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   10752篇
  免费   1134篇
  国内免费   64篇
耳鼻咽喉   90篇
儿科学   348篇
妇产科学   282篇
基础医学   1328篇
口腔科学   228篇
临床医学   1144篇
内科学   2345篇
皮肤病学   104篇
神经病学   774篇
特种医学   779篇
外国民族医学   1篇
外科学   1197篇
综合类   296篇
一般理论   2篇
预防医学   1332篇
眼科学   313篇
药学   797篇
中国医学   9篇
肿瘤学   581篇
  2021年   147篇
  2019年   148篇
  2018年   171篇
  2017年   107篇
  2016年   135篇
  2015年   150篇
  2014年   194篇
  2013年   347篇
  2012年   440篇
  2011年   488篇
  2010年   307篇
  2009年   259篇
  2008年   396篇
  2007年   514篇
  2006年   421篇
  2005年   432篇
  2004年   448篇
  2003年   422篇
  2002年   395篇
  2001年   336篇
  2000年   337篇
  1999年   287篇
  1998年   176篇
  1997年   167篇
  1996年   169篇
  1995年   146篇
  1994年   132篇
  1993年   120篇
  1992年   232篇
  1991年   232篇
  1990年   222篇
  1989年   230篇
  1988年   191篇
  1987年   212篇
  1986年   175篇
  1985年   197篇
  1984年   143篇
  1983年   145篇
  1982年   116篇
  1981年   121篇
  1980年   93篇
  1979年   124篇
  1978年   103篇
  1977年   102篇
  1976年   118篇
  1975年   114篇
  1974年   141篇
  1973年   121篇
  1972年   111篇
  1971年   89篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The efficacy of radiology in evaluating dysphagia was studied in 86 patients by comparison to endoscopic findings. In the 66 patients with endoscopic abnormalities radiology was correct in 54, for a sensitivity of 82%. Sensitivity of radiology improved to 95% if mild esophagitis was excluded. In the 20 patients with normal endoscopy, radiology was normal in 18 (90%). Thus radiology proved to be a reliable means of evaluating the esophagus in patients with dysphagia.  相似文献   
3.
4.
OBJECTIVE: To identify the possible contribution of electromyogram (EMG) to scalp electroencephalogram (EEG) rhythms at rest and induced or evoked by cognitive tasks. METHODS: Scalp EEG recordings were made on two subjects in presence and absence of complete neuromuscular blockade, sparing the dominant arm. The subjects undertook cognitive tasks in both states to allow direct comparison of electrical recordings. RESULTS: EEG rhythms in the paralysed state differed significantly compared with the unparalysed state, with 10- to 200-fold differences in the power of frequencies above 20 Hz during paralysis. CONCLUSIONS: Most of the scalp EEG recording above 20 Hz is of EMG origin. Previous studies measuring gamma EEG need to be re-evaluated. SIGNIFICANCE: This has a significant impact on measurements of gamma rhythms from the scalp EEG in unparalysed humans. It is to be hoped that signal separation methods will be able to rectify this situation.  相似文献   
5.
Although a structural feature common to all dopaminergic agonists and antagonists is a side-chain basic amino group, it is unclear whether this moiety binds to the D-1 dopamine (DA) receptor in the charged or uncharged form. To obtain information on this point, we synthesized permanently charged dimethylsulfonium and quaternary ammonium analogs of chlorpromazine and DA and determined whether these compounds can bind to the D-1 receptor by measuring their abilities to inhibit the binding of SCH 23390, a D-1 receptor antagonist. Chlorpromazine and the dimethylsulfonium and trimethylammonium analogs of chlorpromazine were found to inhibit the binding of [3H]SCH 22390, which was maximally inhibited to the same extent by all three compounds. In addition, inhibition curves for the compounds fit a one-site binding model, indicating binding to a single class of sites. However, while the permanently charged chlorpromazine analogs were able to inhibit [3H]SCH-23390 binding, they were considerably less potent than chlorpromazine. DA and dimethyl DA were also able to inhibit [3H]SCH 23390 binding. However, the permanently charged dimethylsulfonium and trimethylammonium analogs of DA were ineffective in inhibiting [3H]SCH 23390 binding. In addition, the permanently uncharged methylsulfide analog did not inhibit binding. These studies show that permanently charged analogs of chlorpromazine can bind to the striatal D-1 receptor, which is consistent with an anionic recognition site on the D-1 receptor that interacts with antagonists in the cationic form. In addition, it appears that a nitrogen atom is not required for binding to the D-1 receptor, since the sulfonium analog of chlorpromazine bound to the receptor to the same extent as chlorpromazine. However, since the permanently charged or uncharged analogs of DA did not bind to the D-1 receptor, it is still unclear as to whether the charged form of a dopaminergic agonist can bind. The lower potency or ineffectiveness of the permanently charged analogs compared to the parent amines (chlorpromazine, DA, dimethyl DA) in binding to the D-1 receptor may reflect the inability of the permanently charged analogs to undergo hydrogen binding with the anionic site of the receptor.  相似文献   
6.
PURPOSETo investigate the decrease in signal intensity on T1 - weighted MR images of some hemorrhagic intracranial lesions after administration of contrast material.METHODSPostprocessing digital image subtraction was performed in 16 MR studies (13 patients) of lesions that showed hyperintensity on noncontrast T1-weighted images. Repetition time and echo time were identical for all precontrast and postcontrast studies. Regions of interest were measured in each lesion, contralateral white matter, and background (before and after contrast enhancement).RESULTSIn six of 16 MR studies, a significant net decrease in signal intensity was seen within the hemorrhagic lesion after contrast enhancement (reverse enhancement). All the lesions were hematomas within residual or recurrent malignant tumors.CONCLUSIONSDigital image subtraction confirms the existence of reverse enhancement. This phenomenon is due to the combined T2-shortening effects of two paramagnetic substances, methemoglobin and gadolinium, which cause the signal reduction produced by the T2 effects to occur at lower concentrations of gadolinium.  相似文献   
7.
8.
9.
10.
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