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   12379篇
  免费   1357篇
  国内免费   4篇
  2021年   167篇
  2019年   121篇
  2018年   146篇
  2017年   155篇
  2016年   243篇
  2015年   354篇
  2014年   419篇
  2013年   547篇
  2012年   602篇
  2011年   614篇
  2010年   394篇
  2009年   350篇
  2008年   514篇
  2007年   548篇
  2006年   487篇
  2005年   500篇
  2004年   465篇
  2003年   459篇
  2002年   442篇
  2001年   296篇
  2000年   319篇
  1999年   253篇
  1998年   165篇
  1997年   144篇
  1996年   128篇
  1995年   126篇
  1994年   105篇
  1993年   134篇
  1992年   233篇
  1991年   226篇
  1990年   217篇
  1989年   199篇
  1988年   218篇
  1987年   189篇
  1986年   173篇
  1985年   188篇
  1984年   180篇
  1983年   164篇
  1982年   123篇
  1981年   126篇
  1980年   112篇
  1979年   162篇
  1978年   113篇
  1977年   115篇
  1976年   117篇
  1975年   104篇
  1974年   106篇
  1973年   107篇
  1971年   90篇
  1969年   84篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Gordon Murray 《CMAJ》1953,69(3):296-299
  相似文献   
2.
A series of in vitro experiments were conducted to assess three fibrolytic enzyme preparations as potential feed additives in equine diets. The three fibrolytic enzyme preparations were a concentrated cellulase (E1), an acid cellulase (E2) and a concentrated xylanase (E3). The enzymes were evaluated on their ability to modify the cell wall fraction of high-temperature dried lucerne (HTL) under various experimental conditions including differences in temperature, pH, incubation period, substrate levels and particle size to enable selection of the enzyme preparation most effective in the hydrolysis of lucerne. Results showed enzyme activities (as measured by reducing sugar assays) to be greatest at 50 °C, pH 5 and over an incubation period of greater than 20 h. E1 exhibited the greatest effect on total monosaccharide release from the HTL compared to E2 and E3. Moreover, dry matter (DM) and total non-starch polysaccharide (TNSP) losses were also greater in HTL treated with E1 compared to E2 and E3. Therefore, since the cell wall fraction of HTL contained substantial amounts of cellulose, the enzyme with the highest cellulase activity (Enzyme 1) was most effective in hydrolysing the cell walls of HTL. Consequently, it would appear that the application of exogenous fibrolytic enzyme preparations to forages requires the chemical characterisation of the target forage to enable selection of enzymes that are (a) most suitable to degrade the cell wall components of the candidate forage and (b) effective under field conditions.  相似文献   
3.

Introduction  

Total cholesterol (TC) and blood pressure (BP) are likely to take a dynamic course over time in patients with systemic lupus erythematosus (SLE). This would have important implications in terms of using single-point-in-time measurements of these variables to assess coronary artery disease (CAD) risk. The objective of this study was to describe and quantify variability over time of TC and BP among patients with SLE and to determine their correlates.  相似文献   
4.
Are we able to infer what happened to a person from a brief sample of his/her behaviour? It has been proposed that mentalising skills can be used to retrodict as well as predict behaviour, that is, to determine what mental states of a target have already occurred. The current study aimed to develop a paradigm to explore these processes, which takes into account the intricacies of real-life situations in which reasoning about mental states, as embodied in behaviour, may be utilised. A novel task was devised which involved observing subtle and naturalistic reactions of others in order to determine the event that had previously taken place. Thirty-five participants viewed videos of real individuals reacting to the researcher behaving in one of four possible ways, and were asked to judge which of the four ‘scenarios’ they thought the individual was responding to. Their eye movements were recorded to establish the visual strategies used. Participants were able to deduce successfully from a small sample of behaviour which scenario had previously occurred. Surprisingly, looking at the eye region was associated with poorer identification of the scenarios, and eye movement strategy varied depending on the event experienced by the person in the video. This suggests people flexibly deploy their attention using a retrodictive mindreading process to infer events.  相似文献   
5.
6.
7.
Manitoba     
Ross Mitchell 《CMAJ》1944,51(5):475-476
  相似文献   
8.
9.
10.
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