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   3423881篇
  免费   244522篇
  国内免费   10902篇
耳鼻咽喉   45671篇
儿科学   112416篇
妇产科学   94670篇
基础医学   484641篇
口腔科学   94441篇
临床医学   320734篇
内科学   666772篇
皮肤病学   78247篇
神经病学   283706篇
特种医学   129184篇
外国民族医学   1047篇
外科学   500386篇
综合类   72105篇
现状与发展   6篇
一般理论   1346篇
预防医学   272832篇
眼科学   76659篇
药学   250519篇
  12篇
中国医学   7531篇
肿瘤学   186380篇
  2019年   27807篇
  2018年   39058篇
  2017年   29774篇
  2016年   34054篇
  2015年   38473篇
  2014年   53006篇
  2013年   80753篇
  2012年   107920篇
  2011年   114282篇
  2010年   68572篇
  2009年   64955篇
  2008年   106151篇
  2007年   112365篇
  2006年   114029篇
  2005年   109432篇
  2004年   104971篇
  2003年   101125篇
  2002年   97744篇
  2001年   159308篇
  2000年   163462篇
  1999年   138037篇
  1998年   40292篇
  1997年   35793篇
  1996年   35783篇
  1995年   34524篇
  1994年   31883篇
  1993年   29981篇
  1992年   108347篇
  1991年   104772篇
  1990年   101598篇
  1989年   97771篇
  1988年   89806篇
  1987年   88068篇
  1986年   83052篇
  1985年   79358篇
  1984年   59359篇
  1983年   50665篇
  1982年   30181篇
  1981年   26917篇
  1979年   52971篇
  1978年   37614篇
  1977年   31542篇
  1976年   29798篇
  1975年   31378篇
  1974年   37431篇
  1973年   35838篇
  1972年   33489篇
  1971年   31158篇
  1970年   28846篇
  1969年   27307篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Valve-related morbidity and mortality after heart valve replacement with the Hancock I porcine bioprosthesis has been retrospectively analyzed. From June 1974 through December 1976, 253 Hancock I bioprostheses (150 mitral and 103 aortic) were inserted in 220 selected patients who survived the operation and had follow-up until June 1989 (mean follow-up 13.5 years, with an accumulative follow-up of 2956.4 patient-years). One hundred seventeen patients had mitral valve replacement, 70 had aortic valve replacement, and 33 had combined mitral and aortic valve replacement. There were 27 thromboembolic events. The probability of being free from thromboembolism at 14 years was 81.0% +/- 7.4% for the mitral valve replacement group, 85.4% +/- 6.7% for the aortic group, and 67.1% +/- 18.4% for the mitral-aortic group. Fifteen episodes of prosthetic valve endocarditis occurred. There were 10 instances of nonstructural dysfunction (paravalvular leaks) in seven mitral valves (4.6%) and in three aortic valves (2.9%). One hundred twenty-two bioprostheses in 106 patients resulted in structural deterioration. The probability of freedom from structural deterioration at 14 years was 37.2% +/- 3.9% for the mitral group, 43.9% +/- 7.1% for the aortic group, and 30.1% +/- 8.9% for the mitral-aortic group. The logistic regression analysis between age at the time of operation and bioprosthetic life (structural deterioration-free period) demonstrates a linear regression curve (r = 0.53). There were 56 late deaths (27 patients died at reoperation). The actuarial survival rate (including hospital mortality) at 14 years was 57.2% +/- 5.4% for the entire series, with no statistically significant difference between groups. The probability of remaining free from valve-related morbidity and mortality at 14 years was 16.7% +/- 4.8% for the mitral group, 20.8% +/- 6.2% for the aortic group, and 14.0% +/- 7.0% for the mitral-aortic group. The long-term results of this series show that the clinical performance of the Hancock I porcine valve appears satisfactory during the first 6 years. The behavior of this bioprosthesis at 14 years' follow-up changes drastically, because only a minor group of patients is free from valve-related complications, justifying the restriction of its use for selected patients.  相似文献   
992.
Forty-seven patients with oesophageal carcinoma were managed in 6 years' time. Average duration of illness was 5.5 months. History of chronic smoking and/or tobacco chewing was present in 80.85% of patients. Carcinoma included squamous cell variety (80.85%) and adenocarcinoma (19.15%). Thirty-one patients were in stage III while 16 patients were in stage II. Surgery included oesophagogastrectomy/oesophagogastrostomy (16 patients), feeding gastrostomy (11 patients), Mousseau-Barbin tube insertion (10 patients), only 10 patients were subjected to palliative radiotherapy. All patients after palliative treatment died within one year whereas 3-year and 5-year survivals after oesophagogastrectomy/oesophagogastrostomy were 68.75% and 31.25% respectively. Local lymph node metastasis adversely affected the 5-year survival rate.  相似文献   
993.
994.
The neonatal mortality rate has so far been used as the most reasonable risk indicator of pregnancy outcomes in a community. This rate, however, has decreased considerably, and a new indicator is required. The proportions of pre-term infants, infants with foetal growth retardation and high-risk infants were defined on the basis of both weight and gestational age at birth. Using these as pregnancy outcome indicators, perinatal risk factors in a rural community were examined. The study results agreed with the general knowledge on perinatal risk factors. This method can be used as an alternative to the conventional method for assessing the maternal and child health in a community.  相似文献   
995.
A cross-sectional survey of intestinal parasitic infection in a rural community, Nderu, in Kiambu District, Kenya, was carried out in 1985 by examining 1129 individuals from 203 households (about 25% of the total population). This was followed by 3 more cross-sectional surveys, in January, May and October 1986, of 56 families comprising 461 individuals, who had also participated in the first survey. In the first survey, 81.4% of the sample was positive for at least one intestinal parasite and 78% was positive for intestinal protozoa. 72.7% of those infected had multiple infections. The prevalence of most of the protozoa increased with age but that of Giardia lamblia peaked in the 0 to 4 year class at 35.5%. Females were infected more often with several of the protozoa, but males with Ascaris. People living in larger households were more often infected with Entamoeba histolytica and Iodamoeba butschlii, while the opposite was true of H. nana and tended to be for Giardia. Significant positive associations between parasite species were common at all surveys, especially among the amoebae. The majority of negative associations were for Giardia. Unformed stools were significantly associated with Giardia, Blastocystis, and trophozoites of Trichomonas hominis and Chilomastix mesnili. Endolimax nana and Entamoeba coli were found more often in formed stools. Estimates of daily incidence, and duration of infection in days, were calculated for 11 parasites. The longest mean estimated duration of infection for any species was 237 +/- S.D. 151.4 days for H. nana and the shortest was 41.6 +/- S.D. 0.4 days for T. hominis.  相似文献   
996.
Creativity and problem solving are closely related in the learning and practice of nursing. The problem underlying this study concerns the attitudes of professors of nursing in 321 French language community colleges in Quebec toward the creative characteristics of their students. However, given the absence of a valid and reliable French instrument, this study focused on the validation of a French version of Torrance's Ideal Pupil Checklist. Content, construct and criteria validity were all verified, as well as the stability and homogeneity aspects of reliability.  相似文献   
997.
Tubulointerstitial alterations associated with chronic glomerulonephritis (CGN) are definitely dependent on the clinical type of CGN and are accompanied by a decrease of homeostatic functions (the rate of glomerular filtration, osmotic concentration and dilution of urine, hydruresis, the magnitude of CH2O, excretion of ammonium and hydrogen ions, the ratio of ammonium excretion to hydrogen ion excretion). Maximal osmotic concentration and ammonium excretion show an especially considerable decrease. The clinical type permitting one to diagnose rather than to reject the presence of alterations and the status of certain tubular functions, osmotic concentration in particular and, to a less degree, ammonium excretion, permitting to reject the presence of the tubulointerstitial component (TIC) are of known but restricted importance for TIC recognition. The TIC can be diagnosed more adequately in exploring definite pairs of renal functions, particularly osmotic concentration of urine and ammonium excretion and maximal hydruresis and excretion of hydrogen ions. This approach is both helpful in confirming and rejecting the presence of the TIC. Of special value is the combined assessment of the clinical type and maximal osmotic urine concentration data.  相似文献   
998.
Cerebral infarction is rare in premature newborns and is most commonly the result of arterial embolization from the placenta. A focal echodense area was identified on prenatal cranial ultrasonography (US) in a premature infant (34 weeks of gestation). After birth, cerebral infarction was confirmed by magnetic resonance imaging (MRI). The clinical findings, imaging findings and pathogenesis are discussed. New diagnostic methods such as MRI show to be a useful approach in the neonatal period facilitating recognition of cerebrovascular accidents also in low-birth-weight infants.  相似文献   
999.
1000.
Stable xenon (Xe)-enhanced computed tomography is a potentially valuable tool for high resolution, three-dimensional measurement of CBF in patients. However, reports that Xe causes cerebrovascular dilation and increases intracranial pressure (ICP) have tempered enthusiasm for its use. The effects of 5 min of 33% Xe inhalation on ICP (right and left hemispheres) were studied in eight fentanyl-anesthetized Rhesus monkeys after right-sided cortical freeze injury. ICP, CBF, and physiological variables were monitored for up to 6 h postinsult. The preinjury (control) right hemispheric ICP was 8 +/- 5 mm Hg (mean +/- SD) and left hemispheric ICP was 5 +/- 2 mm Hg. Postinjury observations were classified into low (less than 15 mm Hg) and high ICP (greater than or equal to 15 mm Hg) groups. Both right and left ICP values averaged 9 +/- 3 mm Hg in the low ICP group. In the high ICP group, the right ICP was 20 +/- 4 mm Hg and left ICP was 21 +/- 6 mm Hg. ICP was unchanged by Xe inhalation under control conditions as well as in both low and high ICP groups postinjury. Postinjury, the MABP decreased 10-15 mm Hg in the low ICP group and 10-17 mm Hg in the high ICP group 2-3 min after the start of Xe inhalation (p less than 0.05). These results show that 33% Xe inhalation does not increase ICP in fentanyl-anesthetized monkeys but could decrease MABP in stressed states, presumably because of the anesthetic effects of Xe.  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