全文获取类型
收费全文 | 636篇 |
免费 | 54篇 |
出版年
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 31篇 |
2014年 | 36篇 |
2013年 | 46篇 |
2012年 | 35篇 |
2011年 | 32篇 |
2010年 | 35篇 |
2009年 | 38篇 |
2008年 | 30篇 |
2007年 | 27篇 |
2006年 | 27篇 |
2005年 | 31篇 |
2004年 | 23篇 |
2003年 | 7篇 |
2002年 | 19篇 |
2001年 | 17篇 |
2000年 | 11篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 12篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 18篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有690条查询结果,搜索用时 31 毫秒
131.
132.
The period (per) locus has received much attention in molecular evolution
studies because it is one of the best studied "behavioral genes" and
because it offers insight into the evolution of repetitive sequences. We
studied most of the coding region of per in Drosophila willistoni and
confirmed previously observed patterns of conservation and divergence among
distantly related species. Five regions are so highly diverged that they
cannot be aligned, whereas a region encompassing the PAS domain is very
conserved. Structural and nucleotide polymorphism patterns in the
willistoni group are not the same as those observed in previously studied
species. We sequenced the region homologous to the highly polymorphic
threonine-glycine repeat of D. melanogaster in multiple strains of D.
willistoni, as well as in other members of willistoni group, and found an
unusual amount of conservation in this region. However, the next
nonconserved region downstream in the sequence is quite variable and
polymorphic for the number of repeated glycines. The glycine codon usage is
significantly different in this glycine repeat as compared to other parts
of the gene. We were able to plot the directionality of change in the
glycine repeat region onto a phylogeny and find that the addition of
glycines is the general trend with the diversification of the willistoni
group.
相似文献
133.
134.
The aim of the present study is to analyse the influence of different large-sided games (LSGs) on the physical and physiological variables in under-12s (U12) and -13s (U13) soccer players. The effects of the combination of different number of players per team, 7, 9, and 11 (P7, P9, and P11, respectively) with three relative pitch areas, 100, 200, and 300 m2 (A100, A200, and A300, respectively), were analysed in this study. The variables analysed were: 1) global indicator such as total distance (TD); work:rest ratio (W:R); player-load (PL) and maximal speed (Vmax); 2) heart rate (HR) mean and time spent in different intensity zones of HR (<75%, 75–84%, 84–90% and >90%), and; 3) five absolute (<8, 8–13, 13–16 and >16 Km h-1) and three relative speed categories (<40%, 40–60% and >60% Vmax). The results support the theory that a change in format (player number and pitch dimensions) affects no similarly in the two players categories. Although it can seem that U13 players are more demanded in this kind of LSG, when the work load is assessed from a relative point of view, great pitch dimensions and/or high number of player per team are involved in the training task to the U12 players. The results of this study could alert to the coaches to avoid some types of LSGs for the U12 players such as: P11 played in A100, A200 or A300, P9 played in A200 or A300 and P7 played in A300 due to that U13>U12 in several physical and physiological variables (W:R, time spent in 84–90%HRmax, distance in 8–13 and 13–16 Km h-1 and time spent in 40–60%Vmax). These results may help youth soccer coaches to plan the progressive introduction of LSGs so that task demands are adapted to the physiological and physical development of participants. 相似文献
135.
Deltorphin, a heptapeptide that selectively binds to delta receptors, was intracerebroventricularly administered to mice belonging to the strains C57BL/6 and DBA/2 immediately after training in a one-trial inhibitory avoidance task. The retention performance of both strains was improved by the peptide administration, with DBA mice being more sensitive to this effect. The results show different effects of delta and mu receptor agonists on memory consolidation and of strain differences in number and/or distribution of delta opioid receptors in the brain. 相似文献
136.
137.
Differences in forebrain weight, forebrain weight/body weight ratios, and body weight were examined for the RI strains, their progenitor strains, and reciprocal F1 hybrids. The experiment was done in two widely separated laboratories with identical procedures for feeding, watering, and removal of brain tissue. The resulting strain distribution patterns suggested the influence of two or more loci in each laboratory. However, brain weights differed in the two laboratories. Some of the strains examined exhibited increased weights for the variables under consideration, while others exhibited decreased weights or no change at all. Implications for generalizations drawn from observations obtained in any single laboratory were discussed. 相似文献
138.
The authors have investigated the electrical activity of corpus cavernous, first according to Wagner and Gerstenberg’ method, then, since one year, according to Stief method, in the basal state and following intracavernosal injection of vasoactive agents, or following various stimulation tests. They have found again the electrical activity described by these authors, but have been confronted with the difficulty in quantifying the data. Specially single potential analysis seems to them little reliable and reproducible for an objective interpretation. At this stage of their experience, they test two simpler criteria interpretation: the richness of the electrical activity, and the reactivity of the recording to various stimulations. Their preminary results suggest a correlation between those criteria and the state of the autonomic nervous system of the penis. 相似文献
139.
Complete sequences of the rRNA genes of Drosophila melanogaster 总被引:19,自引:0,他引:19
In this, the first of three papers, we present the sequence of the
ribosomal RNA (rRNA) genes of Drosophila melanogaster. The gene regions of
D. melanogaster rDNA encode four individual rRNAs: 18S (1,995 nt), 5.8S
(123 nt), 2S (30 nt), and 28S (3,945 nt). The ribosomal DNA (rDNA) repeat
of D. melanogaster is AT rich (65.9% overall), with the spacers being
particularly AT rich. Analysis of DNA simplicity reveals that, in contrast
to the intergenic spacer (IGS) and the external transcribed spacer (ETS),
most of the rRNA gene regions have been refractory to the action of
slippage-like events, with the exception of the 28S rRNA gene expansion
segments. It would seem that the 28S rRNA can accommodate the products of
slippage-like events without loss of activity. In the following two papers
we analyze the effects of sequence divergence on the evolution of (1) the
28S gene "expansion segments" and (2) the 28S and 18S rRNA secondary
structures among eukaryotic species, respectively. Our detailed analyses
reveal, in addition to unequal crossing-over, (1) the involvement of
slippage and biased mutation in the evolution of the rDNA multigene family
and (2) the molecular coevolution of both expansion segments and the
nucleotides involved with compensatory changes required to maintain
secondary structures of RNA.
相似文献
140.