overall survival (98, 90 and 86%, P=0.001). A breakdown analysis as a function of the three components showed that neither tubule formation nor nuclear pleomorphism was associated with prognosis, and only mitotic count strongly influenced both distant metastasis-free survival (91, 82 and 74%, P=0.014) and overall survival (97, 87 and 85%, P=0.011). Histological grade suffers from a much higher subjectivity than any other microscopic evaluation of biomarkers as it is the sum of three different morphological features. Within the Italian Network for Quality Assessment of Tumor Biomarkers program we observed that histological grade is an independent prognostic variable, but also that this role is ascribable only to the number of mitotic figures. In conclusion, due to the ever smaller size of diagnosed breast cancers, resulting in less cancer tissue for biofunctional and molecular analysis, mitotic count evaluated under strict quality control conditions seems to be an accurate and feasible prognostic variable.  相似文献   
32.
Healing of a tendon graft to a bone tunnel is slower than the healing of a bone plug. Therefore, the device chosen for hamstring fixation may need to maintain its strength and stiffness longer than the device chosen for bone-tendon-bone fixation. We evaluated, in an extraarticular ovine model, how 4 and 12 weeks of implantation affect the strength of a tendon graft fixed to bone with the Evolgate. The long digital extensor tendon was transplanted and fixed with the Evolgate into a 30-mm long, 8 mm diameter bone tunnel drilled in the tibial metaphysis of both posterior limbs of 15 skeletally mature Suffolk sheep. Immediately after implantation, and 4 and 12 weeks later, biomechanical cyclic load tests in 50 N increments were performed until failure to evaluate the ultimate failure load (UFL). Histological analysis was also performed at 4 and 12 weeks. Biomechanical tests revealed a UFL of 339±120 N at time 0, and increases to 635±19 N (4 weeks) and to 867±80 N (12 weeks). The differences between all 3 groups were significant (p<0.001, paired t test). The histological evaluation showed a layer of cellular, fibrous tissue between the tendon and the bone, along the length of the bone tunnel; this layer progressively matured and reorganized during the healing process. The collagen fibers that attached the tendon to the bone resembled Sharpey’s fibers. The strength of the interface significantly and progressively increased between weeks 4 and 12 after transplantation, and was associated with a degree of bone ingrowth noted histologically. The use of the Evolgate seems not to interfere with the bone ingrowth after implantation, allowing an improvement in strength of the bonetendon- device complex.  相似文献   
33.
Summary We have studied the hypoalgesic effect of codeine (100 mg) after blocking the hepatic O-demethylation of codeine to morphine via the sparteine oxygenase (CYP2D6) by quinidine (200 mg). The study was performed in 16 extensive metabolizers of sparteine, using a double-blind, randomized, four-way, cross-over design. The treatments given at 3 h intervals during the four sessions were placebo/placebo, quinidine/placebo, placebo/codeine, and quinidine/codeine. We measured pin-prick pain and pain tolerance thresholds to high energy argon laser stimuli before and 1, 2, and 3 h after codeine or placebo.After codeine and placebo, the peak plasma concentration of morphine was 6–62 (median 18) nmol·.l–1. When quinidine pre-treatment was given, no morphine could be detected (<4 nmol·l–1) after codeine. The pin-prick pain thresholds were significantly increased after placebo/codeine, but not after quinidine/codeine compared with placebo/placebo. Both placebo/codeine and quinidine/codeine increased pain tolerance thresholds significantly. Quinidine/codeine and quinidine/placebo did not differ significantly for either pin-prick or tolerance pain thresholds.These results are compatible with local CYP2D6 mediated formation of morphine in the brain, not being blocked by quinidine. Alternatively, a hypoalgesic effect of quinidine might have confounded the results.  相似文献   
34.
Central dual-energy X-ray absorptiometry (DXA) is the gold standard for non-invasive measurement of bone mineral density (BMD). Using this value and subject demographics, DXA software calculates T-scores and Z-scores. Professional society guidelines for the management of osteoporosis are based on T-scores and Z-scores, rather than on the actual BMD value. Although one expects T-scores and Z-scores to be very similar in young men and women for any given BMD measurement, little literature exists on this issue. Our clinical experience shows that some younger adult individuals (premenopausal women and men younger than 50 yr) have larger than expected difference between their DXA T-score and Z-score. This cross-sectional study evaluates the extent of this discordance between Z-scores and T-scores in a sample of 4275 men and women aged 20–49 yr. All subjects were scanned by central DXA using equipment manufactured by GE Lunar, GE, Madison, WI, or Hologic, Inc., Bedford, MA. Significant differences between Z-scores and T-scores were seen within individuals at the lumbar spine, total hip, femoral neck, and trochanter (p value < 0.001) for both DXA systems. Although these differences were less than half a standard deviation (SD) in most instances, the magnitude of difference was substantial at times, being 1 or more SD in up to 11% of cases (range: −1.95 to +1.54 SD). The smallest differences were seen at the total hip and the largest differences were seen at the femoral neck for both technologies. This is in part because there is no single standard Z-score definition, resulting in different methods of calculation across, and even within, DXA manufacturers. Standardization of Z-score definition and method of calculation is indicated. DXA Z-scores should be interpreted with caution in men and women aged 20–50 yr.  相似文献   
35.
Abstract The femoral neck fracture is actually the most important traumatic event in the elderly, because of its high rate and terrible complications. We reviwed clinical records of 314 patients treated in our institution with a bipolar implant for femoral neck fracture. At a mean follow-up of 5 years, 15 patients (4.8%) were lost to followup so data for 299 patients was studied to identity factors associated with mortality. Ten predictor variables were examined: age, sex, waiting time for surgery, pulmonary dysfunction, fracture etiology, and comorbidity with ischemic heart disease, and heart failure, hypertension, cerebrovascular disease, and chronic renal failure. Cumulative mortality rate during the first 6 months was 19% (55 of 299 patients) and in the first year it was 25% (76 of 299). At logistic regression analysis, mortality was associated with age, male gender, waiting period for surgery and presence of neoplastic disease or pathological fracture. Waiting for surgery was a significant factor for mortality at 6, 12 and 24 months: patients surgically treated in the first 24 hours had lower mortality than those who waited longer. The risk of mortality in the first 6 months doubled for an age increase of 12 years, while mortality within 2 years doubled for an age increase of 9 years. Although the motality rate after surgery for femoral neck fracture was high in the first year (25%), it dropped off in successive years to levels observed in a healthy population. Thus, we agree with the literature that femoral fracture is a risk factor for survival only in the first year after trauma, above all in the elderly.  相似文献   
36.
37.
38.
After introducing the context in which health systems exist in developing as well as in industrialized countries, the author describes the role that hospitals are expected to play as 'enterprises'. The rationale behind such a role is explored and the experience so far available discussed. Evidence from several developing countries suggests caution and tends to discourage radical and indiscriminate introduction of market‐oriented reforms, which international donors seem to be spearheading in Africa's health systems. It is likely, however, that a limited, gradual introduction of selected elements of these reforms (such as some aspects of contracting out, managerial decentralization, the split between purchasing and providing functions) may find its place and eventually have a positive impact on the performance of the health systems. But the 'mystique of markets' must not be allowed to deprive public hospitals of the sense of social utility and of the caring ethos which are essential requisites of a meaningful and effective public health system.  相似文献   
39.
The diagnosis of idiopathic Parkinson's disease (PD) can be achieved with high degrees of accuracy in cases with full expression of classical clinical features. However, diagnostic uncertainty remains in early disease with subtle or ambiguous signs. Functional imaging has been suggested to increase the diagnostic yield in parkinsonian syndromes with uncertain clinical classification. Loss of striatal dopamine nerve terminal function, a hallmark of neurodegenerative Parkinsonism, is strongly related to decreases of dopamine transporter (DAT) density, which can be measured by single photon emission computed tomography (SPECT). The use of DAT‐SPECT facilitates the differential diagnosis in patients with isolated tremor symptoms not fulfilling PD or essential tremor criteria, drug‐induced, psychogenic and vascular Parkinsonism as well as dementia when associated with Parkinsonism. This review addresses the value of DAT‐SPECT in early differential diagnosis, and its potential as a screening tool for subjects at risk of developing PD as well as issues around the assessment of disease progression. © 2007 Movement Disorder Society  相似文献   
40.
OBJECTIVE: This study aims to evaluate the efficiency of top-down and bottom-up processes in the extrastriate cortex of cirrhotic patients without overt hepatic encephalopathy (HE). METHODS: Reaction times (RTs), accuracy and event-related potentials (ERPs) were recorded during the execution of a visual Simon task in 17 cirrhotic patients and 10 healthy controls. Amplitude and latency of the P1 and N1 (indexes of bottom-up processes) and of the N2pc (index of top-down processes) were measured. RESULTS: Patients were slower than controls, and patients with minimal HE (MHE) were slower than patients without MHE. The distribution analysis of RTs showed that the Simon effect decays with slower RTs in all the groups and that the shape of the distribution was different in MHE patients. No differences were found between cirrhotic patients and controls for P1 and N1 amplitude and latency. In contrast, N2pc latency was delayed in cirrhotic patients compared to controls independently of MHE. CONCLUSIONS: In the extrastriate cortex of cirrhotic patients without HE, top-down processes are altered whereas bottom-up processes are preserved. SIGNIFICANCE: The analysis of exogenous and endogenous visual components of ERPs provides a model to study the functional dissociation between top-down and bottom-up processes inside the extrastriate cortex.  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