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   4718篇
  免费   328篇
  国内免费   13篇
耳鼻咽喉   46篇
儿科学   161篇
妇产科学   112篇
基础医学   661篇
口腔科学   149篇
临床医学   427篇
内科学   1169篇
皮肤病学   92篇
神经病学   312篇
特种医学   343篇
外科学   419篇
综合类   51篇
预防医学   410篇
眼科学   50篇
药学   230篇
  1篇
中国医学   24篇
肿瘤学   402篇
  2023年   28篇
  2022年   52篇
  2021年   92篇
  2020年   54篇
  2019年   102篇
  2018年   94篇
  2017年   85篇
  2016年   95篇
  2015年   120篇
  2014年   164篇
  2013年   157篇
  2012年   236篇
  2011年   245篇
  2010年   159篇
  2009年   152篇
  2008年   194篇
  2007年   211篇
  2006年   224篇
  2005年   210篇
  2004年   175篇
  2003年   208篇
  2002年   178篇
  2001年   126篇
  2000年   158篇
  1999年   111篇
  1998年   82篇
  1997年   76篇
  1996年   63篇
  1995年   80篇
  1994年   58篇
  1993年   63篇
  1992年   90篇
  1991年   71篇
  1990年   65篇
  1989年   93篇
  1988年   69篇
  1987年   65篇
  1986年   84篇
  1985年   59篇
  1984年   44篇
  1983年   35篇
  1982年   32篇
  1981年   27篇
  1980年   28篇
  1979年   24篇
  1978年   27篇
  1977年   22篇
  1976年   26篇
  1975年   22篇
  1970年   16篇
排序方式: 共有5059条查询结果,搜索用时 15 毫秒
81.
BACKGROUND: Among members of the family Enterobacteriaceae, the production of plasmid-mediated extended-spectrum beta-lactamases (ESbetaLs) has emerged as an important mechanism of the resistance to beta-lactams. METHODS: The molecular basis of extended-spectrum beta-lactamase in 48 strains of Klebsiella pneumoniae, recovered from neonatal patients with nosocomial septicemia during an outbreak that occurred in November 2000 at a Neonatal Intensive Care Unit of The Andes University Hospital in Venezuela, were investigated. RESULTS: The isolates were resistant to expanded-spectrum cephalosporins, aztreonam, gentamicin, kanamycin, tetracycline, and chloramphenicol, but remained susceptible to cefoxitin, imipenem, amikacin, and tobramycin. Production of ESbetaL activity was confirmed by restoring susceptibility to ceftazidime in the presence of clavulanic acid. All isolates harbored an 87-kilobase plasmid. Analysis of the outer membrane protein patterns did not reveal relevant changes of the porins profile. All resistance markers were transferable to Escherichia coli by conjugation and were lost en bloc after treatment with acridine orange. Isoelectric focusing for beta-lactamases was performed on transconjugants, obtaining 2 bands with isoelectric points of 5.4 and 8.2. Genes encoding both enzymes are located on the single, self-transferable 87-kilobase plasmid pKAM542. Analysis of the plasmid by hybridization revealed the presence of both blaTEM and blaSHV determinants. Cloning and sequencing identified them as blaTEM-1 and blaSHV-5, respectively; the latter was responsible for the ESbetaL activity among nosocomial isolates of K pneumoniae. CONCLUSIONS: Microbiologists, epidemiologists, and clinicians must be aware of potential ESbetaL-encoding organisms to assess proper antimicrobial managements and effective infection controls.  相似文献   
82.
We evaluated the influence of the hereditary make-up on the development of systemic lupus erythematosus (SLE) in two ethnic groups [Gypsy and white Caucasian Mediterranean (WCM) populations], living in the same geographic area. We compared 81 WCM and 25 Gypsy patients with SLE. The control group consisted of 185 healthy unrelated individuals, 105 WC and 80 Gypsies. In the Gypsy population, the onset of SLE occurred at earlier ages than in the other ethnic group (25.9 versus 32.0 years, P = 0.02), and showed lower SLEDAI peak values (4.9 versus 7.0, P = 0.016). The frequency of joint, kidney, gastrointestinal and eye involvement was significantly lower in Gypsy patients. In contrast, SLE-associated antiphospholipid syndrome, thrombosis and livedo reticularis were more frequent in Gypsies than in the majority ethnic group (WCM). In WCM patients, DRB1* 1303-DQB1*0301 haplotype was associated with SLE (P = 0.001, Pc = 0.038). We found SLE to be associated with DR5 (P = 0.006, Pc = 0.05) in the Gypsy population as well as a protective effect of DPB1*0401 when DR5 was not present (P = 0.008, Pc = 0.032). In conclusion, we found some clinical differences between WCM and Gypsy patients with SLE. Furthermore, HLA associations between HLA-DRB1-DQB1 and SLE were different for Gypsy people.  相似文献   
83.
OBJECTIVE: The present study explores the acceptance and consumption of nutritional supplements that form part of a governmental program to support nutritionally vulnerable groups. MATERIAL AND METHODS: Pregnant and lactating women, and mothers of malnourished toddlers, infants and children were interviewed. Data were collected, after introduction with an interview guide with an open-ended format, through face-to-face interviews conducted at home. Interviews were taped with previous informed consent. Analysis included topics and subtopics approached by the interviewed women. RESULTS: The studied population showed good acceptance to the supplement when offered as a drink. When considering benefits, pregnant women thought first of their baby's health than of their own and associated the possible advantages of the supplement to its "vitamin" contents. Acceptance of the flavors was largely influenced by previous contact to specific flavors. Children under 1 year of age preferred the liquid consistency and elderly children favored the puree. Most mothers considered that the offered amount was enough and there was the general impression that, as the time of the intervention elapsed, children showed greater appetite. The diet was not substituted by the supplement. CONCLUSIONS: Acceptance of the supplement may be improved by messages focusing on the well-being and health of the child and insisting on the benefits for the pregnant mother. Community health providers should be involved in supporting the program, recommending consumption and acceptance of the supplement. The identification by mothers of "vitamins" as part of the supplement may be used to reinforce the concept of beneficial effects associated to micronutrient supplementation. Qualitative evaluations should be performed as part of the assessment of community-based programs.  相似文献   
84.
The effects of captopril on myocardial segment function in different degrees of transient coronary occlusion were studied using ultrasonic dimension gauges in 15 open-chest dogs. The occlusion procedures (OP) were performed on the left anterior descending coronary artery (LAD) in eight dogs and on the left circumflex coronary artery (Cx) in seven dogs. To measure the changes in segment shortening in the subendocardium we used eight dogs (ischemic and control zones: four dogs LAD and four dogs Cx). To measure the changes in wall thickening we used seven dogs (ischemic and control zones: three dogs LAD and four dogs Cx). Total coronary OP lasting 1 min and partial OP (70-80%) lasting 1 min and 2 min 30 s, before and after captopril (0.25 mg/kg i.v.) were performed. Left ventricular pressure, dP/dt, coronary flow, and ECG were monitored. Total coronary OP (1 min) changed segment shortening (18% LAD; 14% Cx) and wall thickening (19% LAD; 18% Cx) to values of dyskinesis (-3% and -4% for shortening; -6% and -5% for thickening). Captopril improved regional function maintaining positive values for shortening (4% LAD; 3% Cx) and thickening (0.3% LAD; 4% Cx). Similar responses were obtained during partial OP and captopril. Results suggest that captopril produced a significant improvement in the regional function parameters affected by ischemia both in total and partial obstructions.  相似文献   
85.
In this paper, the approach to the genesis of the acute hypertension of pregnancy, uses a conceptual and methodological perspective adjusted to its multifactorial nature; a set of questions with epidemiologic focus is proposed, in order to vinculate psychosocial factors with the biologic processes characteristic of this health problem.  相似文献   
86.
87.
Purpose

Although suicide rates of prison populations and incidence factors have been reported for high-income countries, data from low- and middle-income regions are lacking. The purpose of the study was to estimate suicide rates among prison populations in South America, to examine prison-related factors, and to compare suicide rates between prison and general populations.

Methods

In this observational study, we collected the numbers of suicides in prison, rates of prison occupancy, and incarceration rates from primary sources in South America between 2000 and 2017. We compared suicide rates among prisoners with incidence rates in the general populations by calculating incidence rate ratios. We assessed the effect of gender, year, incarceration rates and occupancy on suicide rates in the prison populations using regression analyses.

Results

There were 1324 suicides reported during 4,437,591 person years of imprisonment between 2000 and 2017 in 10 South American countries. The mean suicide rate was 40 (95% CI 16–65) per 100,000 person years for male and female genders combined. The pooled incidence rate ratio of suicide between prison and general populations was 3.9 (95% CI 3.1–5.1) for both genders combined, 2.4 (95% CI 1.9–3.1) for men and a higher ratio in women (13.5, 95% CI 6.9–26.9). High occupancies of prisons were associated with lower incidence of suicide (β = − 58, 95% CI − 108.5 to − 7.1).

Conclusions

Suicides during imprisonment in South America are an important public health problem. Suicide prevention strategies need to target prison populations.

  相似文献   
88.
Background and aimsWe aimed to analyze the relationship between the initial chest X-ray findings in patients with severe acute respiratory syndrome due to infection with SARS-CoV-2 and eventual clinical worsening and to compare three systems of quantifying these findings.Material and methodsThis retrospective study reviewed the clinical and radiological evolution of 265 adult patients with COVID-19 attended at our center between March 2020 and April 2020. We recorded data related to patients’ comorbidities, hospital stay, and clinical worsening (admission to the ICU, intubation, and death). We used three scoring systems taking into consideration 6 or 8 lung fields (designated 6 A, 6 B, and 8) to quantify lung involvement in each patient's initial abnormal chest X-ray and to classify its severity as mild, moderate, or severe, and we compared these three systems. We also recorded the presence of alveolar opacities and linear opacities (fundamentally linear atelectasis) in the first chest X-ray with pathologic findings.ResultsIn the χ2 analysis, moderate or severe involvement in the three classification systems correlated with hospital admission (p = 0.009 in 6 A, p = 0.001 in 6 B, and p = 0.001 in 8) and with death (p = 0.02 in 6 A, p = 0.01 in 6 B, and p = 0.006 in 8). In the regression analysis, the most significant associations were 6 B with alveolar involvement (OR 2.3; 95%CI 1.1.–4.7; p = 0.025;) and 8 with alveolar involvement (OR 2.07; 95% CI 1.01.–4.25; p = 0.046). No differences were observed in the ability of the three systems to predict clinical worsening by classifications of involvement in chest X-rays as moderate or severe.ConclusionModerate/severe extension in the three chest X-ray scoring systems evaluating the extent of involvement over 6 or 8 lung fields and the finding of alveolar opacities in the first abnormal X-ray correlated with mortality and the rate of hospitalization in the patients studied. No significant difference was found in the predictive ability of the three classification systems proposed.  相似文献   
89.
Trypanosoma evansi infection in the Philippines is frequently reported to affect the country’s livestock, particularly, the buffaloes. To assess the prevalence and intraspecific diversity of T. evansi in the country, blood samples from water buffaloes in different geographical regions were collected during an outbreak. T. evansi was detected in all 79 animals tested using PCR targeting the RoTat 1.2 VSG gene. Sequencing of the rDNA complete internal transcribed spacer (ITS) region including the 5.8S subunit showed high similarity (99–100%) between Philippine isolates and known T. evansi isolates in Genbank. Tree construction based on the same region confirmed the close relationship between Philippine and reported Thai isolates as compared to Egyptian isolates separated by relatively small genetic distances, 47 polymorphisms, despite the clustering in four branches. Overall, the results of this study prove genetic diversity within T. evansi species despite previous reports on limited heterogeneity among isolates worldwide.  相似文献   
90.
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