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   3838篇
  免费   372篇
  国内免费   214篇
  2024年   4篇
  2023年   92篇
  2022年   65篇
  2021年   133篇
  2020年   150篇
  2019年   252篇
  2018年   219篇
  2017年   166篇
  2016年   216篇
  2015年   213篇
  2014年   273篇
  2013年   464篇
  2012年   219篇
  2011年   220篇
  2010年   195篇
  2009年   219篇
  2008年   196篇
  2007年   186篇
  2006年   121篇
  2005年   103篇
  2004年   96篇
  2003年   77篇
  2002年   76篇
  2001年   66篇
  2000年   54篇
  1999年   45篇
  1998年   19篇
  1997年   37篇
  1996年   28篇
  1995年   30篇
  1994年   34篇
  1993年   20篇
  1992年   21篇
  1991年   18篇
  1990年   16篇
  1989年   9篇
  1988年   10篇
  1987年   9篇
  1986年   13篇
  1985年   4篇
  1984年   7篇
  1983年   9篇
  1982年   5篇
  1981年   4篇
  1980年   1篇
  1979年   3篇
  1978年   2篇
  1977年   4篇
  1971年   1篇
排序方式: 共有4424条查询结果,搜索用时 859 毫秒
1.
2.
3.
4.
5.
This opinion piece offers a commentary on the four papers that address the theme of the development of self and other understanding with a view to highlighting the important contribution of developmental research to understanding of mechanisms of social cognition. We discuss potential mechanisms linking self–other distinction and empathy, implications for grouping motor, affective and cognitive domains under a single mechanism, applications of these accounts for joint action and finally consider self–other distinction in group versus dyadic settings.  相似文献   
6.
7.
Feed represents a substantial proportion of production costs in the dairy industry and is a useful target for improving overall system efficiency and sustainability. The objective of this study was to develop methodology to estimate the economic value for a feed efficiency trait and the associated methane production relevant to Canada. The approach quantifies the level of economic savings achieved by selecting animals that convert consumed feed into product while minimizing the feed energy used for inefficient metabolism, maintenance and digestion. We define a selection criterion trait called Feed Performance (FP) as a 1 kg increase in more efficiently used feed in a first parity lactating cow. The impact of a change in this trait on the total lifetime value of more efficiently used feed via correlated selection responses in other life stages is then quantified. The resulting improved conversion of feed was also applied to determine the resulting reduction in output of emissions (and their relative value based on a national emissions value) under an assumption of constant methane yield, where methane yield is defined as kg methane/kg dry matter intake (DMI). Overall, increasing the FP estimated breeding value by one unit (i.e. 1 kg of more efficiently converted DMI during the cow’s first lactation) translates to a total lifetime saving of 3.23 kg in DMI and 0.055 kg in methane with the economic values of CAD $0.82 and CAD $0.07, respectively. Therefore, the estimated total economic value for FP is CAD $0.89/unit. The proposed model is robust and could also be applied to determine the economic value for feed efficiency traits within a selection index in other production systems and countries.  相似文献   
8.
Numerous studies have shown that providing straw to pigs can reduce undesirable behaviours such as aggression, tail biting and stereotypy. The measurement of various neuromodulators can be helpful in assessing the development of positive behaviours and overall animal welfare. The oxytocin release is frequently linked to positive emotions and positive welfare. It has been suggested that oxytocin modulates the serotoninergic system. This study aims to investigate the potential effect of straw provision in pigs on peripheral levels of oxytocin and serotonin. In total, 18 mini-pigs were involved in an exploratory study conducted in two parallel groups, Enriched (n=10) and Control (n=8) groups. Pigs were divided by group and housed in pens of two individuals. Straw was provided continuously only in Enriched group and renewed each day for 2 weeks. Two blood samples were drawn from each animal 5 to 10 min before providing the straw, and 15 min after providing straw, during the 1st week, to analyse peripheral changes in oxytocin and serotonin before and after straw provision, and determine the existence of a putative short-term effect. The same procedure was carried out for Control group, without straw provision. Long-term effects of straw provision were also examined using blood samples drawn at the same hour from each animal in the 2nd and 3rd weeks. During this time, animals had the permanent possibility to explore the straw in Enriched group but not in Control group. At the end of each week, one animal-keeper completed two visual analogue scales for each mini-pig regarding the difficulty/ease to work with and handle it and its trust in humans. Results showed peripheral oxytocin increases in both groups after 2 weeks (P=0.02). Results did not demonstrate any effect of providing straw to allow exploratory behaviour on peripheral serotonin. Other results were not significant. This preliminary study explored the relationship between peripheral oxytocin and serotonin and the presence of straw that allow pigs to perform exploratory behaviour, suggesting that there was no relationship between them. Some future studies may include crossing oxytocin and serotonin with other parameters, such as behavioural measures, to obtain more information about the true state of the animal and any possible relationship with pig welfare.  相似文献   
9.
An L-rhamnose-binding isolectin named STL3 (subunit Mr, 21.5 k) was isolated from eggs of the steelhead trout (Oncorhynchus mykiss) in addition to STL1 (subunit Mr, 31.4 k) and STL2 (subunit Mr, 21.3 k) that had been already isolated. STLs were composed of non-covalently linked subunits. The primary structures of STL1 and STL3 were analyzed by the combined use of protein sequencing and cDNA sequencing. A cDNA encoding STL2, of which the protein sequence had been previously studied, was also analyzed. The STL1 subunit (289 amino acid residues) had different structural properties compared to those of the STL2 subunit (195 amino acid residues) and the STL3 subunit (195 amino acid residues); e.g., the number of repeated domain (three for STL1, and two for STL2 and STL3), although all of them were composed of tandemly repeated homologous domains (40 to 53% identities).

The lectin levels in various tissues and during the embryonic development showed that STL1 had different distribution and expression profiles from those of STL2 and STL3. Although STL1 could be detected in several tissues and serum of both male and female steelhead trout, STL2 and STL3 were only abundant in the ovary. STL2 and STL3 levels dramatically decreased just after hatching, however, the STL1 level increased temporarily. These results indicate that the multiple lectins from eggs of the steelhead trout form a novel rhamnose-binding lectin family with different structures and tissue distribution to share distinct functions in eggs.  相似文献   
10.
《Anthrozo?s》2013,26(2):128-142
Abstract

Research has shown that the presence of a companion animal reduces anxiety, encourages interaction among humans and enhances the way in which people are perceived. These are all effects which would be useful in a psychotherapeutic setting. On this basis the current study investigated the effect of the presence of a dog on the way in which people perceive psychotherapists. The study utilized an experimental design in which participants viewed a videotape of one of two therapists who were either with or without a dog. It was hypothesized that people would respond more positively to the psychotherapists when accompanied by a dog; specifically, that they would be more generally satisfied and would be more willing to disclose personal information, and that these effects would be influenced by attitudes towards pets. The first two hypotheses were confirmed. The effect was most pronounced among those who were the least positive toward the psychotherapist, demonstrating a ceiling effect. Contrary to the last hypothesis, attitudes toward pets had no influence on the perceptions of psychotherapists. History of pet ownership had only minimal impact on the results. Practical applications and directions for further research are discussed.  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