全文获取类型
收费全文 | 933篇 |
免费 | 54篇 |
国内免费 | 55篇 |
出版年
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
11.
J. Mogdans H. -U. Schnitzler J. Ostwald 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1993,172(3):309-323
1. | Echolocating bats (Eptesicus fuscus) were trained to discriminate between simulated targets consisting of one or two echo-wavefronts with internal time delays of up to 100 s. Spectral and temporal properties and total signal energy of the targets were evaluated and predictions for performances of bats derived from receiver models were compared with measured performances. |
2. | Eptesicus fuscus was able to discriminate a one-wavefront target from two-wavefront targets with distinct internal time delays (12 s, 32–40 s and 52–100 s). Performance was not affected by changes in total signal energy. Bats also successfully discriminated between two-wavefront targets with different internal time delays. |
3. | Performance predicted from differences in total energy between targets did not match the measured performance, indicating that bats did not rely on total echo energy. This finding is also supported by the behavioral data. Performance predicted from spectral and temporal receiver models both matched the measured performance and, therefore, neither one of these models can be favored over the other. |
4. | The behavioral data suggest that Eptesicus fuscus did not transform echo information into estimates of target range separation and, therefore, did not perceive the two wavefronts of each simulated two-wavefront echo as two separate targets. |
12.
Melinda A. Novak Amy Musante Heather Munroe Peggy L. O'Neill Cristofer Price Stephen J. Suomi 《Zoo biology》1993,12(3):285-298
Recent research has indicated that old, individually housed monkeys show little interest in novel objects. Yet unanswered is whether this effect is caused primarily by age or housing condition. The purpose of this study was to assess the role of social living in promoting responsiveness to objects. We measured the rates of object manipulation in older animals, assessed responsiveness over time to particular objects as a measure of habituation, and examined social influences on object use. Several social groups of rhesus monkeys that contained older adults were studied. These groups were housed in indoor pens or in an outdoor enclosure, and all monkeys had continuous access to a variety of objects in their home environment. In contrast to previous studies of individually housed monkeys, our group-housed monkeys showed sustained interest in objects. Old monkeys manipulated objects extensively, and this response was all the more significant, given that the objects were not novel. Monkeys housed in an outdoor enclosure showed object manipulation patterns that were not different from monkeys housed in indoor pens. However, females exhibited much higher object-related responses than males. Social facilitation played a role in the reactions of some monkeys to objects. Patterns of social facilitation as well as avoidance were present in two of the three indoor groups that were observed. Failure to manipulate objects in rhesus macaques appears to be more a function of individual housing than of old age. Factors such as environmental complexity, social needs, and early experience should be considered in order to understand why individually housed rhesus monkeys are unresponsive to objects. © 1993 Wiley-Liss, Inc. 相似文献
13.
Processing of global and local properties——An analysis with event-related brain potentials 总被引:3,自引:1,他引:2
The different processing of global and local properties of compound visual stimuli was studied with event-related brain potentials (ERPs) in the present experiment. It was found that, compared with the identification of global properties, the discrimination of local properties elicited longer RTs, lower accuracies, increased amplitudes of P1, decreased amplitudes of N1, and longer latencies of N2 and P3. The conflict of global and local properties increased the amplitudes of P2, decreased the amplitudes of P3, and prolonged latencies of N2 and P3. These results indicated that the advantage of global processing occurs at an early perceptual stage, and the attentional mechanisms for global and local processing may be different. 相似文献
14.
Ralph M. Perhac Jr. 《人类与生态风险评估》1996,2(2):381-392
The public thinks about (i.e., defines) environmental human health risks in different terms than the “experts.”; And because the manner in which we conceive of risk goes a long way in determining how risk management is conceived and carried out, any definition of risk has important normative elements. I argue that environmental policy based on the public's conception of risk fails to adequately protect fundamental human rights to health and liberty, by taking undue account of certain psychological factors that enter into the public's perception of risk. A survey of some of these factors is offered in an attempt to determine their policy relevance. The traditional scientific conception of risk, although not adequate to entirely define risk policy, serves as an important anchor for the protection of these rights by focusing on the probability or number of adverse health effects. 相似文献
15.
W. Wiggers G. Roth C. Eurich A. Straub 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1995,176(3):365-377
Tongue-projecting salamanders (Bolitoglossini) combine extreme speed and high precision in prey capture. They possess all requirements for stereoscopic depth perception: frontally oriented eyes, a substantial amount of direct ipsilateral projection in addition to the contralateral one, and binocularly driven neurons. Extracellular recordings were made from retinal afferents in the tectum as well as from the somata of tectal neurons. RF-sizes of afferents and tectal neurons were determined, and the response properties of tectal neurons were tested under monocular and binocular conditions with stimuli of different size and velocity. While RF-sizes and response properties of binocular neurons during binocular and contralateral stimulation were similar, ipsilaterally stimulated neurons exhibited much smaller RFs, lower spike rates and different size preferences.Furthermore, the contralateral retinotectal projection from one eye and the ipsilateral from the other are in register. While retinal afferents are distributed linearly over the tectal surface, most tectal neurons are activated by a retinal area corresponding to the frontal visual field; this results in a magnification of this region. The two monocular receptive fields of binocular neurons exhibit zero disparities (horopter) at distances that coincide with the maximum reach of the tongue. We hypothesize that bolitoglossine salamanders (as well as amphibians in general) make use of two kinds of disparities: (1) between the maps in the left and right tectal hemisphere, coding for the lateral eccentricity of an object, and (2) between the ipsilateral and contralateral retinotectal map, coding for the distance. The presence of substantial direct ipsilateral afferents in bolitoglossine salamanders appears to be the basis for a fast computation of object distance, which is characteristic of these animals.Abbreviations
Ax/Ay
coordinates of a recorded afference
-
Nx/Ny
coordinates of a recorded neuron
-
RF
receptive field
-
RFc
contralateral receptive field
-
RFi
ipsilateral receptive field
-
RFx/RFy
coordinates of a receptive field center
-
RGC
retinal ganglion cell 相似文献
16.
Summary Hydrostatic pressure applied to one end of a horizontalChara cell induces a polarity of cytoplasmic streaming, thus mimicking the effect of gravity. A positive hydrostatic pressure induces a more rapid streaming away from the applied pressure and a slower streaming toward the applied pressure. In contrast, a negative pressure induces a more rapid streaming toward and a slower streaming away from the applied pressure. Both the hydrostatic pressure-induced and gravity-induced polarity of cytoplasmic streaming respond identically to cell ligation, UV microbeam irradiation, external Ca2+ concentrations, osmotic pressure, neutral red, TEA Cl–, and the Ca2+ channel blockers nifedipine and LaCl3. In addition, hydrostatic pressure applied to the bottom of a vertically-oriented cell can abolish and even reverse the gravity-induced polarity of cytoplasmic streaming. These data indicate that both gravity and hydrostatic pressure act at the same point of the signal transduction chain leading to the induction of a polarity of cytoplasmic streaming and support the hypothesis that characean cells respond to gravity by sensing a gravity-induced pressure differential between the cell ends. 相似文献
17.
Kenneth H. Norwich 《Acta biotheoretica》1991,39(1):81-90
The process of recognition or isolation of one or several entities from among many possible entities is termed intellego perception. It is shown that not only are many of our everyday percepts of this type, but perception of microscopic events using the methods of quantum mechanics are also intellego in nature. Information theory seems to be a natural language in which to express perceptual activity of this type. It is argued that the biological organism quantifies its sensations using an information theoretical measure. This, in turn, sets the stage for a mathematical theory of sensory perception. 相似文献
18.
Necessary and sufficient spectral conditions are presented for Von Kries chromatic adaptation to give color constancy. Von-Kries-invariant reflectance spectra are computed for illuminant spectral power distributions that are arbitrary linear combinations of the first three daylight phases. Experiments are suggested to test models of color constancy using computed spectra (either exact or approximate) within the illuminant-invariant framework. 相似文献
19.
To be effective, signals must propagate through the environment and be detected by receivers. As a result, signal form evolves in response to both the constraints imposed by the transmission environment and receiver perceptual abilities. Little work has examined the extent to which signals may act as selective forces on receiver sensory systems to improve the efficacy of communication. If receivers benefit from accurate signal assessment, selection could favour sensory organs that improve discrimination of established signals. Here, we provide evidence that visual resolution coevolves with visual signals in Polistes wasps. Multiple Polistes species have variable facial patterns that function as social signals, whereas other species lack visual signals. Analysis of 19 Polistes species shows that maximum eye facet size is positively associated with both eye size and presence of visual signals. Relatively larger facets within the eye''s acute zone improve resolution of small images, such as wasp facial signals. Therefore, sensory systems may evolve to optimize signal assessment. Sensory adaptations to facilitate signal detection may represent an overlooked area of the evolution of animal communication. 相似文献
20.
Lulu Wang 《Molecular & cellular biomechanics : MCB》2020,17(1):33-40
CT and MRI are often used in the diagnosis and monitoring of stroke.
However, they are expensive, time-consuming, produce ionizing radiation (CT),
and not suitable for continuous monitoring stroke. Microwave imaging (MI) has
been extensively investigated for identifying several types of human organs,
including breast, brain, lung, liver, and gastric. The authors recently developed a
holographic microwave imaging (HMI) algorithm for biological object detection.
However, this method has difficulty in providing accurate information on
embedded small inclusions. This paper describes the feasibility of the use of a
multifrequency HMI algorithm for brain stroke detection. A numerical system,
including HMI data collection model and a realistic head model, was developed to
demonstrate the proposed method for imaging of brain tissues. Various
experiments were carried out to evaluate the performance of the proposed method.
Results of experiments carried out using multifrequency HMI have been compared
with the results obtained from single frequency HMI. Results showed that
multifrequency HMI could detect strokes and provide more accurate results of size
and location than the single frequency HMI algorithm. 相似文献