全文获取类型
收费全文 | 1084篇 |
免费 | 72篇 |
国内免费 | 2篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 27篇 |
2020年 | 9篇 |
2019年 | 16篇 |
2018年 | 34篇 |
2017年 | 22篇 |
2016年 | 33篇 |
2015年 | 45篇 |
2014年 | 52篇 |
2013年 | 84篇 |
2012年 | 89篇 |
2011年 | 101篇 |
2010年 | 46篇 |
2009年 | 48篇 |
2008年 | 71篇 |
2007年 | 53篇 |
2006年 | 57篇 |
2005年 | 64篇 |
2004年 | 59篇 |
2003年 | 49篇 |
2002年 | 31篇 |
2001年 | 16篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 13篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 1篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1158条查询结果,搜索用时 375 毫秒
31.
32.
33.
34.
Emrich SJ Li L Wen TJ Yandeau-Nelson MD Fu Y Guo L Chou HH Aluru S Ashlock DA Schnable PS 《Genetics》2007,175(1):429-439
As an ancient segmental tetraploid, the maize (Zea mays L.) genome contains large numbers of paralogs that are expected to have diverged by a minimum of 10% over time. Nearly identical paralogs (NIPs) are defined as paralogous genes that exhibit > or = 98% identity. Sequence analyses of the "gene space" of the maize inbred line B73 genome, coupled with wet lab validation, have revealed that, conservatively, at least approximately 1% of maize genes have a NIP, a rate substantially higher than that in Arabidopsis. In most instances, both members of maize NIP pairs are expressed and are therefore at least potentially functional. Of evolutionary significance, members of many NIP families also exhibit differential expression. The finding that some families of maize NIPs are closely linked genetically while others are genetically unlinked is consistent with multiple modes of origin. NIPs provide a mechanism for the maize genome to circumvent the inherent limitation that diploid genomes can carry at most two "alleles" per "locus." As such, NIPs may have played important roles during the evolution and domestication of maize and may contribute to the success of long-term selection experiments in this important crop species. 相似文献
35.
Sucrose-inducible expression of hepatitis B surface antigen using potato granule-bound starch synthase promoter 总被引:2,自引:0,他引:2
U. K. S. Shekhawat T. R. Ganapathi G. B. Sunil Kumar L. Srinivas 《Plant biotechnology reports》2007,1(4):199-206
NT-1 cells of tobacco (Nicotiana tabacum L.) were transformed with pGBSSHBS and pGBSSHER expression cassettes wherein expression of hepatitis B surface antigen (HBsAg)
was driven by potato granule-bound starch synthase (GBSS) promoter. The transformed nature of the cells was confirmed by PCR
analysis. Expression of HBsAg was confirmed by RT-PCR and Western blotting and levels of expression were assayed by ELISA.
Transformed cell lines exhibited a sucrose-inducible pattern of HBsAg expression. NT-1 medium supplemented with 175 mmol L−1 sucrose gave the highest HBsAg expression of 198 ng g−1 FW after 8 days of induction. Different sugars, for example glucose, fructose, and palatinose, were also tested to study
the inducible nature of GBSS promoter. The results demonstrate that potato GBSS promoter can be used in heterologous host
systems like tobacco NT-1 cell suspension cultures for sucrose-inducible expression of recombinant proteins. 相似文献
36.
37.
38.
Phage Φ80 can infect Escherichia coli in a stealthy manner and persist by forming lysogens. Such Φ80 lysogens are fairly common and often go undetected unless the host is grown at temperatures below 37°C. Since low growth temperatures are required for growing temperature-sensitive mutants and often preferred for large-scale applications such as protein production, Φ80-resistant strains would be useful. We report the construction of E. coli strains that cannot be efficiently lysogenized or infected by bacteriophage Φ80. These strains contain combinations of deletions or mutations in the bacterial attachment site for Φ80 integration and/or deletions in the genes required for phage absorption to the host outer membrane. These strains should help contain and prevent Φ80 infection of E. coli cultures in a laboratory or industrial setting. 相似文献
39.
Aqueous two-phase extraction has been recognized as a versatile downstream processing technique for the recovery of biomolecules. A major deterrent to its industrial exploitation is the slow demixing of the two aqueous phases after extraction, due to their similar physical properties. A method to decrease the demixing times of these systems, employing a travelling acoustic wave field, is reported. The effects of phase composition and microbial cells on demixing in a polyethylene glycol/potassium phosphate two-phase system are studied in detail. As phase composition increased, demixing time decreased gradually. Phase volume ratio was found to have a significant effect on demixing time at low phase compositions. However, at intermediate and high phase compositions, only a small effect on demixing time was observed. The effect of phase composition and volume ratio on demixing behavior was explained based on the droplet size of the dispersed phase, which is the resultant effect of the physical properties of the phases. At all the phase compositions studied, the acoustically assisted process decreased the demixing time by 17-60% when compared to demixing under gravity alone. Increasing the cell concentration increased the demixing time markedly in case of yeast cells. However, it remained practically constant in the case of Lactobacillus casei cells. Application of an acoustic field reduced the demixing times up to 60% and 40% in the case of yeast and L. casei cells, respectively. Visual observations indicated that ultrasonication caused mild circulation currents in the phase dispersion enhancing droplet-droplet interaction, which in turn enhanced the rate of coalescence, eventually resulting in an enhanced demixing rate. 相似文献
40.
Srinivas S Rodriguez T Clements M Smith JC Beddington RS 《Development (Cambridge, England)》2004,131(5):1157-1164
The anterior visceral endoderm (AVE) of the mouse embryo is a specialised extra-embryonic tissue that is essential for anterior patterning of the embryo. It is characterised by the expression of anterior markers such as Hex, Cerberus-like and Lhx1. At pre-gastrula stages, cells of the AVE are initially located at the distal tip of the embryo, but they then move unilaterally to the future anterior. This movement is essential for converting the existing proximodistal axis into an anteroposterior axis. To investigate this process, we developed a culture system capable of imaging embryos in real time with single cell resolution. Our results show that AVE cells continuously change shape and project filopodial processes in their direction of motion, suggesting that they are actively migrating. Their proximal movement stops abruptly at the junction of the epiblast and extra-embryonic ectoderm, whereupon they move laterally. Confocal microscope images show that AVE cells migrate as a single layer in direct contact with the epiblast, suggesting that this tissue might provide directional cues. Together, these results show that the anteroposterior axis is correctly positioned by the active movement of cells of the AVE in response to cues from their environment, and by a 'barrier' to their movement that provides an endpoint for this migration. 相似文献