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   25959篇
  免费   1518篇
  国内免费   96篇
耳鼻咽喉   458篇
儿科学   641篇
妇产科学   526篇
基础医学   3663篇
口腔科学   1884篇
临床医学   2157篇
内科学   5494篇
皮肤病学   717篇
神经病学   1947篇
特种医学   554篇
外科学   2902篇
综合类   107篇
一般理论   11篇
预防医学   2925篇
眼科学   321篇
药学   1818篇
中国医学   236篇
肿瘤学   1212篇
  2023年   243篇
  2022年   423篇
  2021年   848篇
  2020年   521篇
  2019年   755篇
  2018年   933篇
  2017年   639篇
  2016年   710篇
  2015年   819篇
  2014年   1037篇
  2013年   1396篇
  2012年   2000篇
  2011年   2307篇
  2010年   1216篇
  2009年   972篇
  2008年   1546篇
  2007年   1664篇
  2006年   1457篇
  2005年   1339篇
  2004年   1159篇
  2003年   973篇
  2002年   903篇
  2001年   442篇
  2000年   467篇
  1999年   396篇
  1998年   165篇
  1997年   134篇
  1996年   92篇
  1995年   103篇
  1994年   110篇
  1993年   92篇
  1992年   191篇
  1991年   129篇
  1990年   145篇
  1989年   142篇
  1988年   99篇
  1987年   96篇
  1986年   83篇
  1985年   78篇
  1984年   61篇
  1983年   51篇
  1979年   45篇
  1978年   40篇
  1976年   35篇
  1975年   39篇
  1974年   40篇
  1973年   47篇
  1971年   44篇
  1970年   36篇
  1969年   35篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
991.

Introduction and objectives

New biomarkers could improve the predictive capacity of classic risk functions. The aims of this study were to determine the association between circulating levels of apolipoprotein A1 (apoA1), apolipoprotein B (apoB), albumin, and 25-OH-vitamin D and coronary events and to analyze whether these biomarkers improve the predictive capacity of the Framingham-REGICOR risk function.

Methods

A case-cohort study was designed. From an initial cohort of 5404 individuals aged 35 to 74 years with a 5-year follow-up, all the participants who had a coronary event (n = 117) and a random group of the cohort (subcohort; n = 667) were selected. Finally, 105 cases and 651 individuals representative of the cohort with an available biological sample were included. The events of interest were angina, fatal and nonfatal myocardial infarction and coronary deaths.

Results

Case participants were older, had a higher proportion of men and cardiovascular risk factors, and showed higher levels of apoB and lower levels of apoA1, apoA1/apoB ratio, 25-OH-vitamin D and albumin than the subcohort. In multivariate analyses, plasma albumin concentration was the only biomarker independently associated with coronary events (HR, 0.73; P = .002). The inclusion of albumin in the risk function properly reclassified a significant proportion of individuals, especially in the intermediate risk group (net reclassification improvement, 32.3; P = .048).

Conclusions

Plasma albumin levels are inversely associated with coronary risk and improve the predictive capacity of classic risk functions.  相似文献   
992.
Exposure to a novel environment enhances the extinction of contextual fear. This has been explained by tagging of the hippocampal synapses used in extinction, followed by capture of proteins from the synapses that process novelty. The effect is blocked by the inhibition of hippocampal protein synthesis following the novelty or the extinction. Here, we show that it can also be blocked by the postextinction or postnovelty intrahippocampal infusion of the NMDA receptor antagonist 2-amino-5-phosphono pentanoic acid; the inhibitor of calcium/calmodulin-dependent protein kinase II (CaMKII), autocamtide-2–related inhibitory peptide; or the blocker of L-voltage–dependent calcium channels (L-VDCCs), nifedipine. Inhibition of proteasomal protein degradation by β-lactacystin has no effect of its own on extinction or on the influence of novelty thereon but blocks the inhibitory effects of all the other substances except that of rapamycin on extinction, suggesting that their action depends on concomitant synaptic protein turnover. Thus, the tagging-and-capture mechanism through which novelty enhances fear extinction involves more molecular processes than hitherto thought: NMDA receptors, L-VDCCs, CaMKII, and synaptic protein turnover.Frey and Morris (1, 2) and their collaborators (37) proposed a mechanism whereby relatively “weak” hippocampal long-term potentiation (LTP) or long-term depression (LTD) lasting only a few minutes can nevertheless “tag” the synapses involved with proteins synthesized ad hoc, so that other plasticity-related proteins (PRPs) produced at other sets of synapses by other LTPs or LTDs can be captured by the tagged synapses and strengthen their activity to “long” LTPs or LTDs lasting hours or days (8). LTDs and LTPs can “cross”-tag each other; that is, LTDs can enhance both LTDs and LTPs, and vice versa (6, 8). Because many learned behaviors rely on hippocampal LTP or LTD (79), among them the processing of novelty (9, 10) and the making of extinction (1113), interactions between consecutive learnings can also be explained by the “tagging-and-capture” hypothesis (9, 10, 13), whose application to behavior became known as “behavioral tagging and capture” (5, 7, 9, 13). Typically, exposure to a novel environment [e.g., a nonanxiogenic 50 × 50 × 40-cm open field (OF) (5, 7, 9, 10, 14)] is interpolated before testing for another task, which becomes enhanced (410, 13). The usual reaction to novelty is orienting and exploration (14), followed by habituation of this response (1416). Habituation is perhaps the simplest form of learning, and it consists of inhibition of the orienting/exploratory response (14, 16).We recently showed that the brief exposure of rats to a novel environment (the OF) within a limited time window enhances the extinction of contextual fear conditioning (CFC) through a mechanism of synaptic tagging and capture (13), which is a previously unidentified example of behavioral tagging of inhibitory learning. Fear extinction is most probably due to LTD in the hippocampus (11, 12), although the possibility that it may also involve LTP is not discarded (13). The enhancement of extinction by novelty probably relies on the habituation to the novel environment, which is also probably due to LTD (15, 16). The enhancement of extinction by the exposure to novelty depends on hippocampal gene expression and ribosomal protein synthesis following extinction training and on both ribosomal and nonribosomal protein synthesis caused by the novel experience (13). Nonribosomal protein synthesis that can be blocked by rapamycin is believed to be dendritic (13, 17), so it would be strategically located for tagging-and-capture processes, but it has not been studied in synaptic tagging to date (38) or in other forms of behavioral tagging (710). As occurs with the interactions between LTPs and/or LTDs (4), the enhancement of extinction by novelty relies on hippocampal but not amygdalar processes (13).Recent findings indicate that several hippocampal processes related to learning and memory, such as the reconsolidation of spatial learning, are highly dependent on NMDA glutamate receptors, calcium/calmodulin protein kinase II (CaMKII), and long-term voltage channel blockers (L-VDCCs), which, in turn, rely on the proteasomal degradation of proteins (18). Here, we study the effects of an NMDA blocker, 2-amino-5-phosphono pentanoic acid (AP5); the L-VDCC blocker nifedipine (Nife); a CaMKII inhibitor, the autocamtide-2–related inhibitory peptide (AIP); and the irreversible proteasome blocker β-lactacystin (12, 13) on the interaction between novelty and extinction (11). As will be seen, we found that both the setting up of tags by extinction and the presumable production of PRPs by the processing of novelty are dependent on NMDA receptors, CaMKII, and L-VDCCs. This endorses and expands the hypothesis that the novelty–extinction interaction relies on synaptic tagging and capture (13).  相似文献   
993.
Randomized controlled trials (RCTs) are essential to develop advances in heart failure (HF). The need for increasing numbers of patients (without substantial cost increase) and generalization of results led to the disappearance of international boundaries in large RCTs. The significant geographic differences in patients' characteristics, outcomes, and, most importantly, treatment effect observed in HF trials have recently been highlighted. Whether the observed regional discrepancies in HF trials are due to trial‐specific issues, patient heterogeneity, structural differences in countries, or a complex interaction between factors are the questions we propose to debate in this review. To do so, we will analyse and review data from HF trials conducted in different world regions, from heart failure with preserved ejection fraction (HF‐PEF), heart failure with reduced ejection fraction (HF‐REF), and acute heart failure (AHF). Finally, we will suggest objective and actionable measures in order to mitigate regional discrepancies in future trials, particularly in HF‐PEF where prognostic modifying treatments are urgently needed and in which trials are more prone to selection bias, due to a larger patient heterogeneity.  相似文献   
994.

Introduction

Single coronary artery (SCA) with no associated congenital heart disease is a rare congenital anomaly. Most cases are asymptomatic and incidental findings, but SCA can cause ischemia, congestive heart failure, and sudden cardiac death (SCD).

Case report

A 44-year-old woman presented with Takotsubo cardiomyopathy and cardiogenic shock. Selective cannulation of the left coronary artery (LCA) was not possible on coronary angiography (CA); an SCA was revealed arising from the right sinus, continuing distally as the circumflex artery and thereafter as the left anterior descending artery. Coronary computed tomography angiography (CCTA) confirmed left main atresia and no coronary stenosis. Cardiac magnetic resonance imaging (MRI) showed diffuse myocardial edema and no perfusion defects. The patient's clinical course was favorable under conservative management.

Discussion

Our paper describes an incidental finding of right SCA. We report a Lipton type R-I, in which a dominant right SCA supplies the entire myocardium. It is the rarest SCA presentation, with an incidence of 0.0008%; only 15 cases have been reported in the literature, all of which were studied by CA. Of these 15, one had SCD, five angina, one ventricular arrhythmia and one complicated acute coronary syndrome. CCTA confirmed the diagnosis in seven patients, MRI in one and transesophageal echocardiography in another. Nine patients had coronary lesions. Two underwent coronary artery bypass grafting, one percutaneous intervention and 11 conservative treatment.

Conclusion

Right SCA with congenital absence of the LCA is one of the rarest coronary artery anomalies. In a significant percentage of patients it is associated with ischemia and can be life-threatening. CCTA and MRI are the modalities of choice for diagnosis and risk stratification.  相似文献   
995.
West Nile virus (WNV) and Japanese encephalitis virus (JEV) are important mosquito-borne viruses of the Flaviviridae family, associated with encephalitis, mainly in humans and horses. WNV is also pathogen for many bird species. The incidence of human and animal WNV infections in Europe has risen, mostly in recent years, and JEV was detected in 2011 in mosquitoes collected in Italy and may emerge in Europe in the same way as other flaviviruses had emerged recently (USUTU and Bagaza virus) and should be regarded as a potential threat to public health.  相似文献   
996.
Cryptococcosis is a fungal infection of the central nervous system predominantly caused by Cryptococcus neoformans in immunocompromised patients. In several countries worldwide, up to 50% of isolates show in vitro resistance to clinically used antifungals including fluconazole. No prospective data on susceptibility to antifungal drugs are available for Germany. In this study, we characterised all C. neoformans isolates collected from individual patients’ samples at the German reference laboratory for cryptococcosis 2011 and 2017 (n = 133) by multi-locus sequence typing and phenotypic drug susceptibility testing. We identified serotype A/genotype VNI isolates belonging to clonal complexes previously described from Europe, Africa, Asia and South America as the most prevalent agents of cryptococcosis in Germany. Overall, we observed minimal inhibitory concentrations (MICs) above the epidemiological cut-offs (ECVs) in 1.6% of isolates regarding fluconazole and 2.3% of isolates regarding 5-flucytosine. Here, two C. neoformans var. grubii isolates displayed decreased drug susceptibility to fluconazole, one of them additionally to 5-flucytosine. We also found 5-flucytosine MICs above the ECV for two C. neoformans var. neoformans isolates. We identified a novel mutation in the ERG11 gene which might be associated with the elevated fluconazole MIC in one of the isolates. The clinical importance of the detected in vitro resistance is documented by patient histories showing relapsed infection or primary fatal disease. Of note, sertraline demonstrated antifungal activity comparable to previous reports. Systematic collection of susceptibility data in combination with molecular typing of C. neoformans is important to comprehensively assess the spread of isolates and to understand their drug resistance patterns.  相似文献   
997.
998.
From 1978 to 1985 cytogenetic studies were performed on 718 patients with different hematologic diseases. Nine (1.25%) had a constitutional chromosome alteration. One patient had trisomy 21, four had balanced translocations and four had sex chromosome anomalies. Although the frequency of constitutional alterations was twice that seen in the newborn population, an analysis of these data and also from the literature shows a random association between constitutional chromosome alterations and hematologic neoplasias, except for patients with Down's syndrome.  相似文献   
999.
Primary familial brain calcification (PFBC) is a heterogeneous neuropsychiatric disorder, with affected individuals presenting a wide variety of motor and cognitive impairments, such as migraine, parkinsonism, psychosis, dementia, and mood swings. Calcifications are usually symmetrical, bilateral, and found predominantly in the basal ganglia, thalamus, and cerebellum. So far, variants in three genes have been linked to PFBC: SLC20A2, PDGFRB, and PDGFB. Variants in SLC20A2 are responsible for most cases identified so far and, therefore, the present review is a comprehensive worldwide summary of all reported variants to date. SLC20A2 encodes an inorganic phosphate transporter, PiT‐2, widely expressed in various tissues, including brain, and is part of a major family of solute carrier membrane transporters. Fifty variants reported in 55 unrelated patients so far have been identified in families of diverse ethnicities and only few are recurrent. Various types of variants were detected (missense, nonsense, frameshift) including full or partial SLC20A2 deletions. The recently reported SLC20A2 knockout mouse will enhance our understanding of disease mechanism and allow for screening of therapeutic compounds. In the present review, we also discuss the implications of these recent exciting findings and consider the possibility of treatments based on manipulation of inorganic phosphate homeostasis.  相似文献   
1000.
Pentraxin‐3 (PTX3), an acute‐phase protein released during inflammation, aids phagocytic clearance of pathogens and apoptotic cells, and plays diverse immunoregulatory roles in tissue injury. In neuroinflammatory diseases, like MS, resident microglia could become activated by endogenous agonists for Toll like receptors (TLRs). Previously we showed a strong TLR2‐mediated induction of PTX3 in cultured human microglia and macrophages by HspB5, which accumulates in glia during MS. Given the anti‐inflammatory effects of HspB5, we examined the contribution of PTX3 to these effects in MS and its animal model EAE. Our data indicate that TLR engagement effectively induces PTX3 expression in human microglia, and that such expression is readily detectable in MS lesions. Enhanced PTX3 expression is prominently expressed in microglia in preactive MS lesions, and in microglia/macrophages engaged in myelin phagocytosis in actively demyelinating lesions. Yet, we did not detect PTX3 in cerebrospinal fluid of MS patients. PTX3 expression is also elevated in spinal cords during chronic relapsing EAE in Biozzi ABH mice, but the EAE severity and time course in PTX3‐deficient mice did not differ from WT mice. Moreover, systemic PTX3 administration did not alter the disease onset or severity. Our findings reveal local functions of PTX3 during neuroinflammation in facilitating myelin phagocytosis, but do not point to a role for PTX3 in controlling the development of autoimmune neuroinflammation.  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