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   6868篇
  免费   42篇
  国内免费   4篇
教育   5003篇
科学研究   424篇
各国文化   107篇
体育   538篇
综合类   6篇
文化理论   113篇
信息传播   723篇
  2024年   45篇
  2023年   29篇
  2022年   35篇
  2021年   88篇
  2020年   213篇
  2019年   257篇
  2018年   262篇
  2017年   287篇
  2016年   294篇
  2015年   187篇
  2014年   201篇
  2013年   1408篇
  2012年   198篇
  2011年   210篇
  2010年   165篇
  2009年   162篇
  2008年   195篇
  2007年   184篇
  2006年   155篇
  2005年   170篇
  2004年   146篇
  2003年   147篇
  2002年   133篇
  2001年   109篇
  2000年   108篇
  1999年   70篇
  1998年   68篇
  1997年   88篇
  1996年   88篇
  1995年   61篇
  1994年   76篇
  1993年   67篇
  1992年   79篇
  1991年   61篇
  1990年   63篇
  1989年   51篇
  1988年   60篇
  1987年   44篇
  1986年   55篇
  1985年   63篇
  1984年   61篇
  1983年   60篇
  1982年   47篇
  1981年   40篇
  1980年   41篇
  1979年   45篇
  1978年   47篇
  1977年   29篇
  1976年   26篇
  1975年   19篇
排序方式: 共有6914条查询结果,搜索用时 15 毫秒
891.
892.
    

Background and objective

Stroke volume variation (SVV) has high sensitivity and specificity in predicting fluid responsiveness. However, sinus rhythm (SR) and controlled mechanical ventilation (CV) are mandatory for their application. Several studies suggest a limited applicability of SVV in intensive care unit (ICU) patients. We hypothesized that the applicability of SVV might be different over time and within certain subgroups of ICU patients. Therefore, we analysed the prevalence of SR and CV in ICU patients during the first 24 h of PiCCO-monitoring (primary endpoint) and during the total ICU stay. We also investigated the applicability of SVV in the subgroups of patients with sepsis, cirrhosis, and acute pancreatitis.

Methods

The prevalence of SR and CV was documented immediately before 1241 thermodilution measurements in 88 patients.Results: In all measurements, SVV was applicable in about 24%. However, the applicability of SVV was time-dependent: the prevalence of both SR and CV was higher during the first 24 h compared to measurements thereafter (36.1% vs. 21.9%; P<0.001). Within different subgroups, the applicability during the first 24 h of monitoring ranged between 0% in acute pancreatitis, 25.5% in liver failure, and 48.9% in patients without pancreatitis, liver failure, pneumonia or sepsis.

Conclusions

The applicability of SVV in a predominantly medical ICU is only about 25%–35%. The prevalence of both mandatory criteria decreases over time during the ICU stay. Furthermore, the applicability is particularly low in patients with acute pancreatitis and liver failure.
  相似文献   
893.
    
This paper deals with the leader-following consensus problem of multi-agent systems with the consideration that each agent can only transmit its position state to the neighbors at irregular discrete sampling times. In the proposed algorithm, a continuous-discrete time observer is designed for the continuous estimation of both position and velocity from the discrete position information of the neighbors. These estimated states are then used for designing a continuous control law which solves the leader-following consensus problem. Moreover, the dynamics of the leader is not fixed and can be controlled through an external input. The stability analysis has been carried out by employing the Lyapunov approach which provides sufficient conditions to tune the parameters according to the maximum allowable sampling period. The developed algorithm has been simulated and then tested on an actual multi-robot system consisting of three differential drive wheeled robots. Both simulation and hardware results validate the effectiveness of the control algorithm.  相似文献   
894.
    
In the course of a decade of research on learning in technology‐centered classrooms, my research group has gained considerable understanding of why and how students learn science by designing technology. In this article I briefly review two dimensions in which science and technology share fundamental similarities: (a) the production and transformation of representations and (b∥ the action‐oriented language describing the two domains. Because it is fundamentally problematic to derive what ought to happen in science classrooms from other dimensions, I provide three episodes to illustrate what and how students know and learn science during technological design activities. Episodes and analyses embody the two dimensions previously outlined. Because these episodes are representative of the database established during an extensive research program, I suggest there is sufficient ground for using and investigating science‐through‐technology curricula. © 2001 John Wiley & Sons, Inc. J Res Sci Teach 38: 768–790, 2001  相似文献   
895.
Hemispheric laterality may be a useful concept in teaching, learning, training, and in understanding more about human development. To address this issue, a measure of hemispheric laterality was compared to musical and mathematical ability. The Human Information Processing Survey (HIPS) instrument, designed to measure hemispheric laterality, was administered to 101 participants who were then asked to provide a measure of their conceptual aptitude for mathematics and music. Scores were then compared through canonical correlation to test the hypothesis that perceived mathematical ability may be explained by left-brain hemisphere preference and musical by the right hemisphere. A relatively strong correlation was found between music ability and right-brain hemisphere preference. A relationship between math and left-brain hemisphere preference or integrated brain processing scores was found to be marginal. Ramifications to learning are discussed.  相似文献   
896.
This study explored the influence of university-based teacher education courses on preservice teachers as they engaged in the field-based portion of their preparation. Forty-two preservice teachers contributed reflective writings about the successes and challenges they faced during field experiences in light of knowledge and skills learned during their university-based coursework. Participants’ self-reflective writings were coded and analyzed for emerging themes that cut across all responses. The results indicated a shift from concerns about performance of teaching tasks in the classroom to concerns about the performance of students in terms of learning. This shift was consistent with a goal of the preservice program, namely, helping preservice teachers focus on student learning.  相似文献   
897.
This paper outlines an investigation of the incidence and impact of physical, verbal and property-violation bullying in 25 secondary schools within a partnership operating with Keele University. The investigation also considers the impact of antisocial behaviour on pupils and the effectiveness of intervention to secure improved behaviour patterns. Evidence shows that in any year 75 per cent of pupils are bullied but that severe and repeated bullying is likely to be perpetrated and suffered by about seven per cent of pupils. Four behaviour patterns can be identified: bullies, bullies who are also victims, victims and non-participants, and the link between behaviour and factors in developing self-esteem is explored. Successful intervention requires a change of attitude on the part of both pupils and the community, a willingness to report events, and an understanding of respect for personal space.  相似文献   
898.
Discriminating same from different multiitem arrays can be represented as a discrimination between arrays involving low variability and arrays involving high variability. In the present investigation, we first trained pigeons with the extreme values along the variability continuum (arrays containing 16 identical items vs. 16 nonidentical items), and we later tested the birds with arrays involving intermediate levels of variability; we created these testing arrays either by manipulating the combination of same and different items (mixture testing) or by changing the number of items in the same and different arrays (number testing). According to an entropy account (Young & Wasserman, Journal of Experimental Psychology: Animal Behavior Processes 23:157?C170, 1997), the particular means of changing variability should have no effect on same?Cdifferent discrimination performance: Equivalent variability should yield equivalent performance. In this critical test of an entropy account, we found that entropy could explain a large portion of our data, but not the entire collection of results.  相似文献   
899.
The purpose of this ecological study was to examine the impact of a library credit course on graduation rates and GPA using pre-existing records. Over 20?years of aggregate institutional data were analyzed to evaluate the course's impact on first-time-full-time, white, and black students. Results were mixed: students who took the course were less likely to graduate than their peers who did not take the course but enjoyed slightly higher GPAs at graduation. It was discovered that students taking the course are not representative of the overall student body and struggle academically. Implications for revisions to the library credit course are discussed.  相似文献   
900.
This article describes an interdisciplinary continuing education approach for health professionals in a rural remote area implemented by the Northern Educational Centre for Aging and Health (NECAH) at Lakehead University in Thunder Bay, Ontario, Canada. The article discusses issues of rural health care practice and the implications for practitioners’ educational needs. The key components involved in delivering interdisciplinary education and teamwork training are reviewed, followed by a discussion of the relevance of an interdisciplinary participatory approach for rural practitioners given their practice context and work style. Using NECAH's experience in planning and delivering a 5‐day interdisciplinary education program in palliative care as a case example, it is argued that simultanous attention to these issues in the design and delivery of continuing professional education for rural professionals contributes to a relevant educational experience in the short‐term and an increased interdisciplinary collaboration in the long‐term. The article suggests that NECAH's interdisciplinary participatory approach is a significant model for the continuing education of health professionals in rural remote areas.  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