全文获取类型
收费全文 | 900篇 |
免费 | 3篇 |
国内免费 | 3篇 |
专业分类
系统科学 | 7篇 |
丛书文集 | 1篇 |
教育与普及 | 2篇 |
理论与方法论 | 14篇 |
现状及发展 | 78篇 |
研究方法 | 182篇 |
综合类 | 559篇 |
自然研究 | 63篇 |
出版年
2021年 | 1篇 |
2020年 | 4篇 |
2018年 | 6篇 |
2017年 | 13篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 9篇 |
2012年 | 84篇 |
2011年 | 155篇 |
2010年 | 23篇 |
2009年 | 9篇 |
2008年 | 75篇 |
2007年 | 82篇 |
2006年 | 90篇 |
2005年 | 84篇 |
2004年 | 61篇 |
2003年 | 70篇 |
2002年 | 83篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有906条查询结果,搜索用时 15 毫秒
31.
32.
Species formation generates biological diversity and occurs when traits evolve that prevent gene flow between populations. Discerning the number and distribution of genes underlying these traits and, in a few cases, identifying the genes involved, has greatly enhanced our understanding over the past 15 years of species formation (reviewed by Noor and Feder and Wolf et al.). However, this work has almost exclusively focused on traits that restrict gene flow between populations that have evolved as a by-product of genetic divergence between geographically isolated populations. By contrast, little is known about the characteristics of genes associated with reinforcement, the process by which natural selection directly favours restricted gene flow during the formation of species. Here we identify changes in two genes that appear to cause a flower colour change in Phlox drummondii, which previous work has shown contributes to reinforcement. Both changes involve cis-regulatory mutations to genes in the anthocyanin biosynthetic pathway (ABP). Because one change is recessive whereas the other is dominant, hybrid offspring produce an intermediate flower colour that is visited less by pollinators, and is presumably maladaptive. Thus genetic change selected to increase prezygotic isolation also appears to result in increased postzygotic isolation. 相似文献
33.
Kaneko H Dridi S Tarallo V Gelfand BD Fowler BJ Cho WG Kleinman ME Ponicsan SL Hauswirth WW Chiodo VA Karikó K Yoo JW Lee DK Hadziahmetovic M Song Y Misra S Chaudhuri G Buaas FW Braun RE Hinton DR Zhang Q Grossniklaus HE Provis JM Madigan MC Milam AH Justice NL Albuquerque RJ Blandford AD Bogdanovich S Hirano Y Witta J Fuchs E Littman DR Ambati BK Rudin CM Chong MM Provost P Kugel JF Goodrich JA Dunaief JL Baffi JZ Ambati J 《Nature》2011,471(7338):325-330
34.
Wertz IE Kusam S Lam C Okamoto T Sandoval W Anderson DJ Helgason E Ernst JA Eby M Liu J Belmont LD Kaminker JS O'Rourke KM Pujara K Kohli PB Johnson AR Chiu ML Lill JR Jackson PK Fairbrother WJ Seshagiri S Ludlam MJ Leong KG Dueber EC Maecker H Huang DC Dixit VM 《Nature》2011,471(7336):110-114
Microtubules have pivotal roles in fundamental cellular processes and are targets of antitubulin chemotherapeutics. Microtubule-targeted agents such as Taxol and vincristine are prescribed widely for various malignancies, including ovarian and breast adenocarcinomas, non-small-cell lung cancer, leukaemias and lymphomas. These agents arrest cells in mitosis and subsequently induce cell death through poorly defined mechanisms. The strategies that resistant tumour cells use to evade death induced by antitubulin agents are also unclear. Here we show that the pro-survival protein MCL1 (ref. 3) is a crucial regulator of apoptosis triggered by antitubulin chemotherapeutics. During mitotic arrest, MCL1 protein levels decline markedly, through a post-translational mechanism, potentiating cell death. Phosphorylation of MCL1 directs its interaction with the tumour-suppressor protein FBW7, which is the substrate-binding component of a ubiquitin ligase complex. The polyubiquitylation of MCL1 then targets it for proteasomal degradation. The degradation of MCL1 was blocked in patient-derived tumour cells that lacked FBW7 or had loss-of-function mutations in FBW7, conferring resistance to antitubulin agents and promoting chemotherapeutic-induced polyploidy. Additionally, primary tumour samples were enriched for FBW7 inactivation and elevated MCL1 levels, underscoring the prominent roles of these proteins in oncogenesis. Our findings suggest that profiling the FBW7 and MCL1 status of tumours, in terms of protein levels, messenger RNA levels and genetic status, could be useful to predict the response of patients to antitubulin chemotherapeutics. 相似文献
35.
Konhauser KO Lalonde SV Planavsky NJ Pecoits E Lyons TW Mojzsis SJ Rouxel OJ Barley ME Rosìere C Fralick PW Kump LR Bekker A 《Nature》2011,478(7369):369-373
The enrichment of redox-sensitive trace metals in ancient marine sedimentary rocks has been used to determine the timing of the oxidation of the Earth's land surface. Chromium (Cr) is among the emerging proxies for tracking the effects of atmospheric oxygenation on continental weathering; this is because its supply to the oceans is dominated by terrestrial processes that can be recorded in the Cr isotope composition of Precambrian iron formations. However, the factors controlling past and present seawater Cr isotope composition are poorly understood. Here we provide an independent and complementary record of marine Cr supply, in the form of Cr concentrations and authigenic enrichment in iron-rich sedimentary rocks. Our data suggest that Cr was largely immobile on land until around 2.48?Gyr ago, but within the 160?Myr that followed--and synchronous with independent evidence for oxygenation associated with the Great Oxidation Event (see, for example, refs 4-6)--marked excursions in Cr content and Cr/Ti ratios indicate that Cr was solubilized at a scale unrivalled in history. As Cr isotope fractionations at that time were muted, Cr must have been mobilized predominantly in reduced, Cr(III), form. We demonstrate that only the oxidation of an abundant and previously stable crustal pyrite reservoir by aerobic-respiring, chemolithoautotrophic bacteria could have generated the degree of acidity required to solubilize Cr(III) from ultramafic source rocks and residual soils. This profound shift in weathering regimes beginning at 2.48?Gyr ago constitutes the earliest known geochemical evidence for acidophilic aerobes and the resulting acid rock drainage, and accounts for independent evidence of an increased supply of dissolved sulphate and sulphide-hosted trace elements to the oceans around that time. Our model adds to amassing evidence that the Archaean-Palaeoproterozoic boundary was marked by a substantial shift in terrestrial geochemistry and biology. 相似文献
36.
37.
Don't judge species on their origins 总被引:1,自引:0,他引:1
38.
Spatio-temporal transcriptome of the human brain 总被引:1,自引:0,他引:1
39.
40.