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   400篇
  免费   22篇
  国内免费   20篇
  2023年   4篇
  2022年   1篇
  2021年   4篇
  2020年   10篇
  2019年   21篇
  2018年   9篇
  2017年   11篇
  2016年   14篇
  2015年   19篇
  2014年   24篇
  2013年   36篇
  2012年   7篇
  2011年   24篇
  2010年   20篇
  2009年   34篇
  2008年   38篇
  2007年   26篇
  2006年   14篇
  2005年   11篇
  2004年   7篇
  2003年   12篇
  2002年   17篇
  2001年   8篇
  2000年   4篇
  1999年   9篇
  1998年   3篇
  1997年   2篇
  1996年   9篇
  1995年   3篇
  1994年   7篇
  1993年   9篇
  1992年   5篇
  1991年   4篇
  1990年   8篇
  1989年   4篇
  1987年   1篇
  1985年   2篇
  1983年   1篇
排序方式: 共有442条查询结果,搜索用时 15 毫秒
1.
2.
A population‐based cervical screening programme issued invitations to women with no record of a previous smear. This call was very good value, at £5780 per life saved or £159 per life‐year saved at 1991 prices. The first priority for the cervical screening service should be comprehensive coverage.  相似文献   
3.
4.
ABSTRACT

In most mammals, adults produce relatively low frequency vocalizations compared to those of juveniles. This rule is not maintained however at least in four species of ground squirrels, whose juveniles call at the adult's fundamental frequency. These findings have been obtained however with separate sets of juveniles and adults and no data is available concerning the ontogeny linked to these differences. Here we analyze the acoustic structure of alarm calls of the same Yellow Spermophilus fulvus and Speckled S. suslicus ground squirrel individuals, recorded as pups and as adults after hibernation. We found the fundamental frequencies of adults within the same frequency ranges as those of pups, in spite of the significant difference in body mass. In ground squirrels, severing the relationship between body size and call frequency removes some vocal cues to age. We discuss some functional hypotheses advanced to explain manipulations with fundamental frequencies in ground squirrels and other animals, and suggest the lack of data for discussing the mechanisms of such vocal tuning.  相似文献   
5.
ABSTRACT

Seasonal changes of parameters of full song were studied in a free-living population of chaffinches Fringilla coelebs during one entire reproductive period. Approximately 7000 strophes sung by 14 male chaffinches were recorded and analysed by sonography and a particular oscillographic method. While the general pattern of song strophes, i.e. characteristics of elements, number and arrangement of phrases, and final flourish, remained constant throughout the reproductive period, full song varied with respect to the repetition rate of strophes, number of strophe types used, intensity of singing, duration of strophes, and percentage of incomplete strophes sung. These changes are discussed as results of learning processes, social interactions in the population, and endogenous mechanisms activating memorized information.  相似文献   
6.
Social monitoring of the actions of group members is thought to be a key development associated with group living. Humans constantly monitor the behaviour of others and respond to them in a flexible way depending on past interactions and the current social context. While other primates have also been reported to change their behaviour towards other group members flexibly based on the current state of their relationship, empirical evidence is typically linked to contextually specific events such as aggressive or reproductive interactions. In the cooperatively breeding meerkat (Suricata suricatta), we investigated whether subordinate females use frequently emitted, non-agonistic close calls to monitor the location of the dominant female and whether they subsequently adjust their response based on recent social interactions during conflict and non-conflict periods. Subjects discriminated between the close calls of the dominant female and control playbacks, responding by approaching the loudspeaker and displaying submissive behaviour only if they were currently threatened by eviction. Our results suggest that meerkats assess the risk for aggressive interactions with close associates depending on social circumstances, and respond accordingly. We argue that social monitoring based on non-agonistic cues is probably a common mechanism in group-living species that allows the adjustment of behaviour depending on variation in relationships.  相似文献   
7.
An audit of the screening history of all new cervical cancer cases has been a requirement since April 2007. While NHS cervical screening programmes (NHSCSP) guidance requires that women diagnosed with cervical cancer are offered the findings of the audit, as yet there has been no research to investigate the psychological impact that meeting to discuss the findings might have on patients. This is in spite of the fact that cytological under‐call may play a role in as many as 20% of cervical cancer cases. This review draws on the literature concerning breaking bad news, discussing cancer and disclosing medical errors, in order to gain insight into both the negative and positive consequences that may accompany a cervical screening review meeting. We conclude that while patients are likely to experience some distress at disclosure, there are also likely to be positive aspects, such as greater trust and improved perception of care.  相似文献   
8.
ABSTRACT

Probably all odontocetes use echolocation for spatial orientation and detection of prey. We used a four hydrophone “Y” array to record the high frequency clicks from free-ranging White-beaked Dolphins Lagenorhynchus albirostris and captive Harbour Porpoises Phocoena phocoena. From the recordings we calculated distances to the animals and source levels of the clicks. The recordings from White-beaked Dolphins were made in Iceland and those from Harbour Porpoises at Fjord & Baelt, Kerteminde, Denmark during prey capture. We used stringent criteria to determine which clicks could be defined as being on the acoustic axis. Two dolphin and nine porpoise click series could be used to track individual animals, which presumably focused on the array hydrophones or a fish right in front of the array. The apparent source levels of clicks in the individual tracks increased with range. One individual White-beaked Dolphin and three Harbour Porpoises regulate their output signal level to nearly compensate for one-way transmission loss while approaching a target. The other dolphin regulated the output differently. For most of the recordings the sound level at the target remains nearly constant and the echo level at the animal increases as it closes on the target.  相似文献   
9.
ABSTRACT

Calls produced by hybrids resulting from laboratory crosses of tetraploid Hyla versicolor females and either diploid Hyla chrysoscelis (type I) or Hyla arborea (type II) males were induced through manipulation of environmental conditions. Type I hybrids produced trilled calls similar in note repetition to H. versicolor, but more similar in dominant frequency to H. chrysoscelis. Mean duration was shorter than in both parent calls. Type II hybrids produced calls which were longer in duration and lower in note repetition rate than H. versicolor, but shorter in duration and higher in note repetition rate than H. arborea. Dominant frequency of type II hybrids was lower than in H. arborea but not significantly different than in H. versicolor. Hybrid calls were not strictly intermediate, and may provide information regarding parental relationships.  相似文献   
10.
ABSTRACT

In this paper a new method for the automatic classification of bird sounds is presented. Our method is based on acoustic parameters (features) taken from the first harmonic component computed from the sound spectrogram. The features are based on a line segment approximation of the first harmonic component. The final feature vectors, consisting of 16 real numbers, are then classified using a self-organizing map (SOM) neural network. Flight calls of four crossbill species (Loxia spp.) are used as a test example. In the first phase, an unsupervised network was trained and tested using common crossbill L. curvirostra flight calls recorded mainly in the Netherlands. The network was tested using two-barred L. leucoptera, Scottish L. scotica and parrot L. pytyopsittacus crossbill flight calls in the second phase. Finally, the results were validated applying the same network to flight calls of common crossbills and parrot crossbills recorded in Finland. The method automatically separated common crossbill flight calls from those of parrot crossbills. The classification accuracy of the Dutch recordings was 58% in the first phase and 54% in the second phase. The Finnish recordings were classified with 54% accuracy.  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