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   7682篇
  免费   643篇
  国内免费   28篇
耳鼻咽喉   61篇
儿科学   193篇
妇产科学   101篇
基础医学   1041篇
口腔科学   244篇
临床医学   760篇
内科学   1269篇
皮肤病学   63篇
神经病学   908篇
特种医学   298篇
外科学   916篇
综合类   188篇
一般理论   33篇
预防医学   765篇
眼科学   173篇
药学   948篇
中国医学   12篇
肿瘤学   380篇
  2022年   70篇
  2021年   161篇
  2020年   110篇
  2019年   138篇
  2018年   162篇
  2017年   106篇
  2016年   163篇
  2015年   175篇
  2014年   213篇
  2013年   349篇
  2012年   489篇
  2011年   456篇
  2010年   269篇
  2009年   240篇
  2008年   418篇
  2007年   424篇
  2006年   412篇
  2005年   388篇
  2004年   381篇
  2003年   354篇
  2002年   350篇
  2001年   141篇
  2000年   117篇
  1999年   134篇
  1998年   94篇
  1997年   65篇
  1996年   73篇
  1995年   68篇
  1994年   65篇
  1993年   60篇
  1992年   116篇
  1991年   97篇
  1990年   87篇
  1989年   90篇
  1988年   80篇
  1987年   102篇
  1986年   87篇
  1985年   100篇
  1984年   78篇
  1983年   53篇
  1982年   50篇
  1981年   57篇
  1980年   43篇
  1979年   56篇
  1978年   53篇
  1977年   45篇
  1974年   47篇
  1973年   47篇
  1971年   45篇
  1970年   39篇
排序方式: 共有8353条查询结果,搜索用时 46 毫秒
1.
2.
Background: It is widely known that a proportion of university students use drugs. However, much less is known about how they source and supply their drugs. Objectives: In this article, we investigate student drug trading activity, including how they obtained their drugs, whether they sold drugs, and the extent to which their drug trading might be described as a form of “social supply”. Methods: A survey was conducted of all students across seven of the nine universities of Wales. In total, 7855 students submitted a questionnaire and 1877 of these reported drug use in the current academic year. All students who reported using one or more illegal drugs in the current academic year were asked how they obtained their drugs, how they funded their drug use, whether they had sold, traded or given away illegal drugs, along with their motives for drug trading. Results: The results showed that about half of users obtained drugs solely from friends and associates and one-fifth obtained them solely from external dealers. One-quarter used friends and associates as well as external markets. In many cases, supplying drugs amounted to sharing them or giving them away. However, over one-third of students said that they had sold drugs. Conclusions: Overall, the methods of sourcing and supplying drug among university students shares features of both “social supply” and “traditional” drug markets. We conclude that the student drug market investigated is best described as a “hybrid” combination of both.  相似文献   
3.
ABSTRACT

Forest workers, including loggers, foresters, and wildland firefighters, are regularly exposed to some of the most fatal occupational environments in the United States. These hazardous work environments may become even more complex and dynamic when subject to bark beetle outbreaks that have resulted in significant tree mortality. The impacts of tree death from bark beetles are significant, with the cumulative 17-year (2000–2016) footprint for bark beetle caused tree mortality estimated at 54 million acres. However, how workers think about and act in these environments is understudied. This study, therefore, approaches the issue of beetle kill and forest worker safety by examining the perspectives or workers themselves. Its contribution is to leverage ethnographic research to provide insights that can generate new research questions, better inform outreach, and ultimately improve worker safety outcomes. The resulting insights show that beetle kill was understood by workers as a hazard that increased the complexity and dynamism of the work environment, making situational awareness both more necessary and more difficult to maintain. While much research about situational awareness focuses on hazardous situations, it is suggested that building adequate situational awareness should also include broader considerations of organizational communication, as well as training and experience considered over the course of entire careers.  相似文献   
4.
5.
6.
7.
8.
Central dopamine function is reduced by decreasing the availability of the catecholamine precursor, tyrosine, using a tyrosine-free amino acid mixture containing multiple large neutral as well as branched chain amino-acids, which compete with tyrosine for uptake into the brain. Current mixtures are cumbersome to make and administer, and unpalatable to patients and volunteers. Here, we investigate whether individual or limited amino-acid combinations could reduce brain tyrosine levels and hence dopamine function. Measurements of regional brain tyrosine levels, catecholamine and indoleamine synthesis (L-DOPA and 5-HTP accumulation, respectively) were used to identify an effective paradigm to test in neurochemical, behavioral and fos immunocytochemical models. Administration of leucine or isoleucine, or a mixture of leucine, isoleucine, and valine reduced tyrosine and 5-HTP, but not L-DOPA accumulation. A mixture of leucine, valine, and isoleucine supplemented with tryptophan reduced brain tyrosine and L-DOPA, but not 5-HTP. In microdialysis experiments this amino-acid mixture reduced basal and amphetamine-evoked striatal dopamine release, as well as amphetamine-induced hyperactivity. This mixture also reduced amphetamine-induced fos expression in striatal areas. In conclusion, the present study identified a small combination of amino acids that reduces brain tyrosine and dopamine function in a manner similar to mixtures of multiple amino acids. This minimal mixture may have use as a dopamine reducing paradigm in patient and volunteer studies.  相似文献   
9.
Neonatal autopsy findings are valuable additions to the information base for current cases and future perinatal care, so the reported decline in the autopsy rate is disturbing. In order to estimate the prevalence of the neonatal autopsy among a large population of deaths, we surveyed participating institutions of the Study Group for Complications of Perinatal Care. Investigators from 37 neonatal intensive care units, located in 9 children's hospitals, 4 hospitals for women and infants, and 24 full-service pediatric and adult care hospitals, reported their neonatal death and autopsy rates for 1989. The overall neonatal autopsy rate was 51% among 1645 neonatal deaths. The rate was variable, ranging from 22 to 100%. We found the neonatal autopsy rate to be lower than previously reported and not apparently influenced by the type of center or by the type of medical staff at the centers. In order to assess and potentially reverse the current low rate, the influence of neonatal demographic and clinical factors, as well as physician-related factors, must be studied.  相似文献   
10.
Study Objective . To compare digoxin tablets and liquid-filled capsules with respect to excretion of the drug and its metabolites in urine and feces at steady state. Design . A randomized, crossover trial, each period lasting 3 weeks, with no washout period. Setting . A university hospital. Patients . Six patients, five of whom were elderly, with histories of gastrointestinal disorders, such as hypochlorhydria, intestinal bacterial overgrowth, and inflammatory bowel disease. Interventions . The patients received digoxin once/day in either tablet or capsule form for 3 weeks, and then were switched to the other formulation. Total urinary and fecal excretion from the last 3 days of each regimen were analyzed for the drug and metabolites. Measurements and Main Results . No statistically significant differences were found between tablets and capsules in recovery of digoxin or its metabolites in urine or feces (p=0.05). One subject had a 4-fold increase in urinary drug excretion and 50% decrease in fecal excretion after taking the capsules compared with tablets. Intersubject variability in extent and type of metabolite excretion was greater than intrasubject variability. Conclusions . Fecal analyses may be an accurate way to classify patients as formers of digoxin reduction products.  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