全文获取类型
收费全文 | 33479篇 |
免费 | 144篇 |
国内免费 | 112篇 |
专业分类
系统科学 | 306篇 |
丛书文集 | 526篇 |
教育与普及 | 71篇 |
理论与方法论 | 155篇 |
现状及发展 | 14933篇 |
研究方法 | 1309篇 |
综合类 | 16017篇 |
自然研究 | 418篇 |
出版年
2013年 | 206篇 |
2012年 | 539篇 |
2011年 | 971篇 |
2010年 | 162篇 |
2008年 | 492篇 |
2007年 | 535篇 |
2006年 | 596篇 |
2005年 | 754篇 |
2004年 | 1149篇 |
2003年 | 979篇 |
2002年 | 654篇 |
2001年 | 978篇 |
2000年 | 999篇 |
1999年 | 669篇 |
1992年 | 540篇 |
1991年 | 443篇 |
1990年 | 474篇 |
1989年 | 465篇 |
1988年 | 412篇 |
1987年 | 449篇 |
1986年 | 521篇 |
1985年 | 595篇 |
1984年 | 482篇 |
1983年 | 410篇 |
1982年 | 364篇 |
1981年 | 383篇 |
1980年 | 438篇 |
1979年 | 1069篇 |
1978年 | 849篇 |
1977年 | 816篇 |
1976年 | 621篇 |
1975年 | 716篇 |
1974年 | 1001篇 |
1973年 | 844篇 |
1972年 | 868篇 |
1971年 | 1035篇 |
1970年 | 1314篇 |
1969年 | 997篇 |
1968年 | 905篇 |
1967年 | 980篇 |
1966年 | 812篇 |
1965年 | 635篇 |
1964年 | 179篇 |
1959年 | 324篇 |
1958年 | 554篇 |
1957年 | 418篇 |
1956年 | 347篇 |
1955年 | 319篇 |
1954年 | 321篇 |
1948年 | 239篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
851.
Numerous potentially functional but non-genic conserved sequences on human chromosome 21 总被引:28,自引:0,他引:28
Dermitzakis ET Reymond A Lyle R Scamuffa N Ucla C Deutsch S Stevenson BJ Flegel V Bucher P Jongeneel CV Antonarakis SE 《Nature》2002,420(6915):578-582
The use of comparative genomics to infer genome function relies on the understanding of how different components of the genome change over evolutionary time. The aim of such comparative analysis is to identify conserved, functionally transcribed sequences such as protein-coding genes and non-coding RNA genes, and other functional sequences such as regulatory regions, as well as other genomic features. Here, we have compared the entire human chromosome 21 with syntenic regions of the mouse genome, and have identified a large number of conserved blocks of unknown function. Although previous studies have made similar observations, it is unknown whether these conserved sequences are genes or not. Here we present an extensive experimental and computational analysis of human chromosome 21 in an effort to assign function to sequences conserved between human chromosome 21 (ref. 8) and the syntenic mouse regions. Our data support the presence of a large number of potentially functional non-genic sequences, probably regulatory and structural. The integration of the properties of the conserved components of human chromosome 21 to the rapidly accumulating functional data for this chromosome will improve considerably our understanding of the role of sequence conservation in mammalian genomes. 相似文献
852.
The relatively short length of most instrumental climate records restricts the study of climate variability, and it is therefore essential to extend the record into the past with the help of proxy data. Only since the late 1940s have atmospheric data been available that are sufficient in quality and spatial resolution to identify the dominant patterns of climate variability, such as the Pacific North America pattern and the Pacific Decadal Oscillation. Here we present a 301-year snow accumulation record from an ice core at a height of 5,340 m above sea level-from Mount Logan, in northwestern North America. This record shows features that are closely linked with the Pacific North America pattern for the period of instrumental data availability. Our record extends back in time to cover the period from the closing stages of the Little Ice Age to the warmest decade in the past millennium. We find a positive, accelerating trend in snow accumulation after the middle of the nineteenth century. This trend is paralleled by a warming over northwestern North America which has been associated with secular changes in both the Pacific North America pattern and the Pacific Decadal Oscillation. 相似文献
853.
Analysis of the mouse transcriptome based on functional annotation of 60,770 full-length cDNAs 总被引:6,自引:0,他引:6
Okazaki Y Furuno M Kasukawa T Adachi J Bono H Kondo S Nikaido I Osato N Saito R Suzuki H Yamanaka I Kiyosawa H Yagi K Tomaru Y Hasegawa Y Nogami A Schönbach C Gojobori T Baldarelli R Hill DP Bult C Hume DA Quackenbush J Schriml LM Kanapin A Matsuda H Batalov S Beisel KW Blake JA Bradt D Brusic V Chothia C Corbani LE Cousins S Dalla E Dragani TA Fletcher CF Forrest A Frazer KS Gaasterland T Gariboldi M Gissi C Godzik A Gough J Grimmond S Gustincich S Hirokawa N Jackson IJ Jarvis ED Kanai A 《Nature》2002,420(6915):563-573
854.
855.
856.
857.
858.
859.
Porous inorganic solids can be synthesized in complex forms, and here we describe a simple method to create an ultralight, macroporous, crystalline vanadium oxide foam by bubbling oxygen gas produced in situ through a viscous vanadium oxide gel. This foaming process could be extended to other metal oxides. 相似文献
860.