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   3098篇
  免费   233篇
  国内免费   3篇
  2023年   7篇
  2022年   9篇
  2021年   46篇
  2020年   35篇
  2019年   51篇
  2018年   62篇
  2017年   56篇
  2016年   94篇
  2015年   137篇
  2014年   162篇
  2013年   232篇
  2012年   251篇
  2011年   243篇
  2010年   161篇
  2009年   155篇
  2008年   159篇
  2007年   204篇
  2006年   185篇
  2005年   177篇
  2004年   148篇
  2003年   138篇
  2002年   134篇
  2001年   29篇
  2000年   24篇
  1999年   24篇
  1998年   29篇
  1997年   24篇
  1996年   25篇
  1995年   18篇
  1994年   22篇
  1993年   18篇
  1992年   18篇
  1991年   20篇
  1990年   28篇
  1989年   14篇
  1988年   16篇
  1987年   12篇
  1986年   17篇
  1985年   17篇
  1984年   17篇
  1983年   8篇
  1982年   15篇
  1981年   14篇
  1980年   15篇
  1979年   9篇
  1978年   8篇
  1977年   5篇
  1976年   5篇
  1972年   6篇
  1969年   5篇
排序方式: 共有3334条查询结果,搜索用时 15 毫秒
1.
This study evaluated whether showing a video of the different ways of raising goats for milk affected consumer acceptability. Four combinations, 2 Videos (intensive [INT] and semiextensive [SEM] system) × 2 Milk Types (semiskimmed [S] and whole [W] milk), were evaluated by 70 habitual consumers of goat milk, who scored their liking and purchase intention during blind (B), expected (E), and informed (I) acceptability sessions. In the B session, consumers tasted both milk types without information. S samples were preferred over W samples. In the E session, SEM video created high expectations in terms of milk liking and purchase intent, whereas the opposite happened when showing INT video. In the I session, consumers showed a clear preference for combinations created using SEM video, regardless of milk type. W-SEM and S-INT were worse (negative disconfirmation) and better (positive disconfirmation) than expected, respectively. A complete assimilation toward expectations occurred only for S-INT. INT video adversely affected the acceptability of S samples. Concerning purchase intent, W-SEM and S-SEM were worse than expected, but the assimilation was complete only for S-SEM: SEM video increased purchase intent for S samples.  相似文献   
2.
In clinical research and in more general classification problems, a frequent concern is the reliability of a rating system. In the absence of a gold standard, agreement may be considered as an indication of reliability. When dealing with categorical data, the well‐known kappa statistic is often used to measure agreement. The aim of this paper is to obtain a theoretical result about the asymptotic distribution of the kappa statistic with multiple items, multiple raters, multiple conditions, and multiple rating categories (more than two), based on recent work. The result settles a long lasting quest for the asymptotic variance of the kappa statistic in this situation and allows for the construction of asymptotic confidence intervals. A recent application to clinical endoscopy and to the diagnosis of inflammatory bowel diseases (IBDs) is shortly presented to complement the theoretical perspective.  相似文献   
3.
4.
5.
Transgenic Research - Chloroplast transformation has many potential advantages for the production of recombinant proteins in plants. However, it has been reported that chloroplast expression of...  相似文献   
6.
Flow cytometry is a widely recognized method of rapidly assessing the ploidy and proliferation status of experimental and solid tumors. In the present work, a variety of human cancers from various sites (lung, head and neck, etc.), of traditional interest in our laboratory, have been analyzed. In agreement with a number of recent reports, a general heterogeneity of human solid tumors can be evidenced. In particular: (a) solid tumors are characterized by a variable degree of aneuploidy; (b) the internal structure of solid tumors is highly heterogeneous especially with respect to the fraction of aneuploid malignant cells and their distribution through the cycle phases; and (c) some solid tumors are also characterized by the presence, to a variable extent, in the tumor of mass of multiple cell clones. Static fluorimetry of Feulgen-stained (mitotic) single cells offers a way to confirm this kind of observations.  相似文献   
7.
8.
9.
10.
We have studied the pattern of association between the season of conception and cytosolic low molecular weight phosphotyrosine phosphatase (ACP1) genetic polymorphism in 329 consecutively newborn infants from the population of Penne and 361 consecutively newborn infants from the population of Rome. In addition, 329 mothers were studied in the population of Penne. A concordant, highly significant association was observed in the two populations between ACP1 parameters and the season of conception of newborn infants. The total activity of ACP1 shows a minimum in infants conceived in January–February and a maximum in those conceived at the end of the solar year. Analysis of the joint mother-newborn ACP1 distribution in relation to the season of fertilisation has shown that among mothers carrying ACP1*A (the allele showing the lowest activity), the proportion of newborns carrying this allele is higher in those conceived in the first months of the year than in those conceived subsequently. Since ACP1 probably functions as a phosphotyrosine phosphatase and as a flavin mononucleotide phosphatase, low activity could enhance the metabolic rate and would be advantageous in a cold environment. The cycle of variation of ACP1 in infants follows the cycle of solar illumination. It is possible that individuals who have a genetic background allowing them to adapt easily and readily to seasonal demand are more successful in reproducing themselves. The population of zygotes conceived in a given season would therefore reproduce the pattern of gene combination more fit for that season. Received: 15 June 1997 / Accepted: 31 July 1997  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