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   8735篇
  免费   585篇
  国内免费   62篇
耳鼻咽喉   42篇
儿科学   214篇
妇产科学   250篇
基础医学   1390篇
口腔科学   51篇
临床医学   822篇
内科学   2100篇
皮肤病学   145篇
神经病学   846篇
特种医学   315篇
外科学   1538篇
综合类   41篇
一般理论   3篇
预防医学   534篇
眼科学   96篇
药学   459篇
中国医学   7篇
肿瘤学   529篇
  2023年   42篇
  2022年   64篇
  2021年   176篇
  2020年   116篇
  2019年   176篇
  2018年   218篇
  2017年   161篇
  2016年   158篇
  2015年   218篇
  2014年   303篇
  2013年   410篇
  2012年   595篇
  2011年   608篇
  2010年   385篇
  2009年   346篇
  2008年   574篇
  2007年   594篇
  2006年   583篇
  2005年   561篇
  2004年   591篇
  2003年   568篇
  2002年   586篇
  2001年   54篇
  2000年   77篇
  1999年   95篇
  1998年   137篇
  1997年   100篇
  1996年   94篇
  1995年   84篇
  1994年   73篇
  1993年   67篇
  1992年   55篇
  1991年   43篇
  1990年   35篇
  1989年   40篇
  1988年   30篇
  1987年   41篇
  1986年   35篇
  1985年   30篇
  1984年   32篇
  1983年   24篇
  1982年   32篇
  1981年   32篇
  1980年   15篇
  1979年   14篇
  1978年   15篇
  1977年   10篇
  1976年   13篇
  1974年   9篇
  1970年   11篇
排序方式: 共有9382条查询结果,搜索用时 15 毫秒
21.
22.
The mitochondrial genome of the selfed progeny of a plant regenerated from long-term somatic tissue culture displays specific structural rearrangements characterized by the appearance of novel restriction fragments. A mitochondrial DNA library was constructed from this selfed progeny in the SalI site of cosmid pHC79 and the novel fragments were subsequently studied. They were shown to arise from reciprocal recombination events involving DNA sequences present in the parental plant. The regions of recombination were sequenced and the nucleotide sequences were aligned with those of the presumptive parental fragments. We characterized an imperfect short repeated DNA sequence, 242 bp long, within which a 7-bb DNA repeat could act as a region of recombination. The use of PCR technology allowed us to show that these fragments were present in both parental plants and tissue cultures as low-abundance sequence arrangements.  相似文献   
23.
OBJECTIVE: One of the complications of CPB is the systemic inflammatory response syndrome (SIRS). Recent developments tend to minimize the biological impact of CPB in using miniaturized closed circuit with reduced priming volume and less blood-air interface. The benefit of these miniaturized closed circuits in terms of inflammatory response has been proved in coronary surgery. However, in open heart surgery, the CPB circuit is no more closed and the benefit of the miniaturized set-up could disappear. The aim of the study is to compare the SIRS between standard and miniaturized circuits in aortic surgery. METHODS: Forty patients who underwent singular aortic valve replacement were randomly assigned either to a standard CPB (group A, n=20) or to a miniaturized CPB (group B, n=20). Pertinent clinical and surgical data were collected. Hematological parameters (leukocyte and neutrophil counts) and biochemical parameters (C-reactive protein, cytokine tests) were determined pre-, on and post-CPB. RESULTS: There were an increase in leukocyte and neutrophil counts and a decline in hematocrit in both groups. In both groups, there was a raise after CPB, in C-reactive protein, IL-6, TNF-alpha, neutrophil elastase, and IL-10. However, the raises of elastase and TNF-alpha were significantly lower after the weaning of miniaturized CPB (116+/-46 ng/ml and 10+/-4 pg/ml, respectively) compared to standard CPB (265+/-120 ng/ml, P=0.01 and 18+/-7 pg/ml, P=0.03). The raise of IL-10 is also lower with miniaturized circuit (15+/-6 pg/ml) compared to standard circuit (51+/-26, P=0.004). CONCLUSIONS: This study demonstrates in aortic surgery, the lesser inflammatory response of a miniaturized CPB compared to a standard CPB. However, there is always some inflammation after CPB and a small bio-reactive free perfusion circuit is still to be found in open heart surgery.  相似文献   
24.
A strain of Aspergillus fumigatus has been isolated from sediments of a mussel bed. When cultured in hyper saline conditions (with sea-water), it produces a cytotoxic and immunosuppressive toxin, gliotoxin, which is excreted in an exudate. In order to know if this toxin could represent a risk for shellfish consumers, an experiment of bioaccumulation of gliotoxin in mussel has been carried out. After 6 days of contamination, toxin was accumulated in the meat of the mussels, at a level up to 2.9 microg/mg of extract weight, with a mode of contamination different to the classical digestive process described for a majority of marine toxins, but similar to the contamination mode of domoic acid.  相似文献   
25.
Prediction of hemorrhagic transformation (HT) in patients treated by intravenous recombinant tissue-type plasminogen activator (rt-PA) is a challenging issue in acute stroke management. HT may be correlated with severe hypoperfusion. Signal changes may be observed at susceptibility-weighted magnetic resonance imaging (MRI) within large perfusion defects. A signal drop within cerebral veins at T2*-weighted gradient-echo MRI may be expected in severe ischemia, and may indicate subsequent risk of HT. The authors prospectively searched for an abnormal visibility of transcerebral veins (AVV) within the ischemic area in patients with hemispheric ischemic stroke, before they were treated with intravenous rt-PA therapy. Any correlation between AVV and baseline clinical or MRI findings, or further HT, was noted. An AVV was present in 23 of 49 patients (obvious, n = 8; moderate, n = 15), and was supported by severe hemodynamic changes at baseline MRI. The AVV was correlated with the occurrence of parenchymal hematoma type 2 at computed tomography during the first week (r = 0.44, P = 0.002). Five of six type 2 parenchymal hematomas occurred in association with obvious AVV. At multiple regression analysis, two baseline MRI factors had an independent predictive value for HT risk during the first week: the AVV and the cerebral blood volume ratio (Nagelkerke R2 = 0.48).  相似文献   
26.
The role of the basal ganglia in syntactic language processing was investigated with event-related brain potentials in fourteen neurologically impaired patients. Seven of these patients had basal ganglia lesions while 7 other patients primarily had lesions of the left temporo-parietal region excluding the basal ganglia. All patients listened to sentences that were either correct or included a verb argument structure violation. In previous experiments this type of violation elicited a biphasic pattern of an N400-P600 complex in young healthy participants. While the N400 may result from incorrect semantic-thematic role assignment, the P600 reflects the fact that verb information does not license the syntactic structure at present. Results of the patient experiment revealed a double dissociation: patients with left temporo-parietal lesions only show a P600, whereas patients with lesions of the basal ganglia showed no P600, but a negativity with extended duration that resembled an N400. The latter pattern not only confirms previous reports that the basal ganglia modulate the P600 but extends these results by showing that the N400 as a late semantic-thematic integration process appears partially modulated by the basal ganglia.  相似文献   
27.
28.
The prevalence for anorexia nervosa is estimated at 0.5% in the young girls and the highest incidence was found between ten to 19 years. Among women, the prevalence for anorexia nervosa is estimated between 0 to 1.5%. The lifetime prevalence varies between 0.6 and 4%. The methodological limitations relate to the variety of the instruments to diagnose an eating disorder and the lack of definition approved for eating disorders not otherwise specified. The empirical models of the pathogenesis of eating disorders continue to stress the role of social pressure to thinness, this one being transmitted by the media, the family environment and the peers. The methodological limitations continue to pose a challenge in the interpretation of the modulation by the sociocultural factors of the etiologic ways for anorexia nervosa. A complex multifactor aetiology is considered, implying the interaction of genetic predisposition and certain specific environmental risk factors, in particular social factors.  相似文献   
29.
The preoptic area contains most of the luteinizing hormone releasing hormone immunoreactive neurons and numerous monoaminergic afferents whose cell origins are unknown in sheep. Using tract tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the medial preoptic area in sheep. Among the retrogradely labeled neurons, immunohistochemistry for tyrosine hydroxylase, dopamine-β-hydroxylase, phenylethanolamine N-methyltransferase, and serotonin was used to characterize catecholamine and serotonin fluorogold labeled neurons. Most of the afferents came from the ipsilateral side to the injection site. It was observed that the medial preoptic area received major inputs from the diagonal band of Broca, the lateral septum, the thalamic paraventricular nucleus, the lateral hypothalamus, the area dorsolateral to the third ventricle, the perimamillary area, the amygdala, and the ventral part of the hippocampus. Other numerous, scattered, retrogradely labeled neurons were observed in the ventral part of the preoptic area, the vascular organ of the lamina terminalis, the ventromedial part of the hypothalamus, the periventricular area, the area lateral to the interpeduncular nucleus, and the dorsal vagal complex. Noradrenergic afferents came from the complex of the locus coeruleus (A6/A7 groups) and from the ventro-lateral medulla (group A1). However, dopaminergic and adrenergic neuronal groups retrogradely labeled with fluorogold were not observed. Serotoninergic fluorogold labeled neurons belonged to the medial raphe nucleus (B8, B5) and to the serotoninergic group situated lateral to the interpeduncular nucleus (S4). In the light of these anatomical data we hypothesize that these afferents have a role in the regulation of several functions of the preoptic area, particularly those related to reproduction. Accordingly these afferents could be involved in the control of luteinizing hormone releasing hormone (LHRH) pulsatility or of preovulatory LHRH surge.  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