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   8386篇
  免费   681篇
  国内免费   162篇
耳鼻咽喉   46篇
儿科学   172篇
妇产科学   70篇
基础医学   938篇
口腔科学   222篇
临床医学   1178篇
内科学   1544篇
皮肤病学   81篇
神经病学   616篇
特种医学   231篇
外科学   652篇
综合类   719篇
一般理论   10篇
预防医学   1507篇
眼科学   96篇
药学   609篇
  3篇
中国医学   289篇
肿瘤学   246篇
  2024年   23篇
  2023年   222篇
  2022年   346篇
  2021年   479篇
  2020年   332篇
  2019年   375篇
  2018年   334篇
  2017年   314篇
  2016年   302篇
  2015年   324篇
  2014年   482篇
  2013年   766篇
  2012年   448篇
  2011年   470篇
  2010年   404篇
  2009年   349篇
  2008年   395篇
  2007年   354篇
  2006年   285篇
  2005年   251篇
  2004年   253篇
  2003年   217篇
  2002年   163篇
  2001年   165篇
  2000年   125篇
  1999年   104篇
  1998年   98篇
  1997年   96篇
  1996年   91篇
  1995年   76篇
  1994年   69篇
  1993年   40篇
  1992年   59篇
  1991年   44篇
  1990年   43篇
  1989年   42篇
  1988年   44篇
  1987年   32篇
  1986年   33篇
  1985年   28篇
  1984年   29篇
  1983年   22篇
  1982年   14篇
  1981年   16篇
  1980年   15篇
  1979年   11篇
  1978年   10篇
  1976年   11篇
  1975年   5篇
  1974年   5篇
排序方式: 共有9229条查询结果,搜索用时 15 毫秒
51.
分析47例骨髓穿刺干抽的临床和病理改变,干抽占同期1319例骨穿的3.6%。根据骨髓细胞的密度和间质纤维增殖的程度,把干抽的原因分为4类:高细胞伴间质细胞增多者19例(42.2%);间质细胞增多者14例(31.1%);高细胞者8例(17.8%)及低细胞者4例(8.9%)。主要疾病为:急性淋巴细胞白血病(25.5%),急性非淋巴细胞白血病(17.0%),慢性白血病(14.9%),骨髓转移瘤(10.6  相似文献   
52.
The capacity of bone marrow-derived surface immunoglobulin-positive (sIg+) human and mouse immature B cells, generated either in vitro or in vivo, to change their light (L) chain expression, has been assayed by the number of cells which change in vitro from one type of L chain to the other type, or to no sIg at all. Immature sIg+ B cells were generated in vitro from sIg? precursor cells from human or mouse bone marrow. The immature sIg+ cells expressed RAG-1. Human sIg+ cells expressed xfr; and λ L chains in ratios between 1:1 and 3:1, whereas in mouse cells, this ratio ranged from 10:1 to 20:1. Upon reculture of the human and mouse xfr;+sIg+ cells, about half of them remained xfr;+, a quarter became λ+, and another quarter became sIg?. Between 1 and 3% expressed both xfr; and λ chains. Of the human λ+ cells, about two-thirds remained λ+, only 1 to 2% became xfr;+, while the other third became sIg?. Again, between 1 and 3% expressed both xfr; and λ L chains. These results indicate that expression of sIgM in the B cell membrane does not terminate L chain gene rearrangement, and that some order exists in xfr; versus λ gene rearrangements. Hence, human and mouse xfr;+ immature B cells can become λ+, but very few of the λ+ cells can become xfr;+, and both can become sIg?. Further, human CD10+/sIg+ xfr;+ and λ+ cells and mouse B220low/sIglow xfr;+ cells enriched from bone marrow, i.e. immature B cells differentiated in vivo, changed their Ig phenotype upon in vitro culture, but in lower frequencies. By contrast, human and mouse mature B cells did not change their L chain or Ig phenotype. Hence, at least a part of the sIg+ immature B cells in bone marrow retain the capacity to change their L chain and Ig phenotype, and this capacity is lost when they become mature, peripheral B cells.  相似文献   
53.
运用免疫组化ABC法对不同月龄SD大鼠心脏冠状动脉及其分支含神经肽Y神经纤维的分布及其衰老变化作了详细观察.结果表明:左、右冠状动脉及其各级分支具有丰富的神经肽Y能神经分布.在冠状动脉主干及其较大分支上,神经纤维较稠密,主要呈环状或网状分布,在血管围周形成较多束、丛、网,并伸入血管壁内形成壁内的神经网络分布.部分神经纤维的游离末梢有穿过血管内膜伸向腔面的迹象.在细小的冠状动脉分支上,神经纤维密度减低,主要沿血管长袖是纵向分布.两侧冠状动脉系统神经肽Y能纤维分布形式及密度没有差别.老龄组动物,左、右冠状动脉及其分支的神经肽Y能纤维密度趋于下降,纤维变细,呈断续状,膨体数量减少,免疫染色变浅、此外,在心内发现了神经肽Y能神经节.  相似文献   
54.
目的:探讨图、词回忆中的首因和近因效应及其年龄变化规律。方法:采用多维记忆评估量表中的汉词回忆和图画回忆分测验对947人的连续年龄组的大样本进行测试,分析不同通道首因和近因效应的差异和年龄变化规律。结果:受试在汉词和图画自由回忆中,均呈现明显的系列位置效应;受试的首因和近因效应均随年龄的增长而增大。当发展到高峰后则随年龄的增长而减弱,各年龄组间比较有显著差异;首因和近因效应随年龄增长是不平行的,首因效应随年龄的增长变化较大。而近因效应的变化则相对较为平缓;两种不同呈现途径的比较发现,图画回忆的首因和近因效应均高于汉词回忆。结论:视觉和听觉呈现途径均呈现明显的系列位置效应,首因效应和近因效应的发展变化规律与记忆的发展变化规律是一致的。首因效应受年龄的影响较大,在有意义的图画回忆中首因效应和近因效应均高于汉词回忆。  相似文献   
55.
Doris  Weipert  David  Shapiro  Thomas  Suter 《Psychophysiology》1986,23(3):315-322
Forty male college student volunteers were asked either to increase their diastolic pressure or their heart rate while sitting and during orthostatic stress (going from a sitting to a standing position), and half of them were also given second- to-second visual feedback for the target variable. Systolic blood pressure was also continuously recorded. Comparisons were made between baseline and voluntary control conditions, and test trials were included to examine immediate carry-over effects. With voluntary control instructions, substantial increases in tonic levels were obtained for the three cardiovascular variables in both sitting and postural change conditions. In general, the increases were significantly greater for feedback than for no-feedback conditions. Phasic effects of feedback were also observed during postural change conditions: the blood pressure troughs and the heart rate peak occurred earlier with feedback than for instructions only. Immediate transfer effects were obtained in feedback conditions only. The results were discussed in terms of concomitant effects of somatic and cognitive activities. The distinctive feedback effects on the time course of the responses suggest that a precise analysis of response patterns is needed in selecting appropriate feedback methods in the management of orthostatic hypotension.  相似文献   
56.
 We have been using the Gyro centrifugal pump C1E3 for cardiopulmonary bypass in anticipation of high efficiency, low hemolysis, and antithrombogenicity of this pump. However, the clinical evaluation of this pump remains to be clarified, because it has been a short time since the pump appeared in clinical situations. The aim of the present study is to inspect and analyze the Gyro pumps morphologically after clinical use. We examined 80 consecutive pumps after cardiopulmonary bypass for 186 ± 67 min with a mean flow rate of 2.52 ± 0.22 l/min/m2 at a mean rotational speed of 2485 ± 81.1 rpm. Although no abnormal findings were present in 79 pumps, one pump was found to contain effusion at the connection between the impeller body and the shaft. The extudate was supposed to be blood, based upon the results of X-ray spectrometer analysis. The cause was determined to be the upward deviation of the shaft off the impeller body. Scanning electron microscopy showed scratches on a part of the bottom housing and a smooth surface of both the male and female pivots of the pump. Surface profile measurement revealed that the deformity of the female pivots was 0.14 mm (top) and 0.05 mm (bottom). These observations suggest that the floating force and vibration by the rotating impeller acted on the joint zone between the alumina ceramic shaft and the polycarbonate impeller body, resulting in dissection of the adhesive agent from the polycarbonate. Although this abnormality may be rare, the structural design still may need to be improved. Received: November 9, 2001 / Accepted: February 4, 2002  相似文献   
57.
BACKGROUND: General practice in the UK is undergoing a period of rapid and profound change. Traditionally, research into the effects of change on general practice has tended to regard GPs as individuals or as members of a professional group. To understand the impact of change, general practices should also be considered as organisations. AIM: To use the organisational studies literature to build a conceptual framework of general practice organisations, and to test and develop this empirically using case studies of change in practice. This study used the implementation of National Service Frameworks (NSFs) and the new General Medical Services (GMS) contract as incidents of change. DESIGN OF STUDY: In-depth, qualitative case studies. The design was iterative: each case study was followed by a review of the theoretical ideas. The final conceptual framework was the result of the dynamic interplay between theory and empirical evidence. SETTING: Five general practices in England, selected using purposeful sampling. METHOD: Semi-structured interviews with all clinical and managerial personnel in each practice, participant and nonparticipant observation, and examination of documents. RESULTS: A conceptual framework was developed that can be used to understand how and why practices respond to change. This framework enabled understanding of observed reactions to the introduction of NSFs and the new GMS contract. Important factors for generating responses to change included the story that the practice members told about their practice, beliefs about what counted as legitimate work, the role played by the manager, and previous experiences of change. CONCLUSION: Viewing general practices as small organisations has generated insights into factors that influence responses to change. Change tends to occur from the bottom up and is determined by beliefs about organisational reality. The conceptual framework suggests some questions that can be asked of practices to explain this internal reality.  相似文献   
58.
Consumption of excess fat increases risk for many health problems and diseases. In the present study, 188 undergraduate students were studied to understand self-perceptions of dietary-fat intake and the impact of those perceptions. Findings indicated that the majority of participants had inaccurate perceptions about the amount of fat in their diets. Further, compared to people who overestimated dietary-fat intake, people who underestimated fat intake had lower perceived risk of cancer, had lower intentions to change, and demonstrated less knowledge about the dietary-fat content of many foods. Findings suggest that this unrealistic underestimation of fat intake is a cognitive barrier to dietary change and people who underestimate dietary fat intake may require more intensive intervention to change their diets.  相似文献   
59.
Summary The slow potential change (spc) accompanying spreading depression (SD) was studied in rats and in a seizure-sensitive strain of Mongolian gerbil under three different experimental paradigms, each involving the use of naloxone. Gerbils undergoing electroconvulsive shock treatment displayed SD during the post-ictal phase, which was blocked by the intraperitoneal (i.p.) administration of naloxone (20–50 mg kg-1). Topical application of naloxone to the exposed cortex of the anaesthetized gerbil and rat blocked the spc of SD evoked by KCl. Microiontophoretic ejection of naloxone during extracellular recordings reversed cell refractoriness following the spc, demonstrated by the observation of a maintained sensitivity to iontophoretic pulses of glutamate. The results suggest a possible involvement of naloxone-sensitive processes in the mechanism responsible for cortical SD.  相似文献   
60.
The long-term ST database is the result of a multinational research effort. The goal was to develop a challenging and realistic research resource for development and evaluation of automated systems to detect transient ST segment changes in electrocardiograms and for supporting basic research into the mechanisms and dynamics of transient myocardial ischaemia. Twenty-four hour ambulatory ECG records were selected from routine clinical practice settings in the USA and Europe, between 1994 and 2000, on the basic of occurrence of ischaemic and non-ischaemic ST segment changes. Human expert annotators used newly developed annotation protocols and a specially developed interactive graphic editor tool (Semia) that supported paperless editing of annotations and facilitated international co-operation via the Internet. The database contains 86 two- and three-channel 24h annotated ambulatory records from 80 patients and is stored on DVD-ROMs. The database annotation files contain ST segment annotations of transient ischaemic (1155) and heart-rate related ST episodes and annotations of non-ischaemic ST segment events related to postural changes and conduction abnormalities. The database is intended to complement the European Society of Cardiology ST-T database and the MIT-BIH and AHA arrhythmia databases. It provides a comprehensive representation of ‘real-world’ data, with numerous examples of transient ischaemic and non-ischaemic ST segment changes, arrhythmias, conduction abnormalities, axis shifts, noise and artifacts.  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