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   2910篇
  免费   149篇
  国内免费   16篇
耳鼻咽喉   53篇
儿科学   167篇
妇产科学   66篇
基础医学   300篇
口腔科学   41篇
临床医学   230篇
内科学   974篇
皮肤病学   47篇
神经病学   163篇
特种医学   151篇
外科学   235篇
综合类   27篇
一般理论   1篇
预防医学   184篇
眼科学   21篇
药学   251篇
中国医学   1篇
肿瘤学   163篇
  2021年   26篇
  2020年   29篇
  2019年   49篇
  2018年   68篇
  2017年   42篇
  2016年   39篇
  2015年   71篇
  2014年   88篇
  2013年   103篇
  2012年   140篇
  2011年   117篇
  2010年   96篇
  2009年   77篇
  2008年   103篇
  2007年   118篇
  2006年   110篇
  2005年   112篇
  2004年   111篇
  2003年   98篇
  2002年   90篇
  2001年   88篇
  2000年   90篇
  1999年   81篇
  1998年   67篇
  1997年   46篇
  1996年   44篇
  1995年   40篇
  1994年   33篇
  1993年   29篇
  1992年   53篇
  1991年   47篇
  1990年   56篇
  1989年   58篇
  1988年   41篇
  1987年   43篇
  1986年   45篇
  1985年   39篇
  1984年   49篇
  1983年   33篇
  1982年   23篇
  1981年   23篇
  1979年   25篇
  1978年   19篇
  1977年   21篇
  1976年   24篇
  1975年   24篇
  1974年   17篇
  1973年   22篇
  1972年   23篇
  1923年   15篇
排序方式: 共有3075条查询结果,搜索用时 15 毫秒
21.
OBJECTIVE: Because the survival rate has increased for extremely low birth weight neonates, many have raised the concern that the rate of developmental disability among survivors will also increase. To address this concern, we analyzed changes over time in survival and major neurosensory impairment in a sample of extremely low birth weight infants born between July 1, 1979, and June 30, 1994. METHODS: The study sample included 513 infants with birth weights of 501 to 800 g who were cared for in either of the two neonatal intensive care units that serve a 17-county region in northwest North Carolina and who were born to mothers residing in that region. At 1 year of age (corrected for gestation), survivors were examined by a pediatrician and were tested using the Bayley Scales of Infant Development. Major neurosensory impairment was defined as cerebral palsy, a Bayley Mental Developmental Index <68, or blindness. A total of 209/216 (97%) of survivors were examined at 1 year of age. Epoch of birth was defined as follows: epoch 1, July 1, 1979 to June 30, 1984; epoch 2, July 1, 1984 to June 30, 1989; and epoch 3, July 1, 1989 to June 30, 1994. RESULTS: Survival rates for epochs 1, 2, and 3 were, respectively, 24/120 (20%), 63/175 (36%), and 129/218 (59%). In contrast, the proportions with a major neurosensory impairment did not increase over time; rates for successive epochs were 6/24 (25%), 17/61 (28%), and 26/124 (21%). Rates of cerebral palsy were 3/24 (13%), 12/61 (20%), and 9/124 (7%); rates of delayed mental development were 4/24 (17%), 12/61 (20%), and 17/124 (14%); and rates of blindness were 2/24 (8%), 0/62, and 5/124 (4%), respectively. CONCLUSIONS: This analysis suggests that the increasing survival of extremely low birth weight neonates since the late 1970s has not resulted in an increased rate of major developmental problems identifiable at 1 year of age.  相似文献   
22.
In this article we present the elements of one approach to quality improvement and patient safety that we believe can be successful and sustainable in the field of obstetrics and gynecology, along with several strategies (and caveats) that have worked and are working in academic and nonacademic institutions in the United States. Also included are several noteworthy definitions of quality to provide some additional perspectives on what is meant by quality in health care.  相似文献   
23.
24.
25.
26.
SARS-CoV-2 variants of concern (VOCs) have caused a significant increase in infections worldwide. Despite high vaccination rates in industrialized countries, the fourth VOC, Omicron, has outpaced the Delta variant and is causing breakthrough infections in individuals with two booster vaccinations. While the magnitude of morbidity and lethality is lower in Omicron, the infection rate and global spread are rapid. Using a specific IgG multipanel-ELISA with the spike protein’s receptor-binding domain (RBD) from recombinant Alpha, Gamma, Delta, and Omicron variants, sera from health-care workers from the Medical University of Vienna were tested pre-pandemic and post-vaccination (BNT162b2; ChAdOx1 nCoV-19). The cohort was continuously monitored by SARS-CoV-2 testing and commercial nucleocapsid IgG ELISA. RBD IgG ELISA showed significantly lower reactivity against the Omicron-RBD compared to the Alpha variant in all individuals (p < 0.001). IgG levels were independent of sex, but were significantly higher in BNT162b2 recipients <45 years of age for Alpha, Gamma, and Delta (p < 0.001; p = 0.040; p = 0.004, respectively). Pre-pandemic cross-reactive anti-Omicron IgG was detected in 31 individuals and was increased 8.78-fold after vaccination, regardless of vaccine type. The low anti-RBD Omicron IgG level could explain the breakthrough infections and their presence could also contribute to a milder COVID-19 course by cross-reactivity and broadening the adaptive immunity.  相似文献   
27.
BACKGROUND CONTEXT: Injuries at the cervicothoracic junction are common in patients with ankylosing spondylitis. These injuries present challenges for both initial and follow-up imagings. PURPOSE: To describe a case of a patient with ankylosing spondylitis who was treated with laminectomy and a cervicothoracic orthosis for a spinal epidural hematoma after a nondisplaced fracture at the cervicothoracic junction and to discuss the merits of stand-up magnetic resonance imaging (MRI) for follow-up evaluation of this type of injury. STUDY DESIGN/SETTING: Case report. METHODS: Clinical data of a patient with ankylosing spondylitis who sustained a nondisplaced C7 fracture are presented, followed by a detailed review of the literature concerning imaging techniques available for the evaluation of cervical spine trauma in this patient population. RESULTS: The patient was treated with emergent laminectomy and evacuation of the epidural hematoma, followed by definitive management in a cervicothoracic orthosis secondary to medical comorbidities. The patient was then successfully followed postoperatively with stand-up MRI because conventional imaging techniques could not adequately image the injury level in an upright position. CONCLUSIONS: Cervicothoracic injuries are common in patients with ankylosing spondylitis and may be difficult to follow with conventional imaging techniques. Stand-up MRI is a relatively new modality that may offer significant advantages over conventional imaging because of the ability to evaluate the cervicothoracic junction in a more functional position and the lack of a confining space such as that found in standard MRI units.  相似文献   
28.
29.
30.
BACKGROUND: Melatonin, the main secretory product of the pineal gland, inhibits the growth of several types of cancer cells. Melatonin limits human prostate cancer cell growth by a mechanism which involves the regulation of androgen receptor function but it is not clear whether other mechanisms may also be involved. METHODS: Time-course and dose-dependent studies were performed using androgen-dependent (LNCaP) and independent (PC3) prostate cancer cells. Cell number, cell viability, and cell cycle progression were studied. Neuroendocrine differentiation of these cells was evaluated by studying morphological and biochemical markers. Finally, molecular mechanisms including the participation of melatonin membrane receptors, intracellular cAMP levels, and the PKA signal transduction pathway were also analyzed. RESULTS: Melatonin treatment dramatically reduced the number of prostate cancer cells and stopped cell cycle progression in both LNCaP and PC3 cells. In addition, it induced cellular differentiation as indicated by obvious morphological changes and neuroendocrine biochemical parameters. The role of melatonin in cellular proliferation and differentiation of prostate cancer cells is not mediated by its membrane receptors nor related to PKA activation. CONCLUSIONS: The treatment of prostate cancer cells with pharmacological concentrations of melatonin influences not only androgen-sensitive but also androgen-insensitive epithelial prostate cancer cells. Cell differentiation promoted by melatonin is not mediated by PKA activation although it increases, in a transitory manner, intracellular cAMP levels. Melatonin markedly influences the proliferative status of prostate cancer cells. These effects should be evaluated thoroughly since melatonin levels are diminished in aged individuals when prostate cancer typically occurs.  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