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   2382028篇
  免费   199098篇
  国内免费   4244篇
耳鼻咽喉   34416篇
儿科学   73115篇
妇产科学   63224篇
基础医学   336328篇
口腔科学   67729篇
临床医学   216647篇
内科学   470431篇
皮肤病学   48049篇
神经病学   201720篇
特种医学   96396篇
外国民族医学   886篇
外科学   362148篇
综合类   56421篇
现状与发展   1篇
一般理论   994篇
预防医学   191519篇
眼科学   55747篇
药学   178240篇
  5篇
中国医学   4376篇
肿瘤学   126978篇
  2018年   24494篇
  2016年   20795篇
  2015年   23525篇
  2014年   33870篇
  2013年   51359篇
  2012年   69585篇
  2011年   73093篇
  2010年   42934篇
  2009年   41288篇
  2008年   69493篇
  2007年   73844篇
  2006年   74755篇
  2005年   72727篇
  2004年   70000篇
  2003年   67684篇
  2002年   66893篇
  2001年   112569篇
  2000年   116663篇
  1999年   98472篇
  1998年   28000篇
  1997年   25650篇
  1996年   25561篇
  1995年   24703篇
  1994年   23260篇
  1993年   21654篇
  1992年   79465篇
  1991年   76462篇
  1990年   73637篇
  1989年   70924篇
  1988年   65915篇
  1987年   64873篇
  1986年   61397篇
  1985年   58452篇
  1984年   44295篇
  1983年   37735篇
  1982年   22964篇
  1981年   20410篇
  1980年   19106篇
  1979年   41375篇
  1978年   29047篇
  1977年   24394篇
  1976年   22877篇
  1975年   24016篇
  1974年   29684篇
  1973年   28082篇
  1972年   26273篇
  1971年   24184篇
  1970年   22790篇
  1969年   21110篇
  1968年   19162篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
951.
952.
953.
Summary Early recognition of recurrence and work-up of clinically indeterminate lesions may be impaired after reconstruction with silicone implants due to superimposition of the implant or to scarring. This study was undertaken to evaluate the use of contrast-enhanced MRI in patients with silicone implant after breast cancer. Contrast-enhanded MRI was offered to 169 patients. Comparative two- to three-view mammography was also performed in 169 patients, as well as comparative sonography in 144 patients. Conventional imaging and clinical examination detected only 8/13 recurrences, whereas 12/13 were detected by MRI. One recurrence had been visible as a strongly enhancing 2-mm dot in a previous examination (2 years before), but was not called. It was therefore counted as false negative. In addition, multicentricity was detected by MRI alone in two of three cases. MRI correctly diagnosed scar tissue in all cases with indeterminate findings. However, due to false-positive calls caused by enhancing granulomas specificity could not be improved. Contrast-enhanded MRI allowed decisive additional information in our study group and improved the sensitivity significantly (concerning all diagnoses). Contrast-enhanded MRI is recommended in patients with diagnostic problems or high risk of recurrence after silicone implants.   相似文献   
954.
955.
降糖饮降糖作用的实验研究   总被引:2,自引:0,他引:2  
降糖饮以8.1,15.0,30。0g.kg^-1灌胃予鼠,连续10天。结果表明降饮对正常小鼠大鼠血糖血脂无明显影响,但对四氧嘧啶或链脲霉素引起的大鼠高血糖及蛋黄引起的小鼠高脂血症,高胆固醇饲料引起的大鼠高脂血症均有显著降低作用。本研究为降糖饮的应用提供了可靠的药理学依据。  相似文献   
956.
TM4 is a lytic mycobacteriophage which infects mycobacteria of clinical importance. A luciferase reporter phage, phAE40, has been constructed from TM4 and was previously shown to be useful for the rapid detection and drug susceptibility testing of Mycobacterium tuberculosis. However, the lytic nature of the phage results in a loss of detectable light output and limits the sensitivity of detection. We describe several strategies aimed at improving the luciferase activity generated by TM4 luciferase phages, including (i) varying the position of the luciferase gene in the phage genome, (ii) isolating host-range mutants of the phage, and (iii) introducing temperature-sensitive mutations in the phage such that it will not replicate at the infecting temperature. Several new phages generated by these methods show increased intensity of luciferase production compared to the first-generation reporter phage phAE40, and one phage, phAE88, also demonstrates an enhanced duration of luciferase activity. This has allowed the detection of as few as 120 BCG cells and the determination of drug susceptibilities of M. tuberculosis in as little as 1 day.  相似文献   
957.
Oral allergy syndrome induced by spinach   总被引:1,自引:1,他引:0  
  相似文献   
958.
AIMS: Immunohistological and molecular characterisation of a case of peripheral T-cell lymphoma (PTCL) of angioimmunoblastic T-cell lymphoma (AILD) type. METHODS: Frozen and paraffin wax sections of the diagnostic lymph node were stained with a panel of T- and B-cell lineage monoclonal antibodies. DNA was isolated from the paraffin wax embedded biopsy material for T-cell receptor (TCR) and immunoglobulin (Ig) PCR amplification, and resultant PCR products were cloned and sequenced. RESULTS: Immunohistological analysis of the presenting lymph node was consistent with an extensive infiltrate of pleomorphic CD3+CD8+ lymphocytes. Most (>80%) of these infiltrating CD3+ cells were also positive for the TCR VB5.1 gene family product, and were shown to be oligoclonal by TCRB PCR amplification and sequencing. Three oligoclones of B cells were also demonstrable by PCR amplification with Ig heavy chain primers and sequencing, a finding at variance with the diagnosis of AILD. CONCLUSIONS: These data demonstrate the complexity and heterogeneity of PTCL which require extensive histological examination and molecular characterisation.  相似文献   
959.
Human salivary immunoglobulin A (IgA) and serum IgG antibodies to the Streptococcus mutans glucosyltransferases (Gtfs) and to a synthetic peptide of 19 amino acids from a conserved region in the Gtfs (residues 435 to 453) were determined in young adults by enzyme-linked immunosorbent assay. Varying levels of antibody to Gtfs were detected in saliva or serum, with significantly higher levels of antibody to GtfD than to GtfB/C or GtfC. Anti-Gtf IgA levels in saliva did not correlate with those of IgG in serum. Caries-free (CF) volunteers exhibited significantly higher salivary IgA antibody levels to the peptide and to GtfB/C or GtfC than did the caries-active (CA) subjects. Preincubation of CF saliva and serum with the peptide inhibited the antibodies to the Gtfs in a dose-dependent manner, whereas preincubation of the samples from the CA group resulted in only partial inhibition. Our results indicated that this 19-amino-acid peptide includes one of the major B-cell epitopes of Gtfs and that CF individuals have higher titers of antibodies than CA subjects.  相似文献   
960.
Reactive oxygen species and human spermatozoa: physiology and pathology   总被引:20,自引:1,他引:19  
The role of reactive oxygen species (ROS) in the pathophysiology of human sperm function has been emphasized in recent years. ROS production in semen has been associated with loss of sperm motility, decreased capacity for sperm–oocyte fusion and loss of fertility. There is a current presumption that the most prolific source of ROS in sperm suspensions is an NADPH oxidase located in leukocytes or in spermatozoa which produces superoxide which is further converted to peroxide by the action of superoxide dismutase. Hydrogen peroxide has been recognized as the most toxic oxidizing species for human spermatozoa, which are very sensitive to lipid peroxidation owing to the high content of polyunsaturated fatty acids in their plasma membrane, though this is not the sole mechanism by which sperm function might be impaired by ROS. Although the excessive production of ROS is detrimental to human spermatozoa, there is a growing body of evidence which suggests that ROS are also involved in the physiological control of some sperm functions. This review focuses on the nature and source of the ROS generated by human spermataozoa as well as their operational mechanisms and their effects, which may be detrimental or beneficial.  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