全文获取类型
收费全文 | 6227篇 |
免费 | 685篇 |
国内免费 | 2篇 |
出版年
2022年 | 44篇 |
2021年 | 133篇 |
2020年 | 73篇 |
2019年 | 85篇 |
2018年 | 139篇 |
2017年 | 96篇 |
2016年 | 149篇 |
2015年 | 224篇 |
2014年 | 231篇 |
2013年 | 343篇 |
2012年 | 420篇 |
2011年 | 403篇 |
2010年 | 265篇 |
2009年 | 226篇 |
2008年 | 360篇 |
2007年 | 329篇 |
2006年 | 434篇 |
2005年 | 261篇 |
2004年 | 242篇 |
2003年 | 240篇 |
2002年 | 223篇 |
2001年 | 147篇 |
2000年 | 107篇 |
1999年 | 86篇 |
1998年 | 56篇 |
1997年 | 44篇 |
1996年 | 57篇 |
1995年 | 57篇 |
1994年 | 44篇 |
1993年 | 37篇 |
1992年 | 84篇 |
1991年 | 76篇 |
1990年 | 77篇 |
1989年 | 98篇 |
1988年 | 69篇 |
1987年 | 73篇 |
1986年 | 46篇 |
1985年 | 59篇 |
1984年 | 50篇 |
1983年 | 43篇 |
1982年 | 38篇 |
1979年 | 50篇 |
1978年 | 46篇 |
1976年 | 35篇 |
1975年 | 43篇 |
1974年 | 44篇 |
1973年 | 41篇 |
1972年 | 40篇 |
1971年 | 37篇 |
1970年 | 39篇 |
排序方式: 共有6914条查询结果,搜索用时 171 毫秒
201.
Human or rabbit platelets were activated by ADP or 5-hydroxytrypatamine and rapidly fixed with glutaraldehyde. The shape change associated with activation gave rise to an increase in sialic acids removable by neuraminidase. This increase, like the shape change, was prevented by adenosine or methysergide added before ADP or 5-hydroxytryptamine respectively. The results indicate the exposure of additional glycoprotein(s) on the platelet surface. 相似文献
202.
Waves of chemotactic movement during the early phase of aggregation in Dictyostelium discoideum are of 2 kinds, concentric waves produced by cells that emit cyclic AMP signals spontaneously, and spirals generated by excitations relayed continuously around loops of excitable cells. The period of a spiral wave is the time taken for the excitation to make one complete circuit of the pacemaker loop. We have compared signal emission from the 2 types of source in time-lapse films made at a variety of temperatures. Our results show that spiral waves have a characteristic period length throughout most if not all of the early phase of aggregation, and that the period of concentric waves is generally longer and more variable. Temperature has a pronounced effect on period length and a lesser effect on propagation velocity. We find that each individual wave is propagated at constant velocity over distances of 1-2 cm but that the velocity of successive waves declines. This decline probably reflects some cumulative effect of the chemotactic excitations on the excitable properties of the aggregating cells. 相似文献
203.
Summary The fine structure of arcuate neurons of the arcuate nucleus, the ependymal tanycytes and the contact zone of the median eminence was examined following immobilization, an acute stress which significantly activated the hypothalamo-pituitary-adrenal (HPA) axis. Arcuate neurons of immobilized adult male hamsters displayed morphological indications of heightened activity; the number of lysosomes and dense core vesicles (80–120 nm) was increased. A markedly greater number of dense core vesicles was present in axon terminals of the contact zone of the mid-central median eminence and the ventral proximal stalk.Tanycytes of the median eminence exhibited an augmented number of electron dense bodies in both perikarya and end processes. These results indicate that the arcuate neurons, the axons of the contact zone, and the ependymal tanycytes of the hamster medial basal hypothalamus (MBH) may be involved in the response to immobilization.This work was supported by Program Project Grant #NS-11642 相似文献
204.
205.
206.
L J Gross 《Texas reports on biology and medicine》1975,33(3):370-390
Since handwriting is a highly complex, coordinated motor activity, handwrits of pharmacological agents. Its potential has been most evident in research involving therapeutic administrations of anti-psychotic an anti-Parkinsonian drugs, from which consistent and systematic handwriting changes have been observed. This relationship has been found to be particularly significant among the anti-psychotics, since the onset of these graphomotor alterations appear to mark the optmal dose of the drug. Consistent and systematic handwriting changes have not been as evident in inivestigations of drugs used in a nontherapeutic atmosphere. Psychiatric assessments of subjects in ths type of research provided data which indicated that psychological stability may be a factor influencing the susceptibility of one's handwriting to drug induced changes. 相似文献
207.
Accelerated uptake of 5-hydroxytryptamine by human blood platelets enriched in a sialic acid.
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)
The enzymically catalysed incorporation of N-acetylneuraminic acid into human platelets, whether suspended in their own citrated plasma or in buffered saline containing 0.17 mM-sucrose, accelerated the uptake of 5-hydroxytryptamine. This acceleration decreased with time. The observations may be explained by assuming that N-acetylneuraminic acid is a component of a transport receptor for 5-hydroxytryptamine. 相似文献
208.
209.
210.
Brains of young (newly emerged) adult female locusts (Locusta migratoria migratorioides) and of mature (> 9 days old) locusts contain an extractable allatotropic factor, soluble in 100% methanol and in distilled water. This factor stimulates juvenile hormone III (JH III) synthesis and release from corpora allata (CA) that have been excised from donor locusts and then incubated with (radiolabeled methyl)-methionine in vitro in its presence. In addition to JH III, which is the major product synthesized by the CA, other hexanesoluble, radiolabeled compounds–-more polar than JH III–-are also released when CA are incubated in vitro. The activation of CA by the allatotropic factor is rapid and quickly declines when the factor is removed from the medium. Corpora allata excised from young females are marginally active and can be activated by brain allatotropic factor to less of an extent than CA of mature locusts. The content of allatotropic factor in brains of mature locusts is higher than that ascertained in brains of young females. Allatotropic factor is also present in the corpora cardiaca. 相似文献