全文获取类型
收费全文 | 31592篇 |
免费 | 48篇 |
国内免费 | 68篇 |
专业分类
系统科学 | 157篇 |
丛书文集 | 717篇 |
教育与普及 | 82篇 |
理论与方法论 | 201篇 |
现状及发展 | 13543篇 |
研究方法 | 1369篇 |
综合类 | 15235篇 |
自然研究 | 404篇 |
出版年
2013年 | 178篇 |
2012年 | 435篇 |
2011年 | 879篇 |
2010年 | 182篇 |
2008年 | 557篇 |
2007年 | 556篇 |
2006年 | 609篇 |
2005年 | 603篇 |
2004年 | 535篇 |
2003年 | 579篇 |
2002年 | 581篇 |
2001年 | 979篇 |
2000年 | 905篇 |
1999年 | 604篇 |
1992年 | 571篇 |
1991年 | 462篇 |
1990年 | 486篇 |
1989年 | 489篇 |
1988年 | 494篇 |
1987年 | 499篇 |
1986年 | 491篇 |
1985年 | 602篇 |
1984年 | 497篇 |
1983年 | 404篇 |
1982年 | 347篇 |
1981年 | 340篇 |
1980年 | 449篇 |
1979年 | 968篇 |
1978年 | 857篇 |
1977年 | 847篇 |
1976年 | 580篇 |
1975年 | 630篇 |
1974年 | 932篇 |
1973年 | 788篇 |
1972年 | 806篇 |
1971年 | 1021篇 |
1970年 | 1344篇 |
1969年 | 1005篇 |
1968年 | 949篇 |
1967年 | 991篇 |
1966年 | 833篇 |
1965年 | 610篇 |
1964年 | 149篇 |
1959年 | 360篇 |
1958年 | 522篇 |
1957年 | 443篇 |
1956年 | 366篇 |
1955年 | 316篇 |
1954年 | 363篇 |
1948年 | 193篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
781.
782.
783.
784.
785.
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
786.
787.
人类学在聚焦世界各地人们的生活及其方式的过程中,一直致力于成为一门客观性的科学。最近,女性人类学者们的一些活动则为表达主观观点,传达个人情感及检验人类学者和研究群体间的关系开辟了道路。这篇文章审视了我个人一生对中国的美好情感,而我的这种情感于 2000 年参加在北京举行的IUAES(国际人类学民族学联合会中期会议)时达到高潮。 相似文献
788.
Microbial starch-binding domains (SBD) and granule-bound starch synthase I (GBSSI) are proteins which are accumulated in potato starch granules. The efficiency of SBD and GBSSI for targeting active luciferase reporter proteins to granules during starch biosynthesis was compared. GBSSI or SBD sequences were fused to the N- or C-terminus of the luciferase (LUC) gene, via an artificial Pro-Thr encoding linker sequence. The genes were introduced into an amylose-free (amf) potato mutant. It appeared that SBD was superior to GBSSI as a targeting sequence, mainly because the luciferase retained higher activity in the SBD-containing fusion proteins than in the GBSSI-containing ones. 相似文献
789.
We have developed technologies that simplify genomic library construction and screening, substantially reducing both the time and the cost associated with traditional library screening methods and facilitating the generation of gene-targeting constructs. By taking advantage of homologous recombination in Escherichia coli, we were able to use as little as 80 bp of total sequence homology to screen for a specific gene from a genomic library in plasmid or phage form. This method, called recombination cloning (REC), takes only a few days instead of the several weeks required for traditional plaque-lift methods. In addition, because every clone in the mouse genomic library we have constructed has a negative selection marker adjacent to the genomic insert, REC screening can generate gene-targeting vectors in one step, from library screening to finished construct. Conditional targeting constructs can be generated easily with minimal additional manipulation. 相似文献
790.
The extent of linkage disequilibrium in Arabidopsis thaliana. 总被引:20,自引:0,他引:20
Magnus Nordborg Justin O Borevitz Joy Bergelson Charles C Berry Joanne Chory Jenny Hagenblad Martin Kreitman Julin N Maloof Tina Noyes Peter J Oefner Eli A Stahl Detlef Weigel 《Nature genetics》2002,30(2):190-193
Linkage disequilibrium (LD), the nonrandom occurrence of alleles in haplotypes, has long been of interest to population geneticists. Recently, the rapidly increasing availability of genomic polymorphism data has fueled interest in LD as a tool for fine-scale mapping, in particular for human disease loci. The chromosomal extent of LD is crucial in this context, because it determines how dense a map must be for associations to be detected and, conversely, limits how finely loci may be mapped. Arabidopsis thaliana is expected to harbor unusually extensive LD because of its high degree of selfing. Several polymorphism studies have found very strong LD within individual loci, but also evidence of some recombination. Here we investigate the pattern of LD on a genomic scale and show that in global samples, LD decays within approximately 1 cM, or 250 kb. We also show that LD in local populations may be much stronger than that of global populations, presumably as a result of founder events. The combination of a relatively high level of polymorphism and extensive haplotype structure bodes well for developing a genome-wide LD map in A. thaliana. 相似文献