全文获取类型
收费全文 | 6306篇 |
免费 | 452篇 |
国内免费 | 2篇 |
出版年
2023年 | 33篇 |
2022年 | 89篇 |
2021年 | 159篇 |
2020年 | 85篇 |
2019年 | 116篇 |
2018年 | 144篇 |
2017年 | 116篇 |
2016年 | 200篇 |
2015年 | 329篇 |
2014年 | 362篇 |
2013年 | 411篇 |
2012年 | 589篇 |
2011年 | 547篇 |
2010年 | 327篇 |
2009年 | 304篇 |
2008年 | 376篇 |
2007年 | 341篇 |
2006年 | 295篇 |
2005年 | 296篇 |
2004年 | 292篇 |
2003年 | 248篇 |
2002年 | 228篇 |
2001年 | 61篇 |
2000年 | 36篇 |
1999年 | 49篇 |
1998年 | 64篇 |
1997年 | 43篇 |
1996年 | 53篇 |
1995年 | 32篇 |
1994年 | 46篇 |
1993年 | 32篇 |
1992年 | 35篇 |
1991年 | 35篇 |
1990年 | 25篇 |
1989年 | 40篇 |
1988年 | 19篇 |
1987年 | 29篇 |
1986年 | 22篇 |
1985年 | 18篇 |
1984年 | 30篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 18篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有6760条查询结果,搜索用时 15 毫秒
991.
Juan Fernando Paredes Jose Fernando Lopez-Olmeda Jose A Muñoz-Cueto F. Sánchez-Vázquez 《Chronobiology international》2018,35(7):920-932
This research aimed at investigating the light synchronization and endogenous origin of daily expression rhythms of eight key genes involved in epigenetic mechanisms (DNA methylation and demethylation) in zebrafish gonads. To this end, 84 zebrafish were distributed into six tanks, each one containing 14 fish (7 males and 7 females). Animals were subjected to 12 h light:12 h dark cycles (LD, lights on at ZT0 h) and fed randomly three times a day during the light phase. Locomotor activity rhythms were recorded in each tank for 20 days to test their synchronization to light. Then, zebrafish were fasted for one day and gonad samples were collected every 4 h during a 24 h cycle (ZT2, 6, 10, 14, 18, and 22 h). The results revealed that most of the epigenetic genes investigated exhibited a significant daily rhythm. DNA methylation genes (dnmt4, dnmt5, dnmt7) exhibited a daily rhythm of expression with a nocturnal acrophase (ZT14:01~ZT22:17 h), except for dnmt7 in males (ZT2:25 h). Similarly, all DNA demethylation genes (tet2, tdg, mb4, gadd45aa, and apobec2b) revealed the existence of statistically significant daily rhythms, except for gadd45aa in females. In females, tdg, mb4, and apobec2b presented a nocturnal peak (ZT14:20 ~ ZT22:04 h), whereas the tet2 acrophase was diurnal (ZT4:02 h). In males, tet2, tdg, and gadd45aa had nocturnal acrophases (ZT18:26~ZT21:31 h), whereas mb4 and apobec2b displayed diurnal acrophases (ZT5:28 and ZT4:02 h, respectively). To determine the endogenous nature of gene expression rhythms, another experiment was performed: 12 groups of 14 fish (7 males and 7 females) were kept in complete darkness (DD) and sampled every 4 h during a 48 h cycle (CT2, 6, 10, 14, 18, 22, 26, 30, 34, 38, 42, and 46 h). Under DD, most of the genes (7 out of 8) presented circadian rhythmicity with different endogenous periodicities (tau), suggesting that the epigenetic mechanisms of DNA methylation and demethylation in the gonads follow an internal control, functioning as part of the translation network linking the environment into somatic signals in fish reproduction. 相似文献
992.
Jose L. Maestro 《Insect Science》2018,25(5):787-796
Juvenile hormone (JH), a sesquiterpenoid synthetized by the insect corpora allata (CA), plays critical roles in metamorphosis and reproduction. Penultimate or last step of JH synthesis is catalyzed by juvenile hormone acid O‐methyltransferase (JHAMT). Here we report the cloning and expression analysis of the JHAMT orthologue in the cockroach, Blattella germanica (L.) (BgJHAMT). BgJHAMT is mainly expressed in CA, with only expression traces in ovary. Three different isoforms, differing in the 3′‐UTR sequence, were identified. Isoform A shows between 35 and 65 times higher expression than B and C in CA from penultimate nymphal instar and adult females. RNAi‐triggered knock down of BgJHAMT produces a dramatic reduction of JH synthesis, concomitant with a decrease of fat body vitellogenin expression and basal follicle length. BgJHAMT mRNA levels in CA of females along the gonadotrophic cycle parallel, with a slight advancement, JH synthesis profile. BgJHAMT mRNA levels were reduced in starved females and in females in which we reduced nutritional signaling by knocking down insulin receptor and target of rapamycin (TOR). Results show that conditions that modify JH synthesis in adult B. germanica females show parallel changes of BgJHAMT mRNA levels and that the JH‐specific branch of the JH synthesis pathway is regulated in the same way as the mevalonate branch. Furthermore, we demonstrate that nutrition and its signaling through the insulin receptor and TOR pathways are essential for activating BgJHAMT expression, which suggests that this enzyme can be a checkpoint for the regulation of JH production in relation to nutritional status. 相似文献
993.
994.
Community level impacts of invasive mosquitofish may exacerbate the impact to a threatened amphibian 下载免费PDF全文
Kaya Klop‐Toker Jose Valdez Michelle Stockwell Simon Clulow John Clulow Michael Mahony 《Austral ecology》2018,43(2):213-224
Invasive fish threaten many native freshwater fauna. However, it can be difficult to determine how invasive fish impact animals with complex life cycles as interaction may be driven by either predation of aquatic larvae or avoidance of fish‐occupied waterbodies by the terrestrial adult stage. Mosquitofish (Gambusia spp.) are highly successful and aggressive invaders that negatively impact numerous aquatic fauna. One species potentially threatened by Gambusia holbrooki is the green and golden bell frog (Litoria aurea). However, G. holbrooki's role in this frog's decline was unclear due to declines driven by the chytrid fungal disease and the continued co‐existence of these fish and frogs in multiple locations. To clarify the extent to which Gambusia is impacting L. aurea, we conducted 3 years of field surveys across a deltaic wetland system in south‐east Australia. We measured the presence and abundance of aquatic taxa including G. holbrooki, and L. aurea frogs and tadpoles, along with habitat parameters at the landscape and microhabitat scale. Generalized linear models were used to explore patterns in the abundance and distributions of L. aurea and G. holbrooki. We found strong negative associations between G. holbrooki and tadpoles of most species, including L. aurea, but no apparent avoidance of G. holbrooki by adult frogs. Native invertebrate predators (Odonata and Coleoptera) were also absent from G. holbrooki‐occupied ponds. Due to the apparent naivety of adult frogs toward G. holbrooki, the separation of G. holbrooki and tadpoles, plus the abundance of alternative predators in G. holbrooki‐free ponds, we conclude that the impact of G. holbrooki on L. aurea recruitment is likely substantial and warrants management action. 相似文献
995.
Jose A. Carvalho Lourdes Rico Arnoldo Santos‐Guerra Maria C. Duarte Maria M. Romeiras Javier Francisco‐Ortega 《Curtis's Botanical Magazine》2018,35(1):63-74
The Madeiran endemic Echium nervosum W.T. Aiton is illustrated based on plants grown at the Royal Botanic Gardens, Kew. Its ecology; phylogenetic and taxonomic placement, and conservation status are discussed. Twenty‐nine species of Echium are endemic to the Macaronesian Islands and they represent one of the most spectacular and best known examples of adaptive radiation on oceanic islands. 相似文献
996.
Massive up‐regulation of LBD transcription factors and EXPANSINs highlights the regulatory programs of rhizomania disease 下载免费PDF全文
997.
Jose L. Horreo America G. Valiente Alba Ardura Aida Blanco Claudia Garcia‐Gonzalez Eva Garcia‐Vazquez 《Ecology and evolution》2018,8(1):521-529
Biological changes occurring as a consequence of domestication and/or captivity are not still deeply known. In Atlantic salmon (Salmo salar), endangered (Southern Europe) populations are enhanced by supportive breeding, which involves only 6 months of captive rearing following artificial spawning of wild‐collected adults. In this work, we assess whether several fitness‐correlated life‐history traits (migratory behavior, straying rate, age at maturity, and growth) are affected by early exposure to the captive environment within a generation, before reproduction thus before genetic selection. Results showed significant differences in growth and migratory behavior (including straying), associated with this very short period of captivity in natural fish populations, changing even genetic variability (decreased in hatchery‐reared adults) and the native population structure within and between rivers of the species. These changes appeared within a single generation, suggesting very short time of captivity is enough for initiating changes normally attributed to domestication. These results may have potential implications for the long‐term population stability/viability of species subjected to restoration and enhancement processes and could be also considered for the management of zoo populations. 相似文献
998.
999.
1000.
Epithelia and endothelia delineate tissue compartments and control their environments by regulating the passage of ions and solutes. This barrier function is essential for the development and maintenance of multicellular organisms, and its dysfunction is associated with numerous human diseases. Recent advances in biomaterials and microfabrication technologies have evolved in vitro approaches for modelling biological barriers. Current microphysiological systems have become more efficient and reliable in mimicking the cell microenvironment. Additionally, methods for the quantification of barrier permeability have long provided significant insight into their underlying mechanisms. In this review, we outline the current techniques to quantify the barrier function of engineered tissues, and we also give an overview of recent microphysiological systems of biological barriers that emulate the microenvironment and microarchitecture of native tissues. 相似文献