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   380177篇
  免费   24955篇
  国内免费   2810篇
耳鼻咽喉   5198篇
儿科学   8230篇
妇产科学   10119篇
基础医学   53282篇
口腔科学   11814篇
临床医学   30209篇
内科学   78687篇
皮肤病学   8687篇
神经病学   27357篇
特种医学   13967篇
外国民族医学   82篇
外科学   61009篇
综合类   10015篇
现状与发展   1篇
一般理论   64篇
预防医学   17453篇
眼科学   9504篇
药学   31049篇
  1篇
中国医学   2205篇
肿瘤学   29009篇
  2021年   2638篇
  2019年   2743篇
  2018年   4544篇
  2017年   3462篇
  2016年   3549篇
  2015年   4040篇
  2014年   5725篇
  2013年   7426篇
  2012年   10078篇
  2011年   10271篇
  2010年   6226篇
  2009年   5895篇
  2008年   9517篇
  2007年   10370篇
  2006年   10282篇
  2005年   9339篇
  2004年   8859篇
  2003年   8586篇
  2002年   8244篇
  2001年   28326篇
  2000年   28821篇
  1999年   23727篇
  1998年   5184篇
  1997年   4284篇
  1996年   3853篇
  1995年   3502篇
  1994年   3121篇
  1993年   2852篇
  1992年   16092篇
  1991年   14861篇
  1990年   14177篇
  1989年   13983篇
  1988年   12609篇
  1987年   12085篇
  1986年   11153篇
  1985年   10363篇
  1984年   6944篇
  1983年   5628篇
  1982年   2731篇
  1979年   5510篇
  1978年   3354篇
  1977年   2987篇
  1975年   2657篇
  1974年   3075篇
  1973年   2871篇
  1972年   2847篇
  1971年   2791篇
  1970年   2523篇
  1969年   2555篇
  1968年   2267篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Airway hyperresponsiveness (AHR) is a characteristic feature of asthma, but is also frequently demonstrated by children and adults with chronic obstructive lung diseases. AHR is usually measured by bronchial challenges using direct or indirect stimuli. The aim of this study was to compare these two types of bronchial challenge in children with post-infectious bronchiolitis obliterans (BO). Methacholine and adenosine 5'-monophosphate (AMP) challenges were used as tools for the evaluation of AHR to direct and indirect stimuli, respectively, in children with post-infectious BO (n = 28). These results were compared with those of asthmatic (n = 30) and control children (n = 25). Altogether, twenty-two patients (78.6%) with post-infectious BO were hyperreactive to methacholine with a provocative concentration causing a 20% fall in forced expiratory volume in one second (PC20) of <16 mg x mL(-1), but only six (21.4%) were hyperreactive to AMP with a PC20 of <200 mg x mL(-1). All patients with asthma responded positively to methacholine, and most (28, 93.3%) also responded positively to AMP. The majority of controls were insensitive to both challenges. Airway hyperresponsiveness to methacholine is a frequent, but by no means universal, finding in children with post-infectious bronchiolitis obliterans, but is usually not accompanied by airway hyperresponsiveness to adenosine 5'-monophosphate. This finding suggests that airway hyperresponsiveness in patients with post-infectious bronchiolitis obliterans has characteristics that differ from those of asthmatic subjects.  相似文献   
952.
The p53 gene has been implicated as a tumor suppressor gene involved in the pathogenesis of lung cancer. Our previous study revealed that the p53 gene is frequently mutated with a distinct nucleotide substitution pattern in small cell lung cancer specimens in Japanese patients. In this study, we examined 30 primary, resected non-small cell lung cancer samples in Japanese patients using complementary DNA-polymerase chain reaction and sequencing. Mutations changing the p53 coding sequence were found in 14 of 30 tumor samples (47%), while G:C to T:A transversions which are uncommon in other cancers such as colon cancer were the most frequently observed mutations, in agreement with an earlier report on non-small cell lung cancer in American patients. Furthermore, the present study shows for the first time that in univariate and multivariate analyses, the presence of p53 mutations is closely associated with lifetime cigarette consumption.  相似文献   
953.
In this study, an animal model of multiple system organ failure (MSOF) in rabbits, engendered by feeding E. coli prior to severe hemorrhagic shock, was used for the purpose of investigating 1) the relationship between lipopolysaccharide (LPS) and MSOF, and 2) the effectiveness of Re-LPS antiserum in preventing MSOF. The results showed that endotoxemia occurred very early, and its degree correlated well with that of organ dysfunction. Re-LPS antiserum administration abated the toxic effects and lowered the incidence of MSOF. These results suggest that sequential analysis of circulating LPS levels may be useful for the early diagnosis of MSOF, and that gut-derived endotoxin might play an important role in the pathogenesis of experimental MSOF.  相似文献   
954.
Computer analysis of absolute number of peaks per second and the number of peaks in the multipeaked spikes/sec was carried out in the EMG interference recordings of 5 healthy, 6 myopathic and 8 neuropathic subjects. The purpose of the study was to detect diagnostically different patterns. A spike was considered multipeaked if it had 6 or more peaks. The amplitude of elimination (baseline) was examined at 1: 5, 1: 10 and 1: 15 of the average amplitude per second. Both the number of peaks and the number of peaks in multipeaked spikes in the neuropathic and myopathic muscles showed statistically significant differences when compared to healthy muscles. This technique could give an indication for the differential diagnosis of myopathic, neuropathic or healthy state of the muscle.  相似文献   
955.
This paper reviews the major regularities allowing a purposeful search of the materials with the best properties. Discussed are the most important parameters of the materials, type RPC (Rostov piezoceramic) of various purposes. Particular attention is attached to the issues of creation and investigation of the materials intended for ultrasonic diagnostic equipment.  相似文献   
956.
957.
Partially edentulous patients with alveolar defects contraindicating implant placement were treated with bone grafts obtained from the mandibular symphysis. Complications encountered were minor and uneventful. Evaluation 4 months after surgery revealed minimal graft resorption, thus implant placement was possible in all potential sites. Advantages of the symphysis graft include easy access, availability of greater quantities of bone over other intraoral donor sites, low morbidity, no hospitalization, minimal discomfort, no alteration in ambulation, and no cutaneous scar. Compared with other bone regenerative methods for implant placement, a superior quality of bone was found and a shorter healing period is required. Results of this preliminary clinical investigation demonstrate that chin grafts offer a viable alternative for reconstruction of alveolar defects prior to dental implant placement.  相似文献   
958.
959.
The purpose of this investigation was to determine the site utilized by nurses for administering Diphtheria and Tetanus Toxoids and Pertussis (DPT) injections to infants under 7 months of age. Twenty-six of the 28 agencies identified in a metropolitan area as administering DPT injections chose to participate in the study. Those individuals administering DPT injections in the agencies completed a questionnaire with a return rate of 69% (n = 55). Forty-four participants indicated that they used the anterolateral thigh, the recommended site, 100% of the time. The participants in the study administered a total of 1,453 DPT injections per month. Eighty-seven percent of those injections were administered in the anterolateral thigh, 3.6% were given in the deltoid, 5.1% were given in the dorsal gluteal, and 4% were given in the ventrogluteal. The estimated proportion of DPT injections administered at the correct site was 84.65% which is much lower than the critical value 94.06% for alpha = .05 (p less than .00001).  相似文献   
960.
This study was undertaken to clarify the effect of enzymes induced by ethanol consumption on the pharmacokinetics of trichloroethylene (TRI, a highly metabolised substance) and 1,1,1-trichloroethane (1,1,1-TRI, a poorly metabolised substance). Rats maintained on a control liquid diet or a liquid diet containing ethanol (2 g/day/rat) for not less than three weeks were exposed to either TRI (50, 100, 500, and 1000 ppm) or 1,1,1-TRI (50, 100, and 500 ppm) by inhalation for six hours and the concentration of each compound in the blood and the urinary excretion of metabolites (trichloroethanol and trichloroacetic acid) were measured over several hours. Ethanol, which increased the in vitro metabolism of both compounds about fivefold, enhanced the in vivo metabolism of TRI only at high levels of exposure (marginally at 500 and considerably at 1000 ppm), whereas the metabolism of 1,1,1-TRI was enhanced at all concentrations tested. Moreover, there was a definite difference in the effect of induction of enzymes between the two solvents: the enhanced metabolism of TRI in vivo was shown by a decrease in the blood concentration of TRI as well as by an increase in the urinary excretion of its metabolites, whereas that of 1,1,1-TRI was shown by an increase in the urinary excretion of its metabolites alone. These results suggest that the induction of enzymes differentially affects the pharmacokinetics of TRI and 1,1,1-TRI in human occupational exposure: TRI metabolism may be increased only at concentrations much higher than the current occupational exposure limit (mostly 50 ppm), whereas 1,1,1-TRI metabolism may be increased at an exposure similar to occupational exposure.  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