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   3954篇
  免费   195篇
  国内免费   55篇
耳鼻咽喉   45篇
儿科学   88篇
妇产科学   73篇
基础医学   366篇
口腔科学   119篇
临床医学   303篇
内科学   965篇
皮肤病学   53篇
神经病学   444篇
特种医学   164篇
外科学   911篇
综合类   4篇
预防医学   110篇
眼科学   106篇
药学   161篇
中国医学   2篇
肿瘤学   290篇
  2024年   6篇
  2023年   42篇
  2022年   109篇
  2021年   196篇
  2020年   105篇
  2019年   124篇
  2018年   149篇
  2017年   102篇
  2016年   132篇
  2015年   147篇
  2014年   190篇
  2013年   248篇
  2012年   315篇
  2011年   321篇
  2010年   188篇
  2009年   177篇
  2008年   210篇
  2007年   223篇
  2006年   207篇
  2005年   158篇
  2004年   170篇
  2003年   143篇
  2002年   151篇
  2001年   45篇
  2000年   28篇
  1999年   35篇
  1998年   26篇
  1997年   20篇
  1996年   10篇
  1995年   14篇
  1994年   10篇
  1993年   13篇
  1992年   14篇
  1991年   15篇
  1990年   14篇
  1989年   9篇
  1988年   11篇
  1987年   12篇
  1986年   10篇
  1985年   17篇
  1984年   10篇
  1983年   8篇
  1982年   8篇
  1981年   8篇
  1978年   5篇
  1971年   4篇
  1970年   3篇
  1969年   9篇
  1968年   5篇
  1966年   5篇
排序方式: 共有4204条查询结果,搜索用时 0 毫秒
21.
22.
Hypomorphic mutations of the MRE11 gene are the hallmark of the radiosensitive ataxia-telangiectasia-like disorder (ATLD). Here, we describe a new family with two affected siblings, ATLD5 and ATLD6, now aged 37 and 36, respectively. They presented with late onset cerebellar degeneration slowly progressing until puberty and absence of telangiectasias, and were cancer-free. Both patients were wild-type for ATM and NBS1, but compound heterozygotes for MRE11 gene mutations [1422C-->A, T481K; 1714C-->T, R571X]. The 1422C-->A allele was inherited from the mother, whereas the 1714C-->T, allele paternally inherited, was apparently null as a result of nonsense-mediated mRNA decay (NMD). Interestingly, the 1714C-->T mutation is the same as previously identified in an unrelated English ATLD family (probands ATLD3 and ATLD4), suggesting an important role for NMD in saving potentially lethal mutations. Lymphoblastoid cell lines (LCLs) derived from ATLD5 and ATLD6 were normal for ATM, but defective for Mre11, Rad50 and Nbs1 (the MRN complex) protein expression. Their response to gamma-radiation was abnormal, as evidenced by the enhanced radiosensitivity, attenuated autophosphorylation of ATM-S1981 and phosphorylation of the ATM targets p53-S15 and Smc1-S966, failure to form Mre11 nuclear foci and defective G1 checkpoint arrest. The fibroblasts, but not LCLs, from ATLD5 and ATLD6 showed an impaired ATM-dependent Chk2 phosphorylation. These findings further underscore the interconnection between ATM activity and MRN function, which rationalizes the clinical similarity between ataxia-telangiectasia (A-T) and ATLD.  相似文献   
23.
We performed an electron microscopic study of cytologic material from 20 cases of primary lung adenocarcinoma (pleural effusion, 13 cases; fine needle aspiration biopsy, 7 cases). Ultrastructural characteristics related to secretory and storing activity of adenocarcinoma cells were evaluated semi-quantitatively. Data analysis identified three basic cell types (secretory, well or poorly differentiated; storing; and indifferent). We could classify our cases in five groups of pure or mixed cytotypes. Our results demonstrated a subcellular morphological heterogeneity manifested by the presence of different basic cell types: secretory, storing or indifferent features (or both); and different secretory and storage products in the same cell. This heterogeneity of lung adenocarcinoma cells suggests that the neoplasm could arise from a single cell type capable of differentiating along different lines. Cases lacking secretory differentiation seemed to be characterized by more aggressive biologic behavior. A clear correlation between the ultrastructural cytotypes identified and the clinical and prognostic data on the patients was not observed. This may be due to the fact that 75% of the patients were in clinical stage III at the time of diagnosis; also, in this series only five cases did not have characteristics that indicated secretory activity.  相似文献   
24.
25.
Vitamin D has been claimed to be effective in the response to infections, including the respiratory syndrome coronavirus 2 (SARS-CoV-2). It is supposed that lockdown measures and fear of SARS-CoV-2 infection might reduce vitamin D levels through the modification of lifestyle. However, very few data exist on the association between lockdown measures and vitamin D status in humans. For this cross-sectional comparative study, adolescents (n = 298) aged 18 to 19 years were enrolled during the compulsory military fitness-for-duty evaluation between July and December 2020 in Southern Switzerland. Beyond anthropometric measurements, participants filled in a structured questionnaire about their lifestyle and a blood specimen was sampled for the determination of total 25-hydroxy-vitamin D. The obtained data were compared with those of 437 adolescents enrolled at the military fitness-for-duty evaluation during the same period of the year in the context of the CENERI study (2014–2016). The anthropometric measures were similar between the two study groups. The levels of vitamin D were also comparable (77 (64–91) vs. 74 (60–92) nmol/L, p = 0.50; median and interquartile range). A total of 38 (13%) and 43 (9.8%) subjects presented insufficient (<50 nmol/L) levels of vitamin D (p = 0.42) during the current pandemic and in the CENERI study, respectively. These data do not support the hypothesis that during the SARS-CoV-2 pandemic, late adolescents are at higher risk of vitamin insufficiency.  相似文献   
26.
27.
BackgroundThe occurrence of early graft failure (EGF) after heart transplantation (Htx) often requires a mechanical circulatory support (MCS) therapy. The aims of our study were to identify risk factors of mechanically supported severe EGF and evaluate their impact on both early and late outcomes.MethodsBetween January 2000 and December 2019, 499 consecutive adult patients underwent Htx at our institution. Severe EGF was defined as the need for extracorporeal life support (ECLS) within 24 hours after surgery. All available recipient and donor variables were retrospectively analyzed.ResultsOverall, EGF occurred in 58 (11.6%) patients. Post-Htx peripheral or central ECLS was necessary in 32 (6.4%) cases. Independent predictors of severe EGF were, in the recipient group, preoperative transpulmonary gradient (TPG) >12 mm Hg (odds ratio [OR] 4.1, P = .013), preoperative inotropic score >10 (OR 7.3, P = .0001), and pre-Htx ECLS support (OR 5.2, P = .015), while in the donors, a Eurotransplant donor score ≥17 (OR 8.5, P = .005). The absence of EGF was related with a better survival at 1 year and 5 years (94% and 85%, respectively) compared with EGF requiring ECLS population (36% and 28% at 1 year and 5 years, respectively; P < .001). A five-year conditional survival rate did not differ significantly (85% no EGF vs 83% EGF requiring ECLS).ConclusionBoth donor and recipient factors may influence EGF occurrence. Post-Htx ECLS may impact negatively early; however, patients weaned from ECLS eventually benefit from such a rescue treatment with outcomes comparable with Htx patients who did not suffer EGF.  相似文献   
28.
Knowledge of preoperative right heart function of adult patients with cystic fibrosis (CF) awaiting lung transplant (LUTX) is limited. The echocardiography of adult patients with CF enlisted for LUTX was retrospectively analyzed and compared with standards and invasive analyses (right heart catheterization, multigated radionuclide ventriculography). We included 49 patients (reported as mean ± standard deviation; 29 ± 9 years of age; forced expiratory volume in first second of expiration, 31% ± 11% predicted; lung allocation score, 36 ± 5; invasive mean pulmonary artery pressure, 17 ± 5 mm Hg; multigated radionuclide ventriculography right ventricle [RV] ejection fraction, 50% ± 9%). Patients had increased RV end-diastolic area, RV wall thickness, and increased pulmonary artery acceleration time with subnormal tricuspid annular plane systolic excursion, tissue Doppler positive peak systolic velocity, and fraction area change. Subnormal tricuspid annular plane systolic excursion (< 23 mm), tissue Doppler positive peak systolic velocity (< 14 cm/s), and fraction area change (< 49%) had high sensitivity and negative predictive value in predicting impaired RV.ejection fractionA good correlation between echocardiographic estimated and invasively measured systolic pulmonary artery pressure was observed (R2 = 0.554, P < .001). Adults with CF awaiting LUTX have morphologic alterations of the right heart, with subclinical impairment of RV systolic function. Echocardiography may be used as a bedside, repeatable, and reliable noninvasive test to screen further deterioration in RV function while on the waiting list for LUTX. More prospective follow-up echocardiographic studies are necessary to confirm such a hypothesis.  相似文献   
29.
BackgroundWe aim to evaluate the impact of multiparametric magnetic resonance imaging and fusion-target biopsy for early reclassification of patients with low-risk Prostate Cancer in a randomized trial.Materials and methodsBetween 2015 and 2018, patients diagnosed with Prostate Cancer after random biopsy fulfilling PRIAS criteria were enrolled and centrally randomized (1:1 ratio) to study group or control group. Patients randomized to study group underwent multiparametric magnetic resonance imaging at 3 months from enrollment: patients with positive findings (PIRADS-v2>2) underwent fusion-target biopsy; patients with negative multiparametric magnetic resonance imaging or confirmed ISUP - Grade Group 1 at fusion-target biopsy were managed according to PRIAS schedule and 12-core random biopsy was performed at 12 months. Patients in control group underwent PRIAS protocol, including a confirmatory 12-core random biopsy at 12 months. Primary endpoint was a reduction of reclassification rate at 12-month random biopsy in study group at least 20% less than controls. Reclassification was defined as biopsy ISUP Grade Group 1 in >2 biopsy cores or disease upgrading.ResultsA total of 124 patients were randomized to study group (n = 62) or control group (n = 62). Around 21 of 62 patients (34%) in study group had a positive multiparametric magnetic resonance imaging, and underwent fusion-target biopsy, with 11 (17.7%) reclassifications. Considering the intention-to-treat population, reclassification rate at 12-month random biopsy was 6.5% for study group and 29% for control group, respectively (P < 0.001).ConclusionsThe early employment of multiparametric magnetic resonance imaging for active surveillance patients enrolled after random biopsy consents to significantly reduce reclassifications at 12-month random biopsy.  相似文献   
30.
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