全文获取类型
收费全文 | 15639篇 |
免费 | 1293篇 |
国内免费 | 1篇 |
出版年
2023年 | 132篇 |
2022年 | 86篇 |
2021年 | 413篇 |
2020年 | 275篇 |
2019年 | 330篇 |
2018年 | 387篇 |
2017年 | 351篇 |
2016年 | 554篇 |
2015年 | 883篇 |
2014年 | 957篇 |
2013年 | 1188篇 |
2012年 | 1408篇 |
2011年 | 1321篇 |
2010年 | 794篇 |
2009年 | 794篇 |
2008年 | 1019篇 |
2007年 | 871篇 |
2006年 | 833篇 |
2005年 | 756篇 |
2004年 | 682篇 |
2003年 | 571篇 |
2002年 | 575篇 |
2001年 | 143篇 |
2000年 | 105篇 |
1999年 | 131篇 |
1998年 | 128篇 |
1997年 | 110篇 |
1996年 | 90篇 |
1995年 | 84篇 |
1994年 | 72篇 |
1993年 | 66篇 |
1992年 | 75篇 |
1991年 | 57篇 |
1990年 | 49篇 |
1989年 | 54篇 |
1988年 | 36篇 |
1987年 | 47篇 |
1986年 | 34篇 |
1985年 | 47篇 |
1984年 | 41篇 |
1983年 | 34篇 |
1982年 | 36篇 |
1981年 | 34篇 |
1980年 | 29篇 |
1978年 | 24篇 |
1977年 | 35篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1974年 | 20篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Athanassios Alevizopoulos Nicolas Mermod 《BioEssays : news and reviews in molecular, cellular and developmental biology》1997,19(7):581-591
Transforming growth factor-β (TGF-β) and its related proteins regulate broad aspects of body development, including cell proliferation, differentiation, apoptosis and gene expression, in various organisms. Deregulated TGF-β function has been causally implicated in the generation of human fibrotic disorders and in tumor progression. Nevertheless, the molecular mechanisms of TGF-β action remained essentially unknown until recently. Here, we discuss recent progress in our understanding of the mechanism of TGF-β signal transduction with respect to the regulation of gene expression, the control of cell phenotype and the potential usage TGF-β for the treatment of human diseases. 相似文献
3.
4.
5.
Elen Arroyo Peres Márcio Bernardino DaSilva Manuel Antunes Jr Ricardo Pinto-Da-Rocha 《分类学与生物多样性》2018,16(2):171-187
The Brazilian Atlantic Rain Forest is amongst the most diverse biomes in the world, but the processes that shaped its biodiversity are still poorly understood. We used one mitochondrial and two nuclear markers to evaluate the phylogeographic patterns of the endemic harvestman Acutisoma longipes and its closely related species to investigate the biogeographic history of this biome. The results showed low intrapopulation diversity and strong population structure, suggesting poor dispersion amongst locations. Phylogenetic analyses pointed to three main mitochondrial lineages congruent with the geomorphology of the south-eastern region of Brazil (Serra do Mar, Serra da Mantiqueira, and interior plateau). These older divergences occurred in the middle-Neogene, suggesting that events in this period drove the diversification of the species, but Quaternary events also affected the populations locally. We detected some congruence between A. longipes demographic patterns and the areas of endemism delimited for harvestmen, suggesting that some regions of the distribution could have been more stable in the past (especially in Serra da Mantiqueira). Our findings corroborate that harvestmen are a suitable group for the study of ancient biogeographic events in the Atlantic Rain Forest, even at small-scale ranges. Acutisoma hamatum is here considered as a new junior synonym of A. longipes. 相似文献
6.
Clémence L. Gamblin émilie J.-L. Hardy Fran?ois J.-M. Chartier Nicolas Bisson Patrick Laprise 《The Journal of cell biology》2014,204(4):487-495
During epithelial cell polarization, Yurt (Yrt) is initially confined to the lateral membrane and supports the stability of this membrane domain by repressing the Crumbs-containing apical machinery. At late stages of embryogenesis, the apical recruitment of Yrt restricts the size of the apical membrane. However, the molecular basis sustaining the spatiotemporal dynamics of Yrt remains undefined. In this paper, we report that atypical protein kinase C (aPKC) phosphorylates Yrt to prevent its premature apical localization. A nonphosphorylatable version of Yrt dominantly dismantles the apical domain, showing that its aPKC-mediated exclusion is crucial for epithelial cell polarity. In return, Yrt counteracts aPKC functions to prevent apicalization of the plasma membrane. The ability of Yrt to bind and restrain aPKC signaling is central for its role in polarity, as removal of the aPKC binding site neutralizes Yrt activity. Thus, Yrt and aPKC are involved in a reciprocal antagonistic regulatory loop that contributes to segregation of distinct and mutually exclusive membrane domains in epithelial cells. 相似文献
7.
The application of multi-objective optimisation to evolutionary robotics is receiving increasing attention. A survey of the literature reveals the different possibilities it offers to improve the automatic design of efficient and adaptive robotic systems, and points to the successful demonstrations available for both task-specific and task-agnostic approaches (i.e., with or without reference to the specific design problem to be tackled). However, the advantages of multi-objective approaches over single-objective ones have not been clearly spelled out and experimentally demonstrated. This paper fills this gap for task-specific approaches: starting from well-known results in multi-objective optimisation, we discuss how to tackle commonly recognised problems in evolutionary robotics. In particular, we show that multi-objective optimisation (i) allows evolving a more varied set of behaviours by exploring multiple trade-offs of the objectives to optimise, (ii) supports the evolution of the desired behaviour through the introduction of objectives as proxies, (iii) avoids the premature convergence to local optima possibly introduced by multi-component fitness functions, and (iv) solves the bootstrap problem exploiting ancillary objectives to guide evolution in the early phases. We present an experimental demonstration of these benefits in three different case studies: maze navigation in a single robot domain, flocking in a swarm robotics context, and a strictly collaborative task in collective robotics. 相似文献
8.
Guadalupe Herrera Vicente Aleixandra Amparo Urios Manuel Blanco 《FEMS microbiology letters》1993,106(2):187-191
Abstract We have isolated spontaneous mutant strains of Escherichia coli KL16 showing different levels of nalidixic acid (NAL) resistance. From 40 independent mutants, 36 had gyrA and four had gyrB mutations. Most of the gyrA mutations (30/36) conferred high level NAL resistance. In contrast, the only gyrB mutation that conferred a relatively high level of NAL resistance also determined enhanced susceptibility to quinolones with a piperazinyl substituent at C7 position of the quinolone ring (amphoteric quinolones). This gyrB mutation (denoted gyrB1604 ), jointly with a gyrA mutation (denoted gyrA972 ) which confers a high level of quinolone resistance, were used to construct strain IC2476, carrying the two gyr mutant alleles. The susceptibility of this strain to amphoteric quinolones (pipemidic acid, norfloxacin and ciprofloxacin) was similar to that of the gyrA972 single mutant. This result indicates that the change in GyrA subunit which determines a high level of quinolone-resistance has the capacity to mask the hypersusceptibility to amphoteric quinolones promoted by the GyrB1604 mutant subunit. This capacity was further confirmed by studying the effects of ciprofloxacin (CFX) on gyrase inhibition in the gyrA972 gyrB1604 strain. 相似文献
9.
Liakos Panagiotis; Bourmeyster Nicolas; Defaye Genevieve; Chambaz Edmond M.; Bottari Serge P. 《American journal of physiology. Cell physiology》1997,273(4):C1324
Angiotensin II(ANG II) has long been known for its pressor and growth-promotingeffects, which are both mediated by theAT1 receptor. By contrast, theAT2 receptor has recently beenreported to mediate inhibition of proliferation through as yetundefined mechanisms. We report here that in bovine adrenal fasciculata cells ANG II by itself does not affect growth but inhibits basic fibroblast growth factor (bFGF)-induced DNA synthesis and blocks thecells in G1 phase. Consistent withthis, ANG II inhibits cyclin D1 expression and cyclinD1-associated kinase activity. Theantimitogenic effect of ANG II is partly mimicked by theAT2-selective agonist CGP-42112.It is also blocked partly and in an additive fashion by theAT1- andAT2-selective antagonists losartanand PD-123319, indicating the contribution of both receptor subtypes tothis response. AT1-dependentantiproliferation is selectively blocked by the cyclooxygenaseinhibitor indomethacin and restored by prostaglandin E2, whereasAT2-receptor-mediated inhibitionof growth is suppressed by the tyrosine phosphatase inhibitorsorthovanadate and bpV(pic). Both pathways are, however,pertussis toxin sensitive. We hypothesize that, in fasciculatacells, the AT1 receptor inhibitsbFGF-induced proliferation by stimulating prostaglandin synthesis,whereas the AT2 receptor mediatesits effect through a pathway that requires protein tyrosine phosphataseactivation. 相似文献
10.