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   933篇
  免费   54篇
  国内免费   55篇
  2024年   3篇
  2023年   35篇
  2022年   41篇
  2021年   66篇
  2020年   32篇
  2019年   48篇
  2018年   46篇
  2017年   21篇
  2016年   34篇
  2015年   54篇
  2014年   57篇
  2013年   58篇
  2012年   51篇
  2011年   49篇
  2010年   32篇
  2009年   50篇
  2008年   54篇
  2007年   48篇
  2006年   19篇
  2005年   20篇
  2004年   19篇
  2003年   19篇
  2002年   14篇
  2001年   9篇
  2000年   13篇
  1999年   15篇
  1998年   10篇
  1997年   13篇
  1996年   7篇
  1995年   7篇
  1994年   9篇
  1993年   17篇
  1992年   5篇
  1991年   7篇
  1990年   10篇
  1989年   3篇
  1988年   5篇
  1987年   6篇
  1986年   4篇
  1985年   6篇
  1984年   6篇
  1983年   2篇
  1982年   6篇
  1981年   5篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1970年   1篇
排序方式: 共有1042条查询结果,搜索用时 15 毫秒
191.
视觉感知的一系列研究都支持大范围拓扑感知的理论.拓扑性质作为整体性质,是视觉感知的基础.视觉对图形拓扑特征差异的感知要优先于对局部特征差异的感知.采用Y迷宫研究了小鼠对不同拓扑性质图形的识别.训练小鼠学习识别圆环和实心矩形这一对拓扑性质不同的图形,之后用拓扑特征相同或不同的其他图形测试小鼠,这些图形包括空心矩形、实心圆、缺口的圆环、缺口的空心矩形.实验结果表明,学会识别圆环(奖励)和实心矩形(无奖励)的小鼠无法区分实心圆和实心矩形以及圆环和空心矩形,但是能够分别从缺口圆环、缺口的空心矩形、实心圆与空心矩形组成的图形对中识别出空心矩形.因此证实了小鼠的视觉系统能够感知拓扑特征的差异并且具有对拓扑性质的概括能力.结果为拓扑知觉对视觉系统来说是基本的这一假设提供了证据.  相似文献   
192.
The labeling of retina ganglion cell and optic tectum phospholipids was determined in chickens given an intraocular injection of 32P and then either exposed to light or maintained in the dark. Significantly higher labeling was found in the optic tectum phospholipids of light-exposed compared with dark-maintained animals after 3-24 h of labeling. In the ganglion cells, the labeling of phospholipids increased in dark with respect to light at 15 and 30 min of labeling; from 60 min to 24 h, the labeling of phospholipids was significantly higher in light with respect to dark, even if the precursor pool showed a higher labeling in dark at all times studied. When labeling was allowed to proceed in the dark for 30 min and then half of the animals were exposed to light for 15 min, the labeling of ganglion cell phospholipids of light-exposed animals was significantly higher than those of animals kept in the dark. No individual phospholipid accounted for the differences observed in the labeling of the total phospholipid pool. These results are interpreted as an increase in the biosynthesis of phospholipids in the ganglion cell somas in light with respect to dark.  相似文献   
193.
194.
史春妹  谢佳君  顾佳音  刘丹  姜广顺 《生态学报》2021,41(12):4685-4693
东北虎个体的自动识别是种群数量评估和制定有效保护策略的重要基础。以东北虎林园和怪坡虎园38 只虎为研究对象,将目标检测方法首次应用到东北虎个体识别研究中,采用多种深度卷积神经网络模型,以实现虎个体的自动识别。首先通过相机在不同角度对 38 只东北虎进行拍摄取样,建立包含13579张图像的虎样本数据集。由于虎的体侧条纹信息不具有对称性,所以运用单次多盒目标检测(Single Shot MultiBox Detector, SSD)方法,对虎的躯干左侧条纹、右侧条纹以及脸部等不同部位图像,进行自动检测并分割提取,极大节省手工截取时间。在检测分割出的左右侧及脸部不同部位图片基础上,运用上、下、左、右平移变换进行数据增强,使图片数目扩大为原来的5 倍。采用LeNet、AlexNet、ZFNet、VGG16、ResNet34共5 种卷积神经网络模型进行个体自动识别。为了提高识别准确率,运用平均值和最大值不同组合方式来优化池化操作,并在全连接层引入概率分别为0.1、0.2、0.3、0.4的丢弃(Dropout)操作防止过拟合。实验表明,目标检测模型耗时较少,截取分割老虎不同部位条纹能达到0.6 s/张,远快于人工截取速度,并且在测试集上准确率能达到97.4%。不同姿态下的目标部位都能正确识别并分割。ResNet34模型的准确率优于其他网络模型,左右侧条纹以及脸部图像识别准确率分别为93.75%、97.01%和 86.28%,右侧条纹识别准确率优于左侧条纹和脸部图像。研究为野生虎自动相机影像的识别提供技术参考。在未来研究中,对东北虎个体影响数据进行扩充,选取更多影像数据进行训练,使网络具有更强的适应性,从而实现更准确的个体识别。  相似文献   
195.
Being able to abstract relations of similarity is considered one of the hallmarks of human cognition. While previous research has shown that other animals (e.g. primates) can attend to relational similarity, they struggle to focus on object similarity. This is in contrast with humans. And it is precisely the ability to attend to objects that it is argued to make relational reasoning uniquely human. What about invertebrates? Despite earlier studies indicating that bees are capable of learning abstract relationships (e.g. ‘same’ and ‘different’), no research has investigated whether bees can spontaneously attend to relational similarity and whether they can do so when relational matches compete with object matches. To test this, a spatial matching task (with and without competing object matches) previously used with children and great apes was adapted for use with wild-caught bumblebees. When object matches were not present, bumblebees spontaneously used relational similarity. Importantly, when competing object matches were present, bumblebees still focused on relations over objects. These findings indicate that the absence of object bias is also present in invertebrates and suggest that the relational gap between humans and other animals is due to their preference for relations over objects.  相似文献   
196.
The aim of the present study was to compare the perceived risks of air pollution from industry and traffic in the Moerdijk region in The Netherlands, and to identify the demographic and psychometric variables that are associated with these perceived risks. We sent out a questionnaire and risk perceptions were explored using multiple regression models. The results showed that the perceived risks of industrial air pollution were higher than for those of traffic-related air pollution. The perceived risk of industrial air pollution was associated with other variables than that of traffic. For industry, the psychometric variable affect prevailed. For traffic-related air pollution, the demographic variables age and educational level prevailed, although affect was also apparent. Which source was considered as the major source—traffic or industry—depended on a high risk perception of industrial air pollution, and not on variation in risk perception of traffic-related air pollution. These insights can be used as an impetus for the local risk management process in the Moerdijk region. We recommend that local authorities consider risk perception as one of the targets in local risk management strategies as well.  相似文献   
197.
According to the mirror neurons data there exist areas in the premotor cortex that are activated both during action perception and action execution. It was hypothesized that posture maintenance would be impaired by simultaneous action perception in concordance with cognitive dissonance theory. A test was conducted during which 23 neurologically normal humans were to maintain their posture erect on the forceplate and to listen to the action-related sentences. Tests of differences and Friedman analysis of variance proved that listening to sentences that describe different actions and movements in the first and the third person impairs postural control in comparison with listening to sentences that describe objects of nature and everyday life.  相似文献   
198.
199.
200.
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