全文获取类型
收费全文 | 27132篇 |
免费 | 81篇 |
国内免费 | 113篇 |
专业分类
系统科学 | 144篇 |
丛书文集 | 141篇 |
教育与普及 | 75篇 |
理论与方法论 | 120篇 |
现状及发展 | 11243篇 |
研究方法 | 1205篇 |
综合类 | 13919篇 |
自然研究 | 479篇 |
出版年
2013年 | 209篇 |
2012年 | 420篇 |
2011年 | 901篇 |
2010年 | 177篇 |
2008年 | 491篇 |
2007年 | 564篇 |
2006年 | 559篇 |
2005年 | 576篇 |
2004年 | 583篇 |
2003年 | 536篇 |
2002年 | 498篇 |
2001年 | 870篇 |
2000年 | 868篇 |
1999年 | 540篇 |
1994年 | 356篇 |
1992年 | 529篇 |
1991年 | 393篇 |
1990年 | 463篇 |
1989年 | 422篇 |
1988年 | 392篇 |
1987年 | 460篇 |
1986年 | 446篇 |
1985年 | 583篇 |
1984年 | 431篇 |
1983年 | 372篇 |
1982年 | 334篇 |
1981年 | 319篇 |
1980年 | 337篇 |
1979年 | 864篇 |
1978年 | 645篇 |
1977年 | 597篇 |
1976年 | 538篇 |
1975年 | 563篇 |
1974年 | 695篇 |
1973年 | 624篇 |
1972年 | 567篇 |
1971年 | 710篇 |
1970年 | 983篇 |
1969年 | 716篇 |
1968年 | 719篇 |
1967年 | 690篇 |
1966年 | 701篇 |
1965年 | 492篇 |
1959年 | 245篇 |
1958年 | 433篇 |
1957年 | 259篇 |
1956年 | 265篇 |
1955年 | 231篇 |
1954年 | 214篇 |
1948年 | 241篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
851.
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
852.
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.
Rajagopalan H Bardelli A Lengauer C Kinzler KW Vogelstein B Velculescu VE 《Nature》2002,418(6901):934
Genes of the RAF family encode kinases that are regulated by Ras and mediate cellular responses to growth signals. Activating mutations in one RAF gene, BRAF, have been found in a high proportion of melanomas and in a small fraction of other cancers. Here we show that BRAF mutations in colorectal cancers occur only in tumours that do not carry mutations in a RAS gene known as KRAS, and that BRAF mutation is linked to the proficiency of these tumours in repairing mismatched bases in DNA. Our results not only provide genetic support for the idea that mutations in BRAF and KRAS exert equivalent effects in tumorigenesis, but also emphasize the role of repair processes in establishing the mutation spectra that underpin human cancer. 相似文献
857.
858.
859.
A cat cloned by nuclear transplantation 总被引:1,自引:0,他引:1
Shin T Kraemer D Pryor J Liu L Rugila J Howe L Buck S Murphy K Lyons L Westhusin M 《Nature》2002,415(6874):859
Sheep, mice, cattle, goats and pigs have all been cloned by transfer of a donor cell nucleus into an enucleated ovum, and now we add the successful cloning of a cat (Felis domesticus) to this list. However, this cloning technology may not be readily extendable to other mammalian species if our understanding of their reproductive processes is limited or if there are species-specific obstacles. 相似文献
860.