全文获取类型
收费全文 | 757篇 |
免费 | 52篇 |
国内免费 | 2篇 |
出版年
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 18篇 |
2014年 | 27篇 |
2013年 | 31篇 |
2012年 | 40篇 |
2011年 | 41篇 |
2010年 | 33篇 |
2009年 | 26篇 |
2008年 | 60篇 |
2007年 | 39篇 |
2006年 | 42篇 |
2005年 | 41篇 |
2004年 | 35篇 |
2003年 | 45篇 |
2002年 | 55篇 |
2001年 | 12篇 |
2000年 | 4篇 |
1999年 | 12篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1971年 | 6篇 |
排序方式: 共有811条查询结果,搜索用时 31 毫秒
801.
Corey J. Keller Christopher J. Honey Pierre Mégevand Laszlo Entz Istvan Ulbert Ashesh D. Mehta 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2014,369(1653)
The cerebral cortex forms a sheet of neurons organized into a network of interconnected modules that is highly expanded in humans and presumably enables our most refined sensory and cognitive abilities. The links of this network form a fundamental aspect of its organization, and a great deal of research is focusing on understanding how information flows within and between different regions. However, an often-overlooked element of this connectivity regards a causal, hierarchical structure of regions, whereby certain nodes of the cortical network may exert greater influence over the others. While this is difficult to ascertain non-invasively, patients undergoing invasive electrode monitoring for epilepsy provide a unique window into this aspect of cortical organization. In this review, we highlight the potential for cortico-cortical evoked potential (CCEP) mapping to directly measure neuronal propagation across large-scale brain networks with spatio-temporal resolution that is superior to traditional neuroimaging methods. We first introduce effective connectivity and discuss the mechanisms underlying CCEP generation. Next, we highlight how CCEP mapping has begun to provide insight into the neural basis of non-invasive imaging signals. Finally, we present a novel approach to perturbing and measuring brain network function during cognitive processing. The direct measurement of CCEPs in response to electrical stimulation represents a potentially powerful clinical and basic science tool for probing the large-scale networks of the human cerebral cortex. 相似文献
802.
Female collared flycatchers adjust yolk testosterone to male age, but not to attractiveness 总被引:6,自引:2,他引:4
Michl Gabor; Torok Janos; Peczely Peter; Garamszegi Laszlo Z.; Schwabl Hubert 《Behavioral ecology》2005,16(2):383-388
The differential allocation hypothesis predicts that femalesinvest more resources into reproduction when mating with attractivemales. In oviparous animals this can include prefertilizationdecisions such as the production of larger eggs and the depositionof hormones, such as the steroid testosterone, into yolks. Onthe other hand, a compensatory hypothesis posits that femalesallocate more resources into the eggs when mated with malesof inferior quality. In the present study, we show that free-livingfemales of the collared flycatcher (Ficedula albicollis), asmall passerine bird, do not produce larger eggs or depositmore testosterone into eggs when mating with attractive malesreflected by a large forehead patch size, which is contraryto the prediction of the differential allocation hypothesis.However, we found higher yolk testosterone concentrations ineggs laid for young than older males. Because in young malesgenetic quality, parental experience, or willingness to investinto paternal care is likely to be low, high yolk testosteronelevel in their clutches may indicate that their females followa compensatory tactic. They may elicit more paternal care fromyoung, inexperienced males by hormonally increasing nestlingbegging. Laying date was also correlated with yolk testosteronelevel; however, when we controlled for it, male age still remaineda strong determinant of testosterone allocation. 相似文献
803.
804.
Eszter A. Kish Claes-G?ran Granqvist András Dér Laszlo B. Kish 《Cognitive neurodynamics》2015,9(4):459-462
Even a single neuron may be able to produce significant lognormal features in its firing statistics due to noise in the charging ion current. A mathematical scheme introduced in advanced nanotechnology is relevant for the analysis of this mechanism in the simplest case, the integrate-and-fire model with white noise in the charging ion current. 相似文献
805.
806.
807.
The biochemical basis for photosynthetic plasticity in tropical trees of the genus Clusia was investigated in three species that were from contrasting habitats and showed marked differences in their capacity for
crassulacean acid metabolism (CAM). Physiological, anatomical and biochemical measurements were used to relate changes in
the activities/amounts of key enzymes of C3 and C4 carboxylation to physiological performance under severe drought stress. On the basis of gas-exchange measurements and day/night
patterns of organic acid turnover, the species were categorised as weak CAM-inducible (C.aripoensis Britt.), C3-CAM intermediate (C. minor L.) and constitutive CAM (C.␣rosea Jacq. 9.). The categories reflect genotypic differences in physiological response to drought stress in terms of net carbon
gain; in C. aripoensis net carbon gain was reduced by over 80% in drought-stressed plants whilst carbon gain was relatively unaffected after 10 d
without water in C. rosea. In turn, genotypic differences in the capacity for CAM appeared to be directly related to the capacities/amounts of phosphoenolpyruvate carboxylase (PEPCase) and phosphoenolpyruvate carboxykinase (PEPCK) which increased in response to drought in both young and mature leaves. Whilst measured activities
of PEPCase and PEPCK in well-watered plants of the C3-CAM intermediate C. minor were 5–10 times in excess of that required to support the magnitude of organic acid turnover induced by drought, close correlations
were observed between malate accumulation/PEPCase capacity and citrate decarboxylation/PEPCK capacity in all the species.
Drought stress did not affect the amount of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein in any of the
species but Rubisco activity was reduced by 35% in the weak CAM-inducible C. aripoensis. Similar amounts of glycine decarboxylase (GDC) protein were present in all three species regardless of the magnitude of
CAM expression. Thus, the constitutive CAM species C. rosea did not appear to show reduced activity of this key enzyme of the photorespiratory pathway, which, in turn, may be related
to the low internal conductance to CO2 in this succulent species. Immuno-histochemical techniques showed that PEPCase, PEPCK and Rubisco were present in cells of
the palisade and spongy parenchyma in leaves of species performing CAM. However, in leaves from well-watered plants of C. aripoensis which only performed C3 photosynthesis, PEPCK was localized around latex-producing ducts. Differences in leaf anatomy between the species suggest
that the association between mesophyll succulence and the capacity for CAM in these hemi-epiphytic stranglers has been selected
for in arid environments.
Received: 4 July 1997 / Accepted: 27 November 1997 相似文献
808.
The plant homologue of MAP kinase is expressed in a cell cycle-dependent and organ-specific manner 总被引:11,自引:0,他引:11
Claudia Jonak Aniko Páy Laszlo Börge Heribert Hirt Erwin Heberle-Bors 《The Plant journal : for cell and molecular biology》1993,3(4):611-617
In animals, MAP kinase plays a key role in growth factor-stimulated signalling and in mitosis. The isolation of a Medicago sativa cDNA clone MsK7 which shows 52% identity to animal MAP kinases is reported. The deduced protein sequence shows all the important structural features of MAP kinases and also contains the highly conserved Thr-183 and Tyr-185 residues. Northern analysis of synchronized alfalfa cells showed that the MsK7 kinase gene is expressed at low levels in G1 phase but at higher levels in S and G2 phases of the cell cycle. In the plant, only stems and roots were found to contain MAP kinase MsK7 mRNA. Southern and PCR analyses indicated that alfalfa contains at least four highly related MAP kinase genes. 相似文献
809.
810.
Laszlo Csernoch Sandrine Pouvreau Michel Ronjat Vincent Jacquemond 《The Journal of membrane biology》2008,226(1-3):43-55
The elementary Ca2+-release events underlying voltage-activated myoplasmic Ca2+ transients in mammalian muscle remain elusive. Here, we looked for such events in confocal line-scan (x,t) images of fluo-3 fluorescence taken from isolated adult mouse skeletal muscle fibers held under voltage-clamp conditions. In response to step depolarizations, spatially segregated fluorescence signals could be detected that were riding on a global increase in fluorescence. These discrete signals were separated using digital filtering in the spatial domain; mean values for their spatial half-width and amplitude were 1.99 ± 0.09 μm and 0.16 ± 0.005 ΔF/F 0 (n = 151), respectively. Under control conditions, the duration of the events was limited by the pulse duration. In contrast, in the presence of maurocalcine, a scorpion toxin suspected to disrupt the process of repolarization-induced ryanodine receptor (RyR) closure, events uninterrupted by the end of the pulse were readily detected. Overall results establish these voltage-activated low-amplitude local Ca2+ signals as inherent components of the physiological Ca2+-release process of mammalian muscle and suggest that they result from the opening of either one RyR or a coherently operating group of RyRs, under the control of the plasma membrane polarization. 相似文献