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   4635篇
  免费   379篇
  国内免费   14篇
耳鼻咽喉   29篇
儿科学   213篇
妇产科学   151篇
基础医学   695篇
口腔科学   44篇
临床医学   550篇
内科学   897篇
皮肤病学   76篇
神经病学   440篇
特种医学   101篇
外科学   348篇
综合类   23篇
一般理论   4篇
预防医学   552篇
眼科学   110篇
药学   377篇
中国医学   21篇
肿瘤学   397篇
  2023年   48篇
  2022年   70篇
  2021年   122篇
  2020年   76篇
  2019年   135篇
  2018年   148篇
  2017年   118篇
  2016年   116篇
  2015年   122篇
  2014年   192篇
  2013年   226篇
  2012年   365篇
  2011年   363篇
  2010年   214篇
  2009年   188篇
  2008年   322篇
  2007年   298篇
  2006年   302篇
  2005年   287篇
  2004年   321篇
  2003年   262篇
  2002年   224篇
  2001年   41篇
  2000年   25篇
  1999年   31篇
  1998年   67篇
  1997年   43篇
  1996年   25篇
  1995年   22篇
  1994年   35篇
  1993年   31篇
  1992年   11篇
  1991年   9篇
  1990年   7篇
  1989年   10篇
  1988年   16篇
  1987年   5篇
  1986年   7篇
  1985年   4篇
  1984年   12篇
  1983年   9篇
  1982年   12篇
  1980年   7篇
  1979年   5篇
  1978年   5篇
  1977年   8篇
  1975年   4篇
  1974年   6篇
  1973年   5篇
  1923年   4篇
排序方式: 共有5028条查询结果,搜索用时 15 毫秒
11.
12.
In 1998, the New York City Department of Health and the Mayor’s Office of Emergency Management began monitoring the volume of ambulance dispatch calls as a surveillance tool for biologic terrorism. We adapted statistical techniques designed to measure excess influenza mortality and applied them to outbreak detection using ambulance dispatch data. Since 1999, we have been performing serial daily regressions to determine the alarm threshold for the current day. In this article, we evaluate this approach by simulating a series of 2,200 daily regressions. In the influenza detection implementation of this model, there were 71 (3.2%) alarms at the 99% level. Of these alarms, 64 (90%) occurred shortly before or during a period of peak influenza in each of six influenza seasons. In the bioterrorism detection implementation of this methodology, after accounting for current influenza activity, there were 24 (1.1%) alarms at the 99% level. Two occurred during a large snowstorm, 1 is unexplained, and 21 occurred shortly before or during a period of peak influenza activity in each of six influenza seasons. Our findings suggest that this surveillance system is sensitive to communitywide respiratory outbreaks with relatively few false alarms. More work needs to be done to evaluate the sensitivity of this approach for detecting nonrespiratory illness and more localized outbreaks.  相似文献   
13.
14.
A 66-year-old man with atrial fibrillation was referred soon after developing left lower limb and abdominal pain with rectal bleeding. An immediate flush aortogram showed embolic occlusion of the left distal superficial femoral artery and superior mesenteric artery (SMA), 3 cm from its ostium. Recombinant tissue plasminogen activitor (rtPA) 40 mg was selectively in stilled in the SMA in two boluses. Abdominal symptoms resolved within 48 h, and complete recanalization of the SMA was shown on angiography. Exploratory laparotomy after 72 h showed a normal small bowel and right colon, and was completed by femoropopliteal embolectomy. Six months later, the patient remained asymptomatic.  相似文献   
15.
The choroid plexuses (CPs) form a protective interface between the blood and the ventricular cerebrospinal fluid (CSF). To probe into the pathways by which CPs provide brain protection, we sought to evaluate the efficiency of glutathione conjugation in this barrier as a mechanism to prevent the entry of blood-borne electrophilic, potentially toxic compounds into the CSF, and we investigated the fate of the resulting metabolites. Rat CPs, as well as human CPs from both fetal and adult brains, displayed high glutathione-S-transferase activities. Using an in vitro model of the blood-CSF barrier consisting of choroidal epithelial cells cultured in a two-chambered device, we showed that glutathione conjugation can efficiently prevent the entry of 1-chloro-2,4-dinitrobenzene (CDNB) into the CSF, a model for electrophilic compounds. The duration of this enzymatic protection was set by the concentration of CDNB to which the epithelium was exposed, and this barrier effect was impaired only on severe epithelial intracellular glutathione and cysteine depletion. The conjugate was excreted from the choroidal cells in a polarized manner, mostly at the blood-facing membrane, via a high-capacity transport process, which is not a rate-limiting step in this detoxification pathway, and which may involve transporters of the ATP-binding cassette c(Abcc) and/or solute carrier 21 (Slc21) families. Supplying the choroidal epithelium at the blood-facing membrane with a therapeutically relevant concentration of N-acetylcysteine sustained this neuroprotective effect. Thus, glutathione conjugation at the CP epithelium coupled with the basolateral efflux of the resulting metabolites form an efficient blood-CSF enzymatic barrier, which can be enhanced by pharmacologically increasing glutathione synthesis within the epithelial cells.  相似文献   
16.
OBJECTIVE: Dobutamine is commonly used to improve ventricular performance in cardiac surgery. The aim of this prospective randomised controlled study was to assess the effectiveness of using low doses of dobutamine during off-pump coronary artery bypass (OPCAB) surgery in order to reduce haemodynamic compromise due to heart displacement. METHODS: Thirty-two patients undergoing elective coronary artery bypass grafting (CABG) surgery using OPCAB technique for more than two vessels were approached and recruited. We analysed the changes in the thoracic aortic blood flow (TABF) during OPCAB using transoesophageal Doppler and by other conventional monitoring methods as cardiac output, invasive pulmonary and radial pressures and mixed venous oxygen saturation. RESULTS: The two groups were similar in preoperative characteristics. No postoperative complications were observed in the study patients. The heart rate, right atrial pressure, cardiac output measured by thermodilution and TABF changed significantly during the procedure. Also significant changes in descending thoracic aortic diameter were observed. The postoperative creatinine was significantly lower in the dobutamine group (P=0.04). Dobutamine was found responsible for the improvement in the descending TABF (P=0.006). CONCLUSIONS: This study showed that intra-operative intravenous infusion of dobutamine at 5 microg/kg per min in routine OPCAB patients safely increased cardiac output even without such changes been detected by conventional monitoring methods.  相似文献   
17.
Summary The immunoreactivity of polyclonal antiserum to neuron-specific enolase (NSE) has been investigated. Twenty-three cases of malignant lymphoma (ML) were studied and compared with previously published reports. In our study 11 out of 23 cases showed strong or weak NSE positivity; any type of ML could be positive or negative even among B or T cell ML. This study indicated that polyclonal NSE is not a specific marker; it might be an inconstant marker of ML with no apparent correlation between reactivity and morphology or phenotype.  相似文献   
18.
19.
Virus-like particles containing the rotavirus (RV) internal proteins VP2 and VP6 (2/6-VLP) have been shown to induce serum and fecal antibodies as well as protection in mice after intranasal administration with a mutant of E. coli toxin, LT-R192G. To better understand the origin of fecal IgA induced by this protocol, we studied the RV-specific B cell response in systemic and mucosal lymphoid tissues using a flow cytometry assay that allows quantification and phenotypic characterization of RV-specific B lymphocytes. We also assessed the RV-specific antibody-secreting cells in the spleen and intestinal lamina propria (ILP). A remarkably high frequency of RV-specific B cells was found in the respiratory lymphoid tissues and spleen, of which only a minority expressed the alpha4beta7 integrin (intestinal homing receptor). In contrast, but in accordance with alpha4beta7 expression at the induction site, a very low response was observed in intestinal lymphoid tissues (mesenteric lymph nodes and ILP), which did not increase after a second immunization. Thus, intranasal immunization with a nonreplicating antigen does not induce an important number of RV-specific B cells with an intestinal homing profile.  相似文献   
20.
Objective: To report a case of typhoid fever contracted in Portugal in 1994 due to a Salmonella typhi isolate which had reduced susceptibility to fluoroquinolone (MIC 1 mg/L of ciprofloxacin) and high level resistance to nalidixic acid (MIC ≥56 mg/L).
Methods: Molecular studies of reduced susceptibility to fluoroquinolones comprised complementation tests with a wild-type allele and sequencing directly from PCR products of the gyrA gene.
Results: Complementation tests and DNA sequencing showed that a mutation occurred in the gyrA gene of this clinical isolate, resulting in a substitution of phenylalanine for serine at position 83 of GyrA.
Conclusions: Because quinolones may be regarded as a treatment of choice in typhoid fever, it seems important now to recommend cautious use of these drugs as first-line therapy and possibly use of nalidixic acid resistance as a marker for detection of 'first-step' resistance to fluoroquinolones in S. typhi.  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