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   6489篇
  免费   329篇
  国内免费   31篇
耳鼻咽喉   64篇
儿科学   129篇
妇产科学   91篇
基础医学   652篇
口腔科学   103篇
临床医学   389篇
内科学   1992篇
皮肤病学   60篇
神经病学   686篇
特种医学   172篇
外科学   836篇
综合类   41篇
一般理论   5篇
预防医学   424篇
眼科学   240篇
药学   436篇
  1篇
中国医学   16篇
肿瘤学   512篇
  2023年   48篇
  2022年   88篇
  2021年   222篇
  2020年   105篇
  2019年   191篇
  2018年   207篇
  2017年   162篇
  2016年   161篇
  2015年   172篇
  2014年   215篇
  2013年   357篇
  2012年   504篇
  2011年   480篇
  2010年   283篇
  2009年   255篇
  2008年   443篇
  2007年   447篇
  2006年   444篇
  2005年   384篇
  2004年   291篇
  2003年   314篇
  2002年   273篇
  2001年   83篇
  2000年   60篇
  1999年   51篇
  1998年   63篇
  1997年   44篇
  1996年   40篇
  1995年   30篇
  1994年   24篇
  1993年   15篇
  1992年   46篇
  1991年   38篇
  1990年   28篇
  1989年   38篇
  1988年   31篇
  1987年   24篇
  1986年   22篇
  1985年   20篇
  1984年   16篇
  1983年   9篇
  1982年   18篇
  1981年   13篇
  1980年   10篇
  1979年   7篇
  1978年   8篇
  1977年   7篇
  1976年   9篇
  1975年   6篇
  1974年   7篇
排序方式: 共有6849条查询结果,搜索用时 62 毫秒
31.
 Three further cases of mature benign cystic teratomas of the ovary associated with virilization are added to the three previously reported in the literature. They were found in postmenopausal, obese, diabetic women aged 52, 61, and 67 years. The patients presented with hirsutism and voice changes and clitoromegaly was present in one. Testosterone and androstenedione levels were elevated but promptly regressed after removal of the tumours. Histologically, sheets of stromal luteinized cells were found peripherally at the interface between the neoplasm and ovarian tissue. Luteinization of ovarian stroma induced by an unknown factor related to diabetes mellitus is the origin of the virilization. Received: 8 January 1997 / Accepted: 28 February 1997  相似文献   
32.
Our laboratory has characterized a population of stromal cells obtained from adipose tissue termed processed lipoaspirate cells (PLAs). PLAs, like bone-marrow derived mesenchymal stem cells (BM-MSCs), have the capacity to differentiate along the adipogenic, osteogenic, chondrogenic, and myogenic lineages, In order to better characterize these two multi-lineage populations, we examined the surface phenotype of both bone marrow and adipose tissue-derived cells from five patients undergoing surgery. PLA and BM-MSC cells were isolated, subcultivated, and evaluated for cell surface marker expression using flow cytometry. PLA and BM-MSC cells both expressed CD13, CD29, CD44, CD90, CD105, SH-3, and STRO-1. Differences in expression were noted for cell adhesion molecules CD49d (Integrin alpha4), CD54 (ICAM-1), CD34, and CD106 (VCAM-1). While markedly similar, the surface phenotypes of PLA and BM-MSC cells are distinct for several cell adhesion molecules implicated in hematopoietic stem cell homing, mobilization, and proliferation.  相似文献   
33.
34.
The aim of the study was to evaluate the effects of transcutaneous electric nerve stimulation (TENS) on CO(2) laser evoked potentials (LEPs) in 16 normal subjects. The volar side of the forearm was stimulated by 10 Hz TENS in eight subjects and by 100 Hz TENS in the remainder; the skin of the forearm was stimulated by CO(2) laser and the LEPs were recorded in basal conditions and soon after and 15 min after TENS. Both low and high frequency TENS significantly reduced the subjective rating of heat stimuli and the LEPs amplitude, although high frequency TENS appeared more efficacious. TENS seemed to exert a mild inhibition of the perception and processing of pain induced by laser Adelta fibres activation; the implications of these effects in the clinical employment of TENS remain to be clarified.  相似文献   
35.
BACKGROUND: Ambrosia pollen is an important allergen in North America and, as recently discovered, in some European countries. In Italy, the most affected area is the northeast, whereas ragweed has not been reported in the central and southern parts of the country. OBJECTIVE: To identify the source of ragweed pollen detected in Florence and Pistoia in central Italy. METHODS: Ragweed pollen data were collected in Florence and Pistoia for a 6-year period (1999-2004). The relationship between pollen counts and local ground prevalent wind directions was evaluated with analysis of variance and the least significant difference test. Weather conditions were also evaluated on a large-scale circulation pattern by analyzing weather maps and air mass back trajectories. RESULTS: A highly statistically significant relationship between daily prevailing wind direction and pollen count was found in the period under investigation; the ragweed pollen peaks were recorded when winds from northeast in Florence and north-northeast in Pistoia were observed. The synoptic weather situation and the path of back trajectories suggest an area around southern Hungary as a possible source of Ambrosia pollen. Furthermore, the pollen count was above the clinical threshold several times in both Florence and Pistoia. CONCLUSIONS: Several factors indicate that the detection of ragweed pollen in central Italy is due to long distance transport. Taking into consideration the high allergenicity of Ambrosia pollen, the present findings, if confirmed, suggest that the number of sensitized individuals might significantly increase in the near future.  相似文献   
36.
We studied 105 tumor samples obtained from patients diagnosed as having breast carcinomas for HLA class I and II (DR) antigen expression, using a panel of mAbs defining HLA-monomorphic, locus-specific and allele-specific determinants. Peripheral blood lymphocytes from patients were also typed for HLA alleles. The results indicated total HLA class I losses in 55 patients (52.3%), HLA-A locus losses in four patients (3.8%), HLA-B locus losses in eight patients (7.6%), and A, B, locus losses in 10 patients (9.5%). The remaining 28 patients whose tissues reacted positively with monomorphic- and locus-specific mAbs were tested for HLA allelic losses using several anti-HLA mAbs defining A2, A3, A9, B8, B12, etc. Of these 28 patients, 16 (57%) showed one or more losses of HLA reactivity. These results indicated that in 88.5% of patients we detected a particular HLA-altered tumor phenotype. The downregulation of HLA class I antigens in breast carcinomas may thus be more frequent than previously reported, and patients without HLA class I downregulation may be the exception rather than the rule. It cannot be ruled out that HLA alterations are present in some of the 12 patients with an apparently normal HLA phenotype, as some HLA alleles could not be studied because of the lack of appropriate mAbs. These HLA alterations could represent an important step associated with tumor invasion, conferring to the tumor cells the ability to escape from T-lymphocyte recognition.  相似文献   
37.
Summary Sagittal sections of the brain-stem made by MRI reveal differences in the angle formed by the medulla and the cord. In order to study the normal mobility of this region of the CNS during flexion and extension of the head, sagittal MRI studies were made in the sagittal plane in 18 young volunteers. The volunteers were in dorsal decubitus with the cervical spine first flexed and then extended, with the movement localized to the cranio-cervical junction as far as possible. T1-weighted sequences were used, with body coils in 16 cases and surface coils in two. Measurements were related to global cranio-cervical range of movement, movement at the craniocervical junction and spino-medullary movement. Variations in the depth of the free space in front of the medulla, pons and spinal cord during movement were also noted. We also checked for downward shift of the lower part of the 4th ventricle and modification of the shape of the ventricle during flexion-extension. The global range of cranio-cervical movement was between 31 and 100° (average 63°). The range between the cranium and C1C2 was 4 to 39° (average 19°) and the spino-medullary range was from 1 to 32° (average 14°). During flexion, the free space narrowed in front of the pons 11 times, in front of the medulla 14 times and in front of the cervical cord 11 times. There was a downward shift of the lower part of the 4th ventricle during flexion in 4 cases but no change in shape was noted. Though this study is open to criticism from several aspects, it may be concluded that variations of the spino-medullary angle in the sagittal plane during flexion-extension do occur, that they are closely correlated with movements at the cranio-cervical junction, and that the spino-medullary junction moves forward during flexion.
Dynamique de la jonction bulbomédullaire et de la moelle cervicale: Étude in vivo dans le plan sagittal en imagerie par résonance magnétique
Résumé Dans le but d'étudier la mobilité normale de la jonction bulbomédullaire durant la flexionextension de la tête, nous avons exploré en IRM dans le plan sagittal 18 jeunes volontaires. L'appareil Magniscan 0,15 Tesla a été utilisé avec des séquences de spin écho courtes, 16 fois en antenne corps et 2 fois en antenne de surface. Dans les limites de notre méthodologie, le secteur global de mobilité cervico-céphalique varie de 31 à 100° (moyenne 63°), le secteur de mobilité O-C1C2 varie de 4 à 39° (moyenne 19°), le secteur de mobilité bulbomédullaire varie de 1 à 32° (moyenne 14°). Lors de la flexion, l'espace libre diminue 11 fois devant la protubérance, 14 fois devant le bulbe et 11 fois devant la moelle cervicale. La partie basse du V4 s'abaisse dans 4 cas en flexion. Aucune modification de la forme du V4 n'a pu être notée. Bien que cette étude soit critiquable à bien des égards, nous pouvons affirmer: que les variations de l'angle bulbomédullaire dans le plan sagittal durant la flexion-extension de la tête sont effectives; qu'elles sont étroitement corrélées à celles de la charnière cranio-rachidienne; que durant le mouvement de flexion, la jonction bulbomédullaire se déplace en avant.
  相似文献   
38.
39.
Research over the last several decades has led to clear and empirically tractable proposals about the representation of conceptual knowledge in the brain. Here we argue that there are already sufficient data from neuropsychology to strongly constrain extant hypotheses about the representation of conceptual knowledge. One constraint imposed by these neuropsychological data is that recognition of actions and understanding of objects do not necessarily depend on the ability to produce object-associated actions. This conclusion compels a reconsideration of the role played by motor planning and/or execution processes in action and object recognition and understanding.  相似文献   
40.
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