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   4706篇
  免费   317篇
  国内免费   20篇
耳鼻咽喉   19篇
儿科学   149篇
妇产科学   109篇
基础医学   714篇
口腔科学   128篇
临床医学   366篇
内科学   1129篇
皮肤病学   216篇
神经病学   537篇
特种医学   44篇
外科学   324篇
综合类   21篇
预防医学   406篇
眼科学   145篇
药学   373篇
中国医学   33篇
肿瘤学   330篇
  2024年   3篇
  2023年   38篇
  2022年   89篇
  2021年   170篇
  2020年   101篇
  2019年   163篇
  2018年   178篇
  2017年   127篇
  2016年   147篇
  2015年   156篇
  2014年   216篇
  2013年   253篇
  2012年   439篇
  2011年   422篇
  2010年   239篇
  2009年   189篇
  2008年   341篇
  2007年   288篇
  2006年   271篇
  2005年   285篇
  2004年   255篇
  2003年   222篇
  2002年   230篇
  2001年   12篇
  2000年   9篇
  1999年   30篇
  1998年   29篇
  1997年   24篇
  1996年   21篇
  1995年   13篇
  1994年   8篇
  1993年   12篇
  1992年   9篇
  1991年   7篇
  1990年   4篇
  1989年   2篇
  1988年   2篇
  1987年   6篇
  1986年   6篇
  1983年   2篇
  1982年   5篇
  1981年   4篇
  1980年   2篇
  1978年   3篇
  1976年   1篇
  1974年   2篇
  1973年   1篇
  1971年   1篇
  1970年   1篇
  1967年   1篇
排序方式: 共有5043条查询结果,搜索用时 15 毫秒
71.

Background

The right ventricular ejection fraction (RVEF) is a surrogate marker of right ventricular function in pulmonary hypertension (PH), but its measurement is complicated and time consuming. The tricuspid annular plane systolic excursion (TAPSE) measures only the longitudinal component of RV contraction while the right ventricular fractional area change (RVFAC) takes into account both the longitudinal and the transversal components. The aim of our study was to evaluate the relationship between RVEF, RVFAC, and TAPSE according to hemodynamic severity in two groups of patients with PH: pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH).

Methods and Results

Fifty-four patients with PAH (n?=?15) and CTEPH (n?=?39) underwent right heart catheterization and cardiac magnetic resonance (CMR). The ventricular volumes and areas, TAPSE, and eccentricity index were measured. The RVFAC was more strongly correlated with the RVEF (r?=?0.81, p?<?0.0001) than the TAPSE (r?=?0.63, p?<?0.0001). RVEF?<?35% was better predicted by the RVFAC than the TAPSE (TAPSE: AUC?=?0.77 and RVFAC: AUC?=?0.91; p?=?0.042). In the group with the worse hemodynamic status, the RVFAC correlated much better with the RVEF than the TAPSE. There were no significant differences in the CMR data analyzed between the groups of PAH and CETPH patients.

Conclusions

The RVFAC is a good index to estimate RVEF in PH patients; even better than the TAPSE in patients with more severe hemodynamic profile, possibly for including the transversal component of right ventricular function in its measurement. Furthermore, RVFAC performance was similar in the two PH groups (PAH and CTEPH).
  相似文献   
72.
St Jude Total Therapy Study XIIIB for childhood acute lymphoblastic leukemia (ALL) incorporated more stringent risk classification, early intensification of intrathecal chemotherapy, reinduction treatment, and the addition of dexamethasone to postremission therapy to increase the proportion of event-free survivors without jeopardizing their quality of life. Cranial irradiation was reserved for the 12% of patients who had T-cell ALL and a presenting leukocyte count of 100 x 10(9)/L or more, or CNS-3 (5 or more leukocytes/microL with identifiable blast cells in an atraumatic sample or the presence of cranial nerve palsy) status. Among the 247 consecutive patients enrolled in the study, 117 were classified as having lower-risk leukemia and received mainly antimetabolite-based continuation therapy; the 130 cases with higher-risk leukemia received more intensive continuation chemotherapy with multiple drug pairs administered in weekly rotation. The 5-year event-free survival estimate was 80.8% +/- 2.6% (SE); the 8-year rate was 78.6% +/- 5.8%. The 5-year cumulative risk of an isolated central nervous system (CNS) relapse was 1.7% +/- 0.8%, and that of isolated plus combined CNS relapse was 3.0% +/- 1.1%. The 5-year cumulative risks of etoposide-related myeloid malignancies were 1.8% +/- 1.3% in the lower-risk patients who received a cumulative dose of 1.2 g/m(2) and 5.0% +/- 2.0% in the higher-risk patients who received a cumulative dose of up to 14.4 g/m(2) (P = .18). Independent adverse prognostic features included the presence of MLL-AF4 or BCR-ABL fusion gene and minimal residual leukemia of 0.01% or more at the end of the 6-week remission induction phase. Our results suggest the efficacy of early intensification of intrathecal chemotherapy and provide the basis for studies omitting cranial irradiation altogether.  相似文献   
73.
Takayasu arteritis is an inflammatory disease that affects large vessels, especially the aorta and its branches. The clinical features of the disease depend on which arteries are affected. Although pulmonary artery involvement is common, only rarely is this the main clinical manifestation. We describe the case of a young woman with dyspnea who had severe pulmonary hypertension secondary to Takayasu arteritis of the pulmonary artery. She was administered corticosteroid (methylprednisolone) and immunosuppressant (azathioprine) therapy and a stent was implanted in the left pulmonary artery. Both hemodynamic and clinical signs improved.  相似文献   
74.
Burkholderia pseudomallei (Bp) is the causative agent of the infectious disease melioidosis. To investigate population diversity, recombination, and horizontal gene transfer in closely related Bp isolates, we performed whole-genome sequencing (WGS) on 106 clinical, animal, and environmental strains from a restricted Asian locale. Whole-genome phylogenies resolved multiple genomic clades of Bp, largely congruent with multilocus sequence typing (MLST). We discovered widespread recombination in the Bp core genome, involving hundreds of regions associated with multiple haplotypes. Highly recombinant regions exhibited functional enrichments that may contribute to virulence. We observed clade-specific patterns of recombination and accessory gene exchange, and provide evidence that this is likely due to ongoing recombination between clade members. Reciprocally, interclade exchanges were rarely observed, suggesting mechanisms restricting gene flow between clades. Interrogation of accessory elements revealed that each clade harbored a distinct complement of restriction-modification (RM) systems, predicted to cause clade-specific patterns of DNA methylation. Using methylome sequencing, we confirmed that representative strains from separate clades indeed exhibit distinct methylation profiles. Finally, using an E. coli system, we demonstrate that Bp RM systems can inhibit uptake of non-self DNA. Our data suggest that RM systems borne on mobile elements, besides preventing foreign DNA invasion, may also contribute to limiting exchanges of genetic material between individuals of the same species. Genomic clades may thus represent functional units of genetic isolation in Bp, modulating intraspecies genetic diversity.Burkholderia pseudomallei (Bp) is the causative agent of melioidosis, a serious infectious disease of humans and animals and a leading cause of community-acquired sepsis and pneumonia in endemic regions (Currie et al. 2010). Initially thought to be confined to Southeast Asia and Northern Australia, the prevalence of Bp appears to be spreading (Wiersinga et al. 2012), and Bp has been designated a biothreat select agent in the United States. Bp can persist in extreme environmental conditions and can infect several plant and animal hosts, including birds, dolphins, and humans (Wuthiekanun et al. 1995; Howard and Inglis 2003; Sprague and Neubauer 2004; Larsen et al. 2013). Treatment of clinical melioidosis is challenging because the bacterium is inherently resistant to many antibiotics, and Bp infections can persist in humans for more than a decade (Hayden et al. 2012; Wiersinga et al. 2012).The Bp genome comprises one of the largest and most complex bacterial genomes sequenced to date. Consisting of two large circular replicons (chromosomes) with a combined 7.2-Mb genome size (Holden et al. 2004), it contains a rich arsenal of genes related to virulence (e.g., Type III and Type VI secretion systems, polysaccharide biosynthesis clusters), metabolic pathways, and environmental adaptation (Wiersinga et al. 2012). Besides conserved regions, accessory genes on mobile elements and genomic islands may also contribute to phenotypic and clinical differences in microbial behavior (Currie et al. 2000; Sim et al. 2008). Analysis of the Bp genome has revealed previously unknown toxins and mechanisms of antibiotic resistance (Chantratita et al. 2011; Cruz-Migoni et al. 2011).Most large-scale studies of Bp genetic diversity to date have analyzed strains using multilocus sequence typing (MLST). These studies have suggested a high degree of genetic variability between Bp strains and related Burkholderia species (Cheng et al. 2008), and have shown that Bp strains belonging to different sequence types (STs) can often coexist in the same locale and sometimes even within the same sample (Pitt et al. 2007; Wuthiekanun et al. 2009). However, due to the limited number of genes analyzed by MLST, these studies cannot comment on the global proportion of genetic material shared between strains of different STs nor on the relative contribution of recombination, mutation, and horizontal gene transfer on intraspecies genetic diversity. Moreover, although previous studies have applied whole-genome sequencing (WGS) to study global patterns of Bp genetic heterogeneity and evolution, earlier Bp WGS reports have been confined to a limited number of isolates (10–12) derived from diverse geographical regions (Nandi et al. 2010), where geophysical barriers likely limit the propensity of the analyzed strains to exchange genetic material. To achieve a comprehensive understanding of genetic variation among closely related Bp strains, WGS analysis of much larger strain panels, ideally performed on strains isolated from a common region and belonging to the same (or closely related) ST groups, is required.In this study, we attempted to fill this important knowledge gap by performing WGS on 106 Bp strains drawn from a restricted Asian locale (Singapore and Malaysia). The WGS data, exceeding previous Bp WGS studies by 10-fold, enabled us to identify specific genomic clades of Bp, molecular features of Bp recombination at the whole-genome level, and accessory genome features contributing to recombination and horizontal gene transfer. We found a consistent pattern of genetic separation correlating with MLST, recombination haplotypes, shared accessory genes, and restriction modification (RM) systems. We provide evidence that restriction modification, beyond its role as defense against foreign DNA invasion, may have also partitioned the Bp species by restricting gene flow, resulting in the other observed correlations. Because RM systems are widely dispersed through the bacterial kingdom, it is possible that similar principles may apply to other bacterial species, implicating a potential role for epigenetic barriers as a driver of early incipient speciation.  相似文献   
75.
The substantial focus of resilience research on childhood well‐being has resulted in limited knowledge regarding other aspects of resilience in families, such as that of parents. Informed by literature in childhood and family resilience, in this review, we progress conceptual understanding by focusing on parental resilience. The definition of parental resilience, as the capacity of parents to deliver a competent and quality level of parenting to children despite the presence of risk factors, is offered here as a worthwhile framework through which to explore variables thought to contribute to resilience among parents. A conceptual model is proposed whereby parental psychological well‐being and self‐efficacy, family functioning, and social connectedness are specifically addressed, with each posited as playing an important role in parents’ ability to deliver high‐quality parenting. In addition to these factors, how parents accommodate adversity and find meaning in their everyday lives within their families is hypothesised to be an important process in understanding parental resilience.  相似文献   
76.
In this work we analyze the effect of adding CuO to a NiO/Ce0.9Zr0.1O2 oxide by in situ X-ray absorption near-edge structure XANES technique in Ce L3, Ni K and Cu K absorption edges in terms of sample reducibility and catalytic activity. The oxidation states of Ce, Ni and Cu cations are followed up during temperature programmed reduction (TPR) experiments in diluted hydrogen and during catalytic tests for partial oxidation of methane (POM) reaction. Redox behavior was correlated to conventional fixed bed reactor results. The effect of firing temperature, crystallite size, CeO2–ZrO2 support and the presence of Cu and/or Ni as an active phase is also analyzed. Results showed a beneficial effect of CuO addition in terms of Ce and Ni reduction. A stronger interaction of NiO species with the support was revealed upon analysis of XANES reduction profiles in sample NiO/ZDC in contrast to bimetallic CuO–NiO/ZDC sample. Reduction onset temperature was found to depend on Ni crystallite size, being markedly promoted when samples exhibited low values of crystallite size both in supported and non-supported CuO–NiO species. In situ catalytic experiments for partial oxidation of methane showed a clear interplay between the redox behavior from the Ce in the CeO2–ZrO2 support and the Ni from the active phase. Sample NiO/ZDC exhibited a continuous reduction of Ce cations in CH4 : O2 feed flow, carbon formation was detected in X-ray Powder Diffraction (XPD) patterns and Ni re-oxidation was found to take place, clear indications of catalyst deactivation. In contrast, sample CuO–NiO/Ce0.9Zr0.1O2 displayed a slight re-oxidation of Ce and no re-oxidation of Ni altogether with the suppression of carbon formation.

In situ X-Ray Absorption (XAS) experiments in reducing atmospheres (H2 and CH4 : O2) uncovered Ce, Ni and Cu redox interplay during catalytic experiments.  相似文献   
77.

Aim

To compare the evaluation of retinographies by a teleophthalmology nurse and primary care physicians (PCP) with an ophthalmologist referral hospital (gold standard).

Methods

Cross-sectional study on a random sample of 337 patients on the teleophthalmology programme from January 2010 to January 2015. We analyzed the diagnostic evaluation (whether or not it presented findings of RD) and the therapeutic assessment (whether or not referral to the opthalmology department was needed) which were conducted independently on the sample retinographies by the PCP, a nurse and an ophthalmologist (gold standard). Reliability and concordance between the gold standard and the PCP and the nurse were checked and the statistical analyses were supported using SPSSv.23.00 software and diagnostic test reliability calculators (EPIDAT 4.1).

Results

In the diagnosis of RD, the nurse presented: sensitivity (S): 0.96; specificity (Sp): 0.89; PPV: 0.58; NPV: 0.99; Kappa index: 0.67 and PCP: S: 0.98; Sp: 0.99; PPV: 0.96; NPV: 0.99; Kappa index: 0.96.In the referral to ophthalmology assessed by the nurse: S: 0.83; Sp: 0.83; PPV: 0.51; NPV: 0.96; Kappa Index: 0.53 and PCP: S: 0.62; Sp: 0.76; PPV: 0.36; NPV: 0.90; Kappa index: 0.29.

Conclusions

A nursing teleophthalmology programme could perform population screening for RD with the same quality as PCP. This would increase coverage, in addition to providing better use of resources by avoiding intermediate patient appointments through PCP and increased health savings.  相似文献   
78.
Occupational exposure to lead (Pb) requires continuous surveillance to assure, as much as possible, safe and healthful working conditions. This study addresses the suitability of assessing Pb exposure in relevant workers using their exhaled breath condensate (EBC). This study enrolled workers of two different Pb processing industries characterized by moderate and high Pb exposure levels in the work environment, and a group of non-exposed individuals working in offices who served as baseline for Pb exposure. The EBC-Pb of workers reflected the Pb levels in the work environment of all three settings, although the relationship with B-Pb was not clear. The lack of correlation between EBC-Pb and B-Pb most probably indicates the time lag for Pb to enter in the two body pools. The EBC-Pb seems to reflect immediate exposure, providing a prompt signature of Pb in the environmental that may interact directly with the organ. By delivering short-term evaluation of exposure, EBC-Pb represents a clear advantage in biomonitoring and may become an interesting tool for estimating organ burden.  相似文献   
79.
Background: The daily consumption of dietary fiber is frequently below suggested recommendations. Using a double‐blind, controlled, randomized study, we assessed the efficiency and tolerance of a fiber‐enriched orange juice to supplement fiber intake in women. Materials and Methods: After 1 week of noninterventional observation, 192 healthy adult women ingested 400 mL of orange juice for 21 days, which either was not (placebo group) or was enriched with fiber (fiber group). Orange juice ingestion was registered daily and controlled for each week during the study period. Macronutrient, fiber, and energy intake were determined using a 3‐day food record, validated food chemical composition databases, and the “Pro Diet” software. Gastrointestinal symptoms were self‐evaluated daily by scoring 4 grades of symptom intensity and using a visual analog scale to grade pain severity. Results: No changes were observed for macronutrient and energy ingestion. For the placebo group (n = 97), the total fiber intake record was under the daily recommended value. In contrast, the fiber group (n = 95) displayed higher comparative values of total and soluble fiber consumption (P ≤ .001), achieving the daily recommended values of fiber intake. Both groups reported an increased frequency of slight bloating and rumbles over time (P ≤ .05). The fiber group also experienced a higher frequency of slight flatulence over time (P = .002). Conclusion: Consumption of fiber‐enriched orange juice was efficient to achieve the daily fiber intake recommendation for women, was not accompanied by intense adverse events, and may represent a suitable method to supplement fiber intake in woman.  相似文献   
80.
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