全文获取类型
收费全文 | 3278篇 |
免费 | 276篇 |
出版年
2023年 | 13篇 |
2022年 | 21篇 |
2021年 | 62篇 |
2020年 | 37篇 |
2019年 | 36篇 |
2018年 | 73篇 |
2017年 | 51篇 |
2016年 | 79篇 |
2015年 | 138篇 |
2014年 | 150篇 |
2013年 | 170篇 |
2012年 | 218篇 |
2011年 | 232篇 |
2010年 | 144篇 |
2009年 | 115篇 |
2008年 | 180篇 |
2007年 | 175篇 |
2006年 | 186篇 |
2005年 | 150篇 |
2004年 | 184篇 |
2003年 | 161篇 |
2002年 | 162篇 |
2001年 | 26篇 |
2000年 | 21篇 |
1999年 | 27篇 |
1998年 | 36篇 |
1997年 | 26篇 |
1996年 | 35篇 |
1995年 | 31篇 |
1994年 | 20篇 |
1993年 | 17篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 35篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 33篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 22篇 |
1975年 | 14篇 |
1974年 | 17篇 |
1968年 | 18篇 |
排序方式: 共有3554条查询结果,搜索用时 15 毫秒
1.
Halasz Norbert; Nowycky Martha C.; Shepherd Gordon M.; Hofelt Tomas 《Chemical senses》1985,10(2):203-218
aftographic exeperiments on the localization of radiolabelednoradrenaline, dopamine and dopa, as well as immunohistochemicalstudies on hydroxylase-like activity, are summarized and comparedin both rat and turtle olfactory bulbs. Evoked field potentialstudies on effects of dopamine are also discussed. The histochemicalstudies suggest that dopaminergic periglomerular neurons arethe most significant cellular component of the catecholaminergicsystem in the olfactory bulb of both species. Scattered fluorescentcell group was also present in the internal plexiform layerand superficial granule cell layer of the turtle olfactory bulb.Other fibres, not related to intrinsic bulbar neuronal cellbodies, were also labeled, mostly in the granule cell layerbut also in the external plexiform layer. These might belongto a centrifugal catecholaminergic system from brain stem neurons.In the in vitro turtle olfactory bulb, dopamine and apomorphinedepressed the amplitude of field potentials evoked by a singlevolley in the olfactory nerve or lateral olfactory tract, andreduced the depression and latency of reponses when paired volleywere delivered. It is suggested that catecholaminergic systemsplay a key role in modulating mitral cell activity through actionsin both superficial (glomerular) and deep (granule) layers.This may involve direct actions, or other, non-catecholaminergicinterneurons. 相似文献
2.
Martha Macintyre 《The Australian journal of anthropology》2012,23(1):121-122
3.
R I Bayliss 《BMJ (Clinical research ed.)》1982,285(6352):1373-1375
4.
5.
6.
Martha L. Bohórquez Alonso Jorge Martínez Cotrina David Aguilar Pardo Enrique Font Miguel Molina-Borja 《Journal of Ethology》2010,28(2):305-311
Many vertebrate species show display behaviors when predators are in their vicinity. Some of these displays may inform the
predator of the improbability of capturing the prey (i.e., pursuit-deterrent displays) and are potentially advantageous to
both predator and prey. Here we present data on a tail display performed by Gonatodes albogularis, a diurnal tropical gecko. We performed transect surveys in three habitats near Bogotá in Colombia. Geckos detected during
transects were approached by the observer in a standardized way, and details of their tail-waving displays were recorded.
In control recordings animals were watched from a distant site without approaching them. Results showed sexual differences
in tail-waving display: when approached by the observer, males performed this behavior more frequently than females. We found
no significant differences between males and females in flight-initiation distances and height above the substratum when they
were initially located. Results also showed that males displayed more frequently when approached than when the simulated predator
remained stationary. We interpret these results as evidence that the display functions as a pursuit-deterrent signal to potential
predators. However, as some tail displays were performed in the presence of conspecifics, the display may also have a social
function. 相似文献
7.
8.
Brett F BuSha Martha H Stella Harold L Manning J C Leiter 《Journal of applied physiology》2002,93(3):903-910
Imperceptible levels of proportional assist ventilation applied throughout inspiration reduced inspiratory time (TI) in awake humans. More recently, the reduction in TI was associated with flow assist, but flow assist also reaches a maximum value early during inspiration. To test the separate effects of flow assist and timing of assist, we applied a pseudorandom binary sequence of flow-assisted breaths during early, late, or throughout inspiration in eight normal subjects. We hypothesized that imperceptible flow assist would shorten TI most effectively when applied during early inspiration. Tidal volume, integrated respiratory muscle pressure per breath, TI, and TE were recorded. All stimuli (early, late, or flow assist applied throughout inspiration) resulted in a significant increase in inspiratory flow; however, only when the flow assist was applied during early inspiration was there a significant reduction in TI and the integrated respiratory muscle pressure per breath. These results provide further evidence that vagal feedback modulates breathing on a breath-by-breath basis in conscious humans within a physiological range of breath sizes. 相似文献
9.
Twenty-four-hour variations in activity,core temperature,metabolic rate,and respiratory quotient in captive chinese pangolins 总被引:1,自引:0,他引:1
Martha E. Heath 《Zoo biology》1987,6(1):1-10
The circadian rhythms in activity, core temperature (Tc), O2 consumption, CO2 production, and respiratory quotient (RQ) were monitored in four captive Chinese pangolins (Manis pentadactyla). The pangolins were strictly nocturnal, never emerging from their nest before 1600 h, and their intermittent activity continued no later than 0230. As is usual in nocturnal mammals, the highest values observed in Tc, O2 consumption, and CO2 production occurred during the night; the lowest values occurred during the day. The magnitude of the variation in Tc, O2 consumption, CO2 production, and RQ averaged 1.2°C, 1.3 ml O2 kg?1 min?1, 1.2 ml CO2 kg?1 min?1, and 0.24, respectively. The circadian pattern in RQ was independent of activity, Tc, and the metabolic parameters and was of a different character than the patterns exhibited in the other variables. RQ remained constant at either a high or low level for long periods (8–10 h) and then increased or decreased relatively rapidly (1–2h) to the other level as in a square wave, whereas the rhythms in the other variables are similar to sine waves. The sharp increase in RQ was followed by a slow decline in Tc, and the sharp decline in RQ was followed by a slow increase in Tc. 相似文献
10.
Dermatan sulphate proteoglycan from human articular cartilage. Variation in its content with age and its structural comparison with a small chondroitin sulphate proteoglycan from pig laryngeal cartilage. 总被引:4,自引:2,他引:2
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Low molecular mass proteoglycans (PG) were isolated from human articular cartilage and from pig laryngeal cartilage, which contained protein cores of similar size (Mr 40-44 kDa). However, the PG from human articular cartilage contained dermatan sulphate (DS) chains (50% chondroitinase AC resistant), whereas chains from pig laryngeal PG were longer and contained only chondroitin sulphate (CS). Disaccharide analysis after chondroitinase ABC digestion showed that the human DS-PG contained more 6-sulphated residues (34%) than the pig CS-PG (6%) and both contained fewer 6-sulphated residues than the corresponding high Mr aggregating CS-PGs from these tissues (86% and 20% from human and pig respectively). Cross-reaction of both proteoglycans with antibodies to bovine bone and skin DS-PG-II and human fibroblasts DS-PG suggested that the isolated proteoglycans were the humans DS-PG-II and pigs CS-PG-II homologues of the cloned and sequenced bovine proteoglycan. Polyclonal antibodies raised against the pig CS-PG-II were shown to cross-react with human DS-PG-II. SDS/polyacrylamide-gel analysis and immunoblotting of pig and human cartilage extracts showed that some free core protein was present in the tissues in addition to the intact proteoglycan. The antibodies were used in a competitive radioimmunoassay to determine the content of this low Mr proteoglycan in human cartilage extracts. Analysis of samples from 5-80 year-old humans showed highest content (approximately 4 mg/g wet wt.) in those from 15-25 year-olds and lower content (approximately 1 mg/g wet wt.) in older tissue (greater than 55 years). These changes in content may be related to the deposition and maintenance of the collagen fibre network with which this class of small proteoglycan has been shown to interact. 相似文献