全文获取类型
收费全文 | 315篇 |
免费 | 4篇 |
国内免费 | 6篇 |
专业分类
系统科学 | 8篇 |
理论与方法论 | 1篇 |
现状及发展 | 26篇 |
研究方法 | 54篇 |
综合类 | 214篇 |
自然研究 | 22篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 28篇 |
2011年 | 56篇 |
2010年 | 11篇 |
2009年 | 3篇 |
2008年 | 37篇 |
2007年 | 20篇 |
2006年 | 28篇 |
2005年 | 30篇 |
2004年 | 22篇 |
2003年 | 21篇 |
2002年 | 29篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1995年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有325条查询结果,搜索用时 15 毫秒
81.
82.
Losos JB Leal M Glor RE De Queiroz K Hertz PE Rodríguez Schettino L Lara AC Jackman TR Larson A 《Nature》2003,424(6948):542-545
Niche conservatism--the tendency for closely related species to be ecologically similar--is widespread. However, most studies compare closely related taxa that occur in allopatry; in sympatry, the stabilizing forces that promote niche conservatism, and thus inhibit niche shifts, may be countered by natural selection favouring ecological divergence to minimize the intensity of interspecific interactions. Consequently, the relative importance of niche conservatism versus niche divergence in determining community structure has received little attention. Here, we examine a tropical lizard community in which species have a long evolutionary history of ecological interaction. We find that evolutionary divergence overcomes niche conservatism: closely related species are no more ecologically similar than expected by random divergence and some distantly related species are ecologically similar, leading to a community in which the relationship between ecological similarity and phylogenetic relatedness is very weak. Despite this lack of niche conservatism, the ecological structuring of the community has a phylogenetic component: niche complementarity only occurs among distantly related species, which suggests that the strength of ecological interactions among species may be related to phylogeny, but it is not necessarily the most closely related species that interact most strongly. 相似文献
83.
Howitz KT Bitterman KJ Cohen HY Lamming DW Lavu S Wood JG Zipkin RE Chung P Kisielewski A Zhang LL Scherer B Sinclair DA 《Nature》2003,425(6954):191-196
In diverse organisms, calorie restriction slows the pace of ageing and increases maximum lifespan. In the budding yeast Saccharomyces cerevisiae, calorie restriction extends lifespan by increasing the activity of Sir2 (ref. 1), a member of the conserved sirtuin family of NAD(+)-dependent protein deacetylases. Included in this family are SIR-2.1, a Caenorhabditis elegans enzyme that regulates lifespan, and SIRT1, a human deacetylase that promotes cell survival by negatively regulating the p53 tumour suppressor. Here we report the discovery of three classes of small molecules that activate sirtuins. We show that the potent activator resveratrol, a polyphenol found in red wine, lowers the Michaelis constant of SIRT1 for both the acetylated substrate and NAD(+), and increases cell survival by stimulating SIRT1-dependent deacetylation of p53. In yeast, resveratrol mimics calorie restriction by stimulating Sir2, increasing DNA stability and extending lifespan by 70%. We discuss possible evolutionary origins of this phenomenon and suggest new lines of research into the therapeutic use of sirtuin activators. 相似文献
84.
Identification of ten loci associated with height highlights new biological pathways in human growth 总被引:1,自引:0,他引:1
Lettre G Jackson AU Gieger C Schumacher FR Berndt SI Sanna S Eyheramendy S Voight BF Butler JL Guiducci C Illig T Hackett R Heid IM Jacobs KB Lyssenko V Uda M;Diabetes Genetics Initiative;FUSION;KORA;Prostate Lung Colorectal Ovarian Cancer Screening Trial;Nurses' Health Study;SardiNIA Boehnke M Chanock SJ Groop LC Hu FB Isomaa B Kraft P Peltonen L Salomaa V Schlessinger D Hunter DJ Hayes RB Abecasis GR Wichmann HE Mohlke KL Hirschhorn JN 《Nature genetics》2008,40(5):584-591
Height is a classic polygenic trait, reflecting the combined influence of multiple as-yet-undiscovered genetic factors. We carried out a meta-analysis of genome-wide association study data of height from 15,821 individuals at 2.2 million SNPs, and followed up the strongest findings in >10,000 subjects. Ten newly identified and two previously reported loci were strongly associated with variation in height (P values from 4 x 10(-7) to 8 x 10(-22)). Together, these 12 loci account for approximately 2% of the population variation in height. Individuals with < or =8 height-increasing alleles and > or =16 height-increasing alleles differ in height by approximately 3.5 cm. The newly identified loci, along with several additional loci with strongly suggestive associations, encompass both strong biological candidates and unexpected genes, and highlight several pathways (let-7 targets, chromatin remodeling proteins and Hedgehog signaling) as important regulators of human stature. These results expand the picture of the biological regulation of human height and of the genetic architecture of this classical complex trait. 相似文献
85.
Germline KRAS mutations cause Noonan syndrome 总被引:22,自引:0,他引:22
Schubbert S Zenker M Rowe SL Böll S Klein C Bollag G van der Burgt I Musante L Kalscheuer V Wehner LE Nguyen H West B Zhang KY Sistermans E Rauch A Niemeyer CM Shannon K Kratz CP 《Nature genetics》2006,38(3):331-336
Noonan syndrome (MIM 163950) is characterized by short stature, facial dysmorphism and cardiac defects. Heterozygous mutations in PTPN11, which encodes SHP-2, cause approximately 50% of cases of Noonan syndrome. The SHP-2 phosphatase relays signals from activated receptor complexes to downstream effectors, including Ras. We discovered de novo germline KRAS mutations that introduce V14I, T58I or D153V amino acid substitutions in five individuals with Noonan syndrome and a P34R alteration in a individual with cardio-facio-cutaneous syndrome (MIM 115150), which has overlapping features with Noonan syndrome. Recombinant V14I and T58I K-Ras proteins show defective intrinsic GTP hydrolysis and impaired responsiveness to GTPase activating proteins, render primary hematopoietic progenitors hypersensitive to growth factors and deregulate signal transduction in a cell lineage-specific manner. These studies establish germline KRAS mutations as a cause of human disease and infer that the constellation of developmental abnormalities seen in Noonan syndrome spectrum is, in large part, due to hyperactive Ras. 相似文献
86.
Lee K Jeong J Kwak I Yu CT Lanske B Soegiarto DW Toftgard R Tsai MJ Tsai S Lydon JP DeMayo FJ 《Nature genetics》2006,38(10):1204-1209
The hedgehog family of morphogens are regulators of cell proliferation, differentiation and cell-cell communication. These morphogens have been shown to have important roles in organogenesis, spermatogenesis, stem cell maintenance and oncogenesis. Indian hedgehog (encoded by Ihh) has been shown to be expressed in the uterine epithelium under the control of the steroid hormone, progesterone. Although in vivo and in vitro studies have shown that progesterone achieves its effects on uterine function through epithelial-stromal cross-talk, molecular mediator(s) for this cellular communication pathway have not been elucidated. Using new experimental approaches that ablate Ihh specifically in Pgr-positive uterine cells of the mouse, we demonstrate that Ihh is an essential mediator of Pgr action in the uterus, and expression of this factor is critical in mediating the communication between the uterine epithelium and stroma required for embryo implantation. 相似文献
87.
88.
89.
90.
Cotton RG; Human Variome Project Appelbe W Auerbach AD Becker K Bodmer W Boone DJ Boulyjenkov V Brahmachari S Brody L Brookes A Brown AF Byers P Cantu JM Cassiman JJ Claustres M Concannon P Cotton RG den Dunnen JT Flicek P Gibbs R Hall J Hasler J Katz M Kwok PY Laradi S Lindblom A Maglott D Marsh S Masimirembwa CM Minoshima S de Ramirez AM Pagon R Ramesar R Ravine D Richards S Rimoin D Ring HZ Scriver CR Sherry S Shimizu N Stein L Tadmouri GO Taylor G Watson M 《Nature genetics》2007,39(4):433-436
Lists of variations in genomic DNA and their effects have been kept for some time and have been used in diagnostics and research. Although these lists have been carefully gathered and curated, there has been little standardization and coordination, complicating their use. Given the myriad possible variations in the estimated 24,000 genes in the human genome, it would be useful to have standard criteria for databases of variation. Incomplete collection and ascertainment of variants demonstrates a need for a universally accessible system. These and other problems led to the World Heath Organization-cosponsored meeting on June 20-23, 2006 in Melbourne, Australia, which launched the Human Variome Project. This meeting addressed all areas of human genetics relevant to collection of information on variation and its effects. Members of each of eight sessions (the clinic and phenotype, the diagnostic laboratory, the research laboratory, curation and collection, informatics, relevance to the emerging world, integration and federation and funding and sustainability) developed a number of recommendations that were then organized into a total of 96 recommendations to act as a foundation for future work worldwide. Here we summarize the background of the project, the meeting and its recommendations. 相似文献