全文获取类型
收费全文 | 21128篇 |
免费 | 21篇 |
出版年
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 3498篇 |
2017年 | 2824篇 |
2016年 | 2257篇 |
2015年 | 192篇 |
2014年 | 81篇 |
2013年 | 167篇 |
2012年 | 583篇 |
2011年 | 2395篇 |
2010年 | 2525篇 |
2009年 | 1490篇 |
2008年 | 1717篇 |
2007年 | 2208篇 |
2006年 | 51篇 |
2005年 | 232篇 |
2004年 | 181篇 |
2003年 | 136篇 |
2002年 | 78篇 |
2001年 | 43篇 |
2000年 | 78篇 |
1999年 | 24篇 |
1998年 | 33篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1990年 | 20篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1978年 | 6篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1973年 | 11篇 |
1971年 | 5篇 |
1970年 | 7篇 |
1966年 | 5篇 |
1959年 | 7篇 |
1957年 | 6篇 |
1953年 | 5篇 |
1951年 | 8篇 |
1950年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
Between 1998 and 2006, twenty-seven states amended their constitutions to prohibit same sex marriage. The 2008 elections again
saw three states with ballot measures aimed at banning gay marriage. This study examines the determinants of support for those
measures in California and Florida, and includes a similar measure placed on the primary election ballot in California in
2000. Support is measured as the county-wide vote in favor of each gay marriage ban. A number of hypotheses are explored that
examine the urban/rural nature of each county, as well as the political and demographic characteristics of county residents.
It is suggested that states may be best viewed as relatively independent groupings of diverse subcultures, rather than as
homogenous populations with a single political culture. The findings reported here indicate that a host of demographic, political
and religious differences within each state influence residents’ votes on gay marriage bans. 相似文献
202.
Polder-Verkiel SE 《Science and engineering ethics》2012,18(1):117-141
In 2008 a young man committed suicide while his webcam was running. 1,500 people apparently watched as the young man lay dying:
when people finally made an effort to call the police, it was too late. This closely resembles the case of Kitty Genovese
in 1964, where 39 neighbours supposedly watched an attacker assault and did not call until it was too late. This paper examines
the role of internet mediation in cases where people may or may not have been good Samaritans and what their responsibilities
were. The method is an intuitive one: intuitions on the various potentially morally relevant differences when it comes to
responsibility between offline and online situations are examined. The number of onlookers, their physical nearness and their
anonymity have no moral relevance when it comes to holding them responsible. Their perceived reality of the situation and
ability to act do have an effect on whether we can hold people responsible, but this doesn’t seem to be unique to internet
mediation. However the way in which those factors are intrinsically connected to internet mediation does seem to have a diminishing
effect on responsibility in online situations. 相似文献
203.
204.
The Bengalese finch (Lonchura striata var. domestica) is a species of songbird. Males sing courtship songs with complex note-to-note transition rules, while females discriminate
these songs when choosing their mate. The present study uses serial reaction time (RT) to examine the characteristics of the
Bengalese finches’ sequential behaviours beyond song production. The birds were trained to produce the sequence with an “A–B–A”
structure. After the RT to each key position was determined to be stable, we tested the acquisition of the trained sequential
response by presenting novel and random three-term sequences (random test). We also examined whether they could abstract the
embedded rule in the trained sequence and apply it to the novel test sequence (abstract test). Additionally, we examined rule
abstraction through example training by increasing the number of examples in baseline training from 1 to 5. When considered
as (gender) groups, training with 5 examples resulted in no statistically significant differences in the abstract tests, while
statistically significant differences were observed in the random tests, suggesting that the male birds learned the trained
sequences and transferred the abstract structure they had learned during the training trials. Individual data indicated that
males, as opposed to females, were likely to learn the motor pattern of the sequence. The results are consistent with observations
that males learn to produce songs with complex sequential rules, whereas females do not. 相似文献
205.
Non-human primates possess species-specific repertoires of acoustically distinct call types that can be found in adults in
predictable ways. Evidence for vocal flexibility is generally rare and typically restricted to acoustic variants within the
main call types or sequential production of multiple calls. So far, evidence for context-specific call sequences has been
mainly in relation to external disturbances, particularly predation. In this study, we investigated extensively the vocal
behaviour of free-ranging and individually identified Diana monkeys in non-predatory contexts. We found that adult females
produced four vocal structures alone (‘H’, ‘L’, ‘R’ and ‘A’ calls, the latter consisting of two subtypes) or combined in non-random
ways (‘HA’, ‘LA’ and ‘RA’ call combinations) in relation to ongoing behaviour or external events. Specifically, the concatenation
of an introductory call with the most frequently emitted and contextually neutral ‘A’ call seems to function as a contextual
refiner of this potential individual identifier. Our results demonstrate that some non-human primates are able to increase
the effective size of their small vocal repertoire not only by varying the acoustic structure of basic call types but also
by combining them into more complex structures. We have demonstrated this phenomenon for a category of vocalisations with
a purely social function and discuss the implications of these findings for evolutionary theories of primate vocal communication. 相似文献
206.
It has been speculated that cage mesh exerts a shaping influence on reaching behavior by captive apes, which is then misconstrued
as pointing by human observers. Although this notion is clearly falsified by the pointing of captive language-trained apes—who
point in the absence of intervening cage mesh—nevertheless, the degree to which cage mesh might influence pointing hand shapes
by captive great apes in other housing environments remains relatively unexplored. We examined 259 pointing gestures displayed
in archival footage from over 18 h of observation by three nonlanguage-trained chimpanzees housed at a biomedical research
center. We coded points in relation to how close to the boundaries of the diamond-shaped cage mesh their points were displayed.
We found that points with the whole hand were significantly more likely to be displayed away from the mesh boundaries, relative
to points with the index finger or other single-digit points. However, points of each hand shape were displayed at each location,
demonstrating that these physical parameters do not fully account for the number of fingers extended while pointing by chimpanzees. 相似文献
207.
Although rats are able to build complex spatial representations of their surroundings during exploration, the nature of the
encoded information is still a matter for debate. In particular, it is not well established if rats can process the topological
structure of the environment in such a way that they are aware of the connections existing between remote places. Here, rats
were first exposed for four 5-min trials to a complex environment divided into several sectors that were separated by doors
allowing either unrestricted or restricted access to other sectors. In the fifth test trial, we measured the behavior of the
animals while they explored the same environment in which, however, they faced changes that either altered or did not alter
the topological structure of the environment. In experiment 1, closing previously opened doors prevented the rat from having
direct access between corresponding sectors. In experiment 2, opening previously closed doors allowed direct access between
sectors that had not been directly accessible. In each experiment, control doors allowed us to discard the mere influence
of door manipulation. We compared the rats’ exploratory behavior in response to door manipulations that either strongly altered
or did not alter the ability to commute between sectors and found evidence that the animals displayed differential reactions
to the two types of door manipulations. This implies that during exploration rats build a precise map of the connectivity
of space that can be flexibly updated and used for efficient navigation. 相似文献
208.
Uneconomical choices by humans or animals that evaluate reward options challenge the expectation that decision-makers always
maximize the return currency. One possible explanation for such deviations from optimality is that the ability to sense differences
in physical value between available alternatives is constrained by the sensory and cognitive processes for encoding profitability.
In this study, we investigated the capacity of a nectarivorous bat species (Glossophaga commissarisi) to discriminate between sugar solutions with different concentrations. We conducted a two-alternative free-choice experiment
on a population of wild electronically tagged bats foraging at an array of computer-automated artificial flowers that recorded
individual choices. We used a Bayesian approach to fit individual psychometric functions, relating the strength of preferring
the higher concentration option to the intensity of the presented stimulus. Psychometric analysis revealed that discrimination
ability increases non-linearly with respect to intensity. We combined this result with a previous psychometric analysis of
volume perception. Our theoretical analysis of choice for rewards that vary in two quality dimensions revealed regions of
parameter combinations where uneconomic choice is expected. Discrimination ability may be constrained by non-linear perceptual
and cognitive encoding processes that result in uneconomical choice. 相似文献
209.
Different event-related potentials (ERPs) have been shown to correlate with learning from feedback in decision-making tasks
and with learning in explicit memory tasks. In the present study, we investigated which ERPs predict learning from corrective
feedback in a multiple-choice test, which combines elements from both paradigms. Participants worked through sets of multiple-choice
items of a Swahili–German vocabulary task. Whereas the initial presentation of an item required the participants to guess
the answer, corrective feedback could be used to learn the correct response. Initial analyses revealed that corrective feedback
elicited components related to reinforcement learning (FRN), as well as to explicit memory processing (P300) and attention
(early frontal positivity). However, only the P300 and early frontal positivity were positively correlated with successful
learning from corrective feedback, whereas the FRN was even larger when learning failed. These results suggest that learning
from corrective feedback crucially relies on explicit memory processing and attentional orienting to corrective feedback,
rather than on reinforcement learning. 相似文献
210.
Cooper NR Puzzo I Pawley AD Bowes-Mulligan RA Kirkpatrick EV Antoniou PA Kennett S 《Cognitive, affective & behavioral neuroscience》2012,12(2):393-405
Ongoing debate in the literature concerns whether there is a link between contagious yawning and the human mirror neuron system
(hMNS). One way of examining this issue is with the use of the electroencephalogram (EEG) to measure changes in mu activation
during the observation of yawns. Mu oscillations are seen in the alpha bandwidth of the EEG (8–12 Hz) over sensorimotor areas.
Previous work has shown that mu suppression is a useful index of hMNS activation and is sensitive to individual differences
in empathy. In two experiments, we presented participants with videos of either people yawning or control stimuli. We found
greater mu suppression for yawns than for controls over right motor and premotor areas, particularly for those scoring higher
on traits of empathy. In a third experiment, auditory recordings of yawns were compared against electronically scrambled versions
of the same yawns. We observed greater mu suppression for yawns than for the controls over right lateral premotor areas. Again,
these findings were driven by those scoring highly on empathy. The results from these experiments support the notion that
the hMNS is involved in contagious yawning, emphasise the link between contagious yawning and empathy, and stress the importance
of good control stimuli. 相似文献