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   7720篇
  免费   451篇
  国内免费   77篇
耳鼻咽喉   75篇
儿科学   224篇
妇产科学   107篇
基础医学   1057篇
口腔科学   953篇
临床医学   594篇
内科学   1655篇
皮肤病学   184篇
神经病学   452篇
特种医学   482篇
外科学   697篇
综合类   47篇
预防医学   815篇
眼科学   123篇
药学   496篇
中国医学   66篇
肿瘤学   221篇
  2023年   71篇
  2022年   172篇
  2021年   241篇
  2020年   195篇
  2019年   232篇
  2018年   317篇
  2017年   183篇
  2016年   206篇
  2015年   257篇
  2014年   323篇
  2013年   409篇
  2012年   555篇
  2011年   630篇
  2010年   316篇
  2009年   316篇
  2008年   383篇
  2007年   459篇
  2006年   333篇
  2005年   271篇
  2004年   205篇
  2003年   160篇
  2002年   175篇
  2001年   136篇
  2000年   124篇
  1999年   124篇
  1998年   98篇
  1997年   96篇
  1996年   115篇
  1995年   74篇
  1994年   80篇
  1993年   65篇
  1992年   59篇
  1991年   64篇
  1990年   52篇
  1989年   80篇
  1988年   67篇
  1987年   72篇
  1986年   80篇
  1985年   65篇
  1984年   36篇
  1983年   36篇
  1982年   32篇
  1980年   21篇
  1979年   23篇
  1978年   24篇
  1977年   25篇
  1976年   26篇
  1975年   28篇
  1970年   21篇
  1968年   20篇
排序方式: 共有8248条查询结果,搜索用时 31 毫秒
31.
Summary HIV-1 is a polytropic virus that, apart from hematopoietic cells, can replicate in several cells from solid tissues. Virus yields vary widely, closely resembling differences in HIV binding to the cells; the latter phenomenon appears mainly related to the extent of CD4 expression, even though other molecules have been implied in virus-cell interactions, the expression of which on the cell membrane can be modulated by several stimuli. During the course of HIV replication, a series of cytokines is produced and released in parallel to virus growth, particularly IL-6 and TNF-. In fact, exposure of fibroblasts or epithelial cells to these HIV-in-duced cytokines causes an increase of CD4 expression, HIV adsorption to uninfected cells, and release of infectious virions by infected cells. In cells exposed to interferon-, IL-6 and TNF- allow the virus to bypass interferon inhibition of virus release. The fact that HIV-1 adsorption and spread can be mediated by HIV-induced cytokines may be relevant in AIDS pathogenesis, accelerating virus transmission both within the organ and to infiltrating cells, activating a self-maintaining mechanism of infection.  相似文献   
32.
We are concerned in this paper with learning classification procedures from known cases. More precisely, we provide a diagnostic model that discriminate between cerebellum-pontine angle (CPA) tumors and otorhinolaryngological (ENT) disorders. Usually, in order to distinguish between CPA tumors and ENT disorders one must perform clinical-neurological examination together with expensive radiological imagery (CT and MRI). The proposed model was obtained through artificial intelligence methods and presented a good accuracy level (88.4%) when tested against new cases, considering only clinical examination without radiological imagery results.  相似文献   
33.
34.
Objectives: To describe the physical growth patterns of infants born to narcotic dependent mothers (INDM) over a 12 months period and, if possible, to relate the growth to drug taking patterns during pregnancy.
Methodology: The growth of a cohort of 43 INDM was measured during the first 12 months of life. Weight and length measurements were compared with percentile charts and converted to Z scores. Questionnaire data about drug taking practices, demographic variables and the neonatal period (including withdrawal scores) were obtained.
Results: Twenty-four (55.8%) of INDM had evidence of neonatal drug withdrawal requiring treatment with phenobarbitone. At birth, Z scores for weight and length indicated relative intrauterine growth retardation. By 12 months, there had been some catch up growth, but Z scores for weight and length were still below zero. Persistent weight retardation at 12 months was correlated with methadone dosage during pregnancy, but not the need for phenobarbitone therapy.
Conclusions: The growth patterns of INDM in the first 12 months of life indicated that at birth there was evidence of intrauterine growth retardation, but by 12 months the growth was little different from the rest of the community. There appears to be some influence of narcotic agents taken while pregnant on subsequent growth of INDM.  相似文献   
35.
This study was designed to look at the differences in visuospatial abilities between boys and girls before they can speak fluently. At the mandatory two year follow up visit, children were given the opportunity to build a tower and a bridge. In children whose birth weight was > or = 2500 g, the capacity for erecting a tower was the same in both sexes, but for building a bridge striking differences were noted according to their sex. Among the 376 children of this category, 41 out of 199 boys (21%) were able to build a bridge in comparison with 15 out of 177 girls (8%). This difference is highly significant. In children whose birth weight was < or = 2500 g, no differences were noted either for building a tower or a bridge. By showing that boys outnumber girls among the most skilled toddlers in spatial abilities, this work confirmed the action of a male related factor on cerebral lateralisation.  相似文献   
36.
Persistent hyperinsulinemic hypoglycaemia of infancy (PHHI) is the most frequent cause of hypoglycaemia in infancy. Clinical presentation is heterogeneous, with variable onset of hypoglycaemia and response to diazoxide, and presence of sporadic or familial forms. Underlying histopathological lesions can be focal or diffuse. Focal lesions are characterised by focal hyperplasia of pancreatic islet-like cells, whereas diffuse lesions implicate the whole pancreas. The distinction between the two forms is important because surgical treatment and genetic counselling are radically different. Focal lesions correspond to somatic defects which are totally cured by limited pancreatic resection, whereas diffuse lesions require a subtotal pancreatectomy exposing to high risk of diabetes mellitus. Diffuse lesions are due to functional abnormalities involving several genes and different transmission forms. Recessively inherited PHHI have been attributed to homozygote mutations for the beta-cell sulfonylurea receptor (SUR1) or the inward-rectifying potassium-channel (Kir6.2) genes. Dominantly inherited PHHI can implicate the glucokinase gene, particularly when PHHI is associated with diabetes, the glutamate dehydrogenase gene when hyperammonaemia is associated, or another locus.  相似文献   
37.
38.
OBJECTIVE: The ketogenic diet is a high-fat, low-protein, low-carbohydrate diet developed in the 1920s for the treatment of children with difficult to control seizures. Despite advances in both the pharmacotherapy and the surgery of epilepsy, many children continue to have difficult-to-control seizures. This prospective study sought to determine the ketogenic diet's effectiveness and tolerability in children refractory to today's medications. METHODS: One hundred fifty consecutive children, ages 1 to 16 years, virtually all of whom continued to have more than two seizures per week despite adequate therapy with at least two anticonvulsant medications, were prospectively enrolled in this study, treated with the ketogenic diet, and followed for a minimum of 1 year. Seizure frequency was tabulated from patients' daily seizure calendars and seizure reduction calculated as percentage of baseline frequency. Adverse events and reasons for diet discontinuation were recorded. RESULTS: The children (mean age, 5.3 years), averaged 410 seizures per month before the diet, despite an exposure to a mean of 6.2 antiepileptic medications. Three months after diet initiation, 83% of those starting remained on the diet and 34% had >90% decrease in seizures. At 6 months, 71% still remained on the diet and 32% had a >90% decrease in seizures. At 1 year, 55% remained on the diet and 27% had a >90% decrease in seizure frequency. Most of those discontinuing the diet did so because it was either insufficiently effective or too restrictive. Seven percent stopped because of intercurrent illness. CONCLUSIONS: The ketogenic diet should be considered as alternative therapy for children with difficult-to-control seizures. It is more effective than many of the new anticonvulsant medications and is well tolerated by children and families when it is effective.  相似文献   
39.
40.
OBJECTIVE: To determine the coverage and focus of cervical cancer screening (Pap smears) in a population-based sample in Brazil. METHODS: Cross-sectional cluster survey covering 1730 women aged 20 years or older with a history of sexual activity. Information was collected on social, demographic and behavioral variables, knowledge of and use of the Pap test. RESULTS: Of women aged 25-59 years, who are the target population of the national cervical cancer screening program, 78.7% had had at least one Pap test in their lifetime, and 68.8% had had a Pap test in the last 3 years. Statistics for focus of the program showed that of the 637 women who reported having a Pap test in the last year, only 20.6% actually required one. The remainder were either outside the age range or had had another test less than 30 months previously. Prevalence of not having been tested in the previous 3 years was highest among black (41.7%) and low-income women (64.3%), and among those at greatest risk for cervical cancer (62.3% for women with three or more risk factors). Focus was inversely related to socioeconomic status. CONCLUSION: Coverage rates were similar to those reported in other national studies, but this is the first report to examine the focus of the national program. We show that 8 of every 10 Pap tests were not necessary. Coverage levels remain unacceptably low among women of low socioeconomic status and those at greatest risk for cervical cancer.  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