全文获取类型
收费全文 | 1739篇 |
免费 | 126篇 |
出版年
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 17篇 |
2016年 | 41篇 |
2015年 | 61篇 |
2014年 | 90篇 |
2013年 | 105篇 |
2012年 | 149篇 |
2011年 | 192篇 |
2010年 | 131篇 |
2009年 | 100篇 |
2008年 | 103篇 |
2007年 | 85篇 |
2006年 | 75篇 |
2005年 | 68篇 |
2004年 | 85篇 |
2003年 | 83篇 |
2002年 | 75篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 17篇 |
1998年 | 33篇 |
1997年 | 11篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 5篇 |
排序方式: 共有1865条查询结果,搜索用时 31 毫秒
991.
A major goal of contemporary studies of embryonic development is to understand large sets of regulatory changes that accompany the phenomenon of embryonic induction. The highly resolved sea urchin pregastrular endomesoderm–gene regulatory network (EM-GRN) provides a unique framework to study the global regulatory interactions underlying endomesoderm induction. Vegetal micromeres of the sea urchin embryo constitute a classic endomesoderm signaling center, whose potential to induce archenteron formation from presumptive ectoderm was demonstrated almost a century ago. In this work, we ectopically activate the primary mesenchyme cell–GRN (PMC-GRN) that operates in micromere progeny by misexpressing the micromere determinant Pmar1 and identify the responding EM-GRN that is induced in animal blastomeres. Using localized loss-of -function analyses in conjunction with expression of endo16, the molecular definition of micromere-dependent endomesoderm specification, we show that the TGFβ cytokine, ActivinB, is an essential component of this induction in blastomeres that emit this signal, as well as in cells that respond to it. We report that normal pregastrular endomesoderm specification requires activation of the Pmar1-inducible subset of the EM-GRN by the same cytokine, strongly suggesting that early micromere-mediated endomesoderm specification, which regulates timely gastrulation in the sea urchin embryo, is also ActivinB dependent. This study unexpectedly uncovers the existence of an additional uncharacterized micromere signal to endomesoderm progenitors, significantly revising existing models. In one of the first network-level characterizations of an intercellular inductive phenomenon, we describe an important in vivo model of the requirement of ActivinB signaling in the earliest steps of embryonic endomesoderm progenitor specification. 相似文献
992.
993.
Lynne Quarmby 《Current biology : CB》2009,19(4):R158-R160
994.
995.
Summary We have established cell lines with a hypotriploid chromosome number from four testicular tumours. Each line had at least
one Y chromosome and most of the informative centromere and enzyme markers were heterozygous implying that the tumours originated
from germ cells before the first meiotic division. The small metacentric marker chromosome (i12p), specific for testicular
tumours, was present in all tumour cell lines and up to three copies were found in some lines. Rearrangements of chromosome
1 and 11 were each found in three out of four tumours. The rearrangements of chromosome 1 all resulted in duplication of 1q
and deletion of short-arm material from the same chromosome giving loss of heterozygosity for enzyme markers on 1p. Loss of
satellite material from chromosome 13 and the centromere region of chromosome 9 were found in single cases. This study shows
that even where the chromosome number of tumour cells is near triploid, regions of the genome can be deleted. The chromosomes
most frequently involved in rearrangements, 1, 11, and 12 all contain sites of ras oncogenes and it is suggested that loss of normal alleles could result in homozygosity for mutant oncogenes which may play
a part in tumour progression. 相似文献
996.
997.
998.
Lynne M. Quarmby 《Environmental microbiology》2017,19(2):415-416
999.
Leanne N. Phelps Manuel Chevalier Timothy M. Shanahan Julie C. Aleman Colin Courtney-Mustaphi Christopher Albert Kiahtipes Oliver Broennimann Rob Marchant John Shekeine Lynne J. Quick Basil A. S. Davis Antoine Guisan Katie Manning 《Ecography》2020,43(8):1118-1142
A comprehensive understanding of the relationship between land cover, climate change and disturbance dynamics is needed to inform scenarios of vegetation change on the African continent. Although significant advances have been made, large uncertainties exist in projections of future biodiversity and ecosystem change for the world's largest tropical landmass. To better illustrate the effects of climate–disturbance–ecosystem interactions on continental-scale vegetation change, we apply a novel statistical multivariate envelope approach to subfossil pollen data and climate model outputs (TraCE-21ka). We target paleoenvironmental records across continental Africa, from the African Humid Period (AHP: ca 14 700–5500 yr BP) – an interval of spatially and temporally variable hydroclimatic conditions – until recent times, to improve our understanding of overarching vegetation trends and to compare changes between forest and grassy biomes (savanna and grassland). Our results suggest that although climate variability was the dominant driver of change, forest and grassy biomes responded asymmetrically: 1) the climatic envelope of grassy biomes expanded, or persisted in increasingly diverse climatic conditions, during the second half of the AHP whilst that of forest did not; 2) forest retreat occurred much more slowly during the mid to late Holocene compared to the early AHP forest expansion; and 3) as forest and grassy biomes diverged during the second half of the AHP, their ecological relationship (envelope overlap) fundamentally changed. Based on these asymmetries and associated changes in human land use, we propose and discuss three hypotheses about the influence of anthropogenic disturbance on continental-scale vegetation change. 相似文献
1000.