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   2356480篇
  免费   172142篇
  国内免费   3342篇
耳鼻咽喉   32140篇
儿科学   76135篇
妇产科学   62863篇
基础医学   348983篇
口腔科学   63749篇
临床医学   212270篇
内科学   458364篇
皮肤病学   51900篇
神经病学   186173篇
特种医学   88135篇
外国民族医学   489篇
外科学   354576篇
综合类   47537篇
现状与发展   12篇
一般理论   862篇
预防医学   183711篇
眼科学   54393篇
药学   175442篇
  12篇
中国医学   4580篇
肿瘤学   129638篇
  2021年   19397篇
  2019年   19961篇
  2018年   27513篇
  2017年   20623篇
  2016年   23038篇
  2015年   25926篇
  2014年   36450篇
  2013年   54446篇
  2012年   75287篇
  2011年   79967篇
  2010年   47356篇
  2009年   44804篇
  2008年   74928篇
  2007年   79758篇
  2006年   80577篇
  2005年   78006篇
  2004年   74554篇
  2003年   71841篇
  2002年   69518篇
  2001年   108757篇
  2000年   111463篇
  1999年   93517篇
  1998年   27015篇
  1997年   23676篇
  1996年   24075篇
  1995年   22731篇
  1994年   20906篇
  1993年   19730篇
  1992年   72008篇
  1991年   70077篇
  1990年   68395篇
  1989年   65667篇
  1988年   60304篇
  1987年   59129篇
  1986年   55221篇
  1985年   53010篇
  1984年   39315篇
  1983年   33399篇
  1982年   19865篇
  1979年   35870篇
  1978年   25653篇
  1977年   21232篇
  1976年   20335篇
  1975年   21819篇
  1974年   26149篇
  1973年   24803篇
  1972年   23201篇
  1971年   22041篇
  1970年   20249篇
  1969年   19315篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
HPLC analysis of the embryo-toxic fraction of human uterinefluid, collected between the 22nd and 25th days of the menstrualcycle, revealed the presence of cholic acid at high concentrations.It is suggested that cholic acid could be responsible for theembryo-toxicity of the uterine environment, which follows thereceptive period for implantation.  相似文献   
942.
A review of the pathological material from 42 children with non-Hodgkin's lymphoma seen over a 44 month period revealed 10 large cell tumours. Of these, six were classified as peripheral T-cell lymphoma, an entity rarely reported in childhood. Three patients were boys and three girls (median age 9.5 years), and extranodal presentation was a feature of two patients. Five had high-grade tumours; of these, three were classified as large cell anaplastic, Ki-1 positive and two as pleomorphic large cell. The remaining patient had a low-grade tumour of angioimmunoblastic type. T-cell subsets were examined in three cases and showed the following phenotypes: CD4-, CD8-; CD4+, CD8-; CD4-, CD8+. Three of the patients with high-grade tumours died, with a mean survival of 22 weeks. The remaining patients are alive and clinically disease-free for between 10 and 24 months after treatment.  相似文献   
943.
A 16-year-old boy, the only affected member of the family, noticed early onset contracture of the elbows, and developed slowly progressive humeroperoneal weakness and atrophy, and bilateral equinus. The severe restriction of the forward flexion of the neck and thoracolumbar spine, resembled a rigid spine syndrome. An electrocardiogram showed atrioventricular conduction abnormalities. Muscle biopsy was consistent with mild myopathy. The overall conventional findings of a detailed electromyographic study in the limbs and erector trunci muscles, as well as the results of conduction velocity, automatic analysis of the voluntary pattern and single fiber electromyography studies were consistent with myopathy, although some atypical findings were found. The controversy about neurogenic and myopathic features in Emery-Dreifuss disease is discussed. The unspecific value of the flexion limitation of the spine, and the uncertain nosological position of the rigid spine syndrome are also commented.  相似文献   
944.
This paper describes the first application of structural modeling to neuroscience. Structural modeling (also known as path analysis) is a method to assess the relative impact of directional links in a system and how these interrelations may change under different conditions. The objective was to demonstrate how structural modeling can be used to determine the functional interrelationships between brain structures that form the auditory system. Using structural modeling, changes in auditory system 2-DG uptake were examined during long- and short-term habituation of the acoustic startle reflex. Models were based on the anatomical connections between central auditory system structures. Using functional 2-DG data, the correlations between these structures were calculated and numerical weights were computed for each anatomical link. The analysis revealed that the lemniscal path was dominant during short-term habituation, while during long-term habituation this influence was modified through extra-lemniscal pathways. The models are discussed in the context of previous findings to demonstrate how structural modeling can not only complement, but also extract more information from 2-DG mapping experiments.  相似文献   
945.
To study the type of adaptive modification (tolerance vs. sensitization) in different organism's indices following intermittent cocaine (COC) administrations, acute COC (2 mg/kg, SC)-induced changes in heart and breathing rate, response to increasing noxious stimulation, spontaneous EEG and event-related evoked and slow brain potentials (ERP) registered from the occipital cortex and hippocampal CA1 region were investigated in naive rabbits and one subchronically treated with COC (6 injections at a same dose). Tolerance developed for bradycardia, depression of noxious responsiveness, cortical desynchronization and increase of main components of cortical ERP, typical to acute COC, while the changes in breathing and hippocampal ERP were stable. These changes as well as a significant increase due to COC administrations of the basal values of an animal's noxious responsiveness and increase in relative changes in main component of cortical ERP (N205) are considered as a consequence of adaptive changes in neurophysiological/neurochemical substrate accepting COC action and mediating phenomena tolerance-sensitization and dependence typical to the drug.  相似文献   
946.
Qualitative and quantitative characteristics of clostridial metabolites (short-chain carbonic acids and alcohols) were analyzed in associations of these bacteria with facultative anaerobes. Various bacterial groups were found to vary as regarded the composition and quantitative ratio of the major bacterial metabolites. These data may become the criteria for the indication of pathogenic clostridia in mixed cultures after anaerobic passages for 24-48 h at 37 degrees in a medium with 1% glucose.  相似文献   
947.
948.
In this report, we examine the functional significance of the molecular microheterogeneity of alpha-fetoprotein (AFP). In doing so, we have taken the direct approach of purifying the naturally occurring isomeric forms of fetal-derived AFP using a preparative anion exchange column linked to an automated fast protein liquid chromatography (FPLC) system followed by parallel testing of each isolated molecular variant for in vitro immunoregulatory activity. The data obtained demonstrate the presence of seven distinct variants of AFP as defined by their retention volumes on FPLC elution profiles, by their pIs on analytical IEF gels, and by Western blot analysis. Molecular mass determination by SDS-PAGE showed each isomer to be equivalent in size to 69,000-dalton native unfractionated AFP molecules. All the immunosuppressive activity of AFP was localized to a single variant representing only 6% of the total composition of native AFP. The immunoregulating isomer termed AFP-1 was the least acidic of the seven isolated variants with a pI of 5.1 and displayed a sialic acid content of 1 mol/mol of protein. The inhibitory activity of AFP-1 could be readily measured on T cell-dependent antibody synthesis, Con A-induced stimulation of Lyt-1+23- thymocyte DNA synthesis, and lymphokine-activated NK cell activity. All other isomers were without effect in these test systems. The immunosuppressive AFP-1 isomer also displayed the strongest growth-promoting influence on cultured bone marrow lymphocytes. There was no correlation between functional activity and degree of expression of sialic acid residues on the AFP molecules. These findings demonstrate that the immunoregulating function of AFP is confined to a distinct and relatively small subpopulation of native AFP molecules and should therefore contribute to the resolution of outstanding questions regarding the structure/function relationship of this onco-fetal glycoprotein.  相似文献   
949.
A G Lewis 《Postgraduate medicine》1989,86(3):141-4, 147-51
Initial assessment of common forefoot deformities by the primary care physician is quite feasible. A thorough history, examination of the foot with the patient standing and seated, assessment of the patient's footwear, and radiographic evaluation can often lead to gratifying relief with use of simple office measures. Even in cases that require referral to an orthopedic surgeon, interim relief of symptoms and the patient's increased awareness of the problem and its cause enhance the patient's understanding and the final outcome as well.  相似文献   
950.
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