全文获取类型
收费全文 | 5047篇 |
免费 | 23篇 |
国内免费 | 36篇 |
专业分类
系统科学 | 76篇 |
丛书文集 | 140篇 |
教育与普及 | 185篇 |
理论与方法论 | 10篇 |
现状及发展 | 305篇 |
研究方法 | 691篇 |
综合类 | 3697篇 |
自然研究 | 2篇 |
出版年
2014年 | 7篇 |
2012年 | 364篇 |
2011年 | 426篇 |
2010年 | 94篇 |
2009年 | 20篇 |
2008年 | 335篇 |
2007年 | 419篇 |
2006年 | 367篇 |
2005年 | 427篇 |
2004年 | 379篇 |
2003年 | 365篇 |
2002年 | 333篇 |
2001年 | 277篇 |
2000年 | 409篇 |
1999年 | 102篇 |
1998年 | 16篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 12篇 |
1991年 | 22篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 27篇 |
1985年 | 26篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 26篇 |
1981年 | 34篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1971年 | 12篇 |
1970年 | 27篇 |
1966年 | 9篇 |
1959年 | 38篇 |
1958年 | 53篇 |
1957年 | 42篇 |
1956年 | 27篇 |
1955年 | 32篇 |
1954年 | 30篇 |
1953年 | 23篇 |
1952年 | 9篇 |
1951年 | 12篇 |
1949年 | 6篇 |
1948年 | 15篇 |
排序方式: 共有5106条查询结果,搜索用时 15 毫秒
991.
Sequence and analysis of chromosome 2 of the plant Arabidopsis thaliana 总被引:21,自引:0,他引:21
Lin X Kaul S Rounsley S Shea TP Benito MI Town CD Fujii CY Mason T Bowman CL Barnstead M Feldblyum TV Buell CR Ketchum KA Lee J Ronning CM Koo HL Moffat KS Cronin LA Shen M Pai G Van Aken S Umayam L Tallon LJ Gill JE Adams MD Carrera AJ Creasy TH Goodman HM Somerville CR Copenhaver GP Preuss D Nierman WC White O Eisen JA Salzberg SL Fraser CM Venter JC 《Nature》1999,402(6763):761-768
Arabidopsis thaliana (Arabidopsis) is unique among plant model organisms in having a small genome (130-140 Mb), excellent physical and genetic maps, and little repetitive DNA. Here we report the sequence of chromosome 2 from the Columbia ecotype in two gap-free assemblies (contigs) of 3.6 and 16 megabases (Mb). The latter represents the longest published stretch of uninterrupted DNA sequence assembled from any organism to date. Chromosome 2 represents 15% of the genome and encodes 4,037 genes, 49% of which have no predicted function. Roughly 250 tandem gene duplications were found in addition to large-scale duplications of about 0.5 and 4.5 Mb between chromosomes 2 and 1 and between chromosomes 2 and 4, respectively. Sequencing of nearly 2 Mb within the genetically defined centromere revealed a low density of recognizable genes, and a high density and diverse range of vestigial and presumably inactive mobile elements. More unexpected is what appears to be a recent insertion of a continuous stretch of 75% of the mitochondrial genome into chromosome 2. 相似文献
992.
A structural change in the kinesin motor protein that drives motility 总被引:34,自引:0,他引:34
Rice S Lin AW Safer D Hart CL Naber N Carragher BO Cain SM Pechatnikova E Wilson-Kubalek EM Whittaker M Pate E Cooke R Taylor EW Milligan RA Vale RD 《Nature》1999,402(6763):778-784
Kinesin motors power many motile processes by converting ATP energy into unidirectional motion along microtubules. The force-generating and enzymatic properties of conventional kinesin have been extensively studied; however, the structural basis of movement is unknown. Here we have detected and visualized a large conformational change of an approximately 15-amino-acid region (the neck linker) in kinesin using electron paramagnetic resonance, fluorescence resonance energy transfer, pre-steady state kinetics and cryo-electron microscopy. This region becomes immobilized and extended towards the microtubule 'plus' end when kinesin binds microtubules and ATP, and reverts to a more mobile conformation when gamma-phosphate is released after nucleotide hydrolysis. This conformational change explains both the direction of kinesin motion and processive movement by the kinesin dimer. 相似文献
993.
Prion diseases can be infectious, sporadic and genetic. The infectious forms of these diseases, including bovine spongiform encephalopathy and Creutzfeldt-Jakob disease, are usually characterized by the accumulation in the brain of the transmissible pathogen, an abnormally folded isoform of the prion protein (PrP) termed PrPSc. However, certain inherited PrP mutations appear to cause neurodegeneration in the absence of PrPSc, working instead by favoured synthesis of CtmPrP, a transmembrane form of PrP. The relationship between the neurodegeneration seen in transmissible prion diseases involving PrPSc and that associated with ctmPrP has remained unclear. Here we find that the effectiveness of accumulated PrPSc in causing neurodegenerative disease depends upon the predilection of host-encoded PrP to be made in the ctmPrP form. Furthermore, the time course of PrPSc accumulation in transmissible prion disease is followed closely by increased generation of CtmPrP. Thus, the accumulation of PrPSc appears to modulate in trans the events involved in generating or metabolising CtmPrP. Together, these data suggest that the events of CtmPrP-mediated neurodegeneration may represent a common step in the pathogenesis of genetic and infectious prion diseases. 相似文献
994.
研究了卷积码的有限响应输入序列的特性和卷积码的误比特率的实用特性,提出了汉明距的一种解析求解法.利用这些特性和解析求解法,能够完全取代编码器设计中现有的计算机模拟方法,在搜索好码和计算误比特率方面具有明显的优越性,并可应用于Turbo码中交织器的设计 相似文献
995.
996.
997.
998.
999.
1000.