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   1084969篇
  免费   74518篇
  国内免费   1394篇
耳鼻咽喉   15229篇
儿科学   34958篇
妇产科学   28870篇
基础医学   155209篇
口腔科学   29761篇
临床医学   96492篇
内科学   206052篇
皮肤病学   24544篇
神经病学   82196篇
特种医学   43329篇
外国民族医学   201篇
外科学   164576篇
综合类   21952篇
现状与发展   1篇
一般理论   274篇
预防医学   75972篇
眼科学   24679篇
药学   87015篇
  7篇
中国医学   2809篇
肿瘤学   66755篇
  2019年   7928篇
  2018年   11488篇
  2017年   9076篇
  2016年   10258篇
  2015年   11443篇
  2014年   15507篇
  2013年   22585篇
  2012年   31103篇
  2011年   32843篇
  2010年   19230篇
  2009年   18074篇
  2008年   30406篇
  2007年   32615篇
  2006年   33206篇
  2005年   31551篇
  2004年   30223篇
  2003年   29082篇
  2002年   27991篇
  2001年   60397篇
  2000年   61888篇
  1999年   51285篇
  1998年   12595篇
  1997年   11149篇
  1996年   11135篇
  1995年   10449篇
  1994年   9457篇
  1993年   8955篇
  1992年   38093篇
  1991年   36545篇
  1990年   36011篇
  1989年   34540篇
  1988年   31087篇
  1987年   30211篇
  1986年   28422篇
  1985年   26662篇
  1984年   19331篇
  1983年   16237篇
  1982年   8926篇
  1979年   17209篇
  1978年   11526篇
  1977年   10321篇
  1976年   8923篇
  1975年   10147篇
  1974年   11755篇
  1973年   11367篇
  1972年   10848篇
  1971年   10179篇
  1970年   9323篇
  1969年   9005篇
  1968年   7988篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
Dehydrogenase activity is frequently used to assess the general condition of microorganisms in soil and activated sludge. Many studies have investigated the inhibition of dehydrogenase activity by various compounds, including heavy metal ions. However, the time after which the measurements are carried out is often chosen arbitrarily. Thus, it can be difficult to estimate how the toxic effects of compounds vary during the reaction and when the maximum of the effect would be reached. Hence, the aim of this study was to create simple and useful mathematical model describing changes in dehydrogenase activity during exposure to substances that inactivate enzymes. Our model is based on the Lagergrens pseudo-first-order equation, the rate of chemical reactions, enzyme activity, and inactivation and was created to describe short-term changes in dehydrogenase activity. The main assumption of our model is that toxic substances cause irreversible inactivation of enzyme units. The model is able to predict the maximum direct toxic effect (MDTE) and the time to reach this maximum (TMDTE). In order to validate our model, we present two examples: inactivation of dehydrogenase in microorganisms in soil and activated sludge. The model was applied successfully for cadmium and copper ions. Our results indicate that the predicted MDTE and TMDTE are more appropriate than EC50 and IC50 for toxicity assessments, except for long exposure times.  相似文献   
134.
As countries implement Article 11 of the World Health Organization (WHO) Framework Convention on Tobacco Control, graphic warning labels that use images of people and their body parts to illustrate the consequences of smoking are being added to cigarette packs. According to exemplification theory, these case examples—exemplars—can shape perceptions about risk and may resonate differently among demographic subpopulations. Drawing on data from eight focus groups (N = 63) with smokers and nonsmokers from vulnerable populations, this qualitative study explores whether people considered exemplars in their reactions to and evaluations of U.S. graphic health warning labels initially proposed by the Food and Drug Administration. Participants made reference to prior and concurrent mass media messages and exemplars during the focus groups and used demographic cues in making sense of the images on the warning labels. Participants were particularly sensitive to age of the exemplars and how it might affect label effectiveness and beliefs about smoking. Race and socioeconomic status also were salient for some participants. We recommend that exemplars and exemplification be considered when selecting and evaluating graphic health warnings for tobacco labels and associated media campaigns.  相似文献   
135.
136.
137.
138.
Objective: Asthma disproportionately impacts and has poorer outcomes in low-income, minority, and inner-city children. The home environment has a profound impact on a child's asthma. Home-based asthma visits have the potential to positively impact a child's asthma, especially in targeted populations. The purpose of this integrative review is 1.) to explore the effectiveness of home-based education and environmental measures and 2.) to explore specific indicators and tools to measure pediatric asthma control and program effectiveness. Data Sources: Medline, CINHAL, and Ovid databases were searched from 2010 to 2017 utilizing the keywords healthy homes AND asthma and home based interventions AND asthma. Study Selections: A total of 71 articles were retrieved of which 27 articles met the inclusion criteria of English language, human subjects, and the inclusion of pediatric populations. Three additional articles were hand-searched from previous references. In total, 30 articles were reviewed. A quality appraisal was conducted utilizing standardized appraisal tools. Results: Home-based asthma education and environmental interventions have proven to be effective. The programs reviewed varied in types of interventions, intensity and duration, the type of provider, length of follow-up, and outcome measures. Successful programs were patient-centered, included a home assessment and individualized education and interventions, and were collaborative. Multiple outcome indicators such as health care utilization, asthma control, missed days of school or productivity, asthma symptoms, and verification of environmental remediation have been utilized. Conclusion: Home-based asthma programs can be beneficial to children with poorly controlled asthma and have the potential to be cost-effective.  相似文献   
139.
Electrocardiogram (ECG) signal gives a lot of information on the physiology of heart. In reality, noise from various sources interfere with the ECG signal. To get the correct information on physiology of the heart, noise cancellation of the ECG signal is required. In this paper, the effectiveness of extended Kalman smoother (EKS) with the differential evolution (DE) technique for noise cancellation of the ECG signal is investigated. DE is used as an automatic parameter selection method for the selection of ten optimized components of the ECG signal, and those are used to create the ECG signal according to the real ECG signal. These parameters are used by the EKS for the development of the state equation and also for initialization of the parameters of EKS. EKS framework is used for denoising the ECG signal from the single channel. The effectiveness of proposed noise cancellation technique has been evaluated by adding white, colored Gaussian noise and real muscle artifact noise at different SNR to some visually clean ECG signals from the MIT-BIH arrhythmia database. The proposed noise cancellation technique of ECG signal shows better signal to noise ratio (SNR) improvement, lesser mean square error (MSE) and percent of distortion (PRD) compared to other well-known methods.  相似文献   
140.
Infantile hemangiomas (IHs) are the most common benign tumor of infancy, characterized by a natural history of early proliferation in the first months of life to eventual involution during childhood, often with residual fibrofatty tissue. Once involution has been achieved, IHs do not typically recur. We present two cases of exogenous growth hormone therapy resulting in the recurrence of IHs in late childhood, supported by radiological, immunohistochemical, in vitro, and in vivo evidence.  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